Experimental Study Ontreatment And Reuse Of Backwash Mud Water In Waterworks

The backwash mud water of the water plant comes from the sand filter and the deep treatment activated carbon filter.At present,most of the water is directly discharged to the nearby water body,and the environmental pollution problem cannot be ignored.This paper investigated and analyzed the water quality characteristics of backwash mud water in Beihekou Water Plant of Nanjing City with water from the Yangtze River.The30-day continuous monitoring average values of turbidity,ammonia nitrogen,total nitrogen,total phosphorus and COD_Cr of sand filter backwash mud water were 125NTU,0.05mg/L,3mg/L,0.15mg/L,and 7mg/L,respectively;the particle size of the particles in the backwash mud water of the carbon filter was concentrated in 2-5?m,the average number of free bacteria was 650 CFU,and the organic matter was predominated by tryptophan and soluble microbial products.The pilot study on the filtration treatment of sand filter backwash mud water was carried out.The experimental results of two different packed filter columns showed that,when the filtration rate was 2m3/?m2·h?,for the quartz sand filter column,the average removal rates of turbidity,ammonia nitrogen,total nitrogen,total phosphorus and COD_Cr were 58.6%,15%,28%,30%,and 29.8%,respectively;for the filter column with 50%quartz sand+50%plastic ball,it had better removal effect on these pollution factors,and the average removal rates were 65.5%,35.2%,34%,42%,and 42.2%,respectively.The effluent water quality met the Class II water standard of the Surface Water Environmental Quality Standard?GB3838-2002?.The carbon filter backwash mud water and raw water were mixed according to different ratios.The feasibility of backwash mud water reuse as water source of the water plant was analyzed.The results showed that,compared with the conventional process without mud water reuse,when the backwash mud water was directly reused,the concentration of nitrate nitrogen and the total number of bacteria in the effluent of the sedimentation tank increased.After the backwash mud water was reused and the PAC enhanced coagulation was carried out,the number of particles related to the total number of bacteria in the effluent of the sedimentation tank was significantly reduced to 4000/mL,and the normal coagulation without mud water reuse was about 10000/mL.The experiment explored the ultra-filtration membrane treatment effect of backwash mud water.By detecting the water quality index of the inlet and outlet water such as the trans-membrane pressure difference and the total number of bacteria,the operating parameters were determined.The results showed that,under the optimal conditions of the coagulant PAC 15 mg/L,pre-settling time 10 minutes,flux 20L/?m²·h?,working cycle 60minutes,backwashing intensity 6L/h and backwashing time 60s,the total number of bacteria in filtered water was below 10CFU/mL,tryptophan and the dissolved microorganisms were basically removed and could be recycled to the water plant clear water pool.The research results provided an alternative technical path for the treatment of sand filter and carbon filter backwash mud water.