Study On Discharge Control And Direct Reuse Optimization Technology Of Wastewater From Filter Production

Filter is the core unit in water treatment and it guarantees the hygienic safety of drinking water.The water quality in the initial stage of filtration is poor.If it is not discharged,it will affect the water quality safety of waterworks.However,there is still no specific standard and basis for the discharge technical indicators and control parameters of initial filtration water.In the process of filter backwashing,a large amount of backwashing wastewater will be produced for a short time.If it is discharged directly,it will waste water resources and pollute the environment.Direct reuse of wastewater from waterworks is one of the effective measures to save water resources.It is necessary to study and evaluate measures and safety of reuse.In this paper,the initial filtration water and backwash wastewater were taken as the research objects.It mainly studied on the control of initial filtration water discharge and the related technologies of direct reuse of filter production wastewater by combining production test with small scale test.By changing the operation parameters such as filtration cycle and discharge time of the filter,the characteristics and influencing factors of water quality change of initial filtration water were analyzed.And the water quality control parameters and optimal discharge control conditions of initial filtration water discharge were discussed.The effects of direct reuse of production wastewater on conventional water treatment and pre-oxidation processes were studied based on the analysis of characteristics of wastewater from filter production.The effects of different recirculation ratios of wastewater and different oxidation methods were compared.According to the water quality characteristics of backwash wastewater at different stages,the optimal combination of reuse schemes was compared.And the relevant suggestions were put forward in order to provide reference for the optimal operation of water plants and the improvement of water quality.The main conclusions are as follows:(1)The turbidity were higher in the initial stage of discharge of initial filtration water,the turbidity reached 0.92 NTU,and the average number of particles was about 3000/mL.It was mainly composed of particulate matter with particle size of 2-5 μm.The turbidity and the number of particles had similar change rules and certain correlation.The turbidity and particle number decreased most in the first 30 seconds and then gradually became stable.When the discharge time exceeds 2 minutes,the turbidity was basically below 0.3 NTU.The quality of initial filtration water was related to discharge time,filtration period,influent quality of filter and backwashing effect.It can better improve the quality of the initial filtration water and ensure the quality of the filter effluent by controlling reasonably filtration period and discharge time of initial filtration water,having good coagulation and sedimentation treatment before filtration,optimizing the backwashing process and other measures.Under the condition of low turbidity,the number of particles in this water plant can reflect the change of water quality more timely than turbidity.The combination of particle number and turbidity was proposed as the control parameters for the discharge of initial filtration water.It was suggested that the final discharge turbidity of initial filtration water should be controlled below 0.3NTU.The particle size beyond 2μm should be controlled below 200/mL.From the point of view of water quality safety and economy,it was more appropriate to control the optimal discharge time of initial filtration water in 2～5 minutes,the upper limit should be taken when the turbidity of the inlet water of the filter is high.(2)Direct reuse of wastewater from filter production can enhance the effect of coagulation treatment.Considering the variation of water quality index parameters,and in order to prevent excessive water impact load and improve the assurance rate of water quality safety,it was suggested that the optimal reflux ratio should be controlled at 6%.In this case,CODMn and UV254 removal rates were the highest,respectively 47.67%and 30.01%.And the turbidity removal rate after sinking was 93.71%,the particle number was 1950/mL,(3)In the case of direct reuse of wastewater,KMnO4 had the best pre-oxidation effect among the three oxidants when oxidants are used alone.It was suitable to control the dosage of KMnO4 at 0.3 mg/L.In this case,the turbidity removal rate was 97.94%and the particle number was 1111/mL.The combined oxidation of KMnO4 and NaCIO was better than the effect of oxidant alone.(4)The filter backwashing wastewater varied greatly in different stages.The wastewater from different backwashing stages of the filter was mixed and reused.After coagulation.sedimentation,filtration and disinfection,the turbidity,pH,CODMn.UV254,Al and the total bacteria count in the effluent of the four schemes can meet the hygienic standard of drinking water.The fourth scheme,which mixed wastewater of air-water backwashing and water flushing,had relatively good effluent quality.The effluent turbidity,CODMn and Al content were the lowest,but AOX was relatively high.The first scheme was that AOX was the lowest in the mixed reuse effluent of the whole backwashing process,and it saved the most water and was the most convenient for operation and management.In order to improve the utilization rate of water resources and ensure the safety of effluent,it was suggested that the whole process of filter backwashing wastewater should be mixed and reused,or the two stages of air-extracting backwashing and water flushing should be mixed and reused.