Research On Drinking Water Plant (DWP) Streams Recycle For Strengthen Of Low Turbidity Water Coagulation Efficiency And Water Quality Safety

With the increasingly serious water pollution and shortage,a large number of cities use the reservoir water,mountain streams and lakes as the drinking water source.Lake water is the main source of drinking water in China,which has low inorganic and organic pollution.The stable quality of lake water leads to more difficult to treat the water.For low turbidity and temperature,the number of colloidal particles per unit volume is small and the probability of particles colliding with each other is reduced,which enhanced removal difficulty of pollutants.Therefore,based on the background of water scarcity and low turbidity,the production wastewater is reclaimed as a kind of resource.This is a new and feasible method for treating low turbidity water while reducing water consumption.Firstly,the beaker test was used to evaluate sedimentation characteristics to investigate the properties of sedimentation sludge.The sedimentation sludge water,filter backwash water and mixed water are separately defined as working conditions ?,? and ?.The recycle experiment was carried out on basis of this three conditions and coagulation experiment was also conducted based on mixed water turbidity as control factor.Through the comparison of three groups experiment,the optimum turbidity range of mixed water turbidity was determined,and the feasibility of reusing coagulation was verified.A 5m3 / h pilot plant was set up to more accurately reflect the effect of different sinking conditions in actual production based on beaker test results.From the characteristics of production wastewater and the actual production,different mixed water turbidity conditions under the conditions of the recycle process parameters were established to determine the best mixed water turbidity and the rate of dosage-saving range.The effects of wastewater reuse on effluent quality were further analyzed,and the multiple genetic end point biological group toxicity test were used to evaluate the genetic toxicity of wastewater reuse.The results showed that there was a best mixing water turbidity range for production wastewater reuse.When the sludge water is reused separately,the optimum mixed water turbidity range is 40⁶0NTU and the corresponding dosage-saving rate is about 15³7%.when the sludge water and backwash water are reused simultaneously,the optimum mixed water turbidity range is 125¹75NTU and the best rate is about 16%³0%.Both of sedimentation water and filter water were conducted the T-test.The results showed that the reuse of production wastewater could not significantly increase the concentration of contaminants in sedimentation and filter water.Compared with water quality of conventional process,recycle method could significantly strengthen the removal of dissolved organic matter.From the microscopic morphology of the settling floc microstructure,the mechanism of coagulation and recirculation was analyzed.When the sedimentation floc AHF was combined with PACl and Al2?SO4?3,the removal rates of turbidity,DOC and UV254 were significantly increased.When the dosage of PACl-AHF was 6 mg Al/L,DOC and UV254 were 90%,79.2% and 90.1%,respectively.When the dosage of Al₂?SO₄?^3-AHF was 8 mg Al/L,the removal rates of turbidity,DOC and UV254 were 75.1%,69.3% and 78.4%,respectively.The particle size of PACl-AHF is larger than that of Al₂?SO₄?^3-AHF.When the sedimentation flocs break,the main peak curve of particle size distribution is obviously shifted compared to traditional flocculant condition.However,the breakage process has little effect of particle size distribution with use of Al₂?SO₄?^3-AHF.According to fitting results of four adsorption models,multi-layer physical adsorption is the main process for removal DOC by AHF.AHF surface functional groups,hydrogen bond and the surface floc gel are also major factors for removal DOC by AHF.The different genetic endpoint toxicological tests show that the reuse of production wastewater does not cause the accumulation of genotoxic substances such as mutations,chromosomal aberrations and DNA damage caused by filtered water and disinfectant water.The test results of Ames?in vivo micronucleus and mouse sperm abnormality showed that reuse of wastewater could promote removal of genotoxic substances such as mutagenesis,chromosome damage and germ cell mutagenesis.SOS / umu test and in vivo micronucleus test showed that there was no significant effect of genotoxic substances on reuse of production wastewater.According to the criteria of the genetic toxicological evaluation system,the enriched concentration of all refluxing water samples is negative.Results showed that the carcinogenic risk is far below the international standard,hence the effluent is at a safer level from the genotoxic aspect.At the same,the inhibition rate and enzyme activity of Daphnia magna showed that the inhibitory rate of R1 to R3 was lower than that of C1 to C3 under the enrichment concentration of 0?DMSO?² leq / ml.The SOD and CAT of Daphnia magna showed significant dose-response relationship with water concentration.The values of C1 and R1,C2 and R2,C3 and R3 were tested for p>0.5,which means no significant difference.As the above results,direct reuse of wastewater and control mixed water turbidity has obvious economic benefits for treatment of low turbidity water.Furthermore,it also could enhanced coagulation?saving dosage and improved effluent quality.There was not accumulation of pollutants and increase of genetic toxicity,which enhance the safety of effluent.