Comparison of storage, treatment, utilization,
and disposal systems
for human and livestock wastes
by: Ron Fleming and Marcy Ford
Ridgetown College - University of Guelph, Ridgetown, Ontario
November, 2002
A - Introduction
Background
Systems have been in place for many years to handle, store, treat, dispose of, or use
excrement from humans and from farm animals. In towns and cities we see sewage treatment
facilities to process human wastes and purify the water portion to the level where it can be
discharged to surface water. A solid portion is often treated and spread onto farm fields as a
source of plant nutrients or it is land-filled. In much of rural Ontario, individual homes use septic
systems, where wastes are treated typically in a treatment bed on the owner’s property. These
systems are able to handle the large volumes of very dilute wastes generated by humans. On
livestock farms, we see a different approach. In most cases, the livestock manure (which contains
feces and urine and may also contain dilution water, bedding, or spilled feed) is stored for up to a
year and spread onto crop land where the nutrients can be used for crop growth and the organic
matter used to maintain soil health.
In the past few years, there has been an increased interest in manure “treatment”
technologies on farms. Research has been carried out around the world to find the best methods
to treat manure - for odour control, to kill pathogens, for volume reduction, for concentration of
nutrients, for creation of saleable organic products, to reduce labour costs, etc. There have been
suggestions that some of the systems used for human waste treatment may be appropriate on
farms for livestock manure.
The purpose of this report is to briefly describe the main systems in use today in Ontario
(and in many other regions) and to put into perspective some of the features of the various
systems used for human wastes and livestock manure.
What do we measure?
The primary constituents that municipal wastewater treatment plants monitor include the
following: biochemical oxygen demand (BOD), total suspended solids (TSS), total phosphorus
(TP), total Kjeldahl nitrogen (TKN), and bacteria such as E. coli, fecal coliform, and total
coliform. The same constituents are used to measure the performance of individual septic systems
for human wastes.
BOD5
The biochemical oxygen demand is a measure of the dissolved oxygen required to
stabilize the organic matter in five days. It is an indicator of the amount of organic
material present in a liquid.
TSS
Total suspended solids are the organic and inorganic solids that are not dissolved
and may be removed by coagulation or filtration.
N
Nitrogen is a valuable nutrient used for crop growth. It is present in several forms,
the main ones being: organic nitrogen, ammonia, nitrite, and nitrate. Total kjeldahl
nitrogen (TKN) includes organic nitrogen and ammonia. While nitrogen is valuable
for crop growth, in surface water, it can accelerate the growth of aquatic plants. In
groundwater, nitrates pose a health threat if they enter drinking water supplies.
P
Phosphorus exists in both the organic and inorganic form. We often are interested
in total phosphorus or phosphate, a form of phosphorus . Phosphorus, like
nitrogen, can cause eutrophication in surface water - a nutrient enrichment causing
microbial and algae growth. These conditions deplete oxygen to the point where
chemical-reduction processes can render the water body unsuitable for many forms
of aquatic life, reduce the recreational value of the water, and make it unacceptable
for use as a source of drinking water.
Bacteria
The concentration of bacteria is usually regulated through limits for E. coli, fecal
coliform and total coliform bacteria. Fecal coliform bacteria and E. coli are
organisms that can be quantitatively related to the presence of sewage or fecal
matter. They are not necessarily pathogenic - i.e. capable of causing disease.
However, they are used as “indicators” of the potential presence of pathogenic
bacteria (or other organisms) that may be present in water.
For livestock manure, the three main crop nutrients: N, P, and K and the dry matter (DM)
content are the most frequently measured parameters. Dry matter content is typically measured,
rather than total suspended solids.
K
Potassium is a crop nutrient that is found in manure in significant amounts.
“Environmental” effects of excess K are typically not a issue.
DM
Dry matter, sometimes referred to as Total Solids (TS), is the mass of solids, as a
percentage of the overall mass of diluted manure.
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Ridgetown College - University of Guelph
2002
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Typical Concentrations
Typical concentrations of some of the discussed parameters measured to monitor waste
properties are listed in Table 1.
Table 1 - Comparison of typical waste stream characteristics (note: all values are rounded to 2
significant figures) (source: Fleming and Ford, 2001)
Parameter
Liquid swine*
manure
Units
Liquid dairy
manure
mg / L
14 000
DM
%
10
TS
mg / L
100 000
98 000
700
TN
mg / L
3 800
4 600
40
TP
mg /L
800
1 600
BOD5
Total coliform
number / 100 mL
bacteria
*
swine manure is from feeder pigs
9.5 x 107
Raw human
sewage
28 000
220
9.8
0.070
7.9
4.0 x 106
1.0 x 106
B - Human: Wastewater Treatment Plants
The percentage of Canadians served by wastewater treatment has been increasing. In
1999, 73% of Canadians were served by municipal sewer systems. The level of sewage treatment
used across Canada is gradually improving as more municipalities upgrade their existing
wastewater treatment facilities. Municipal wastewater, consisting mainly of human waste, is the
largest source of nitrogen and phosphorus released to the Canadian Environment. In 1999, about
82,750 tonnes of total nitrogen and 4950 tonnes of total phosphorus were released to lakes,
rivers, and coastal waters from municipal sewage. Some municipal wastewater treatment plants
are required to use advanced phosphorus removal methods before discharging their waste effluent
into particularly sensitive waters. Repair and replacement of sewage systems have reduced leaks
and pollutant loadings (Environment Canada, 2001).
Treatment Plant Classification
Treatment plants can be classified as ‘primary’, ‘secondary’, or ‘tertiary.’ The effluent
quality progressively improves as you move from primary to secondary to tertiary treatment.
1. Primary Treatment
This form of treatment is usually limited to the use of a separator to remove the larger
solids, sand, and grit in the wastewater from the liquid. This is the most basic level of treatment
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2002
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acceptable for municipal plants in Ontario. There is a great deal of pressure to upgrade existing
primary plants to meet the performance standards of secondary plants.
2. Secondary Treatment
Secondary treatment involves both separators and reactors. Reactors tend to oxidize,
reduce, immobilize, or physically condition their contents and create gaseous products in the
process. This form of treatment is largely a biological process that requires air to stimulate the
growth of bacteria and other organisms which will eventually consume most of the waste
materials. As this process continues and the settled sludge mixes with newer sludge, gradually a
culture of organisms develop that is capable of consuming the organic material in the sewage
within four to eight hours.
Secondary plants tend to be either ‘lagoon-based’ or ‘mechanical.’ A further classification
can be made in the reactor portion of biological secondary plants. The biomass of organisms
contained within the reactor can be either: a) ‘suspended’ by mixing - known as ‘Suspended
Growth Biological Treatment’; or b) supported by attachment to a solid, inert medium - referred
to as an ‘Attached Growth Biological Treatment’ system.
3. Tertiary Treatment
Tertiary treatment is defined as any additional treatment to remove suspended solids,
nitrogen, phosphorus, or other dissolved substances remaining after secondary treatment.
Effluent filtration through a granular medium is the most common form of tertiary treatment
applied in Ontario. In practice, chemically-assisted filtration normally achieves better effluent
qualities than particle straining alone.
Major Treatment Technologies
The level of sewage treatment is generally improving in Canada as more municipalities
upgrade their wastewater treatment facilities. In 1991, tertiary treatment was provided to 36 % of
the Canadian municipal population. This percentage increased to 38 % in 1996. Secondary
treatment was provided to 34 % of the Canadian population in 1996, up from 29 % in 1991.
Ontario’s population is largely served by tertiary treatment, with substantial increases in this level
of service since 1983 in response to programs aimed at cleaning up the Great Lakes (Chambers et
al., 2001).
Table 2 gives a summary of the systems being used by communities in Ontario. The third
most common system, Conventional Activated Sludge, is actually the predominant wastewater
treatment technology in Ontario, on a treatment volume basis. It was used at 21.3 % of the total
facilities, including nine of the largest 10 facilities, and 33 of the largest 45 facilities. Since
‘Extended Aeration’, ‘Conventional Seasonal Lagoon,’ and ‘Conventional Activated Sludge’ are
used at 68 % of the total facilities in Ontario, the following portion of this report will be limited to
the description of these three treatment plants. These systems are all considered to be ‘Suspended
Growth Biological Treatment’ systems.
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Ridgetown College - University of Guelph
2002
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Table 2 - Wastewater treatment systems used in Ontario (source: Doyle, 2002)
Technology
Number
% of Total
Extended Aeration
109
24.4
Conventional Lagoon- Seasonal
101
22.6
Conventional Activated Sludge
95
21.3
Primary
23
5.1
Aerated Cell Plus Lagoon
19
4.3
Conventional Lagoon - Continuous
15
3.4
Contact Stabilization
14
3.1
Conventional Lagoon - Annual
14
3.1
Oxidation Ditch
10
2.2
Aerated Lagoon
8
1.8
Exfiltration Lagoon
8
1.8
Rotating Biological Contactor
5
1.1
1. Activated Sludge Treatment Process
This is the most common form of secondary treatment in Ontario. It includes
Conventional Activated Sludge (the majority of larger plants in Ontario) and Extended
Aeration (most of the smaller plants). Conceptual schematics of the two systems are found in
Figures 1 and 2.
Treatment begins with screening of the sewage to remove larger debris. Grit removal is
designed to remove larger settleable inorganic materials to reduce abrasive wear on mechanical
systems later in the treatment process. Primary sedimentation removes most of the remaining
solids and organic material. Screens, settling tanks, and skimming devices are commonly used for
the separation.
The activated sludge process involves an aerated or mixed reactor, also known as an
aeration tank. There is a primary clarifier before this aeration tank and a secondary clarifier or
sedimentation tank after the aeration tank. The distinction between the Conventional Activated
Sludge and the Extended Aeration treatment systems, especially for municipal plants, is that
Extended Aeration rarely involves primary sedimentation or a primary clarifier. Also, Extended
Aeration treatment facilities tend to have much longer hydraulic detention times than
Conventional Activated Sludge systems. As microorganisms grow and are mixed by the addition
of the air, the individual organisms gather together or flocculate to form an active mass called
‘activated sludge.’ The mixture of activated sludge and wastewater in the aeration basin flows to
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2002
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Figure 1 Conventional Activated Sludge system
the secondary clarifier, where the activated sludge settles. A portion of the settled sludge is
returned to the aeration basin to maintain the desired food-to-microorganism ratio to allow the
rapid breakdown of organic matter. Since more activated sludge is produced than can be used in
the process, some of it is wasted from the aeration basin to the sludge-handling system for
treatment and ultimate disposal. Air is normally introduced in the aeration basin either by
diffusers or by mechanical mixers.
Figure 2 Extended Aeration system
Chlorine is the most common disinfectant used to destroy disease-causing organisms in the
wastewater effluent. Typically, as illustrated, chlorine contact tanks are provided at the end of the
secondary or tertiary treatment processes. They are designed for a minimum of 30 minutes
contact time at average plant flow. The treated wastewater then leaves the plant and enters a
water source. Chlorination is the least expensive disinfection method. However, it may produce
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2002
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undesirable effects in the river, either when it combines with organic matter or if the residual is
too high - causing an acute toxicity to fish and aquatic insects.
Ultraviolet light is an excellent disinfection method and does not leave any known residue.
This method disinfects by altering the DNA in microorganisms and preventing them from
propagating. Detention times are only one minute as opposed to 30 minutes for chlorine, and
ultraviolet radiation has a non-toxic effluent. Despite the advantages of ultraviolet radiation in the
disinfection process, chlorine is still the most commonly used.
2. Lagoon Treatment Process
Conventional seasonal lagoons (depicted in Figure 3) are commonly used to treat
wastewater in smaller communities. Lagoons function both as aeration and settling tanks. They
are typically two metres deep and rely on oxygen transfer between air and the water surface.
These types of facilities also rely on photosynthetic oxygen generation by algae to promote the
growth of aerobic bacteria that degrade or metabolize influent organic matter. Seasonal lagoons
have their effluent released only seasonally and must accommodate a large volume of wastewater.
The screening process that removes large settleable inorganics is similar to that of the activated
sludge process. Lagoons often are constructed as earthen basins. They tend to have long
hydraulic detention periods and, as a result, a certain amount of nitrification is achieved. Higher
temperatures and lower organic loadings generally encourage this production of the nitrate
nitrogen. The chlorine disinfection process, before the release of the effluent into a body of
water, is similar to the activated sludge process previously described.
Figure 3 Conventional Seasonal Lagoon system
Sewage Sludge Treatment and Disposal
Sewage sludge results from the decomposition and settling of solids at sewage treatment
plants. It usually contains considerable amounts of organic matter, between 0.1 to 0.3 % total
nitrogen, and between 0.05 to 0.15 % total phosphorus (Payne, 2002). Magnesium, zinc, copper,
boron and other “heavy metals” may also be present. Only stabilized sewage sludges with low
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2002
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metal concentrations are suitable for land application and are considered biosolids. Municipal
sewage biosolids (MSB) refers to the nutrient-rich organic materials removed during the
treatment of domestic sewage in a wastewater treatment facility.
Stabilization is accomplished by digestion or by some other acceptable means, such as
adding lime. Digestion is the decomposition by either anaerobic or aerobic bacteria. Aerobic
thermophilic digestion has become a popular stabilization process. Digestion may involve
decomposition by anaerobic bacteria of the solids removed after settling in the primary and
secondary clarifiers . This process is carried out in a digester and produces biosolids which can be
used as soil conditioners. Methane gas is a product of digestion and it is used as fuel for heat
exchangers and boilers. In smaller plants the process can be carried out in a single digester, while
larger plants require two or more tanks to handle the larger volume of sludge. Digestion reduces
the number and type of pathogens - viruses, bacteria, fungi, and parasites. It also reduces the
volume of material, and stabilizes organic matter, thereby reducing the potential for odours.
Dewatering is the removal of water from the sludge using either vacuum filtration,
centrifuges, or belt presses.
Vacuum filters are used to reduce the water content of the sludge. The filter is a
porous drum wrapped in a steel-coil blanket that picks up the sludge. The rotation
of the drum reduces the quantity of water in the sludge with the aid of a partial
vacuum inside the drum. A scraper edge removes the dewatered sludge from the
outside of the drum. This sludge is then transferred to a storage area.
A centrifuge is a horizontal or vertical cylinder which is continually turned at high
velocities. This mechanical solid-liquid separator relies on centrifugal forces to
separate the liquid and solid components of the sludge onto the inside wall of the
cylinder into two layers. An auger which turns slightly faster than the cylinder
moves the solids to the conic part of the unit where they are discharged.
Belt presses consist of a flat, woven, fabric belt that runs horizontally between
rollers. The liquid component of the sludge is forced through the belt by the
rollers and the solids are carried along and belt and deposited in a collection
chamber.
Sludge dewatering facilities produce two streams. One stream is processed solids and the
other stream is liquids. The liquid stream is returned to the head of the plant to be treated once
more, since it contains high concentrations of suspended solids and BOD.
Utilization of Biosolids
Biosolids can be dealt with in a number of ways. These include direct application to farm
land, disposal at a landfill, incineration, composting, or further processing such as lime
stabilization or pelletization. In all cases, biosolid disposal requires the approval of the Ministry
of the Environment.
•
Incineration
-
Fleming and Ford
the complete combustion of organic matter and other
volatile compounds
a controlled process involving the burning of gaseous
combustible residuals
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2002
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•
Composting
by heat drying
-
creates a residual ash
-
removal of moisture from the biosolids and partial
combustion of the organic matter
volatile matter is removed and the biosolids are stable
enough for use as a compost
gases involved in the drying process are reheated to
eliminate odours
the biosolids, after drying, are processed into a soil
conditioner
-
•
Composting
by microbial
action
-
-
•
Thermal Drying
(Pelletization)
-
•
Chemical
Stabilization
-
•
Burial / Landfilling
-
•
Land Application
Fleming and Ford
-
a process in which organic matter undergoes biological
decomposition to produce a stable end product that is
acceptable as a soil conditioner
methods of composting include open windrow and
mechanical systems
biosolids are heated in a dryer to evaporate any moisture
products of this process are uniform-size, dust-free, odour
pellets that can be stored for long periods of time
pellets can be used as an organic additive to fertilizers
most common form is lime stabilization which involves
mixing biosolids with lime
pathogen levels are controlled with the increased
temperature and pH levels
biosolids can then be converted into an alkaline soil
conditioner suitable for use as a low-grade fertilizer or
landfill cover
this process actually increases the volume of biosolids
digested sludge or biosolids are buried at a suitable site (i.e.
appropriate distance from populated areas, leachate
protection, runoff and erosion control, and protection
against gas movement)
biosolids may be used as a daily landfill cover to limit
surface infiltration
permitted only at licenced landfill sites
applied to crop land, thus reducing the demand for
commercial fertilizers, improving soil fertility, enhancing soil
structure, and improving soil moisture retention and
permeability
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2002
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-
-
-
ideal for crops such as corn, soybeans, canola, and cereals
and can also benefit pasture land.
can be used in forestry to encourage tree growth, and
therefore timber production, or to rehabilitate soils affected
by mining or quarrying.
soil tests ensure suitability of the application site based on
levels of nutrients, metals, and pH of the soil
guidelines concerning biosolids land application require that
the land is suitable, located a specified distance from
residences, wells, and water sources and that the timing and
method of application must be appropriate for the specific
site considerations and crop management
a field would receive biosolids once every five years,
normally
Sewage Treatment Plants - Potential Water Quality Impacts
All treated wastewater from a sewage treatment plant is discharged to streams or other
surface water. While this can affect the quantity of flow in a stream, these systems are designed
to minimize any impact on water quality. The cause of potential water quality impacts of sewage
treatment plants fall into three main areas:
1. Bypasses
Bypasses of municipal wastewater or raw sewage occur when the peak capacity of the
sewage treatment facility is exceeded, usually during periods of heavy rainfall. The flow is
deliberately redirected away from any further treatment and is released to the body of water.
Occasionally during the construction and expansion of facilities, bypasses are necessary to prevent
the raw sewage from backing up into homes, businesses, and streets and to avoid the shutdown of
the entire facility. The capacities of wastewater treatment plants are designed to handle shortterm peak flows well above daily averages, so that normal fluctuations in the flow do not cause
plant upsets. Diversion of flow is prohibited from any portion of the treatment facility except
during emergency conditions. A treatment plant would ideally expand prior to reaching its
maximum capacity. In most cases, raw sewage receives at least primary treatment and chlorine
disinfection before discharge into the watercourse (Hartley, 2001).
When there is a bypass incident, the facility operators must immediately notify the Medical
Officer of Health, the Ministry of Health, and the Water Supply Section of the Works and
Emergency Services Department (WES), detailing the volume and duration of the discharge.
Municipalities report bypasses to the Ministry of the Environment and Energy. The WES is
responsible for providing annual summary reports to the Ministry of Environment and Energy of
any by-passes of sewage to a receiving water body as a result of equipment failure or system
overload. Data showed that 75 of the 204 reporting Ontario municipal wastewater treatment
plants had bypasses in 1991, most of which occurred during the spring thaw months of March and
April. The corresponding total annual diverted volume for1991 was 2.2. million m3 for primary
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2002
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plants and 9.6 million m3 for secondary plants, representing 0.11 and 0.46 %, respectively, of the
total effluent volume treated (Chambers et al., 2001).
For the year 1998, 83 facilities were included in a report by Doyle, with 43 incidents of
bypass of either primary treatment, secondary treatment, or both treatments. Table 3 summarizes
the volume of diverted flow and the length of time the bypass incident lasted. The treatment
capacity for the province in 1998 was 6 784 016 m3 / day. The total bypassed flow from both
primary and secondary treatment in 1998 was 13 173 419 m3 (the equivalent of less than two
days’ processing for one year’s recorded bypass incidents). This diverted quantity of wastewater
represented 0.53 % of the total annual effluent volume for 1998 (Doyle, 2002).
Table 3 - Summary of 83 wastewater treatment facility bypasses for 1998 (source: Doyle, 2002)
Bypass volume (m3)
Treatment
bypassed
Number of
facilities
primary
Primary
17
Secondary
18
Primary and
Secondary
Total
secondary
Total bypass time (h)
primary
1 893 172
secondary
987
8 067 835
1 645
8
2 048 663
1 163 749
1 383
1 474
43
3 941 835
9 231 584
2 370
3 120
If discharged without treatment, wastewater will continue to consume dissolved oxygen
from the receiving water (i.e. exerts a biochemical oxygen demand (BOD)). Without oxygen,
aquatic life cannot be sustained. Phosphorous, nitrogen, and pathogenic organisms can pose a
threat to the water quality of a receiving body and to public health when wastewater enters a
watercourse without sufficient treatment. Phosphorous and nitrogen, as previously mentioned,
promote the growth of aquatic vegetation and algae. Coliform bacteria may not cause disease,
but may indicate the presence of pathogenic organisms. These organisms may cause the following
illnesses in humans: intestinal infections, dysentry, hepatitis, typhoid fever, and cholera.
2. Spills
Raw sewage spills can be caused by blocked sewage lines, electrical failures, equipment
malfunction, operator error, or the corrosion or collapse of aging sewer lines. The Medical
Officier of Health and the Commissioner of the Works and Emergency Services Department
(WES) reported in 2000 that in the previous five years there had been a total of five sewage spills
in the City of Toronto (Basrur and Gutteridge, 2000). These incidents had been contained and
monitoring of the water did not reveal any irregularities or serious health threats to Toronto
residents. The potential contaminants of a raw sewage spill are similar to those mentioned above
for treatment plant bypasses.
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Ridgetown College - University of Guelph
2002
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3. Land Application of Biosolids
The land application of biosolids is a similar technique to spreading liquid manure on
cropland. The potential impacts on water quality are also the same. (Refer to: Livestock Manure
Systems - Potential Water Quality Impacts).
C - Human: Septic Systems
Septic systems are found in rural areas where municipal sewage treatment services are not
available. About 8 million Canadians, slightly more than one-quarter of the population, are served
by septic systems (Environment Canada, 2001). Most systems consist of an underground tank
and a leach drain, or absorption field, that operate together to purify household wastewater (see
Figure 4). Wastewater flows from the house by gravity to the septic tank. If the system is
properly sized and functioning correctly, the sewage remains in the tank for the amount of time
necessary to allow anaerobic bacteria to break
down the solids. Incoming household wastewater
displaces a quantity of effluent which flows from
the tank outlet by gravity. The effluent enters the
buried absorption field where it seeps into the
surrounding soil. The liquid becomes filtered as it
travels downwards through the soil. Aerobic
bacteria in the soil further break down the liquid.
Some moisture usually transpires into the air above
the buried absorption or leach field, mostly during
Figure 4 Typical septic system layout
the summer. The remaining effluent moves
(Vogel and Rupp, 1999)
downward in the soil and eventually reaches
groundwater.
The absorption or leach field should be situated an appropriate distance from the home or
well, away from any shade trees, and on the downhill side of the house. The soil of the absorption
field must have an acceptable percolation rate. In other words, the soil must have characteristics
that enable moisture to seep through it reasonably freely.
The Septic Tank
Sewage flows to the large septic tank through the sewer line which is an extension of the
home’s main drain. The tank, typically made of concrete or fibreglass, is vented by this line back
into the home to prevent the build-up of gases. At the opposite end of the septic tank, a second
pipe leads to the leaching bed. Single chambered tanks are no longer permitted to be installed in
Ontario. Regulations in Ontario now require that septic tanks be double-chambered. Normally,
the first chamber is larger than the second. Baffles used in these tanks prevent solids from moving
directly through the tank and plugging the leach field lines. Double-chambered septic tanks tend
to allow sufficient time for the suspended solids to settle out of the effluent stream.
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2002
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Figure 5 Typical two-chambered septic tank (Joy, 2002)
The septic tank functions as a breeding ground for important anaerobic bacteria, fungi,
yeasts, and actinomycetes. Movement in the tank stops once the comparatively rapidly moving
wastewater has entered. The only movement is some temporary surface rippling. The stilling of
the tank serves two functions. Anaerobic creatures thrive since they grow much better in still than
in moving water, and the solids are able to sink to the bottom due to the motionless water.
Microorganisms attack and digest the organic solids as they are sinking.
Methane and other gases are produced in the process. A scum forms over the surface of
the liquid in the tank. Gases bubble to the surface and bring along fine particles of solid material
which combine with oil and grease to form this layer of scum. The scum layer reduces the
movement of the liquid beneath it and insulates the anaerobic bacteria from any air that seeps into
the tank.
Bacteria will continue to thrive and break down the organic material into its constituent
elements as long as the temperature does not drop below freezing. Anaerobic bacteria are not
capable of completely transforming the organic matter into its component elements. Only aerobic
bacteria (in the presence of sufficient oxygen) can properly break down the organic matter. When
attacking organic substances, anaerobic creatures produce water, ammonia, hydrogen sulphide,
phosphorus, and heat. In a physical sense, the anaerobic bacteria are altering the organic
materials by transforming them from a solid state to a liquid state. The anaerobic community
cannot digest material such as stone or plastic and these materials remain in the tank. Eventually
these materials must be removed by pumping. As with proper maintenance of the tank, this is
recommended every three to five years.
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Ridgetown College - University of Guelph
2002
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The Absorption Field
The effluent from the septic tank travels
to the absorption field through perforated plastic
pipe. The liquid is still ‘septic’ and must be
treated because it contains substances that
promote the decomposition of vegetation and
animal matter, as well as harmful pathogens,
bacteria, and viruses. The liquid flows out of the
pipe and through a layer of coarse gravel
surrounding the pipe. Most of the liquid passes
into the soil by gravity. Some of the liquid leaves
the soil entirely by evaporation or by the process Figure 6 Cross-sectional view of absorption
of transpiration where the roots of plants take up field layers (Vogel and Rupp, 1999)
water and this water evaporates from the leaves
of the plant. Worms and nematodes aerate the soil, providing the oxygen required for aerobic
organisms to digest and chemically oxidize the organic waste present in the effluent. The wastes
of aerobic bacteria are soluble, stable compounds that act as food to plants.
The soil acts as a filter and prevents the larger bacteria from moving far. Clay, in
particular, absorbs viruses and locks them in place to prevent their movement. Soil mainly
consists of small pieces of inorganic particles and organic matter in various stages of decay.
Every particle of clay and a form of organic matter known as humus carry a minute electric
charge. Microorganisms also carry an electric charge on their protein coating. Because of the
electrical charges they may be attracted to the charged soil particles and held in place. As the
effluent flows further downward through the soil it will continue to be filtered. Eventually, much
of this water reaches the groundwater.
The efficiency of the absorption field becomes threatened when the soil immediately
surrounding the pipes becomes saturated and clogged with fine particles of organic matter. The
soil will lose its ability to function as a filter and the effluent will build up and appear on the
ground surface. The drain or absorption field can become an effective filter once more by
removing the old gravel and clogged earth, treating the nearby soil, and replacing the gravel and
covering it with a fresh layer of soil.
Alternatives to Conventional Septic Systems
1. Shallow Buried Trenches
This alternative system uses shallow buried trenches in the leaching field to dispose of the
septic tank effluent through small diameter pressurized pipes. These pipes are contained in
chambers in the upper soil layers. Shallow buried trenches are intended for smaller building lots
and less permeable soils such as heavy clay soils. The system tends to make the effluent more
available for plant root uptake.
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Ridgetown College - University of Guelph
2002
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2. Chambered Systems
The chambered system is a replacement for the conventional stone and pipe leaching bed.
The pipes are not pressurized and there is no crushed stone layer. As an alternative to gravelfilled trenches, they provide more infiltration surface area.
3. Peat Filter Systems
Peat-based leaching beds treat septic tank effluent. After percolating through the peat
filter, wastewater exits the bottom of the shell and infiltrates the soil through the crushed stone
bedding. The compact design makes this filter system well-suited to lots with insufficient space
for conventional treatment trenches. The peat filter must be replaced on average every eight
years.
4. Artificial Media Filters
Artificial media filters provide further treatment to septic tank effluent before entering the
leaching bed. These filters use an absorbent synthetic media to provide aerobic treatment.
Wastewater is sprinkled over the filter and slowly percolates through the media. Air circulation
through the media is accomplished by fans or by natural convection. These systems can be
housed in an above-grade structure or buried in a concrete or fibreglass tank.
Septic System - Potential Water Quality Impacts
Groundwater resources may become contaminated or polluted from a septic system’s
absorption field effluent. This is particularly likely to occur when water tables are high or when
the effluent flows into saturated soil which is not capable of properly purifying the wastewater.
An average of 61 % of septic field systems in various surveys of cottage systems in Ontario were
not properly designed, constructed and maintained (Chambers et al., 2001). Septic system
effluent constituents that can contaminate groundwater include: bacteria and viruses, nitrate,
phosphate (a common form of phosphorus), and organic substances.
1. Bacteria and viruses
The contamination of groundwater by bacteria and viruses is a serious contamination
problem. The majority of bacteria and viruses are small enough in size to move through soil
pores. If they are not destroyed they may leach downwards to the water table. Adsorption slows
the downward movement of bacteria and viruses. The process is particularly effective with an
increasing clay content of soils. In sandy soils, however, adsorption is weak and the adsorbed
organisms may not likely be bound permanently to the soil and can become re-suspended in the
water moving through soil pores that eventually reaches the groundwater. Microorganisms
including coliform bacteria and viruses tend to move only a few dozen centimeters within the
percolating waters in unsaturated soil layers although much greater distances can be achieved
under saturated flow conditions. Release of adsorbed microorganisms and their downward
leaching has been noted during periods of heavy rainfall when water is rapidly percolating through
the soil (Cogger, 1988).
Results of various studies have shown that unsaturated soils remove a large percentage of
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the bacteria and viruses present in the septic system effluent. Substantial bacterial and viral
removal occurs within the first 30 cm of unsaturated soil. Within 60 to 120 cm of the bottom of
the trenches, removal of these contaminants is nearly complete. Bacterial and viral survival is
prolonged by saturated conditions most commonly as a result of high water tables. There is a
potential for bacterial and viral persistence when there is a zone of saturated soil beneath the
absorption trenches (Cogger, 1988).
2. Nitrate
Excessive amounts of nitrate in drinking water can lead to methemoglobinemia
(sometimes referred to as blue baby syndrome), a condition which prevents the normal uptake of
oxygen by the blood. Infants are especially susceptible to this condition. Nitrate is a highly
soluble compound that is readily transported to groundwater. The three main mechanisms that
can reduce nitrate concentration include the uptake of nitrate by plants, microbial denitrification,
and dilution of groundwater.
Plants use nitrate if it is accessible to their roots during the growing season. Nitrogen
from septic tank effluent is only available to plants surrounding the absorption trenches and this
nutrient is continuously added to the soil throughout the year, whether the plants can effectively
use it or not. As a result, plants are not effective throughout the entire year at using the nitrate
released from septic systems.
Denitrification is the process carried out under anaerobic conditions in the soil that
reduces nitrate to nitrogen gas. It is most effective in wet soils that are otherwise unsatisfactory
for wastewater treatment.
The most commonly used method to control nitrate concentrations is through dilution in
the groundwater aquifer. Nitrate can reach unacceptable levels in groundwater beneath soils that
are otherwise acceptable for septic tank effluent treatment (Cogger, 1988).
3. Phosphate and Organic Substances
The environmental problem most commonly associated with phosphate (a form of
phosphorus) is the eutrophication of lake water (mentioned earlier). Phosphate pollution from
septic tank effluent is of much less concern in comparison to nitrate or bacteria and viruses since
phosphorus is adsorbed tightly to soil minerals and its potential for movement is limited. Very
little phosphate moves through soil and groundwater to lakes. Phosphate movement is evident,
however, in some sandy soils with limited phosphate fixation capacity, especially surrounding
older or heavily loaded systems with higher water tables.
The organic matter in wastewater also includes trace amounts of toxic man-made organic
compounds derived from household products such as solvents. These compounds are sometimes
slow to degrade, and have the potential to contaminate groundwater if they percolate through the
soil in sufficient quantities. If the concentration of this type of contaminant gets too high it may
also negatively influence the performance of the septic tank. A number of studies, however, have
shown that the levels of these toxic organic compounds created no serious problems (Cogger,
1988).
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2002
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D - Livestock Manure Systems
Handling and Transfer to Storage
Most livestock farmers handle manure in one of two forms - either as a liquid or as a solid.
Liquid manure contains feces and urine and may also contain washwater, spilled water (e.g. from
drinkers), precipitation into the storage, spilled feed, and bedding. Normally solid manure contains
feces, some or all of the urine, bedding, spilled feed, and little or no additional water. The main
factors considered in choosing between a liquid and solid manure system are: labour, economics,
environmental concerns, and animal welfare. Liquid systems are used by most large dairy
operations, some large beef operations, most swine operations, and some caged laying hen
operations. Solid systems tend to be popular with smaller dairy and beef operations, some large
beef operations, broiler chicken operations and most caged laying hen operations. Some farms
have both solid and liquid manure systems.
There are a number of methods used to collect and transfer manure to storage. In some
cases, the storage is a part of the housing system (e.g. bedded manure that the animals move
around on) or the manure falls through slatted floors into a tank under the animals. These systems
can require very little labour, outside of actual spreading. In other cases, manure is removed from
the barn regularly (e.g. every day or every week) and stored until the timing is right to spread the
manure onto the fields.
The number of livestock farms in Ontario and the amount of manure produced per year
are included in Table 4.
Table 4 - Ontario livestock farms and amounts of manure produced annually (source: Goss et al.,
2002) (based on 1996 and 1997 Census data)
Total Manure Produced (million L/yr)
Ontario Region
Total Livestock
Farm Numbers
Total for Ontario
28 885
Poultry
1 850
Cattle
19 350
Swine
9 654
Storage
Most farms in Ontario store manure for long periods of time and spread the manure onto
fields at times when the greatest amounts of nutrients can be used by the crop. Other factors
considered in determining a spreading time include: soil moisture levels, making best use of
labour resources, minimizing adverse environmental impacts, availability of a custom applicator,
and economics. While some storage capacities may be less than 200 days, a normal minimum
storage period recommended or required is about 250 days. This allows most farmers flexibility in
applying manure to cropland. In addition, there is a growing number of farms with up to 400 days
of manure storage capacity.
Solid manure is usually stacked on a concrete pad. This storage should have a system to
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collect and store contaminated runoff resulting from precipitation onto the stack. Alternatively,
some solid manure storages are covered to exclude precipitation.
Liquid manure storages may be concrete tanks directly under barns. A number of farmers
have uncovered clay-lined earthen storages. Many farmers have uncovered circular concrete or
steel tanks. There are also a number of covered concrete storages. Liquid manure storages
typically become anaerobic - little or no oxygen is present. This leads to odour production, and
siting formulas are typically used to maintain enough distances to non-compatible land uses to
minimize odour conflicts.
Treatment
While many farmers are using or have tried some form of treatment (e.g. liquid manure
additives, solid manure composting, aeration, solid-liquid separation), the majority of farmers use
no treatment system.
Land Application
The goal of land application is to make use of the nutrients and organic matter in manure.
This can reduce crop production costs, as it reduces the need for inorganic fertilizer. Similar
systems are used for land application of sewage biosolids. Often, manure is spread onto the land
and incorporated into the soil within a day or two. Some farmers inject manure directly into the
soil. This requires more energy, but reduces losses of ammonia-N to the air. Under certain
cropping regimes, incorporation may not be practical (e.g. no-till, spreading onto hay). In 1996,
384 000 tonnes of nitrogen and 139 000 tonnes of phosphorus were applied as manure to
cropland in Canada (Chambers et al., 2001).
Livestock Manure Systems - Potential Water Quality Impacts
The areas of concern with respect to water quality are very similar with all organic
nutrient sources. In most cases, manure systems make efficient use of the manure constituents for growing crops and building soil health. These systems provide a way for recycling nutrients
back to the soil, rather than disposing of them, which is the end result of human wastewater
treatment systems. The greatest potential for water quality impacts is in the following areas:
1. Runoff from solid manure storages
The runoff that results from precipitation onto solid manure storages can leach nutrients
and bacteria from the manure. Many farms do not have a system to catch and store this liquid.
This is especially a concern if the runoff source is located beside a stream or a surface inlet for a
drainage system. While this runoff may not be as concentrated as raw manure, it can have an
impact on water quality. Some farms have runoff storages, or have structures that significantly
reduce the quantity of runoff. Others have vegetative areas that the runoff must cross, which
helps to treat the wastewater. Vegetative filter strips facilitate the infiltration of the water into the
soil and the utilization of the nutrients by the plants growing there.
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2002
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2. Over-application of manure
If manure spreading is viewed by the farmer as a “disposal” method, there is a tendency to
over-apply the manure to fields. Nutrients are applied at rates higher than what the crop can use.
With nitrate, this can lead to leaching downward through the soil profile. A certain amount of this
nitrate, depending on many factors, may eventually reach groundwater. Phosphorus is not as
mobile but can accumulate in the soil to levels where leaching can become a problem. Currently, a
great deal of effort is going into promoting the more widespread use of nutrient management
plans. This is one of the most effective ways to avoid the problem of over-application of
nutrients, from whatever source.
3. Macropore flow of liquid manure to subsurface tile drainage systems
Under certain conditions, liquid manure has gained access to subsurface tile drain systems
shortly after spreading. This, then can reach surface water. The management techniques needed to
avoid this potential problem are fairly well established now.
4. Runoff from fields
If manure is spread onto a field and heavy rains fall on the field before the manure is
incorporated, there is a risk of manure runoff. The greatest risk of this happening is with winterspread manure, a practice which is no longer considered acceptable in Ontario (mainly because of
this increased risk). The risk in this case is from the spring melt, not necessarily the heavy rains.
5. Accidental spills of liquid manure
Occasionally, manure storage systems or spreading equipment fail, resulting in the leaking
of liquid manure. In some cases, manure has gained access to surface waters, where it can cause
serious environmental harm (especially in the short term).
This section has addressed concerns with livestock manure, but because the management
of land applied sewage biosolids is somewhat similar, the same issues can apply to the application
of biosolids to farmland.
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Ridgetown College - University of Guelph
2002
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E - Summary of Losses and Transformations
Situation #1
Assume: 1000 L of raw sewage enters a sewage treatment plant. This is roughly the
amount (with dilution liquid) produced by four humans.
Assuming the wastewater underwent secondary treatment at a conventional activated
sludge system facility, the concentrations of parameters listed below would be achieved. The
volume of wastewater lost as grit and screenings is assumed to be negligible. An effluent volume
of approximately 999.4 L is considered to be exiting the plant.
Material #1 - Raw Sewage
(1000 L)
TSS
BOD 5
TKN
TP
total coliform bacteria
200 g
170 g
30 g
7g
5 x 107 per
100 mL
(source: Doyle, 2002)
Secondary Effluent discharged to
surface water (999.4 L)
TSS
BOD5
TKN
TP
total coliform bacteria
(source: Doyle, 2002)
15 g
15 g
20 g
3.5 g
200 - 1000
per 100 mL
600 g of Biosolids
(Anaerobic dewatered liquid)
TS
BOD5
TKN
TP
total coliform bacteria
(Source: 1
180 g (ref1)
N/a
Í
10 g
Í
3.5 g
N/a
OMAFRA, 2000)
The reduction of the parameters considered at the aeration stage are not considered significant
since the volatile organic compounds and ammonia levels are low. Parameters are provided for
the effluent exiting the treatment facility and for the sewage biosolids. Wasted sludge from both
the primary and secondary clarifier is considered. The mass of biosolids was found given that the
primary clarifier removes 60 % of the TSS and given that from 0.3 to 0.5 g of sludge is produced
for every gram of BOD5 removed in the secondary clarifier (Zhou, 2002). The total coliform
bacteria effluent value is based on a chlorine dosage rate of 2 - 8 mg/L and a total chlorine
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2002
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residual of 2.5 - 3.5 mg/L (Qasim, 1994). Data are not provided for sewage sludge since it is an
intermediate of the treated biosolids. The biosolids considered received anaerobic treatment and
were de-watered to a total solids concentration of 30 % (OMAFRA, 2000)
Situation #2
Assume: 1000 L of raw sewage enters an individual residence septic system. This is
roughly the amount (with dilution liquid) of ‘medium concentration’ wastewater produced by four
humans.
The amount of the parameters below that have been lost to the air is considered negligible.
This quantity of these parameters that is normally lost to the air varies seasonally. The
constituents reported for the septic tank effluent are concentrations reported prior to this material
entering the leaching bed. The concentrations of these parameters in the groundwater are outside
the footprint of the leaching bed but no more than 10 m away.
Material # 2 - Untreated Domestic
Wastewater (1000 L)
TSS
BOD5
TN
TP
total coliform bacteria
220 g
220 g
40 g
8g
107 - 10 8 per
100 mL
(source: ‘Medium concentration’
wastewater - Tchobanoglous and Burton,
1991 )
1000 L of Septic Tank Effluent
(prior to entering leaching bed)
68 - 624 g (ref2)
140 - 666 g (ref2)
N/a
7.2 - 17 g (ref3)
104 - 105 per
100 mL (ref3)
(Source: 2 Viraraghavan and Warnock, 1976
3 Anderson et al., 1994 )
TSS
BOD5
TN
TP
total coliform bacteria
1000 L of groundwater
(no more than 10 m from the leaching bed)
TSS
40 g (ref2)
BOD5
35 g (ref2)
TN
N/a
TP
0.3-18 g (ref4) or 4.4 g (ref2)
total coliform bacteria
0-17per
100 mL (ref5)
(source: 2 Viraraghavan and Warnock, 1976
4 Schiff, 1993
5 Ritter et al., 1994)
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2002
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Situation #3
Assume: 1000 L of livestock manure enters a manure collection and storage system. This
is roughly the amount (with dilution liquid) produced by 172 feeder pigs.
The raw manure parameters will only be altered slightly following storage in a manure
collection basin that is open to the air. The ammonia-nitrogen levels will decrease somewhat due
to losses to the atmosphere during storage and spreading. The other parameters will remain
virtually the same until the manure is applied to cropland.
Material # 3 - Feeder Pig Manure (1000 L)
TSS
BOD5
TN
TP
total coliform bacteria
N/a
28 000 g
46 000 g
1 600 g
4 x 108 per
100 mL
(source: Fleming and Ford, 2001)
Land Applied Manure (1000L)
TSS
BOD5
TN
TP
total coliform bacteria
N/a
28 000 g
N/a
1 600 g
4 x 108 per
100 mL
(source: Fleming, 2002)
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2002
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F - Summary
The methods of storage and treatment of human and animal wastes vary significantly.
Breaking down organic matter and destroying pathogens is the goal of human waste treatment. A
small portion of the nutrients may be used on land for crop growth. A large amount of treated
wastewater is discharged to the environment - it is the water that is re-used. In contrast, livestock
manure systems aim to make use of nutrients for growing crops. Typically there is no attempt to
break down organic matter before it is applied to the soil. Similarly, there is no attempt to destroy
pathogens, although steps are taken during storage and land application to reduce the risk of any
pathogens surviving in the manure from entering surface water or groundwater. Both livestock
manure and human waste have the potential to contaminate water resources (surface water or
groundwater), though steps are taken in all cases to minimize any risks.
It may not be fair to compare human and animal waste due to their very different storage,
handling and treatment systems. An understanding of these different methods of treatment is
necessary before alternative methods of waste handling and treatment can be developed.
Acknowledgments
Special thanks to the following individuals for supplying important information for the completion
of this report:
D. Joy, Professor, School of Engineering, University of Guelph
M. Payne, Biosolids Utilization Specialist, Ontario Ministry of Agriculture and Food
H. Zhou, Professor, School of Engineering, University of Guelph
References - Related Reading
Anderson, D.L. et al. 1994. Insitu lysimeter investigation of pollutant attenuation in the vadose
zone of fine sand. Proceedings of the 7th International Symposium on Individual and
Small Community Sewage Systems. ASAE.
Basrur, S. 2000. Toronto Staff Report: Raw Sewage Discharges in Lake Ontario. Available in
pdf form:
www.city.toronto.on.ca/legdocs/2000/agendas/committees/hl/hl000925/it008.pdf. Date
accessed: May 30, 2002.
Chambers, P.A., M. Guy, E.S. Roberts, M.N. Charlton, R. Kent, C. Gagnon, G. Grove, and N.
Foster. 2001. Nutrients and their impact on the Canadian environment. Agriculture and
Agri-Food Canada, Environment Canada, Fisheries and Oceans Canada, Health Canada,
and Natural Resources Canada. (CD-ROM).
Cogger, C. 1988. On-Site Septic Systems: The risk of groundwater contamination. Journal of
Environmental Health 51(1): 12 - 16.
Fleming and Ford
Ridgetown College - University of Guelph
2002
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Doyle, E. 2002. Wastewater Collection and Treatment. Toronto: Ministry of the Attorney
General. Walkerton Inquiry Commissioned Paper 9. Walkerton Inquiry CD-ROM.
Available online at: www.walkertoninquiry.com. Date accessed: July 4, 2002.
Environment Canada, Indicators and Assessment Office, Ecosystem Science Directorate, and The
Environmental Conservation Service. 2001. Nutrients in the Canadian Environment:
Reporting on the State of Canada’s Environment. State of the Environment Report.
Available online at: www.ec.gc.ca/soer-ree/English/National/soeass.cfm. Date accessed:
May 29, 2002.
Fleming, R. and M. Ford. 2001. Humans versus Animals - Comparison of Waste Properties.
Available online at: www.ridgetownc.on.ca/Research/Reports/Subject/manure.htm. Date
accessed: May 29, 2002.
Goss, M.J., K.S. Rollins, K. McEwan, J.R. Shaw and H. Lammers-Helps. 2002. The
Management of Manure in Ontario with Respect to Water Quality. Toronto: Ministry of
the Attorney General. Walkerton Inquiry Commissioned Paper 6. Walkerton Inquiry
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2002.
Hartley, M. 2001. Municipal Wastewater Spills and Bypasses Report. Grand River
Conservation Authority. Available online in pdf form at:
pages.sprint.ca/travellerdreams/files/wwtp.PDF. Date accessed: July 4, 2002.
Joy, D. 2002. Personal Correspondence. University of Guelph.
Ontario Soil and Crop Improvement Association. 1999. Septic Smart: New Ideas for Household
Septic Systems on Difficult Sites. Booklet designed by the LandOwner Resource Centre,
Manotick, ON.
OMAF [Ontario Ministry of Agriculture and Food]. 2000. Sewage Biosolids: Managing
Urban Nutrients Responsibly for Crop Production. Government factsheet.
Payne, M. 2000. Land Application of Sewage Biosolids for Crop Production. Ontario Ministry
of Agriculture, Food and Rural Affairs. Factsheet No. 00-023.
Payne, M. 2002. Personal Correspondence. Ontario Ministry of Agriculture and Food.
Qasim, S. R. 1994. Wastewater Treatment Plants - Planning, Design, and Operation.
Lancaster, Pennsylavania: Technomic Publishing Co. Inc.
Ritter, W.F. et al., 1994. Alternative On-Site Wastewater Systems Impacts on Ground-Water
Quality. Presented at the NABEC-94 Conference, Guelph, Ontario, July, 1994.
Fleming and Ford
Ridgetown College - University of Guelph
2002
Page 24
Schiff, S., et al. 1993. Septic Systems and Phosphorous. Presented as the conference on problem
environments for septic systems and communal treatment options (Waterloo) - May, 1993.
Tchobanoglous, G. and F. L. Burton. 1991. Wastewater Engineering: Treatment, Disposal, and
Reuse, Third Edition. New York, NY: McGraw - Hill, Inc.
Viraraghavan, T. and Warnock, R.G. 1976. Groundwater Pollution from a Septic Tile Field.
Water, Air, and Soil Pollution 5(1976): 281 - 287.
Vogel, M.P. and G.L. Rupp. 1999. Septic Tank and Drainfield Operation and Maintenance.
1999. Montana State University Extension Service. Available online at:
www.montana.edu/wwwpb/pubs/mt9401.html. Date accessed: July 25, 2002.
Zhou, H. 2002. Personal Correspondence. University of Guelph.
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2002
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