Performance Of GAC-Sand Dual Media Filter On Turbidity, Organic Matters And Ammonia Removal

Granular active carbon-Sand dual media filte（rGAC-Sand filter）could beused as a rapid filter to replace traditional sand filter in drinking watertreatment. It could improve water quality through filtration, adsorption andbiodegradation. Therefore, it could ensure the removal of turbidity, in themeantime, increase the removal efficiency of organic matters and ammonia.Based on the raw water quality of Dongjiang river and the characteristicof a water treatment plant in the southern part of China, substituting theoriginal conventional filtration process with GAC-Sand filter was studied. Thetest lasted12months.The average effluent turbidity and particle counts of GAC-Sand filterwere0.094NTU and58CNT/mL, which were lower than that of Sand filter.Backwashing combined air and water was more effectively to control theturbidity of the initial filter effluent. Velocity, flow surges had no significanteffects on the effluent of turbidity and particles.GAC-Sand filter had effective removal on organic matters, which wassignificantly higher than sand filter. Removal rate of COD_Mnchanged duringthe whole period, the initial rate was above60%, after one year operation, theremoval rate declined to30%. More obviously, removal rate of UV₂₅₄declinedfrom the initial of80%to40%. Organic matters were removed notably in thecarbon layer （especially in the upper0.4meters carbon layer）, while there wasonly little remove capacity in sand layer. Backwashing could improve theorganic matters removal. The organic matters removal rate was lower with thehigher velocity （6¹0m/h）. Flow surges had effects on the removal of organicmatters.NH₄⁺-N and NO2--N could be removed notably by GAC-Sand filter,which were better than results of sand filter. The average NH₄⁺-N removalrate of GAC-Sand filter was79%. Dissolved oxygen （DO） was the limitingfactor on ammonia removal. Backwashing, velocity, flow surges andtemperate affected little on the effluent of NH₄⁺-N and NO2--N, differenceshows on the removal rate along the layer. Ammonia removal could beaffected by chlorinated backwashing water, so non-chlorinated backwashingwater was the suggestion for GAC-Sand filters. Pre-chlorinated had little influence on nitrification. Also, GAC-Sand filters had a strong ability to resistthe ammonia fluctuation，the different removal capacity in summer and winterwas due to difference of DO in the water.Compared with other processes, GAC-Sand filter had a better economicapplicability. Extra0.01⁰.02RMB/m³operation cost would be cost by usingGAC-Sand filter than sand filter. Effluent turbidity of GAC-Sand filter wasbetter than sand filter and O3-BAC process. The reducing of COD_MnandUV₂₅₄in GAC-Sand filter were higher than those of the sand filter. GAC-Sandfilter showed the most effective capacity on the removal of ammonia andnitrite nitrogen.GAC-Sand filter was suitable for micro-polluted or seasonal pollutedwater, especially for raw water with ammonia pollution.