Construction, Performance And Characteristics Of Granular Activated Carbon-Sand Dual Media Filter

Granular activated carbon (GAC)-sand dual media filter, of which the upper layerand the lower layer were filled with GAC and sand respectively, could be used tosubstitute the sand filter in drinking water treatment. GAC-sand dual media filter couldremove turbidity, meanwhile it could also remove organic matter and ammoniumthrough activated carbon adsorption and microbial activity.The filter media and operation parameters were determined, and turbidity could bebelow0.10NTU, which was lower than that of sand filter. To solve the problem of poorwater quality during filter ripening period, the method of adding subfluidizationbackwashing after normal backwashing was developed. The maximum turbidity ineffluent was lowered from0.25-0.45NTU to less than0.20NTU, while the turbiditycould be below0.10NTU after5min operation, and the effluent quality could reach thegoal of USEPA on turbidity control during filter ripening period.GAC-sand dual media filter could remove more than30%of CODMn, which washigher than the9.2%removal efficiency of sand filter. GAC-sand dual media filtercould remove more than30%of UV254, while sand filter showed no removal. Theorganic matter was mainly removed through GAC adsorption. The nitrifying ability ofGAC-sand dual media filter was strong, and the average effluent concentration ofammonium and nitrite was0.10mg/L and0.002mg/L respectively, which was lowerthan that of sand filter. To solve the short of dissolved oxygen (DO) during nitrification,aeration equipment was set in the GAC layer, the aerated GAC-sand dual media filtercould increase the ammonium removal capacity from0.5-1.0mg/L in conventionalwater treatment process to3.0mg/L.The biomass and microbial activity decreased along the filter depth. The microbialdiversity was high in the middle and lower GAC layer, and their microbial communitystructures were similar to each other. While microbial diversity was relatively lower inthe upper GAC layer and sand layer, and their microbial community structures weredistant from each other. The diversity of ammonia oxidizing bacteria (AOB) increasedalong the filter depth, and the dominant AOB in the filter belonged to Nitrsomonas. During operation with high ammonium concentration for a long period, theammonium could be removed through nitrification and denitrification. Do was the keyparameter affecting ammonium removal capacity.The difference of operation cost between GAC-sand dual media filter and sandfilter was mainly due to higher price of GAC. Extra0.02RMB/t would be cost by usingGAC-sand dual media filter, while0.03RMB/t would be cost by using aerated GAC-sand dual media filter, and could be accepted financially.There was no need for the water treatment plants (WTPs) to add more operationprocess when GAC-sand dual media filter was used to substitute the sand filter. Thefilter was advised to be used in the WTPs, whose raw water was slightly polluted orseasonally, or there was little space for the WTPs to expand, or financially limitedWTPs. In conclusion, the GAC-sand dual media filter will be a promising drinkingwater technology in China.