Reactivation of Fecal Coliforms after Anaerobic Digestion and Dewatering

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.