The effects of different carriers on removal performance and membrane fouling by HMBR in treating sewage with low carbon-to-nitrogen ratio

A hybrid membrane bioreactor (HMBR) with biological-band carriers (reactor A) and a HMBR with suspended-honeycomb carriers (reactor B) were used for treatment of sewage with low carbon-to-nitrogen ratio (3–5). The pollutant removal performance and membrane fouling in HMBRs was investigated under different hydraulic retention times (HRT) (5 h and 9 h). The results demonstrated that both HMBRs can be effective for the removal of chemical oxygen demand (COD), NH3-N and total nitrogen (TN). The rate of TN removal in reactor A was higher than that in B. Moreover, it was found reactor A was more advantageous for the degradation of biodegradable organic matter than that of B. The biomass in reactors was characterized by mixed liquor adherent solids (MLAS), particle size distributions, mixed liquor suspended solids (MLSS) and concentration of extracellular polymeric substance (EPS). The results showed that MLAS content and particle size distribution in reactor A were higher than in B, whereas concentrations of MLSS and EPS exhibited the opposite trend. When systems were run under different HRTs, the increased rate of trans-membrane pressure (TMP) in reactor A was slower than that in B. Therefore, reactor A was considered superior to reactor B in pollutant removal and controlling membrane fouling.