Fate ofE. ColiAcross Mechanical Dewatering Processes

Abstract

Five UK sludge treatment plants have been monitored for Escherichia coli (E.coli) variation after mechanical belt press and centrifuge dewatering processes. A complementary laboratory trial was also completed to examine the effects of varying centrifugal force on raw sludge E.coli content. An E.coli balance between the numbers contained in the flows entering and exiting four full scale centrifuge dewatering systems indicated a minimum 63 % increase in E.coli numbers between the input feed and sludge cake for a digested sludge input to the centrifuge. For two of the centrifuge sites this increase was statistically significant and corresponded to an increase in E.coli concentration ranging up to 1.4 Log after centrifugation. However, E.coli variation was found to be dependent on the type of sludge, as centrifuge dewatering of raw sludge at full scale resulted in a 40 % decrease in E.coli numbers. The complementary laboratory centrifuge work confirmed that E.coli numbers decreased in raw sludge after centrifugation. E.coli numbers were not observed to increase in digested sludge which had been dewatered using a belt press. A decrease of 44 % was observed.

Can sludge dewatering reactivate microorganisms in mesophilically digested anaerobic sludge? Case of belt filter versus centrifuge

“…Since Fecal Coliforms comprise a number of coliform bacteria including E. coli, the initial and final concentrations of Fecal Coliforms are higher than E. coli. This trend is in conformity with the previous findings that report belt filter process does not cause an increase in the number of indicator bacteria (Erdal et al, 2003;Monteleone et al, 2004).…”

“…Biological activity is reduced along with the organic matter content of sludge during anaerobic digestion. However, it has recently been reported that significantly higher densities of Fecal Coliform and/or Escherichia coli have been measured in dewatered cake samples compared to the samples collected after anaerobic digestion (Hendrickson et al, 2004;Iranpour et al, 2003;Cheung et al, 2003;Monteleone et al, 2004;Qi et al, 2004). This finding is more pronounced in the centrifuge dewatered sludge cakes rather than in belt filter dewatered cakes (Cheung et al, 2003;Erdal et al, 2003;Hendrickson et al, 2004;Higgins et al, 2007;Qi et al, 2007).…”

“…Similarly, in their investigation concerning a mesophilic anaerobic digester, Cheung et al (2003) found that there were approximately 2.17 log units of increases in the E. coli densities after dewatering process. For the four mesophilic treatment plants investigated in the U.K., Monteleone et al (2004) recorded the increases as 63%, 74%, 394% and 3452% for E. coli content of centrifugally dewatered sludge. Our study supports these previously made observations in such a way that the increase in microbial content is only observed after centrifuge dewatering and not after belt filter dewatering.…”

Balancing hygienization and anaerobic digestion of raw sewage sludge

“…Results reported in the literature regarding the occurrence and levels of faecal coliforms and E. coli seem incongruent (Chauret et al, 1999;Monteleone et al, 2004;Guzmá n et al, 2007a). The biosolid matrixes exert great influence over the results obtained using the present standardized methods for enumerating faecal coliforms bacteria and consequently for E. coli.…”

Use of RNA-based genotypic approaches for quantification of viable but non-culturable Salmonella sp. in biosolids

“…FC growth after stabilization has been the subject of several studies and many of them observed the indicator organism regrowth in biosolids (Cheung et al 2003;Erdal et al 2003;Iranpour et al 2003;Monteleone et al 2004;Qi et al 2004). For example in a study by Jolis (2006) biosolids samples classified as Class A investigated for FC reactivation and regrowth was observed in biosolids samples when incubated at 35 degrees 8C for 48 hours after stabilization.…”