Reactivation potential of indicator bacteria in anerobically digested sludges after dewatering processes

Erkan, Müge
Anaerobic digestion process which has long been known to successfully reduce the organic content of sludge is one of the most common alternatives to meet pathogen reduction requirements for particular classes of biosolids. However, it has recently been reported that, significantly higher densities of indicator bacteria have been measured in dewatered cake samples compared to samples collected right after anaerobic digestion. In addition, this increase in bacterial population has been commonly observed after centrifugation but not after belt filter dewatering. Even though several theories have emerged to explain this occurrence, with the use of molecular tools such as Quantitative Polymerase Chain Reaction (Q‐PCR) in recent studies, much of the attention was given to the reactivation of the indicator bacteria which might enter a viable but non‐culturable state (VBNC) during digestion process. The main objective of this research is to examine different treatment plants in Turkey to observe whether the aforementioned phenomenon is valid in these plants as well. Towards this end, the impact of dewatering processes v on indicator bacteria counts was investigated by performing both standard culturing methods (SCM) and Q‐PCR on sludge samples collected after digestion and dewatering from selected full‐scale treatment plants. Results indicated that, in treatment plants operating belt filter dewatering, reduced concentrations of indicator bacteria do not change after the dewatering process. However, indicator bacteria content of sludge increase immediately after centrifuge dewatering. Based on the results obtained by Q‐PCR, reactivation of VBNC bacteria was speculated to be the main reason for the increases obtained.


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Citation Formats
M. Erkan, “Reactivation potential of indicator bacteria in anerobically digested sludges after dewatering processes,” M.S. - Master of Science, Middle East Technical University, 2011.