Study On The Characterization And Treatment Process Of Heterocyclic Herbicide Wastewater

Since there were few studies on the treatment of herbicide wastewater at home and abroad,especially heterocyclic urea herbicide wastewater,the degradation characteristics and ultraviolet absorption of tebuthiuron wastewater by oxidation of combined UV irradiation and ozonation were investigated.Factors affecting the oxidation rate of wastewater,such as the initial pH value,ozone dosage,initial concentration of wastewater,and ozone oxidation mechanism were studid.Furthermore,the change of TOC,biodegradability,ultraviolet spectrum and HPLC pre and post the reaction were analyzed.Finally,the combined UV irradiation and ozonation technology were applied to pretreat tebuthiuron industrial wastewater in order to design combined process of O₃/UV and biochemical treatment.The main conclusions are as follows:(1) Tebuthiuron wastewater has characteristic absorption peak at wave length 254nm. The results show that initial pH is the dominating factor in the process of treatment.COD removal rate varies linearly with initial pH.Removal=0.1514+0.03376pH;The effect of scavenger on the rate of tebuthiuron removal shows that when pH value is up to 11.3,OH^- as initiator can induce ozone decomposition to produce hydroxyl radical.So indirect reaction takes the leading position of the ozone oxidization reaction in alkaline condition;Ozone dosage has an optimum value;COD removal rate can obtain a higher value with lower initial concentration of wastewater.The results indicate that removal rate of A₂₅₄ is fit for zero-order kinetics,and the removal rate at pH11.3 is higher than at pH6.5.(2) The change of TOC follows zero-order kinetics with reaction rate constantκ_TOC=0.072mg·L^-1min^-1.A₂₅₄ varies linearly with the equation A₂₅₄=-0.00358t+0.9395.By means of UV-vis and HPLC,the results shows that the characteristic absorption peak at wave length 254nm disappears,which indicates refractory organic chemicals are mineralized. Meanwhile,the ratio between BOD and COD increases from 0.12 up to 0.58.Tebuthiuron is finally mineralized to SO₄^2- ions,NO₃^- ions and NH₄⁺ ions.(3) The industrial wastewater has the characteristics of flocculation in alkaline condition. O₃/UV oxidation experiment and electro-catalytic oxidation experiment are carded out respectively.The results show that the biodegradability is improved greatly by O₃/UV oxidation which indicates refractory organics are converted into easily biodegradable matter By combind O₃/UV oxidation and biochemical treatment,effluent COD reduces to 250mg/L. Applying the O₃/UV oxidation+biochemical treatment+secondary O₃/UV oxidation process combination,the final COD lowers to 78mg/L which fully provs that the process combination for the treatment of heterocyclic urea herbicide wastewater is effective.