Cyanide Removal By Fenton And Treatment Project Of Electroplating Wastewater Containing Low Concentration Of Cyanide

After the new discharge standard of wastewater goes into effect, it is urgent for the treatment of electroplating wastewater due to a shortage of technology to cope with the low concentration of cyanide in the wastewater. The wastewater from a plating factory in Jinhua of Zhejiang province was treated on a bench scale to investigate the efficiency of Fenton reagent oxidation. Based on the optimized parameters from the bench experiments, the wastewater treatment station was then designed and constructed, which has met the new discharge standard very well.The main factors affecting the remove efficiency of cyanide, such as initial pH, the molar ratio of H2O2/FeSO4, H2O2 dosage and reaction time, were carefully explored and optimized for the wastewater treatment. It was found that the remove efficiency of cyanide was up to 93% under the conditions of initial pH value 3.5, molar ratio of H2O2/FeSO4 3.5, H2O2 dosage 5.0g·L-1 and reaction time 60min. Fenton was therefore proved to be highly efficient for the removal of trace cyanide from wastewater.There are four types of wastewater discharged by the electroplating factory. Based on the experiments results, the processes for the wastewater treatment were designed as follows, (1) the wastewater containing high concentration of cyanide was treated by alkaline chlorination method, (2) the wastewater containing chromium(VI) was treated by sodium metabisulfite to reduce it into elemental precipitate, and (3) comprehensive wastewater containing low concentration of cyanide was treated with Fenton reagent to remove cyanide. Then, the wastewater was mixed with (4) galvanizing wastewater and subsequently treated by neutralization, flocculation, and biological contact oxidation processes.The influent wastewater contained cyanide 9.0-60mg·L-1, while the concentration of cyanide in the effluent dropped below 2.0 mg·L-1, resulting in removal efficiencies of around 98%. The investment of the facilities was￥1.569 million, and the operating costs was￥6.9 per cubic meter wastewater.So the experiments and engineering showed that it was effective and efficient for Fenton to treat the low concentration of cyanide.