Fate of coliforms and coliphages in the sequencing batch reactor (SBR)

Abstract

Performance of the SBR in terms of commonly used physical, chemical and biological parameters has confirmed it to be a viable wastewater treatment option. This study further investigates the use of total coliforms, fecal coliforms and coliphages to evaluate the removal of selected microbiological indicators of potential pathogens by the SBR. Results from a pilot-scale SBR which received clarified sewage from a local treatment works treating a combined (domestic and industrial) sewage showed that increases in REACT time led to increases in the overall removal of the selected microorganisms. On average, up to 96% of total coliform and fecal coliform removals and up to 90% of coliphage removal was possible with the SBR operated with 2.5 h of REACT. During FILL, a long FILL (3h) resulted in reduction of coliforms while there was generally only a small reduction of coliphages. During REACT, a short REACT resulted in increase in selected microorganisms and the increase in coliphage numbers was sequential to that of coliforms. The SETTLE period was found to be crucial. An effective SETTLE could be achieved by operating the SBR with a REACT time of 2-2.5 h.