Effect of Hydraulic Retention Time on Treatment Performance in an Anoxic/Oxic Electro-Membrane Bioreactor

Bacterial profile, nutrients removal performance, and membrane fouling behavior were evaluated in an anoxic/oxic electro-membrane bioreactor (A/O e-MBR) treating municipal wastewater at different hydraulic retention times (HRTs) (30, 20, and 15h). The results demonstrated that HRT reduction from 30 to 15h had a negligible effect on chemical oxygen demand (COD), ammonium (NH4+-N), and total phosphorus (TP) removal, showing efficiencies above of 98%, 99%, and 95%, respectively, for any experimental runs. On the other hand, total nitrogen (TN) removal improved significantly from 80.7% to 90.5% as the HRT was reduced from 30 to 15h. Activity batch assays have shown a higher specific nitrate uptake rate (SNUR) at the shorter HRT. Results of DNA sequencing analysis indicated a larger amount of denitrifying bacteria genus and a greater relative abundance of Nitrospira genus at shorter HRTs, supporting the higher SNUR and the greater TN removal. The membrane fouling rate increased by about 16 times during the period with HRT of 15h. Besides, some fouling propensity parameters have shown a worse mixed liquor filterability in this period.