Most distributed wastewater systems consist of conventional septic systems. The array of these systems provides safe and sanitary service to more than 20% of the U.S. population. Nationwide, millions of homes and businesses are served by distributed systems. Solids accumulation in any wastewater system — centralized or distributed — can be significant, and without programs to manage these solids, system performance is compromised.
Managing residuals generated by distributed systems is an essential program element listed by the U.S. Environmental Protection Agency in its Voluntary National Guidelines for Management of Onsite and Clustered (Decentralized) Wastewater Treatment Systems (EPA 832-B-03-001). Septage, grease-trap wastes, and solids from onsite aerobic biological systems must be managed as a part of the onsite infrastructure. Some model programs exist throughout the nation, and these are the result of cooperation among state regulators, waste haulers, and the industry groups who manage septage and fats, oils, and grease (FOG) residuals.
In North Carolina, almost half of homes are served by onsite systems. The North Carolina Division of Environmental Health has rules for siting, sizing, design, installation, and operation of these systems, but the residuals generated by these systems are accommodated through rules promulgated and enforced by the North Carolina Division of Waste Management (NCDWM). To remain effective, solids management efforts must incorporate science into policy and practice. These are the goals of our state effort: sound science, effective policy, and effective management.
Federal mandates to handle septage and grease-trap waste are contained in 40 CFR 503, which establishes clear requirements for septage, and 40 CFR 257, which provides requirements for grease-trap wastes, such as FOG. The three options generally recognized by federal rules for handling these materials are
- treatment at an approved wastewater facility,
- treatment at a special waste-handling facility, and
- land application.
When these solids are applied to land, the material’s pH must be adjusted to 12 or higher (but less than 12.5) and held there for at least 30 minutes. NCDWM has extended this to require a pH of 12 at the time of land application to ensure compliance with federal rules. (State personnel can verify a pH of 12 at the time of land application with litmus paper.)
Some jurisdictions allow commingling of septage and grease-trap wastes, while others prohibit this practice. NCDWM allows commingling, and this provides for much more seamless management of these materials. Septage contains essential plant nutrients. Land application programs or dewatering at specially designed facilities, followed by composting of the solid fraction and land application of the liquid fraction, offer an excellent opportunity to beneficially use the constituents contained in these materials. In addition, some facilities are examining the fuel value of dewatered FOG waste and dewatered FOG/septage waste. The FOG adds to the energy value of the material, and addition of the dewatered and dried biofuel material to power-generation facilities is a possibility.
Septage is hauled to dewatering facilities and generally followed by composting or energy recovery from the solids and land application of the liquid leachate.
The goal of these efforts is to accomplish beneficial use in which nutrients, organic matter, or energy value in septage and FOG is recovered and used beneficially. These types of energy producers have even more potential where solids from larger wastewater treatment plants can be commingled with the septage/FOG solids to produce significantly increased amounts of methane for energy production.
The North Carolina Septage Management Program serves as a model for other jurisdictions. State rules require registration and annual training for all individuals involved in handling these residuals. The land application and compost section within NCDWM maintains more than 500 active permits for beneficial use of waste residuals.
The section works cooperatively with waste haulers and the industry groups to offer training programs for haulers and land-appliers. Both groups are required to receive annual training in order to maintain the permits required to operate in North Carolina. In addition, representatives from the section visit septage and FOG operations annually to ensure that management practices comply with federal and state rules.
The regulatory agencies in North Carolina recognize the value that septage and FOG management firms provide in ensuring properly operating wastewater facilities. Without approved septage operations, tanks may not be maintained properly or in a timely manner. This could result in serious malfunction of the onsite infrastructure vital to half the population of North Carolina. Without properly operated FOG management programs, accumulated FOG would be discharged to wastewater collection systems and exacerbate already stressed sewerage by promoting clogging and blockages. A core cause of most of the sanitary sewer or combined sewer overflows in the municipal wastewater collection system is FOG accumulation.
Our collective challenge
Solids accumulate in wastewater systems; the challenge in communities large and small is to manage these residuals in an environmentally sound and sustainable manner. The privately owned and operated septage management and compost operations permitted through NCDWM serve the residents and commercial facilities in North Carolina well by ensuring that these materials are handled properly and used beneficially. The cooperation exhibited between the state and the industry serves as an example for sustaining infrastructure at all levels. State-level residuals management programs are the foundation for this industry. Technologies are developing to expand options available for managing residuals. Permitting agencies and the industry will benefit from adoption of appropriate technologies that can meet program goals.
Robert Rubin is an emeritus professor in the Biological and Agricultural Engineering Department at North Carolina State University (Raleigh). From 1999 through 2005, he was a visiting scientist at the U.S. Environmental Protection Agency in Washington, D.C.
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