Performance And Membrane Process Characteristics Of Anaerobic Forward Osmosis Membrane Bioreactor For Urban Sewage Reclamation

As a new membrane technology, forward osmosis(FO) draws worldwide attention in recent years due to its advantages of high rejection rate, and excellent effluent quality, low energy consumption and low fouling potential. Wastewater, which contains a wealth of water and organic resources, can be reclaimed to reduce the pollutant discharge; and recycle the energy and resource. In this study, an anaerobic FO membrane bioreactor(FOMBR) was designed and operated for domestic wastewater treatment, and its performance on pollutant removal and energy recycle as well as its membrane fouling characteristics were investigated to provide reference for the further research.An FO system was firstly built for sewage concentration. By the FO membrane, the volume of wastewater was concentrated to 1/10, and the concentrated sewage had a chemical oxygen demand(COD) concentration of about 3000 mg/L. The concentrations of pollutants in the effluent, including COD, ammonia, total nitrogen(TN) and total phosphorus(TP), reached the standard of I-A of the urban sewage discharge standard(GB18918-2002). The water flux of the system was influenced by the draw solution(DS) concentration and the crossflow velocity. With high DS concentration, the water flux increased, while the membrane fouling was more severe. With a too low crossflow velocity, the water flux would be reduced due to the membrane fouling. FO membrane fouling could be remitted by physical cleaning and chemical cleaning, with a flux recovery of 97%.The concentrated sewage was then treated in an anaerobic bioreactor. The removal efficiency of COD was over 75%, while those of nitrogen and phosphorus were much less. The treatment efficiency was improved with a longer hydraulic retention time(HRT), but was inhibited if it’s too high. As the HRT increased, the total methane production was increased, while the production rate was declined. Additionally, the impacts of sodium chloride(Na Cl) and ammonia on methane production were investigated and it was shown that both Na Cl and ammonia had negative influence on the gas production, and the suppression was greater with the presence of both than either single one.An anaerobic FOMBR system was also built for domestic wastewater treatment, and its removal efficiencies of COD, ammonia nitrogen, TN and TP were over 95%. The gas production rate increased with the increase of DS concentration, but on the contrary, the gas production efficiency decreased. The initial water flux of the anaerobic FOMBR was increased with the increase of DS concentration, and meanwhile the membrane fouling became more severe. The detection of mixed liquor characteristics showed that polysaccharides and humic substances were the dominant contents in the mixed liquor, while the concentration of protein was relatively low.