New techniques in single-family, onsite and cluster technology are stirring up interest in the wastewater treatment industry
If you ask most municipal engineers or environmental officials who manage wastewater about the latest advances in wastewater treatment technology, most will respond that little has changed in the last 10 years. Upgrading technology usually means to restore and replace worn parts and to add advanced control systems to improve the efficiency and operation of centralized sewer systems. There is minimal pressure to radically alter existing systems or practices.
However, if the same question is posed to engineers or community leaders in many small towns, you will learn that they are keenly interested in new single-family, onsite and cluster technology and advanced wastewater treatment. The word is getting out about new developments in pretreatment filters used before the septic tank, nutrient removal technologies and new subsurface disposal techniques. Officials also are aware that increased management is needed for these advanced systems and are looking for new public or private entities to be formed to meet that need. The pace of change and potential for improvement are arguably the greatest in the whole wastewater technology field.
Clearly, the perspective is very different. What both sides do recognize is that concern about water quality at the state, local and national level has increased dramatically over the last 10 years. Meeting tougher water quality requirements has now become a broader watershed management issue that will force centralized and decentralized system engineers and officials to be on the same team. New waste load allocations, assigned through NPEDS permits, will increase the burden on municipalities faced with growing populations and service areas.
Managed decentralized systems can enable an area to grow without adding costly central treatment capacity. The improved effluent quality produced by advanced onsite systems also may make expensive nutrient removal upgrades to the central unit processes unnecessary. Municipal sewage authorities can integrate the management of these advanced systems as part of a combined centralized and decentralized infrastructure program.
What is a Decentralized Wastewater System?
Decentralized wastewater systems are defined as managed collection, treatment, and/or disposal and reuse of wastewater from individual homes, clusters of homes, isolated communities, industries or institutional facilities. Currently, over 26 million septic systems recycle at least five billion gallons of effluent daily in the United States. More than 37 percent of new construction uses onsite and cluster wastewater systems.
The operation of these systems is based on managing both the solid and liquid fractions of the wastewater near their point of origin. In some cases, it also involves transporting the liquid portion for further treatment and reuse at cluster treatment sites. Areas with a pay-as-you-go approach to infrastructure development favor this approach. An example is Los Angeles, California, where large, new office buildings could not be sewered because the central sewer system was at capacity. In an effort to continue development, an onsite wastewater recycling and reuse system was developed, with the clean effluent now being used for irrigation of landscape plantings. Two new outlet malls in southern Connecticut use a similar system. These malls could not have been developed without the advanced onsite system. In both cases, the systems are managed by a contract similar to one required for any mechanical system serving a commercial development.
Advanced Onsite System Technology
There is a variety of alternative onsite technologies being tested and installed nationwide, with many more under development. As with all new technology, each new system is most cost-effective within a particular set of environmental parameters.
Recirculating sand filters are used in areas with restrictive soils where surface discharge is permitted. They also are suitable in combination with absorption systems to enhance pathogen reduction, lower absorption area requirements and pre-treat wastewater from commercial establishments such as neighborhood shopping centers or restaurants. These filters consistently produce effluent with less than 10 milligrams per liter of five-day biochemical oxygen demand (BOD5) and total suspended solids. When integrated with a septic tank, they can reduce total nitrogen to less than 10 milligrams per liter.
Advances also are being made by engineered absorption components. In states such as Colorado, 70 percent of new construction uses lightweight plastic chambers. Nationwide, over 10,000 new, engineered plastic absorption systems are built each month. Many are installed at a reduced size, expanding the use of this technology to smaller lots on repairs or to older lots platted before recent codes required lower densities with septic systems. Most frequently the technology is used because of the ease of transport and quick installation. In areas with more remote and difficult terrain (e.g., the Rocky Mountains or eastern Oregon), stone and pipe are rarely used due to the high cost of transporting and placement of this material.
Increasing reliability by the use of dual leachfields, pioneered in Fairfax, Virginia, in the 1970s, is emerging again in California where long-term life cycle management is promoted by local authorities. This approach uses two leachfields with effluent diverted to one or the other. This process allows the reserve field to rest and naturally recover. Aerobic bacteria invade the resting field followed by worms that open up the soil, restoring it to near new conditions. The recovery rate has been documented at 1.8 percent a month, meaning four or five years is required for recovery in cold, wet climates. The reserve field also enables immediate adjustment in cases of extreme water use such as ongoing lengthy showers or excessive clothes washing. In this situation, the health department may switch to the reserve field or use both.
Currently in most communities, the health department relies on homeowners to inspect and maintain their septic systems. If this responsibility is neglected, the reserve field can save the homeowner thousands of dollars in landscape repair should the leachfield get overloaded with solids. The initial investment in the reserve field approach is most cost-effective in situations where a homeowner plans to invest heavily in landscaping and irrigation. Georgetown Divide Public Utility District, in California, is a community that has switched to this approach for all mound systems.
Off the shelf systems now are available that can remove nitrogen, absorb phosphorus and disinfect with ultraviolet light. These systems disperse effluent over very large areas in very limited soils. Manufacturers are working with retailers to deliver such systems to the public.
Advanced treatment processes can also restore valuable water resources. One of the newest technologies that has evolved with the microprocessor revolution and has become cost-effective for single-family homes is the Sequencing Batch Reactor (manufactured by Thomas Inc.). This reactor uses a microprocessor to manage the filling or processing and decanting of treated effluent. Using this technology, and adding ultraviolet disinfection and subsurface disposal with interactive management, recently transformed a site with a failing septic system into an extremely valuable estate next to fisheries on Puget Sound. Washington's Department of Environmental Quality approves the use of this technology for very limited waterfront sites, avoiding the cost of extending sewers to these locations.
In Michigan, another new filtering process where iron-impregnated sand media is dosed by dispersing effluent off the roof of Infiltrator chambers positioned above the sand is being tested. This international effort to maintain quality in the Great Lakes is the result of combined work between experts in Ontario and Michigan State University. The experimental filter was built with funds from the National Onsite Demonstration Project. This technology, if successful, will replace a vault system for cottages on Crystal Lake in Benzie County, Michigan.
The availability of advanced onsite systems provides a wastewater solution other than sewering in areas with restrictive soils and tough environmental constraints. These development challenges previously forced developers and small communities to install sewers because there were few other cost-effective choices. In the past, some planning agencies even cited the limitations of traditional onsite systems as a reason to halt development and defend restrictive land-use plans. Alternative onsite technologies will allow future land-use discussions to stand on their individual merits. The selection of advanced onsite wastewater treatment also will provide planners with the opportunity to preserve the rural character of small communities frequently lost when sewers are installed and high-density development follows.
Onsite Vs. Sewering
In an April 1997 Report to Congress on the Use of Decentralized Wastewater Treatment Systems, the Environmental Protection Agency supported the use of alternative onsite systems as an appropriate solution for small communities. The EPA report states, "Adequately managed decentralized wastewater systems are a cost-effective and long-term option for meeting public health and water quality goals, particularly in less densely populated areas." This is a major national shift from the policy that sewers are essential to all community development.
Sewers typically make up 60 to 80 percent of the cost of municipal wastewater systems. In rural areas and areas with shallow water tables, bedrock or adverse topography, the higher figure is not unusual. Alternative, or small diameter sewers, and septic tank effluent pump (STEP) systems, reduce this cost by 20 to 30 percent. Areas such as Anne Arrundel County, Maryland, and Austin, Texas, have turned to onsite management systems instead of sewering because the price of sewering for these urban fringe areas was prohibitive.
Other areas striving to maintain their rural character have also decided to pursue decentralized wastewater management programs. Towns such as Old Saybrook, Connecticut, have pushed their case to the Connecticut Supreme Court. This seasonal resort community now has an agreement from the Department of Environmental Protection allowing structural changes, adding new advanced onsite systems in the beach communities in consort with a management program for all their onsite septic systems. The high price tag for sewers keeps this community focused on decentralized wastewater management as its best solution. A moratorium on all outfalls into Long Island sound also limits its options.
In small towns, the Connecticut Department of Environmental Protection requires that advanced recirculating filters be managed by private contractors. For example, in Old Lyme, a modern shopping center includes a full-service food market that generates high-strength waste that must be pretreated and disposed of using subsurface disposal. Town officials, adamant about maintaining the town's rural New England character, are depending on this new technology. The recirculating gravel filter (RGF) removes over 98 percent of the waste, making it possible to efficiently site the soil absorption system.
A similar RGF subsurface disposal system enables patrons to dine in a historic mill converted to a picturesque country restaurant in Chester, Connecticut. Nat Jacobson, a local engineer, pioneered this technology with the DEP. The effort is supported by requiring maintenance contracts to ensure regular inspection and maintenance of the system. While this was not officially recognized as a demonstration system, the close cooperative relationship between the engineers, contract operators and regulatory officials assured the success of this technology and opened the door for development of previously limited sites in the state.
In Washington State, where new development stretches government resources to meet the growth with sewers, developers can build neighborhood shopping centers with aerobic pretreatment systems. BOD5 in these shopping centers frequently exceeded 1,000 milligrams per liter. With the use of a Nibbler System (an aerobic treatment system specifically designed to treat restaurant grease), effluent strength is reduced to less than half of septic tank effluent. This makes it possible to use subsurface absorption in this application. Without this pretreatment system, managed by contract with the manufacturer, development would not be possible without creating serious water quality problems.
Advanced System Management
The advanced treatment systems require maintenance. In the past with traditional septic systems, this part of the process was left up to homeowners. Often they paid very little attention to their septic systems until something came bubbling up from the ground. The new advanced systems will require consumer and community awareness and professional maintenance programs run by either public or private utilities or companies. Small communities will need to change their views about the responsibility for decentralized systems. What was previously a private, individual responsibility will become a community-supported solution that needs to operate effectively to preserve water quality.
The development of remote sensing and monitoring is currently being explored by a number of companies. This includes the possibility of using Supervisory Control and Data Acquisition (SCADA) systems in the onsite arena. Currently, advanced onsite systems typically use "control boxes" that turn electric pumps on and off, monitor septic tank levels and sound an alarm when an unusual condition occurs. The alarm goes off at a panel in the house. The homeowner must then call in a report, otherwise there is the danger of overloading the leachfield and polluting the environment. Remote sensing can take the homeowner out of this loop by sending a signal directly to a central monitoring office. Other information, such as pressure in the dosed leachfield lines, also can be transmitted to indicate any effluent distribution problems. In more complex systems, the communication is interactive. Pump dosing frequencies can be changed, along with other system controls from a remote base.
Rural electric cooperatives have extensive management expertise. If managing onsite wastewater systems is needed by their constituents to encourage growth, they may get into the wastewater management business. An example is the collaboration between the Tennessee Valley Authority and Joe Wheeler Electric Cooperative in northern Alabama to manage a wastewater system. This system, planned for new subdivisions, is in an area with heavy clay soils, long considered unsuitable for conventional septic systems. In this case, the electric cooperative is working with the Energy Power Research Institute (EPRI) by lending its expertise in wetlands technology to the development of cluster wastewater treatment systems. The utility plans to remotely manage these systems using a programmable control system that monitors system operation.
Electric utility interest in managing advanced decentralized systems is promising. Control systems, standard for electric utilities, are just emerging in the wastewater field. This type of management makes it possible for developers to build knowing the wastewater management service will be provided, just as if they were connecting to a regional municipal system.
Stinson Beach Water Authority in California is an example of a diversified utility delving into the wastewater management business. This water utility has been managing individual onsite systems for more than 20 years. There are no sewers, cluster or community-based systems within this district. Operating permits issued by this utility vary with the complexity of the onsite technology. The utility also monitors ground water and surface water to ensure that all systems in the district meet quality standards.
Georgetown Divide Public Utility District (a major pioneer in onsite management) also has more than 20 years of experience. Its support for developers in its district enables the planning of subdivisions with alternative onsite and cluster systems. These are all soil-based, ground water recharge systems. Residents pay monthly service charges based on the system that serves them. Those on the cluster system pay more due to the maintenance requirements for the collection system. This district has a full-time manager to oversee the construction and maintenance of the onsite systems. Regular inspection and interaction with the homeowners provides a common concern for protecting the systems from harsh chemical or toxic compounds that could disrupt the system and affect water quality.
Hamilton County, Ohio, represents the latest and most comprehensive decentralized system management program in the nation. It manages 9,145 operating permits for extended aeration units, samples 197 of 314 collector lines and storm sewer outfalls, and where cost effective, aggressively coordinates sewer extensions. Permit renewals follow a thorough annual inspection of individual treatment units. Field inspectors make an effort to review the condition of the treatment system with the homeowner and health officials offer innovative educational programs.
The Hamilton County Health Department leads the way in extended aeration management by recording the condition of all systems using a Geographic Information System (GIS) tied to a regional GIS that serves the entire Cincinnati Metropolitan Area. This integrated geographic database permits tracking of all disease outbreaks. It compares any waterborne diseases with the latest onsite survey and collector line sampling results.
Health officials can review this data by watershed and evaluate the occurrence with the last recorded extended aeration performance and collector outfalls. Any correlation with the onsite treatment systems is quickly targeted. Results show a significant improvement in water quality. The $40 per year permit renewal fee covers all activities, with start-up funds provided by the county to establish the program. Homeowners contract with manufacturers and local plumbers to maintain their home aeration systems. Annual service contracts range from $200 to $300 per year.
Research, Development, Technical Assistance and Training
Since the Clean Water Act was authorized in 1972, the federal government has invested a modest level of resources in advancing the onsite field. In early years, funding was available for research, technology development and management improvements for onsite system approaches. Over time however, funding for the research program in the Office of Wastewater was reduced to zero. Undoubtedly, the assumption was that septic systems were only temporary, low-tech solutions.
Since 1979, the Small Flows Clearinghouse at West Virginia University has received EPA funding for information collection and dissemination on decentralized, onsite, alternative collection and small treatment technologies. The Small Flows Clearinghouse manages the National Onsite Demonstration Project that has supported advanced onsite technical installations, community education, technology transfer and other related programs in a number of communities.
Other non-governmental organizations including the National Onsite Wastewater Recycling Association (NOWRA) have formed to advance the decentralized wastewater field. A second such organization, the Consortium of Institutes for Decentralized Wastewater Management, is an affiliate of universities and colleges involved in decentralized wastewater treatment research, education and training. The Consortium has goals of advancing the field through dialog, debate and information transfer across the country.
A third collaboration is the National Decentralized Water Resources Capacity Development Project that includes the Electric Power Research Institute (EPRI), the National Rural Electric Cooperative Association (NRECA), the Water Environment Research Foundation (WERF), the Consortium, NOWRA and the Coalition of Alternative Wastewater Treatment (CAWT). Federal appropriations by the U.S. Congress have recently been directed to the Capacity Development Project to undertake projects in training, research and development in conjunction with the EPA.
Future Environmental Protection Agency and Government Support
The recent EPA Report to Congress states that significant changes in government will be needed to create the management programs required to support the use of more advanced onsite and cluster systems. Past federal efforts have primarily focused on preparing technology manuals. The guidance documents that encouraged full-scale, comprehensive management programs were largely ignored. This situation is changing.
In the last session of Congress, over four million dollars were allocated to the National Decentralized Water Resources Capacity Development Project to encourage the development of innovative decentralized approaches. This money will be used to fund selected projects in the areas of education and training, regulatory reform, management-related demonstration projects and research studies and to evaluate earlier studies.
A $250,000 project, coordinated by the National Decentralized Water Resources Development Project, will identify and prioritize decentralized wastewater treatment research needs in a risk management framework. A second $5 million dollar project will be directed at projects to overcome the EPA-identified barriers to effective use of decentralized wastewater treatment, including support of training centers and educational/engineering school curriculum development, regulatory reform and model code development; and a wide variety of management, planning and demonstration projects.
Today, in municipalities nationwide, choosing between sewers and traditional septic systems is not the only option. Both technologies will continue to play a valuable part in future water quality management programs. Alternative technologies are bursting onto the scene with a variety of management entities in place. Local electric utilities, water utilities and others are in the management arena. New wastewater technology, in partnership with increased service and improved management, will become a part of the foundation of our cities and towns. Both onsite and central sewers have their respective strengths. With significant advancements in onsite cluster treatment technology, remote monitoring and interactive control systems, the more complex technologies can be cost-effectively managed. Barriers to commercial development in scattered locations with restrictive soil can now be overcome by advanced technologies and managed by utilities.
With today's growing economy and the expansion into environmentally-sensitive rural areas, many communities will be managing both onsite wastewater and sewering programs. Expanding the technological options, developing better management strategies and creating effective integration of these programs will enable communities to meet the pressing need to protect and improve our water resources for the future.