BIODEGRADATION OF CYANIDE FROM INDUSTRIAL WASTEWATER

Abstract

Cyanides are highly toxic. Therefore its treatment from water or wastewater is essential. Cyanides are produced by certain bacteria, fungi and algae, and may be found in plants and some foods, such as lima beans and almonds. Although cyanides are present in small concentrations in these plants and microorganisms, their large-scale presence in the environment is attributed to the human activities as cyanide compounds are extensively used in industries. Bulk of cyanide occurrence in environment is mainly due to metal finishing and mining industries. From an economic standpoint, the biological treatment method is cost-effective as compared to chemical and physical methods for cyanide removal. Biological treatment of cyanide under anaerobic as well as aerobic conditions is possible. Biodegradation of cyanide compounds by two microorganisms have been reported. Several microbial species can effectively degrade cyanide into less toxic products. During metabolism, they use cyanide as a nitrogen and carbon source converting it to ammonia and carbonate, if appropriate conditions are maintained. Although, many attempts have been made for biological treatment of low concentrated, simple cyanide compounds in batch reactors, but reports on biodegradation of metal complexed cyanides are very few. Biodegradation studies were carried out for studying the effectiveness of two microorganisms. For pure cultures of Pseudomonas fluorescens and Pseudomonas putida were used for the study. The growth of microorganisms in the enrich medium and medium with cyanide ions was observed by measuring cell density. The microorganisms adopted to grow at maximum cyanide concentrations were harvested and its ability to degrade cyanide was measured in biodegradation process. The effect of pH, temperature and initial concentrations on the removal efficiency were studied for the two microorganisms. In the present study Pseudomonas fluorescens was found to have the maximum efficiency about pH 8, 7, 6 conditions and Pseudomonas putida was found to have the maximum efficiency about pH 9, 8, 7 and temperature range of 25-30 °C for NaCN, Zr N) FeeN)compounds respectively. The growth of microorganisms was delayed in the presence of high concentrated cyanide solutions. It was found that cyanide was utilised as sole nitrogen source by microorganisms. Also, with the increase in initial concentration of cyanide, the percent removal decreased.