Study On Flocculants Mitigate Membrane Fouling In MBR

By adding poly dimethyldiallylammonium chloride(PDMDAAC), PAC and composite flocculant by PDMDAAC and PAC in membrane bioreactor(MBR) to examine the effect of mitigate MBR membrane fouling at continuous operation, respectively. Several variable indexes including MBR operation cycle, activated sludge capillary suction time(CST), Zeta potential, the sludge volume index(SVI), content of extracellular polymeric substancesd, activated sludge morphological and other parameters were tested to identify the three additional flocculant less optimal dose and dosing method.The results showed that: by adding flocculants can effectively mitigate membrane fouling. Three different flocculants mitigate membrane fouling at the same dose dosing effect PDMDAAC best, followed by composite flocculant, PAC worst. In the test of additional dose and dosing interval, PDMDAAC, composite flocculant and PAC all exhibited dose than dosing method was more effective to mitigate membrane fouling. According to experiments in trends of transmembrane pressure(TMP) can be determined first plus 400 mg/L PDMDAAC, the best additional dose of 90 mg/L. Optimal dose of 90 mg/L could significantly prolong the MBR continuous operation cycle, which operation cycle was 3.4 times than the reactor without additional dose of flocculant, while the PAC optimal dosage was 120 mg/L. Through mass ratio 6: 4 composite PDMDAAC and PAC, the composite flocculant not only effectively mitigate membrane fouling, but also can be used to reduce the high costs by PDMDAAC. Integrated TMP growth trends and changes in SVI value can be determined optimal composite flocculant additional dose of 60 mg/L. Adding flocculant can not only reduce CST and SVI, but also increase the Zeta potential and reduces the concentrations of the extracellular polymeric substances, which makes the sludge floc closer and the cake layer thinning on membrane surface. As resulate, the MBR was extended the operating cycle under constant flow. Flocculants had no significant effect on the MBR effluent, the average removal rate of COD, TN were 93.1 % and 89.1 % by dosing PDMDAAC in the MBR reactor respectively, the effluent concentrations of 45, 5 mg/L or less, to achieve an A emissions standards.