Impact of membrane addition for effluent extraction on the performance and sludge characteristics of upflow anaerobic sludge blanket reactors treating municipal wastewater

• Impact of membrane addition on the performance of UASB reactor was investigated.
• Membrane incorporation resulted in a drop in sludge settleability of the UASB.
• Deterioration of sludge settleability led to an increase in sludge washout.
• Despite the increased sludge washout, high quality permeate was obtained.
• UASB is a suitable alternative for coupling membranes in AnMBR systems.

In this study, the impact of membrane incorporation for effluent extraction on the performance of an upflow anaerobic sludge blanket (UASB) reactor treating municipal wastewater was investigated in terms of system performance and sludge characteristics. A laboratory-scale system was operated in two different operational stages: (i) as a sole UASB reactor and (ii) as an anaerobic membrane bioreactor (AnMBR). Membrane incorporation induced an accumulation of fine particles and a decrease in extracellular polymeric substances (EPS), resulting in a decrease in particle size distribution (PSD) and, thus, a drop in sludge settleability. Deterioration of sludge settleability led to an increase in sludge washout, with a resultant increase in chemical oxygen demand (COD) and total suspended solids (TSS) in the UASB effluent. However, suspended solids-free permeate with an average COD of 42 mg/L was obtained and despite the sludge bed deterioration, the average transmembrane pressure (TMP) value was 85 mbar indicating no severe membrane fouling. Pyrosequencing analysis demonstrated the increase in microbial community indexes of the UASB sludge after membrane addition, exhibiting an increase in both richness and evenness. Considering all responses of the UASB reactor to membrane incorporation, the overall results put UASB reactor forward as a suitable alternative for coupling membranes in AnMBRs.

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