Study on effect of hydraulic retention time as factor affecting performance of hybrid biofilm-activated sludge process

The effect of hydraulic retention time(HRT) on the performance of hybrid biofilm-activated sludge process on treating domestic waste water as well as characteristics of microorganisms was investigated respectively in this paper.The results demonstrated that HRT performed a slight influence on COD removal in contrast to a considerable effect of HRT on nitrogen removal.Moreover,decreasing HRT was able to increase sludge concentration,resulting in a substantial increase of removal for COD volume loadings.Analysis on oxygen uptake rate(OUR) of bacteria suggested that activity of microorganisms in such a system was enhanced when longer HRT was used.Therefore,HRT at the range of 6～8 h is recommended within hybrid biofilm-activated sludge process system.