Environmental Science and Engineering

Factors Affecting the Performance of Primary Treatment in Decentralized Wastewater Systems

Publication Date: February 2008
Cooperating Institution: ARCADIS
Principal Investigator: Vic D'Amato
Project Budget: $123,951
Project Identifier: 04-DEC-7


Approximately 23 percent of the estimated 115 million occupied homes in the United States are served by decentralized wastewater systems, the vast majority of which include a septic tank, grease trap, or both for primary treatment. These are efficient, simple treatment units whose performance is critically important to the overall functioning of decentralized wastewater systems.

Current primary unit design and operational practices tend to be driven by highly prescriptive regulations, industry standards and guidance materials which rely on limited and often dated scientific information and past practices and may be incomplete in their consideration of the factors that may influence primary treatment unit performance in decentralized wastewater systems. Although septic tanks and grease traps are generally robust and efficient primary treatment units, the optimization of their design and operation has been limited. Further research may be warranted to answer outstanding questions and optimize practices; however it should be conducted within the framework of overall decentralized system performance objectives and functions.

The objective of this project was to take a fresh look at the existing body of work addressing the performance of primary treatment units in decentralized wastewater systems, with a goal of establishing what is known, what is not known and what future research may be warranted. Design, construction/installation, and operation, monitoring and maintenance issues were each considered, with a focus on those factors most likely to affect primary unit treatment objectives, including influent characteristics, sizing, hydraulic design, compartmentation, influent and effluent appurtenances and seasonal effects, among others.

Relevant publications were thus identified, compiled, analyzed and synthesized with important research recommendations defined to support the development of several interrelated products, designed to be useful tools for WERF subscribers, practitioners, researchers, policymakers and other stakeholders:

  • Research Digest
  • Bibliographic Database
  • (3) Communications Documents:
    1. Technical Guide: This six-page bulletin concisely communicates the main technical findings of the project. It primarily targets designers, engineers, regulators, and educators, but other stakeholders may use the guide to further their knowledge in the subject.
    2. Program Points: This fact sheet will be useful to policymakers, as it communicates the relevance of this research project to their concerns, namely public health, environmental protection, economics, and growth and development.
    3. Research Considerations: This fact sheet is targeted primarily to the research community. It summarizes the major project observations and recommendations on how research has been and should be conducted in the decentralized field. Recommendations for further research are also included.
  • User-friendly compact disk – read only memory (CD-ROM) for web interface