Effect of calcium addition on sludge properties and membrane fouling potential of the membrane-coupled expanded granular sludge bed process

The expanded granular sludge bed reactor (EGSB) is considered a promising technology for anaerobic wastewater treatment, and the effluent quality can be further improved by membrane treatments. To mitigate membrane fouling of the membrane-coupled anaerobic process, 2.5 mM CaCl2 was added in a laboratory-scale EGSB reactor (3 L in volume). The effluent was subjected to short-term dead-end ultrafiltration (UF) tests to evaluate the membrane fouling potential. The results showed that Ca2+ addition to EGSB efficiently alleviated the fouling of the subsequent UF treatment compared with the control. The fouling potential was not diminished when Ca2+ was directly added to the efficient of the control EGSB. Further investigations revealed that the addition of Ca2+ to the EGSB resulted in an increase in the content of extracellular polymeric substances ([PS) of the granule by 24.1%. The addition of Ca2+ also reduced the concentration of the soluble extracellular polymeric substance (sEPS) (or soluble microbial product SMP) in the efficient by 47.7-60.7% compared with the control system. Analysis of the fouling model revealed that Ca2+-P addition reduced the cake resistance (R-c) by 42.8% and delayed the transition from the standard pore blocking model to the cake filtration model. The results indicate that fouling relevant compounds, such as sEPS (aromatic proteins, tryptophan proteins and polysaccharides) and fulvic acids are included in the sludge when Ca2+ is added to the reactor, thus preventing them from reaching the membrane surface. (C) 2015 Elsevier B.V. All rights reserved.