Reactivation of Fecal Coliforms after Anaerobic Digestion and Dewatering

Abstract

In August of 2001, the largest known installation of a phased temperature anaerobic process at a 60-MDG wastewater treatment plant was placed into operation. The facility met the time and temperature requirement for Class A biosolids. Testing of the biosolids following thermophillic/anaerobic digestion followed by mesophilic/anaerobic digestion revealed no detectable levels of fecal coliform bacteria in the treated biosolids. However, subsequent testing of the biosolids following dewatering by high solid centrifugation revealed high levels of fecal coliform bacteria. These biosolids, following high solid centrifugation, did not meet Class B requirements.This study indicated a very serious reactivation of fecal coliform bacteria following high solid centrifugation. Fifty-three percent of the fecal coliforms isolated were identified as Eschericia coli with two of the isolated organisms identified as E.coli 0157:H7. E.coli 0157:H7 has been shown to be capable of formation of an autoinducer in the presence of norephinephrine. The autoinducer triggers the growth of gram-negative bacteria or the conversion of gram-negative bacteria such as fecal coliforms from a non-culturable to culturable state. It is, therefore, hypothesized that the presence of E.coli 0157:H7 may be involved in the reactivation of fecal coliform bacteria.

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

“…Improved culturability of bacteria due to the shear applied in centrifuges (Cheung et al, 2003;Qi et al, 2007), false positive results associated with enumeration techniques (Qi et al, 2004), contamination from the centrifuge (Hendrickson et al, 2004), the effect of floc break up on improved culturability (Cheung et al, 2003), removal of growth inhibitors during dewatering (Qi et al, 2007) and effect of day-light throughout the storage of biosolids (Gö zen and Ö rmeci, 2010) have been investigated as the potential factors that promote bacterial 1,00E+00 w a t e r r e s e a r c h 4 7 ( 2 0 1 3 ) 4 2 8 e4 3 8 regrowth. However, none of these factors has been found to be correlated with the bacterial regrowth.…”

“…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).…”

“…Several suggestions have been made to explain this occurrence including false positive results associated with enumeration techniques (Qi et al, 2004), contamination from the centrifuge (Hendrickson et al, 2004), effect of floc break up on improved culturability (Cheung et al, 2003), removal of growth inhibitors during dewatering (Qi et al, 2007) and effect of day-light throughout the storage of biosolids (Gö zen and Ö rmeci, 2010). Recently, Chen et al (2011a) have suggested that both odor production and regrowth are signals of microbial activity which is induced upon the increase in shear and oxygen levels during centrifuge dewatering.…”

Effect of Dewatering on Fecal Coliforms and Methanogens in Anaerobically Digested Biosolids

“…Many have reported higher fecal coliform (FC) populations, on a dry solids basis, in centrifugally dewatered biosolids compared to the digester effluents (Iranpour et al, 2002(Iranpour et al, , 2003Erdal et al, 2003;Hendrickson et al, 2004;Monteleone et al, 2004;Qi et al, 2004;Cooper et al, 2005. In some cases, populations easily met U.S. EPA Class A biosolids limits prior to dewatering, but failed this standard after dewatering.…”

“…For example, it has been hypothesized (e.g. Hendrickson et al, 2004;Higgins et al, 2007) that an activating substance (such as an autoinducer) is released during centrifugation. Another possibility is that biodegradable organics might be released, or removed, which would affect the population dynamics in the dewatered solids.…”