Kinetic study of degradation of p-nitro phenol by a mixed bacterial culture and its constituent pure strains

Abstract

Para-nitrophenol (PNP) is one of the major environmental waste water pollutant. It is found in industrial effluents of different industries like, chemical, dyes and plastic manufacturing industries. When this untreated industrial effluents come in contact with the ground water through soil percolation etc contaminates the environment. PNP is a chemical compound that has a hydroxyl group and a nitro group attached to an aromatic benzene ring at the para position. PNP is an important intermediate in the manufacturing of azo dyes and a number of pesticides such as parathion, fluorodifen, nitrofen, bifenox, p-aminosalicylic acid and p-acetaminophenol. Thus removal of PNP from these waste water is of paramount importance for maintenance of a healthy environment. In addition to chemical treatments which have certain disadvantages like production of toxic intermediates etc, biological treatment of PNP is a good method to remove PNP from waste water. Thus the objective of the present study is to compare biodegradation of PNP by a mixed bacterial culture isolated from ECW soil and its constituent pure bacterial cultures. Psychrobacter sp, Stenotrophomonas sp, Bacillus sp and E.coli are present in the mixed bacterial culture. The mixed bacterial culture was acclimatized to a high concentration of PNP by gradually increasing the proportion of p-nitrophenol in the MS media to 400mg/L. The pure cultures and their indigenous mixed bacterial culture, as isolated from the ECW soil sample, were grown in a batch process in MS media supplemented with 400mg/L p-nitrophenol as the sole source of carbon. The kinetic parameters like specific growth rate constant, maximum specific growth rate constant, specific degradation rate constant, maximum specific degradation rate constant and saturation constant for each system were determined. Performance of different bacterial species and their mixed consortium in degrading p-nitrophenol were studied and compared. Though among the pure cultures Bacillus sp. was the best PNP degrading bacterial species, the mixed bacterial consortium is preferred for further studies as a mixed culture is more stable than a pure culture and can tolerate and nullify the inhibitory effects of other pollutants if present. Moreover, it was found from kinetic data analysis using MATLAB®7.4 that the mixed bacterial culture followed Haldane model for degrading PNP.