Studies on Biodegradation of P-Nitrophenol by Arthrobacter chlorophenolicus and Its Metabolites

The biodegaradation of p-nitrophenol was studied experimentally at different initial p-nitrophenol concentrations under different environmental and operational conditions (like incubation temperature, pH, inoculum size etc.) by using microbial strain Arthrobacter chlorophenolicus A6. The rate of degradation of pnitrophenol was observed maximum at incubation temperature 30 ̊C and pH 7 ± 0.2, inoculum size OD600 = 0.2, incubation rotor speed 150 rpm, pH in the range 5-8 and temperature 25-35 ̊C. In experiments on kinetic studies the initial concentration of biomass is fixed OD600=0.2 and variation in biomass concentration has been experimentally observed with time at pnitrophenol concentrations (10-200 mg/l). The value of maximum specific growth rate is found to be equal to 2.370 h -1 and it is achieved at initial p-nitrophenol concentration of about 70 mg/l. The p-nitrophenol is inhibitory type substrate and the inhibition effect of p-nitrophenol becomes predominant above 70 mg/l. The various growth kinetic models are available in literature to represent the growth kinetics data of an inhibitory compound. The results illustrate that most of the experimental data points close to the prediction by Haldane model and lie within the permissible range of ±10%. It is therefore concluded that Haldane model is the most suitable kinetic model for biodegradation of p-nitrophenol on Arthrobacter chlorophenolicus A6 for the substrate concentration ranging from 10-200 mg/l. Haldane kinetic model is used for further studies. For the present study on p-nitrophenol using Arthrobacter chlorophenolicus A6 the value of max specific growth rate, saturation constant and inhibition constant are 2.372 h -1 , 860.681 mg/l and 6.180 mg/l respectively upto 200mg/l concentration of p-nitrophenol, i.e. Sm = (Ks x Ki) 1/2 = 71.8. In view of the above studies it can be concluded that Arthrobacter chlorophenolicus can be successfully used to treat waste water containing phenolic compounds such as p-nitrophenol.