Study On The Treatment Technology Of High-concentration Cyanide-containing Pesticide Wastewater

The cyanide-containing wastewater mainly derives from chemical Engineering industry such as metal working and pesticide production. It is very important to treat this kind of wastewater because of the redundant toxic contaminants it contains. Acidify recovery process and alkaline chlorinating process are usually used, which have some problems.The physico-chemical treatment process of high-concentration cyanide-containing pesticide wastewater from the Nanjing First Pesticide Corporation Ltd. is discussed in this thesis. Treatment of cyanide-containing pesticide wastewater with complexing precipitation, Fenton oxidation and ClO2 extensive oxidation is experimented systematically. Relative principles and working conditions are also discussed. The experiment data are obtained from trail test, while the reactive principles of the different treating steps are also investigated. The original cyanide-containing pesticide wastewater studied here contains high-concentration of salt, redundant toxic contaminants, refractory organic pollutants and high values of colority, which can be described as: pH>13, COD 20000~ 40000 mg/L,CN- 6000~20000mg/L, colority 5000 times, and salt >8%. The results of the experiments show that the optimal conditions of complexing precipitation are: FeSO4 dosage 1.4 times of the theoretical value, aeration during 3h, aeration quantity 40L/(L?h). Some results such as filtrate's pH, COD and colority removal, and CN- removal are found to be 5~6, more than 92%, and more than 99.99%, respectively. The optimal conditions of Fenton oxidation process are: pH 3, reaction during 3h, 30%H2O2 dosage 20ml/L, FeSO4?7H2O dosage 3.0g/L , neutralizing during 6h, while the more than 60%COD removal and more than 90%colority removal are observed. The optimal conditions of ClO2 extensive oxidation are: pH ca.11, 1% ClO2 dosage 20ml/L, reaction during 4h, COD removal more than 40%.The experimental results show that less than 400mg/L COD, less than 0.5mg/L CN- concentration, pH 6~8, and almost colorless and transparent effluent are obtained by the three steps treating process, of which the running cost 30% times of the traditional treating process. A novel treating technique, the complexing precipitation followed by Fenton oxidation and ClO2 extensive oxidation process, are suggested in the present study on pilot-scale test. It can be foreseen that this new process is not only applied to the treatment of high-concentration cyanide-containing wastewater, but also suitable to the efficient treatment of refractory organic wastewater.