Comparison of storage, treatment, utilization, and ... · wastewater treatment facilities....

Comparison of storage, treatment, utilization, and disposal systems

for human and livestock wastes

by: Ron Fleming and Marcy FordRidgetown College - University of Guelph, Ridgetown, Ontario

November, 2002

A - Introduction

BackgroundSystems 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 treatmentfacilities to process human wastes and purify the water portion to the level where it can bedischarged to surface water. A solid portion is often treated and spread onto farm fields as asource of plant nutrients or it is land-filled. In much of rural Ontario, individual homes use septicsystems, where wastes are treated typically in a treatment bed on the owner’s property. Thesesystems are able to handle the large volumes of very dilute wastes generated by humans. Onlivestock farms, we see a different approach. In most cases, the livestock manure (which containsfeces and urine and may also contain dilution water, bedding, or spilled feed) is stored for up to ayear and spread onto crop land where the nutrients can be used for crop growth and the organicmatter 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 methodsto treat manure - for odour control, to kill pathogens, for volume reduction, for concentration ofnutrients, for creation of saleable organic products, to reduce labour costs, etc. There have beensuggestions that some of the systems used for human waste treatment may be appropriate onfarms 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 varioussystems 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 totalcoliform. The same constituents are used to measure the performance of individual septic systemsfor human wastes.

BOD5 The biochemical oxygen demand is a measure of the dissolved oxygen required tostabilize the organic matter in five days. It is an indicator of the amount of organicmaterial present in a liquid.

Fleming and Ford Ridgetown College - University of Guelph 2002

TSS Total suspended solids are the organic and inorganic solids that are not dissolvedand 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 kjeldahlnitrogen (TKN) includes organic nitrogen and ammonia. While nitrogen is valuablefor crop growth, in surface water, it can accelerate the growth of aquatic plants. Ingroundwater, nitrates pose a health threat if they enter drinking water supplies.

P Phosphorus exists in both the organic and inorganic form. We often are interestedin total phosphorus or phosphate, a form of phosphorus . Phosphorus, likenitrogen, can cause eutrophication in surface water - a nutrient enrichment causingmicrobial and algae growth. These conditions deplete oxygen to the point wherechemical-reduction processes can render the water body unsuitable for many formsof aquatic life, reduce the recreational value of the water, and make it unacceptablefor use as a source of drinking water.

Bacteria The concentration of bacteria is usually regulated through limits for E. coli, fecalcoliform and total coliform bacteria. Fecal coliform bacteria and E. coli areorganisms that can be quantitatively related to the presence of sewage or fecalmatter. They are not necessarily pathogenic - i.e. capable of causing disease.However, they are used as “indicators” of the potential presence of pathogenicbacteria (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 apercentage of the overall mass of diluted manure.


Typical ConcentrationsTypical 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 2significant figures) (source: Fleming and Ford, 2001)

Parameter Units Liquid dairymanure

Liquid swine*

manureRaw human

sewage

BOD5 mg / L 14 000 28 000 220

DM % 10 9.8 0.070

TS mg / L 100 000 98 000 700

TN mg / L 3 800 4 600 40

TP mg /L 800 1 600 7.9

Total coliformbacteria

number / 100 mL 9.5 x 107 4.0 x 106 1.0 x 106

*swine manure is from feeder pigs

B - Human: Wastewater Treatment Plants

The percentage of Canadians served by wastewater treatment has been increasing. In1999, 73% of Canadians were served by municipal sewer systems. The level of sewage treatmentused across Canada is gradually improving as more municipalities upgrade their existingwastewater treatment facilities. Municipal wastewater, consisting mainly of human waste, is thelargest source of nitrogen and phosphorus released to the Canadian Environment. In 1999, about82,750 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 plantsare required to use advanced phosphorus removal methods before discharging their waste effluentinto particularly sensitive waters. Repair and replacement of sewage systems have reduced leaksand pollutant loadings (Environment Canada, 2001).

Treatment Plant ClassificationTreatment 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 TreatmentThis 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


acceptable for municipal plants in Ontario. There is a great deal of pressure to upgrade existingprimary plants to meet the performance standards of secondary plants.

2. Secondary TreatmentSecondary treatment involves both separators and reactors. Reactors tend to oxidize,

reduce, immobilize, or physically condition their contents and create gaseous products in theprocess. This form of treatment is largely a biological process that requires air to stimulate thegrowth of bacteria and other organisms which will eventually consume most of the wastematerials. As this process continues and the settled sludge mixes with newer sludge, gradually aculture of organisms develop that is capable of consuming the organic material in the sewagewithin four to eight hours.

Secondary plants tend to be either ‘lagoon-based’ or ‘mechanical.’ A further classificationcan be made in the reactor portion of biological secondary plants. The biomass of organismscontained within the reactor can be either: a) ‘suspended’ by mixing - known as ‘SuspendedGrowth Biological Treatment’; or b) supported by attachment to a solid, inert medium - referredto 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 treatmentapplied in Ontario. In practice, chemically-assisted filtration normally achieves better effluentqualities 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 % ofthe Canadian municipal population. This percentage increased to 38 % in 1996. Secondarytreatment 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 levelof service since 1983 in response to programs aimed at cleaning up the Great Lakes (Chambers etal., 2001).

Table 2 gives a summary of the systems being used by communities in Ontario. The thirdmost common system, Conventional Activated Sludge, is actually the predominant wastewatertreatment technology in Ontario, on a treatment volume basis. It was used at 21.3 % of the totalfacilities, including nine of the largest 10 facilities, and 33 of the largest 45 facilities. Since‘Extended Aeration’, ‘Conventional Seasonal Lagoon,’ and ‘Conventional Activated Sludge’ areused at 68 % of the total facilities in Ontario, the following portion of this report will be limited tothe description of these three treatment plants. These systems are all considered to be ‘SuspendedGrowth Biological Treatment’ systems.


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 ProcessThis is the most common form of secondary treatment in Ontario. It includes

Conventional Activated Sludge (the majority of larger plants in Ontario) and ExtendedAeration (most of the smaller plants). Conceptual schematics of the two systems are found inFigures 1 and 2.

Treatment begins with screening of the sewage to remove larger debris. Grit removal isdesigned to remove larger settleable inorganic materials to reduce abrasive wear on mechanicalsystems later in the treatment process. Primary sedimentation removes most of the remainingsolids and organic material. Screens, settling tanks, and skimming devices are commonly used forthe separation.

The activated sludge process involves an aerated or mixed reactor, also known as anaeration tank. There is a primary clarifier before this aeration tank and a secondary clarifier orsedimentation tank after the aeration tank. The distinction between the Conventional ActivatedSludge and the Extended Aeration treatment systems, especially for municipal plants, is thatExtended Aeration rarely involves primary sedimentation or a primary clarifier. Also, ExtendedAeration treatment facilities tend to have much longer hydraulic detention times thanConventional Activated Sludge systems. As microorganisms grow and are mixed by the additionof 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


Figure 1 Conventional Activated Sludge system

Figure 2 Extended Aeration system

the secondary clarifier, where the activated sludge settles. A portion of the settled sludge isreturned to the aeration basin to maintain the desired food-to-microorganism ratio to allow therapid breakdown of organic matter. Since more activated sludge is produced than can be used inthe process, some of it is wasted from the aeration basin to the sludge-handling system fortreatment and ultimate disposal. Air is normally introduced in the aeration basin either bydiffusers or by mechanical mixers.

Chlorine is the most common disinfectant used to destroy disease-causing organisms in thewastewater effluent. Typically, as illustrated, chlorine contact tanks are provided at the end of thesecondary or tertiary treatment processes. They are designed for a minimum of 30 minutescontact time at average plant flow. The treated wastewater then leaves the plant and enters awater source. Chlorination is the least expensive disinfection method. However, it may produce


Figure 3 Conventional Seasonal Lagoon system

undesirable effects in the river, either when it combines with organic matter or if the residual istoo 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 frompropagating. Detention times are only one minute as opposed to 30 minutes for chlorine, andultraviolet radiation has a non-toxic effluent. Despite the advantages of ultraviolet radiation in thedisinfection process, chlorine is still the most commonly used.

2. Lagoon Treatment ProcessConventional seasonal lagoons (depicted in Figure 3) are commonly used to treat

wastewater in smaller communities. Lagoons function both as aeration and settling tanks. Theyare 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 thegrowth of aerobic bacteria that degrade or metabolize influent organic matter. Seasonal lagoonshave 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 activatedsludge process. Lagoons often are constructed as earthen basins. They tend to have longhydraulic detention periods and, as a result, a certain amount of nitrification is achieved. Highertemperatures and lower organic loadings generally encourage this production of the nitratenitrogen. The chlorine disinfection process, before the release of the effluent into a body ofwater, is similar to the activated sludge process previously described.

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 % totalnitrogen, 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


metal concentrations are suitable for land application and are considered biosolids. Municipalsewage biosolids (MSB) refers to the nutrient-rich organic materials removed during thetreatment of domestic sewage in a wastewater treatment facility.

Stabilization is accomplished by digestion or by some other acceptable means, such asadding lime. Digestion is the decomposition by either anaerobic or aerobic bacteria. Aerobicthermophilic digestion has become a popular stabilization process. Digestion may involvedecomposition by anaerobic bacteria of the solids removed after settling in the primary andsecondary clarifiers . This process is carried out in a digester and produces biosolids which can beused as soil conditioners. Methane gas is a product of digestion and it is used as fuel for heatexchangers and boilers. In smaller plants the process can be carried out in a single digester, whilelarger plants require two or more tanks to handle the larger volume of sludge. Digestion reducesthe number and type of pathogens - viruses, bacteria, fungi, and parasites. It also reduces thevolume 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 aporous drum wrapped in a steel-coil blanket that picks up the sludge. The rotationof the drum reduces the quantity of water in the sludge with the aid of a partialvacuum inside the drum. A scraper edge removes the dewatered sludge from theoutside 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 highvelocities. This mechanical solid-liquid separator relies on centrifugal forces toseparate the liquid and solid components of the sludge onto the inside wall of thecylinder into two layers. An auger which turns slightly faster than the cylindermoves 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 betweenrollers. The liquid component of the sludge is forced through the belt by therollers and the solids are carried along and belt and deposited in a collectionchamber. 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 oncemore, since it contains high concentrations of suspended solids and BOD.

Utilization of BiosolidsBiosolids 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 limestabilization or pelletization. In all cases, biosolid disposal requires the approval of the Ministryof the Environment.

• Incineration - the complete combustion of organic matter and othervolatile compounds

- a controlled process involving the burning of gaseouscombustible residuals


- creates a residual ash

• Composting - removal of moisture from the biosolids and partial by heat drying 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 toeliminate odours

- the biosolids, after drying, are processed into a soil conditioner

• Composting - a process in which organic matter undergoes biological by microbial decomposition to produce a stable end product that is action acceptable as a soil conditioner

- methods of composting include open windrow andmechanical systems

• Thermal Drying - biosolids are heated in a dryer to evaporate any moisture(Pelletization) - 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

• Chemical - most common form is lime stabilization which involves Stabilization 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

• Burial / Landfilling - digested sludge or biosolids are buried at a suitable site (i.e.appropriate distance from populated areas, leachateprotection, runoff and erosion control, and protectionagainst gas movement)

- biosolids may be used as a daily landfill cover to limit surface infiltration

- permitted only at licenced landfill sites

• Land Application - applied to crop land, thus reducing the demand forcommercial fertilizers, improving soil fertility, enhancing soilstructure, and improving soil moisture retention andpermeability


- ideal for crops such as corn, soybeans, canola, and cerealsand can also benefit pasture land.

- can be used in forestry to encourage tree growth, andtherefore timber production, or to rehabilitate soils affectedby mining or quarrying.

- soil tests ensure suitability of the application site based onlevels of nutrients, metals, and pH of the soil

- guidelines concerning biosolids land application require thatthe land is suitable, located a specified distance fromresidences, wells, and water sources and that the timing andmethod of application must be appropriate for the specificsite considerations and crop management

- a field would receive biosolids once every five years,normally

Sewage Treatment Plants - Potential Water Quality ImpactsAll 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 designedto minimize any impact on water quality. The cause of potential water quality impacts of sewagetreatment 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 isdeliberately 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 preventthe raw sewage from backing up into homes, businesses, and streets and to avoid the shutdown ofthe entire facility. The capacities of wastewater treatment plants are designed to handle short-term peak flows well above daily averages, so that normal fluctuations in the flow do not causeplant upsets. Diversion of flow is prohibited from any portion of the treatment facility exceptduring emergency conditions. A treatment plant would ideally expand prior to reaching itsmaximum capacity. In most cases, raw sewage receives at least primary treatment and chlorinedisinfection before discharge into the watercourse (Hartley, 2001).

When there is a bypass incident, the facility operators must immediately notify the MedicalOfficer of Health, the Ministry of Health, and the Water Supply Section of the Works andEmergency Services Department (WES), detailing the volume and duration of the discharge.Municipalities report bypasses to the Ministry of the Environment and Energy. The WES isresponsible for providing annual summary reports to the Ministry of Environment and Energy ofany by-passes of sewage to a receiving water body as a result of equipment failure or systemoverload. Data showed that 75 of the 204 reporting Ontario municipal wastewater treatmentplants had bypasses in 1991, most of which occurred during the spring thaw months of March andApril. The corresponding total annual diverted volume for1991 was 2.2. million m3 for primary


plants and 9.6 million m3 for secondary plants, representing 0.11 and 0.46 %, respectively, of thetotal effluent volume treated (Chambers et al., 2001).

For the year 1998, 83 facilities were included in a report by Doyle, with 43 incidents ofbypass of either primary treatment, secondary treatment, or both treatments. Table 3 summarizesthe volume of diverted flow and the length of time the bypass incident lasted. The treatmentcapacity for the province in 1998 was 6 784 016 m3 / day. The total bypassed flow from bothprimary and secondary treatment in 1998 was 13 173 419 m3 (the equivalent of less than twodays’ processing for one year’s recorded bypass incidents). This diverted quantity of wastewaterrepresented 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) Total bypass time (h)

Treatmentbypassed

Number offacilities

primary secondary primary secondary

Primary 17 1 893 172 987

Secondary 18 8 067 835 1 645

Primary andSecondary

8 2 048 663 1 163 749 1 383 1 474

Total 43 3 941 835 9 231 584 2 370 3 120

If discharged without treatment, wastewater will continue to consume dissolved oxygenfrom 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 athreat to the water quality of a receiving body and to public health when wastewater enters awatercourse 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 followingillnesses in humans: intestinal infections, dysentry, hepatitis, typhoid fever, and cholera.

2. SpillsRaw 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 MedicalOfficier 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 spillsin the City of Toronto (Basrur and Gutteridge, 2000). These incidents had been contained andmonitoring of the water did not reveal any irregularities or serious health threats to Torontoresidents. The potential contaminants of a raw sewage spill are similar to those mentioned abovefor treatment plant bypasses.


Figure 4 Typical septic system layout(Vogel and Rupp, 1999)

3. Land Application of BiosolidsThe 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 ManureSystems - Potential Water Quality Impacts).

C - Human: Septic Systems

Septic systems are found in rural areas where municipal sewage treatment services are notavailable. About 8 million Canadians, slightly more than one-quarter of the population, are servedby septic systems (Environment Canada, 2001). Most systems consist of an underground tankand a leach drain, or absorption field, that operate together to purify household wastewater (seeFigure 4). Wastewater flows from the house by gravity to the septic tank. If the system isproperly sized and functioning correctly, the sewage remains in the tank for the amount of timenecessary to allow anaerobic bacteria to breakdown the solids. Incoming household wastewaterdisplaces a quantity of effluent which flows fromthe tank outlet by gravity. The effluent enters theburied absorption field where it seeps into thesurrounding soil. The liquid becomes filtered as ittravels downwards through the soil. Aerobicbacteria in the soil further break down the liquid. Some moisture usually transpires into the air abovethe buried absorption or leach field, mostly duringthe summer. The remaining effluent movesdownward in the soil and eventually reachesgroundwater.

The absorption or leach field should be situated an appropriate distance from the home orwell, away from any shade trees, and on the downhill side of the house. The soil of the absorptionfield must have an acceptable percolation rate. In other words, the soil must have characteristicsthat enable moisture to seep through it reasonably freely.

The Septic TankSewage 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 backinto the home to prevent the build-up of gases. At the opposite end of the septic tank, a secondpipe leads to the leaching bed. Single chambered tanks are no longer permitted to be installed inOntario. 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 movingdirectly through the tank and plugging the leach field lines. Double-chambered septic tanks tendto allow sufficient time for the suspended solids to settle out of the effluent stream.


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 movingwastewater has entered. The only movement is some temporary surface rippling. The stilling ofthe tank serves two functions. Anaerobic creatures thrive since they grow much better in still thanin 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 ofthe liquid in the tank. Gases bubble to the surface and bring along fine particles of solid materialwhich combine with oil and grease to form this layer of scum. The scum layer reduces themovement of the liquid beneath it and insulates the anaerobic bacteria from any air that seeps intothe tank.

Bacteria will continue to thrive and break down the organic material into its constituentelements as long as the temperature does not drop below freezing. Anaerobic bacteria are notcapable of completely transforming the organic matter into its component elements. Only aerobicbacteria (in the presence of sufficient oxygen) can properly break down the organic matter. Whenattacking organic substances, anaerobic creatures produce water, ammonia, hydrogen sulphide,phosphorus, and heat. In a physical sense, the anaerobic bacteria are altering the organicmaterials by transforming them from a solid state to a liquid state. The anaerobic communitycannot digest material such as stone or plastic and these materials remain in the tank. Eventuallythese materials must be removed by pumping. As with proper maintenance of the tank, this isrecommended every three to five years.


Figure 6 Cross-sectional view of absorptionfield layers (Vogel and Rupp, 1999)

The Absorption FieldThe effluent from the septic tank travels

to the absorption field through perforated plasticpipe. The liquid is still ‘septic’ and must betreated because it contains substances thatpromote the decomposition of vegetation andanimal matter, as well as harmful pathogens,bacteria, and viruses. The liquid flows out of thepipe and through a layer of coarse gravelsurrounding the pipe. Most of the liquid passesinto the soil by gravity. Some of the liquid leavesthe soil entirely by evaporation or by the processof transpiration where the roots of plants take upwater and this water evaporates from the leavesof the plant. Worms and nematodes aerate the soil, providing the oxygen required for aerobicorganisms to digest and chemically oxidize the organic waste present in the effluent. The wastesof 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, inparticular, absorbs viruses and locks them in place to prevent their movement. Soil mainlyconsists 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 electriccharge. Microorganisms also carry an electric charge on their protein coating. Because of theelectrical charges they may be attracted to the charged soil particles and held in place. As theeffluent flows further downward through the soil it will continue to be filtered. Eventually, muchof this water reaches the groundwater.

The efficiency of the absorption field becomes threatened when the soil immediatelysurrounding the pipes becomes saturated and clogged with fine particles of organic matter. Thesoil will lose its ability to function as a filter and the effluent will build up and appear on theground surface. The drain or absorption field can become an effective filter once more byremoving the old gravel and clogged earth, treating the nearby soil, and replacing the gravel andcovering it with a fresh layer of soil.

Alternatives to Conventional Septic Systems

1. Shallow Buried TrenchesThis 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 inchambers in the upper soil layers. Shallow buried trenches are intended for smaller building lotsand less permeable soils such as heavy clay soils. The system tends to make the effluent moreavailable for plant root uptake.


2. Chambered SystemsThe 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 gravel-filled trenches, they provide more infiltration surface area.

3. Peat Filter SystemsPeat-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 stonebedding. The compact design makes this filter system well-suited to lots with insufficient spacefor conventional treatment trenches. The peat filter must be replaced on average every eightyears.

4. Artificial Media FiltersArtificial 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 circulationthrough the media is accomplished by fans or by natural convection. These systems can behoused in an above-grade structure or buried in a concrete or fibreglass tank.

Septic System - Potential Water Quality ImpactsGroundwater 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 whenthe 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 werenot properly designed, constructed and maintained (Chambers et al., 2001). Septic systemeffluent 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 soilpores. If they are not destroyed they may leach downwards to the water table. Adsorption slowsthe downward movement of bacteria and viruses. The process is particularly effective with anincreasing clay content of soils. In sandy soils, however, adsorption is weak and the adsorbedorganisms may not likely be bound permanently to the soil and can become re-suspended in thewater moving through soil pores that eventually reaches the groundwater. Microorganismsincluding coliform bacteria and viruses tend to move only a few dozen centimeters within thepercolating waters in unsaturated soil layers although much greater distances can be achievedunder saturated flow conditions. Release of adsorbed microorganisms and their downwardleaching has been noted during periods of heavy rainfall when water is rapidly percolating throughthe soil (Cogger, 1988).

Results of various studies have shown that unsaturated soils remove a large percentage of


the bacteria and viruses present in the septic system effluent. Substantial bacterial and viralremoval occurs within the first 30 cm of unsaturated soil. Within 60 to 120 cm of the bottom ofthe trenches, removal of these contaminants is nearly complete. Bacterial and viral survival isprolonged by saturated conditions most commonly as a result of high water tables. There is apotential for bacterial and viral persistence when there is a zone of saturated soil beneath theabsorption 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 ofoxygen by the blood. Infants are especially susceptible to this condition. Nitrate is a highlysoluble compound that is readily transported to groundwater. The three main mechanisms thatcan 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. Nitrogenfrom septic tank effluent is only available to plants surrounding the absorption trenches and thisnutrient is continuously added to the soil throughout the year, whether the plants can effectivelyuse it or not. As a result, plants are not effective throughout the entire year at using the nitratereleased from septic systems.

Denitrification is the process carried out under anaerobic conditions in the soil thatreduces nitrate to nitrogen gas. It is most effective in wet soils that are otherwise unsatisfactoryfor wastewater treatment.

The most commonly used method to control nitrate concentrations is through dilution inthe groundwater aquifer. Nitrate can reach unacceptable levels in groundwater beneath soils thatare 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 fromseptic tank effluent is of much less concern in comparison to nitrate or bacteria and viruses sincephosphorus is adsorbed tightly to soil minerals and its potential for movement is limited. Verylittle phosphate moves through soil and groundwater to lakes. Phosphate movement is evident,however, in some sandy soils with limited phosphate fixation capacity, especially surroundingolder or heavily loaded systems with higher water tables.

The organic matter in wastewater also includes trace amounts of toxic man-made organiccompounds derived from household products such as solvents. These compounds are sometimesslow to degrade, and have the potential to contaminate groundwater if they percolate through thesoil in sufficient quantities. If the concentration of this type of contaminant gets too high it mayalso negatively influence the performance of the septic tank. A number of studies, however, haveshown that the levels of these toxic organic compounds created no serious problems (Cogger,1988).


D - Livestock Manure Systems

Handling and Transfer to StorageMost 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. fromdrinkers), precipitation into the storage, spilled feed, and bedding. Normally solid manure containsfeces, some or all of the urine, bedding, spilled feed, and little or no additional water. The mainfactors 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 dairyoperations, some large beef operations, most swine operations, and some caged laying henoperations. Solid systems tend to be popular with smaller dairy and beef operations, some largebeef operations, broiler chicken operations and most caged laying hen operations. Some farmshave both solid and liquid manure systems.

There are a number of methods used to collect and transfer manure to storage. In somecases, the storage is a part of the housing system (e.g. bedded manure that the animals movearound on) or the manure falls through slatted floors into a tank under the animals. These systemscan require very little labour, outside of actual spreading. In other cases, manure is removed fromthe barn regularly (e.g. every day or every week) and stored until the timing is right to spread themanure onto the fields.

The number of livestock farms in Ontario and the amount of manure produced per yearare 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 LivestockFarm Numbers

Poultry Cattle Swine

Total for Ontario 28 885 1 850 19 350 9 654

StorageMost 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 factorsconsidered in determining a spreading time include: soil moisture levels, making best use oflabour resources, minimizing adverse environmental impacts, availability of a custom applicator,and economics. While some storage capacities may be less than 200 days, a normal minimumstorage period recommended or required is about 250 days. This allows most farmers flexibility inapplying manure to cropland. In addition, there is a growing number of farms with up to 400 daysof manure storage capacity.

Solid manure is usually stacked on a concrete pad. This storage should have a system to


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 farmershave uncovered clay-lined earthen storages. Many farmers have uncovered circular concrete orsteel tanks. There are also a number of covered concrete storages. Liquid manure storagestypically become anaerobic - little or no oxygen is present. This leads to odour production, andsiting formulas are typically used to maintain enough distances to non-compatible land uses tominimize odour conflicts.

TreatmentWhile 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 useno treatment system.

Land ApplicationThe 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. Similarsystems are used for land application of sewage biosolids. Often, manure is spread onto the landand incorporated into the soil within a day or two. Some farmers inject manure directly into thesoil. This requires more energy, but reduces losses of ammonia-N to the air. Under certaincropping 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 tocropland in Canada (Chambers et al., 2001).

Livestock Manure Systems - Potential Water Quality ImpactsThe 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 nutrientsback to the soil, rather than disposing of them, which is the end result of human wastewatertreatment 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 adrainage system. While this runoff may not be as concentrated as raw manure, it can have animpact on water quality. Some farms have runoff storages, or have structures that significantlyreduce the quantity of runoff. Others have vegetative areas that the runoff must cross, whichhelps to treat the wastewater. Vegetative filter strips facilitate the infiltration of the water into thesoil and the utilization of the nutrients by the plants growing there.


2. Over-application of manureIf 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 thisnitrate, depending on many factors, may eventually reach groundwater. Phosphorus is not asmobile but can accumulate in the soil to levels where leaching can become a problem. Currently, agreat deal of effort is going into promoting the more widespread use of nutrient managementplans. This is one of the most effective ways to avoid the problem of over-application ofnutrients, from whatever source.

3. Macropore flow of liquid manure to subsurface tile drainage systemsUnder 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 toavoid this potential problem are fairly well established now.

4. Runoff from fieldsIf 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 winter-spread manure, a practice which is no longer considered acceptable in Ontario (mainly because ofthis 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 causeserious environmental harm (especially in the short term).

This section has addressed concerns with livestock manure, but because the managementof land applied sewage biosolids is somewhat similar, the same issues can apply to the applicationof biosolids to farmland.


Material #1 - Raw Sewage (1000 L)

TSS 200 gBOD5 170 gTKN 30 gTP 7 gtotal coliform bacteria 5 x 107 per

100 mL(source: Doyle, 2002)

Secondary Effluent discharged tosurface water (999.4 L)

TSS 15 gBOD5 15 gTKN 20 gTP 3.5 gtotal coliform bacteria 200 - 1000 per 100 mL(source: Doyle, 2002)

600 g of Biosolids (Anaerobic dewatered liquid)

TS 180 g (ref1)BOD5 N/aTKN Í 10 gTP Í 3.5 g total coliform bacteria N/a

(Source: 1 OMAFRA, 2000)

E - Summary of Losses and Transformations

Situation #1Assume: 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. Thevolume of wastewater lost as grit and screenings is assumed to be negligible. An effluent volumeof approximately 999.4 L is considered to be exiting the plant.

The reduction of the parameters considered at the aeration stage are not considered significantsince the volatile organic compounds and ammonia levels are low. Parameters are provided forthe effluent exiting the treatment facility and for the sewage biosolids. Wasted sludge from boththe primary and secondary clarifier is considered. The mass of biosolids was found given that theprimary clarifier removes 60 % of the TSS and given that from 0.3 to 0.5 g of sludge is producedfor every gram of BOD5 removed in the secondary clarifier (Zhou, 2002). The total coliformbacteria effluent value is based on a chlorine dosage rate of 2 - 8 mg/L and a total chlorine


1000 L of groundwater (no more than 10 m from the leaching bed)

TSS 40 g (ref2)BOD5 35 g (ref2)TN N/aTP 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, 19935 Ritter et al., 1994)

Material # 2 - Untreated DomesticWastewater (1000 L)

TSS 220 gBOD5 220 gTN 40 gTP 8 gtotal coliform bacteria 107 - 108 per

100 mL(source: ‘Medium concentration’wastewater - Tchobanoglous and Burton,1991 )

1000 L of Septic Tank Effluent(prior to entering leaching bed)

TSS 68 - 624 g (ref2)BOD5 140 - 666 g (ref2)TN N/aTP 7.2 - 17 g (ref3)total coliform bacteria 104 - 105 per

100 mL (ref3)(Source: 2 Viraraghavan and Warnock, 1976

3 Anderson et al., 1994 )

residual of 2.5 - 3.5 mg/L (Qasim, 1994). Data are not provided for sewage sludge since it is anintermediate of the treated biosolids. The biosolids considered received anaerobic treatment andwere de-watered to a total solids concentration of 30 % (OMAFRA, 2000)

Situation #2Assume: 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 fourhumans.

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. Theconstituents reported for the septic tank effluent are concentrations reported prior to this materialentering the leaching bed. The concentrations of these parameters in the groundwater are outsidethe footprint of the leaching bed but no more than 10 m away.


Material # 3 - Feeder Pig Manure (1000 L)

TSS N/aBOD5 28 000 gTN 46 000 gTP 1 600 gtotal coliform bacteria 4 x 108 per

100 mL(source: Fleming and Ford, 2001)

Land Applied Manure (1000L)

TSS N/aBOD5 28 000 gTN N/aTP 1 600 gtotal coliform bacteria 4 x 108 per

100 mL(source: Fleming, 2002)

Situation #3Assume: 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 dueto losses to the atmosphere during storage and spreading. The other parameters will remainvirtually the same until the manure is applied to cropland.


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. Asmall portion of the nutrients may be used on land for crop growth. A large amount of treatedwastewater is discharged to the environment - it is the water that is re-used. In contrast, livestockmanure systems aim to make use of nutrients for growing crops. Typically there is no attempt tobreak down organic matter before it is applied to the soil. Similarly, there is no attempt to destroypathogens, although steps are taken during storage and land application to reduce the risk of anypathogens surviving in the manure from entering surface water or groundwater. Both livestockmanure and human waste have the potential to contaminate water resources (surface water orgroundwater), 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 isnecessary before alternative methods of waste handling and treatment can be developed.

AcknowledgmentsSpecial thanks to the following individuals for supplying important information for the completionof this report:

D. Joy, Professor, School of Engineering, University of GuelphM. Payne, Biosolids Utilization Specialist, Ontario Ministry of Agriculture and FoodH. 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 vadosezone of fine sand. Proceedings of the 7th International Symposium on Individual andSmall Community Sewage Systems. ASAE.

Basrur, S. 2000. Toronto Staff Report: Raw Sewage Discharges in Lake Ontario. Available inpdf form:www.city.toronto.on.ca/legdocs/2000/agendas/committees/hl/hl000925/it008.pdf. Dateaccessed: 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 andAgri-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 ofEnvironmental Health 51(1): 12 - 16.


Doyle, E. 2002. Wastewater Collection and Treatment. Toronto: Ministry of the AttorneyGeneral. 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 TheEnvironmental 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. Dateaccessed: May 29, 2002.

Goss, M.J., K.S. Rollins, K. McEwan, J.R. Shaw and H. Lammers-Helps. 2002. TheManagement of Manure in Ontario with Respect to Water Quality. Toronto: Ministry ofthe Attorney General. Walkerton Inquiry Commissioned Paper 6. Walkerton InquiryCD-ROM. Available online at: www.walkertoninquiry.com. Date accessed: July 4,2002.

Hartley, M. 2001. Municipal Wastewater Spills and Bypasses Report. Grand RiverConservation 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 HouseholdSeptic Systems on Difficult Sites. Booklet designed by the LandOwner Resource Centre,Manotick, ON.

OMAF [Ontario Ministry of Agriculture and Food]. 2000. Sewage Biosolids: ManagingUrban Nutrients Responsibly for Crop Production. Government factsheet.

Payne, M. 2000. Land Application of Sewage Biosolids for Crop Production. Ontario Ministryof 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-WaterQuality. Presented at the NABEC-94 Conference, Guelph, Ontario, July, 1994.


Schiff, S., et al. 1993. Septic Systems and Phosphorous. Presented as the conference on problemenvironments for septic systems and communal treatment options (Waterloo) - May, 1993.

Tchobanoglous, G. and F. L. Burton. 1991. Wastewater Engineering: Treatment, Disposal, andReuse, 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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