Skip to main content

DISINFECTION OF FECAL COLIFORMS AND SALMONELLA IN THERMOPHILICALLY DIGESTED BIOSOLIDS

Buy Article:

$9.50 plus tax (Refund Policy)

Or sign up for a free trial

Several wastewater treatment plants that were investigated in this study produce biosolids that meet the Class A pathogen reduction requirements for both fecal coliforms (indicator) and SALMONELLA sp. (pathogen). The U.S. EPA Part 503 Biosolids Rule specifies that the Class A limits for these bacteria shall be met at the last point of plant control, which is usually interpreted as the truck loading facility when the biosolids are prepared for transport or at the farm for land application. However, a recurrence of fecal coliforms was observed in post-digestion biosolids from the City of Los Angeles Hyperion and Terminal Island Treatment Plants and in the biosolids at the farm for land application. Biosolids sampled from dewatering centrifuges, silos and the farm sometimes contained fecal densities in densities up to 107 MPN/g dry wt, causing exceedance of the Class A limit for fecal coliforms. In contrast, recurrence of Salmonella sp. was never observed, which indicates that fecal coliforms are a poor indicator of the pathogen content in biosolids after digestion. Regrowth tests with fecal coliforms in biosolids from several locations in the post-digestion train indicated the presence of a self-disinfecting effect that caused killing of fecal coliforms spiked to biosolids from the digester. Such an effect was not present in centrifuge and silo biosolids. Hence, the dewatering centrifuge was identified as the most likely location where the recurrence of fecal coliforms originated. Laboratory simulations of centrifuge dewatering achieving only 10% total solids could not confirm the field observations and the possible role of centrifuge dewatering in the recurrence of fecal coliforms remained unknown. Comparison of observations at three wastewater treatment plants indicated that the recurrence of fecal coliforms can possibly be related to the following combination of factors: i) contamination of Class A biosolids with fecal coliforms from external sources; ii) a large drop of the post-digestion biosolids temperature to below the maximum for fecal coliform growth; iii) the loss of a self-disinfecting effect that causes killing of fecal coliforms in digested sludge. Recurrence of fecal coliforms in biosolids during postdigestion and at the farm was prevented by insulation of the post-digestion train of the Hyperion Treatment Plant, which maintained a biosolids temperature above the maximum for growth of fecal coliforms. When silo and farm biosolids were subsequently stored at 21 °C, no recurrence of fecal coliforms was observed for at least 6 days.
No Reference information available - sign in for access.
No Citation information available - sign in for access.
No Supplementary Data.
No Article Media
No Metrics

Document Type: Research Article

Publication date: 01 January 2004

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
X
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