Insight Into PAC Dosage And Refreshment Ratio On MBR Performance And Membrane Fouling

Worldwide shortage of water and energy,strict standards for wastewater discharge,and environmental protection emphasizes the need for sustainable wastewater treatment processes.MBR shows unique advantages including small footprint,low sludge yield and more effective removal of pollutants than conventional activated sludge method.In this paper,a comparative research was conducted to study the effect of the dosage of powder activated carbon(PAC)and its replenishment ratio on the performance of MBR and membrane fouling mechanism.The effects of different dosages of PAC on membrane fouling and MBR performance were investigated.The addition of PAC reduced the filtration resistance by 9.08%,decreased the fouling rate by more than 18.3%,and prolonged the service life of the membrane by over 1.6 times.PAC decreased the concentration of soluble microbial product(SMP)and reduced membrane fouling,while the protein/polysaccharide ratio decreased.PAC reduced the adsorption and deposition of proteins and polysaccharides on the membrane surface or within the pores.The resistance of reversible and irreversible fouling was related to the dosage of PAC.At the dosage of 2 g/L,PAC was beneficial to alleviate membrane fouling.The effects of PAC replenishment ratio on membrane fouling and microbial community in PAC-MBR were studied.PAC replenishment had no effect on the removal of organic matter and nitrogen.With the increasing ratio of PAC refreshment,SMP content decreased and extracellular polymeric substances(EPS)content increased.The change of SMP content was consistent with the change of fouling rate in TMP,and the lower EPS concentration could slow down the adhesion of the sludge to the membrane.The replenishment of PAC aggravated the accumulation of polysaccharide in SMP,while the accumulation of polysaccharides decreased as the ratio of PAC replenishment increased.When PAC refreshment ratio was 1.67%,the protein content in SMP decreased by 13.4%.The content of polysaccharides and protein in EPS increased with the increase of the replenishment ratio of PAC,and PAC replenishment increased P/C value and enhanced sludge flocculation.The fouling rate and resistance analysis further confirmed that PAC replenishment could slow down membrane fouling tendency of MBR.Molecular weight distribution measurement revealed the synergistic effect of PAC adsorption/biodegradation and membrane interception on removal of organic matter.FTIR and SEM-EDX analysis showed that PAC replenishment reduced the contamination of the filter cake layer,reduced the concentration of polysaccharide,protein,and slowed down the adsorption and precipitation of calcium phosphorus compounds,silicate and sulfate on the surface of the membrane.In addition,the growth rate of sludge was positively correlated with the ratio of PAC replenishment(P=0.98).Moreover,the high-throughput sequencing showed that due to fresh PAC added,the increased abundance of Proteobacteria,Bacteroidetes and Nitrospira guaranteed the pollutant removal,and the membrane fouling caused by Planctomycetes and Betaproteobacteria decreased.An optimal PAC replenishment ratio of 1.67% achieved the effective membrane fouling mitigation and enhanced dominant bacterial structure.PAC refreshment is considered to be a promising way to advance the application of MBR.