Intermittent filtration and gas bubbling for fouling reduction in anaerobic membrane bioreactors

The effect of intermittent filtration combined with gas bubbling on membrane fouling in a submerged anaerobic membrane bioreactor (SAnMBR) treating synthetic municipal wastewater was investigated. The experiments were performed using a bench-scale UASB reactor with a submerged tubular ulrafiltration membrane operated at room temperature and a hydraulic retention time (HRT) of 8 h. Results show that for a continuous filtration mode, the filtration run lasted 20.3 h, while for intermittent filtration tests without gas bubbling, 10 min on–1 min off and 4 min on–1 min off, the duration were 32 and 52 h, respectively. Moreover, when the gas bubbling was introduced, filtration runs were more than ten times longer than without it. Under tested organic loading rate of 1.2 kg COD m−3 d−1 COD removal efficiencies were between 96.3% and 98.7%. An early blockage in intermittent filtration tests without gas bubbling was related to the presence of the carbohydrate fraction of extracellular polymeric substances (EPSc) and soluble microbial products (SMPc). The better performance obtained with nitrogen bubbling was caused by the increased internal mixing, which induced a greater removal of organic matter in the reactor. The results suggest that the operation mode 4 min on–1 min off with intermittent filtration and gas bubbling in the period of relaxation was more effective in minimizing membrane fouling.