Study On The Performance Of Anaerobic Self-forming Dynamic Membrane (AnSFDM) For Wastewater Treatment And Mechanism Of AnSFDM Formation And Fouling

Anaerobic self-forming dynamic membrane bioreactor (AnSFDMBR), a technological combination of self-forming dynamic membrane bioreactor(SFDMBR) and anaerobic digestion, has emerged as a promising substitute of the conventional MBR. In SFDMBRs, the initial sludge layers formed on the coarse-pore materials, called self-forming dynamic membrane (SFDM), fulfill the function of solid-liquid separation. The capital cost is reduced by displacing the micro/ultrafiltration membrane with cheap coarse filter modules, and membrane fouling is mitigated owing to the large diameter simultaneously.In this study, we introduced an AnSFDM system with high aperture non-woven fabric as filter module and by gravity-flow filtration mode. The wastewater treatment effect of the AnSFDMBR and the filtration characteristics during the whole operation were monitord to evaluate its application feasibility. The composition (SS, EPS, SMP, inorganic substances), physiochemical properties (RH, Zeta Potential, compressibility), and topography (PSD, SEM) of AnSFDMs were analyzed by means of dividing one filtration process into3stages in order to investigate the formation and fouling mechanisms of AnSFDMs. Moreover, the AnSFDMBR performance and AnSFDM formation/fouling under different agitation conditions were investigated to explore influence of the mixed liquor properties and hydraulic shearing force on the AnSFDM.The AnSFDMBR exhibited satisfying wastewater treatment effect with average effluent COD of72.55mg/L and removal efficiency of92.94%. It deserves to be specially noted that the anaerobic self-forming dynamic membrane(AnSFDM) alone showed good rejection capability of for SS and COD with low effluent turbidity of1.0-1.5NTU and apparent reduction of supernatant COD concentration of52.96%. The AnSFDM can form in50min and the effective operation stage can last12-15d with a relatively stable effluent flux of20-30L/m2h. The mechanisms of AnSFDM formation and fouling were detected by dividing the whole filtration process into3stages. In the formation stage, the increment of filtration resistance based on the naked non-woven fabric was caused by the blocking of the large aperture of the surface of non-woven fabric. Therefore, large particles, whose size is larger than or similar to the aperture of membrane module, is the main contributor of AnSFDMs formation. Though the sediment amount of sludge flocs in this stage is less than the other two stages, the effect of which to the decreasing of flux and the increasing of resistance is evident. During the stable stage, the porous of AnSFDM was further narrowed because of the deposition of smaller particles and EPS/SMP and other colloidal matter, which has weak effect to the resistance but obvious action on the rejection ability of the AnSFDM. The most considerable filtration resistance in clogged stage is due to the combination of EPS and other foulants deposition/release and compactness of the AnSFDM. During clogged stage, the surface of AnSFDM was covered overall and the porous was almost clogged completely, then the sludge toward on the surface later was tucked into the AnSFDM and the whole AnSFDM was compacted more tightly. The consolidation of the conglutination between foulants caused by the increase of EPS/SMP content is another main factor for specific resistance increase. The compact stucture and EPS content increase of the AnSFDM in clogged stage caused the abruptly increase of specific resistance and the deterioration of permeation capability.AnSFDMBR performance and conditions of AnSFDM formation/fouling were detected in3parallel AnSFDMBRs operated under different stirring intensities (150,300and450rpm). Results showed that either low or high agitation intensity had a negative effect on membrane permeability. The hydraulic shearing force produced by agitation, on the one hand, can control the movement of particles towards the AnSFDM surface so as to mitigate membrane fouling; On the other hand, the sludge flocs can be broken by this shearing force and cause the decrease of particle size with severe release of EPS, which will make membrane fouling more serious. High agitation intensity following intensive scouring on AnSFDM surface, small particle size, high EPS content could be adverse to AnSFDM formation and had a positive effect on blocking and compression of AnSFDM to increase membrane fouling. The compact and low-porosity AnSFDM under high agitation intensity can present a good rejection effect for organic molecular. Under Low agitation intensity, the shearing force cannot resist the drag force by high flux, which facilitated to AnSFDM formation but was not favor to mitigation of AnSFDM fouling.