Study On The Performance Of UCT-MBR Enhanced By Chemical Method

To meet the stricter the first level A criteria of the discharge standard for pollutants from municipal wastewater treatment plant and to make TP concentration lower than 0.5 mg/L,chemical dose was adopted to enhance phosphorus removal in wastewater treatment.In this study,the operation efficiency enhanced by chemical method based on UCT-MBR process was investigated.Particular care was addressed to the stability of operation and sludge characteristics and membrane fouling,the conclusions achieved are followed:(1)Comparing the phase 1 and 3,the removal efficiencies of COD?NH4+-N?TN were about 92.32-93.07%?100%?75.1%-76.4% and effluent concentrations were all meeting the first level A criteria of the discharge standard.However,effluent TP concentrations in phase 1 and 3 were 0.72mg/L and 1.45mg/L,respectively,higher than 0.5 mg/L,the corresponding removal efficiencies were 85.37% and 71.11%,respectively.(2)The comparison of removal efficiency among fly ash,aluminum sulfate and ferric chloride were made.It was found that aluminum sulfate achieved the optimal removal efficiency.10mg/L and 50mg/L of aluminum sulfate were dosed in anoxic reactor to enhance phosphorus removal and to further reduce the effluent TP concentration.The effluent TP concentrations were reduced to 0.47mg/L and 0.4mg/L,respectively,and all met the first level A criteria of the discharge standard.The removals of COD,NH4+-N,TN removal were not affected.It was obtained that the degradation of COD has a correlation with phosphorus release by the process experiments.Low concentration of aluminum sulfate could promote phosphorus release ability slightly but restrain denitrifying phosphorus removal.High concentration of aluminum sulfate could restrain phosphorus release ability obviously and TN removal efficiencies were promoted in different concentrations.(3)Low concentration of aluminum sulfate could improve phosphorus release rate under anaerobic condition,but high concentration dose not only inhibited the rate and amount of phosphorus release,but also restrained the phosphorus intake ability.Moreover,the dose of aluminum sulfate could enhance the denitrification rate obviously.Low concentration of aluminum sulfate could improve nitrification ability while high concentration dose restrained.(4)The dose of aluminum sulfate has no significant effect on microbial community in terms of “phylum” and “genus” level.At the “phylum” level,Proteobacteria,Bacteroidetes and Nitrospirae were the most dominant microbes in all sludge samples with the proportion of 71.9%.It was found that low concentration of aluminum sulfate decreased their abundance to 70.5% and high concentration had restrained them obviously,with the proportion of 53.5%.At the “genus” level,low concentration of aluminum sulfate could promote and improve the abundance of Dechloromonas,Saprospiraceae,Candidatus_Accumulibacter,Nitrospira and Nitrosomonas.However,high concentration would restrain them.The dose of aluminum sulfate would also restrain the abundance of Candidatus_Competibacter(decreased from 11.53% to 7.11%)while promote the reproduction and metabolism of Anaerolineaceae(increased from 4.16% to 9.56%).(5)Take phase 3 and 4 as an example,the dose of aluminum sulfate could enlarge the sludge particle size(increased from 24.7um to 32.9um).The proportions of sludge particle size smaller than 10 um and 20 um decreased from 10.0%,41.5% to 6.9%,28.5% and the obstruction of small size sludge to membrane holes was also reduced,hence the membrane fouling was mitigated.(6)Take phase 1 and 2 as an example,TMP rising rate was decreased from 1.13KPa/d before the dose of aluminum sulfate to 0.57KPa/d after the dose.By analyzing the EPS concentration in mixed liquid,it was found that EPS concentration was declined from 81.15-82.82mg/g MLSS to 46.55-48.50mg/g MLSS,as well as PN/PS ratio from 8 to 3,which meant protein was the main fouling contributor.In addition,the EPS content on the membrane surface was decreased from 540.06ug/m2 to 451.91ug/m2 obviously,while the proportion of polysaccharide increased,which meant polysaccharide is more likely to cause membrane fouling.Analyzing the resistance of membrane surface pollutants,we find that sludge layer resistance and gel layer resistance are the main contributors to membrane resistance,the proportions increased from 62.81% to 71.45%.(7)The batch experiment was used to study the reaction kinetics of the system.Based on the Monod equation,the COD semi saturation constant of aluminum sulfate was 12.92 mg/L and 55.33 mg/L,and the maximum ratio of substrate reaction was 0.043 h-1 and 0.124 h-1 respectively.