Coagulation + Electrocatalysis To Treat Seed Dressing Wastewate

Seed coating agent,as an environmental friendly pesticide preparation in agriculture,is widely used in the field of agriculture because it can make seeds resistant to diseases and pests.During the production and processing of seed coating agent,a large number of wastewater with high COD,high suspended solids and organic matter containing more and strong toxicity will be discharged,so it has gradually attracted the attention of the society.In this paper,coagulation+electrocatalytic oxidation pretreatment process is used to treat seed coating wastewater for the first time,so as to improve the biochemical performance of seed coating wastewater and meet the requirements of influent quality for biological treatment.In addition,this paper also studies the mechanism and reasons for the improvement of biochemical performance of seed coating wastewater after electrocatalysis,which provides theoretical data reference for subsequent seed coating wastewater treatment.In the pretreatment stage of coagulation process,this paper uses the single factor method to carry out the experiment,takes the wastewater transmittance and wastewater DOC removal rate as the characterization indexes,optimize the types and dosage of coagulant and coagulant aid,and the initial pH value of wastewater.The results showed that when 2.5 g/L polyaluminium chloride(PAC)was added as coagulant and 2 mg/L polyacrylic amide(PAM)as coagulant aid,and the initial pH value of wastewater was adjusted to 8,the coagulation effect reached the best effect.The COD value of wastewater decreased from 9500 mg/L to 4309 mg/L,and the COD removal rate was 54.64%.In addition,the B/C value of wastewater is increased from 0.17 to 0.28,which improves the biodegradability of wastewater,but it still does not meet the inlet requirements of biochemical wastewater treatment,so it is necessary to further pretreat the wastewater.In the pretreatment stage of electrocatalytic process,the single factor method was used to carry out the experiment.The highly toxic pesticide carbofuran and its intermediate furanol were used as the characterization indexes to optimize the electrolyte type,electrolyte concentration,current density,initial pH value of wastewater and initial dilution multiple of wastewater.The results show that the electrocatalytic effect is the best when 0.04 mol/L sodium sulfate is added as electrolyte,the current density is 10 m A/cm~2,the initial pH of wastewater is 8 and the dilution multiple is 5.The COD value of wastewater decreased to 3512 mg/L,and the B/C value of wastewater increased to 0.53,which met the requirements of biochemical treatment.In addition,the removal rate of carbofuran,the pesticide with the highest concentration and the strongest toxicity,is 90.36%,which is the main reason for the improvement of biochemical performance of wastewater.In the study of electrocatalytic mechanism of seed coating wastewater,the first intermediate product furanol after electrocatalytic degradation of carbofuran,which is a pesticide with high toxicity and concentration,was selected as the research object to explore the electrocatalytic effect and process mechanism under different electrolytes,the degradation path when sodium sulfate was used as electrolyte and the feasibility of sodium chloride as electrolyte.The results show that the electrocatalytic effect of furanol is better than that of sodium sulfate when sodium chloride is added as electrolyte,which is related to the indirect oxidation of furanol by active chlorine.The degradation path of furanol is obtained by UV-Vis analysis.The result is that C on the furan ring is replaced by-OH group to form 2,2-dimethyl-2,3-dihydro-1-benzofuran-3,7-diol,and the-OH group is oxidized to carbonyl to form 2,2-dimethyl-3-oxo-2,3-dihydro-1-benzofuran-7-alcohol.In addition,it is also proved that when sodium chloride is used as electrolyte,there will be chlorinated by-products in the effluent,which will increase the toxicity of the effluent.Therefore,sodium chloride is not suitable for the electrolyte of seed coating agent waste hydropower catalytic treatment.