Experimental Study On Controlling Membrane Fouling By PAC In MBR

Membrane bioreactor(MBR) has much more advantages compared with other wastewater treatment processes.But the widespread application of the membrane bioreactor is constrained by membrane fouling,to settle the problem is the main aspect of research in this field.The purpose of this study was to investigate the control of PAC on membrane fouling.The effect of powdered activated carbon(PAC) on effluent quality and membrane fouling in MBR were investigated through parallel tests.The reactors were fed with synthetic domestic sewage.The results showed that:There was no significant improvement of effluent with the addition of PAC in the experiment.In both reactors the removal rates of COD and ammonia were higher than 95%.The removal rates of COD and ammonia were higher in reactor 2 because of the PAC addition on the whole。Membranes in two reactors showed the similar decreasing law of membrane flux.It was found that washing period became short when sludge concentration increased and small when HRT was longer.When PAC dosage was 1g/L,the decreasing rate of flux could be slowed effectivelly if the sludge concentration was not too high;When PAC dosage was 2g/L,the decreasing rate of flux was quicker,but this result was not sure because Filamentous bacterium grew quickly in this phase.The cake layer on membrane was very loose,and was washed away easily when there was PAC dosage in reactor.The effect of chemical washing was very well,and the washing order of "hydraulic washing +acid washing+alkali washing+oxidant washing(NaClO)" obtained the best effect.Sludge concentration was higher,since the growing environment was improved when there was PAC in reactor.The biological activated carbon(BAC) could resistance hydraulic shear stress to a certain extent,so the distribution of sludge diameter could be better.The average diameter of sludge was 82.90μm in the reactor with PAC addition while it was just 23.76μm in the reactor without PAC addition,and the settleability of sludge in the reactor with PAC addition was improved,but SV30 was still more than 90%,and the SVI was higher than 150mL/g.There was a certain mount of Epistylis in mature sludge,but on the fifth phase Filamentous bacterium grew quickly,and the filtration capacity became worse in both reactors.PAC could lower the cake resistance,so the total resistance was decreased. Filtration experiment showed that cake resistance made up over 90%of total resistance whatever there was PAC dosage.The resistance was very high when the sludge concentration was too high as well as when there was too much Filamentous Bacterium.It was found that,the variation of filtration resistance was fit to the standard blocking filtration model in first 1 minite's process,and then fit to cake filtration model in later process,the later phase controled the filtration.The specific resistance to filtration of sludge in the reactor with PAC addition was reduced,because the PAC dosage improved distribution of sludge diameter,decreased the viscosity of mixture and raised resisted pressure well.