Microbial community structure analysis in a hybrid membrane bioreactor via high-throughput sequencing.

Compared to the suspended culture (sludge) of a conventional bioreactor, hybrid membrane bioreactors (HMBRs) are more effective at removing pollutants owing to the addition of fillers addition of fillers that facilitate biofilm formation. However, the microbial community structure and composition in an HMBR remain unclear. We ran three laboratory-scale HMBRs at room temperature under different sludge retention times (SRTs; 10 d, 20 d, and 30 d) to compare the microbial diversity and community structure among the membrane surface, suspended filler surface, and mixed liquor using high-throughput sequencing. The results showed that SRT can markedly affect microbial community structure in the HMBR, and different trends appeared in the three functional units. The largest number of mutual operational taxonomic units was found in the activated sludge mixture and suspended carrier with an SRT of 20 d and 30 d. Species belonging to Proteobacteria in the 10 d SRT group had the greatest contribution to between-group differences. A longer SRT could mitigate membrane fouling by decreasing the relative abundance of Thauera and Sphaerotilus attached on the membrane surface. Comamonadaceae, a family of denitrifying bacteria, offer high denitrification potential for bioreactors operating under a long SRT.

Box-Behnken response surface approach to identify factors affecting membrane fouling in a hybrid membrane bioreactor treating domestic sewage.

The effect of hydraulic retention time (HRT) and sludge retention time (SRT) on extracellular polymer substrate (EPS) content and resistance of a hybrid membrane bioreactor (HMBR) treating domestic sewage was analyzed by Box-Behnken response surface methodology. The quadratic response surface model demonstrated significant effects of both HRT and SRT on EPS content (both P value < 0.05), SRT on membrane resistance (P value = 0.0119), and their interaction was significant (P value = 0.0273) for EPS but not membrane resistance (P value = 0.0609). Model optimization indicates that the optimal conditions for the HMBR to control membrane fouling were an HRT of 10 h and SRT of 30 days. Under these optimal conditions, both the EPS content and the predicted membrane resistance closely matched the actual average value with the error about 8%. Thus, the feasibility of applying response surface methodology to an HMBR for treating domestic sewage was demonstrated. According to the detection result of the three-dimensional fluorescence (excitation-emission matrix), humic acid-like and fulvic acid-like substances gain much higher levels in the suspended carriers than those in the membrane and sludge, suggesting that these are key components of the membrane pollutants. Graphical abstract .