Skip to main content

Comparison of Different Culturing Methods for Enumeration of E. coli in Thermophilically Digested Biosolids

Buy Article:

$17.50 plus tax (Refund Policy)

Or sign up for a free trial


Pathogen removal in sludge treatment is an important step. Several Class A processes that utilize thermal treatment to achieve pathogen reduction have observed large increases in indicator bacteria, namely fecal coliform or E. coli, after centrifuge dewatering. In many cases, the densities before dewatering were below the detection limit. One hypothesis to explain this observation is that the bacteria were poorly enumerated after the thermophilic processes, but some were still viable and were able to be recovered after dewatering. Bacteria can be non-culturable based on type of media used and methods used for enumeration. To investigate the non-culturable hypothesisE. coli was enumerated using EPA Method 1680 and other culturing methods using microplates for investigation of non-culturable E. coli. Effect of hydraulic retention time (HRT) on pathogen removal was investigated for two enhanced digestion processes in addition to a conventional mesophilic anaerobic digestion (MAD) process. The enhanced digestion processes were dual digestion process: Autothermal Thermophilic Aerobic Digestion (ATAD) followed by MAD and acid/gas phase digestion process: Acid Phase Digestion (APD) followed by MAD. This study suggests that EPA Method 1680 could be underestimating E. coli density and a need to develop new culturing methods that are able to enumerate injured microorganisms. ATAD is more effective in pathogen removal when compared to APD. Class A Biosolids requirements was achieved with E. coli density below 3 log10 for only 3.5 d HRT for ATAD-MAD process, with enumeration conducted with all the culturing methods investigated for this study. The better performance of ATAD can be linked to O2 input for this process since both APD and ATAD processes were operated at the same temperature and HRTs. Additional research is necessary for comparing the effect of O2 input and HRT on pathogen removal for ATAD.

Document Type: Research Article


Publication date: January 1, 2011

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

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
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