Trends in the Design of Wastewater Collection and Treatment Systems

WWETCO FlexFilter

Q&A With Mark Boner, Creator of the FlexFilter™ Technology

Q: What trends do you see in the design and construction of wastewater collection and/or treatment systems?

A: More stringent treatment requirements are being imposed by the regulatory community. Two major issues driving these mandates include the control and treatment of wet weather flow, and nutrient removal.

Whether from combined sewers or leaky sanitary sewers, wet weather peaks can quickly exceed the system hydraulics or the safe biological treatment capacity. When trying to solve this problem using conventional bio-treatment, a contradiction becomes obvious between too much tankage for a manageable healthy biology during dry weather and too little tankage with the risk of biomass washout during the infrequent wet periods.

More stringent limits on nutrients will require additional biological treatment and/or chemical precipitation and filtration. Nutrient removal technologies are also more sensitive to wet weather peaks. These combined factors suggest there is a need for new technologies and more flexible solutions to manage and protect the treatment plant for these more restrictive requirements on wastewater infrastructure.

Q: What factors or issues are driving these trends?

A: The Clean Water Act (CWA), the CSO Control Policy and the “By-Pass Rule” are the regulatory drivers – administered through the NPDES Permit Program – that require Publicly Owned Treatment Work’s (POTW’s) to implement wet weather controls. The Bypass Rule has created one of the greatest controversies of the past decade as it has been interpreted by some as requiring biological treatment of all flows, placing many plants in violation of the CWA even though they comply with permit limits. CSO controls are being driven by consent order, requiring upgrades at the wastewater plant and in the collection system.

The EPA Nutrient Strategy is the driving force behind States developing and adopting numeric water quality standards for the control of nitrogen and phosphorus discharges through TMDL regulations and NPDES permits. Many States have already adopted stringent limits; most will eventually follow, which will require wastewater facility upgrades in biological and physical/chemical treatment systems.

Q: How is your company responding to these trends in the wastewater collection and/or treatment market? For example, are you launching or have you recently launched any new or upgraded products? Are you conducting specific research and development?

A: WWETCO, a WesTech subsidiary, has played a key role in science-based studies and development of technologies for the control and treatment of wet weather wastewaters and nutrients. These efforts led to the development of a passive-type flow control device and a simple high-rate filtration technology that can serve multiple purposes at the POTW.

The WWETCO FlexFilter™ uses a synthetic fiber media that is compressed laterally to form a porosity gradient that removes large and small particles of varying characteristics from the top to the bottom of the media bed. The FlexFilter versatility includes:

  1. Tertiary filtration with metal salts producing reuse quality (TP< 0.1 mg/L).
  2. High-rate biological filtration capturing and returning high solids overflow from secondary clarifiers when processing wet weather flows.
  3. CSO filtration producing secondary-type numeric criteria.
  4. Bio-filtration of sewage reducing both particulate and soluble BOD.
  5. Remote CSO and SSO treatment.

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