Processes And Equipments Of Fast Treatment In Urban Heavily Polluted River

In this study,Jizhuangzi Stream was selected as the treatment target,investigations of water quality characteristics of Jizhuangzi Stream affected by combined sewer overflow(CSO)during the rainy season were taken.Based on analysis of dissolved air flotation separation and enhanced sedimentation technology,air flotation separation equipment was designed and optimized,which provides feasible technology and key equipment for emergency treatment of heavy polluted river water.City river often suffer from CSO pollution impact in rainy season.CSO is a kind of high concentration organic and nutrients wastewater,The sewers cause immediate and long-term damages on the quality of receiving water bodies,as it contains a mixture of variable pathogenic organisms,viruses,cysts,suspended solids,chemicals,and organics.The highest turbidity reached 100 NTU,and the concentration of chemical oxygen demand(COD)was 120 mg/L,The concentration of dissolved oxygen(DO)in river was reduced to 2 mg/L.The receiving water body accelerates water eutrophication due to the import of a large amount of organic matter.But at the same time,with the extension of rainwater discharge time,the clean rainwater could reduce the pollutant concentration of the river.The channel polluted by overflow pollution was difficult to recover by self purification,so artificial assistive technique was needed.Dissolved air flotation(DAF)treatment of polluted river water has the characteristics of short coagulation reaction(less than 3 minutes)and high speed of floc separation.Keeping the gas–liquid separation pump pressure in 0.38~0.40 MPa,the removal efficiencies of turbidity and TP reached as high as 90% and 80%,respectively,after 2~4 min separation time.The purification performance of aluminum series coagulant was proven to be better than that of iron system coagulant.Enhanced precipitation treatment of polluted river water test showed that the magnetic precipitation significantly accelerated the floc settling velocity compared with normal precipitation,the reaction time could be reduced to 3 min to achieve a good purification performance,50% floc yield were reduced at the same time.The combined magnetic precipitation and Fenton process presented good synergistic purification performance on polluted river water with high COD concentration,combined process significantly reduced the concentration of COD and accelerated the settling rate of flocs at the same time,and the effluent COD concentration was lower than 20 mg/L.The clay surface Zeta potential was significantly improved using dilute acid solution of Chitosan,indicating that the purification performance of high algae water significantly increased with Chl-a removal efficiency of 90%.According to the requirement of emergency treatment of heavy polluted river,a full-scale DAF integrated equipment was established.The equipment produces dissolved air water by a gas-liquid separation pump,driven by a mobile power device,the moisture content of the scum produced by the equipment was low,and the equipment could be installed and used quickly and conveniently on the river course site.The production test showed: When PAC dosage was 45~80 mg/L,the coagulation time was 5 min,dissolved air in water reflux ratio was 20%,retention time of air flotation separation zone was 24 min.The removal efficiency of total phosphorus(TP),turbidity and Chl-a by purification equipment was stable at 70%~80%,and the effluent DO could be improved.