Study On The Effect Of Organic Flocculant On MBR Wastewater Treatment Performance And Membrane Fouling Behavior

Membrane fouling during the application of membrane bioreactor(MBR)has always been a hot spot in the study of membrane water treatment.Adding flocculants to improve the properties of the MBR mixture and slow down the occurrence of membrane fouling is one of the effective the solution to many questions.The good place of organic flocculants is their small amount,excellent effect,less affected by p H and temperature,and low residual sludge output,and have been widely used.However,the dosage of organic flocculant needs to be strictly controlled.If the dosage is too small,the effect may not reach the expected result,and if the dosage is too large,it may cause organic pollution.Therefore,this paper selects four typical organic flocculants,through the beaker test and batch membrane filtration experiment,selects one with better effect as the dosing agent for continuous process experiment,and the MBR wastewater treatment efficiency and membrane fouling control effect were also studied.The following research results were obtained:(1)Perform a beaker test on PAM,PDMDAAC,chitosan,and starch.By studying the effects of four dosing agents on sludge supernatant COD,supernatant turbidity,sludge specific resistance of activated sludge and SV30,it was concluded that the optimal dosage of PAM,PDMDAAC,Chitosan and starch was 4mg/L,500mg/L,40mg/L,30mg/L.(2)Under the optimal dosage,the concentration gradient was further divided,and the removal effect of organic flocculants with different concentration gradients on pollutants,the critical flux and the membrane under high flux were measured through batch membrane filtration experiments contamination rate.The results show that when the dosages of PAM,PDMDAAC,chitosan and starch are 5mg/L,300mg/L,35mg/L and 40mg/L respectively,the pollutant removal effect is the best,the effect is the pollutant removal effect,and the membrane critical flux is the largest,and the membrane fouling rate is the lowest.Finally,combined with a comprehensive economic analysis,chitosan was selected as the dosing agent for continuous process experiments,and the dosing amount was 35 mg/L.(3)A small-scale experimental device with chitosan added as the experimental group(K-MBR)and no chemical added as the blank group(C-MBR)was constructed,the third stage continuous process test was carried out,and the settling and filtration properties of sludge were compared and analyzed.The test mainly measured the operating cycle of MBR,transmembrane pressure difference TMP,activated sludge capillary water absorption time(CST),Zeta potential,sludge particle size(PSD)distribution,sludge concentration,and relative sludge hydrophobicity(RH)and extracellular polymer content.The results show that the operation time of K-MBR and C-MBR is 47 days and 27 days,respectively.The increase rate of TMP in blank group was 1.7 times of that in experimental group.Compared with the blank group,the addition of chitosan reduced the sludge capillary absorption time,and the distribution of activated sludge potential and sludge particle size was wider,and the sludge concentration was higher,reduced SVI value,better effluent water quality,reduced SMP content in the reactor,and the addition of chitosan did not reduce the content of extracellular polymer.It was found that the pollutants formed irregular flocs on the outer layer of the membrane.The results of sludge filtration resistance show that,it is found that after adding chitosan,the particle size of the sludge is increased,and larger gel masses are formed to accumulate on the outside of the membrane causes the resistance of the gel layer to expand.Based on the above analysis,it is believed that the mechanism of chitosan alleviating membrane pollution is that the macromolecular organic matter in the sludge mixture is adsorbed by chitosan,forming the adsorption bridging effect.In addition,chitosan molecules can neutralize the negatively charged macromolecules in the sludge supernatant through the electric neutralization,and make them gather into large particle flocs.Moreover,chitosan can transfer the organic matter in the liquid to the solid,which increases the concentration of EPS in the mixture,while reduces the content of SMP.The high concentration of EPS increases the hydrophobicity of the flocs in the sludge mixture,which prevents the pollutants from combining closely with the membrane,and the membrane pollution is alleviated.