If you are experiencing problems downloading PDF or HTML fulltext, our helpdesk recommend clearing your browser cache and trying again. If you need help in clearing your cache, please click here . Still need help? Email help@ingentaconnect.com

Increases in Indicator Bacteria Densities after Digestion and Dewatering

$17.50 plus tax (Refund Policy)

Buy Article:

Abstract:

In the last few years, a number of utilities have reported substantial, sudden increases in fecal coliform and/or E. coli densities in anaerobically digested biosolids immediately after dewatering. This sudden increase has been termed “reactivation”. Storage of the cake samples results in further increases in the indicator densities, with peak densities approaching 107 to 108 organisms per gram dry solids (DS). This additional increase during storage has been termed “regrowth”. The reactivation and regrowth phenomenon has been found to be more prevalent in plants that utilize centrifuge dewatering. A number of different process types have reported reactivation and regrowth, including mesophilic, thermophilic, temperature phased anaerobic digestion, pre-pasteurization, and autothermal aerobic digestion. The sudden increase is generally low in mesophilic anaerobic digestion (MAD) processes, with typical increases in densities of 0–1 order of magnitude being reported. However, during regrowth, the density can increase by another 1–2 orders of magnitude. For thermophilic and Class A processes, the densities have increased up to 5 orders of magnitude when comparing pre- and post-dewatering samples, with additional increases of several orders of magnitudes during regrowth. Plants utilizing belt filter press dewatering have not reported reactivation and regrowth to the extent that plants with centrifuge dewatering have reported.

The reasons for the sudden increase are not clear, but several proposed theories include: resuscitation of non-culturable bacteria; centrifuge contamination; and release of bacteria due to floc-breakup/shear. On-going work is examining these different mechanisms to better understand this problem. Regrowth appears to be due to the release of substrate during the dewatering process which supports bacterial growth. The shear imparted to the floc releases biomolecules that can be utilized for growth. An interesting parallel to this work is research on odors produced by cakes. This research has shown that shear during centrifugation releases protein, which supports bacterial growth and the biodegradation of this protein leads to the production of odorous compounds. Odors produced by belt filter press cakes have been shown to be much lower compared to centrifuge cakes.

The increases in indicator bacteria are a concern since regulatory requirements for Class A and B biosolids utilize, in part, indicator bacteria limits. From a public health perspective, pathogen reactivation and/or regrowth is a significant concern. On-going research is examining whether pathogens are also being reactivated and are regrowing, and data will hopefully be available in the form of a WERF report during the summer of 2007.

For additional references on this topic, please see the attached list of references.

Document Type: Research Article

DOI: http://dx.doi.org/10.2175/193864707787975507

Publication date: January 1, 2007

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.

    WEF Members: Sign in (right panel) with your IngentaConnect user name and password to receive complimentary access.
  • Subscribe to this Title
  • Membership Information
  • About WEF Proceedings
  • WEFTEC Conference Information
  • ingentaconnect is not responsible for the content or availability of external websites

Tools

Favourites

Share Content

Access Key

Free Content
Free content
New Content
New content
Open Access Content
Open access content
Subscribed Content
Subscribed content
Free Trial Content
Free trial content
Cookie Policy
X
Cookie Policy
ingentaconnect 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