Sewage Treatment Systems Components
Listed below is the basic overview of the different types of STS components, the different type of STS systems and the associated maintenance with each system
Septic tanks are the most common first step in a wastewater treatment system to homeowners who are not on sanitary sewer. The tanks are manufactured from precast concrete, polyethylene plastic, or fiberglass. The septic tank provides some treatment of the effluent from the house by allowing for the settling of solid materials, and separation of scum, fats and greases. The partially clarified liquid, or effluent, is then drained by gravity to a secondary treatment that can be a variety of different systems.
Septic tanks are simple to operate and maintain. The tanks can last anywhere from 20 to 30 years with proper care and maintenance.
Operation & Maintenance
Routine pumping and inspection of the septic tank (every 2-5 years) at a cost of approximately $100 to $200 per year. Pump the tank based on the size of the tank and the number of people using it. Clean the effluent filter seasonally. Avoid dumping/flushing fats, oils, greases, non-biodegradable products, bacterial additives, excessive cleaning supplies, etc. down toilets and drains.
Soil Absorption Trenches
The effluent that leaves your septic tank or pretreatment device and is then drained by gravity to plastic perforated pipes laid in gravel trenches in the soil. Approved alternatives such as chamber products or bundled expanded polystyrene distribution products may also be used. The soil is used as the primary treatment media to remove the smaller suspended particles (TSS) and organic material (BOD). Research confirms that 2 to 4 feet of unsaturated soil is needed to completely remove bacteria, viruses and protozoans from sewage.
Soil absorption trenches are passive, simple and low maintenance systems. With the right soils, they can effectively treat sewage. They are also a reasonably priced system where soil conditions permit their installation.
These systems require soils that are not seasonally saturated with water to ensure treatment, and prevent ponding or nuisance conditions in yards. Over time, the soil absorption trench will develop a biomat consisting of suspended particles, organic matter and bacterial slimes which will eventually clog the trenches and lead to system failure. Lowering the amount of suspended particles, organic and bacterial load to the trenches by pretreating the wastewater can help extend trench life.
Operation & Maintenance
Rotate distribution device(s) semi-annually to allow resting. Ensure all surface water is directed away from trenches. Walk trenches regularly to check for “soft spots.” Keep all heavy machinery and vehicles off of leach field. Do not plant trees or heavy rooted vegetation near leach field.
Pretreatment to Soil Absorption Trenches
This system design includes a mechanical pretreatment device that reduces the suspended solids, organic material and bacteria in the effluent. Pretreatment devices consist of a multi-chamber tank that is divided into two or more sections to provide for settling of solids and effluent treatment. These devices use different biological processes to treat sewage including continuous flow, suspended growth aerobic systems (most common), fixed media processing and optional recirculation, and sequencing batch reactors. Aerobic conditions are required for treatment, subsequently most system add oxygen to the treatment process. These systems can substantially reduce the total suspended solids (TSS), organic matter (BOD), fecal coliform (and other pathogenic bacteria). Some systems use recirculation of effluent to reduce ammonia and nitrogen in the effluent. The treated effluent is discharged to a soil absorption trench. Due to the high level of pretreatment, the size of the soil absorption trench can be reduced by 25 to 30%, thus reducing system costs. The significant reduction of fecal coliform can also allow for less thickness of soil necessary for treatment, and one or two foot soil depth credits (reduction of soil thickness needed by 1-2 feet) can be used to help overcome site limitations such as bedrock or seasonal high water table.
A variety of pretreatment units are available across the state with varying costs, performance levels and operation and maintenance requirements. Pretreatment devices help overcome site limitations like high seasonal water table by providing higher levels of treatment to allow for less useable soil thickness on the lot. They also help to provide treatment when the system is located near or could impact sensitive water environments. These devices also allow for a smaller area for the soil absorption trenches, thus reducing costs associated with the soil absorption component.
Pretreatment units are mechanical devices that require regular maintenance by a qualified service provider. Components will have to be replaced over time. A service contract must be maintained to ensure that the system receives proper care and maintenance.
Operation & Maintenance
Suggested annual inspection and maintenance of mechanical components. This can include inspecting air pump filters (cleaning or replacing as necessary) cleaning diffusors and aspirators, performing sludge level readings, verification of float settings, cleaning/maintenance of disinfection unit(s), checking air pressure of aerator, and flushing of distribution pipe to remove bio-slimes/build-up at a cost of $100-$200 annually. Regular pumping of the tank (every 2-5 years) at a cost of $100-$200 annually.
Peat Biofilter with Soil Absorption
A peat filter produces secondary-level treatment of septic tank effluent by filtering it through a layer of sphagnum peat before sending it to the soil absorption system. Peat is partially decomposed organic material with a high water-holding capacity, large surface area, and chemical properties that make it effective in treating wastewater. Un-sterilized peat is also home to a number of different microorganisms, including bacteria, fungi, and tiny plants. All of these characteristics make peat a reactive and effective filter. The peat is contained in modules placed above ground or at ground level. Wastewater flows into a septic tank where the large solids settle out. The liquid effluent either gravity flows, or in some models, is pumped in doses to the peat filter where it is pretreated and delivered to the soil absorption system for final treatment. Depending on the installed depth of the peat filter, a dose pump may be required to lift effluent to the soil absorption system. With a gravity distribution to the filter, wastewater may pond on top of the peat compressing it, reducing the flow of wastewater through the filter. With a pressure distribution system, wastewater is applied evenly over the peat surface, allowing rapid infiltration. Due to the high level of pretreatment, the size of the soil absorption trench can be reduced by 25 to 30%, thus reducing system costs. The reduction of fecal coliform can also allow for less thickness of soil necessary for treatment, and one or two foot soil depth credits (reduction of soil thickness needed by 1-2 feet) can be used to help overcome site limitations such as bedrock or seasonal high water table.
Peat's high cation exchange capacity means the peat can effectively hold positively charged molecules including ammonium, metals, pesticides, some organic molecules, and possibly viruses. As a filter medium peat is effective in situations where loadings are seasonal or intermittent. The treatment capacity can be expanded through modular design.
Peat filters require more maintenance than conventional septic to soil absorption trenches. Treatment media has a limited useful life of 10-15 years and has to be replaced with new media depending on the use.
Operation & Maintenance
A maintenance contract is recommended; the system may require quarterly to yearly maintenance. Maintenance includes inspecting all components and cleaning and repairing when needed. The peat module(s) are low-maintenance and require no annual pumping or backwashing. They should be raked annually to break up any biomat that may be forming and to level the media. Because of the high organic content of peat, the filter media must be periodically replaced. Life expectancy of the peat media in a filter is estimated to be ten to fifteen years. Daily running costs for a peat filter are based on the operation of a small submersible pump, and average less than one dollar per month for an individual home (2002). Overall operational costs of $200-$500 per year include pumping, repairs, maintenance, and electricity.
Sand Mounds with Pressure Distribution
A septic tank and sand mound system is a technology used for treating and disposing of wastewater in areas unsuitable for conventional septic tank soil absorption systems. Mounds are pressure-dosed sand filters placed above, and discharging directly to, the natural soil. Their main purpose is to provide additional treatment to the wastewater before it enters the natural environment. Treatment occurs through physical, biological, and chemical means as the wastewater filters down through the sand and the natural soil. Mound systems are designed to overcome site restrictions such as slow or fast permeability of soils, shallow soil over bedrock, and a perched seasonal water table through elevation of the system with sand. The three components of a mound system are a septic tank or pretreatment unit(s), dosing chamber, and the elevated mound. (See figure below for an illustration.) Some mound systems are designed with a pretreatment unit(s) to reduce waste strength and/or to reduce the mound sizing (see Pretreatment to soil absorption page). The dosing chamber follows the septic tank or pretreatment component and contains a pump, which pressure doses the effluent to evenly distribute the wastewater over the infiltration surface of the mound. The mound is constructed with a soil cover that can support vegetation, and a fabric covered coarse gravel aggregate or gravelless product in which a network of small diameter perforated pipe is placed. The network of perforated pipe is designed to distribute the effluent evenly through the gravel from where it trickles down to the sand media and hence, into the plowed basal area (natural soil).
Mound systems allow the development of the use of some sites that would otherwise be unsuitable for in-ground or at-grade onsite systems due to seasonal perched water or other site limitations. The natural soil utilized in a mound system is the upper most horizon, which is typically the most permeable. A mound system does not have a direct discharge to the ground, streams, or other bodies of water; and construction damage is minimized since there is little excavation required in the mound area.
Cost is somewhat higher compared to a conventional system due to specialized construction, materials and transportation costs, and possible engineering design fees. Since there is usually limited usable soil available at mound system sites, extreme care must be taken not to damage this layer with construction equipment; the size and shape of mound systems, and their elevation above the natural grade may present some concerns related to grading, landscaping and aesthetics for the site. The mound may have to be partially rebuilt if seepage or leakage occurs; all systems require pumps or siphons.
Operation & Maintenance
Suggested annual inspection of mechanical components and flushing of distribution pipe including monitoring the dose volume and operating pressure head of the distribution system to remove bio-slimes/build-up at a cost of $150-$300 annually. Also recommend checking the mound for vegetative cover, erosion, or settling and any evidence of seepage. Ensure all surface water is diverted away from the mound and check for ponding in the distribution area. Regular pumping of the septic tank (every 2-5 years) at a cost of $100-$200 annually.
Septic Tank/Pretreatment to Low Pressure Pipe (LPP)
A low pressure pipe (LPP) system is a shallow, pressure-dosed soil absorption system. LPP systems were developed as an alternative to conventional soil absorption systems to eliminate problems such as clogging of the soil from localized overloading, mechanical sealing of the soil trench during construction, anaerobic conditions due to continuous saturation, and a perched seasonal water table. The LPP system uses several design features to overcome site challenges including: shallow placement, narrow trenches, pressure-dosing with uniform distribution of the effluent, design based on loading, resting and re-aeration between doses. The main components of a LPP system are a septic tank or an aerobic unit, a dosing chamber (a submersible effluent pump, float controls, a high water alarm, and a supply manifold), and small diameter distribution laterals with small perforations (holes). The septic tank is where large solids are removed and primary treatment occurs. Partially clarified effluent then flows by gravity from the tank to a pumping chamber, where it is stored until it reaches the level of the upper float control, which activates the pump with each dose providing 3 to10 times the lateral pipe volume. The level controls can be set for a specific pumping sequence, or timed dosing, which allows timed breaks between doses and increased time for the soil to absorb the effluent under less saturated conditions. Demand dosed pump sequences deliver effluent based on demand. The pump turns off when the effluent level falls to the level of the lower float control. The pumping chamber is usually sized to provide excess storage of at least one day's capacity in case there is a power failure or pump malfunction.
Shallow placement of trenches in LPP installations promotes evapotranspiration and enhances growth of bacteria. Improved distribution through pressurized laterals disperses the effluent more uniformly throughout the entire drain field area. Periodic dosing and resting cycles enhance and encourage aerobic conditions in the soil. Shallow, narrow trenches reduce site disturbances and thereby minimize soil compaction and loss of permeability. LPPs allow placement of the drain field area upslope of the home site. The problem of peak flows associated with gravity-fed conventional septic systems is overcome.
Cost is higher than those of conventional systems due to specialized construction and possible engineering design fees. In some cases, the suitability could be limited by the soils, perched seasonal water table, slope, and space characteristics of the location. A potential exists for clogging of holes or laterals by solids or roots.
Operation & Maintenance
A properly designed and installed LPP system requires very little ongoing maintenance. Regular pumping of the septic tank and pumping chamber (every 2-5 years) at a cost of $100-$200 annually. Some solids may accumulate at the end of the lateral lines, which should be flushed out once a year. Turn-ups installed at the distal ends of laterals facilitate this process. Annual service contract, if required, between $100-$300. Check for ponding in distribution area, surface water infiltration, and the vegetative cover for erosion. Ensure standing water is diverted away from system. Review and document event counters, time meters, flow meters, and alarm conditions when present.
Spray irrigation is an efficient way to nourish plants and apply reclaimed wastewater to the land; however in order to protect public health and reduce odors, the wastewater must be treated to a very high level before being used in this type of system. Treatment is achieved through the use of septic tanks through mechanical filtration, pretreatment, and disinfection systems. After treatment, filtration, and disinfection, the effluent is sent under pressure through the mains and lines of the spray distribution system at pre-set times and rates. Vegetation and soil microorganisms metabolize most nutrients and organic compounds in the wastewater during percolation through the first several inches of soil. The cleaned water is then absorbed by deep-rooted vegetation, or it passes through the soil to the ground water. The irrigated area must be vegetated and landscaped to minimize runoff and erosion. When properly designed and installed, most spray systems provide uniform distribution to plants and eliminate discharge to streams. Spray irrigation is sometimes permitted as an alternative wastewater disposal method for sites previously considered unsuitable for onsite systems such as difficult sites with slowly permeable soils, with seasonal perched water or shallow ground water or bedrock, or complex topographies.
Because irrigation systems are designed to deliver wastewater slowly at rates beneficial to vegetation, and because the wastewater is applied either to the ground surface or at shallow depths, irrigation may be permitted on certain sites with high bedrock, perched seasonal water tables or shallow groundwater, or slowly permeable soils. Irrigation systems also can be designed to accommodate sites with complex terrains. Spray irrigation saves on potable water because the wastewater is used for irrigation. Above-ground spray system components are easier to inspect, control, and service than subsurface drip irrigation components.
Cost is higher than those of conventional systems. Temperature factors in Ohio may preclude the use of spray irrigation during certain times of the year. The wastewater may need to be stored in holding tanks during the coldest period of the year, because plant growth is limited and the nitrogen in effluent discharged during this time will be mineralized and unavailable for plant uptake. Sites near surface water or shallow groundwater often are restricted, especially when these are used as drinking water sources. Depending on the level of treatment, spray systems generate aerosols, which can pose a threat to public health; therefore, regulations may require large separation distances or buffer zones that make spray systems inappropriate for small lots. Minimum setbacks of as much as 50 feet of forested buffer or 150 to 500 feet from neighboring residences and water sources are not unusual.
Operation & Maintenance
Recommended – Monthly: walk over spray area and examine for ponding of effluent, bad odors, damage to spray heads, surfacing liquids, vegetation problems, surface soil collapse. Quarterly: Conducted by a qualified operator - proper spray sequence, proper pump function, proper liquid levels. Biannually: erosion, storage unit capacity. Annually: effluent sampling by a certified laboratory, test water supplied to spray irrigation area for pH, total Kjeldahl nitrogen, fecal coliform bacteria, chlorine, TSS, and BOD. A management contract with an approved operator or operations firm is also suggested. O&M estimated at $300-$400 annually but may be less depending on the type of pretreatment used.
Drip Distribution Systems are installed very shallow in the soil, at the surface of the ground or on top of a bed of sand, depending on the specific limiting conditions on the property. These systems are pressurized to ensure even distribution of wastewater into the soil. They utilize small diameter tubing with pressure compensating emitters to apply wastewater uniformly over an infiltration surface. Drip Distribution systems are typically split into at least two zones and works on the principle of timed micro-dosing to maintain aerobic conditions in the soil. Timed micro-dosing applies effluent to the soil at uniform intervals throughout a 24-hour period, which allows for improved wastewater treatment. When properly sited, designed, installed and operated, drip systems can help overcome the typical problems associated with uneven wastewater distribution which often result in the surfacing of wastewater in the distribution field, sewage odors and other nuisance conditions.
Treats sewage and distributes the effluent in smaller doses. These systems can be installed on wooded lots and challenging terrains. Due to the micro-timed dosing of this system this would lessen the likelihood of failure and creating a public health nuisance. The ability to split the soil distribution component into two or more zones allows the use of multiple smaller suitable areas on a lot, thus increasing its probability of being a build able lot.
These systems require an on-going service contract and are one of the more expensive on-site systems.
Operation & Maintenance
Regular pumping of the septic tank (every 2-5 years) at a cost of approximately $50-100 per year. Most systems require inspection at least twice a yr up to four times a year to monitor flow, system performance, perform system flushing depending on the system configuration. Average Maintenance cost of Drip Distribution Service contract is $350.00 per year.
Single Pass Intermittent Sand Filter/Bioreactor
Single Pass Intermittent Sand Filters (ISFs) are fixed-film biological treatment units. In ISFs, wastewater is applied in intermittent doses to a bed of sand or other suitable media. The wastewater first receives primary treatment in a septic tank or an aerobic treatment unit, and then is pumped from a screened vault in the septic tank or separate dosing tank to the water-tight lined sand bed or module where it is evenly distributed over the top of the sand filter bed. The design can also use a series of siphons in lieu of a dosing tank where the use of electricity is not feasible due to system location or social and religious beliefs. Media alternative to sand has been utilized in some designs. As the wastewater passes through the sand filter, treatment is accomplished by physical, chemical and biological actions. The main treatment is accomplished by the microorganisms attached to the filter media. The treated wastewater is collected in underdrains at the bottom of the sand filter and is then transported to the soil absorption system. ISFs are designed such that the pretreated wastewater passes through the sand filter bed once. With proper design and media sizing ISF’s achieve reductions in biochemical oxygen demand (BOD), total suspended solids (TSS), and fecal coliform.
Intermittent Sand Filters (ISFs) are simple in design and relatively passive to operate because the fixed-film process is very stable and few mechanical components are used. High flow variations after equalization in a septic tank are not a problem because the residual peaks and valleys are absorbed in the pressurization tank or in the last compartment of the preceding septic tank. A malfunctioning ISF clogs and backs up rather than release poorly treated effluent. ISFs tolerate fluctuations in flow, especially changes from negligible flow to very high flows thus are appropriate for seasonal use. Construction costs for ISFs are moderately low, and the labor is mostly manual.
Cost is somewhat higher than those of conventional systems due to cost of sand media, pump(s) and possible engineering design fees. The land area required may be a limiting factor. Regular (but minimal) maintenance is required. If appropriate filter media are not available locally, costs could be higher. Premature clogging of the filter media can result from exceeding design loading rates.
Operation & Maintenance
Intermittent Sand filters require annual maintenance, although the complexity of maintenance is generally minimal. The majority of operation and maintenance involves monitoring the influent and effluent and checking the dosing equipment periodically. Pumps and controls should be checked every 3 months, and the septic tank or aerobic unit should be checked for sludge and scum buildup and pumped as needed. In addition, vegetative cover should be checked for erosion, settling, or any evidence of seepage. All surface water should be diverted away from the system and should check for any ponding in distribution area. Monitor the dose volume and operating pressures. Regular pumping of the septic tank (every 2-5 years) at a cost of $100-$200 annually. An annual service contract estimated to cost $150-$300.
Operation and Maintenance of a Household Sewage Treatment System
Owning a household sewage treatment system is a big financial investment in your property. It is a mini- wastewater treatment plant right in your yard. Proper operation and maintenance of your system is very important to make sure it operates effectively and efficiently for many years and does not create nuisance conditions or contaminate water resources.
Septic Systems 101 recording This video is basic operation and maintenance of septic systems.
Know Your System
- Learn about your household sewage system. Obtain and keep a sketch of the system with a detailed record of repairs, pumping, inspections, and other maintenance activities.
- Have your household sewage system inspected and maintained regularly.
- Keep your septic tank cover accessible for inspection and cleaning. Install risers if necessary.
- Call a registered sewage system contractor or your local health department if you experience problems or if there are any signs of system failure.
- Always obtain required permits when making or allowing repairs to your system.
- Divert sources of water, like roof drains, footer drains, and sump pumps away from the system. Excess water saturates the soil leading to system failure.
- Keep a good vegetative cover over the system in order to help remove excess water and prevent erosion.
- Do Not allow anyone to drive or park anything over any part of the septic system.
- Never dig or build anything over your system. This includes hard surfaces such as concrete or asphalt.
- Conserve water to avoid overloading the system. Promptly repair leaky faucets or toilets, and install water saving devices.
- Don’t use septic tank additives. These products usually do not help and can be harmful to the operation of your system.
- Eliminate or reduce the use of a garbage disposal. The additional waste produced by a garbage disposal will lead to extra maintenance requirements.
- Don’t use you toilet or disposal as a trash can. Coffee grounds, dental floss, disposable diapers, kitty litter, sanitary napkins, tampons, cigarette butts, condoms, fat, grease, oil, automotive fluids and paper towels should never be disposed of in the system.
- Never pour chemicals or cleaners such as paints, varnishes, thinners and pesticides down the drain/toilet. Harsh chemicals can kill beneficial bacteria that treat wastewater.
- Never climb down into a septic tank. The natural treatment process in septic tanks produces toxic gases that can kill.
Pump Your Tank(s)
Most households that are not served by public sewers depend on a household sewage system to collect and treat wastewater. Your septic tank is the primary treatment device that collects and settles wastewater from your home. Your household sewage system represents a significant investment that you will want to protect. Failed sewage systems are costly to replace and proper ongoing maintenance can extend their life. Preventive maintenance will not only protect your investment, but will also protect the environment and the public health.
Pumping the septic tank removes the build-up of sediments that reduces the performance of the tank that would lead to failure of the absorption field. · The septic tank holds the wastewater in the tank long enough for solids and liquids to separate. The wastewater forms three layers inside the tank. Sediments lighter than water (such as greases and oils) float to the top forming a layer of scum. Sediments heavier than water settle at the bottom of the tank forming a layer of sludge. This leaves a middle layer of partially clarified wastewater. The layers of sludge and scum remain in the septic tank where bacteria found naturally in the wastewater work to break the solids down. The sludge and scum that cannot be broken down are retained in the tank until the tank is pumped.
Inspect or have your septic tank inspected once each year. Ensure that the buildup of sludge and scum does not limit the ability to settle solids. Check to ensure the baffles or tees are in good condition. If the tank has an effluent filter, have it checked and cleaned if needed. Check for root intrusion or evidence of ground or surface water entering the tank.
Many septic tank owners believe that if they haven’t had any problems, they don’t need to have their septic tanks pumped. If the solids are not removed, eventually they will flow out of the tank damaging the rest of the system.
- Always use a septage hauler registered by your local health department.
- More frequent pumping is necessary if a garbage disposal is used.
- Biological and chemical additives are not necessary, may cause harm to the system, and do not eliminate the need for pumping the septic tank.