Sludge reduction based on microfauna predation in a submerged membrane bioreator

Supplementing untreated sludge in a sequencing batch way was adopted to study sludge reduction in a submerged membrane bioreactor(MBR).The variations of microfauna and sludge concentration was investigated for 34 days in this research in order to understand the microfauna community dynamic in the MBR and to estimate the contribution of microfauna predation for the sludge reduction.Thirteen species of protozoa and metazoa were observed with high population density,in which Aeolosoma hemprichii Ehrenberg was the dominant with a density of 338.5 individual per milliliters.The succession of the dominant microfauna groups in the reactor was as following: Ciliated protozoa-Rotaria-Aeolosoma hemprichii Ehrenberg.The sludge reduction was found to be closely related to the structure of the microfauna community.In the starting period,the sludge mass kept stable.After 20 days,the sludge mass in the reactor increased significantly due to the growth of Aeolosoma hemprichii Ehrenberg,who caught protozoa and Rotaria as food,leading to a subsequent decrease in the microfauna population.Therefore,how to stabilize the microbial structure of microfauna community was critical for a long-term sludge reduction in MBR.The total mass of supplemented sludge was 126.9 g and the total reduced mass was 100.2 g in the MBR,leading to a 78.96% of reduction.Microfauna predation accounted for 73.9% of the total reduction mass,which suggested the great importance of microfauna predation for the sludge reduction in MBR.