Study On Treatment Of Heterocyclic Pesticide Wastewater Using Ultrasonic/Ozone Combined Process

Heterocyclic pesticide is one kind of refractory industry wastewaters due to its complicated components, high concentrations of organic pollutants, poor biodegradability and strong biological toxicity. It also contains large amounts of heterocyclic compounds, whose presence makes it difficult to treat this kind of wastewater. In this study, ultrasonic (US)/ozone (O3) combined process was employed to treat heterocyclic pesticide wastewater for increasing biodegradability and reducing biological toxicity.The experimental results showed that the US/O3 had effective treatment performance on the wastewater. COD was removed by 67.2%, the ratio of BOD5/COD was increased from 0.03 to 0.55 and the biological toxicity was reduced by 78.85% with EC50 from 11% to 52%. While using sole US process and sole O3 process, COD removal efficiencies reached 33.7% and 58.6%, BOD5/COD values were increased from 0.03 to 0.08 and 0.33, and the biological toxicity was reduced by 45.45% and 76.09% with EC50 from 11% to 16% and 46%, respectively.Influences of initial pH, ultrasonic frequency, ultrasonic power, probe diameter and O3 consumption amount on COD removal were studied. Initial pH was found to have a high influence on COD removal and alkaline conditions were more favorable. Low ultrasonic frequency was better for COD removal. The influences of ultrasonic power and probe diameter were small, and COD removal efficiency just first went up and then declined with the reaction time. With the increase of O3 consumption amount, COD removal was effectively improved. The optimal operational parameters for the combined process on COD removal were initial pH 9, ultrasonic frequency 20 kHz, ultrasonic power 300 W and the consumption amount of O3454.8 mg/(L-min).With the increase of reaction time, the biodegradability of the wastewater was improved drastically and the biological toxicity of the wastewater was reduced obviously. However, the BOD5/COD value woud drop slowly when pH surpassed 9 and the reaction time was more than 120 min. The biological toxicity woud rise slowly when pH was over 11 and the reaction time exceeded 120 min. Initial pH apparently affected both the biodegradability and the biological toxicity of the wastewater treated by US/O3, and the ratio of BOD5/COD and EC50 would rise continuously with an increase of initial pH. GC-MS results showed that the pollutants in heterocyclic pesticide wastewater were evidently removed and even vanished.There existed both direct reaction and indirect reaction in US/O3.The ratio of direct and indirect oxidation was 39.29:60.71 when initial pH was 13.59 and the consumption amount of O3 was 550 mg/(L·min). Initial pH was found to have small effect on the ratio of direct and indirect reaction, and the proportion of indirect oxidation would rise slowly with the increase of initial pH.