Study On Wastewater Treatment Engineering Technology Of Polysilicon Industry

In the production of polysilicon,the consumption of water is large,a lot of acid and salt will be produced in the process of production,which leads to serious waste water pollution.Due to the complex composition of polysilicon wastewater,in the process of polysilicon wastewater treatment,it is necessary to consider the actual situation and pollutant composition of a variety of wastewater,resulting in the complexity of polysilicon wastewater treatment.Chemical precipitation method and coagulation precipitation method are the most commonly used wastewater treatment methods in polysilicon industry.However,the complexity of wastewater will lead to high cost of reagent use and unstable treatment efficiency.Therefore,it is hoped that other water treatment methods can be used to reduce the cost in the actual wastewater treatment process.In this paper,through the combination of coagulation and biological treatment,the treatment scheme of polysilicon wastewater is set up,and the selection of coagulant,the removal efficiency of coagulant for pollutants and the removal efficiency of pollutants in biological treatment unit are studied from the small-scale test.Then the wastewater treatment system of polysilicon industry is constructed,including defluorination unit,denitrification and organic matter unit and sludge removal unit,and the size of each structure is calculated.Finally,the debugging,operation and optimization of the wastewater treatment system are carried out.The main conclusions are as follows:(1)In the small-scale test,the selection of coagulant and its removal rate of pollutants were studied.For the wastewater with high fluorine content and COD,the best coagulant is PAC and PAM,and the best dosage of PAC is 65mg/L.when PAC:PAM is 10,the pollutant removal efficiency is the highest.The coagulation and sedimentation system has a good removal effect on F~-and SS.When the F~-concentration of influent water is 550mg/L,the removal effect of F~-is more than98%,the SS of influent water is about 1000mg/L,and the removal efficiency of SS is more than 95.1%.In this process system,the removal rate of COD in the coagulation and sedimentation process is only about 55%~60%.(2)The biological treatment unit adopts the water treatment process of hydrolytic acidification biological contact oxidation.The COD concentration of the influent water of the system is about 1300mg/L.the removal rate of COD in the biological treatment unit can reach about 96.6%,the removal rates of total nitrogen and ammonia nitrogen are about 10%-20%and below 5%,and 63%-87%,respectively.(3)Based on the results of the pilot test,the treatment process of polysilicon production wastewater is determined as follows:polysilicon industry wastewater?regulating tank?primary coagulation reaction tank?primary sedimentation tank?secondary coagulation reaction tank?secondary sedimentation tank?hydrolysis acidification tank?biological contact oxidation tank?sedimentation tank?disinfection tank?effluent.The designed water inflow is 1200m~3/d,and the discharge standard meets the class I B standard.The design sewage treatment cost is 1.24 yuan/ton.After the completion of the project,the start-up of the biological system adopts the intermittent inoculation continuous flow load lifting mode.After the operation is stable,the COD,SS and F~-treatment efficiency of the wastewater reach 98%,97.8%and 99.5%respectively.The wastewater discharge standard has reached the first-class standard of comprehensive wastewater discharge.(4)In view of the occasional fluctuation of the ammonia nitrogen concentration near the standard discharge after wastewater treatment.Polysilicon wastewater treatment process can be optimized from four aspects:increasing pretreatment links,strengthening biochemical treatment system,increasing advanced treatment system and comprehensive domestic sewage,and improving the biodegradability of wastewater.