Onsite sewage facility

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Onsite sewage facilities (OSSF), also called septic systems, are wastewater systems designed to treat and dispose of effluent on the same property that produces the wastewater, in areas not served by public sewage infrastructure.

Contents

A septic tank and drainfield combination is a fairly common type of on-site sewage facility in the Western world. OSSFs account for approximately 25% of all domestic wastewater treatment in the US. Onsite sewage facilities may also be based on small-scale aerobic and biofilter units, membrane bioreactors or sequencing batch reactors. These can be thought of as scaled down versions of municipal sewage treatment plants, and are also known as "package plants." [1]

Process description

The primary mechanism of biological waste recycling in the natural environment is performed by other organisms such as animals, insects, soil microorganisms, plants, and fungi, which consume all available nutrients in the waste, leaving behind fully decomposed solids that become part of topsoil, and pure drinking water that has been stripped of everything that can possibly be consumed and utilized. This natural biological purification requires time and space to process wastes.

In virtually all engineered onsite sewage facilities, recycling and decomposition by natural organisms is still the primary mechanism of sewage disposal. Giving the organisms the time they need to decompose wastes is accomplished by establishing minimum sewage retention and settling times, and minimum liquid flow distances between sewage disposal sites and surface water or water wells.

Differences

It is normal for animals such as mice, rats, flies, and parasites to participate in the fully natural biological waste recycling process. Engineered facilities typically attempt to exclude them to prevent out of control population explosions and infestation, and prevent spread of vermin and disease.

Although the solids collected by onsite sewage facilities can potentially be used as compost to build topsoil, these solids are often incompletely decomposed due to either a lack of onsite storage space to wait for decomposition (municipal facilities), or because the solids are being stacked in a layered structure of new waste solids on top of previously decomposed solids (septic tanks and outhouses). Due to the incomplete state of decomposition, when removed from an onsite sewage facility, these solids are typically referred to as sludge rather than compost, and have powerful offensive odors arising from the microorganisms still consuming nutrients in the sludge.

A septic tank being installed. The next step is to plug it to the intake and outtake pipes and backfill it with soil. Septic tank 1.jpg
A septic tank being installed. The next step is to plug it to the intake and outtake pipes and backfill it with soil.

Engineered facilities that use water suspension to transport solids (private septic systems and municipal facilities) typically form a floating layer in their primary settling tank, consisting of low-density liquids such as oils, buoyant solids, and soap foam. This is referred to as scum and is slowly decomposed by microorganisms, eventually falling to the bottom of the settling tank as part of the sludge. When private septic tanks are emptied of solids, the tank is typically vacuumed empty and the incompletely digested scum is added to the incompletely digested sludge, further adding to its aroma and bioactivity.

If left completely undisturbed and exposed to the open air through a vent, the sludge and scum in a settling tank will eventually be turned completely into low-odor compost. By building two tanks side by side, and diverting sewage between them, one tank can be allowed to rest while the other is in use, and the resting tank can be safely and easily cleaned out by hand before it is used again. This has been proposed as a solution for onsite sewage facilities in subsistence agriculture economies where hand labor is the most abundant.

Although human body waste is no different from the waste of any other animal, municipal facilities may be required to bury the collected solids in landfills, due to the risk of toxic contaminants placed into the shared communal sewage system, by humans unaware of the harm they are causing. Municipal facilities may also collect runoff from roadways, which contains traces of all the various chemicals used in vehicles such as brake fluid and engine oil, and those used in melting ice and snow. Private septic systems typically do not experience these issues, as the homeowner is directly aware that they must not pour toxic chemicals down the drain.

Improving treatment through performance requirements

Most onsite wastewater treatment systems are of the conventional type, consisting of a septic tank and a subsurface wastewater infiltration system (SWIS). Site limitations and more stringent performance requirements have led to significant improvements in the design of wastewater treatment systems and how they are managed. Over the past 20 years the onsite wastewater treatment system (OWTS) industry has developed many new treatment technologies that can achieve high performance levels on sites with size, soil, ground water, and landscape limitations that might preclude installing conventional systems. New technologies and improvements to existing technologies are based on defining the performance requirements of the system, characterizing wastewater flow and pollutant loads, evaluating site conditions, defining performance and design boundaries, and selecting a system design that addresses these factors.

After solid matters are retained in the tank, liquid wastes are moved through these pierced PVC pipes to be evenly evacuated onto the gravel layer. Drain field in progress.jpg
After solid matters are retained in the tank, liquid wastes are moved through these pierced PVC pipes to be evenly evacuated onto the gravel layer.

Performance requirements can be expressed as numeric criteria (e.g., pollutant concentration or mass loading limits) or narrative criteria (e.g., no odors or visible sheen) and are based on the assimilative capacity of regional ground water or surface waters, water quality objectives, and public health goals. Wastewater flow and pollutant content help define system design and size and can be estimated by comparing the size and type of facility with measured effluent outputs from similar, existing facilities. Site evaluations integrate detailed analyses of regional hydrology, geology, and water resources with site specific characterization of soils, slopes, structures, property lines, and other site features to further define system design requirements and determine the physical placement of system components.

Most of the alternative treatment technologies applied today treat wastes after they exit the septic tank; the tank retains settleable solids, grease, and oils and provides an environment for partial digestion of settled organic wastes. Post-tank treatment can include aerobic (with oxygen) or anaerobic (with no or low oxygen) biological treatment in suspended or fixed-film reactors, physical/chemical treatment, soil infiltration, fixed-media filtration, and/or disinfection. The application and sizing of treatment units based on these technologies are defined by performance requirements, wastewater characteristics, and site conditions.

Usage and norms by country

Canada

Under Canadian federalism, environment is a shared power between federal and provincial governments. [2] However, waste water management mostly falls within provincial, territorial and municipal jurisdiction, while the federal government has jurisdiction over wastewater on federal land and on First Nations reserves. [3] Each province and territory has its own norms and regulations concerning the design and installation of onsite sewage facilities, such as whether a permit is required to do so and how to obtain it, the type, size and location of the system (usually according to on-site soil characteristics and other factors), etc. : [4]

Province or territoryDepartment or MinistryAct — Regulation
Prince Edward Island Department of Technology and EnvironmentEnvironmental Protection — Act Sewage Disposal Regulation
Newfoundland and Labrador Department of HealthPublic Health Act — Sanitation Regulation
Nova Scotia Department of the EnvironmentEnvironment Act — On-site Sewage Disposal Regulation
New Brunswick Department of Health and Community ServicesHealth Act — Regulation 88-200
Quebec Department of EnvironmentEnvironmental Quality Act — Q-2, r. 22 - Regulation Respecting Wastewater Disposal Systems for Isolated Dwellings
Ontario Ministry of Municipal Affairs and HousingOntario Building Code Part 8
Manitoba Department of the EnvironmentEnvironment Act — Private Sewage Disposal Systems and Privies Regulation
Saskatchewan Department of HealthPublic Health Act — Plumbing and Drainage Regulation
Alberta Ministry of LabourSafety Codes Act — Alberta Private Sewage Systems Standards of Practice
British Columbia Ministry of Health ServicesHealth Act — Sewerage System Regulation
North West Territories Department of Health and Social ServicesPublic Health Act — General Sanitation Regulations
Yukon Territory Department of HealthPublic Health and Safety Act — Sewage Disposal System Regulations

Europe

The potential market volume of on-site treatment is suggested to be about 35 million population equivalents for Europe. [5]

United States

In the United States, on site sewage facilities collect, treat, and release about 4 billion US gallons (15,000,000 m3) of treated effluent per day from an estimated 26 million homes, businesses, and recreational facilities nationwide (U.S. Census Bureau, 1997). Recognition of the impacts of onsite systems on ground water and surface water quality (e.g., nitrate and bacteria contamination, nutrient inputs to surface waters) has increased interest in optimizing the systems' performance. Public health and environmental protection officials now acknowledge that onsite systems are not just temporary installations that will be replaced eventually by centralized sewage treatment services, but permanent approaches to treating wastewater for release and reuse in the environment. Onsite systems are recognized as viable, low-cost, long-term, decentralized approaches to wastewater treatment if they are planned, designed, installed, operated, and maintained properly (USEPA, 1997). NOTE: In addition to existing state and local oversight, decentralized wastewater treatment systems that serve more than 20 people might become subject to regulation under the USEPA's Underground Injection Control Program, although EPA has proposed not to include them (64FR22971:5/7/01).

Although some onsite wastewater management programs have functioned successfully in the past, problems persist. Most current onsite regulatory programs focus on permitting and installation.

Few programs address onsite system operation and maintenance, resulting in failures that lead to unnecessary costs and risks to public health and water resources. Moreover, the lack of coordination among agencies that oversee land use planning, zoning, development, water resource protection, public health initiatives, and onsite systems causes problems that could be prevented through a more cooperative approach. Effective management of onsite systems requires rigorous planning, design, installation, operation, maintenance, monitoring, and controls.

Public health and water resource impacts

State and tribal agencies report that onsite septic systems currently constitute the third most common source of groundwater pollution and that these systems have failed because of inappropriate siting or design or inadequate long-term maintenance (USEPA, 1996a). In the 1996 Clean Water Needs Survey (USEPA, 1996b), states and tribes also identified more than 500 communities as having failed septic systems that have caused public health problems. The discharge of partially treated sewage from malfunctioning onsite systems was identified as a principal or contributing source of degradation in 32 percent of all harvest-limited shellfish growing areas. Onsite wastewater treatment systems have also contributed to an overabundance of nutrients in ponds, lakes, and coastal estuaries, leading to the excessive growth of algae and other nuisance aquatic plants (USEPA, 1996b). In addition, onsite systems contribute to contamination of drinking water sources. USEPA estimates that 168,000 viral illnesses and 34,000 bacterial illnesses occur each year as a result of consumption of drinking water from systems that rely on improperly treated ground water. Malfunctioning septic systems have been identified as one potential source of ground water contamination (USEPA, 2000).

In 2022, trials were underway on Cape Cod, Massachusetts of septic systems that reduce nitrogen pollution using wood chips and limestone. [6]

See also

Related Research Articles

<span class="mw-page-title-main">Imhoff tank</span>

The Imhoff tank, named for German engineer Karl Imhoff (1876–1965), is a chamber suitable for the reception and processing of sewage. It may be used for the clarification of sewage by simple settling and sedimentation, along with anaerobic digestion of the settled sludge. It consists of an upper chamber in which sedimentation takes place, from which settled solids slide down on the inclined bottom slopes towards a lower chamber in which the sludge accumulates. The two chambers are otherwise unconnected, with the more liquid sewage flowing only through the upper sedimentation chamber and only a slow flow of sludge in the lower digestion chamber. The lower chamber requires separate biogas vents and pipes for the removal of digested sludge, typically after 6–9 months of digestion. The Imhoff tank is in effect a two-story septic tank and retains the septic tank's simplicity while eliminating many of its drawbacks, which largely result from the mixing of fresh sewage and septic sludge in the same chamber.

<span class="mw-page-title-main">Septic tank</span> Method for basic wastewater treatment (on-site)

A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the treatment efficiency is only moderate. Septic tank systems are a type of simple onsite sewage facility. They can be used in areas that are not connected to a sewerage system, such as rural areas. The treated liquid effluent is commonly disposed in a septic drain field, which provides further treatment. Nonetheless, groundwater pollution may occur and is a problem.

<span class="mw-page-title-main">Wastewater treatment</span> Converting wastewater into an effluent for return to the water cycle

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<span class="mw-page-title-main">Composting toilet</span> Type of toilet that treats human excreta by a biological process called composting

A composting toilet is a type of dry toilet that treats human waste by a biological process called composting. This process leads to the decomposition of organic matter and turns human waste into compost-like material. Composting is carried out by microorganisms under controlled aerobic conditions. Most composting toilets use no water for flushing and are therefore called "dry toilets".

<span class="mw-page-title-main">Biosolids</span> Decontaminated sewage sludge

Biosolids are solid organic matter recovered from a sewage treatment process and used as fertilizer. In the past, it was common for farmers to use animal manure to improve their soil fertility. In the 1920s, the farming community began also to use sewage sludge from local wastewater treatment plants. Scientific research over many years has confirmed that these biosolids contain similar nutrients to those in animal manures. Biosolids that are used as fertilizer in farming are usually treated to help to prevent disease-causing pathogens from spreading to the public. Some sewage sludge can not qualify as biosolids due to persistent, bioaccumulative and toxic chemicals, radionuclides, and heavy metals at levels sufficient to contaminate soil and water when applied to land.

<span class="mw-page-title-main">Constructed wetland</span> Artificial wetland to treat wastewater, greywater or stormwater runoff

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<span class="mw-page-title-main">Waste stabilization pond</span> Ponds designed and built for wastewater treatment

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<span class="mw-page-title-main">Activated sludge</span> Wastewater treatment process using aeration and a biological floc

The activated sludgeprocess is a type of biological wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa. It is one of several biological wastewater treatment alternatives in secondary treatment, which deals with the removal of biodegradable organic matter and suspended solids. It uses air and microorganisms to biologically oxidize organic pollutants, producing a waste sludge containing the oxidized material.

<span class="mw-page-title-main">Industrial wastewater treatment</span> Processes used for treating wastewater that is produced by industries as an undesirable by-product

Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater may be reused or released to a sanitary sewer or to a surface water in the environment. Some industrial facilities generate wastewater that can be treated in sewage treatment plants. Most industrial processes, such as petroleum refineries, chemical and petrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans. This applies to industries that generate wastewater with high concentrations of organic matter, toxic pollutants or nutrients such as ammonia. Some industries install a pre-treatment system to remove some pollutants, and then discharge the partially treated wastewater to the municipal sewer system.

<span class="mw-page-title-main">Septic drain field</span> Type of subsurface wastewater disposal facility

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<span class="mw-page-title-main">Secondary treatment</span> Biological treatment process for wastewater or sewage

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<span class="mw-page-title-main">Sewage sludge treatment</span> Processes to manage and dispose of sludge during sewage treatment

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An aerobic treatment system (ATS), often called an aerobic septic system, is a small scale sewage treatment system similar to a septic tank system, but which uses an aerobic process for digestion rather than just the anaerobic process used in septic systems. These systems are commonly found in rural areas where public sewers are not available, and may be used for a single residence or for a small group of homes.

<span class="mw-page-title-main">Sewage treatment</span> Process of removing contaminants from municipal wastewater

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<span class="mw-page-title-main">Fecal sludge management</span> Collection, transport, and treatment of fecal sludge from onsite sanitation systems

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<span class="mw-page-title-main">Pit additive</span> Material to reduce fecal sludge build-up

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<span class="mw-page-title-main">Vermifilter</span> Aerobic treatment system, consisting of a biological reactor containing media

A vermifilter is an aerobic treatment system, consisting of a biological reactor containing media that filters organic material from wastewater. The media also provides a habitat for aerobic bacteria and composting earthworms that purify the wastewater by removing pathogens and oxygen demand. The "trickling action" of the wastewater through the media dissolves oxygen into the wastewater, ensuring the treatment environment is aerobic for rapid decomposition of organic substances.

The Thomas P. Smith Water Reclamation Facility (TPSWRF) is owned and operated by the city of Tallahassee, Florida. The facility provides sewage treatment services for Tallahassee, Florida and the surrounding areas.

<span class="mw-page-title-main">Decentralized wastewater system</span> Processes to convey, treat and dispose or reuse wastewater from small communities and alike

Decentralized wastewater systems convey, treat and dispose or reuse wastewater from small and low-density communities, buildings and dwellings in remote areas, individual public or private properties. Wastewater flow is generated when appropriate water supply is available within the buildings or close to them.

References

  1. ↑ Package Plants (Report). Wastewater Technology Fact Sheets. Washington D.C.: U.S. Environmental Protection Agency (EPA). September 2000. EPA 832-F-00-016.
  2. ↑ Scott, Dayna (2018). "Federalism, the Environment and the Charter in Canada". Articles & Book Chapters. Osgoode Hall Law School of York University.
  3. ↑ Becklumb, Penny (2013). "Federal and Provincial Jurisdiction to Regulate Environmental Issues". Library of Parliament. Retrieved 2020-04-10.
  4. ↑ "Your Septic System. Where Does the Water Go?". Canada mortgage and Housing Corporation. 2006. Archived from the original on 2006-03-12.
  5. ↑ Eggimann S., Truffer, B., Feldmann, U., Maurer, M. (2018). "Screening European market potentials for small modular wastewater treatment systems – an inroad to sustainability transitions in urban water management?". Land Use Policy. 78: 711–725. doi:10.1016/j.landusepol.2018.07.031. S2CID   158778849.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. ↑ David Abel (17 May 2022). "As pollution worsens on Cape Cod, some are investing hopes in a new type of septic system". The Boston Globe .
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