Filtration performance and cleaning strategy of thermophilic AnMBR treating food waste
Membrane fouling is a major challenge in the operation of an anaerobic membrane bioreactor,fouling is the main reason restricting membrane practical application.In this study,food waste was taken as the substrate,the filtration performance and cleaning strategy of a hollow fiber AnMBR was evaluated under thermophilic condition(50±1)℃ and a hydraulic retention time of 15 days.Results showed that the AnMBR system run stably under these conditions with the rejection rates of 96％,98％and 93％for COD,carbohydrates and proteins,respectively.The solid content of the digestate maintained at about 28 g·L-1 during the stable period,and rapid membrane fouling occurred when it run at a flux of 7.8 LMH,while the filtration duration could be significantly extended by 27 days when it run at a flux of 5.4 LMH.In addition,the main fouling resistance was resulting from development of a cake layer and organic pollution.After physical cleaning,a chemical cleaning of fouled membrane by soaking in 1 g·L-1 sodium hypochlorite solution for 15h and then in 2 g·L-1 citric acid solution for 2 h could restore the membrane permeability.A batch experiment to study the effect of sodium hypochlorite on the activity of anaerobic microorganisms showed that a concentration lower than 0.25 g·L-1 of sodium hypochlorite had slight effect on the activity of functional methanogens.The study showed that in AnMBR,both membrane filtration and cleaning improved the process performance on treating high concentration food waste,and the continuous operation of the membrane could be achieved by optimizing the membrane cleaning strategy.
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