Study On Optimization Of Disinfection In Conventional Technics Following Biological Aerated Filter

The chlorine disinfection of potable water has played avital role in controlling the water-causing diseases and improving thesafety of water mieroorganism, thus contributing largely to lowering the rate of the water-causing diseases.The effluent of biofilter contents plenty microorganism which can be killed by chlorine.Thus, the following conventional process will loss the bioaugmentation by those microorganism.Sodium hypochlorite was added to different spots of the processes to analyse the effection to the water purification and disinfection.The results are as following:(1) When treating the micro-polluted raw water by conventional process with sodium hypochlorite added at the clean water pond, the removal rate of ammonia, CODMn, turbidity in the effluent were: 45.6%, 56.6% and 98.3%, with the ammonia exceed the limited level. For the high-polluted raw water, the removal rate of ammonia, CODMn, turbidity in the effluent were: 42.6%, 44.5%and 99.0%, with the ammonia and CODMn exceed the limited level.(2) When treating the micro-polluted raw water by conventional process with sodium hypochlorite added before the process, the removal rate of ammonia and CODMn in the effluent were: 53.3% and 53.2%, with the ammonia exceed the limited level. For the high-polluted raw water, the removal rate of ammonia and CODMn in the effluent were: 46.3%and42.0%, with the ammonia and CODMn exceed the limited level.(3) Biofilter can reduce ammonia substantially but can hardly remove Organic Contaminants with such short Hydraulic Retention Time.By returning sludge from sedimentation tank to coagulation tank, the removal rate of contamination was increased. For micro-polluted raw water, under sludge returning rate of 12.5%, removal rate of ammonia and CODMn in effluent were: 89.7% and 66.6%,all indicators were up to the standard. For high-polluted raw water, under sludge returning rate of 20%, removal rate of ammonia and CODMn in effluent were: 99.4%and 74.4%, all indicators were up to the standard.(4) As to micro-polluted raw water, there was no significant difference in ammonia reduction when adding sodium hypochlorite at clean-water tank or before sand filtration or following biopretreament, the removal rate of CODMn were 69.2%,62.6% and 66.6%. In conclusion, adding sodium hypochlorite in clean-water tank has the least effection to the process.While adding before the sand filtration can weaken biological degradation of CODMn, Adding sodium hypochlorite just after the biofilter impair biological degradation in the following units,but with strong oxidizing property of sodium hypochlorite, CODMn in effluent can be degradated to meet the limited level. To sum up, when treating micro-polluted raw water, sodium hypochlorite can be added at clean-water tank or before sand filtration or in biofilter effluent.(5) As to high-polluted raw water, the removal rate of ammonia when adding sodium hypochlorite at clean-water tank or before sand filtration or following biopretreament were : 98.5%,100% and 95.1%, the removal rate of CODMn were: 78.8%,76.3% and 41.7%. Ammonia and CODMn in effluent when adding sodium hypochlorite before coagulation were out of limits.In conclusion, sodium hypochlorite should be added at clean-water tank or before sand filtration to make sure the water can meet the quality standard.