Research On The Influence Of The Mixed Liquor Chauacteristics On The Ceramic MBR Membrane Fouling Formation

Ceramic Membrane Bioreactor has been used more and more in wastewater treatment for its good chemical stability, mechanical strength, antimicrobials pollution, thermostability, high separation efficiency and non-aging ability. But like other Membrane Bioreactor, membrane fouling is still the utmost problem for its widely application.In this study, in order to study on the influence of the mixed liquor characteristics on the ceramic membrane fouling and find some corresponding countermeasures to control it, pilot-scale ceramic microfiltration equipment was designed to treat real domestic sewage from a wastewater treatment plant.The pilot-scale Membrane Bioreactor has been operated for69days and used a pneumatic pump to suction10minutes and stop2minutes, the back washing cycle was one hour, the back washing time was45seconds, the quantity of water used in backwashing was3.2L/h, the water pressure of back washing was13kPa, the DO was set between4and8mg/L and the HRT was about13hours.According to the whole operation, the article mainly made a research on the variation of the activated sludge properties and its influence on the membrane fouling. We found that the small particles in supernatant adhered to the membrane surface preferentially and even entered into the hole of the membrane at the very beginning which lead to the rapid reduction of the membrane permeate flux and the sharp rise of operation pressure. As the development of the gel layer and the deposition of the cake layer, the operation pressure rise slowly and the permeate flux is relatively stable. But when the cake layer was compacted and the MLSS was too high, the operation pressure rose and the permeate flux reduce quickly again. So it is necessary to control the deposition of the cake layer and reduce the adherence of the small particles at the beginning. According to the analysis of the particle size distribution at different time, we found that the particle size turned to decrease. When EPS (Extracellular Polymeric Substances) and SMP (Soluble microbial products)—two most important factors of the membrane fouling was detected, we found that the quantity of EPS was much higher than the SMP, the fluctuation of the two ones was tiny, the high (protein/polysaccharide, P/C ratio) of the EPS made an important influence on the deposition of the cake layer, while the high quantity polysaccharide in the SMP made an important influence on the formation of sticky gel layer. As the increase of SRT, the high molecular weight substances in the supernatant increased for the interception by the cake layer and the accumulation of old and dead cell. The quantity of EPS existed in the fouling was higher than that in the activated sludge, but the quantity of SMP was similar.We use FESEM to featured the morphology of the fouling and found quite a lot pollutant fill in the pore and even enter into the supporting layer which made the boundary difficult to be distinguished and the cover of the pollutant made the membrane pore nonuniform and indistinct. There were similar biological fouling between the membrane fouling and the activated sludge. When we use FTIR to detect the dry membrane fouling and activated sludge powder, we found the location of their adsorption peaks were similar. We found the mainly components were different protein, polysaccharide and nucleic acid. Inorganic salt formed the adsorption together with some particulates and made the pore block fouling.The cleaning of the membrane made a wide significance on the recovery and recondition of the membrane, we choose0.033%NaCIO and1%citric acid to clean the fouled membrane, at last we got the membrane permeate flux recover to88.43%. The analysis of the membrane resistance pressure indicated that the resistance pressure came from the cake layer took up95.82%of the total resistance pressure and was the main part of the resistance, while the resistance pressure came from the pore block and adherence took up2.13%of the total ones, much less than the cake layer one, but its impact on the membrane fouling was significant.Appropriate back washing and scrubbing with sponge can control the fouling from the formation of cake layer, but the formed secondary membrane would be removed at the same time, which would accelerate the formation of irreversible fouling.