Wastewater Treatment in the 21st Century: Technology, Operation, Management, and Regulatory Issues.
The concept of wastewater management started on a small scale, focusing mainly on disposal of human waste and on systems such as privies. In the course of the 20th century the focus shifted to treatment of wastewater prior to disposal, with large-scale, pipe-and-plant surface-water discharge systems in densely populated areas and millions of septic systems in rural areas. During the coming century the wastewater industry will move toward on-site decentralized systems. The prime reason for this trend is that nonseptic on-site systems offer cost-effective environmental and public health protection from wastewater. Small wastewater systems also offer advantages such as recycling and reuse of effluent, a limiting effect on the movement of pollutants in the environment, and safety from short-term operational problems. This paper provides information on a variety of small systems currently available and expresses an opinion about the need for management infrastructure and regulatory reform to make possible the wide spread use of such systems.
Editor's note: Through NEHA's long-standing relationship with NSF International, NEHA was granted permission by NSF International to share with the Journal's readership various papers that were presented January 12-15, 2000, at the "NSF International Small Drinking Water and Wastewater Systems International Symposium and Technology Expo" in Phoenix, Arizona. This paper, "Wastewater Treatment in the 21st Century: Technology Operation, Management, and Regulatory Issues," is one of them.
It is important to note that these papers were screened by an NSF International advisory committee prior to their presentation at the conference, but they have not been peer reviewed by NEHA's Journal program for technical accuracy.
Because these papers contain useful and interesting ideas and information that may be either delayed or lost if the papers were sent through the Journal's normal peer review process, NEHA has decided to publish them as presented, with only minor editorial modifications.
We hope you look forward to more of these papers in future issues of the Journal!
As we prepare to enter the 21st century, it is time to evaluate our methods of on-site wastewater management. The evaluation should address not only the tools of the trade (i.e., on-site wastewater treatment and disposal technologies), but also the process in which the technologies are used (i.e., the operation and management of the systems and the regulatory framework). Advances in technologies for small-scale collection, treatment, and disposal, as well as the availability of remote monitoring systems, now make it possible to offer the most advanced wastewater treatment options in low-density areas at a cost lower than that of conventional large-scale pipe-and-plant systems. The reasons are as follows. Generally, in small communities, houses are spread out, and the density is low, which makes the use of an on-site system for an individual home or for a cluster of homes a cost-effective option. Wastewater management systems can be engineered to minimize the collection cost as far as possible, typically to le ss than 30 percent of the total cost, with currently available on-site wastewater treatment and dispersal technologies. Because there are now available a variety of pre-engineered, prepackaged treatment systems for small flows, it is not necessary to collect a large quantity of raw wastewater at one point for treatment. Thus, minimizing the collection network for raw or partially treated wastewater can minimize the total cost of any wastewater project in any small community, new or existing. The total cost includes the operation and maintenance costs for the expected life of the wastewater system.
For most of the 20th century, a standard septic-tank drainfield system has been the primary means of on-site wastewater management. Census data from 1990 estimate that more than 25 million homes in the country are not connected to a central wastewater system and use some form of on-site system, most likely a septic-tank drainfield system. Probably the first advance in this technology was the use of a pump to overcome gravity when a "suitable" drainfield site was at a higher elevation than the house. A conventional septic system uses soil to treat primary or raw wastewater discharged from a septic tank.
Research studies have documented how a drainfield works at a given point in time on a given site; the real impact millions of drainfields have on the environment and public health, however, is not adequately documented. Conservative rules for locating and sizing septic systems as specified in state or local health department regulations are the primary reason no major environmental or public health problems have been associated with the use of millions of septic systems so far. No one really knows what kind of treatment a subsurface drainfield actually achieves on a long-term basis. It is hard to collect effluent samples below a subsurface drainfield. Thus, it is not possible to monitor the performance of such a system. The performance of a septic drainfield system is taken for granted as long as conservative siting and design standards are followed during installation.
As it becomes clear that on-site systems will be used on a permanent basis and will be needed in areas not suitable for treating primary or raw sewage (i.e., land that does not percolate), we must look for systems that treat wastewater to secondary or higher quality before discharge. We also need site-assimilative systems for safe dispersal, recycling, or reuse of treated effluent. Finally, we need an infrastructure to operate and maintain small systems on a permanent basis, and we need a regulatory framework that allows people to manage on-site systems in a cost-effective and environmentally sound manner.
Wastewater can be managed in small quantities with a variety of technologies. Technologies are available for collection and treatment of raw wastewater, as well as for disposal, dispersal, recycling, or reuse of treated effluent. Since the small systems are typically spread out over a large area, day-today monitoring becomes a real challenge. Fortunately, we now have access to telemetry systems (i.e., remote monitoring), which can operate small systems and send the performance information to a central computer by telephone line or by other means of communication. Thus, the tools are available to manage wastewater on site in small quantities in an environmentally sound and cost-effective manner. Widescale use of these tools, however, is not possible, mainly because maintenance infrastructures are lacking and the regulatory framework is inadequate.
Total cost of wastewater systems, both the capital cost and the costs of permanent operation and maintenance, can be minimized with on-site technologies. The capital cost typically includes cost for collection, treatment, and disposal, along with the cost of engineering and construction management.
The main reason for collecting raw or partially treated wastewater from more than one structure is to reduce the cost of the treatment and disposal system. At the same time, a cost is associated with the installation and operation of the collection system itself. Thus, one needs to determine the optimum amount of collection system that results in the minimum total cost of the wastewater management system. Typically, in small communities, the housing density is low and variable. The downtown business district may have commercial structures very close to each other, while the residential neighborhoods may have houses on large lots. The total cost of the wastewater system can be minimized if a number of small treatment and disposal systems are used instead of a collection method that uses one treatment and disposal system for the entire community During the planning phase, one needs to analyze the costs of various options, starting with the bare minimum amount of collection to the use of a collection system for the entire community.
Wastewater may be collected in raw form, typically with a gravity or vacuum collection system, or it may be collected as effluent from a septic tank or grinder pump, typically with small-diameter pipe pressure or a gravity system. The Alternative Wastewater Collection Systems Manual, published by the U.S. Environmental Protection Agency (U.S. EPA) gives details on small-diameter gravity, pressure, and vacuum collection systems. It also compares these alternatives with the conventional collection approach of gravity sewer and pump stations. It is a challenge to wastewater engineers first to select an appropriate technology for collection and second to optimize the level of collection system such that the total cost of a project is minimized. Sometimes excessive collection infrastructure is viewed as an investment toward a future need for wastewater services. Such an approach could, however, easily lead to unnecessarily higher capital cost that may never be recovered if the expected demand does not materialize . Instead of spending resources for a collection system that may not be needed in the foreseeable future, small communities should address their current needs first and establish a management infrastructure--a utility--that can adequately address additional needs if they arise.
Alternative collection systems such as septic-tank effluent gravity systems (STEGs), septic-tank effluent pump systems (STEPs), grinder pumps (GPs), and vacuum systems typically use components that require routine operation and maintenance, just like pump stations in a conventional system. For example, the solids collected in septic tanks (interceptor tanks) may need to be removed, the pumps (effluent or grinder) may need to be replaced, screen pump vault or effluent filters may need to be cleaned, or the pneumatic valves used in vacuum sewers may need maintenance or replacement. Adequate access to such components must be possible at all times, and some type of monitoring tool must be used to watch the performance of pumps or other electromagnetic components and liquid levels in the tanks. All such services must be performed by a management entity that is responsible for operating the entire wastewater system. The cost of installing, operating, and maintaining the collection system should be weighed against the savings in treatment and disposal systems.
The most important objective of any wastewater system should be to treat the wastewater adequately before it is released, recycled, or reused. Thus, the treatment component of a wastewater system must be appropriately addressed and funded. The scientific principles of wastewater treatment are well researched and documented, and they are taught in engineering schools, A number of companies manufacture a variety of on-site systems that treat wastewater in small quantities, typically less than 1,000 gallons per day. New concepts and systems are being developed. Nevertheless, the vast majority of structures that are not connected to a central sewerage system today use a very simple and passive wastewater treatment system called a septic-tank drainfield system.
The septic-tank drainfield system has two components--a septic tank that separates heavy solids and light material from raw wastewater and a subsurface drainfield, which is a series of subsurface trenches. This system depends primarily on soil surrounding the trenches for treatment of the septictank effluent. Since septic-tank effluent--primary effluent--has high levels of organic matter, a bio-mat is formed at the soil and gravel interface in the trenches. The main idea behind the passive system is that a certain quantity and quality of unsaturated welldrained soil--along with the bio-mat-can treat septic-tank effluent to the degree necessary to protect groundwater or surface water present in the area. The soil acts as a medium and offers biophysical treatment of septictank effluent. Since the drainfield is installed underground, there is no mechanism for inspection or maintenance of this treatment system, nor is there an effective way of monitoring the effluent quality Performance of septic systems is take n for granted as long as certain predefined soil and site conditions are present on the site, the system is sized according to loading rates specified in the regulations, and the specified distances separate the system from sensitive areas. State or local health department regulations prescribe soil and site conditions, along with design standards necessary for use of septic systems, in terms of depth and type of suitable soil, permeability or percolation rate, and distance to surface water, groundwater, and other environmentally sensitive areas, Using these prescriptive regulations, a sanitarian or a licensed soil evaluator typically performs soil and site evaluations, and the proposed site is either accepted or rejected. Rejection of a site usually means the lot is condemned as far as habitable-building purposes go, even when it is good in all other ways for development. At the same time, acceptance of a site based just on soil and site characteristics should not be considered assurance of long-term environ mental protection.
The idea of treating wastewater to a secondary or better quality before discharging effluent into soil is drawing a lot of attention. This may be due to the fact that we are running out of sites that are considered "good" for septic systems, or it may be due to the realization that we can do better. Today, a number of pre-engineered, prepackaged small wastewater treatment systems allow subsurface dispersal of effluent on any site that limits the use of septic-tank effluent. These treatment systems also should be used for sites that are considered "good" for septic systems--just as it makes no sense to discharge primary effluent into surface water, so it also makes no sense to discharge primary effluent into the subsurface environment. With the availability of small on-site treatment systems, any site that has potential for a residential or a commercial building can have a wastewater system, provided the owner is willing to pay the costs associated with the engineering, installation, and operation of such a s ystem. When a connection to a central wastewater system is not available, a wastewater solution can be found for any area through the use of an adequate nonseptic on-site system.
Raw wastewater or septic-tank effluent can be treated to any of the following levels: secondary, advanced secondary (secondary treatment followed by disinfection), or tertiary (secondary treatment with significant nutrient reduction and disinfection). The treatment technologies can be grouped into five categories:
1. aerobic treatment units (ATUs) comprise the following technologies:
* suspended growth--flow-through or sequencing batch reactor,
* attached growth--trickling filter with forced aeration, and
2. media filters--single-pass or recirculating--can use a variety of filters, including
* a combination of suspended and attached growth;
* sand filters,
* peat filters,
* foam filters, and
* textile filters;
3. natural systems for polishing or recycling of secondary effluent include
* wetlands and
* greenhouse systems;
4. waterless toilets and graywater systems (as alternatives to flush toilets) may take the form of
* composting toilets or
* incinerating toilets; and
5. disinfection systems for secondary or higher-quality effluent include
* ultraviolet light and
* chlorination and dechlorination.
Aerobic Treatment Units
ATUs offer an alternative to septic tanks, and they treat raw wastewater to secondary treatment standards (BOD,//TSS [less than] 30 mg/L). In some ATUs, a trash tank, for primary treatment, precedes the aeration tank. A number of pre-engineered ATUs are available, and they are generally used on sites that soil and site evaluations find unsuitable for a septic drainfield system. To evaluate the performance of small ATUs, NSF and Baylor University have a testing-and-certification facility that applies the ANSI/NSF Standard 40 for Class I effluent limits. Typically, the effluent from ATUs, after further polishing and disinfection, is discharged into a surface-water body or on top of the ground, resulting in a point-source discharge into an adequately sized subsurface system instead of a nonpoint-source discharge.
Subsurface disposal of secondary-quality effluent is technically possible on sites that are not suitable for primary effluent (i.e., septic-tank effluent). Actually, subsurface dispersal of secondary effluent by methods such as filter beds or drip/spray systems can have less impact on the receiving environment than surface discharge. Plants can take up nutrients such as nitrogen and phosphorus when the secondary effluent is dispersed into ground at a shallow depth, typically within the top 12 inches of soil. Sites at which the soil has low permeability, at which the depth to an impermeable layer is shallow, or at which the depth to seasonal groundwater is shallow can be used for subsurface dispersal of effluent from adequately operating ATUs. The ATUs must be operated and maintained by professional operators to produce high-quality effluent on a permanent basis. When not adequately operated and maintained, any ATU--or, for that matter, a septic tank or any other treatment system--will discharge inadequately treated effluent into the environment and cause problems.
Used primarily to treat septic-tank effluent, media filters sometimes also are used to polish effluent from ATUs. The most commonly used media filters are sand filters (single-pass or recirculating). Recently, other types of media, such as peat, synthetic foam, and textiles, have been evaluated and have been shown to treat septic-tank effluent to better-than-secondary quality As with ATUs, we now have access to pre-engineered, prepackaged media filters that can be easily installed and used for advanced treatment of septic-tank effluent. Instead of engineering a media filter or an ATU for individual small applications, it is advisable to obtain such treatment devices from companies that market them and to use engineering resources to develop subsurface dispersal systems that will minimize environmental impact. After adequate disinfection, effluent from both the media filters and the ATUs also can be recycled for flushing toilets or other nonpotable uses, thus reducing the need for subsurface dispersal.
The performance of any media filter will depend on the quality of the media, the recirculation rate, the volume of the recirculation tank, the kind of distribution system used to spread effluent on top of the media, and the ventilation of the media filter itself. Use of an effluent filter in a septic tank and regular maintenance of the septic tank also are necessary if the media filter is to perform adequately. It may be necessary to change media filters of some types after a certain number of years.
Media filters have been demonstrated to be very effective at reducing organic and bacteriological contaminants from septic-tank effluent. They also can convert most of the nitrogen to a nitrate form (nitrification), thus maximizing the potential for plant uptake if the effluent is adequately dispersed into the shallow root zone with shallow-trench dispersal, drip, or spray There is a potential for a high degree of denitrification when recirculation through the septic tank is adequately designed.
Wetlands and other natural systems are being used to treat septic-tank effluent from single-family homes or--mainly in southern states--from a community The performance of wetland systems depends on the design, the vegetation used in the wetland, the climate, and the operation of the system. Such systems tend to require large land areas and typically have little or no mechanism for adjusting performance according to variations in the inflow quality At the same time, this kind of treatment has much lower energy requirements than do other options. An adequately engineered wetland system can offer a cost-effective method for removing nutrients and other constituents from primary or secondary effluent.
The use of a greenhouse system, a wetland operated in an enclosed and controlled environment, can lower or eliminate dependence on climatic conditions. Greenhouse systems offer a reliable treatment mechanism that can produce high-quality effluent on a consistent basis. They also can be used to significantly lower or eliminate discharge of effluent into the environment by using plant uptake and evapo-transpiration as the primary mechanisms for assimilating effluent.
Most of the time, natural systems provide cost-effective further treatment of secondary-quality effluent, discharge from ATUs, or discharge from media filters. They serve to further reduce the impact of nutrient and bacteriological pollutants on the environment.
Composting or incinerating toilets can be used to reduce the quantity of wastewater generated from a facility and also to influence the quality of wastewater. One must, however, deal with the residual products from such a facility--either composted material or ash--by recycling compost in the yard as a fertilizer or by sending ash to a landfill. The remaining wastewater is called "graywater," and it can be treated adequately with natural systems such as wetlands--or with other systems--prior to subsurface dispersal. Typically pollutant loads in graywater are greater than those in the effluent from a well-maintained media filter or an ATU; hence, adequate treatment and disposal of graywater must not be overlooked. Use of waterless toilets is attractive for remote, nonresidential areas (e.g., golf courses and rest areas in parks), where access to water and wastewater facilities is costly.
Effluent Dispersal Systems
Small wastewater treatment systems, just like large ones, need a mechanism for discharging treated effluent. As noted earlier, subsurface dispersal (nonpoint-source discharge) is the primary mechanism for disposing effluent from small on-site treatment systems. The three major parameters that influence the performance of subsurface dispersal systems are effluent characteristics, method of application, and soil and site characteristics. Of these three parameters, the first two are more manageable than the third. Highly treated effluent, when applied in small and frequent doses (this approach is called time dosing), can be adequately dispersed in a variety of soil and site conditions. The following technologies are available for subsurface dispersal of effluent from small treatment systems:
* trenches--gravity- or pressure-dosed, with or without gravel;
* drip--at or below grade;
* spray--above ground;
* filter bed--raised system on a sand-lined bed;
* evapo-transpiration beds; and
* greenhouse with storage tank.
Since most of the disposal technologies listed above use soil as a media for receiving the partially treated effluent, soil evaluation has been an integral aspect of on-site wastewater systems. A variety of treatment systems, however, now make it possible to achieve the necessary degree of treatment outside the soil. Thus, soil and site evaluation--as done for septic systems--may not be necessary In particular, there needs to be a change in the regulatory requirements for conducting soil evaluation prior to installation of a subsurface dispersal system when nonseptic on-site treatment systems are used. A variety of systems for dispersal of less than 1,000 gallons per day of treated effluent can be pre-engineered, installed, and operated in a manner that will ensure adequate assimilation of treated effluent within the zone of influence specified for that system. The site characteristics and environmental sensitivity of the proposed location will determine the appropriate type of pre-engineered dispersal syste m. Effluent dispersal systems should be selected and sized according to the assimilative capacity of the site relative to design flow and nutrient loading--not according to soil characteristics. Soil and site conditions that are viewed as limitations for septic drainfields must not be viewed as limitations for the use of effluent dispersal systems.
The ability of soil and site to effectively absorb and move the effluent away from the disposal site with a minimum movement of pollutants is the main issue of concern when highly treated effluent is discharged into a subsurface disposal system. Effluent dispersal systems must be viewed as site-assimilative systems, not just as soil absorption systems. For given soil and site conditions, an appropriate effluent dispersal system can be selected, installed, and operated to prevent the following occurrences:
* a point-source discharge (i.e., a stream flowing out of the area where the system is installed);
* a public nuisance (e.g., a puddle of water on or around the area where the system is operating);
* an obvious or even a perceived health hazard from the system; and
* groundwater or surface water contamination from organic, inorganic, bacteriological contaminants discharged into the system.
The above-mentioned treatment and dispersal technologies can be grouped according to wastewater system types. Within each type a number of engineering designs and methods can be used to achieve the necessary performance goals on the sites where the systems are used:
* System Type I--conventional gravity septic-tank effluent drainfields,
* System Type II--pressure-dosed septic-tank effluent drainfields,
* System Type III--drip dispersal of septic-tank effluent,
* System Type IV--waterless toilets and graywater systems,
* System Type V--shallow gravity trenches for secondary or better effluent,
* System Type VI--shallow pressure-dosed trenches for secondary or better effluent,
* System Type VII--drip dispersal for secondary or better effluent,
* System Type VIII--filter beds for secondary or better effluent,
* System Type IX--evapo-transpiration beds for secondary or better effluent,
* System Type X--spray dispersal for advanced-secondary effluent, and
* System Type XI--greenhouses for advanced-secondary effluent.
Two parameters that have a major influence on the functioning of a subsurface dispersal system are the depth of soil to limiting conditions (impermeable layer or seasonal water table) and the permeability of soil (the percolation rate, the hydraulic conductivity, or the texture/structure). Sites can be grouped into four types according to the values of these two parameters. Within each site group, parameters such as slope, vegetation, and environmental sensitivity will determine the types and designs of appropriate wastewater systems. Most state regulations specify the soil depth and permeability required for a septic drainfield. With these limits as reference points, a four-quadrant matrix can be developed. Figure 1 presents an example of a matrix that matches wastewater system types with site groups.
Remote Monitoring System
Most of the wastewater systems mentioned above use electro-mechanical devices such as pumps, blowers, and remote-monitoring float switches to achieve treatment and dispersal goals. The performance of treatment and dispersal systems depends heavily on the reliable operation of these devices. A remote-monitoring telemetry system should be used to adequately monitor the operations of these devices on a continuous basis and to detect any problems quickly. Control panels now available for small systems are capable of operating the electro-mechanical devices as well as of reporting the conditions of these devices to a central computer over telephone lines or by other means. Such systems can send signals to a central computer on a routine basis or to an operator during an emergency situation, reporting information on various parameters such as pump run time, duration of power outage, high-water conditions, and so forth. By using such remote-monitoring systems, a wastewater utility can operate a number of small waste water systems installed over a large geographical area in a cost-efficient manner.
Operational information gathered from remote-monitoring systems can be used to prepare routine reports on the performance of the wastewater systems and to determine the amount of wastewater managed. Such reports can be useful for billing the user as well as for supplying information to the regulatory agency responsible for ensuring adequate operation. The information also can guide planning for efficient, routine replacement of pumps and other devices, thus minimizing or preventing serious out-of-compliance situations.
Operation and Management
Centralized wastewater treatment plants are operated by a utility, public or private, whose trained and licensed operators monitor and maintain the plant so that discharge meets performance standards. Basically homeowners and businesses pay a hook-up fee to connect to a centralized system, then pay a regular usage fee, transferring all responsibility for their wastewater to the utility. Today most people who use small on-site systems do not have this option. Public acceptance of small on-site systems can be enhanced only when such systems offer the same wastewater services as a centralized system. When an on-site system can offer operational comfort to users and an environmental protection guarantee to the regulators, it will be considered the equivalent of a centralized system. We now have technologies that can meet both of these requirements in cost-effective ways. Making those technologies available to people, however, requires an infrastructure similar to that of a utility and that infrastructure is still in its infancy.
Today a few management entities offer wastewater services to people who use small on-site systems; however, most people still have no access to such services. At the beginning of a new century we need to think seriously about how to develop a regulatory system that will allow people to obtain wastewater services from a utility that uses small on-site systems in the same way they get other services--solid waste, telephone, cable, gas, and power. We also need to discuss what kinds of services utilities should offer and what role such companies could play in the on-site industry. When a utility is responsible for permanent operation and maintenance of an on-site system, it is possible to address simple issues, such as access to system components for maintenance and inspection, in a timely manner. The current regulatory requirements of soil and site evaluation, engineering design, and multiple reviews should not apply to a licensed utility. A qualified and licensed utility should be permitted to do all the pre-i nstallation work (e.g., engineering, site and soil evaluation, selection of a wastewater system) and should be allowed to install and operate on-site systems. The utility also should be allowed to use the best technology available for wastewater treatment and dispersal, and should be regulated according to the performance of the systems, in terms of both operational services to the customers and protection of the environment and public health.
Under the utility model, the roles of manufacturers, engineers, soil and site evaluators, and installers can be defined in a manner that would promote the most efficient use of their services. Today the requirements of soil and site evaluation and of engineering often do not add any real value to the operation of individual home and small commercial wastewater systems. Most of the current regulations for on-site systems still require soil and site evaluation to determine if the proposed site is suitable for an on-site system. Such pass/fail criteria for a site are not necessary because it is now possible to have a wastewater system for any site. Once a decision is made for development in an area that is not served by a centralized wastewater system, an on-site system utility can offer all the services necessary for adequate treatment and dispersal of wastewater. The environmental and public health regulators then can ensure that the services offered by the utility provide safe, adequate, and proper protectio n of the environment and public health by making sure that the utility is using the best technologies available for wastewater treatment and dispersal and by monitoring the performance of the on-site systems and their impact on the environment.
A utility company can help the on-site industry weed out poorly designed or poorly manufactured wastewater technologies. At present, there is no real mechanism for measuring the long-term performance of small wastewater treatment and dispersal systems. A utility company responsible for acquiring, installing, and operating a wastewater system in a manner that meets performance standards and satisfies customers in a cost-effective way will always strive to use the best possible technology.
A utility company also can educate people about the environmental impacts of wastewater and about the importance of reusing or recycling adequately treated wastewater. There is tremendous interest in the use of environmentally friendly systems and the reuse of treated wastewater. One must, however, realize that improperly managed wastewater systems can create environmental and public health problems. Only under a proper management framework should people have access to advanced, environmentally friendly wastewater systems.
Finally a utility company can help people get the best possible wastewater system at the least possible cost by acquiring products and services in quantity Today most people who apply for an on-site system permit--typically to a health department--get most of the pre-installation services (e.g., soil evaluation and design) from a health department employee, usually a sanitarian. These employees often are trained in only one type of on-site system--the septic-tank drainfield system. When it is determined, however, that soil and site conditions are not suitable for a septic system, the homeowner is asked to retain the services of the private sector for help with alternative systems and has to purchase the products and services necessary for installation of those systems. Thus, the current regulatory system is the main reason there are so many septic-tank drainfields in the country and so few alternative on-site systems that treat wastewater to secondary or higher quality before discharge.
The process that could establish a wastewater utility model in a state must start with changes in legislation. Most important, we need legislation that sets a time frame for phasing in the use of appropriate on-site systems under the utility model and phasing out the use of conventional septic-tank systems.
Government agencies that are responsible for regulating wastewater systems must focus on two important issues: (1) adequate treatment of wastewater and dispersal or reuse of effluent, and (2) environmental and public health protection from wastewater. The regulators must keep these issues in focus and develop regulatory strategies around them. The science and technologies for treating wastewater and for ensuring drinking-water quality are well established. The regulatory programs must be developed to allow wastewater professionals to operate in the competitive marketplace by offering on-site wastewater systems in a cost-effective and environmentally sound manner.
Unfortunately such a regulatory framework does not exist today for small on-site systems. The regulatory agencies responsible for on-site systems are more involved with pre-installation issues that typically have fewer direct implications for the long-term performance of a small wastewater system. For a utility to function and offer wastewater solutions to the public, the regulatory framework will have to shift 180 degrees. We need a solution-driven, performance-based regulatory framework with a heavy emphasis on post-installation issues such as system operations, monitoring of the environment, and education and training.
A solution-driven regulatory system means that if regulations are used to prescribe wastewater systems, those regulations must lead to a set of solutions for any given site and situation. The solutions should apply the best technologies available for treatment and dispersal. One way to achieve such a goal is to develop a manual of practice (MOP) for all available small-scale wastewater treatment and dispersal technologies and to update the MOP so that it stays current as technologies are developed by the onsite industry Development of the MOP must be a joint effort of the public sector; state-level technical staff; and wastewater professionals, engineers, and manufacturers from the private sector. It should include information on sizing, layout, start-up process, operation and maintenance requirements, operational cost, expected performance, zone of influence, and other issues connected to the use of the technology The MOP then can be used by a utility licensed to offer wastewater services through small-scal e wastewater technologies.
Technology performance data collected by the utilities can be used to revise or delete MOP content. The utility will be the party most interested in looking at the long-term ability of a wastewater system to meet performance standards and satisfy customers at a reasonable cost. Thus, the best source for information on the long-term use of a technology would be a utility Since at present there are no such utilities, the first version of the MOP might be based on wastewater engineering textbooks, third-party test reports, sensible ideas and claims made by engineers and manufacturers, and information gathered from U.S. EPA and from demonstration projects. Today, a utility could choose from more than 100 pre-engineered options for managing wastewater on site.
A performance-based regulatory framework should be developed from a clear understanding of how an on-site system needs to function. A widespread myth among regulators and soil evaluators is that an on-site system can work only if there is deep, dry well-drained, permeable soil (good soil) on a lot. This belief is based on a limited understanding of subsurface water movement, commonly determined by percolation or saturated-hydraulic conductivity tests or estimated on the basis of soil texture. In reality subsurface water movement is a complex phenomenon and is very hard to predict just from observation of soil characteristics. Regulations should clearly define what types of conditions must exist on and around the area where site-assimilative systems are to be installed and operated instead of arguing about the hydraulic conductivity or percolation rate of the soil. The performance-based regulations should assign limits for effluent prior to discharge, according to environmental sensitivity and size of the sys tem. The regulations also should assign mass-loading limits for inorganic material, total nitrogen, total phosphorus, and pollutants at the boundary of the site-assimilative system.
The boundary around a nonpoint-source discharge system can be viewed as the zone of influence for the site-assimilative system. By defining the zone of influence we can move away from regulating soil criteria, site criteria, and setback distances and allow the industry to develop new technologies that have smaller and smaller zones of influence. A recycle/reuse system, such as a system in which toilets use effluent to flush and effluent is recycled for plant growth in a greenhouse, would have the smallest zone of influence--0 feet around the greenhouse. A lined evapo-transpiration bed may have a zone of influence of 0 feet below the system and 10 feet around the system. For any dispersal system, water quality outside the zone of influence must be no different from rain or surface-water quality allowed for public contact. Adequate penalties must be enforced when a utility violates predefined standards for effluent or mass loading of pollutants.
A performance standard also should include customer satisfaction with the overall wastewater services offered by the utility Customer satisfaction can be measured according to parameters such as sewage backup in the house, odor or noise nuisance, surfacing of effluent in the yard, and unattended alarm calls, all of which could result from inadequate operation of the systems. The performance-based regulations must indicate a method for establishing a violation and penalties for violations of each standard. The penalties should take the form of monetary fines and revocation of licenses. Under a free-market model, an adequate number of utilities would be available to offer dependable services to all the citizens, as long as the citizens pay the fees (sewer bills) and the regulators strictly enforce performance standards. If a utility is allowed to operate while violating the performance standards, there will be no incentives to offer wastewater services that use adequate treatment and dispersal technologies. Ut ilities should be informed about the expected performance standards, the methods by which performance will be measured, and the consequences of not meeting the standards. At the same time, a utility needs a legal framework that gives it authority to collect service fees and to take action against those who do not pay the fees.
Small wastewater systems that allow effective recycling and reuse of adequately treated effluent on site with a minimum degree of collection will be the method of choice for wastewater treatment in the 21st century Many technologies for treatment and effluent dispersal are currently available, and new ones are being developed. Once the infrastructure for operation and management of these technologies is established and a performance-based regulatory framework is adopted nationwide, extensive application of small-scale wastewater treatment technologies will be possible.
(Adapted with permission from NSF Proceedings of the Small Drinking Water and Wastewater Systems International Symposium and Technology Expo, January 12-15, 2000, Phoenix, Arizona.)
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|Author:||Jantrania, Anish R.|
|Publication:||Journal of Environmental Health|
|Date:||Sep 1, 2000|
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