Study On The Influence Of Aluminum Salt On Microbial Community And Contaminant Removal In Activated Sludge

Aluminum coagulant has been widely used for chemical phosphorus removal and enhancing granulation in sewage treatment, but its influence on the microbial ecology of activated sludge is not clear. Using a set of SBR reactors, this paper presented an experimental study on the activated sludge growth and pollutant removal characteristics under the addition of the poly aluminum chloride (PAC) in synthetic domestic wastewater. The microbial biomass was analyzed by measuring the MLSS and MLVSS and using the traditional bacteria counting method, while fluorescence in situ hybridization (FISH) technology was used for microbial communities study. The ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were relative quantitative analyzed. The main results and conclusions are as follows.(1) Biomass analysis showed that, MLSS and MLVSS concentrations were almost doubled in the reactor under PAC addition, plate count test results showed that the total number of aerobic bacteria in Reactors without adding PAC and adding PAC was 1.3×107 CFU/g and 5.2×107 CFU/g dry sludge respectively, that illustrated total aerobic bacteria count per unit weight of sludge increased for about 3 times comparing with the reactor with no PAC addition.(2) According to FISH results, the number of AOB in Reactors without adding PAC and adding PAC was 1.7×105 CFU/mL and 2.0×105 CFU/mL sludge respectively, the umber of NOB bacteria was1.0×105 CFU/mL and 1.1×105 CFU/mL sludge respectively, as a result of the test, the number of nitrification bacteria was almost same in the two reactors. PAC has no affection on the growth and reproduction of nitrification bacteria. (3) PAC addition significantly increased the removal efficiency of TP, average phosphorus removal rate was 54%and 91%respectively in Reactors without adding PAC and adding PAC. PAC also can enhance the removal efficiency of COD. The average effluent COD concentration was 16.26 mg/L, the removal rate was about 94% in the reactor without adding PAC, when adding PAC, the average effluent COD concentration was 9.86mg/L, the removal rate was about 97%. Under stable operational conditions, nitrogen exists in the form of nitrate nitrogen in both of reactors, ammonia and nitrite were very low, average nitrate nitrogen concentrations of the effluent was 10.05mg/L and 10.23mg/L; ammonia concentration was 0.18mg/L and 0.16mg/L, average concentrations of nitrite was 0.024mg/L and 0.019mg/L respectively in Reactors without adding PAC and adding PAC. This shows that SBR reactor has good denitrification effect using its oxygen-aerobic environment, PAC has no effect on the removal of ammonia nitrogen.(4) The concentration of PAC adding was 50mg/L (equivalent to the Al concentration was 7.4mg/L), Under stable operational conditions, the residual aluminum concentration in the effluent was lower than 0.5mg/L, it shows that aluminum content in the effluent is low,more than 90%of the aluminum was trapped in the sludge.