C+S September 2021 Vol. 7 Issue 9 (web)

Introduction Wastewater treatment system designers often face the challenge of meeting stringent permit limits yet providing a system with minimal operations and maintenance requirements. Mechanical treatment systems, traditionally specified in these large and commercial applications are highly engineered and very good at what they do. However, many engineering firms and developers are realizing that there are options in the marketplace today that may be well-suited for these high-performance applications and can be less expensive. Passive, sand-lined systems, including large, decentralized combined treatment and dispersal systems, have demonstrated to en - gineers, treatment plant operators, and developers that a high level of wastewater treatment does not have to be expensive or require a high level of maintenance. How Passive Combined Treatment and Dispersal (CTD) Systems Work The ability of sand-lined treatment and dispersal systems to achieve outstanding wastewater treatment without the need of mechanical operations may not be obvious to the casual observer. A CTD system may appear like a conventional dispersal field, however, it is quite dif - ferent. The system has primary treatment followed by the CTD, which has proprietary features and specified media. The bulk of the treat - ment process takes place in a relatively controlled environment and throughout the vast area of the dispersal field. This differs from most mechanical systems where the treatment area is limited to the confines of a tank. In passive treatment systems, the effluent dispersal area (EDA) pro - vides much more area overall and subsequently exponentially more surface area for the attachment of bacteria that naturally purify the ef - fluent. Utilizing this expansive EDA for treatment eliminates the need to enhance the treatment process with blowers or aerators and provides stable and robust performance. Third-party testing has demonstrated that the Advanced Enviro-Septic (AES) treatment system meets sec - ondary treatment levels from at project start-up surpassing the NSF/ ANSI 40 Certification allowance of not meeting treatment levels from the beginning of the test for up to 21 days. It also eliminates problems Passive Decentralized Wastewater Treatment Systems Offer High Performance and Low Operation and Maintenance Costs for Large Projects By Donald Prince

with intermittent use since sufficient bacterial development is present at any given time and makes these systems ideal for seasonal facilities. Due to the simplified performance of passive technologies, maintenance is similar to that required of a conventional onsite wastewater system: pump the primary tank as required, maintain the vegetation over the system to prevent woody vegetation from becoming established, and walk the site to observe for erosion or ground burrowing rodents. If required, sampling can be accommodated per permit requirements. Considering the comparative costs of a passive CTD system, these systems avoid the use of costly mechanical components and ongoing contracts for periodic maintenance. They also combine the processes of treatment and treated effluent dispersal into a single bed or trench footprint. Generally, this enables a size reduction compared to conven - tional dispersal systems based upon the high treatment level and low risk of organic clogging to the receiving surface beneath the system. Designing Passive Wastewater Treatment for New Residential Communities Development of residential communities in areas without sewer infra - structure can be complicated in terms of wastewater treatment system cost containment and long-term performance. Direct discharge of treated wastewater is highly regulated, and treatment and monitoring requirements are often difficult and expensive to meet. Typically, the least regulatory-restrictive method of wastewater disposal is subsur - face dispersal. Mechanical treatment systems, while certainly capable, can become expensive in up-front costs, ongoing maintenance require - ments, and where an additional dispersal field is required for subsur - face disposal. Conventional dispersal fields can be simple to operate but may be difficult to locate and blend into the terrain due to the size requirements. In this case, secondary treatment occurs in the native soil, where biomat development can affect long-term performance. Passive CTD systems offer the best attributes of both mechanical and conventional dispersal field systems. They provide better than secondary-treated effluent reliably to the native soil, thereby avoiding biomat development and resulting in consistent dispersal over the life of the system. Reductions in field sizing afforded by these systems


september 2021


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