Study On Sludge Properties And Membrane Permeability Of The Membrane Bioreactor Process

In recent years,China's limited water resources have been continuously polluted,resulting in deterioration of water quality and serious damage to aquatic ecosystems.The membrane bioreactor(MBR)process is applied with its advantages of high quality effluent.However,during the operation of the MBR process,there is a problem that the transmembrane pressure difference is increased or the membrane permeability is lowered,which affects the continuous operation of the MBR.Recent studies on the influencing factors of the MBR indicate that the parameters associated with membrane clogging are more critical factors affecting the continued operation of the MBR.to this end,this paper investigated the relationship between sludge characteristics of the MBR process mixture and membrane clogging,analyzed the correlation between sludge characteristics and membrane permeability decline,identified key membrane clogging factors,and established a membrane clogging prediction model;the effect of cleaning on membrane permeability recovery and the effect of aeration intensity on membrane clogging were also investigated.The main findings of this paper are as follows:(1)The relationship between the characteristics of the mixed liquor sludge was studied.The results show that with the increasing concentration of the mixed liquid suspended solids(MLSS),the mixed liquor volatile suspended solids(MLVSS)and the soluble chemical oxygen demand(sCOD)increase continuously,and the average value of MLVSS/MLSS during operation is 0.7.The activated sludge of MBR system has good sewage treatment capacity,while the extracellular polymeric substance(EPS)has a downward trend during concentration.In addition,the capillary suction time(CST)and the diluted sludge volume index(DSVI)increase with the increase of the MLSS concentration,and the dewatering and sedimentation of sludge gradually deteriorate.Analysis of the correlation between the MLSS and other sludge characteristics by SPSS software shows that MLSS has strong correlation with MLVSS,EPS,sCOD and CST,while the DSVI has a weak correlation with the MLSS concentration.(2)The effect of sludge properties on membrane flux and membrane permeability was investigated.The results showed that the correlation between sludge properties and membrane flux and membrane permeability was analyzed by SPSS software.The correlation between the MLSS concentration and membrane flux and membrane permeability was the largest.The partial correlation analysis further proves that the MLSS concentration is the most important factor affecting membrane clogging.In addition,a predictive model of membrane flux and membrane permeability is obtained by fitting the MLSS concentration to membrane flux and membranepermeability:J_?=21.33-0.68MLSS?J_?=21.16-0.68MLSS?L_?=391.51-15.99MLSS?L_?=384.27-15.73MLSS.(3)Study the changes of critical flux under different the MLSS concentrations(8g/L?13 g/L?20 g/L)and different aeration strengths(0.2 m~3/(m~2·h)?0.4 m~3/(m~2·h)?0.6 m~3/(m~2·h)?0.8 m~3/(m~2·h)).The results show that the value of critical flux decreases with the increase of sludge concentration,and increases with the increase of aeration intensity.However,the increase of the critical flux value is not without an upper limit.When the aeration amount reaches a certain critical value,the aeration amount is increased,and the critical flux is no longer increased.In addition,when the reactor is operated at high MLSS concentration,the effect of aeration intensity on critical flux is not significant.