TREATMENT PERFORMANCE, MICROBIAL ACTIVITY AND COMMUNITY DYNAMICS IN INCLINED PLATE MEMBRANE BIOREACTORS FOR MUNICIPAL WASTEWATER TREATMENT UNDER DIFFERENT SLUDGE RETENTION TIME

Two identical bench scale inclined plate-membrane bioreactors (ip-MBRs) were operated with treating real municipal wastewater for almost 3 months under two different solid retention times (SRT): short (20 days) and infinite. Both reactors were operated at the same hydraulic retention time (6 h) and sludge recycle ratio of 300% at the tropical temperature of 28-30 degrees C. Sludge samples were collected and analysed by terminal restriction fragment length polymorphism (TRFLP) targeting bacterial the 16S rRNA gene and bacterial ammonia monooxygenase gene (amoA). Enzymatic activities of sludge were quantified using fluorogenic substrate assay. Under short SRT condition (20 days), treatment performances of both systems were deteriorated due to the accumulation of dense sludge in anoxic tank leading to the decrease of MLSS in aerobic tank. The average removal efficiency of COD, ammonia and total nitrogen decreased to 58, 34 and 30%, respectively. Thereafter, no sludge discharge period (infinite SRT) was instead applied and both systems could recover the high efficiencies of COD and ammonia removal more than 90% and total nitrogen removal up to 70%. Among the enzymatic activities tested (glucosidase, aminopeptidase and esterase), only glucosidase activity gradually declined with time under the infinite SRT in both reactors. There was no significant differences in these enzymatic activities between the two reactors (p>0.05). Multidimensional scaling (MDS) plots of TRFLP profiles demonstrated that the microbial community compositions in both reactors showed similar sequential shifts with the increase in total mass of sludge. These findings revealed the influence of SRT to treatment efficiency and microbial dynamics, which were notably reproducible in the two identical ip-MBRs.