GUIDELINES FOR FOOD WASTE DISPOSAL
A STUDY IN FOOD WASTE CHARACTERIZATION & BIOGAS GENERATION
PREPARED BY: MICHAEL SARGENT
AUGUST 2011
GUIDELINES FOR FOOD WASTE DISPOSAL
A Study in Food Waste Characterization and Biogas Generation
SUBMITTED TO:
Professor Greg Harrington
Professor Traci Nathans-Kelly
Professor Jae Park
PREPARED BY:
Michael S. Sargent
Master of Environmental Engineering Candidate
August 2011
TABLE OF CONTENTS
ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
LIST OF ACRONYMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vi
ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vi
1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. FOOD WASTE CHARACTERIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Residential Food Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1. Food Distinction & Sorting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2. Decomposition & Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.3. Assessment of Food Waste in Madison, WI . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Commercial Food Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3. WASTE MANAGEMENT ALTERNATIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. Landfilling & Incineration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1.1. Collection & Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1.2. Landfill Methane Gas Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1.3. Energy Potential & Anaerobic Digestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2. Food Waste Disposer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2.1. Design & Brief History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2.2. Application Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.2.3. Application Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2.4. BOD & COD Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2.5. Effluent Characteristics & Energy Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2.6. Energy Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3. Composting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3.1. Collection & Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3.2. Methane Gas Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.3.3. Energy Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4. EXPERIMENTAL METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1. Selection of Food Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.1.1 Food Categorization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.1.2 Foods Tested . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.2. Selection of Disposer Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.3. Design & Construction of Disposer Test Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.4. Testing Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.4.1. COD Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.4.2. Nitrate Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.4.3. Phosphorous Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5. RESULTS & DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.1. COD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.2. Nitrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.3. Phosphorous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6. CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
7. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
iii
ACKNOWLEDGEMENTS
I would like to thank Professor Jae Park and Hiroko Yoshida for offering inspiration and
continued support throughout this project. ACKNOWLEDGEMENT ACKNOWLEDGMENT
I also extend my gratitude to Chelsea Rowe, Lyndsey Thruman, and Jack Shumann for assistance
with laboratory proceedings. It wasn’t always fun, but you were always there to lend a helping
hand.
Lastly, I would like to thank all of my friends and family for their generous, approximately 40
gram by weight, food donations to this project. I appreciate you opening your refrigerators and
cupboards to further my education and the environmental sciences.
LIST OF FIGURES
FIGURE
PAGE
1.1: MSW Materials Recovered & Generation from 1960 - 2009 (US EPA) . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2: MSW Handling from 1960 - 2009 (US EPA 2009) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1: Total Annual MSW Generation by Weight (US EPA 2009) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2: Breakdown of Percent by Weight for Madison, WI MSW Sort (Yoshida 2010) . . . . . . . . . . . . . . . . . . . 9
3.1: Landfill Methane Balance (Smith 1997) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2: Waste Composition at Dane County Landfill (Yoshida 2010) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.3: Food Waste Disposer Assembly (http://www.shajalique.id.au) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.4: Phase Breakdown of Anaerobic Digestion (Springer 2010) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.5: Composting Process (Amlinger 1996) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1: Food Pyramid (previous) to MyPlate (current) (USDA.gov) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.1: COD Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.2: Standard Deviation of % Change for COD Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.3: Nitrate Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
5.4: Standard Deviation of % Change for Nitrate Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
5.5: Phosphorous Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.6: Standard Deviation of % Change for Phosphorous Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
v
LIST OF ACRONYMS
Anaerobic Digestion (AD)
Biochemical Oxygen Demand (BOD)
Chemical Oxygen Demand (COD)
Chicago Climate Exchange (CCX)
Clean Air Act (CAA)
Code of Federal Regulations (CFR)
Combined Sewer Overflow (CSO)
Compressed Natural Gas (CNG)
Dissolved Oxygen (DO)
Energy-from-Waste (EfW)
Environmental Protection Agency (EPA)
Fats, Oil, and Grease (FOG)
Food Waste Disposer (FWD)
Global Warming Potential (GWP)
Greenhouse Gas (GHG)
Hazardous Air Pollutants (HAPs)
Landfill Gas (LFG)
Madison Metropolitan Sewerage District (MMSD)
Maximum Contaminant Level Goals (MCLG)
Municipal Solid Waste (MSW)
New York City Department of Environmental Protection (NYCDEP)
Non-Methane Organic Compound (NMOC)
Regional Greenhouse Gas Initiative (RGGI)
Resource Conservation and Recovery Act (RCRA)
Source Separated Organics (SSO)
Theoretical Oxygen Demand (ThOD)
Total Suspended Solids (TSS)
United States (US)
Wastewater Treatment Plant (WWTP)
Waste-to-Energy (WtE)
ABSTRACT
There are many alternatives when it comes to remediation of food waste. In recent years focus
has been shifting towards maximizing the energy potential of food waste. The purpose of this
study was to assess various food waste effluents generated by a food waste disposer (FWD) for
impact on COD, nitrate, and phosphorous. Another goal was to review findings from past
studies and compare current food waste diversion practices by method, energy yield potential,
and greenhouse gas emissions. Food waste diversion alternatives assessed include landfilling &
incineration, food waste disposers, and composting.
Food wastes were collected and characterized based on availability and the USDA’s MyPlate
food grouping system. A control sample of tap water and 39 food waste samples were
processed individually through a FWD. The effluent produced by each sample was collected and
tested separately using Hach testing kits for COD, nitrate, and phosphorous.
In analysis of COD test results it was concluded foods from the Grains Group and the Dairy
Group caused the greatest concentration increases. This was also true for nitrate testing. It was
also found the Grains Group showed the highest deviation for COD testing. It should be noted,
however, some foods within the Grains Group caused an observed decrease in concentration in
COD testing. Foods from the Dairy Group caused a significantly higher increase in phosphorous
concentration than foods from any other group. However, the Dairy Group showed the highest
deviation for both nitrate and phosphorous testing.
vii
1. INTRODUCTION
The total amount of MSW going to landfills dropped by more than 13 million tons, from 145.3
million to 131.9 million tons in 2009 (see Table 1.2). However, the rate of municipal solid waste
(MSW) generation is still arguably high. As Figure 1.1 shows some materials are being recovered
from this waste. Recovery is still low relative to the rate of generation. Furthermore, even with
decreasing generation and better rate of recovery there are many consequences to MSW
generation, a primary being the generation of greenhouse gasses (GHG).
Organic waste diversion has been largely accepted worldwide as a means to reduce GHG
emissions from landfills. The European Commission’s Landfill Directive requires member states
to divert 65% of organic waste (relative to 1995 levels) from landfills by 2016 (CECD 2003). In
2009, the Chicago Climate Exchange formulated the protocol for evaluating organic waste
diversion programs and began assigning GHG emission offset credits. (Levis et al., 2010).
MSW Generation (million tons)
300
250
200
Total Materials
Recovered
150
Total
Generation
100
50
0
1960
1970
1980
1990
2000
Year
2005
2007
2008
2009
Figure 1.1: MSW Materials Recovered & Generation from 1960 - 2009 (US EPA)
Food waste comprises the largest fraction of organic waste currently sent to landfills (Table
1.1). Unlike other organic waste, such as yard waste and paper waste, the programs and
facilities to manage food waste are less established and organized in the United States. A recent
survey conducted by Biocycle found that 90 municipalities in the United States have an organic
waste diversion program. This number has more than doubled since 2008 (Levis et al., 2010.
This shows an increasing number of municipalities are promoting & facilitating source
separation of organic waste and centralized treatment. This is a conscious effort to extend the
1
usable life of local landfills, recover valuable recyclable materials, and reduce the emission of
methane and other hazardous gases.
Weight Generated
Weight Recovered
PAPER & PAPERBOARD
68.43
42.50
Recovery as Percent
of Generation
62.1%
GLASS
11.78
3.00
25.5%
Material
METALS

Steel
15.62
5.23
33.5%

Aluminum
3.40
0.69
20.3%

Other Nonferrous
1.89
1.30
68.8%
TOTAL METALS
20.91
7.22
34.5%
PLASTICS
29.83
2.12
7.1%
RUBBER & LEATHER
7.49
1.07
14.3%
TEXTILES
12.73
1.90
14.9%
WOOD
15.84
2.23
14.1%
OTHER MATERIALS
4.64
1.23
26.5%
171.65
61.27
35.7%
TOTAL MATERIALS IN
PRODUCTS
OTHER WASTES

Food*
34.29
0.85
2.5%

Yard
33.20
19.90
59.9%

Misc. Inorganics
3.82
Negligible
Negligible
TOTAL OTHER WASTES
71.31
20.75
29.1%
TOTAL MSW
242.96
82.02
33.8%
Table 1.1: Generation and Recovery of Materials in MSW (US EPA 2009)
(million tons and percent generation of each material)
*NOT all food considered was acceptable for FWD processing
Most remediation practices commonly utilized by municipalities to dispose of food waste can
be considered environmentally noxious: stored inside buildings (even refrigerated); piled in
bags on sidewalks; collected in trucks; and shipped to distant landfills, where it generates
leachate and greenhouse gases. These processes are not cheap, hygienic, environmentally
friendly, nor sustainable. While it may not be the largest weight produced by weight, food
waste is arguably the least managed and should be considered for better environmental
practices.
Unfortunately, given the complexity of organic waste flows in the urban environment it is
difficult to accurately estimate and model the overall environmental impact of organic waste
diversion efforts. This is why it is important to begin isolating and assessing organic waste on a
smaller scale. This study aims to separate organic food waste into recognizable food groups and
identify the consequences of processing said waste in a food waste disposer (FWD). Knowing
more facets, consequences, etc. of food waste management and processing will help future
studies continue to better evaluate diversion efforts and continue the increases in recovery
observed in Table 1.2 and Figure 1.2.
Recovered for
Recycling
Recovered for
Composting*
Combustion
with Energy
Recovery**
Discards to
Landfill, other
disposal***
Total Materials
Recovery
Total
Generation
1960
1970
1980
1990
2000
2005
2007
2008
2009
5.6
8.0
14.5
29.0
53.0
59.3
63.1
61.8
61.3
Negligible
Negligible
Negligible
4.2
16.5
20.6
21.7
22.1
20.8
0.0
0.4
2.7
29.7
33.7
31.6
32.0
31.6
29.0
82.5
112.7
134.4
145.3 139.4 140.9 138.2 135.6 131.9
5.6
8.0
14.5
33.2
88.1
121.1
151.6
208.3 242.5 252.4 255.0 251.0 243.0
69.5
79.9
84.8
83.9
82.0
Table 1.2: Yearly MSW Activity [million tons], (US EPA 2009)
* Composting of yard trimmings, food waste, and other MSW organic material. Figures do not account
for backyard composting.
** Includes combustion of MSW in mass burn or refuse-derived fuel form, and combustion with energy
recovery of source separated materials in MSW (e.g., wood pallets, tire-derived fuel).
*** Discards after recovery minus combustion with energy recovery. Discards include combustion
without energy recovery.
3
MSW Generation (million tons)
300
250
200
Discards to Landfill,
other disposal
150
Combustion with Energy
Recovery
100
Recovered for
Composting
Recovered for Recycling
50
0
1960 1970 1980 1990 2000 2005 2007 2008 2009
Year
Figure 1.2: MSW Handling from 1960 - 2009 (US EPA 2009)
2. FOOD WASTE CHARACTERIZATION
The Code of Federal Regulations (CFR) 40§ 243.101(1) defines food waste as “organic residues
generated by the handling, storage, sale, preparation, cooking, and serving of foods, commonly
called garbage.” Food waste accounts for approximately 12.9% of the total municipal solid
waste (MSW) generated in the United States on the weight basis (US EPA 2009). The amount of
food waste generated in the United States is above 200 million tons annually (Figure 1.2).
While acknowledging changes in the dietary habits, one study reported that since the 1970s,
food waste generation has increased by 50% on a calorie basis (Hall et al. 2009). This study
suggests current “unhealthy” dietary trends are causing increases in food consumption and
subsequent food waste generation. However, it is also important to consider that dietary trends
are not fixed and highly variable based on location, culture, etc. Food waste should be
evaluated and characterized objectively no matter what the source and cause. Food waste is all
considered organic matter. Subsequently, this study will aim to establish essential guidelines for
foods based on unique groups. For more information on this topic see 4.1.1. Food
Categorization.
2.1. Residential Food Waste
Food waste alone accounts for 3.2 to 4.1 kg per person per week (Diggelmann 1998). As shown
in Figure 2.1, this annually accounts for approximately 14.10% of total MSW by weight. It
should be noted that MSW is typically categorized by weight because this is a highly influential
factor affecting transportation costs of MSW. For example, a high volume, light weight stack of
boxes is much more efficiently transported to a remediation facility than a low volume, high
weight pile of bricks.
5
1.50%
Containers & Packaging
19.20%
29.50%
Nondurable Goods
Food Scraps*
Yard Trimmings
13.70%
Durable Goods
22.00%
Other Wastes
14.10%
Figure 2.1: Total Annual MSW Generation by Weight (US EPA 2009)
*Considered acceptable for processing through a FWD
2.1.1. Food Distinction & Sorting
Source Separated Organics (SSO) is any system or program established for waste generators to
separate any organic waste from other waste streams at the source for separate collection &
disposal. This does not necessarily only refer to food separation from municipal solid wastes. It
can also refer to other organics such as yard waste, paper products, and wood waste.
It is important to establish guidelines for any SSO to distinguish what waste is appropriate for
separation. Improper separation can lead to inevitable failure of a SSO for many reasons e.g.,
clogged food waste disposer, potentially hazardous waste generation, solids mixing with
compost, etc.
2.1.2. Decomposition & Handling
The typical food waste composition is 50.5% Carbon, 6.72% Hydrogen, 39.6% Oxygen, 2.74%
Nitrogen, and 0.44% Sulfur (Diggelmann 1998). Food waste decomposes similar to most organic
matter. Bacteria, fungi, oxygen, and moisture collectively break down food waste back into
basic organic components. Food cannot decompose in the absence of bacteria and/or fungi.
Collectively called saprophytes, these microbes are the primary catalyst in the decomposition of
all dead organic matter e.g., food waste, cow manure, and yard waste. Saprophytes can be
ingested or may be transferred to food by direct contact (“How Does Food Decompose?” 2010).
Proper safety methods should always be exercised when handling food. During this study, lab
assistants washed hands and between testing of every sample. Latex gloves were also worn
when handling any raw meat.
Many forms of bacteria & fungi may or may not be present during decomposition of food
waste. As previously noted, organic matter typically requires some form of moisture and
oxygen combination to decompose. Saprophytes cannot survive without the moisture and
water. The amount of oxygen and moisture surrounding food waste is subject to high degree of
variance given location of the waste. A short supply of either will limit the number of microbes
that can live on the food. This is the principle behind vacuum packing and freeze drying as
methods of preserving food. However, some bacteria e.g., Clostridium botulinum, the bacteria
that cause botulism, can decompose food without oxygen, so long as water is present. In this
process, called anaerobic decomposition (AD), dangerous toxins are produced. Dented,
compromised canned goods are generally a primary source for Clostridium botulinum in
residential kitchens (“How Does Food Decompose?” 2010).
Temperatures between 40 and 140 °F are ideal for food waste decomposition (Hall et al. 2009).
At these temperatures microbe and enzyme activity is optimized, making food energy more
available to the bacteria and fungi allowing them grow and multiply more rapidly. However, it
should be noted that food can decompose at lower temperatures, even below freezing. This is
why food does not keep indefinitely when stored in a refrigerator. Decomposition at lower
temperatures simply occurs at a slower rate (Wright 2010).
There are methods to avoid contamination from bacteria and fungi. In cooking, food-borne
bacteria are killed at temperatures between 145 and 180 degrees Fahrenheit. This range occurs
because various bacteria are killed at different temperatures (Hall et al. 2009). In food packing,
high sugar, salt or acid content creates a hostile environment for fungi and bacteria. Candying,
salt curing and pickling are methods commonly used to preserve food (“How Does Food
Decompose?” 2010).
2.1.3. Assessment of Food Waste in Madison, WI
A waste characterization study was conducted for Madison, Wisconsin in 2010 (Table 2.1). The
characterization included two waste sorts, one conducted in July and the second in October.
The composition of waste was measured on a weight basis. The results show 16.8% of the
waste sent to landfill in Madison was suitable for food waste disposer (FWD) processing
(Yoshida 2010).
7
MATERIALS
JULY SORT
OCTOBER SORT
AVERAGE 2010 SORT
Food Waste*
17.7%
15.8%
16.8%
Contaminated Paper
9.8%
7.5%
8.7%
Pet Waste
3.2%
6.0%
4.6%
Disposable Diapers
2.8%
6.5%
4.7%
Yard/Plant Trimmings
5.8%
4.6%
5.2%
Newspaper
1.9%
1.4%
1.7%
Magazines & Catalogs
1.6%
1.3%
1.5%
Res. Mixed Paper
4.2%
6.9%
5.6%
Corrugated Cardboard
0.8%
0.8%
0.8%
Plastic Bottles
1.6%
1.3%
1.5%
Glass Bottles & Jars
1.8%
1.4%
1.6%
Steel/Tin/Bimetal Cans
1.2%
0.9%
1.1%
Aluminum Cans
0.4%
0.2%
0.3%
Residual
47.2%
45.4%
46.3%
Total Organics
39.3%
40.4%
39.9%
Table 2.1: Percent by Weight of Madison, WI MSW Sort (Yoshida 2010)
*Considered acceptable for processing through a FWD
With information from Table 2.2 it can be inferred if all the organic waste were to be taken
from the landfill, the diversion rate would increase to 73% whereas the current diversion rate is
59%. Currently, close to 90% of yard waste and 80% of recyclables have already been diverted
from the landfill. If Madison were to achieve 100% diversion of recyclables, the results would
only add another 5% to the total current diversion rate.
Organics Currently
Sent to Landfill
Yard Waste
Brought Drop off
Source Separated
Organic (SS0)
Food
Waste
Food
Soiled
Paper
Yard
Waste
Diapers
Pet Waste
Total
6,619
3,419
2,055
1,838
1,818
15,749
0
0
4,648
0
0
4,648
6,619*
3,419
6,703
1,838
1,818
20,397
Table 2.2: Composition of Source Separated Organics (tons)
*Considered acceptable for processing through a FWD
Studies such as this help better appropriate funding for management of MSW disposal
practices. The City of Madison should consider alternative waste management practices while
continuing to improve existing recycling programs. Since food waste is the largest contributor
to divertible waste at 16.80% of waste (Table 2.2 and Figure 2.2), it is the ideal source to direct
better diversion resources. For example, it would be more beneficial to begin a food waste
education & collection and education program than it would to create a similar program to
educate residents about pet waste, disposable diapers, etc. However, Madison is a unique
community and these findings may not be applicable nationwide.
Food Scraps*
Contaminated Paper
Pet Waste
Disposable Diapers
Yard/Plant Trimmings
Newspaper
Magazines & Catalogs
Res. Mixed Paper
Corrugated Cardboard
Plastic Bottles
Glass Bottles & Jars
Steel/Tin/Bimetal Cans
Aluminum Cans
Residual
16.80%
Figure 2.2: Breakdown of Percent by Weight for Madison, WI MSW Sort (Yoshida 2010)
*Considered acceptable for processing through a FWD
9
2.2. Commercial Food Waste
Retail stores and restaurants are primary sources of what is known as commercial food waste.
Usually, this consists of items that have reached their sell-by or use-by date. Most of this food is
edible at the time of disposal. However, stores and restaurants have widely varying policies
pertaining the handling the excess and expired food. Some sources put effort into preventing
access to poor or homeless people, while some work with charitable organizations to distribute
food to those in need (Karrman et al. 2001).
Contractual arrangements with food suppliers also create an indirect contribution to
commercial food waste. Failure to supply agreed quantities to clients e.g., restaurants, retail
stores, etc., renders farmers or processors liable to have their contracts terminated.
Subsequently, farmers and processors will often produce more than actually required in order
to meet contractual obligations. While this margin of error does help the farmers and
processors, surplus production is often simply discarded and can have great adverse
consequences for the environment (Karrman et al. 2001).
There are source separation organics (SSO) programs in place for commercial food waste. In
these programs commercial sources will voluntarily separate food waste. However, costs and
safety concerns associated with food waste storage and employee handling usually creates
concern for participating farmers and processors. Financial incentives are usually offered to
promote participation. This also helps with cost of transporting and storing the food waste. For
over 50% of the communities with commercial food waste collection programs studied in 2004,
it was found materials are collected via a single contracted hauler. About 1/5 of communities
studied reported food waste was collected through private haulers in open competition.
Municipal collection of commercial food waste is a relatively rare occurrence (de Konig 2004).
3. WASTE MANAGEMENT ALTERNATIVES
There are many alternatives when it comes to remediation of food waste. In recent years focus
has been shifting towards maximizing the energy potential of food waste. This study will focus
on three common alternatives for food waste remediation: landfilling & incineration, food
waste disposers, and composting.
3.1. Landfilling & Incineration
Landfills include internal waste disposal sites, where a producer of waste agrees to manage in
situ disposal of site waste, as well as drop-off sites utilized by multiple waste producers. Many
landfills are also used for varying waste management purposes, such as the temporary storage,
consolidation & transfer, or processing of waste material i.e., sorting, treatment, and recycling
(Bagchi 2004).
The recovery of food waste is much lower than the recovery of other organic fractions of MSW.
In the US, it has been estimated as little as 2.6% of post-consumer food waste is recovered. This
is significantly smaller than the 64.1% of yard waste diverted annually (US EPA 2009). The vast
majority of the food waste is sent to landfills without any treatment. This trend has not
changed since the 1950s while the recycling and recovering of other waste streams has
expanded rapidly since the 1970s (US EPA 2009).
The decomposition of food waste is a primary source of odor at landfills. Typically, compacted,
exposed waste is covered daily with a layer of soil while a landfill is in operation. Alternative
cover materials include but are not limited to: several sprayed-on foam products, chipped
wood, and temporary blankets. However, even with daily covering, food waste in a landfill still
causes concern for attracting animals and rodents.
Incineration is an alternative treatment comparable to landfilling. It is sometimes described as
"thermal treatment". Similar to landfilling, waste is collected and brought to a central site.
However, unlike landfilling the solid organic wastes are subjected to combustion converting
them into residue and gaseous products. Incineration is carried out both on a small scale by
individuals and on a larger scale by industry. It is an attractive remediation alternative because
the process reduces waste volumes approximately 20 to 30% of the original volume (Bernstad
& Jansen 2001). It is also a controversial method of waste disposal, due to potential emission of
gaseous pollutants. The process also contributes waste emissions in the form of bottom ash, fly
ash, and sludge. Bottom ash and fly ash are typically not of concern with food incineration.
With incineration of food waste overall emissions are considered input-specific i.e., based on
the composition and condition of food waste incinerated. Some of emissions to air e.g., dioxins,
11
CO, particles, SO2, NOx, HCl, are assumed to be process-specific and based on the technology in
the specific incineration plant (Bagchi 2004).
3.1.1. Collection & Handling
Food waste that is sent to a landfill is typically comingled with other MSW at the source. A
primary concern for an SSO is the time between collections. The longer food waste sits in a bin
before collection, the more problematic it may become in terms of bacteria & fungi growth,
odor, and rodent attraction. Overfilled bins can also be of concern because the spillage of food
waste only perpetuates the aforementioned problems.
3.1.2. Landfill Methane Gas Emissions
At landfills, anaerobic decomposition of organic waste produces landfill gas (LFG). Two primary
LFGs are methane (CH4) and carbon dioxide (CO2). It is estimated 24% of methane emissions in
the United States is from landfills and open dump sites (US EPA 2009). Methane is considered
to be one of the major drivers of global climate change because in a time frame of 100 years it
is 21-25 times more potent of a greenhouse gas (GHG) than carbon dioxide. Methane is also
highly combustible. Subsurface migration of methane has resulted in explosions at properties
neighboring landfills in the past.
Figure 3.1: Landfill Methane Balance (Smith 1997)
As methane gas moves through the soil layer, it is oxidized and converted into carbon dioxide
though microbial activities in the soil (Figure 3.1). Generally, it is believed that 10% of the
methane in LFG is oxidized and turned into Global Warming Potential (GWP) neutral biogenic
carbon dioxide. This 10% reduction in fugitive methane emissions by soil cover has been
adopted in many protocols including, the GHG emission inventory for the Intergovernmental
Panel on Climate Change, US EPA’s mandatory GHG emissions reporting program, the carbon
credit calculation protocol under the Kyoto Protocol, the Chicago Climate Exchange (CCX),
Regional Greenhouse Gas Initiative (RGGI), and the more recent protocol for the Climate Action
Reserve (Yoshida 2010). A study conducted by Solid Waste Industry for Climate Solutions in
2007 indicated oxidation efficiencies range from 22 to 55%. This number has also been
estimated to be as high as 80% by Schultz et al. (2004), depending on the soil type and the rate
of LFG emission. Fugitive methane emissions are difficult to assess and industry standards have
yet to be firmly established and accepted.
More uncertainties exist during landfill operations besides assessment of methane gas
emissions. One example is the rate of carbon sequestration. Another uncertainty is the
emission of nitrous oxide. Nitrous oxide is more than 298 times potent a GHG than carbon
dioxide (IPCC 2007). When the organic material containing nitrogen goes through the
decomposition process, nitrous oxide is emitted and contributes to global warming. The
decomposition process at the landfill occurs under mainly anaerobic conditions and under
these conditions very little nitrous oxide can be emitted to the atmosphere. Due to the
heterogeneous nature of landfills, it is almost impossible to generalize operational efficiency.
This shortfall imposes a serious limitation in carrying out GHG emission analyses for waste
management systems and further analysis of the impact of food waste diversion from landfills.
LFG is regulated by two legal actions: the Resource Conservation and Recovery Act (RCRA) and
the Clean Air Act (CAA). The RCRA set the criteria for design of landfills and landfill gas
collection systems under 40 CFR §258. The CAA regulates the emission of NMOCs as a form of
Hazardous Air Pollutants (HAPs). Landfills, larger than 2.75 million short tons and of that have
either commenced construction, started receiving waste, or were modified after May 30, 1991,
are considered as “new sources” and are regulated under New Source Performance Standard
Rule. Most commonly, thermal treatments, such as flaring, combustion in engines, turbines, or
boilers for energy recovery, are utilized for destroying NMOCs (Yoshida 2010).
3.1.3. Energy Potential
A common approach used by landfills to minimize methane gas emission is to capture and
combust the LFG. LFG contains not only methane but also non-methane organic compounds
(NMOCs) including volatile organic compounds (VOCs) and hazardous air pollutants (HAPs),
such as benzene, toluene, ethyl benzene, and vinyl chloride. Exposure to some NMOCs can
impose a health risk. The formation of ground level ozone and photochemical smog has also
attributed to VOCs.
13
LFG collection systems are not air-tight systems. Leakage of LFG occurs through punctures in a
rubber liner, natural leakage through the soil, and natural diffusion through the rubber & soil
liners. The default capturing efficiency for LFG collection systems used by EPA is 75%, but this
number is not always the best assumption. The estimated average of European countries is 54%
(Smith et al. 2001). A study in Portland, Oregon found efficiency to be as low as 22.6% (Visse
2004). The most recent study by Spokas et al. (2006) concluded LFG capturing rate is highly
dependent on the type of final soil cover in place where a landfill is no longer accepting waste.
For example, a collection system could potentially achieve 90% collection efficiency under final
soil cover. However, this could potentially decrease the collection rate to as low as 50% under
daily or intermediate soil cover (Spokas et al 2006). The methane content of the LFG also varies
depending on the age of the landfill. In the early stages of a landfill, the methane content in the
LFG is typically below 40%, to the point that LFG cannot be combusted through standard
technologies. As a landfill matures the methane generation increases and energy potential is
much greater. However, depending on the size and organic waste content of the landfill this
potential will eventually peak and begins to decline (Bagchi 2004).
Like landfills, incinerators are also able to yield energy from waste. Through conversion of
waste materials into heat, gas, steam, and ash incinerators are able to produce thermal energy
and electricity. Waste-to-Energy (WtE) and Energy-from-Waste (EfW) are terms for facilities
that burn waste in a furnace or boiler to generate heat, steam or electricity. In the Bernstad &
Jansen study site-specific data on emissions of these compounds was used to evaluate the WtE
potential of incineration. It should be noted fly ash was transported for further treatment and
sludge and bottom ash were landfilled and this was accounted for in the study energy
calculations. The energy recovery in the plant studied was high, due to heat recovery from
exhaust gases; 108% when adding electric and thermal energy production, 20.3% as electricity,
and 87.7% as thermal energy (Bernstad & Jansen 2001). From this it can be inferred that 8% of
the energy input was actually generated during the incineration process. This demonstrates
food waste incineration does have energy production potential. However, other remediation
alternatives still remain to be considered for energy potential.
3.1.4. Current Practice in Madison, WI
The Dane County Landfill was opened in 1986 and is owned and operated by the Dane County
Department of Public Works, Highway and Transportation. The City of Madison contributes
47.2% of total MSW received by the Dane County Landfill. About 65% of the waste is MSW
while the rest is mainly construction and demolition waste. The potential diversion of organic
waste by the City of Madison is estimated to decrease the MSW acceptance rate at the Dane
County Landfill by 16.10% (Figure 3.2).
16.10%
Organic Waste from
Madison*
Residual Waste from
Madison
52.90%
MSW not from Madison
31.10%
Figure 3.2: Waste Composition at Dane County Landfill (Yoshida 2010)
*NOT all food considered was acceptable for FWD processing
The Dane County Landfill is currently capturing energy through LFG extrapolation wells. Once
moisture is removed, the collected LFG is combusted for energy recovery. The Dane County
Landfill is now equipped with three 800 kW and one 1600 kW generator sets. These generate
approximately 2,752 MWh of energy per year, which constitutes an electricity recovery
efficiency of ~22%. Dane County is planning to install two additional 800 kW generators in the
near future to accommodate the anticipated increase in landfill methane generation. The waste
heat from electricity generation is currently not utilized. Thus, the electricity production from
the organic fraction of MSW is given by:
Electricity generated = Methane collected x Lower Heating Value of Methane (38.3 MJ/m3) x
electricity recovery efficiency (~22%) x 0.278 kWh/MJ
Methane
Collected (Nm3)
Electricity
Generated (kWh)
Electricity Generated
(kWh/ton)
Conventional
Sanitary Landfill
8.49E+05
3.94E+06
250
Bioreactor Landfill
9.39E+05
4.36E+06
277
Table 3.1: Energy Generation from Madison Landfill
15
3.2. Food Waste Disposer
Food waste alone accounts for 3.2 to 4.1 kg per person per week (Diggelmann 1998). From this
figure, it has been approximated that the total amount of food waste that can be ground
through a disposer is 44 kg/person/yr. That leads to approximately 58% of food waste that
could be potentially annually diverted from landfills.
Source separation is the first step in implementing an alternative management program for
food waste. In the US, the addition of a garbage collection bin for most organic wastes is the
most common practice (Bolzonella et al. 2003). This separation can also be done at a waste
transfer station by manual or mechanical sorting. For example, in the City of Aarhus, Demark,
the organic wastes are collected in green bags and the residuals are in black. The organic
wastes in green bags are sorted at the optical sorting facility (Kirkeby et al. 2006). It is also
common to designate an organic waste drop-off spot to improve the efficiency of collection and
this practice is often found in dense urban settlements (Tchobanoglous et al. 2002).
Processing through a food waste disposer (FWD) is now becoming a more popular alternative
approach to food waste diversion. Municipalities have been hesitant to promote food waste
disposers because of uncertainties regarding consequences on the wastewater collection
system and health concerns. New York City has even gone as far as to ban FWDs entirely.
However, recent studies are beginning to show FWDs do not yield such adverse consequences.
FWDs are becoming a solution rather than a problem. For example, Milwaukee is currently
working with the FWD manufacturer InSinkErator to promote separation of all food waste and
processing through a disposer (personal conversation with Michael Kelleman of InSinkErator).
3.2.1. Design & Brief History
Food waste disposers were invented in the 1940s, initially as a convenience for residential
kitchens and cooks. The post-WWII housing boom helped make FWDs a more common fixture
in most homes.
Figure 3.3: Food Waste Disposer Assembly (http://www.shajalique.id.au)
FWDs became a standard appliance by the end of the 20th century. The market for commercial
food waste disposers in restaurants, cafeterias, and markets, etc. had also grown. FWDs also
became common internationally primarily in response to significant concerns about diverting
organic food waste from landfills and increasing the beneficial use of food waste for land
application (de Koning 2004).
Commercial and residential FWDs are almost identical in design. The only difference is a higher
waste volume capacity and stronger motor for commercial FWDs. The common residential FWD
utilizes a 1,400 rpm rotating disk with a varying number of 3-4 mm holes (Figure 3.3). Most
residential disposers have a 600 W electric motor, used on average 2.4 times/day and 30
seconds each cycle.
A FWD should be described as a mill rather than a cutter. A FWD contains no knives for cutting.
It works with a rotary disk provided with 5 mm holes in which two hammer-cheeks mobile in
horizontal direction are fastened. When active, the hammer-cheeks in the rotary disk force
food through the 3-4 mm holes in the grind ring and effectively shred the waste without cutting
(Terpstra 1995).
17
3.2.2. Application Advantages
The following are various conclusions drawn from studies supporting FWDs as a means of food
waste diversion:









The utilization of FWDs results in a reduced incidence of disease-causing vector
attraction in comparison to food waste storage/collection inherent with most source
separated organic (SSO) collection programs (Terpstra 1995, Shpiner 1997, and
Bolzonella et al. 2003).
The increased use of FWDs increases the renewable energy value of a Wastewater
Treatment Plant (WWTP) through high anaerobic digestion biogas yields (Hernandez et
al. 2002) & (Hall et al. 2009).
Less food waste in Municipal Solid Waste (MSW) reduces transportation emissions and
associated costs (Karlberg et al. 1999, and Kegebein et al.).
Removal of kitchen food waste from compost produces cleaner and better compost
with less adverse impacts on ground soils (de Konig 2004).
Increased use of FWDs reduces space concerns for food waste storage (de Konig 2004).
Nutrient recycling from organic wastes increases when WWTP biosolids are land-applied
(Diggelmann et al. 1998).
Diversion of food waste creates a healthier MSW working environment (Karlberg et al.
1999).
Increased use of FWDs reduces MSW garbage collection amount and frequency (Shpiner
1997 and Diggelmann et al. 1998).
The high carbon content of food waste improves the overall WWTP nitrogen and
phosphorus nutrient removal process (Diggelmann et al. 1998 and Rosenwinkel &
Wendler).
The following reasons promote FWD processing given the high (approximately 70%) water
content of most food waste:



A WWTP is a more natural system of waste processing than hauling the waste to a “solid
waste” remediation facility (Diggelmann et al. 1998).
Diverting water in the form of food waste to a WWTP reduces leachate from landfill and
compost systems, which reduces potential contamination to groundwater (Diggelmann
et al. 1998).
As previously noted in 3.1. Landfilling & Incineration, a WWTP system anaerobic
digestion process will produce a viable energy source, whereas, incineration offers a
very small net energy gain. Incineration also produces highly contaminated emissions
requiring additional treatment unlike anaerobic digestion (Diggelmann et al. 1998).

FWDs reduce the potential of uncontrolled biochemical processes in landfills i.e.,
leachate treatment (Rosenwinkel & Wendler).
Composting requires stricter operational control to avoid anaerobic conditions, and
results in the loss of most nutrients (Diggelmann et al. 1998).

3.2.3. Application Disadvantages
Unlike curbside programs that compost not only food waste but also yard waste and a large
amount of food soiled paper, FWDs are only targeting a portion of the total divertible organics
stream. Furthermore, in situations where a municipal wastewater treatment facility is already
overburdened, there is not a way to collect and use the methane produce through the process,
or there is no efficient way to get rid of the resulting and increased amount of sludge at the end
of the process, FWDs may not be a viable option for food waste diversion. Critics have also cited
issues with increased water or electricity usage, clogging drains, changes in nutrient load and
removal (nitrate and phosphorous), and a potential increase in biochemical oxygen demand
(BOD) during treatment. However, many studies are proving these concerns to be inaccurate.
Nevertheless, FWDs are not flawless. Increasing food waste diversion through FWDs will
undoubtedly have some adverse consequences. The following are conclusions drawn from
various studies:







Widespread utilization of FWDs will show an increased potential loadings impact on
combined sewer overflows (Rosenwinkel & Wendler).
The average sink flows at a rate of approximately 2 gallons of water per minute, or
about 700 gallons per year based on minute-per-day use. Besides potentially
increasing a water bill, added water consumption associated with FWD utilization is a
major concern in drought areas.
Grease and solids could potentially build-up in the sewer collection system. This
would increases maintenance costs in the collection system (NYCDEP “The Impact of
Food Waste Disposers in New York City”).
With more organics in the water come an inherent increase of loadings of BOD and
total suspended solids (TSS) to the WWTP (Shpiner 1997).
Although actual figures are not known it is understood that energy consumption for
both disposer use and WWTP aeration costs will increase (Rosenwinkel & Wendler).
WWTP biosolids generation will increase and disposal costs could potentially increase.
(de Konig 1997).
Increased use of FWDs requires a high upfront investment of a disposer unit by the
user, not a municipality (Diggelman 1998 and Karman et al. 2001).
19
3.2.4. BOD & COD Loading
Natural organic detritus and organic waste from waste water treatment plants, failing septic
systems, and agricultural and urban runoff, acts as a food source for water-borne bacteria.
Bacteria decompose these organic materials using dissolved oxygen (DO), subsequently
reducing the DO present for fish. Biochemical oxygen demand (BOD) is a measure of the
amount of oxygen that bacteria will consume while decomposing organic matter under aerobic
conditions. BOD is determined by incubating a sealed sample of water for five days and
measuring the loss of oxygen from the beginning to the end of the test. Samples are typically
diluted prior to incubation. This prevents bacteria from depleting all of the oxygen in the bottle
before the five day testing period (Shpiner 1997).
Chemical oxygen demand (COD) does not differentiate between biologically available and inert
organic matter. It is a measure of the total quantity of oxygen required to oxidize all organic
material into carbon dioxide and water. COD values are always greater than BOD values, but
COD measurements can be made in a few hours while BOD measurements take five days
(BOD5) (Rosenwinkel & Wendler). This study will utilize COD testing to assess FWD effluent.
An analysis of tributary waters was recently conducted in New York City to estimate the impact
of city-wide adoption of FWDs. Installation of FWDs was only predicted to increase BOD and
TSS loadings in the total CSO stream by only 5% for BOD and TSS by 2% over baseline loads
(NYCDEP). While this does not show direct impact on the loading at a WWTP, it does suggest
adoption of FWDs is not as adverse as once thought.
3.2.5. Effluent Characteristics & Energy Usage
A Japanese study found the following characteristics of FWD effluent: particle dispersion to be
between 2-5 mm; a grinding distribution of heaviest components show 62% of particles are
<1.7 mm, 86% are <2.83 mm, and 94% are <3.36 mm; and approximately 98% of all particles
pass through a 2 mm sieve (Karlberg et al. 1999).
A recent study conducted for New York City found water demand with FWDs would be
approximately 3 million gallons per day by 2035, even under worst case assumptions. This
represents a minor incremental increase when compared against the system’s 1.3 billion gallon
average annual daily water demand. Therefore, no potential significant impact on the City’s
water supply system is expected with city-wide use of FWDs (NYCDEP).
Most disposers have a 600 W electric motor, used on average 2.4 times/day and 30 seconds
each time (Karrman et al. 2001). Disposer electrical consumption is <3 kW-h/household/yr
(Waste Management Research Unit – Griffith University 1994). Also, the New York City
Department of Environmental Protection (NYCDEP) indicates that using the upper time limit for
disposer usage of 2 min/day and the most common 0.5 hp motor, a FWD consumes less than a
75 W light bulb uses in 10 minutes.
3.2.6. Energy Potential & Anaerobic Digestion
Increased use of FWDs will undoubtedly increase loading at local WWTPs. To offset ensuing
increases in energy costs it is best to capture energy from the waste through anaerobic
digestion (AD) in the form of methane gas. This process is particularly suited to organic material
and is commonly used for effluent and sewage treatment across the US. Anaerobic digestion is
a relatively cheap and simple process that can significantly reduce the volume of organic
matter. Furthermore, wastewater with high organic content will subsequently yield more
methane.
Methane capture in a digester can be utilized to power a gas engine and produce electrical
power. Some or all of this power can be used to run the WWTP. Additional heat from the
engine is then used to heat the digester which facilitates the decomposition process. However,
it should be noted the power potential is limited. A 2004 study from Marashlin et al. found in
the UK there is about 80 MW total of AD power generation, with potential to increase to 150
MW. Unfortunately, this is insignificant compared to the average power demand in the UK of
about 35,000 MW. In the UK the potential for biogas generation from non-sewage waste
biological matter e.g., energy crops, direct food waste AD, abattoir waste, etc., is estimated to
be much higher at about 3,000 MW.
21
Figure 3.4: Phase Breakdown of Anaerobic Digestion (Springer 2010)
Anaerobic digestion occurs in four stages: hydrolysis, acidogenesis, acetogenesis and
methanogenesis (Figure 3.4). During hydrolysis, the first stage, bacteria transform proteins,
carbohydrates, and fats into amino acids, monosaccharides, and fatty acids respectively. In the
second stage, acidogenic bacteria transform the products of the first reaction into short chain
volatile acids, ketones, alcohols, hydrogen, and carbon dioxide. During acetogenesis, the third
stage, the rest of the acidogenesis products i.e., the propionic acid, butyric acid, and alcohols
are transformed by acetogenic bacteria into hydrogen, carbon dioxide, and acetic acid. The
fourth and final stage is called methanogenesis. Through this stage, microorganisms convert the
hydrogen and acetic acid formed by the acid formers to methane gas and carbon dioxide
(Verma 2002).
AD can also occur at varying temperatures. There are two conventional operational
temperature ranges for anaerobic digesters, which are determined by the species of
methanogens in the digesters, these ranges are known as mesophilic and thermophilic.
Mesophilic occurs optimally at 30 - 38 °C or at ambient temperatures between 20 - 45 °C where
mesophiles are the primary microorganism present. Thermophilic digestion occurs optimally
between 49 °C and 57 °C and at elevated temperatures up to 70 °C where thermophiles are the
primary microorganisms present (Verma 2002).
In the thermophilic range, decomposition and biogas production occur more rapidly than in the
mesophilic range. However, the process is highly sensitive to disturbances, such as changes in
organics content of the feed material or temperature. While all anaerobic digesters reduce the
viability of weed seeds and disease-producing (pathogenic) organisms, the higher temperatures
of thermophilic digestion result in more complete destruction. Although digesters operated in
the mesophilic range must be larger (to accommodate a longer period of decomposition within
the tank i.e., residence time), the process is less sensitive to upset or change in operating
regimen (Verma 2002).
To optimize the digestion process, the digester must be kept at a consistent temperature; rapid
changes will potentially kill bacteria. In most areas of the United States, AD tanks require some
level of insulation and/or heating. Madison, Wisconsin is not exception to this rule. Some
installations circulate the coolant from their biogas-powered engines in or around the digester
to keep it warm, while others burn part of the biogas to heat the digester. In a properly
designed system, heating generally results in an increase in biogas production during colder
periods (Hernandez 2002).
Other factors affect the rate and amount of biogas output including: pH, water/solids ratio,
carbon/nitrogen ratio, mixing of the digesting material, the particle size of the material being
digested, and retention time. These are all highly variable given the nature of FWD effluent and
subsequent processing at a WWTP. Pre-sizing/screening and adequate mixing of the feed
material for a uniform consistency allows the bacteria to work more quickly. The pH is typically
self-regulating in most digesters. However, in some cases bicarbonate of soda can be added to
maintain a consistent pH. This may be done when wastewater high in nitrogen content is
added. It may also be necessary to supplement the digester influent with water if it is too dry or
if the nitrogen content is very high. A carbon/nitrogen ratio of 20/1 to 30/1 is ideal for
maximizing gas yields (Verma 2002).
The material drawn from an AD is called sludge, or effluent. It is rich in nutrients (ammonia,
phosphorus, potassium, and more than a dozen trace elements) and is a common soil
conditioner. It can also be used as a livestock feed additive when dried. Any toxic compounds
such as pesticides, etc. that are in the digester feedstock material may become concentrated in
the effluent. Therefore, it is important to test the effluent before any large scale application
(Hernandez 2002).
3.3. Composting
Composting is currently the most common food waste diversion alternative (de Konig 2004). It
is an aerobic decomposition process which requires a constant supply of oxygen. This can be
achieved by mechanically turning the compost pile (windrow composting) or forcing air into
piles via blowers or agitators (aerated static pile and in-vessel composting). Once waste is
matured it is considered safe for use in agriculture, gardening, and landscaping. Composting
23
can be done at various scales, ranging from backyard composting to large-scale engineered
composting systems (Tchobanoglous et al. 2002).
As noted, composting is an aerobic degradation process and under a well-controlled
environment, methane emission from composting is less than 1% of the total organic carbon in
the feed material. However, at a home composting site, due to the low turn frequency, and
poor temperature and humidity control, some anaerobic degradation also takes place. This
leads to much higher releases of methane into the atmosphere (Wright 2010).
3.3.1. Collection & Handling
Since 1992, the City of Madison has distributed home composting bins to approximately 18,500
households. A pilot study for the home composting program showed the average household in
Madison composts 660 lbs. of waste every year, of which, 250 lbs. are food waste. This results
in the diversion of 1,732 metric tons of food waste from the landfill. This study did not account
for households with homemade compost bins or bins purchased from local suppliers. According
to a community survey, about 29% of food waste and 18% of soft yard waste are currently
composted (Yoshida 2010).
The typical residential food waste collection program includes year-round curbside collection of
food waste combined with yard waste. In a study conducted by Kegebin et al., communities in
various states across the Midwest were surveyed about local food waste collection programs. It
was found only 4% of communities reported that their program was drop-off only. The majority
of communities with residential programs also have food waste collection available for at least
some portion of their multi-family housing, typically up to 8-units, and most also have a
program available for the commercial sector as well. It is less common in schools and
universities. Over 90% of the communities reported that they accept meat and dairy in the food
waste stream, not just vegetative waste, while just one program reported that they have a pilot
to compost pet waste. No program is reported to accept diapers (Kegebin 2004).
Almost 50% of the communities give residents a choice of 32, 64, or 96-gallon carts while 23%
provide only 96-gallon carts. When food waste are co-collected with yard waste the larger
volume calls for a larger cart. In the commercial sector, where food wastes are often the only
items in the cart, 64-gallon containers are preferred due to the high water content and weight
of food waste alone. This makes storing and disposing of food waste much easier and cleaner.
Less than 10% use bags, either plastic or paper, to collect organics manually. Approximately
75% percent of the communities reported they collect organics weekly. Every-other-week
collection of recycling was reported to be quite popular with 55% of the households
participating. Only 4% of the communities, all of which were located in the northwestern US,
reported that they had every-other-week collection of trash. This may be a growing trend in the
United States as cities begin to mimic communities in Canada and abroad that have successfully
increased diversion through every-other-week garbage collection with weekly organics
collection In most communities studied, participation in the residential food waste program is
voluntary (only 9% reported that participation is mandatory). Nearly 70% of communities
reported that the food waste program requires an additional fee, and only 31% reported that
the fees are fixed in the MSW collection fees (Kegebin 2004).
3.3.2. Greenhouse Gas Emissions
Composting conducted through a SSO is a multi-phase process. First, received material is
grinded and reduced to the desired particle size. Next it is mixed with bulking agents to
optimize the following: carbon/nitrogen ratio in a range of 25/1 to 30/1, moisture content, and
porosity. The mixed material is then placed into windrows or vessels for compost processing.
During the active processing phase of composting, temperatures are usually in the thermophilic
range (49 °C - 57 °C). High heat destructs pathogens and sterilizes weed seeds. At temperatures
cooler than 49 °C the process slows. The curing process follows after the microorganisms have
consumed the readily available carbon and stabilized. The composting and curing processes
together can take anywhere from 3 to 6 months. Once the stabilization is completed, the
material is screened to remove contaminates and then sold to the market (Tchobanoglous et al.
2002).
The study conducted by Amlinger (1996) found the methane emissions from home composting
bins to be three times higher than from windrow engineered composting systems. When land
applied, 2% of nitrogen and 95% of carbon in compost will be emitted to the atmosphere as
NO2 and CO2. The rest of the nitrogen, carbon, and phosphorus remain in the soil. Home
composting of organic waste results in 136 kg of CO2 eq. per ton of organic waste treated. This
is lower than current rate of 220 kg of CO2 eq. and would have the benefit of reducing GHG
emissions as a whole. Furthermore, home composting produces a high strength (BOD) leachate
when food waste is present. There is no readily available mechanism to manage this leachate
and it could create health and safety concerns wherever compost is utilized (Yoshida 2010).
3.3.3. Energy Potential
Compost gives off heat energy and methane just like wastewater (Figure 3.5). However, both
heat and methane must be captured to fully harness energy potential of organic decomposition
through composting. Current commercial and residential compost practices do not have
sufficient means to capture energy under aerobic conditions. This is a major detriment to the
widespread implementation of composting as a diversion alternative.
25
Figure 3.5: Composting Process (Amlinger 1996)
Recently the city of Boston tried adopting a program to harness both heat and methane energy
from compost. Similar to an anaerobic digester this would be a large facility to house the food
waste and capture heat energy and methane gas as it is released. However, unlike an AD, the
facility would be open to aerobic conditions (Nickisch 2008). Results of the Boston pilot
program are currently unknown.
4. EXPERIMENTAL METHODS
As noted, this study is intended to improve guidelines for food waste disposal. The primary goal
of this study is to assess the processing of select food wastes through a food waste disposer
and subsequent impact on characteristics of FWD effluent.
4.1. Selection of Food Waste
The USDA has recently released the MyPlate food guidance system as a guideline to daily
dietary needs (Figure 4.1). This is intended to replace the commonly known and referenced
Food Pyramid. The new MyPlate is less cluttered and placement of food within the groups is
more open to interpretation than the dated food pyramid. For this study foods were selected
from the five new primary groups: fruits, vegetables, protein, grains, and dairy. Only basic food
servings were studied in testing. Although it is safe to process such food wastes in a food waste
disposer, complex and unique dishes e.g., tuna casserole, turkey wrap, pepperoni pizza, etc.,
were not considered.
Figure 4.1: Food Pyramid (previous) to MyPlate (current) (USDA.gov)
4.1.1. Food Categorization
Grains are divided into two subgroups whole grains and refined grains. Whole grains contain
the entire grain kernel ― the bran, germ, and endosperm. Examples include, but are not limited
to: whole-wheat flour, bulgur (cracked wheat), oatmeal, whole cornmeal, and brown rice.
Refined grains have been milled, a process that removes the bran and germ. This is typically
done to give grains a finer texture and prolong shelf life. However, it also removes dietary fiber,
iron, and most B vitamins. Some examples of refined grain products are: white flour degermed
cornmeal, white bread, and white rice (http://www.choosemyplate.gov).
27
Any vegetable or 100% vegetable juice counts as a member of the Vegetable Group. Vegetables
may be raw or cooked; fresh, frozen, canned, or dried/dehydrated; and may be whole, cut-up,
or mashed. Vegetables are organized into 5 subgroups, based on their nutrient content. These
groups are as follows: dark green vegetable, starchy vegetable, red & orange vegetable, beans
& peas, and other vegetables (http://www.choosemyplate.gov).
Any fruit or 100% fruit juice counts as part of the Fruit Group. Fruits may be fresh, canned,
frozen, or dried, and may be whole, cut-up, or pureed. There are no subgroups for fruits.
All fluid milk products and many foods made from milk are considered part of the Dairy Foods
Group. Foods made from milk that retain their calcium content are also part of the group.
Foods made from milk that have little to no calcium, such as cream cheese, cream, and butter,
are excluded from this group. Calcium-fortified soymilk (soy beverage) is also considered a dairy
product. Common subgroups in the Dairy Group are milk, cheese, milk-based desserts, yogurts,
and calcium-fortified soymilk (http://www.choosemyplate.gov).
All foods made from meat, poultry, seafood, beans and peas, eggs, processed soy products,
nuts, and seeds are considered part of the Protein Foods Group. However, it should be noted
beans and peas are also part of the Vegetable Group (http://www.choosemyplate.gov).
4.1.2. Foods Tested
Lagerkvist & Karlson, 1983 and Nilsson et al, 1990 both indicate about 20% of food waste
suitable for composting is not suitable for FWD processing. Starchy vegetables such as potatoes
and corn are not recommended for use in a FWD. They tend to collect in the primary drain line
and may clog the unit. Fibrous vegetables such as artichokes are also not recommended for use
in a FWD. The fibers tend to wrap around the FWD impeller and may strain the motor. Although
listed in the Table 4.1, these foods were NOT processed. It should be assumed these food
wastes are either landfilled or composted.
Foods were selected solely on grouping and availability. There are clearly many more foods that
could have been assessed for this experiment. However, this is a preliminary assessment and
should not be taken to be all-encompassing for foods available to the public. Table 4.1 shows a
list of food tested by weight, subsequent approximate portion, food group, and food subgroup.
GRAINS
FOOD
Oatmeal
Honey Maid Graham
Crackers
Whole Wheat Bread
Buttermilk White Bread
Popcorn
Spaghetti
Saltine Cracker
White Rice
WEIGHT (g)
43
APPROX. PORTION
1 Single-Serve Package
SUBGROUP
Whole Grain
46
3 Cracker Sheets
Whole Grain
42
42
40
40
39
40
1 Slice
1 Slice
3 & 1/2 Cups
50 Strands/Noodles
12 Crackers
1/2 Cup
Whole Grain
Refined Grain
Whole Grain
Refined Grain
Refined Grain
Refined Grain
FOOD
Broccoli
Spinach
WEIGHT (g)
41
39
APPROX. PORTION
1/3 Cup
1 Cup
Red Cabbage
41
4 Leaves
Tomatoes
42
4 Small Tomatoes
Carrots
41
6 Baby Cut
Baked Beans
Corn*
Potato*
Iceberg Lettuce
Mushrooms
Onion
Coffee Grounds**
40
N/A
N/A
40
39
40
42
1/4 Cup
N/A
N/A
5 Pieces
3 Mushrooms
1/3 Onion
1/2 Cup
SUBGROUP
Dark Green Vegetables
Dark Green Vegetables
Red & Orange
Vegetables
Red & Orange
Vegetables
Red & Orange
Vegetables
Beans & Peas
Starchy Vegetables
Starchy Vegetables
Other Vegetables
Other Vegetables
Other Vegetables
Beans & Peas
WEIGHT (g)
41
42
41
41
APPROX. PORTION
2 Slices
1/4 Cup
1/2 Cup
1/4 Cup
SUBGROUP
Cheese
Yogurt
Milk-Based Desserts
Milk-Based Desserts
VEGETABLES
DAIRY
FOOD
Cheese (Kraft American)
Yogurt (Strawberry)
Ice Cream
Chocolate Chips
Table 4.1: Foods Tested
*Not recommended for FWD processing
**Due to low nutritional value, placement in this group is not necessarily considered a
recommended portion of the USDA MyPlate program
29
FRUITS
FOOD
Navel Orange
Nectarine
Apple
Banana
Del Monte Fruit Cocktail
Dark Sweet Pitted Cherries
Red Seedless Grapes
Strawberry
Peach
Pineapple
WEIGHT (g)
69
40
60
46
42
42
42
37
38
38
APPROX. PORTION
1 Peel
1/2 Nectarine
1/4 Apple
1 Peel
1/4 Cup
10 Cherries
7 Grapes
1 Large Strawberry
1/4 Peach
1/4 Cup
SUBGROUP
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
WEIGHT (g)
40
44
37
42
40
38
45
APPROX. PORTION
1/4 Cup
1/3 Bratwurst
1/4 Breast
1/4 Cup
1/3 Cup
5 Shells
1 Egg
SUBGROUP
Meats
Meats
Poultry
Seafood
Nuts & Seeds
Eggs
Eggs
PROTEIN
FOOD
Beef Sirloin
Bratwurst (uncooked)
Chicken
Chunk Tuna in Olive Oil
Sunflower Seeds
Eggs (shells)
Eggs (w/o shell)
Table 4.1 Cont.: Foods Tested
4.2. Selection of Disposer Unit
There are many manufacturers of FWDs. Between manufacturers, variances in disposer design
are few and far between. The major variable between disposers available to the public is power
of the motor. An InSinkErator Badger 5, 0.5 hp food waste disposer was selected for testing.
This model was chosen for the following reasons: InSinkErator leads in sales of FWDs in the
United States, 0.5 hp is the most common size motor in residential FWDs, and this particular
continuous feed disposer was selected over a batch feed disposer to ensure the FWD could be
properly flushed with clean tap water between testing cycles.
4.3. Design & Construction of Disposer Test Unit
The disposer unit was not mounted to a conventional kitchen sink. This would have proven
unnecessary and too difficult to collect effluent samples from the drain line. Instead the
disposer was custom-mounted to a wooden box. The drain line was left exposed in order to
easily collect effluent samples in a bucket. The FWD was fitted with a plug and a surge protector
with a grounded switch was used to activate and deactivate the unit. Brackets were also
mounted to the box to minimize vibration and guarantee stability of the unit.
4.4. Testing Procedure
It is estimated a concentration of less than 1% solids (10,000 mg/L) will not cause an increase in
solid sedimentation within wastewater collection systems, or for every 12 gal of water (45 L)
there should be no more than 1 lb (454 g) of ground garbage (Shpiner 1997). From this
information it was established approximately 40 g samples would be placed in the FWD and
flushed with one gallon of water. Real world food waste would presumably become diluted
when introduced into the collection system. However, this figure was used to approximate the
effluent in a “worst case” scenario i.e., should the collection system become inundated with
food waste and there is not enough water to maintain flow to the WWTP.
Samples were tested for COD, nitrate, and phosphorous. Overall, 39 food samples were
processed through the FWD. A control sample of water was also run through the FWD and
tested. Madison tap water was used throughout the testing from the same source. Between
processing of food samples through the FWD, the unit was run and flushed with one gallon of
clean tap water to ensure no contamination between samples. The internal chamber of unit
was also inspected for any obstructions and/or remnants between testing cycles. Any resulting
obstructions e.g., fat, onion peel, etc. were physically removed and the unit would be flushed
once again prior to testing of the next sample.
4.4.1. COD Testing
The Chemical Oxygen Demand (COD) test measures the oxygen equivalent consumed by
organic matter in a sample during strong chemical oxidation. It is often used as a measurement
of pollutants in natural and waste waters and to assess the strength of waste such as sewage
and industrial effluent waters. In potable drinking water plants, COD values should be less than
10 mg/L 02 at the end of the treatment cycle (Levis et al. 2010).
COD test results are expressed in mg/L O2. The strong chemical oxidation conditions are
provided by the reagents used in the analysis. Potassium dichromate is used as the oxygen
source with concentrated sulfuric acid (H2SO4) added to yield a strong acid medium. COD for
domestic wastewater is generally about 2.5 times greater than the BOD5 (Shpiner 1997).
Both organic and inorganic constituents of the sample are subject to oxidation; however the
organic component predominates and is of greater interest for FWD effluent. COD is a defined
test; digestion time, reagent strength, and sample COD concentration all affect the extent of
sample oxidation.
31
The oxidation of the organic matter is not always 100% complete. Volatile organics, ammonia
and aromatic hydrocarbon are not oxidized to any great degree during the procedure. This can
prove problematic when assessing a large spectrum of food waste (Shpiner 1997).
The major disadvantage of the COD test is the results are not directly applicable to the BOD
results without correlation studies over a long period of time. BOD can be considered a more
"natural" test in determining the oxygen required to oxidize organic matter. However it does
not account for rapid changes in conditions. COD is often preferred for daily analysis since it is
inherently more reproducible, accounts for changing conditions and takes a short time to
complete. The COD test was chosen over BOD test for the following reasons: COD results are
available much sooner, the COD test requires fewer manipulations of the sample, the COD test
oxidizes a wider range of chemical compounds, and COD testing can be standardized more
easily (Shpiner 1997).
4.4.2. Nitrate Testing
Nitrate (NO3-) is a water-soluble molecule made up of nitrogen and oxygen. It is formed when
nitrogen from ammonia or other sources combines with oxygenated water. Nitrate is a natural
constituent of plants and is found in vegetables at varying levels depending on the amount of
fertilizer applied and on other growing conditions. According to the World Health Organization,
most adults ingest 20-70 mg of nitrate per day with most of this coming from foods like lettuce,
celery, beets, and spinach. When foods containing nitrate are eaten as part of a balanced diet
the nitrate exposure is not thought to be harmful (Peterson 2001).
Water naturally contains less than 1 mg of nitrate per liter and is not a major source of
exposure. Higher levels indicate water has been contaminated. Common sources of nitrate
contamination include fertilizers, animal wastes, septic tanks, municipal sewage treatment
systems, and decaying plant debris (Peterson 2001). Through continued growth of FWD use,
food waste could also be considered a potential source of nitrate contamination.
State and federal laws set the maximum allowable level of nitrate in public drinking water at 10
mg per liter. These laws apply to all city and village water supplies and are used as an advisory
for private wells.
Infants who are fed water or formula made with water that is high in nitrate can develop a
condition that doctors call methemoglobinemia, also called "blue baby syndrome" because the
skin appears blue-gray or lavender in color. This color change is caused by a lack of oxygen in
the blood (Manassaram 2006).
Some scientific studies have found evidence suggesting women who drink nitrate-contaminated
water during pregnancy are more likely to have babies with birth defects. Nitrate ingested by
the mother may also lower the amount of oxygen available to the fetus. People who have heart
or lung disease, certain inherited enzyme defects, or cancer may be more sensitive to the toxic
effects of nitrate than others. In addition, some experts believe that long-term ingestion of
water high in nitrate may increase the risk of certain types of cancer (Manassaram 2006).
The dimethylphenol method, using Hach TNTplus vials was used to assess the amount of nitrate
in FWD effluent. In this test, a solution of diphenylamine and ammonium chloride in sulfuric
acid is used. In the presence of nitrates, diphenylamine is oxidized, giving a blue coloration to
sample kits. Other oxidants such as chlorate, bromate, etc. interfere by similarly oxidizing
diphenylamine. They may be removed by reduction with sodium sulfite. Where nitrite is
present, a false negative result may be observed due to sulfite reducing nitrate in the presence
of nitrite.
4.4.3. Phosphorous Testing
During the natural process of weathering, rocks gradually release phosphorus as phosphates
which are soluble in water. Phosphates exist in three forms: orthophosphate, metaphosphate
(or polyphosphate), and organically bound phosphate. Each phosphate compound contains
phosphorous in a different chemical arrangement. These forms of phosphate occur in decaying
plant and animal remains, as free ions or weakly chemically bounded in aqueous systems,
chemically bounded to sediments and soils, or as mineralized compounds in soil, rocks, and
sediments (Karlberg 1999).
Orthophosphate forms are primarily produced by natural processes. However, major maninfluenced sources can include: treated and untreated sewage, runoff from agricultural sites,
and some lawn fertilizers. Orthophosphate is readily available to the biological community and
typically found in very low concentrations in unpolluted waters. This study will assess effluent
for organic phosphate which is typically estimated by testing for total phosphate. The organic
phosphate is the phosphate found in plant tissue, waste solids, or other organic material
(Karlberg 1999).
Elevated concentrations of phosphate in water will stimulate the growth of plankton and
aquatic plants which provide food for larger organisms including: zooplankton, fish, humans,
and other mammals. Initially, increased productivity will cause an increase in the fish
population and overall biological diversity of the system. As the phosphate loading continues
and there is a build-up of phosphate in the lake or surface water ecosystem, the aging process
of lake or surface water ecosystem will subsequently accelerate. This is commonly referred to
33
as eutrophication or the enhanced production of primary producers resulting in reduced
stability of the ecosystem. This aging process can result in large fluctuations in the lake water
quality and trophic status and in some cases periodic blooms of cyanobacteria. Excessive
nutrient inputs of nitrogen and phosphate have been shown to be the main cause of
eutrophication in lakes over the past 30 years (Manassaram 2006). Lake Mendota and Lake
Monona in Madison, Wisconsin are not exempt from this trend.
The biological overproduction characterized by eutrophication can lead to a variety of problems
ranging from anoxic waters to toxic algal blooms and decrease in diversity, food supply and
habitat destruction (Manassaram 2006). A very common algal bloom and form of
cycanobacteria is known as blue-green algae. When present in large groups or blooms, these
algae appear as a blue-green discoloration in the water. This type of algae is usually found in
freshwater and is most common in areas with high levels of nutrients and warm, sunny, and
calm conditions such as Madison, Wisconsin. Many blue-greens grow attached on the surface
of rocks and stones (epilithic), on submerged plants (epiphytic) or on the bottom sediments of
lakes (epipelic). Some species of blue-green algae produce chemicals that are harmful to both
animals and humans.
These algal blooms have been linked to health problems ranging from skin irritation to liver
damage to death, depending on type and duration of exposure (Ricklefs 1993). Blue-green
algae can literally suffocate organisms by depleting water of life-sustaining oxygen by causing
hypoxic or anoxic conditions. The livelihood of fish, shellfish, and livestock has also been
endangered through contact with this toxin. It should be noted phosphates are not toxic to
people or animals unless they are present in very high levels. Digestive problems can occur
from extremely high levels of phosphate. The soluble or bio-available phosphate is then used by
plants and animals (Manassaram 2006).
In testing, the determination of total phosphate was done by the ascorbic acid method, using
TNTplus vials (Hach Methods 10210). In this test the orthophosphate reacts, in acid medium,
with ammonium molybdate and potassium antimonyl tartrate to form phosphomolybdic acid.
This is reduced by ascorbic acid to form strong colored molybdenum blue. It is then measured
spectrophotometrically at 880 nm. Arsenate, chromium (VI), and nitrite interfere giving the
resulting phosphate concentration.
5. RESULTS & DISCUSSION
5.1. COD
GRAINS
FOOD
Oatmeal
Honey Maid Graham
Crackers
Whole Wheat Bread
Buttermilk White Bread
Popcorn
Spaghetti
Saltine Cracker
White Rice
Mean
COD [mg/L]
(1*102)
1.967
% Increase from
Control (Tap Water)
946.28
SUBGROUP
Whole Grain
2.904
1,444.68
Whole Grain
0.681
0.588
0.589
0.267
3.942
0.332
1.409
262.23
212.77
213.30
42.02
1,996.81
76.60
649.34
Whole Grain
Refined Grain
Whole Grain
Refined Grain
Refined Grain
Refined Grain
COD [mg/L]
(1*102)
0.395
0.267
0.281
0.321
0.451
0.585
0.253
0.295
0.379
0.848
0.408
% Increase from
Control (Tap Water)
VEGETABLES
FOOD
Broccoli
Spinach
Red Cabbage
Tomatoes
Carrots
Baked Beans
Corn*
Potato*
Iceberg Lettuce
Mushrooms
Onion
Coffee Grounds**
Mean
110.11
42.02
49.47
70.74
139.89
211.17
34.57
56.91
101.60
351.06
116.76
SUBGROUP
Dark Green Vegetables
Dark Green Vegetables
Red & Orange Vegetables
Red & Orange Vegetables
Red & Orange Vegetables
Beans & Peas
Starchy Vegetables
Starchy Vegetables
Other Vegetables
Other Vegetables
Other Vegetables
Beans & Peas
Table 5.1: COD Test Results
*Not recommended for FWD processing
**Due to low nutritional value, placement in this group is not necessarily considered a
recommended portion of the USDA MyPlate program
35
DAIRY
FOOD
Cheese
Yogurt (Strawberry)
Ice Cream
Chocolate Chips
Mean
COD [mg/L]
(1*102)
1.776
0.562
1.336
1.550
1.306
% Increase from
Control (Tap Water)
COD [mg/L]
(1*102)
0.570
0.430
0.551
0.636
0.596
0.628
0.573
0.329
0.434
0.503
0.525
% Increase from
Control (Tap Water)
844.68
198.94
610.64
724.47
594.68
SUBGROUP
Cheese
Yogurt
Milk-Based Desserts
Milk-Based Desserts
FRUITS
FOOD
Navel Orange
Nectarine
Apple
Banana
Del Monte Fruit Cocktail
Dark Sweet Pitted Cherries
Red Seedless Grapes
Strawberry
Peach
Pineapple
Mean
203.19
128.72
193.09
238.30
217.02
234.04
204.79
75.00
130.85
167.55
179.26
SUBGROUP
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PROTEIN
FOOD
Beef Sirloin
Bratwurst (uncooked)
Chicken
Chunk Tuna in Olive Oil
Sunflower Seeds
Eggs (shells)
Eggs (w/o shell)
Mean
Tap Water
% Increase from
COD [mg/L]
2
Control
(Tap Water)
(1*10 )
0.536
185.11
0.572
204.26
0.427
127.13
0.667
254.79
0.608
223.40
0.258
37.23
0.820
336.17
0.555
195.44
COD [mg/L] (1*102)
0.188
Table 5.1 Cont.: COD Test Results
SUBGROUP
Meats
Meats
Poultry
Seafood
Nuts & Seeds
Eggs
Eggs
% Increase from Control (Tap Water)
600
GRAINS
VEGETABLES
400
DAIRY
649.34
FRUITS
594.68
PROTEINS
200
179.26
116.76
0
195.44
Primary Food Group
Figure 5.1: COD Test Results
52.95
94.86
GRAINS*
VEGETABLES
280.60
733.28
DAIRY
FRUITS
98.43
PROTEIN
Figure 5.2: Standard Deviation of % Change for COD Test Results
*Ideal for potential further food product study and subgroup evaluations
COD increases are the primary indication of loading and a source of concern for burden on a
WWTP. Subsequently, it is very important to accurately assess the changes in COD and
potential causes. Figure 5.1 shows foods from the Grains Group and Dairy Group had significant
37
increases in COD from the tap water control (649.34% and 594.68% respectively). While COD
levels remained relatively low and treatable by a WWTP, this could prove problematic with
widespread adoption and utilization of FWDs as a means to divert organic food waste.
Foods tested from the Grain Group proved to have the highest deviation in increase of COD
(Figure 5.2). It would be advantageous for research purposes to continue assessment of foods
within subgroups of this group to better distinguish what particular grains are worst utilized in
FWD processing. This could potentially lower the deviation within the Grain Group and better
inform FWD users.
Both saltine and honey graham crackers had significant (>1000%) increases in COD. However,
these food products come from separate subgroups within the Grain Group. It was observed
during testing that both these foods occupied a significant volume within the disposer, whereas
other grains were able to be placed within the FWD with no noticeable concerns for
volume/space. Given time and funding constraints of this study it was assumed the best means
of assessing food samples with FWD processing would be mass to volume water. However,
further examination of the food bulk/volume compared to COD could potentially yield novel
information on this topic.
5.2. Nitrate
GRAINS
0.112
% Change from Control
(Tap Water)
133.33
Whole Grain
0.242
404.17
Whole Grain
0.102
0.070
0.095
0.077
0.073
0.045
0.102
112.50
45.83
97.92
60.42
52.08
-6.25
112.50
Whole Grain
Refined Grain
Whole Grain
Refined Grain
Refined Grain
Refined Grain
FOOD
N [mg/L]
Oatmeal
Honey Maid Graham
Crackers
Whole Wheat Bread
Buttermilk White Bread
Popcorn
Spaghetti
Saltine Cracker
White Rice
Mean
SUBGROUP
VEGETABLES
FOOD
N [mg/L]
Broccoli
Spinach
Red Cabbage
Tomatoes
Carrots
Baked Beans
Corn*
Potato*
Iceberg Lettuce
Mushrooms
Onion
Coffee Grounds**
Mean
0.058
0.062
0.057
0.050
0.056
0.055
0.049
0.042
0.084
0.154
0.067
% Change from Control
(Tap Water)
20.83
29.17
18.75
4.17
16.67
14.58
2.08
-12.50
75.00
220.83
38.96
SUBGROUP
Dark Green Vegetables
Dark Green Vegetables
Red & Orange Vegetables
Red & Orange Vegetables
Red & Orange Vegetables
Beans & Peas
Starchy Vegetables
Starchy Vegetables
Other Vegetables
Other Vegetables
Other Vegetables
Beans & Peas
Table 5.2: Nitrate Test Results
*Not recommended for FWD processing
**Due to low nutritional value, placement in this group is not necessarily considered a
recommended portion of the USDA MyPlate program
39
DAIRY
FOOD
N [mg/L]
Cheese
Yogurt (Strawberry)
Ice Cream
Chocolate Chips
Mean
0.095
0.075
0.086
0.242
0.125
% Change from Control
(Tap Water)
97.92
56.25
79.17
404.17
159.38
SUBGROUP
Cheese
Yogurt
Milk-Based Desserts
Milk-Based Desserts
FRUITS
FOOD
N [mg/L]
Navel Orange
Nectarine
Apple
Banana
Del Monte Fruit Cocktail
Dark Sweet Pitted Cherries
Red Seedless Grapes
Strawberry
Peach
Pineapple
Mean
0.077
0.074
0.105
0.112
0.157
0.090
0.080
0.067
0.067
0.082
0.091
% Change from Control
(Tap Water)
60.42
54.17
118.75
133.33
227.08
87.50
66.67
39.58
39.58
70.83
89.79
SUBGROUP
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PROTEIN
FOOD
N [mg/L]
Beef Sirloin
Bratwurst (uncooked)
Chicken
Chunk Tuna in Olive Oil
Sunflower Seeds
Eggs (shells)
Eggs (w/o shell)
Mean
0.045
0.047
0.057
0.059
0.061
0.044
0.043
0.051
Tap Water
Table 5.2 Cont.: Nitrate Test Results
% Change from Control
(Tap Water)
-6.25
-2.08
18.75
22.92
27.08
-8.33
-10.42
5.95
N [mg/L]
0.048
SUBGROUP
Meats
Meats
Poultry
Seafood
Nuts & Seeds
Eggs
Eggs
% Increase from Control (Tap Water)
180
160
140
GRAINS
120
VEGETABLES
100
DAIRY
80
60
159.38
FRUITS
112.50
PROTEINS
89.79
40
20
38.96
5.95
0
Primary Food Group
Figure 5.3: Nitrate Test Results
16.25
57.40
GRAINS
125.71
VEGETABLES
DAIRY*
FRUITS
PROTEIN
164.08
67.92
Figure 5.4: Standard Deviation of % Change for Nitrate Test Results
*Ideal group for potential further study of food products
The maximum contaminant level goal (MCLG) for nitrate is 10 mg/L or 10 ppm (US EPA 2010).
The tap levels observed in the tap water used in testing were well below the MCLG at 0.048
mg/L. All observed increases in nitrate concentrations also remained within the MCLG. Both
41
meat and both egg samples led to decreases in nitrate concentration. Mushrooms also caused a
decrease in nitrate concentration.
As shown in Figure 5.3, the addition of samples from all food groups led to an overall increase
in nitrate concentration. The addition of dairy products led to the greatest increase in nitrate
concentration (159.38%). Proteins led to the smallest increase in nitrate concentration (5.95%).
However, foods from both Dairy and Protein Groups were relatively small compared to those
from the Vegetable and Fruit Groups. More food products should be tested to affirm the
variances observed in Figure 5.3.
Nitrates come primarily from plants. Increased concentrations should have been highest in the
vegetables. However, this was not observed. This could be a result of a lack of diversity within
the vegetable group. It could also be the result of testing error during the procedure. Further
study should also be conducted of the Vegetable Group.
Furthermore, food products from the Dairy Group are ideal candidates for further nitrate
testing. Only four dairy products were processed. The standard deviation between nitrate
concentrations within this group was greater than any group tested (Figure 5.4). Increasing the
number of dairy samples tested could potentially bring down the standard deviation between
observed samples.
5.3. Phosphorous
GRAINS
0.208
% Increase from
Control (Tap Water)
156.79
Whole Grain
0.246
203.70
Whole Grain
0.171
0.121
0.187
0.411
1.198
0.160
0.338
111.11
49.38
130.86
407.41
1,379.01
97.53
316.98
Whole Grain
Refined Grain
Whole Grain
Refined Grain
Refined Grain
Refined Grain
FOOD
P [mg/L]
Oatmeal
Honey Maid Graham
Crackers
Whole Wheat Bread
Buttermilk White Bread
Popcorn
Spaghetti
Saltine Cracker
White Rice
Mean
SUBGROUP
VEGETABLES
FOOD
P [mg/L]
Broccoli
Spinach
Red Cabbage
Tomatoes
Carrots
Baked Beans
Corn*
Potato*
Iceberg Lettuce
Mushrooms
Onion
Coffee Grounds**
Mean
0.256
0.242
0.264
0.131
0.208
0.152
0.119
0.293
0.155
0.713
0.253
% Increase from
Control (Tap Water)
216.05
198.77
225.93
61.73
156.79
87.65
46.91
261.73
91.36
780.25
212.72
SUBGROUP
Dark Green Vegetables
Dark Green Vegetables
Red & Orange Vegetables
Red & Orange Vegetables
Red & Orange Vegetables
Beans & Peas
Starchy Vegetables
Starchy Vegetables
Other Vegetables
Other Vegetables
Other Vegetables
Beans & Peas
Table 5.3: Phosphorous Test Results
*Not recommended for FWD processing
**Due to low nutritional value, placement in this group is not necessarily considered a recommended
portion of the USDA MyPlate program
43
DAIRY
FOOD
P [mg/L]
Cheese
Yogurt (Strawberry)
Ice Cream
Chocolate Chips
Mean
1.976
0.642
0.775
0.267
0.915
% Increase from
Control (Tap Water)
2,339.51
692.59
856.79
229.63
1,029.63
SUBGROUP
Cheese
Yogurt
Milk-Based Desserts
Milk-Based Desserts
FRUITS
FOOD
P [mg/L]
Navel Orange
Nectarine
Apple
Banana
Del Monte Fruit Cocktail
Dark Sweet Pitted Cherries
Red Seedless Grapes
Strawberry
Peach
Pineapple
Mean
0.203
0.166
0.143
0.272
0.151
0.177
0.155
0.132
0.137
0.091
0.163
% Increase from
Control (Tap Water)
150.62
104.94
76.54
235.80
86.42
118.52
91.36
62.96
69.14
12.35
100.86
SUBGROUP
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PROTEIN
FOOD
P [mg/L]
Beef Sirloin
Bratwurst (uncooked)
Chicken
Chunk Tuna in Olive Oil
Sunflower Seeds
Eggs (shells)
Eggs (w/o shell)
Mean
0.320
0.540
0.483
0.647
0.266
0.095
0.320
0.382
Tap Water
Table 5.3 Cont.: Phosphorous Test Results
% Increase from
Control (Tap Water)
295.06
566.67
496.30
698.77
228.40
17.28
295.06
371.08
P [mg/L]
0.081
SUBGROUP
Meats
Meats
Poultry
Seafood
Nuts & Seeds
Eggs
Eggs
% Increase from Control (Tap Water)
1,000
GRAINS
800
VEGETABLES
DAIRY
600
1,029.63
FRUITS
400
200
PROTEINS
316.98
371.08
212.72
100.86
0
Primary Food Group
Figure 5.5: Phosphorous Test Results
59.80
230.36
442.62
GRAINS
VEGETABLES
DAIRY*
213.09
FRUITS
PROTEIN
912.73
Figure 5.6: Standard Deviation of % Change for Phosphorous Test Results
*Ideal group for potential further study of food products
The critical levels of phosphorus in water, above which eutrophication is likely to be triggered,
are approximately 0.03 mg/L of dissolved phosphorus and 0.1 mg/L of total phosphorus.
Phosphorous concentration limits in effluent vary based on region and usually range from 0.1-2
45
mg/L, with many established at 1.0 mg/L (US EPA 2010). Many FWD effluent samples exceeded
phosphorous eutrophication and effluent concentration limits. However, it should be
considered the samples processed (40 g/gal) were assumed to be the upper limit for mass to
volume acceptable to maintain sufficient flow in a collection system. Once introduced into
municipal collection systems, FWD effluent will presumably become diluted and these
concentrations should not be of concern. However, in regions with flow concerns e.g., drought
areas, areas with low populations, etc., utilization of FWDs may be unreasonable.
Removal processes for phosphates from wastewaters utilize incorporation into suspended
solids and the subsequent removal of those solids. Phosphates can also be incorporated into
chemical precipitates that are insoluble or of low solubility or into biological solids e.g.,
microorganisms from food waste. Subsequently, further investigation into the total suspended
solids (TSS) in various FWD effluents should be cross-referenced with phosphorous generation
in respective effluents. However, this was deemed impractical given funding and time
constraints for this study.
As shown in Figure 5.5, the addition of samples from all food groups led to an overall increase
in phosphorous concentration. The addition of dairy products led to the greatest increase in
phosphorous concentration (1,029.63%). Fruits led to the smallest increase in phosphorous
concentration (100.86%). However, the number of samples tested from the Dairy Group was
relatively small compared to the Fruit Group. More food products should be tested to affirm
the discrepancies observed in Figure 5.5. Furthermore, a 1,029% increase in phosphorous
concentration could yield very adverse consequences on the cost of treatment at a WWTP.
Food products from the Dairy Group are ideal for further phosphorous testing. Only four dairy
products were processed. The standard deviation between phosphorous concentrations within
this group was greater than any group tested (Figure 5.6). Increasing the number of dairy
samples tested could potentially bring down the standard deviation between observed
samples.
6. CONCLUSIONS
Diversion of organic waste is a means of reducing LFG emissions and preserving valuable
volume within landfills. The benefit of organic waste diversion is not only limited to a reduction
in the amount of methane generated in landfills. By diverting organic waste from a landfill, the
emission of LFG will also slow down and extend the travel time though the soil cover, which will
decrease methane emission from the landfill further. The degree of settling will also be
minimized due to the low biodegradability of waste entering the landfill. The diversion of the
biodegradable fraction also increases compaction of MSW at landfills and in some previous
cases reduced the leachate production by 80 - 90% (Smith et al. 1997).
In this study several significant trends were noticed in the results for COD, nitrate, and
phosphorous testing of the FWD effluent. For COD and nitrate testing, foods from the Grains
Group and the Dairy Group caused the greatest concentration increases. It should be noted,
however, some foods within the Grains Group caused an observed decrease in concentration in
nitrate tests. Further study should be conducted to verify these results. Lastly, foods from the
Dairy Group caused a significantly higher increase in phosphorous than foods from any other
group. The Dairy Group was the smallest group tested. Further testing of Dairy Group foods
should be conducted to help distinguish which dairy products have the greatest impact on
phosphorous in FWD effluent.
The results of this study will give insights into future planning efforts for organic waste
management. It was found the Grains Group showed the highest deviation for COD testing. The
Dairy Group showed the highest deviation for both nitrate and phosphorous testing. In future
studies these respective groups should be examined closer to better assess which foods are
causing this deviation and why. This will help increase the efficiency of FWDs and allow the
public to utilize them with minimal impact on effluent.
This should be considered a preliminary study report. This report primarily focuses on the
impact of food waste disposer utilization and subsequent fluctuations in COD, nitrate, and
phosphorous. Alternative methods for food waste diversion were considered in this report i.e.,
landfilling & incineration, and composting. However, a more thorough analysis is required in
order to consider the wider range of environmental impacts associated with all of the organic
food waste remediation. This is the only way to develop a truly accurate comparison between
food waste diversion alternatives.
47
7. REFERENCES
2010. “How Does Food Decompose?” Article available at http://www.ehow.com/howdoes_4574259_food-decompose.html.
Amlinger, Florian. 1996. The Science of Composting.
Bagchi, Amalendu. February 2004. Design of Landfills and Integrated Solid Waste Management.
Bernstad, A. and Jansen, J. 2011. “A Life Cycle Approach to the Management of Household Food Waste.”
Bolzonella, David, Paolo Pavan, Paolo Battisoni, and Franco Cecchi. Department of Science and
Technology. University of Verona. 2003. “The Under Sink Garbage Grinder: A Friendly
Technology for the Environment.”
CECED – European Committee of Manufacturers of Domestic Appliances. Spring 2003. “Food Waste
Disposers – An Integral Part of the EU’s Future Waste Management Strategy.”
de Koning, Dr.ir. J. and Prof.ir. J.H.J.M. van der Graaf. Delft University of Technology. April 1996.
“Kitchen Waste Disposer Effects on Sewer System and Wastewater Treatment.”
de Koning, Dr.ir. J. Delft University of Technology. July 2004. “Environmental Aspects of Food Waste
Disposers.”
Diggelmann, Dr. Carol. Department of Civil and Environmental Engineering – University of Wisconsin.
January 1998. “Life- Cycle Comparison of Five Engineered Systems for Managing Food Waste.”
Hall, K. D., Guo, J., Dore, M., and C.C. Chow. 2009. “The Progress Increase of Food Waste in America and
its Environmental Impact.”
Hernandez, Gerald L., Kenneth R. Redd, Wendy A. Wert, An Min Liu, and Tim Haug. Biocycle Magazine.
January 2002. “Los Angeles Digesters Produce Energy from Airport Food Residuals.”
Hernanadez, Gerald L., Redd, Kenneth R., Wert, Wendy A., Liu, An Min, and Haug, Tim. “Hyperion
Advanced Digestion Pilot Program.”
<http://www.choosemyplate.gov>
Karlberg, Tina and Norin, Erik. VA-FORSK REPORT. 1999. “Food Waste Disposers – Effects on
Wastewater Treatment Plants. A Study from the Town of Surahammar.”
Karrman, Olofsson, Persson, Sander, and Aberg. Recycling Board of Goteborg, Sweden. 2001. “Food
Waste Disposers – A Solution for Sustainable Resource Management? A Pre-Study in Goteborg,
Sweden.”
Kegebein, Jorg, Erhard Hoffmann, and Prof. Hermann H. Hahn. Institute for Municipal Water Treatment,
University of Karlsruhe. 2004. “Co-Transport and Co-Reuse – An Alternative to Separate BioWaste Collection?”
Levis, Barlaz, Themelis, and Ulloa. February 2010. “Assessment of the State of Food Waste Treatment in
the United States and Canada.”
Manassaram, Deana. 2006. “A Review of Nitrates in Drinking Water: Maternal Exposure and Adverse
Reproductive and Developmental Outcomes”.
Marashlian, Natasha and Mutasem, El-Fadel. American University of Beirut, Lebanon. October 2004.
“The Effect of Food Waste Disposers on Municipal Waste and Wastewater Management.”
New York City Department of Environmental Protection. June 1997. “The Impact of Food Waste
Disposers in Combined Sewer Areas of New York City.”
Nickisch, Curt. March 2008. “Boston Wants to Harness Composting Energy”.
Peterson, Chester. 2001. “Lower the Nitrates”.
Rosenwinkel, K.-H. and D. Wendler. Institute for Water Quality and Waste Management, University of
Hanover (ISAH). “Influences of Food Waste Disposers on Sewerage System, Wastewater
Treatment and Sludge Digestion.”
Shpiner, Ram. Submitted to the Senate of the Technion – Isreal Institute of Technology. January 1997.
“The Effect of Domestic Garbage Grinding on Sewage Systems and Wastewater Treatment
Plants”.
Shpiner, Ram. Submitted to the Senate of the Technion – Isreal Institute of Technology. January 1997.
“The Effect of Domestic Garbage Grinding on Sewage Systems and Wastewater Treatment
Plants.”
Smith. September 1997. Measurement and Modeling of Methane Fluxes from Landfills. Available online
at http://igac.jisao.washington.edu/newsletter/highlights/1997/landfills.php.
Terpstra, Prof. drs. P.M.J. Agricultural University Wageningen. April 1995. “Kitchen Waste Disposal
Treatment: An Evaluation.”
US Environmental Protection Agency (2009) Municipal Solid Waste Generation, Recycling, and Disposal
in the US: Facts and Figures for 2008. Washington DC.
Verma, Shefali. May 2002. “Anaerobic Digestion of Biodegradable Organics in Municipal Solid Wastes”.
Waste Management Research Unit – Griffith University. August 1994. Executive Summary. “Economic
and Environmental Impacts of Disposal of Kitchen Organic Wastes Using Traditional Landfill –
Food Waste Disposer – Home Composting.”
49
Wright, Laura. 2010. “How to Wage War on Food Waste”.
Yoshida, H. and Gable, J. 2010. “Madison Organic Waste Diversion Project Greenhouse Gas Emissions
Analysis.”