Wastewater management systems come in different sizes and forms; ranging from the basic conventional septic tank drainfield systems, to a complex nutrient reduction and disinfection treatment and subsurface drip system or an above ground spray dispersal system; for either a single home or for a group of homes or a business. We now have come a long way from using outhouses or cesspools or even a conventional septic drainfield system in areas that are not served by a centralized wastewater management system. There are proprietary treatment and disposal systems available in the market that can treat and dispose wastewater in an environmentally sound manner on sites that have challenging soil and site conditions normally not suitable for operating a conventional septic drainfield system (i.e. no "perc" land). Today it is possible to develop a wastewater treatment and disposal system that can address both the customer's need (i.e., quantity and quality of sewage to be managed) and environmental protection requirements (i.e., adequate assimilation of pollutants) for any site.
Technologies are also available for remote monitoring of the operation of complex wastewater systems. Just a few years ago, such options were not available for managing wastewater at small scale. Now communities have a number of options available for managing wastewater in a cost-effective and environmentally sound manner. Selecting an appropriate option is a challenge from both technical and socioeconomical points of view. Quite often a debate on selection of wastewater systems gets off-track and issues not related to wastewater such as good soil/bad soil, zoning growth, etc. get in the way of the planning process. During the planning phase of a wastewater system in any community, the focus should be on three important issues: the wastewater (quantity and quality); the needs of the citizens in terms of the current and future requirements; and the environment that must be protected from the wastewater.
The term "Integrated Planning" here means planning activities using ALL the available options/tools for doing something, in this case, managing wastewater. The term also applies to all of the activities necessary for adequate management of wastewater: collection, treatment, disposal of effluent; and treatment and disposal of residual solids (septage or sludge). The term "On-Site Systems" used in this paper means treatment of wastewater and disposal of treated wastewater (effluent) into environment primarily via subsurface disposal ore recycling systems, on a relatively small scale (less than one million gallons per day). This paper presents information on currently available on-site technologies for managing wastewater; discusses operation and maintenance infrastructure requirements for such technologies; and presents thoughts on what is needed in terms of regulatory reform in order for communities to effectively incorporate the use of on-site systems during the integrated planning of a wastewater management program.
ON-SITE VERSUS CENTRALIZED WASTEWATER SYSTEMS
Three basic components of any wastewater system are collection, treatment, and disposal. Out of these three components, collection is the least important for treatment and disposal of wastewater. Common sense says the Pipes Don't Treat Sewage! However, majority of cost (some times, more than 60% of total cost) in a typical centralized system is allocated to collection system, i.e., to collect and to bring millions of gallons of wastewater to a central location for treatment and disposal. Specially, in a small community where the total quantity of wastewater generated is less than one million gallons per day, the cost of just collecting sewage could be more than $20,000 per connection. On-site systems are the wastewater management systems that can be used for treatment and disposal of wastewater at or near the place where wastewater is generated. With the availability of small-scale treatment and disposal technologies, collection of large quantity of wastewater is not necessary and the collection system can be minimized while planning for a wastewater system for areas that are not currently served by a centralized wastewater system.
Two major differences between the on-site systems and conventional centralized systems are the extent of collection system and type of disposal system. Typical on-site system could serve a single residence or a non-residential entity (such as a school, office building, restaurant, etc.) or a small group of individual facilities with a relatively small collection system. Primary objective of the on-site system should be to keep the collection component of the total wastewater system as small as possible, and to focus mainly on necessary treatment and disposal of wastewater. Also, a typical on-site systems used a soil based (not soil dependent) sub-surface disposal system (also known as non-point source discharge), as opposed to a typical centralized system that uses surface water discharge (also known as point source discharge) of treated effluent. Discharges in surface water is also an option for small-scale systems, however, it is typically not necessary and it should be used only when there is no land available for subsurface disposal (e.g., a house on a lake with no back or front yard). As far as possible, small on-site system should consider non-point source discharge option for final disposal to minimize the adverse environmental impact of nutrient. Other options for managing treated effluent at small scale includes recycling and reuse, thus minimizing the need for discharge. Concepts that would allow recycling/reuse of treated effluent include irrigation (subsurface or surface drip or above ground spray), evapo-transpiration or greenhouse (plant uptake of moisture and nutrient), the use of effluent for non- potable purpose such as flushing toilets, and use of composting toilets with graywater irrigation system.
At a small community level, the decision makers normally are not aware of all the options available for on-site wastewater management. There is a wide spread misunderstanding that the only way wastewater may be managed in the area that is not served by a central sewer system is by using a "septic system" (i.e., a septic tank gravity drainfield system). The use of conventional septic system is heavily dependent upon soil and site characteristics. There is normally a long list of soil and site criteria presented in the septic system regulations (either state or local regulations) that specify what site and soil conditions are necessary for the approval of a site for installing a septic system. When such conditions are not present on a lot or in an area, that lot or that area is normally declared unsuitable for wastewater system (i.e., no "perc" land), and thus not inhabitable or not buildable even for non- residential purposes, unless and until a centralized sewer system (sewer and treatment plant) require large quantity of wastewater in order for it to be cost-effective, and hence normally not considered for small scale operation such as a small shopping center or a small sub-division. Thus, lack of exposure to and lack of understanding of a variety of small scale on-site wastewater systems (also called "alternative" on-site systems) have led to misuse (or abuse) of the on-site systems regulations as growth control or defactozoning tools. The decision makers in small communities should know the fact that the use of on-site systems, although most of the time soil based, is not soil dependent or limited. And, soil and site conditions that are not suitable for one type of system such as a septic drainfield are suitable for a number of other on-site wastewater systems currently available.
So, how to evaluate wastewater management options for a small
community? There are five important factors one needs to
consider while planning for a wastewater system:
For each of these factors there are several sub-factors that must be considered during the planning phase. An appropriate (not an alternative or a conventional) wastewater system that meets the current demands for wastewater management, that is expandable to meet the future demands, that is affordable from both capital and operational cost, and that an protect the receiving environment (i.e, the environment into which the effluent is discharged) from bacteriological and nutrient pollution can be selected by adequately addressing all of the above mentioned five factors. On the other hand, a system that is selected without adequately addressing one more of these factors will not serve the community in a satisfactory manner.
WASTEWATER & RECEIVING ENVIRONMENT
Whether you are considering a centralized multi-million gallons
per day wastewater system or a single family home wastewater
system, it is important to know that you are dealing with
wastewater, and you must know the quantity and quality of
wastewater that needs to be managed along with the variability
(daily or seasonal) in wastewater quantity and quality. For a
large scale system, a good understanding of wastewater quantity,
quality and variability is developed at the beginning stage.
However, sometimes very little or no attention is given to this
very important factor for an on-site system. There is a great
deal of difference between the quality (i.e., the strength) of
residential wastewater and restaurant wastewater. Many times, an
on-site wastewater system for a restaurant is specified and
installed following the requirements of a residential septic
system (septic regulations). The result is not pretty! The
factors to consider in order to adequately understand the
wastewater that needs to be managed using on-site systems
Knowing the wastewater is just the beginning of the planning phase. The second important item to understand is the Receiving Environment (R.E.), which is the environment into which the treated wastewater (effluent) will be released via a disposal system. The disposal system can be a trench or a bed with or without gravel, or a dispersal or recycling system such as drip or spray irrigation, or a reuse or zero/minimum discharge system such as an evapo-transpiration bed, greenhouse system along with reuse for non-potable purposes, or point-source discharge into surface water bodies such as an out-fall into a creek, river, or ocean. One needs to understand the "carrying capacity" of the R.E. in order to determine how much treatment is necessary before releasing the effluent into the environment. In my opinion, carrying capacity is the ability of the R.E. to assimilate pollutants without causing any long-term degradation in the environmental quality. Use of such a measure is common for establishing discharge standards (i.e., NPDES permits) for large wastewater treatment plants. Objective of any wastewater management system must be to release the treated wastewater into the R.E. in a manner that allows quick and effective assimilation of the pollutants without exceeding the carrying capacity of the R.E., thus minimizing the degradation of the quality of the R.E.
How to determine the carrying capacity of the R.E., or even how to determine what the R.E. is for an on-site system, is a scientific and technical challenge. The debate over this issue can go on for ever. Meanwhile for no real reasons some communities are asked to spend enormous amount of public funds to install new sewer lines or to extend existing sewer systems in an area that have either failing septic systems or have no systems. Currently, assessment of carrying capacity for onsite system is done primarily by subjective evaluation of soil such as its texture, structure color, etc. Use of "perc" test is still quite common to evaluate site and to determine the size of a drainfield. Some states are now moving towards the use of other techniques to conduct objective evaluation, such as conducting an Infiltration Test (Amoozemeter), or even conducting a test that simulates operation of a small trench (Orenco Infiltration Test Kit) in an area where the actual trench would later be installed and dosed in a manner the simulation was conducted. Use of a real infiltration test is a better way of determining site's ability to move water i.e., soil's permeability/conductivity than just relying on the subjective evaluation of soil.
ON-SITE WASTEWATER MANAGEMENT SYSTEMS
On-site wastewater management systems are technologies or tools that can adequately treat and dispose or recycle wastewater in an environmentally sound manner in areas that are not served by a centralized wastewater treatment and disposal system. As mentioned earlier, three components of any wastewater management system are collection, treatment, and disposal. Out of these three components, treatment and disposal are more important for on-site wastewater management than the collection. Generally, in small communities, houses are spread-out and the density is quite low, which makes the use of on-site system for an individual home or at most a group of five homes quite a cost-effective option. At present, a conventional septic tank drainfield system is the most commonly used onsite wastewater management system for an individual home. According to the 1990 census report, there are more than 25 million homes in the nation that are served by such a system. Today, there is a wide spectrum of on-site systems available for effective treatment and disposal of wastewater for an individual home or a group of homes or for non-residential structures in the area not served by a centralized wastewater system.
A septic system (one of the most basic form of an on-site system) is widely accepted as a conventional, "low tech", and inexpensive wastewater treatment and disposal system for areas that are not served by sewer. A typical septic tank system relies primarily on soil and the biomat for the further treatment of primary effluent. A septic tank that is not adequately maintained, i.e., not pumped out at a correct frequency (whatever that may be!), will discharge untreated sewage into drainfield, thus relying on soil and the biomat for the complete treatment of wastewater (a very tall order!). A list of soil parameters and site conditions are normally presented in the regulations (state or local) that determines the suitability of a site for operation of a conventional septic drainfield. Traditionally, subjective evaluation of soil (texture, structure, color, horizons, gray mottles, etc.) is conducted on a site that is proposed for installation of a septic system. The result of such an evaluation is either an approval of the site for a certain size of septic drainfield (that normally translates to a certain number of bedrooms in a home or a certain number of seats in a restaurant!) or a rejection of the site for installation of a septic drainfield (that normally translates to condemnation of the lot for any activity that would generate wastewater!). Such a pass/fail approach for deciding whether the site is good for an on-site system or not is wrong and serverno real purpose in the current time, except may be to use the wastewater as a defacto zoning tool, in communities where a centralized sewer system is not available. A better approach is to develop a regulatory system in which an appropriate wastewater system gets installed and operated in an environmentally sound manner for any site that is proposed for residential or commercial development. Only way a proposed site should be declared unsuitable for development is when the cost associated with the adequate management of wastewater is not affordable to the developer. In my opinion, there is a system available that is suitable for managing wastewater in an environmentally sound manner for any site.
Raw wastewater or septic tank effluent can be treated to either
secondary or tertiary level using a variety of treatment systems
currently available in the market. Treatment technologies
can be grouped into the following categories:
Aerobic treatment units (ATUs) offer an option to septic tanks, and they can treat raw wastewater to a secondary treatment standards, mainly lower organic pollutants in the effluent. There are a number of pre-engineered ATUs currently available in the market, and they are generally used for sites that are declared unsuitable for septic drainfield system based on soil and site evaluation. Typically, the effluent from such ATUs after further polishing treatment and disinfection is allowed to be discharged into surface water or on the ground resulting into a point-source discharge. Subsurface disposal of secondary quality effluent is technically possible on sites that are not suitable for primary quality (septic tank) effluent. Actually, subsurface dispersal of secondary effluent using concepts such as a filterbed or a drip system will reduce the impact on the R.E. compared to surface discharge. However, when not adequately operated and maintained, any ATUs, or for that matter, even a septic tank will discharge untreated sewage into the R.E.
Media filters are primarily used for treatment of the septic tank effluent and sometimes used for polishing of ATUs' effluent. Sandfilters (single pass or recirculating) are the most commonly used media filter. But now the use of the types of media such as peat, synthetic foam, or textile media has been evaluated for treating primary quality effluent (septic tank effluent) to a better than secondary quality effluent. Just like ATUs, you now have access to pre-engineered, pre-packaged media filter that can be installed easily in the filed and used for advanced treatment of septic tank effluent for individual homes. The performance of any media filter will depend on the quality of media, distribution system for spreading septic tank effluent on top of the media, quality and maintenance of septic tank (watertight tanks, use of effluent filter, regular pumping, etc.), and adequate ventilation to maintain aerobic condition in the media filter itself. Depending on the type of media used, one may need to change the media after a certain number of years. Media filters are demonstrated to be very effective for reducing organic and bacteriological contaminants form septic tank effluent. They can also convert most of the nitrogen to nitrate form (i.e., nitrification), thus maximizing the potential for plant-uptake if/when the effluent is adequately dispersed into shallow root-zone using shallow trench or drip dispersal system.
Use of natural system such as a wetland for treating septic tank effluent for a single family home or a community scale system has been demonstrate in some part of the country (mainly in southern states). However, performance of wetland type systems is quite dependent on the climate and it is practically impossible to operate such a system to obtain uniform quality of effluent consistently. Use of greenhouse type of system i.e., wetland operated in a controlled environment can lower or eliminate the dependence on climatic conditions and offer a reliable treatment mechanism that can produce high quality effluent on a consistent basis. Under certain conditions, greenhouse or evapo- transpiration beds can be used for lowering or eliminating discharge of effluent into the R.E.; by using plant up-tank and evaporation as the primary mechanisms for assimilating effluent into the environment. Most of the times, natural systems can be used in a cost-effective manner for further treatment of secondary quality effluent (discharge from ATUs or media filters) to reduce the impact form nutrient and bacteriological pollutants on the R.E. In general, use of natural systems for treating primary effluent should be avoided!
Use of water-less toilets such as composting or incinerating toilets can reduce the quantity of wastewater generated from a facility and can also change the quality of wastewater. However, one needs to deal with the residual products from such a facility (either composted material or ash) for final disposal by using (recycling) compost in the yard as a fertilizer or by sending the ash to the landfill. The remaining wastewater from the facility is called "graywater" and it may be treated adequately be using natural systems such as a wetland. Typical, pollutant load in the graywater is more than that in the effluent from a well maintained media filter or an aerobic treatment unit. Hence, adequate treatment and disposal of graywater must not be overlooked. Use of water-less toilet is quite adequate for remote areas that are non-residential, e.g., golf courses or rest areas in parks, etc. where both access to water and wastewater facility is costly.
Most likely an onsite wastewater treatment system will need a
mechanism for the discharge of treated effluent. As noted
earlier, subsurface disposal (non-point source discharge) is the
primary mechanism used for disposing effluent from onsite
systems. Disposal technologies available for onsite
systems can be grouped as following:
since most of the disposal technologies listed above use soil as a receiving media for the partially treated effluent, soil evaluation has been an integral part of the onsite wastewater business. With the availability of a variety of treatment systems as discussed above, the use of soil for treatment of effluent is NOT necessary. Soil and site's ability to effectively absorb and move (transmit) the effluent away from the disposal site with the minimum movement of pollutants is the only issue of concern when highly treated effluent (better than secondary or tertiary quality) is discharged into subsurface disposal system. Installation of at or above-grade filterbed, drip, spray, or minimum or zero discharge system can be achieved on almost any site when adequate square footage of space is available. Performance of such systems is not dependent on type or depth or color of soil present at the site. Thus, when planning for a wastewater system for a community, the approach one should take is to find an adequate treatment and disposal technologies for the given soil and site conditions, and not to look for soil and site conditions that are necessary for a conventional septic system. In order for small communities to be able to consider an appropriate on-site systems for managing wastewater, two important things needs to happen: establishment of an operation & maintenance infrastructure (utility) that can take the responsibilities of operation and maintenance of on-site wastewater management systems, and a thorough change in the regulatory system that governs the use of on-site systems in the unsewered area.
OPERATION & MAINTENANCE INFRASTRUCTURE
Any wastewater system, on-site or centralized, needs adequate operation and maintenance in order for it function properly and to minimize adverse impact on the environment. Large scale centralized wastewater treatment plants are operated by adequately trained and licensed operators, who monitor the performance of the treatment system on a continuous basis and perform necessary scheduled and emergency maintenance on the systems. Such a professional service is also needed for small scale wastewater system. A conventional septic system is generally maintained based on operational inconvenience to homeowner, such as sewage backup in the house or sometime sewage surfacing on top of the drainfield. Maintenance based on treatment requirements i.e., quality of effluent or impact on environment, is rare if not non-existent. The criteria used for site selection and sizing of a conventional drainfield try to account for the lack of regular maintenance, by using a conventional drainfield like most conservative estimates of soil's ability to treat septic tank effluent. Such conservatism in site selection criteria and sizing of the system does not always offer the necessary environmental protection from on-site systems.
With the availability of a variety of advanced treatment systems, the conservatism used for the site selection criteria and for the sizing criteria of an on-site system CAN be replaced with an infrastructure that offers professional operation and maintenance of such system. Of course, the on-site systems generally are scattered over a large area and hence it's a challenge to offer operation and maintenance services in a cost-effective manner. However, with the advances in the area of remote monitoring systems, it is now possible to keep a constant watch on the operation of a large number of scattered on-site systems from a central location. Most of the aerobic treatment units and media filters use a pump and/or a blower for the treatment. Performance of such systems, i.e., the effluent quality, is mainly dependent upon the performance of the component that operates the system (pump, blower, etc.). with a control panel that is designed to operate the components as well as to send electronic signal about the status of these components to a centralized computer system on a routine basis or to the operators in emergency, it is now possible to operate a large number of systems professionally on a cost-effective basis.
Public acceptance of on-site systems can be enhanced only when such systems offer the wastewater services that are just like a centralized sewer system. For a typical homeowner, it's important that sewage does not backup in the house, there are no "sewage alarms" to worry about, there is no odor from the sewage system, and the sewage system does not interfere with the expansion or resale of the property. When an on-site system can offer such operational comfort to the citizens and offer environmental protection guarantee to the regulators, their use can be considered as "equivalent" to a centralized sewer system. We now have the technologies that can achieve both of these requirements in a cost-effective manner. However, we are still in an infancy stage of the development of an infrastructure similar to a utility that can make these technologies available to the citizens on a large scale basis; and we are also in the similar stage in terms of the regulations that govern the use of on-site systems by the citizens.
WHAT ABOUT REGULATIONS?
There is a tremendous need for reforming the current regulatory system that oversees the implementation of on-site systems. The use of on-site wastewater systems is typically regulated by the health departments at a state or a local level with main focus on public health protection from the sewage. Majority of the regulations currently in place for on-site systems in the county agree based on a premise that no one will maintain the on-site system and so the only way to assure necessary safety from the operation of such systems is to develop very restrictive soil/site criteria for evaluating the suitability of a proposed site and add all the safety factors into sizing criteria for the system. Assumption here is that if a system is installed deep in the ground on a relatively large lot with deep permeable soil using inflated sizing criteria, it will at least work operationally for a few decades (i.e., no back-up in the house or no sewage on the ground). Such a philosophy completely ignores the facts that the soil is not the only medium that can treat wastewater; wastewater can be adequately treated outside the soil on a permanent basis; and such treatment systems can be operated and maintained by professional operators. The use of all available on-site treatment and disposal technologies in a cost- effective manner will require drastic changes in the existing paradigm and a new way of regulating on-site systems.
Until now on-site system regulations are written primarily with the focus on developing "prescription" for selecting a site and sizing a system based on presumed flow data and loading rates that are somehow related to soil permeability or texture classification (prescriptive regulations). Most of the times the regulations do not adequately address the first important parameter that should be addressed for any wastewater system, i.e., the wastewater, either from quantity point of view or from a quality point of view. Under such a regulatory framework, more than 90% of time an resources are spent in the pre-installation stage, i.e., soil/site evaluation & re- evaluation, engineering design & re-design, regulatory review & re-review of the design, argument about the flow numbers and loading rates, and issuance of a construction permit of r the system. Very little time and resources are spent on the quality assurance of the components (such as septic tank!), or on the quality assurance of installation of the system. Under the current regulatory system in most of the states, once the system is installed, a life-long permanent operating permit is issued that allows the owner to use the system without having to worry about adequate operation and maintenance of the system.
a "performance" based regulatory system, similar to the one used for the large scale wastewater treatment systems, is needed for the on-site system. Under such a system, soil and site conditions may be studied, only if necessary, to determine which on-site system is suitable for that site or to determine if the site is suitable for the proposed on-site system. Under the performance based regulatory system, soil and site evaluation will not be done to determine if the site is suitable for an on- site system, i.e., there will not be any pass/fail site criteria for the use of on-site systems. All the sites are suitable for some types of on-site wastewater management systems, it's just the question of defining the performance requirements and finding a system that will meet those requirements. Performance requirements can be specified in a simple manner, indicating the quality of effluent that is necessary prior to discharge and the quality of environment that must be maintained on and around the disposal system. Regulatory focus can then be shifted to making sure that the specified performance standards are achieved, and if needed, the adjustments to the system's operation are done in a timely manner to protect the public health and the environment.
The intent of both the prescriptive and performance based regulations for on-site system is the same, i.e., to protect the public health and the environment from the use of on-site wastewater systems by requiring a safe, adequate, and proper system for all the sites that need a wastewater system. However, the regulatory process and the role of regulators will be quite different under these two types of regulations. Currently, the role of on-site systems regulators and the use of the regulatory resources are over-emphasized up front, i.e., in pre-installation phase of the process. Under the performance based regulatory system, regulatory resources can be allocated adequately for both the pre and post-installation phase; and the regulatory intent can be achieved without interfering with the local zoning or growth issues.
Thus, we need to develop a regulatory system from the ground up that will allow the wastewater professionals to offer much needed wastewater services to those citizens who do not have access to or can't afford a centralized sewer system. Developing such a regulatory system will also allow the decision makers to effectively integrate the use of available onsite wastewater systems during the planning phase of wastewater infrastructure in their communities.
COST OF MANAGING WASTEWATER
Appropriate treatment and disposal of wastewater is NOT cheap, at the same time it does not have to be outrageously expensive. With adequate planning and value-added engineering, it is possible to offer affordable wastewater systems to every citizen in a state. Both, the capital and the operation and maintenance cost of a wastewater system must be considered in the planning stage. I personally think that on-site systems when adequately evaluated can lower both the capital and the operational cost. With the tools available today, an on-site system that can treat wastewater to tertiary standards and dispose the effluent with no adverse impact on the environment or public health can be installed for less than $15,000 for a typical residential home, and can be effectively operated at the cost of less than $4 per 1000 gallons of wastewater treated. However, many changes need to occur in the current regulatory framework and other aspects of both public and private sector before a widespread use of appropriate on-site systems become the reality. Some of the needed changes have started occurring and I am confident that within the next few years, communities will have better access to the use of on-site wastewater systems.
Vera MacConnell, Research Technician, I on November 5, 1998.
Last Updated on 3/28/05 by Roland O. Coburn, Research Tech. I
Please address any questions to Dr. David Lindbo, Assistant Professor/Extension Specialist or visit his homepage.