Removal Of Pollutants In Cooling Wastewater And Membrane Cleaning Wastewater From Thermal Power Plant

The main research object in this dissertation is the reverse osmosis membrane cleaning wastewater and circulating cooling wastewater from a thermal power plant.Circulating cooling wastewater contains a higher concentration of nitrate,and reverse osmosis membrane cleaning wastewater contains more organics.The idea of this research is to use the biological denitrification biofilter and membrane bioreactor to remove the nitrate nitrogen and organic contaminants from the circulating cooling wastewater and membrane cleaning wastewater,respectively.In case of adequacy of food during denitrification,the latter could also provide carbon source.The effluent should meet the requirement of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant(DB 12/599-2015).The effects of different operating parameters on membrane fouling and removal of organic contaminants in the membrane cleaning wastewater were compared in the bench-scale test.The hydraulic retention time had a great effect on the removal efficiency of organics and membrane fouling rate.Reducing the hydraulic retention time would cause the high concentration of organics in the effluent and fast membrane fouling rates.The effect of sludge age on the removal of organics is not significant,but the membrane fiber length has a greater impact on the membrane fouling rate.The optimal operating conditions were as follows:the membrane flux was 8 L/(m~2·h),the hydraulic retention time was 4 h,the sludge age was 15 days,and the COD in the effluent was below 30 mg/L,with a relatively low fouling rate.The effects of different cleaning methods on membrane flux recovery were compared.The best cleaning method was as follows in sequence:physical cleaning with top water,soaked in 0.05%HCl for 1 h and soaked in sodium hypochlorite at 3000mg/L for 2.5-3 h,the membrane flux could be recovered to 80%compared to the new membrane.Filtration rates had an obvious effect on removals of nitrate nitrogen using denitrification biofilter to some extent.Comparison test showed that filtration rate of2.39 m/h was better in removal of nitrate nitrogen than that of 3.19 m/h.