Study On The Screening And Characteristics Of Cyanide-degrading Fungi

Cyanide is highly toxic to living organisms; it is a well-known toxic compound as a metabolic inhibitor and as a pollutant for water bodies. However, large amounts of cyanide are used in industries involved in the products such as metal-plating, synthetic fibers, plastics etc. To protect the environment and water bodies, wastewater containing cyanide must be treated strictly before discharging into the environment. Currently, wastewater containing cyanide is treated by chemical oxidation methods. However, these methods are expensive and use hazardous chemicals as the reagents. Moreover, these techniques cannot completely degrade all cyanide in many cases. Because a wide range of microorganisms can degrade cyanide, biological treatment using these microorganisms would be a cost-effective and environmentally acceptable method for cyanide removal compared with chemical oxidation methods, so biological treatment has been widely studied by experts in domestic and abroad.Recently most studies for cyanide-degrading strains focus on bacteria, However, the application of biological treatment using bacteria in industrial wastewater has been hampered by its low tolerance capacity of heavy metals.Some of fungi can tolerate high concentration of heavy metals and degrade toxic materials better, and produce abundant enzyme, which can be used in degrading cyanide. There are few studies on fungi to degrade Cyanide.In this research, cyanide-degrading fungi screened from metal-plating wastewater and sludge is used to study the degradation characters and effects. Fourstrains of fungi had been isolated and screened; these strains are identified as Penicillum, Trichoderma, Geotrichum candidum and yeast with optical microscope, scanning electronic microscope (SEM) and transmission electronic microscope (TEM). The study on Penicillum showed that the optimum culture time of Penicillum was 27 hours and the optimum cyanide-degrading conditions of the fungus were temperature 30°C, pH 6, 130rpm rate of rotary shaker and inoculum 6%. The cyanide-degrading rate of the fungus was more than 95% after 16 hours under the optimum conditions. The cyanide-remaining concentration was about 0.5mg/L. the fungus can use cyanide as carbon and nitrogen source. Under cyanide-containing medium without additional carbon and nitrogen sources, the remaining cyanide concentration after 16h was 0.22mg/L, satisfies the 1st level of discharge standard of national GB 8978-1996. After the fungus had been acclimated by industrial cyanide-degrading wastewater, the cyanide-degrading rate in 16h was above 98% under pH rranging frome 6 to 9. When initial CN' concentration in industrial wastewater was rranged from 44.7mg/L to 84.5 mg/L, the remaining CN' concentration all meet 1st level of discharging standard, The reaction could be considered as approximately first-order reaction. Its cyanide-degrading rate constants were rranged from 0.2998 to 0.7385h~-1.The results of this study can provide practical and reference values for the biological treatment using cyanide-degrading fungi in the industrial wastewater application.