Performance of submerged anaerobic membrane bioreactor at different SRTs for domestic wastewater treatment.

Three submerged anaerobic membrane bioreactors (SAnMBR) with solids retention times (SRTs) of 30, 60 and 90d were set up for domestic wastewater treatment. Total COD removal rates higher than 83% were achieved. Maximum biogas production was 0.5L CH4d(-1) (0.010L CH4 (gMLVSS)(-1)d(-1); MLVSS: mixed liquor volatile suspended solids) at a SRT of 90d. A longer SRT benefited biomass accumulation and biogas production due to enhanced dominancy of methanogens. With the SRT increasing from 30 to 90d, enhancement of hydrolysis from 35 to 56% was identified as the major reason for the better efficient acidification and methanogenesis observed. Best treatment performance and membrane fouling control were observed for the SAnMBR operated at a SRT of 60d. Soluble microbial products or specific soluble microbial products that accumulated with SRT decrease from 60 to 30d led to a faster membrane fouling. With an increase of SRT from 60 to 90d, higher mixed liquor suspended solids concentration caused more particle deposition on the membrane surface, while more soluble microbial products or specific soluble microbial products was attributed to more metabolism products generation.

Submerged anaerobic membrane bioreactor for low-strength wastewater treatment: effect of HRT and SRT on treatment performance and membrane fouling.

Three 6-L submerged anaerobic membrane bioreactors (SAnMBRs) with solids retention times (SRTs) of 30, 60 and infinite days were setup for treating synthetic low-strength wastewater at hydraulic retention times (HRTs) of 12, 10 and 8 h. Total COD removal efficiencies higher than 97% were achieved at all operating conditions. Maximum biogas production rate was 0.056 L CH(4)/g MLVSS d at an infinite SRT. A shorter HRT or longer SRT increased biogas production due to increased organic loading rate or enhanced dominancy of methanogenics. A decrease in HRT enhanced growth of biomass and accumulation of soluble microbial products (SMP), which accelerated membrane fouling. A drop in carbohydrate to protein ratio also inversely affected fouling. At 12-h HRT, the effect of SRT on biomass concentration in SAnMBRs was negligible and membrane fouling was controlled by variant surface modification due to different SMP compositions, i.e., higher carbohydrate and protein concentrations in SMP at longer SRT resulted in higher membrane fouling rate. At 8 and 10-h HRTs, infinite SRT in SAnMBR caused highest MLSS and SMP concentrations, which sped up particle deposition and biocake/biofilm development. At longer SRT, lower extracellular polymeric substances reduced flocculation of particulates and particle sizes, further aggravated membrane fouling.