Skip to main content


Buy Article:

$17.50 plus tax (Refund Policy)

Or sign up for a free trial


Water treatment plants have historically disposed of water treatment residuals through discharge to rivers or lagooning, either permanently or semi-permanently. Consequently, little thought was given to the residuals treatment processes during plant design. However, as a result of more stringent discharge limitations and decreasing land availability, mechanical dewatering systems are becoming more common, often with the objective of zero discharge plant operation.

At the same time that the number of installations generating residuals return streams has grown, an increasing number of states have established guidelines that limit the turbidity in plant return streams to less than 2 NTU to minimize possible recycle of Cryptosporidium to the plant headworks. Meeting these guidelines has forced the design of water treatment plants to include evaluation of return stream quality and possible treatment process options.

The number of return streams generated at a water treatment plant complicates the return stream treatment process. These return flows, which include spent filter backwash, thickening decant, and dewatering filtrate, have varying solids concentrations, chemistry, and are often generated on an intermittent basis. In addition, installations that use membrane separation technologies as part of their water treatment trains can be affected by the presence of polymer in return streams. All of these conditions present challenges to combined treatment. As a result, a variety of treatment systems have emerged for residuals return streams. These systems include processes that range from conventional clarification, thickening, and lagoon treatment to ballasted flocculation, high rate clarification, and membrane treatment.

This paper investigates the state of the practice of return stream treatment implemented to meet the 2 NTU turbidity guideline. Since the selection of return stream treatment systems is based on a number of factors, including the type and operation of the raw water treatment processes, space availability, and plant staff preferences, different treatment systems are discussed, along with discussion of the selection, design criteria, and available pilot data from a high rate clarification process.

Document Type: Research Article


Publication date: 2007-01-01

More about this publication?
  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

    A subscription to the Proceedings of the Water Environment Federation includes access to most papers presented at the annual WEF Technical Exhibition and Conference (WEFTEC) and other conferences held since 2000. Subscription access begins 12 months after the event and is valid for 12 months from month of purchase. A subscription to the Proceedings of the Water Environment Federation is included in Water Environment Federation (WEF) membership.

    WEF Members: Sign in (right panel) with your IngentaConnect user name and password to receive complimentary access. Access begins 12 months after the conference or event
  • Subscribe to this Title
  • Membership Information
  • About WEF Proceedings
  • WEFTEC Conference Information
  • Learn about the many other WEF member benefits and join today
  • Ingenta Connect is not responsible for the content or availability of external websites
  • Access Key
  • Free content
  • Partial Free content
  • New content
  • Open access content
  • Partial Open access content
  • Subscribed content
  • Partial Subscribed content
  • Free trial content
Cookie Policy
Cookie Policy
Ingenta Connect website makes use of cookies so as to keep track of data that you have filled in. I am Happy with this Find out more