Pilot-scale Study On Micro-polluted Water Source Treatment Using Combined Process Of Zeo-carbon Composite Packing Bio-filters With O₃-BAC

At present, water quality is deteriorating day by day in our country, the pollution phenomenon of drinking water sources is increasingly serious, organic matters, ammonia nitrogen and other pollutants in contaminated source water can not be effectively removed by conventional water treatment process, water quality of effluent can not meet drinking water standards. Therefore, searching micro-polluted source water treatment process with high removal efficiency and low cost has become an important and urgent topic.In this research topic, the contaminated Fuyang river source water was chosen as raw water, pilot-scale study of advanced treatment process"coagulation sedimentation + Zeo-carbon composite packing bio-filter + O₃-BAC" was conducted. A new type of composite filter-media Zeo-carbon was adopted, and its static adsorption performance for ammonia nitrogen and organic matters was studied; the influences of hydraulic loading, gas-water ratio, temperature and packing height on pollutant removal efficiency were analyzed to optimize operation parameters of Zeo-carbon composite packing bio-filter, and its removal effects were analyzed; in order to get further understanding of Zeo-carbon composite packing bio-filter in theory, the dynamic model of Zeo-carbon composite packing bio-filter was established according to the test conditions and theoretical analysis; the optimal operation parameters of O₃-BAC process were determined by analyzing the influences of ozone dosage, filtration rate of BAC column, packing height of BAC and temperature on decontamination effects, and its removal effects were analyzed; on the basis, the water purification effects of "coagulation sedimentation + Zeo-carbon composite packing bio-filter + O₃-BAC" were studied under dynamic test conditions.The results of Zeo-carbon static adsorption experiments showed that it had certain removal effect for UV₂₅₄ and NH₄⁺-N in raw water, and had rapid absorption characteristic. After 40min, the removal rates of UV₂₅₄ and NH₄⁺-N were 21.7% and 34.5%, respectively.The NH₄⁺-N adsorption capability of Zeo-carbon was affected by adsorption time, packing amount, concentration of ammonia nitrogen and so on. Within a certain range, the removal rate of ammonia nitrogen increased with the increase of adsorption time, packing amount, ammonia nitrogen concentration. According to Zeo-carbon static adsorption experiments, isothermal adsorption equation of Zeo-carbon for NH₄⁺-N is lg q_e = 1.4698lgC_e+0.7763.The results showed that the optimal operation conditions of Zeo-carbon composite packing bio-filter were as follows: influent flowrate of 98.0L/h, hydraulic load of 5.0m/h, gas-water ratio of 1.0. Under the optimal conditions, and at temperatures ranging between 21 and 27.5℃, its removal effect was good, and the average removal rates of turbidity, COD_Mn, UV₂₅₄, NH₄⁺-N, NO₂^--N, chroma were 72.8%, 30.2%, 25.5%, 76.8%, 79.3%, 69.4%, respectively. According to test data, its dynamic model on organic pollutants removal was established under the condition of low substrate, and the dynamic model was as follows: S/S0=exp (-0.0418h/q^0.7414).The optimal operation conditions of O₃-BAC process were determined as follows: ozone contact time of 12¹5min, ozone dosage of 2.0mg/L, BAC column filtration rate of 6.0m/h. Under the optimal conditions, and at temperatures ranging between 21 and 27.5℃, the decontamination effciency of O₃-BAC process was the best, and the average removal rates of turbidity, COD_Mn, UV₂₅₄, NH₄⁺-N, NO₂^--N, chroma by O₃-BAC process were 61.2%, 56.6%, 65.9%, 68.3%, 98.3%, 85.8%, respectively.Controlling the filtration rate of BAC column as 6.0m/h, the decontamination effects of BAC column at different height were analyed. The results showed that the removal of turbidity mainly within the first 200mm height, the removal of organic matters and ammonia nitrogen mainly within the first 600mm height, therefore, the appropriate packing height of BAC column was 600mm.Polyaluminium Chloride (PAC) was used as coagulant in this test, the optimal dosage was determined as 25mg/L through jar test. The operating parameters of coagulation tank, inclined plate sedimentation tank, Zeo-carbon composite packing bio-filter, ozone contact tank and the BAC filter in combined process were as follows: PAC dosage of 25mg/L, coagulation tank hydraulic retention time of 20min, inclined plate sedimentation tank hydraulic retention time of 60min, Zeo-carbon composite packing bio-filter filtration rate of 5.0m/h, and its corresponding empty bed contact time (EBCT) was 12min, air-water ratio of 1.0, ozone contact time of 12¹5min, ozone dosage of 2.0mg/L, BAC filtration rate of 6.0m/h, and its corresponding EBCT was 10min. Under above operating conditions, the average removal rates of COD_Mn, UV₂₅₄, NH₄⁺-N, NO₂^--N, turbidity and chroma were 76.9%, 80.5%, 93.9%, 99.7%, 97.3%, 95.8%, respectively. The average concentrations of COD_Mn, UV₂₅₄, NH₄⁺-N, turbidity and chroma in effluent were 1.81mg/L, 0.031cm-1, 0.12mg/L, 0.29NTU, 1.5 degree, respecyively, and the average concentration of NO₂^--N was less than 0.003mg/L, below the detection limit, and water quality of effluent is superior to Standards for Drinking Water Quality (GB 5749-2006).