Membrane Formation And Fouling In Self-forming Dynamic Membrane Bioreactor And Control Strategy

Self-forming Dynamic Membrane Bioreactor (SFDMBR) employes inexpensive mesh filter materials, such as non-woven fabric, replaces conventional microfiltration/ultrafiltration membranes as filtriation modules. It uses formed Dynamic Membrane (SFDM) deposited on the mesh materials by active sludge in the intinal separation process, to acquire approximately separate results of conventional membranes.The permeability performance, structure and compossibility evolution of SFDM is very different with conventional MBR, even more complicated. As a result, the SFDM permeability, structure and compossibility evolution was studied to have a better understanding of SFDM formation and fouling mechanisms. Results show that SFDM exhibited obvious retention of COD, and at the same time, rejected a portion of NH4+-N with small molecules. According to the characteristics of effluent turbidity, the SFDM can form rapidly during intinal 1h, to achieve strong SS rejection.The permeate flux declined quickly, and after 5 h it changed slowly. The resistance increased rapidly in the initial 5 h and then increased slowly. The situation was continuing until dynamic balance was break, and SFDM resistance increased rapidly again. The resistance increased fast at the beginning because a lot of biomass deposited on the non-woven fabric; it then increased fast because small particles blocked, gel layer formed in the bottom of SFDM and sludge compressibility in the long-term operation occured.The results of FTIR, EEM and EPS analysis show that EPS was main foulants. Protein mostly deposited from mixed liquor, while polysaccharides partly deposited from mixed liquor and partly was released form bottom anaerobic biomass to form gel layer with surrounding bottom biomass, resulting in increased resistance.On the base of understanding SFDM formation and fouling mechnasims, membrane fouling in three parallel SFDMBRs operated under different aeration intensities (200,500 and 800 L/h) was studied to have a better understanding of the membrane fouling mechanisms. The research showed that different aeration intensities can change the shear force and DO, which has different effects on SFDM formation and the fouling process.The results showed that either small or large aeration intensity had a negative influence on membrane permeability. Low aeration intensity could not remove unnecessary matters deposited on the SFDM surface. It means large particle deposited on the SFDM, the biomass was high and SFDM formation time was short. The formed SFDM has large porosity and cake resistance was low, but resistance increased rapidly and membrane fouling was serious.High aeration intensity had a positive effect on cake layer removal. It resulted in small particle deposited on the SFDM, least deposited biomass, the lowest flux decline fate, the longest time, the lowest porosity, and the largest specific cake resistance. Moreover, the large aeration intensity resulted in a severe breakup of sludge flocs, and promoted the elease of colloids and solutes from the microbial flocs to the bulk solution. When the aeration intensity increased to 800 L/h, EPS concentration became greater than before and turned to be the major foulants, with increased specific cake resistance and serious membrane fouling. EPS was the main membrane foulant.