A Local Solution to the Challenge of Carbon
Neutrality and Excess Phosphorus: Anaerobic Manure
Digesters
Riley Ebel
Jessie Ralph
Liilia Namsing
Aaron Yappert
Beam Kitikhun
ENVS 401
Professor Klyza, Professor Baker-Medard, Diane Munroe
December 2015
Table of Contents
1. Introduction ............................................................................................................................. 3
1.1 Carbon Neutrality ................................................................................................................ 3
1.2 Phosphorus in Lake Champlain ............................................................................................. 4
1.3 Project Overview ................................................................................................................. 4
1.4 Current Energy Profile ......................................................................................................... 5
2. Manure Digestion ..................................................................................................................... 6
2.1 Producing Biogas from Dairy Waste at the Goodrich Farm ....................................................... 6
2.2 Greenhouse Gas (GHG) Emissions Implications of Anaerobic Digestion .................................... 9
2.3 Benefits of Renewable Natural Gas .......................................................................................10
3. Methane Accounting ................................................................................................................10
3.1 Baseline Emissions .............................................................................................................11
3.2 Environmental Protection Agency (EPA)...............................................................................11
3.3 California Air Resource Board (CARB) ................................................................................12
3.4 Regional Greenhouse Gas Initiative (RGGI) ..........................................................................12
3.5 Main Variables ...................................................................................................................12
3.6 Results and Discussion ........................................................................................................14
3.6.1 Baseline Emissions .......................................................................................................14
3.6.2 GHG Emissions Implication of the Switch from #6 Fuel Oil to Renewable Natural Gas ........16
3.7 Recommendations to Reach Carbon Neutrality.......................................................................18
4. Phosphorus .............................................................................................................................20
4.1 Threat to Bodies of Water ....................................................................................................21
4.1.1 The Implications of Phosphorus Runoff in the Lake Champlain Basin ................................22
4.2 Phosphorus and Agricultural Land Use..................................................................................22
4.2.1 Fertilizer Spreading Practices .........................................................................................23
4.2.2 Additional Phosphorus Reduction Strategies ....................................................................27
4.3 Future of Phosphorus Reduction ...........................................................................................28
4.3.1 Phosphorus Separation Technologies ..............................................................................28
4.4 Middlebury College and Phosphorus Reduction .....................................................................30
4.5 Results and Discussion ........................................................................................................31
4.5.1 Models ........................................................................................................................31
4.5.2 Recommendations ........................................................................................................36
5. Conclusion ..............................................................................................................................36
1
Acknowledgements .....................................................................................................................38
6. Bibliography ..........................................................................................................................39
Appendix A: EPA........................................................................................................................43
Appendix B: CARB, COP ............................................................................................................46
Appendix C: RGGI ......................................................................................................................48
2
1. Introduction
1.1 Carbon Neutrality
In 2007, the Board of Trustees of Middlebury College adopted a policy objective of
carbon neutrality by 2016 for campus operations. The college then became a signatory of the
American College and University Presidents’ Climate Commitment in 2008. These two
initiatives began the process of reducing greenhouse gas (GHG) emissions on campus and the
conversion to clean fuel sources.
The college’s first step in reducing GHG emissions came through the construction of a
biomass gasification facility, which became operational in 2009. The plant draws on sustainably
harvested biomass and waste wood and it reduced the use of on-campus #6 fuel oil by nearly one
million gallons. Continued improvements in operational efficiency of the plant have reduced fuel
oil usage even further. Coupled with this was an initiative to increase the energy efficiency of the
campus. $1.7 million was spent on 62 efficiency projects, which led to a reduction in energy
demand of 3.4 million kWh. With the addition of two solar projects, the college’s total reduction
of GHG emissions was 55%, declining from 30,644 metric tonnes in 2008 to 13,848 metric
tonnes in 2014 (Figure 1; Byrne, 2015b).
The college is now attempting to reduce the remaining 13,848 metric tonnes of GHG
emissions, specifically targeting the use of 640,000 gallons of #6 fuel oil, through the
implementation of a renewable natural gas anaerobic manure digester. The proposed digester
project will be built on the 850-cow Goodrich Farm in Salisbury, Vermont.
3
35,000
30,000
MTCDE Emissions
25,000
20,000
15,000
10,000
5,000
0
2007
2008
2009
2010
2011
2012
2013
2014
Year
Figure 1. Middlebury College Historical Fiscal Year GHG Emissions. (Data from Middlebury College Annual GHG
Inventory.)
1.2 Phosphorus in Lake Champlain
One potential co-benefit of the manure digestion project at the Goodrich Farm is the
production of a manure-derived liquid fertilizer that can be applied to fields through liquid
injection. These application practices along with changes in manure management have the
potential to reduce phosphorus runoff thereby improving the quality of nearby waterways. Due to
the prevalence of agricultural land and dairy farms in close proximity to Lake Champlain and its
tributaries, Lake Champlain receives an unhealthy dosage of nutrients from these facilities as a
result of runoff events. One nutrient that has proven particularly problematic in the lake is
phosphorus, which when released into local water bodies in excess amounts can lead to rapid
algal growth and eutrophication (“Lake Champlain Basin Program: State of the Lake 2015,”
2015).
1.3 Project Overview
The goals of this project are threefold. First, we wanted to assess if Middlebury College
will achieve carbon neutrality through the implementation of the Lincoln Renewable Gas
biomethane digester located at the Goodrich Farm. The second goal serves to assess how many
offsets the college might need to purchase should carbon neutrality not be achieved in its entirety
4
through the proposed digester project. Third, this project aims to assess, broadly, the impacts of
phosphorus runoff into Vermont watersheds through traditional farm fertilization methods and
discuss how the more concentrated liquid byproducts of manure digestion can be better utilized
to reduce the ecological impacts of excess phosphorus in Vermont waterways. Achieving these
goals will in part help the college serve as a leader in environmental sustainability as well as, and
perhaps more importantly, illustrate the numerous advantages of small scale manure digester
projects to not only the farm(s), but to the greater community through energy production and
phosphorus reduction.
1.4 Current Energy Profile
Currently, the majority of energy used on the Middlebury College campus comes from
the combustion of biomass, which consists of locally sourced woodchips. The second biggest
energy source is #6 fuel oil followed by other fuel sources, such as #2 fuel oil, diesel, biofuel,
and natural gas. This energy is mainly used for heating and cooling, generating electricity, and
for college-owned vehicles. About 20% of electricity is generated on campus from the steam
byproduct from the combustion of natural gas and biomass, while the rest is purchased from
Green Mountain Power. Depending on daily energy needs, biomass derived energy is used first,
followed by natural gas, and finally, during peak consumption days, fuel oil and biofuel. Energy
usage tends to be the highest during the colder days in winter and the warmer days in summer, as
heating and cooling needs peak respectively (Byrne, 2014).
The college voluntarily monitors all its greenhouse gas (GHG) emissions associated with
the aforementioned energy sources. Carbon dioxide makes up about 98% of all the college
associated GHG emissions, with the remaining 2% being methane and nitrous oxide. Middlebury
College also includes emissions from college-funded travel and waste management in its annual
GHG inventory (Byrne, 2014). During the fiscal year of 2013/2014 about 7,272 metric tonnes of
carbon dioxide equivalent (MTCDE) were emitted by the combustion of #6 fuel oil, which is
estimated to be about 50% of the college’s total carbon emissions. This was followed by
emissions associated with college staff travel totaling to about 24%, and the combustion of #2
fuel oil and diesel, which made up about 13.5% of total emissions. Other emissions associated
with electricity, vehicle fuel, and waste management made up the remaining 12.5% (Byrne,
2014). Switching from the use of fuel oils and natural gas to renewable natural gas (RNG) will
reduce the current net carbon emissions further. The remaining emissions will be offset by
investments into new energy efficiency projects on campus, and as a last resort through the
purchasing of carbon offsets.
When estimating its net carbon emissions, the college includes emissions from the main
campus as well as the Bread Loaf campus and the Snow Bowl. In 2006, the Snow Bowl became
the first carbon neutral ski area in the country, after the college began purchasing carbon offsets
from Vermont-based Native Energy. These offsets cover ski area emissions plus estimated
carbon emissions for skier travel to and from the Snow Bowl.
5
In the college’s carbon accounting scheme, only emissions released within the physical
boundary of the college or from operations of which 50% or more is owned by the college are
accounted for. Biomass is currently considered carbon neutral because the land where the
woodchips are harvested from continues to grow trees that sequester carbon at a faster rate than
the rate at which carbon dioxide is emitted by the college. When burned as a fuel source, there is
no net increase in the amount of carbon dioxide in the atmosphere. The RNG is considered
carbon neutral based on similar assumptions (Byrne, 2015b). This is different from burning fossil
fuels, which causes a net increase of carbon dioxide in the atmosphere.
The majority of electricity purchased from Green Mountain Power is generated from
nuclear power or from renewable energy sources like hydropower. Although nuclear energy is
not considered a renewable source, the associated carbon dioxide emissions are very low and as
such do not contribute much to the college’s carbon footprint.
2. Manure Digestion
2.1 Producing Biogas from Dairy Waste at the Goodrich Farm
Biogas is a mixture produced from dairy wastes through anaerobic digestion, which
breaks down organic material in an oxygen-free environment. This mixture is mainly composed
of methane and carbon dioxide and is produced naturally within manure piles or lagoons on dairy
farms, where the gas and associated GHGs are released into the atmosphere (Krich et al., 2005).
As of 2007, the uncontrolled anaerobic decomposition of manure in Vermont released about
140,000 metric tonnes of MTCDE into the atmosphere, of which 95% can be traced back to dairy
farms (Dowds, 2009). Anaerobic digesters allow farms to control and capture biogas as a
renewable source of energy to be used on site, or elsewhere.
Biogas can be stored before or after processing and can either be used directly in a
combustion engine to create electricity and heat, or can be further refined and upgraded to
biomethane or RNG. Anaerobic digestion occurs in two basic stages: organic waste products are
first decomposed by acid-forming bacteria into fatty acids, hydrogen sulfide, hydrogen gas and
carbon dioxide. Then, methane forming bacteria metabolize the fatty acids and hydrogen gas into
methane and carbon dioxide gases. This raw biogas has a methane content between 55-70% and
a carbon dioxide content between 30-45%, along with some other trace contaminants including
water vapor, hydrogen, and hydrogen sulfide gases (Petitioner’s Exhibit LRNG-DKS-2, 2015).
At this point, the raw biogas can be refined or “scrubbed” to remove carbon dioxide and trace
contaminants. In order for biogas to be considered a RNG product and subsequently utilized as a
direct substitute for geologic gas, the raw biogas must be refined to yield a methane content
greater than 95%.
6
Figure 2. Image of digester models to be used at the Goodrich Farm. (Image from Elmar Broering of WELTEC
Biopower in Petitioner’s Exhibit LRNG-DKS-2.)
Digester systems generally include a digester mechanism, equipment for handling and
storing effluent gas, a flare and in some cases, equipment to refine biogas to renewable natural
gas (Dowds, 2009). There are several different manure digester system types including complete
mix (to be used at the Goodrich Farm), fixed film, and covered lagoon systems. The Goodrich
Farm will be installing three complete mix digesters manufactured by WELTEC Biopower. The
digesters are circular tanks made of stainless steel in which manure is heated and mixed with
microorganisms (Figures 2 & 3; Hamilton, 2012). In these systems, biogas is displaced by
incoming manure and biogas production is generally controlled by adjusting volume so liquids
remain in the digester for about 20 to 30 days (Petitioner’s Exhibit LRNG-DKS-2, 2015). Biogas
is stored in the tanks above the substrate and later pushed through a pipeline to the gas-upgrading
unit. The digester system also includes a flare for biogas venting—if the gas cannot be
transported directly to the upgrade equipment, the biogas emergency flare incinerates the gas.
The flare is fully enclosed and has a capacity of 99% of gas production (Figure 4).
7
Figure 3. Diagram of different components of the WELTEC Biopower complete mix digester. (Image from Elmar
Broering in Petitioner’s Exhibit LRNG-DKS-2.)
Figure 4. Diagram of flare system included with digester manufactured by WELTEC Biopower.
Finally, the system within the control room has metering and measurement for three
major biogas components: Methane (0-100% vol), oxygen (0-25% vol) and hydrogen sulfide (03000 ppm). Digester tanks are heated using a forced hot water system utilizing coils that use
non-upgraded biogas produced by the digesters for fuel. A natural gas boiler with 700 kW
8
capacity burns the biogas produced by the digester. This heating process also works to reduce
emissions by producing and using the gas to facilitate the digester onsite. Lincoln RNG is also
exploring the use of a solar thermal system as a potential replacement for biogas fuel in the
future (Petitioner’s Exhibit LRNG-DKS-2, 2015).
The pipeline-grade RNG would be transported from the digester facility to Middlebury
College and other buyers via the underground pipeline constructed and operated by Vermont Gas
Systems, Inc. (VGS). This pipeline would supply the “gas island” distribution facility in
Middlebury, and it would later be incorporated into VGS’ expanding distribution network in
Addison County once it has been completed (Vermont Public Service Board, 2015).
2.2 Greenhouse Gas (GHG) Emissions Implications of Anaerobic
Digestion
There are two major beneficial greenhouse gas implications of anaerobic digestion
designated through subsequent capture and combustion of methane on dairy farms. Firstly,
because raw methane has a significantly higher global warming potential (GWP) than CO2,
combusting processed RNG as CO2 rather than allowing methane to be released into the
atmosphere inherently reduces direct carbon dioxide equivalent GHG emissions—the conversion
of methane to CO2 and water serves as a net GHG emissions reduction (Dowds, 2009). Secondly,
the combustion of biogas or RNG is used to generate heat or electricity, which displaces fuel
consumption that would have happened in the absence of the digester. The latter potential benefit
creates a more indirect emissions reduction.
It is important to note that the digester operation does release emissions through leakage
and destruction of excess methane via flare and that the methane offset is equal to the difference
between the emissions from baseline manure management practices and emissions from the
digester system. Manure that is stored in slurries or anaerobic lagoon systems (like those
previously used at the Goodrich Farm) release significantly more methane, creating high baseline
emissions. Replacing these high GHG releasing practices with a digester process will result in
significant emissions reductions, although recent protocols do require accounting for emissions
from the digesters themselves, so we cannot assume a digester emissions factor of zero (EPA,
2008). Direct emissions of the digester systems—including the leakage from the digester and
incomplete combustion of biogas noted above—may result in the escape of between 1 and 3% of
total methane produced in the digester into the atmosphere (Dowds, 2009).
9
2.3 Benefits of Renewable Natural Gas
Renewable natural gas (RNG) or biomethane is a pipeline quality gas that is
interchangeable with natural gas. The natural process of anaerobic digestion produces biogas, a
mixture of methane, carbon dioxide, and other impurities. Through a simple refinery process
biogas can be converted to biomethane, which can then be used to generate electricity and heat.
Biomethane has a methane content nearly identical to traditional natural gas and can therefore be
mixed freely within existing natural gas distribution systems. The benefits of RNG lie in the
lifecycle: biogas is generally thought to be a carbon neutral resource due to the fact that the
carbon emitted during combustion was initially fixed by plants through the process of
photosynthesis. By combusting RNG, carbon dioxide that was originally in the atmosphere
returns to the carbon cycle, resulting in no change in the total carbon dioxide of the cycle.
Additionally, if left in an anaerobic lagoon, methane and carbon dioxide in manure would
naturally decompose and release CH4 into the atmosphere. By capturing and converting the dairy
waste into a refined biogas that can be combusted, RNG replaces fossil fuel natural gas and also
reduces the amount of potent greenhouse gases that would be released into the atmosphere as a
byproduct of dairy farming (Eggleston et al., 2006). While we were unable to find peer reviewed
literature attesting to the fact that biomethane is carbon neutral, in this report we analyze our data
under the same assumption as Middlebury College and experts of other organizations that
believe this renewable natural gas is carbon neutral.
3. Methane Accounting
Carbon accounting is the process by which organizations account for and report their
greenhouse gas emissions (Schaltegger and Csutora, 2012). This involves the direct
measurement of carbon and other GHG emissions as well as the measurement of carbon dioxide
equivalents that will not be released into the atmosphere as a result of different mitigation
programs like the proposed manure digestion project at the Goodrich Farm. In 2007 the college
began an annual GHG emissions inventory, tracking its energy use and associated emissions
across operations in which the college has at least a 50% stake.
Accounting for the carbon emissions reductions associated with Middlebury College’s
use of RNG is not only important for estimating the benefits of a cleaner energy source, but also
to account for the removal of methane from the atmosphere through the implementation of the
digester project. Methane is a much stronger GHG with a global warming potential about 25-28
times that of carbon dioxide and it is the second most prevalent GHG emitted in the United
States (Chianese et al., 2009). It is estimated that emissions associated with dairy cattle manure
account for 35% of all the livestock manure methane emissions in the United States (McGinn
and Beauchemin, 2012). Therefore, the implementation of this digester project not only allows
10
the college to reduce its carbon footprint but it also benefits the environment by limiting the
release of a highly potent GHG into the atmosphere.
3.1 Baseline Emissions
In order to evaluate the methane reduction associated with the digester project, the first
task was trying to quantify the baseline methane emissions associated with the current manure
management practices at the Goodrich Farm. Baseline emissions refer to the emissions that
would have occurred from a manure management system prior to the implementation of an
emissions mitigation project. In this case, the digester will replace the existing manure
management system with the intent of capturing and destroying the otherwise released methane
(Eastern Research Group, Inc., 2011). At the Goodrich Farm, the majority of the manure is
stored as a liquid in earthen ponds outside the animal housing facilities, and smaller amounts are
spread on fields as fertilizer throughout the year (Smith, 2015). As such, the baseline methane
emissions for this project are those associated with the aforementioned manure management
practices.
There is currently no standardized method for accounting for the methane emissions
associated with different manure management systems on dairy farms. Therefore for this project,
we evaluated three different protocols in an effort to understand how methane accounting results
vary given different methods and to recommend which is the most appropriate for the digester
project at the Goodrich Farm.
We used models from the U.S. Environmental Protection Agency (EPA), the California
Air Resources Board (CARB) and the Regional Greenhouse Gas Initiative (RGGI). The EPA
model represents methane accounting at the federal level, while the CARB model is very similar
to models widely used in the private sector and is a component in one of the nation's most robust
state-level carbon cap-and-trade programs. The RGGI model has been adopted by the Vermont
Legislature and, along with the CARB model, represents site-specific projects with reasonable
accuracy.
3.2 Environmental Protection Agency (EPA)
The U.S. EPA protocol for accounting agricultural methane emissions was developed
based on the Intergovernmental Panel on Climate Change (IPCC) Good Practice Guidance and
Uncertainty Management in National Greenhouse Gas Inventories Tier II protocol. This is one
of the models used by the U.S. EPA to generate their annual report on national GHG emissions
and sinks (EPA, 2014). In order to calculate the baseline methane emissions based on this model,
we used both site-specific data and literature data to estimate the baseline emissions. See
Appendix A for details regarding calculations.
11
3.3 California Air Resource Board (CARB)
CARB uses the California Compliance Offset Protocol for Livestock Projects (COP),
which provides a means to quantify and report GHG emissions reductions associated with
installation of a biogas control system (BCS) or digester for manure management on dairy and
swine farms. The protocol is based on the Climate Action Reserve’s Livestock Project Protocol
Version 2.2 and includes updates from version 3.0, published in 2011. This protocol can
appropriately quantify GHG reductions at an offset project anywhere in the U.S. and was
developed through Climate Action Reserve, which is a California Offset Project Registry. Both
site-specific data and literature data were used to estimate baseline emissions. See Appendix B
for details and calculations.
3.4 Regional Greenhouse Gas Initiative (RGGI)
The Regional Greenhouse Gas Initiative (RGGI) is a mandatory carbon dioxide cap-andtrade state-level consortium for power plants located in the Northeast United States. Member
states can engage in carbon credit trading with the intent of capping GHG emissions in the
region. Credits can be earned through the permanent destruction of GHG emissions that would
otherwise have occurred under normal conditions. In this regard, RGGI outlines multiple
accounting schemes to assess the reduction in GHG emissions on a project-by-project basis.
Under RGGI, anaerobic manure digesters that meet operational requirements constitute
permanent and additional reductions in methane emissions and therefore are eligible to earn
carbon credits. Member states, including Vermont, are free to adopt RGGI regulations that detail,
among other things, how baseline emissions should be calculated for manure digester projects
(RGGI, 2013).
Similarly to other emission calculation protocols, the RGGI protocol quantifies methane
emissions that occur within the project boundary given the existing manure management system.
The RGGI protocol, through the calculation of eliminated methane emissions, will allow
regulators to assess how many offset credits a project may receive. See Appendix C for details
regarding calculations.
3.5 Main Variables
Baseline modeled methane emissions from anaerobic storage or treatment systems can be
quantified based on a number of important variables. Although the three protocols (EPA, CARB
and RGGI) differ slightly in treatment of some of these variables, there are a few essential and
consistent contributors to methane emissions on dairy farms.
12
Livestock Category and Population
Designation of livestock category, e.g. lactating dairy cows, heifers, etc., accounts for
differences in methane generation among livestock type due to differences in the organic solids
within their manure. Generally, manure from milking cows produces more methane during
anaerobic decomposition than heifers; as such, designating type of animal is important to
accurately determine methane emissions. Similarly, animal population is essential to calculate
methane emissions: population is monitored monthly and dictates the amount of methane
produced on the farm.
Organic Solid Content in Manure
Organic solids, specifically volatile solids (VS), represent the portion of manure, that
when anaerobically digested, leads to a methane by-product (Eggleston et al., 2006). VS
excretion rates are best calculated with the use of published sources that estimate average daily
excretion based on feed, livestock type and storage system. Variations in VS concentrations are
important to note: for example, dairy cows contain more VS than heifers and storage in a slurry
or lagoon allows for more efficient breakdown and methane production than dry stacking or
other methods. The amount of volatile solids available for degradation within a system also
depends on the previous month’s available and degraded volatile solids within the system.
The maximum methane producing power in manure (B0), which ultimately dictates how much
methane is released by organic solids in manure varies by species and diet, and is also based on
biodegradable volatile solid.
Temperature at the Site
Liquid-based systems are very sensitive to temperature fluctuations, so accurate and
specific monthly or annual temperature data are important to consider. Temperature and climate
at the site directly affect natural digestion rates and in a location with high seasonal temperature
variation like Vermont, methane production from a lagoon is not constant. Generally, warmer
temperatures facilitate more VS breakdown and subsequent methane emissions.
Manure Management System Characteristics
This variable includes the type of system used to manage the manure and usually a
system specific methane conversion factor that reflects the portion of B0 that is achieved.
Retention time and temperature are important factors in the management system: manure that is
managed as a liquid in warm conditions promotes methane formation and has high system
methane conversion factors. Manure that is managed as dry material in cold temperatures
produces significantly less methane. At the Goodrich Farm, the manure is held in a lagoon as a
13
liquid and produces varying amounts of methane depending on changing temperature throughout
the year.
3.6 Results and Discussion
3.6.1 Baseline Emissions
Baseline emissions represent methane released from standard manure storage in open-air
slurry pits. Because the digester will be drawing manure from two farms in addition to the
Goodrich Farm, baseline emissions were evaluated for all three farms. The neighboring farms
store manure in open-air pits similar to those used on the Goodrich Farm, and because they are
located within Addison County, they experience the same average monthly temperature.
The three protocols showed considerable variability in the baseline emissions (Figure 5).
The EPA protocol estimated emissions 63.1% lower than the CARB protocol and the RGGI
protocol estimated emissions 32.1% lower than the CARB protocol. Though differences among
the estimated baselines are unsurprising, the magnitude of the differences suggests that methane
accounting protocols have yet to achieve sufficient accuracy for informed decision-making. This
being said, some of the difference can be explained by the scope of the protocols. The EPA
model is designed to function as a national GHG inventory and therefore uses a state-specific
conversion factor for volatile solids into methane. Though this may be sufficient on the national
scale when site-specific data cannot be attained for every digester project in the United States, it
fails to best estimate a single project.
The CARB and RGGI protocols are much more sensitive to site-specific factors but still
show substantial differences. The RGGI protocol applies a factor of 1/2 to all manure added to a
slurry pit over the course of the reporting period (typically one month). Alternatively, the CARB
protocol applies a factor of 4/5 to all manure added to the slurry pit over the course of the
reporting period. These factors are intended to model the proportion of volatile solids within the
manure available to be broken down throughout the reporting period. This factor is necessary
because manure added later in the reporting period will have less time to break down while
manure added at the start of the period will spend more time in the digester. This factor attempts
to rectify these differences. We believe that the difference between these factors in the CARB
and RGGI models may contribute to the different modeled baseline emissions (See Appendices
B and C for equations).
14
8000
7036
7000
MTCDE per Year
6000
4778
5000
4000
3000
2598
2000
1000
0
EPA
CARB
RGGI
Figure 5. Total calculated baseline methane emissions of all project-associated farms. Values above bars represent
metric tonnes of CO2 equivalents released per year. Standard manure management practices include 100% of
manure contained in open-air slurry pits and are the same across all three farms. Total manure inputs from 1800
milking dairy cows and 400 heifers.
In order to facilitate an understanding of how these baseline emissions would factor into
the college’s net emissions, we averaged the CARB and RGGI baseline emissions. We did not
include the EPA estimate due to its imprecision for single-digester sites. This average value,
5,907 MTCDE, is representative of typical farm emissions. Native Energy, a Vermont-based
energy and offset consulting firm, estimated, prior to project permitting, that Goodrich Farm
would produce 5,500 MTCDE per year prior (Byrne, 2015a). However, calculations were not
provided and after speaking with regional experts, this value seems to reasonably reflect the
emissions at a typical farm the size of the Goodrich Farm. Given these two corroborating
sources, we think the averaged CARB/RGGI value is sufficiently accurate. However, it must be
acknowledged that the significant differences between the models suggest there is need for a
comprehensive review of methane accounting in the United States to better represent baseline
emissions. Furthermore, though we can use standardized variables, no generalization can replace
site-specific measurements of the Goodrich Farm conducted by trained professionals.
Though the digester will lead to a net energy output, there are several project components
that will require significant energy inputs. The digester tanks are heated by a forced hot water
system that will require 497 MTCDE per year of energy via carbon neutral biogas produced by
the digester itself. Furthermore, the biogas upgrade equipment will require an estimated energy
input that will lead to emissions of 895 MTCDE per year; however, this energy will be provided
15
through the existing power grid and will constitute net release of carbon (Steckler, 2015).
Additional manure will be trucked to the Goodrich Farm to supplement manure produced by the
host farm. This trucking will emit 97 MTCDE. Collectively, these energy inputs will amount to
992 MTCDE per year to operate the digester system. These emissions must be subtracted from
the overall modeled baseline emissions to determine the offset credits provided by the project.
After subtraction, the final credits earned through the project total 4,915 MTCDE per year
(Figure 6).
7000
6000
5907
4915
MTCDE per Year
5000
4000
3000
2000
992
1000
0
Baseline Emissions*
Digester Operation
Emissions
Final Credits
Figure 6. Offset credits accrued through the destruction of methane via anaerobic manure digestion. *Baseline
emissions represent an average of the baseline emissions of the CARB and RGGI protocols. Values above bars
represent MTCDE.
3.6.2 GHG Emissions Implication of the Switch from #6 Fuel Oil to Renewable
Natural Gas
Most of Middlebury College’s energy budget is used to facilitate heating and cooling on
campus and #6 fuel oil remains the main fuel source. #6 fuel oil is a liquid fuel derived from
petroleum that is considered a residual fuel. It is an extremely heavy, viscous liquid that gives off
some of the highest concentrations of particulate matter and GHG emissions of any fuel. Natural
gas, which is primarily composed of methane, is a much lighter gas that produces significantly
lower GHG emissions when burned in a boiler than residual or distillate fuels. Currently, the use
of #6 fuel oil at the college emits 7,272 MTCDE per year. By switching to carbon neutral
renewable natural gas, the college will be able to eliminate all #6 fuel oil use, and the associated
7,272 MTCDE per year.
16
Figure 7. Projected college emissions after full implementation of the Goodrich Farm anaerobic manure digester.
Values above bars represent MTCDE.
The anaerobic digester located at the Goodrich Farm will lead to a 84.5% reduction in the
college’s remaining GHG emissions, from 13,848 MTCDE to 1,661 MTCDE (Figure 7). Since
the initial commitment to carbon neutrality in 2007, the college will have made a 94.5%
reduction in overall GHG emissions. These results are based on the averaged baseline emissions
from the CARB and RGGI protocols, the college gaining 100% of project credits, while taking
into account project emissions. As such, this project is not only reducing methane emissions at
the Goodrich Farm, but also reducing carbon outputs on campus.
However, due to contractual negotiations, it is possible that the college may not receive
100% of the credits associated with the digester project. If the college were to receive a portion
of the credits relative to its gas purchase, 75% of total project output, then remaining emissions
would be 2,890 MTCDE (Figure 8).
17
Figure 8. Projected remaining emissions for the college per offset credit scenario. Contractual negotiations may
dictate that the college does not receive 100% of project credits, as they are only purchasing 75% of the project’s
gas. Values above bars represent MTCDE under the two credit allotment scenarios. Data from Middlebury College
Annual GHG Inventory
3.7 Recommendations to Reach Carbon Neutrality
1) Utilize the maximum capacity of digester
Our results are based on a 2,200-cow population contributing manure to the digester. The
digester being installed at the Goodrich Farm, however, has the capacity to process manure from
about 4,000 cows. So, there is potential for more methane emission offsets if more farms
contribute manure to the digester or the population of cows at the Goodrich Farm increases in the
future. Most possible manure additions in the future would likely be from other farms in the area.
A calculation of baseline emissions at maximum digester capacity with a population of 2,700
milking cows and 800 heifers, totaling 3,500 cows, shows an additional 3,000 MTCDE of
possible offsets from this additional manure being added to the digester. With additional manure
comes additional trucking and associated emissions adding up to an extra 100 MTCDE;
however, the increased digester offset benefits significantly outweigh the costs. Therefore, using
more of the digester capacity could be a good way for the college to increase offsets in the
future.
18
2) More efficiency projects on campus
The college has invested $1.7 million in 62 different efficiency projects since 2008 that
have contributed to the carbon neutrality goal; these include a number of solar projects, efficient
design in new buildings and sustainable dining among many others. Despite this robust list of
projects, there are many other options available to the college to continue reducing the carbon
footprint on campus. Weatherizing the older buildings on campus would be a great way shrink
our carbon footprint through increased energy efficiency. As a majority of fuel used on campus
goes towards heating and cooling, a tighter envelope in some of the older buildings would help
minimize heated or cooled air from escaping through windows, doors and other cracks.
Additionally, the school could look into the installation of more solar projects on campus to meet
energy demand. Whether these installations are on roofs or elsewhere, solar panels directly on
campus would provide a self-contained renewable energy source.
3) Buy offsets
As a last resort, Middlebury can purchase offsets from various sources that would
counteract the unavoidable GHG emission by paying for reductions at projects that avoid or
capture GHG somewhere else. Ideally, as Middlebury continues to move towards the carbon
neutrality goal, offset purchases will decrease and eventually not be required at all once
emissions are considered at net zero (Figure 9).
19
Figure 9. Middlebury College’s carbon emissions reductions through the digester project and projected remaining
emissions that would need to be offset.
4. Phosphorus
Phosphorus is an element that is crucial for all forms of life. It is an important mineral
nutrient in many agricultural systems because it fosters the growth of crops; sufficient quantities
of phosphorus are critical for the development of plant seeds and roots. While phosphorus is a
naturally occurring substance in many ecosystems, it is also generally a limiting nutrient for
further plant growth (Hart et al., 2004). A limiting nutrient is a chemical that is necessary in an
ecosystem to support plant growth but may only be available in small quantities (Bachman, n.d.).
Once the supply of this nutrient has been depleted, plant growth stops unless additional amounts
of the nutrient are applied.
Over the course of this project, our group not only wanted to explore the benefits of
anaerobic manure digestion in terms of achieving carbon neutrality, but we also wanted to
determine if manure digestion could have any co-benefits for the ecosystems surrounding
digester sites. One of the byproducts of manure digestion and separation is a manure derived
20
liquid fertilizer with a high nutrient content. Vermont, like many other places, has been
struggling with phosphorus accumulation in its bodies of water and this product could provide an
option to mitigate excessive agricultural runoff into Lake Champlain’s watersheds through its
application practices. In this section we explore the potential co-benefits of manure digestion on
phosphorus runoff as well as additional ways farmers can reduce their field runoff.
4.1 Threat to Bodies of Water
Although phosphorus is necessary for farmers to achieve maximum yields, the loading of
phosphorus into waterways through runoff can be extremely detrimental to aquatic
environments. Phosphorus is also a limiting nutrient in bodies of water for aquatic life
(Bachman, n.d.). While the terrestrial levels of phosphorus that are lost due to agricultural runoff
may be insignificant to the farmer who is applying fertilizers, small amounts of additional
phosphorus can still wreak havoc on aquatic ecosystems (Hart et al., 2004).
Phosphorus loading into waterways during runoff events is an environmental problem
because it can lead to the eutrophication of a body of water (Hart et al., 2004). Eutrophication is
“a biological process in which there is excessive algal growth in water due to an excess of
nutrients and in particular phosphates and nitrates. The eventual decomposition of the algae
depletes the water of available oxygen, resulting in a sterile body of water” (Schaschke, 2014).
Although eutrophication can be a natural process, it has been accelerated by human activities in
many watersheds. Blooms in the growth of algae can occur with the inputs of phosphorus that
occur during runoff events. According to some research, one pound of phosphorus can trigger the
growth of 300 to 500 pounds of algae (“What’s the Fuss about Phosphorus?”, n.d.).
Unfortunately, this rapid and excessive growth can be detrimental to other parts of aquatic
ecosystems. Algal growth can prohibit light penetration into the water body, which impacts
aquatic plant growth and affects the visibility of some fish species. Additionally, other aquatic
life forms depend on dissolved oxygen in the water and if the oxygen levels drop too much, areas
of the water body can become dead zones where there isn’t enough oxygen to support life
(Chrislock et al., 2013).
It is important to note however that agriculture isn’t the only source of phosphorus
pollution in waterways. Stream bank erosion also contributes to the amount of phosphorus that
ends up in bodies of water. Soils containing phosphorus are washed into waterways as stream
banks gradually erode under the flow of water, releasing the nutrients into the water as well.
Additionally, wastewater treatment plants are point sources of phosphorus pollution into
watersheds (“Lake Champlain Basin Program: State of the Lake 2015,” 2015). In some regions,
urban activities contribute the most phosphorus runoff into nearby watersheds. Paved roads
prevent the absorption of these nutrients into the soil. These impermeable surfaces allow rain to
wash nutrients accumulated on these solid surfaces directly into storm drains and water bodies.
Fertilizing personal lawns can also contribute to phosphorus runoff from urban areas (“What’s
the Fuss about Phosphorus?”, n.d.).
21
4.1.1 The Implications of Phosphorus Runoff in the Lake Champlain Basin
In the state of Vermont, phosphorus runoff has created a serious problem in Lake
Champlain. Lake Champlain sits on the border of Vermont and New York with the northern end
extending into Canada. At 120 miles in length and reaching nearly 400 feet deep, Lake
Champlain is the sixth largest lake in the United States (“Lake and Basin Facts,” n.d.). A large
amount of phosphorus ends up in Lake Champlain after flowing through the extensive Lake
Champlain Basin watershed. According to the Lake Champlain Basin Program’s most recent
“State of the Lake Report,” for every square mile of lake surface area there are eighteen square
miles of watershed draining into the lake (“Lake Champlain Basin Program: State of the Lake
2015,” 2015).
Lake Champlain’s tributaries deposit nearly 921 million tonnes of phosphorus into the
lake each year. However, certain watersheds and tributaries contribute far more to this total
phosphorus loading than others. The three primary sources of the excess quantities of this
nutrient that end up in the lake are runoff from developed land use, agricultural land use, and
sediments from stream banks that are gradually eroded and deposited into waterways. These
various sources of phosphorus loading in the Lake Champlain watershed contribute different
quantities in each tributary (“Lake Champlain Basin Program: State of the Lake 2015,” 2015).
The excess phosphorus that flows into Lake Champlain through these tributaries can also
lead to increased algal growth and eutrophication. Some algal blooms of bacteria such as toxic
cyanobacteria, also known as blue-green algae, can be dangerous to humans and other living
organisms. This type of bacteria can be particularly harmful if ingested and poses a threat to the
use of lake water as untreated drinking water (“Lake Champlain Basin Program: State of the
Lake 2015,” 2015).
Currently, Vermont has a number of programs in place in an attempt to reduce runoff to
waterways. These programs include protecting stream banks from erosion, fighting for higher
water quality through new water quality laws, and establishing a Total Maximum Daily Load for
phosphorus runoff (which is currently under review for implementation) (“Lake Champlain
Basin Program: State of the Lake 2015,” 2015; "Lake Champlain Phosphorus TMDL: A
Commitment to Clean Water," n.d.).
4.2 Phosphorus and Agricultural Land Use
The state of Vermont is situated in a temperate zone where soils are prone to periods of
weathering. Vermont’s climate has therefore required farmers to use additional fertilizers on
their fields in order to achieve higher crop yields because agricultural soils have a low naturally
present nutrient content (Aguiar, 2015). In order to achieve maximum possible yields in
agricultural settings, farmers must add additional phosphorus to the soils in the form of fertilizers
(Hart et al., 2004). According to Murray Hart et al., global phosphate use greatly increased
22
throughout the 20th century likely because farmers were encouraged to continue applying
additional phosphorus to their fields (2004). We now know that the continued application of
phosphorus to fields doesn’t necessarily lead to greater benefits for crops because phosphorus
can be easily over applied, especially when fields are fertilized with manure. The ratio of
nitrogen, another limiting nutrient important for plant growth, to phosphorus in manure is around
1:1; however, the quantity of phosphorus needed by most crops is about eight times less than the
amount of nitrogen (Zhang et al., n.d.). This means that farmers apply fertilizer to meet the
nitrogen needs of their crops and as a result, excess phosphorus builds up in the soil because
there is more available than can be absorbed by the soil and used by crops. As phosphorus
continues to build up in the soil due to these fertilizer application techniques, excess nutrients
become susceptible to runoff from precipitation or flooding and end up flowing into nearby
watersheds.
4.2.1 Fertilizer Spreading Practices
For farming operations that work with large quantities of animals to supply a product
such as meat or milk, one of the byproducts is the large quantity of manure produced by the
livestock. This manure contains significant amounts of key nutrients for crops such as nitrogen
and phosphorus. This allows for a cyclical farming operation as farmers fertilize fields growing
feed, like corn, for their livestock with the manure produced by these animals. In Vermont, dairy
operations are common and follow this cycle of using animal manure to fertilize feed products.
Access to large amounts of manure provides farmers with a couple of options as to how
they can apply the manure to their fields. Some farmers spread manure in a more solid state that
contains at least 15% solids over the surface of their fields. The consistency of manure in solid
form can vary and can make it difficult for farmers to evenly spread this type of fertilizer.
Manure can also be used on fields in a liquid form through various distribution techniques
(Kaasik, 2012). Through the course of our research, we have explored the use of one of the
byproducts of anaerobic manure digestion as a liquid fertilizer for fields. After the digester
process has captured methane from the manure, the manure is put into a separator, which
physically separates the solid and liquid components of the manure. At the Goodrich Farm, this
is done using a screw press (Figure 10). While the dry solids go on to make bedding for the
cows, the separated liquid provides an alternative to traditional manure spreading techniques
(Smith, 2015).
23
Figure 10. Screw press separator. (Image from AGRO).
Phosphorus loading into watersheds as a result of fertilizer inputs on agricultural land
depends on how these inputs are applied and as a result, various theories exist as to the best
manure management practices. According to a study by Kleinman et al., the authors suspected
that the addition of phosphorus to the soil surface through application of manure or other
fertilizers causes a temporary spike in the amount of phosphorus that can potentially be washed
off of the field and into a waterway. For this reason the timing of fertilizer application can play a
key role in phosphorus loading. However, it may not always be easy to time fertilizer application
perfectly, especially if an unexpected rainstorm hits soon after manure is applied to fields. The
study also finds that the concentrations of phosphorus already present in the soil can impact the
amount of runoff (Kleinman et al., 2002). This finding has important implications for the current
and common practice of overloading agricultural soils to achieve necessary nitrogen
concentrations. Over application can lead to more phosphorus in runoff as the soils gradually
become highly concentrated with this nutrient.
One of the more common methods of applying manure fertilizers to fields is through
surface spreading (Figure 11). This technique is commonly seen in Vermont where the manure is
held in lagoons. The unseparated mixture is pumped into tanks that are transported through the
fields by truck and the manure is sprayed on the soil surface from the back of the truck.
24
Figure 11. Example of farmer using surface spreading manure application on field. (Image from Utah State
University Manure Solutions).
According to Dan Smith, manure at the Goodrich Farm is spread onto the fields twice a
year, once after first cutting and once after harvest. The Goodrich Farm applies nearly a quarter
of their manure fertilizer with this technique (Smith, 2015). The problems highlighted earlier by
Kleinman et al. often occur when manure is spread using this technique. Furthermore, Kleinman
et al. express concerns that surface applications, such as the spreading of manure or fertilizers on
field surfaces, can increase the vulnerability of these field inputs to runoff (2002).
Alternatives to this type of surface fertilizer application are injection, knifing, or
immediate incorporation (Kleinman et al., 2002). Although integrating phosphorus into the soil
can increase soil erosion (also a contributor to phosphorus loading), the contribution of
phosphorus runoff from these mixed soils amounts to less than runoff from soils that have only
received surface fertilizer application. Mixing the soil and added fertilizer together increases the
absorption of the phosphorus into the soil and decreases P surface runoff (Kleinman et al., 2002).
These incorporation techniques are possible for liquid forms of fertilizer including the liquid
byproduct of manure digestion and separation.
The fertilizer byproduct of the manure digestion and separation project changes the way
that the Goodrich Farm and the other farms that provide manure for this project will fertilize
their fields. In the case of the Goodrich Farm, this change in the consistency of the manure
fertilizer will lead to a change in fertilizer application practices. Rather than spreading partially
solid manure from the back of a truck driving through fields, farmers can now use the drag-lining
method to inject the high nutrient content liquid product into the soil (Smith, 2015). In this
method of liquid injection, a tractor is connected to a hose, which delivers pumped liquid
25
fertilizer or manure to the tractor. The tractor also drags a piece of tillage equipment. The tillage
equipment allows for the liquid, which is pumped through the hose, to be incorporated into the
soil as the tractor drives up and down the fields (Wright and Bossard, n.d.).
The drag-lining method of fertilizer injection, also known as the drag hose method
(Figure 12), is not the only existing method that can be used to inject the liquid byproduct of
manure digestion and separation into the soil. Some other existing means of manure injection
were developed to allow the farmer to inject the fertilizer into the soil without tilling the soil.
These other methods of fertilizer injection include trailing shoe spreaders––a practice that allows
the liquid manure to be inserted into the soil surface, open slot injectors––a system that inserts
liquid fertilizer a small distance into the soil by making small openings in the soil with discs or
knives, and closed slot injectors––in which the liquid fertilizer is injected to a shallow depth in
the soil and the slots are closed afterwards (Kaasik, 2012).
Figure 12. Example of drag lining or drag hose method of manure incorporation (Image from Houzz).
As mentioned above, these methods of liquid injection allow for more efficient mixing of
the fertilizers and the surrounding soils. According to Dan Smith, liquid injection can also reduce
some of the negative odors associated with spreading manure on fields (2015). However, when
considering methods to reduce potential phosphorus runoff from agricultural land, there are
several other practices and standards that should be taken into account.
26
4.2.2 Additional Phosphorus Reduction Strategies
i. Conservation Management Practices
There are many factors that can affect the quantity of phosphorus washed into
surrounding waterways from agricultural land. As a result, various recommended conservation
agricultural practices exist, but the ‘best management approach’ to these agricultural practices
depends on specific factors that vary on a farm-by-farm basis. For this reason, in order to make a
widespread difference in the amount of phosphorus runoff we see from agricultural operations,
farms will likely use various ‘best management practices’ to protect their soil from runoff and
erosion.
These conservation practices include a variety of tillage forms, crop rotation, and
conservation drainage. In addition to these farming practices, riparian buffer zones near
waterways can reduce the potential for the loading of phosphorus into watersheds (Weisman,
n.d.). In Vermont, according to Act 64, these vegetative buffer zones are required to help protect
local aquatic ecosystems that neighbor agricultural lands. This regulation also requires that
manure application on agricultural lands not occur within twenty-five feet of a waterway and that
farmers maintain a buffer with perennial vegetation (Vermont Agency of Agriculture, 2006). The
decision on which of these conservation practices is best to use in a given farming situation
depends on the characteristics of the agricultural land.
ii. Total Maximum Daily Load
In Vermont, one of the ways that government agencies are working to control the amount
of phosphorus that ends up in Lake Champlain is through a phosphorus Total Maximum Daily
Load (TMDL). A TMDL sets a limit for the amount of phosphorus that can enter the lake in
order to meet water quality standards. This standard essentially places a cap on the amount of
phosphorus entering Lake Champlain’s watersheds ("Lake Champlain Phosphorus TMDL: A
Commitment to Clean Water," n.d.). While the EPA rejected Vermont’s 2002 Lake Champlain
TMDL in 2011, the development of a new TMDL has been underway since 2013. These updated
water quality standards for the state have been finalized and the implementation process will
commence over the course of the next two years while the EPA monitors state efforts
(Watershed Management Division, 2015).
The implementation of a new TMDL for Lake Champlain would require polluters to find
ways to reduce their impact. Although TMDLs are an important part of pollution regulation, in
Vermont they also put pressure on farmers to come up with solutions to reduce their phosphorus
loading. For Lake Champlain, the EPA set standards for phosphorus loading in the various lake
watersheds (Phosphorus TMDLs for Vermont Segments of Lake Champlain, 2015). These
allocations differ depending on the lake segments as some segments have greater problems with
managing phosphorus runoff and different major sources of phosphorus. Additionally, in many
27
of these segments, high reductions in phosphorus loading from agricultural land must be made in
order to meet these TMDL standards (Phosphorus TMDLs for Vermont Segments of Lake
Champlain, 2015). As a result of these regulations, the new TMDL may make liquid injection
and other conservation management practices more appealing in the agricultural sector. The
TMDL might also encourage the development of more phosphorus monitoring stations, which
could measure the difference in phosphorus runoff attributed to various agricultural practices.
iii. Nutrient Trading Schemes
Lake Champlain is not the only water body that has struggled with phosphorus loading;
the Chesapeake Bay has also struggled with water pollution from nutrients including phosphorus.
The Chesapeake Bay also has a TMDL cap on nutrient loading into its watershed and
policymakers there have explored the idea of nutrient trading programs in the region. Not only
does a nutrient ‘cap and trade’ program help the region reach its TMDL goal, but it also has the
potential to reduce cleanup costs. This market based approach to cleanup benefits polluters who
adopt cleaner practices, including farmers who can sell excess permits if they adopt conservation
agricultural practices. The ability of farmers to profit from the reduction in their phosphorus
loading to waterways could reduce some of the economic stress farmers feel meeting TMDL
requirements. The nutrient trading approach has been one response in some areas to meet water
quality standards (Quinlan, 2012).
Vermont has also considered nutrient trading to reduce phosphorus pollution in Lake
Champlain. However, this type of plan requires strong regulations that demand polluters to clean
up their pollution. Currently, Vermont still does not have any trading plans in place but is in the
process of considering an initiative that would incorporate a nutrient trading scheme to meet
Lake Champlain TMDL requirements (Hirschfeld, 2014; Vermont Agency of Agriculture, Food
and Markets and the Vermont Department of Environmental Conservation, 2014).
4.3 Future of Phosphorus Reduction
4.3.1 Phosphorus Separation Technologies
Currently, across the U.S., TMDLs, conservation management practices, and liquid
injection techniques are being used to reduce total phosphorus runoff from agricultural
processes. However, additional technologies exist that can be used in tandem with manure
digesters on farms to further reduce phosphorus over application and runoff. These technologies
involve the separation of phosphorus from other nutrients present in manure. This separation
would result in a phosphorus product that provides the farmer with significantly more control
over its application on fields. These technologies could reduce the overloading of phosphorus in
agricultural soil due to more exact application. Additional phosphorus that does not get applied
to a farmer’s fields could then be sold to other regions where farmers lack phosphorus. This
28
creates a new market for separated nutrients. Phosphorus can be removed from the manure
through chemical, physical, or biological separation methods. We have explored the potential of
a few of these technologies and their implications for use along with a manure digester project.
Interestingly, the digester project at the Goodrich Farm already employs a method of
physical separation of manure into solid and liquid components through the use of a screw press
(Figure 10). This process in itself can reduce phosphorus content in the liquid component by
around 20% as the separated solids which then become bedding for the cows capture these
nutrients (Focus on Vermont Farm Projects: Single and Two-Stage Dairy Manure Separation,
2015). However, additional types of phosphorus separation can further reduce the quantities of
phosphorus present in the manure and liquid fertilizer by-product of separation.
i. Decanter Centrifuge Separation
Once the manure has been physically separated with a screw press, Native Energy
proposes the use of a decanter centrifuge to further separate phosphorus. In this process, the
liquid component of manure separation enters the centrifuge where it is spun at a high speed until
the particles containing phosphorus stick to the barrel surface. This process has the ability to
remove about 70% of the remaining phosphorus in the liquid and the centrifuge output is dry
phosphorus “cake” that can be used as needed by the farmer after spreading the remaining liquid
manure or sold to other farms (Focus on Vermont Farm Projects: Single and Two-Stage Dairy
Manure Separation, 2015). According to Native Energy’s assessment of a two-stage separation
process using a decanter centrifuge, a farmer with 500 cows will make over half a million dollars
over 10 years after the implementation of such a project. These benefits take into account the
operating and upfront costs of the project as well as the profits made through the sale of excess
phosphorus cakes (Vermont Farm Projects: Single and Two-Stage Separation, 2014).
The manure-derived phosphorus cakes can help reduce agricultural runoff from fields
when applied instead of raw dairy manure. A study comparing the runoff potential of dairy
manure and biosolid cakes found even with the same phosphorus loading rates, the
concentrations of phosphorus in runoff was significantly higher when manure was applied as
opposed to the cake treatments (Brandt and Elliott, 2003).
Currently, Green Mountain Power is working with Native Energy on the implementation
of a manure separator project on Vermont dairy farms (“Community Energy & Efficiency
Development Fund 2015 Annual Plan,” 2014). Additionally, Green Mountain Power’s proposed
Community Digester in St. Albans will explore the potential of dry nutrients (such as the
phosphorus cakes) to be applied precisely or exported to other parts of the country where farmers
lack access to sufficient quantities of phosphorus (“Linking Community and Technologies to
Capture and Convert Nutrients to improve water quality in Lake Champlain,” n.d.).
29
ii. Dissolved Air Flotation
In addition to the centrifuge as a phosphorus separating option, David Dunn from Green
Mountain Power also suggested dissolved air flotation as a potential technique to reduce
phosphorus (Dunn, 2015). One of the downsides that Dunn mentioned regarding the centrifuge
was its high-energy load. In comparison, the dissolved air flotation option has a lighter energy
load. This technology removes suspended solids from the liquid by using air bubbles to float the
solids to the surface and scrapes them away ("About Dissolved Air Flotation," 2015).
In cases where this technology has been used to treat polluted water from wastewater
treatment plants, average reductions of total phosphorus were between 55 and 81% (Kolvunen
and Heinonen-Tanski, 2008). While applications of dissolved air flotation are more common
with wastewater treatment in treatment lagoons, this technology can also be used to target the
nutrient filled runoff from agricultural fields at certain points throughout the year (“Algal
Removal Using Dissolved Air Flotation,” 2015). Companies that specialize in nutrient recovery
from waste have also explored the use of dissolved air flotation to capture nutrients from manure
in dairy operations ("Dissolved Air Flotation," N.d.). DAF systems are also often smaller and
have lower installed costs than other water clarifying technologies (Ross and Valentine, 2008).
These separator options could help provide another alternative to traditional manure
spreading techniques. Options like Dissolved Air Flotation and centrifuge technology can be
used in tandem with the digester and would allow a farmer to take full advantage of the manure
produced from his or her animals. One thing standing in the way of further use and development
of these options is likely the cost of such projects. High upfront or user costs might make
phosphorus separation less feasible for the smaller scale farms that are found throughout the state
of Vermont.
4.4 Middlebury College and Phosphorus Reduction
Middlebury College’s investment in the Goodrich Farms anaerobic digester project not
only has the potential to help the college reach its goal of carbon neutrality, but also encourages
the reduction of phosphorus loading by changing agricultural practices. The liquid byproduct of
anaerobic manure digestion and separation encourages dairy farmers to change their fertilizer
application techniques in favor of a practice that can lead to better manure management.
Furthermore, it would reduce some of the pressures on farmers from TMDL standards as the
separation process reduces manure phosphorus content and allows for an injection method that
reduces runoff. Middlebury’s support for and encouragement in the development of the project
demonstrates the college’s concern for its surrounding environment and the desire to be a good
community member. Middlebury’s investment in this type of project will hopefully spread
information about the potential for additional manure digester projects in Vermont.
30
4.5 Results and Discussion
4.5.1 Models
After exploring the potential for phosphorus loading reductions with the use of a manure
digestion and separation project on dairy farms, we sought to determine where a digester project
would have the greatest impact on phosphorus loading. In order to determine where Vermont
watersheds suffered the most from agricultural phosphorus runoff, we modeled phosphorus
loading into Lake Champlain. In addition, we wanted to support our research on the co-benefits
of manure digestion we examined various phosphorus loading scenarios that use different best
management practices to reduce total phosphorus loading.
In order to model where agricultural phosphorus runoff reductions would have the
greatest impact in Lake Champlain, we used data from the Vermont Center for Geographic
Information to map Vermont’s watersheds feeding into Lake Champlain, and to determine where
in Vermont land was used for agricultural purposes. Then, to model the possible phosphorus
loading from Vermont’s agricultural lands in each of these watersheds, we used coefficients
representing agricultural runoff from Troy et al.’s “Updating the Lake Champlain Basin Land
Use Data to Improve Prediction of Phosphorus Loading” (2007) in ArcMap. We applied these
coefficients to the areas where land use was defined by agriculture in order to map where
phosphorus runoff was the most problematic.
Our resulting analysis (Figure 13) models annual phosphorus loading in kilograms per
acre from land used for agricultural purposes in the Champlain Basin. The areas with the greatest
phosphorus output came from the Missisquoi, Pike, and Otter Creek watersheds. This map also
has the potential to suggest sites for future manure digester locations. The watersheds with
higher contributions of phosphorus to Lake Champlain would be great sites to place manure
digesters. If dairy operations existing within these watersheds were located near a waterway, a
manure digester could significantly reduce the runoff from surrounding farms.
31
Figure 13. GIS analysis of annual phosphorus loading from agricultural lands by each Vermont watershed flowing
into Lake Champlain. Data from Vermont Center for Geographic Information and Troy et al., 2007.
To further support this recommendation, we sought to determine how great of an impact
the liquid fertilizer byproduct of manure digestion could make on resulting phosphorus runoff
when the fertilizer is injected into the soil rather than spread over the surface. We were unable to
find previous studies that modeled these various manure applications on Vermont soils, however,
Eric Smeltzer, from the Vermont Agency of Natural Resources provided us with the Lake
Champlain BMP Scenario Tool developed for the EPA to help model different phosphorus
loading scenarios. This multifaceted tool compares the results of various field management
practices if used on land within major Lake Champlain watersheds to determine their impacts on
phosphorus loading in nearby waterways. This tool describes how various agricultural
management practices impact field runoff and helped us make an informed recommendation for
dairy farmers in Vermont regarding their agricultural practices.
32
We were able to use this scenario tool to explore the phosphorus reduction potential of a
few manure management practices we explored earlier in our research. Tables 1, 2, 3, and 4
document the results of this tool when calibrated for two different watersheds using two different
best management practices. We decided to use this tool as a way to model and compare the
potential benefits of two different management strategies that could be implemented with the
liquid fertilizer byproduct of manure digestion.
We chose to focus our scenario modeling on the Otter Creek and Missisquoi River
watersheds based on the results of our phosphorus loading model (Figure 13). These areas were
highlighted in our analysis due to the significantly higher modeled phosphorus loading from
agricultural land in these areas. We selected land use types from the available options based on
agricultural land types that would be most likely to exist on Vermont dairy farms and therefore
would have the potential to see the benefits of the liquid fertilizer byproduct from a manure
digester. This narrowed our selection down to corn-hay rotation and continuous corn. However,
these two land use types occur on various types of soil or have different hydrologic soil groups
(HSG). The HSG is used to describe the type of soil and runoff potential. We also provided the
phosphorus loading from these specific land groups before the implementation of a best
management practice (BMP). If the original phosphorus loading from the land type was
insignificant, we did not consider it in our analysis. For both the Otter Creek and Missisquoi
Watersheds we focused on two BMP strategies for which we provide the effectiveness of the
strategy and the potential phosphorus reductions that result from their use.
In Tables 1 and 3, we focused on the management practice of manure injection with a
reduced phosphorus fertilizer. This practice describes the fertilizer application practices we are
recommending with the use of a manure digester and separator. The columns in each table
labeled BMP (Best Management Practice) Efficiency and TP (Total Phosphorus) Reduction are
the main foci of the scenario tools. In each scenario involving liquid injection with reduced
phosphorus manure, the best management practice reduced the total phosphorus loading. The
positive, though small, impact on phosphorus loading demonstrates further potential for the use
of manure digester and separation technologies in phosphorus reduction.
33
Table 1. Changes in phosphorus load for different agricultural land types in Otter Creek with application of manure
injection with reduced phosphorus manure as a best management practice.
Land Use Type
HSG
TP Load
(kg/yr)
BMP
Efficiency
TP Reduction (kg/yr)
with BMP
Corn-hay rotation on non-clayey soils
A
724.76
5%
33.89
Corn-hay rotation on non-clayey soils
B
4,909.27
3%
170.14
Corn-hay rotation on non-clayey soils
C
1,972.69
3%
63.08
Corn-hay rotation on clayey soils
D
34,306.24
3%
1,149.88
Continuous corn on non-clayey soils
B
796.85
9%
70.31
Continuous corn on non-clayey soils
C
374.55
9%
32.06
Continuous corn on clayey soils
D
5,399.27
5%
264.79
Data from Lake Champlain BMP Scenario Tool
Table 2. Changes in phosphorus load for different agricultural land types in Otter Creek with application of cover
crop, conservation tillage and manure injection as a best management practice.
Land Use Type
HSG
TP Load
(kg/yr)
BMP
Efficiency
TP Reduction (kg/yr)
with BMP
Corn-hay rotation on non-clayey soils
A
724.76
39%
283.26
Corn-hay rotation on non-clayey soils
B
4,909.27
43%
2,094.62
Corn-hay rotation on non-clayey soils
C
1,972.69
46%
912.37
Corn-hay rotation on clayey soils
D
34,306.24
64%
22,013.17
Continuous corn on non-clayey soils
B
796.85
43%
339.99
Continuous corn on non-clayey soils
C
374.55
46%
173.23
Continuous corn on clayey soils
D
5,399.27
64%
3,464.53
Data from Lake Champlain BMP Scenario Tool
34
Table 3. Changes in phosphorus load for different agricultural land types in Missisquoi River with application of
manure injection with reduced phosphorus manure as a best management practice.
Land Use Type
HSG
TP Load
(kg/yr)
BMP
Efficiency
TP Reduction (kg/yr) with
BMP
Corn-hay rotation on non-clayey soils
A
853.18
5%
39.89
Corn-hay rotation on non-clayey soils
B
3,047.29
3%
105.61
Corn-hay rotation on non-clayey soils
C
9,527.40
3%
304.65
Corn-hay rotation on clayey soils
D
6,435.00
3%
215.69
Continuous corn on non-clayey soils
B
1,087.63
9%
95.97
Continuous corn on non-clayey soils
C
2,208.51
9%
189.05
Continuous corn on clayey soils
D
1,990.34
5%
97.61
Data from Lake Champlain BMP Scenario Tool
Table 4. Changes in phosphorus load for different agricultural land types in Missisquoi River with application of
cover crop, conservation tillage and manure injection as a best management practice.
Land Use Type
HSG
TP Load
(kg/yr)
BMP
Efficiency
TP Reduction
(kg/yr)
Corn-hay rotation on non-clayey soils
A
853.18
39%
333.45
Corn-hay rotation on non-clayey soils
B
3,047.29
43%
1,300.18
Corn-hay rotation on non-clayey soils
C
9,527.40
46%
4,406.42
Corn-hay rotation on clayey soils
D
6,435.00
64%
4,129.13
Continuous corn on non-clayey soils
B
1,087.63
43%
464.06
Continuous corn on non-clayey soils
C
2,208.51
46%
1,021.43
Continuous corn on clayey soils
D
1,990.34
64%
1,277.13
Data from Lake Champlain BMP Scenario Tool
Tables 2 and 4 look at the same two watersheds, but we ran the scenario tool using a
different BMP. This BMP involves a series of management practices that we have explored
through our research: cover crop, conservation tillage, and manure injection. The resulting
efficiency and total phosphorus reduction for this combination of management practices were
significantly greater than the scenario solely focusing on manure injection and reduced
phosphorus fertilizer.
Although the scenario tool offered many more options for BMPs, we chose these
scenarios to highlight the potential of manure injection. While the sole use of manure injection
and reduced phosphorus manure does not make a huge impact on phosphorus load reduction, it
still is an additional benefit to farmers who currently work with manure digesters. Additionally,
the second scenario that employed a trio of management practices suggests that farmers using a
liquid injection fertilizer application method with a byproduct of manure separation should also
explore the conservation management practices described above. The combination of these
35
efforts significantly increases the phosphorus reductions from agricultural land used for different
purposes with varying soil types. Not only do these data encourage the use of various
conservation management practices, but they also highlight the potential co-benefit of manure
digesters in that they can provide farmers with an easily injectable fertilizer source. The large
phosphorus loading reductions modeled in this scenario tool from the combination of cover crop,
conservation tillage, and manure injection, highlight how significantly these practices can help
farmers comply with TMDL requirements in their watershed.
4.5.2 Recommendations
Based on our models, we believe that the co-benefits of anaerobic manure digestion
through the production of a liquid fertilizer make a strong case for the future siting of manure
digester projects in the Champlain Basin and in other regions where phosphorus runoff has
become an issue. A digester project would encourage farmers who put manure in the digester to
use the liquid byproduct as a fertilizer on their fields and reduce their environmental impact both
through the capture of methane and through the mitigation of phosphorus runoff. In Vermont, we
recommend the siting of digester projects located in Otter Creek and the Missisquoi and Pike
watersheds where runoff has been particularly problematic. If there aren’t any large farms in
these areas, we recommend the construction of a community digester where farmers could truck
their manure off site but could still reap the benefits of phosphorus mitigation through the use of
the liquid fertilizer byproduct.
Additionally, when the technology becomes more economically feasible, we recommend
the addition of phosphorus separators such as the decanter centrifuge to digester projects. These
nutrient separators would further reduce dairy farm impacts on nearby watersheds in Vermont.
The resulting dry nutrients produced in the separation project could also profit farmers if excess
nutrients were sold to areas that had phosphorus shortages.
Finally, we would recommend the addition of monitoring stations in Lake Champlain
tributaries to make more accurate assessments regarding problem watersheds in the basin. These
stations could also support the modeling data if they show a significant decline in phosphorus
with an increase in the number of manure digesters and separators.
5. Conclusion
As 2016 draws nearer, Middlebury College has partnered with an anaerobic digester
project at the Goodrich Farm to facilitate some of the final GHG emissions reductions needed to
reach net zero. In 2013, with the addition of the biomass plant and various efficiency projects,
emissions were reduced from ~30,500 MTCD to 13,848 MTCD, a 55% reduction. With the
digester project, the college will switch from the use of #6 fuel oil to RNG, producing a 53%
reduction from 2013 emissions. In addition, an average of baseline methane emissions modeled
36
by RGGI and CARB at the Goodrich Farm representing the maximum offset potential estimates
an additional 35% reduction with the implementation of the digester and subsequent capture and
destruction of methane. These two aspects of the digester project therefore put projected 2016
reductions at 94.5% from 2008, with about 1,661 MTCDE still left to be offset. Although this
project may not completely get the college to net zero, it plays a major role in that reduction and
has the potential to provide more offsets in the future.
Methane accounting is still a new and developing process that is ultimately determined
by site-specific variables. As such, the way protocols assess and implement variables can change
estimates drastically and represent different offset results. The more detail available about on-site
practices, the more accurately offsets can be estimated; but it is important to note these variations
within the context of the abstract world of carbon accounting. Different levels of emissions
evaluations are necessary for different scales, however, and coarser protocols like the EPA
model should be applied to larger scale projects while more specific calculations (RGGI and
CARB) can be used for the finer scale.
The digester project also offers the Goodrich Farm a way to reduce potential phosphorus
overload and contamination in the Otter Creek watershed. Digester and phosphorus separation
technologies can develop in tandem and contribute to more holistic conservation management
practices. Overall, the digester project is a multifaceted way to reduce the carbon footprint for
both the college and Goodrich Farm. It reduces the output of three different pollutants: CO2 from
fuel oil, methane from open manure lagoons and phosphorus from spreading. This combination
reflects how complex pollution and emission issues are and how remediation efforts can
effectively reflect that complexity. Solutions like manure digesters provide yet another pathway
to reduce emissions that can work congruently with other efficiency projects.
Middlebury College’s partnership with the digester project also supports the development
of digesters as a valuable energy efficiency strategy in Vermont. With some fine-tuning, it has
the potential to develop into a standard of practice on farms across the state. It also shows that
benefits generated with digester technology are not confined to the farm: offsets and energy
efficiency benefits can be distributed to the larger community through the distribution of RNG
and injectable phosphorus fertilizer. As technology continues to improve in the renewable energy
market, more integrative techniques have also become more cost effective and encourage
partnerships within communities. With this project, the college continues to work towards a
carbon neutral goal and also encourages the use of a relatively new technology that supports the
farming community and watershed ecosystems of Vermont as a whole. In the end, although
carbon neutrality is a goal specific to campus, the energy efficiency solutions are a team effort.
37
Acknowledgements
We would like to extend a thank you to our community partners Jack Byrne, the
Directory of Sustainability Integration at Middlebury College, and Dan Smith, the CEO of
LincolnRNG. Both helped immensely with our understanding of the proposed project, the goals
of their organizations, and our success would not have been possible without them.
Additionally, thank you to David Dunn and Patrick Wood who provided us with further
information on the manure digestion process and models used to account for methane emissions
reductions from these types of projects. We would also like to extend a thank you to William
Hegman of the Middlebury College Geography Department for his assistance in creating our GIS
model and to Eric Smelter for providing us with the EPA’s Scenario Tool for Lake Champlain,
which gave us a more precise idea of the impacts of liquid injection technology on phosphorus
runoff.
38
6. Bibliography
"About Dissolved Air Flotation." Dissolved Air Flotation Corporation. Dissolved Air Flotation
Corporation, n.d. Web. Retrieved from http://www.dafcorp.com/aboutdaf on 30 Nov.
2015.
Aguiar Jr., T.R., K. Rasera, L.M. Parron, A.G. Brito, M.T. Ferreira. Nutrient removal
effectiveness by riparian buffer zones in rural temperate watersheds: The impact of
no-till crops practices. Agricultural Water Management 149. (2015): 74-80. Print.
AGRO. Screw Press. n.d. Web. Retrieved from http://www.agropulping.com/wet-washingsystems.html on 4 Dec. 2015.
“Algal Removal Using Dissolved Air Flotation.” FRC Systems International. Web. Retrieved
from http://frcsystems.com/algae-removal-using-dissolved-air-flotation-daf/ on 17 Nov.
2015.
Arabi, Mazdak, Jane R. Frankenberger, Bernie A. Engel, and Jeff G. Arnold. “Representation
of Agricultural Conservation Practices with SWAT.” Hydrological Processes 22.16
(2008): 3042-3055. Print.
Bachman, Marilyn. Part 2 The Concept of Limiting Nutrients. (n.d.): 4-16. Print.
Brandt, R. C., and H. A. Elliott. Phosphorus Runoff Losses from Surface-Applied Biosolids and
Dairy Manure. Rep. University Park: Penn State U, 2003. Print.
Byrne, Jack. “LRNG-PJN-1.” Letter to Patrick J. Norton. 20 Feb. 2015a. MS. Middlebury
College, Middlebury, Vermont.
Byrne, Jack. “Middlebury College Biomass Tour.” Personal interview. 12 Oct. 2015b.
Byrne, Jack. 2014. Middlebury College’s Annual GHG Inventory. Middlebury College Office of
Sustainability. Middlebury VT. Print.
Chianese, D. S., C. A. Rotz, and T. L. Richard. "Simulation of Methane Emissions from
Farms to Assess Greenhouse Gas Reduction Strategies." Transactions of the ASABE 52.4
(2009): 1313-323. Print.
Chrislock, Michael F., Enrique Doster, Rachael A. Zitomer, and Alan E. Wilson.
“Eutrophication: Causes, Consequences, and Controls in Aquatic Ecosystem.” Nature
Education Knowledge. Web. Retrieved from http://www.nature.com/scitable/know
ledge/library/eutrophication-causes-consequences-and-controls-in-aquatic-102364466 on
2 Nov. 2015.
“Community Energy & Efficiency Development Fund 2015 Annual Plan.” Green Mountain
Power. 2014. Print.
"Dissolved Air Flotation." Manure Systems Inc. N.p., n.d. Web. Retrieved from
http://manuresystemsinc.com/solutions/equipment/dissolved-air-flotation/ on 13 Dec.
2015.
Dowds, Jonathan. “Anaerobic Digestion: A Farm Methane Mitigation Strategy for
Vermont Dairies.” n.p. 2009. Print.
Drag hose Injector. Digital image. N.p., n.d. Web. Retrieved from
http://forums2.gardenweb.com/discussions/1672474/rototilling-vs-old-fashoned-plowing
on 5 Dec. 2015.
Dunn, David. “Interview with David Dunn.” Personal Interview. 28 Oct. 2015.
Eastern Research Group, Inc. A Protocol for Quantifying and Reporting the Performance of
39
Anaerobic Digestion Systems for Livestock Manures. Lexington, MA: U.S.
Environmental Protection Agency AgSTAR Program, 2011. Print.
"Economics of the Basin." Lake Champlain Basin Atlas. Lake Champlain Basin Program,
2004. Web. Retrieved from http://atlas.lcbp.org/HTML/so_econ.htm on 12 Nov. 2015.
Focus on Vermont Farm Projects: Single and Two-Stage Dairy Manure Separation. N.p.:
Native Energy, May 2015. Print.
Hamilton, Douglas W. “Anaerobic Digestion of Animal Manures: Methane Production Potential
of Waste Materials.” 2012. BAE-1762. Division of Agricultural Sciences and Natural
Resources: Oklahoma State University. Print.
Hart, Murray R., Bert F. Quin, and Long M. Nguyen. "Phosphorus Runoff from
Agricultural Land and Direct Fertilizer Effects: A Review." Journal of Environmental
Quality 33.6 (2004): 1954-72. Print.
Hirschfeld, Peter. "State Considers Pollution Trading Scheme To Reduce Phosphorus In Lake
Champlain." VPR. N.p., 24 Oct. 2014. Web. Retrieved from
http://digital.vpr.net/post/state-considers-pollution-trading-scheme-reducephosphorus-lake-champlain#stream/0 on 30 Nov. 2015.
Eggleston H.S., Buendia L., Miwa K., Ngara T. and Tanabe K. 2006 IPCC Guidelines for
National Greenhouse Gas Inventories. Hayama, Japan: IGES, 2008. Print.
Kaasik, Allan. "Techniques for Application of Manure to Land." Sustainable Agriculture. Ed.
Christine Jakobsson. Uppsala University: Baltic U Programme, 2012. 132-35. Print.
Kleinman, Peter J., et al. "Effect of Mineral and Manure Phosphorus Sources on Runoff
Phosphorus." Journal of Environmental Quality 31.6 (2002): 2026-33. Print.
Kolvunen, J., and H. Heinonen-Tanski. "Dissolved Air Flotation (DAF) for Primary and Tertiary
Treatment of Municipal Wastewaters." Environmental Technology 29.1 (2008): n. pag.
Taylor & Francis. 28 May 2008. Web. Retrieved from
http://www.ncbi.nlm.nih.gov/pubmed/18610550 on 13 Dec. 2015.
Krich, Ken et al. “Biomethane from Dairy Waste: A Sourcebook for The Production and Use of
Renewable Natural Gas in California.” July 2005. Print.
"Lake and Basin Facts." Lake Champlain Basin Program. N.p., n.d. Web.
Retrieved from http://www.lcbp.org/about-the-basin/facts/ on 12 Nov. 2015.
"Lake Champlain Basin Program: State of the Lake 2015." Lake Champlain Basin Program:
State of the Lake 2015. Lake Champlain Basin Program, n.d. Web. Retrieved from
http://sol.lcbp.org/ on 12 Nov. 2015.
"Lake Champlain Phosphorus TMDL: A Commitment to Clean Water." Lake Champlain
Phosphorous TMDL: A Commitment to Clean Water. United States Environmental
Protection Agency, n.d. Web. Retrieved from http://www3.epa.gov/region1/eco/
tmdl/lakechamplain.html on 12 Nov. 2015.
“Linking Community and Technologies to Capture and Convert Nutrients to improve water
quality in Lake Champlain,” n.d. Print.
Manure digester. Digital image. Weltec Biopower. N.p., n.d. Web. 5 Dec. 2015.
McGinn, S. M., and K. A. Beauchemin. “Dairy Farm Methane Emissions Using a Dispersion
Model.” Journal of Environmental Quality 41 (2012): 73-79. Web. Retrieved from
http://www.ncbi.nlm.nih.gov/pubmed/22218175 on 16 Dec. 2015.
Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F.
Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and
H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change
40
2013: The Physical Science Basis. Contribution of Working Group I to the Fifth
Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D.
Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and
P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and
New York, NY, USA.
N.d. Utah State University Manure Solutions. Web. Retrieved from
http://extension.usu.edu/waterquality/htm/agriculturewq/manuresolutions/.
“Updated 2014-2036 Timeline for Completing the Vermont Lake Champlain Restoration
Plan-[Phosphorus Total Maximum Daily Load (TMDL)].” Montpelier: Watershed
Management Division, 2015. Print.
Petitioner’s Exhibit LRNG-DKS-2. Elmar Broering/WELTEC technical and informational
letter (revised), LincolnRNG Petition for Certificate of Public Good under 30 V.S.A. §
248 on 5 Dec. 2015.
Phosphorus TMDLs for Vermont Segments of Lake Champlain. Rep. Boston: Environmental
Protection Agency, 2015.
Quinlan, Paul. "Chesapeake Bay: Cap and Trade for Water Pollution -- 'trendy, Hip, Glitzy'
and Controversial." Greenwire. N.p., 8 May 2012. Web. Retrieved from
http://www.eenews.net/stories/1059964052 on 30 Nov. 2015.
"Restoring Lake Champlain." Watershed Management Division. Vermont Department of
Conservation, n.d. Web. Retrieved from http://www.watershedmanagement.vt.gov/erp/
champlain/ on 30 Nov. 2015.
Regional Greenhouse Gas Initiative (RGGI). Model Rule: Part XX CO2 Budget Trading
Program. Rep. N.p: n.p., 2013. Print.
Ross, Charles C., and G. Edward Valentine. Use of Coupled Biological/Dissolved Air Flotation
Processes for Treatment of Food and Dairy Processing Wastewaters. Smyrna, GA:
Environmental Treatment Systems, Inc., 2008. PDF.
Schaltegger, Stefan, and Maria Csutora. "Carbon Accounting for Sustainability and
Management. Status Quo and Challenges." Journal of Cleaner Production 36 (2012): 116. Print.
Schaschke, Carl. “Eutrophication.” A Dictionary of Chemical Engineering. Oxford University
Press, 2014. Web. Retrieved from http://www.oxfordreference.com/view/10.1093/
acref/9780199651450.001.0001/acref-9780199651450-e-1047 on 2 Oct. 2015.
Smith, Dan. "Tour of the Goodrich Farm." Personal interview. 27 Oct. 2015.
Steckler, David. Summary of Prefiled Testimony of David Steckler. LincolnRNG Petition for
Certificate of Public Good under 30 V.S.A. § 248 on 5 Dec. 2015.
Tetra Tech Inc. Sheet of Lake Champlain BMP Scenario Tool prepared for U.S. EPA Region 1New England. 9 Sep. 2015. Print.
Troy, Austin, Deane Wang, David Capen, and Rubenstein School of Environment and Natural
Resources UVM, comps. Updating the Lake Champlain Basin Land Use Data to Improve
Prediction of Phosphorus Loading. Tech. no. 54. N.p.: Lake Champlain Basin Program,
2007. Lake Champlain Basin Program. Print.
The Vermont Agency of Agriculture. “Accepted Agricultural Practice Regulations.” N.p. 2006.
"U.S. Greenhouse Gas Inventory Report: 1990-2013." U.S. Greenhouse Gas Inventory Report:
1990-2013. U.S. EPA, 15 Apr. 2014. Web. Retrieved from
http://www3.epa.gov/climatechange/Downloads/ghgemissions/US-GHG-Inventory-2015Main-Text.pdf on 12 Nov. 2015.
41
Vermont Agency of Agriculture, Food and Markets and the Vermont Department of
Environmental Conservation. Development of a Nutrient Trading Initiative in the Lake
Champlain Basin. N.p.: n.p., 2014. Print.
Vermont Farm Projects: Single and Two-Stage Separation. N.p.: Native Energy, January 2014.
Print.
Vermont Public Service Board. 2015. “Petition for a Certificate of Public Good by Lincoln
Renewable Natural Gas.” Print.
Weisman, Barbara. “Conservation Practices.” Minnesota Department of Agriculture. Web.
N.p., n.d. Web. Retrieved from http://www.mda.state.mn.us/protecting/conservation/
practices.aspx on 5 Nov. 2015
"What's the Fuss about Phosphorus?" Lawn to Lake. Lake Champlain Basin Program, n.d.
Web. Retrieved from http://www.lawntolake.org/phos.htm on 12 Nov. 2015.
“What Is Biomethane.” Biomehtane.org.uk. 2012. Web. Retrieved from
http://www.biomethane.org.uk/index.html on 1 Nov. 2015.
Wright, Peter, and Shawn Bossard. “Manure Application with a Degree.” Dairy Environmental
System. Cornell University. N.d. Retrieved from 9 Nov. 2015.
Zhang, Hailin, Gordon Johnson, Mitch Fram. “Managing Phosphorus from Animal Manure.”
Division of Agricultural Sciences and Natural Resources. N.d. Retrieved from
http://animalwaste.okstate.edu/bmps/f-2249web.pdf on 11 Nov. 2015.
42
Appendix A: EPA
Methodology for estimating methane emissions from dairy manure management was
taken from the U.S. Greenhouse Gas Inventory Report: 1990-2013 Annex 3. Following annual
data was collected for using the model:
Animal population data: This includes determining animal type e.g. lactating dairy cows,
heifers, etc., which accounts for differences in methane generation among livestock type.
This was site-specific data obtained from the Public Service Board of Vermont.
Typical animal mass (TAM) by animal type: The TAM refers to the annual average live
weight of an animal based on livestock type. The EPA estimate of the average TAM in
the State of Vermont was used. The data was obtained from the U.S. Greenhouse Gas
Inventory Report: 1990-2013, Annex 3, Table A-204 (EPA, 2014).
Waste management system type (WMS): The WMS refers to the types of systems used
to manage manure. This includes determining manure storage facility and type e.g. dry or
liquid storage and the amount of manure spread annually. This was site-specific data
obtained from the Public Service Board of Vermont.
Volatile solids (VS) production rate by animal type: The VS content of manure is the
fraction of the diet consumed by cattle that is not digested and thus excreted as fecal
material, which combined with urinary excretions constitutes manure. The EPA estimate
of the average VS production rate in the State of Vermont was used. The data was
obtained from U.S. Greenhouse Gas Inventory Report: 1990-2013, Annex 3, Table A-206
(EPA, 2014).
Methane producing potential (B0) of the volatile solids by animal type: The B0 is the
maximum amount of methane that can be produced from a given quantity of manure per
animal type. The EPA estimate of the average B0 in the State of Vermont was used. The
data was obtained from the U.S. Greenhouse Gas Inventory Report: 1990-2013, Annex 3,
Table A-204 (EPA, 2014).
Methane conversion factors (MCF) by manure management system: The MCF is the
maximum amount of methane per animal type and WMS that would be created if the
volatile solids were completely converted into methane. The EPA estimate of the average
MCF in the State of Vermont was used. The data for the state of Vermont was obtained
from the U.S. Greenhouse Gas Inventory Report: 1990-2013, Annex 3, Table A-210
(EPA, 2014).
43
To calculate the total baseline methane emissions in carbon dioxide equivalents the
following equation was used:
Where,
BE
A
WMS
NA
TAMA
VSA
DM
365.25
B0
MCF
=
=
=
=
=
=
=
=
=
=
0.662
0.001
GWP
=
=
=
Baseline emissions (metric tonnes of CO2 equivalent/year)
Animal type
Waste management system
Number of animals for animal type
Typical animal mass (kg)
Volatile solids production rate (kg VS/1000 kg animal mass/day)
Distribution of manure by WMS for each animal type (%)
Days per year
Maximum CH4 producing capacity (m3 CH4/kg VS)
Methane conversion factor for the animal type and waste management system
(%)
Density t 25oC (kg CH4/m3 CH4)
Conversion factor of kg CH4 per year to metric tonnes of CH4 per year
The 100 year methane global warming potential for the conversion of CH4 to
CO2 equivalent
The CH4 emissions for each WMS and animal type were summed to determine the total
baseline CH4 emissions (Table A1).
44
Table A.1. Values used to calculate baseline methane emissions based on the EPA method.
* We were unable to acquire the exact percentages of the amount of manure distributed between different
management systems at the Goodrich Farm, as such average manure distribution values provided by the
EPA for Vermont were used.
** The latest GWP taken from IPCC Fifth Assessment Report (Myhre et al. 2013).
45
Appendix B: CARB, COP
The procedure to determine the modeled project baseline methane emissions follows
Equation 5.3, which combines Equation 5.3 and 5.4 of the protocol. The following inputs were
used in Equation 5.3 based on site-specific information about the mass of volatile solids (VS)
degraded by the anaerobic storage system and available for methane conversion.
Population and Livestock Category (PL): The procedure requires a designation of
livestock category, e.g. lactating dairy cows, heifers, etc., which accounts for differences
in methane generation among livestock type. This information was obtained from Table
A.2 of Appx. A. The population figure is site-specific data that should be monitored each
month and averaged for annual total population.
Annual Volatile Solids degraded in anaerobic manure (VSL): VS content of manure is the
portion of animal intake that is not digested and subsequently excreted along with urine
as manure expressed in a dry matter weight basis (EPA, 2014). VS values must be
calculated for all livestock categories. Volatile solids degraded annually were calculated
using livestock population (PL), estimated volatile solids produced by livestock category
(obtained in Appx. A of the COP document), reporting days per month and the previous
month’s available and degradable VS.
MassL: Mass refers to annual average live weight of animals based on livestock category
(L). This value is necessary in the conversion of VS from kg/day/1000kg to
kg/day/animal. Site-specific livestock mass information was not available, so value was
obtained as Typical Average Mass (TAM) from Table A.2 in Appx. A.
Maximum methane producing capacity for livestock category ‘L’ (B0,L): B0,L is the
maximum methane producing capacity of an amount of manure. This information was
obtained as a default from Table A.3 in Appx. A
Density and conversion factor of methane (MCF): MCF refers to the amount of potential
methane produced given a certain management type. Methane production is a function of
the anaerobic conditions present in a system, its temperature and the retention time of
manure in that system. For anaerobic lagoons and slurries, this value requires a sitespecific calculation of volatile solids degraded by anaerobic storage system. In this
equation, this is expresses as ‘degraded volatile solids” or “VSdeg”. This value is equal to
the monthly available VS multiplied by the van’t Hoff-Arrhenius factor (F), which
converts total available VS to methane convertible VS based on the monthly temperature
of the system.
46
Once these variables were collected, the following equation was used to estimate baseline
emissions:
BECH4,AS = ∑VSdeg,AS,L x B0,L x 0.68 x 0.001 x GWP
Where,
BECH4,AS
=
VSdeg,AS,L
=
B0,L
=
0.68
0.001
GWP
=
=
=
Total annual project baseline methane emissions from anaerobic
manure storage systems, in carbon dioxide equivalent (t CO2e/yr)
Annual volatile solids degraded in anaerobic manure system ‘AS’ from
livestock category ‘L’
Maximum methane producing capacity of manure for livestock category
‘L’
Density of methane
Methane conversion factor from kg to metric tonnes (mt)
The 100 year methane global warming potential for the conversion of CH4
to CO2 equivalent
Table B.1. Values used to calculate baseline methane emissions based on the CARB method.
47
Appendix C: RGGI
CO2e (tons) = (Vm x M)/2000 x GWP
48
49
50
51