Skip to main content


Buy Article:

$17.50 plus tax (Refund Policy)

Or sign up for a free trial


The City of St. Petersburg, Florida uses belt filter presses (BFPs) to dewater anaerobically digested waste activated sludge (WAS) at its four regional water reclamation facilities. These BFPs are nearing the end of their useful life and require replacement or major overhaul in the near future. As part of a dewatering upgrade project initiated by the City, belt filter presses, screw press and centrifuge dewatering technologies were evaluated. The compatibility of the selected dewatering process with possible future Class A quality biosolids disposal and/or reuse options was also considered.

To evaluate the effects of Class A treatment options on the dewatering options, the following three means of achieving Class A biosolids were considered in this study: heat drying, the FKC screw press Class A process, and conversion of the existing mesophilic digestion process to the three phase digestion process (Drury et al., 2002).

The existing BFPs generated cake concentration in the range of 12% to 14%, with polymer dose varying mainly in the range of 10 to 15 pounds of active polymer per dry ton (1b/DT). Previous pilot testing of a more advanced BFP model resulted in cake solids of 18.4 to 19.9 % with polymer dose ranging from 23 to 32 active 1b/DT. Centrifuges pilot testing resulted in cake solids concentrations from 19.8% to 22.3% using polymer dose of 25.7 to 29.2 1b/DT. Screw press pilot testing resulted in cake solids concentrations ranged from 14.3% to 17% depending on polymer dose and solids loading rate, using the Ciba Zetag 7878 polymer. Due to the highly buffered nature of the digested biosolids, a large dose of lime (950 lb Ca(OH)2/DT) was required to generate class A biosolids.

Using the pilot test results and the results of a survey of installed operational facilities, a qualitative decision matrix was generated and presented to the City staff in a workshop. Detailed present and lifecycle cost estimates were generated for the centrifuge and screw press technologies. The analysis indicated that centrifuges had the lowest lifecycle cost under all considered Class A and Class B biosolids conditions, with the cost difference increasing under Class A biosolids conditions. The FKC Class A process had lower capital but higher lifecycle cost compared to the 3-phase digestion option of generating Class A biosolids. A new technology evaluation decision matrix was assigned weighting factors and scores by City staff and resulted in the centrifuge technology having the most favorable cost. The final decision on the selection of the dewatering technology will be made following additional planned pilot testing of BFPs and centrifuges.

Document Type: Research Article


Publication date: 2005-01-01

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