Removal of Hygienically Relevant Microbes in Changing Operational Methods from Standard Activated Sludge Methods to Stepwise Advanced Treatment

Abstract

 The quality of secondary treated water and the removal performance of hygienically relevant microbes (HRM) during the changing operation from the standard activated sludge method to the stepwise advanced treatment method is unreported. Therefore, we clarified the secondary treated water quality (biochemical oxygen demand, total nitrogen, and total phosphorus) and removal performance of HRM (total coliforms, Escherichia coli, fecal streptococci, enterococcus form) in the changing operational process through one year of parallel operation with a stepwise advanced treatment control system. The secondary treated water in both systems consistently met the target water quality, verifying that the changing operation was appropriate. The total coliforms and E. coli in the experimental system converged to the control system concentration level, but the fecal streptococci, enterococcus form did not. The sludge return ratio correlated highly with the nitrification ratio in the reaction tank, temperature, and biodiversity index, and was useful as an indicator of the changing operational status. The logarithmic removal ratio of HRM was highly related, with the sludge return ratio > total nitrogen > Metazoans. We have clarified the notable points in the changing operation process, and the treated water quality and removal performance of HRM.