Studies on Microbial Degradation of Chlorinated Organic Compounds

Abstract

Chlorinated organic compounds which are toxic to higher forms of life are also recalcitrant to microbial degradation. Among the toxic chlorinated organic compounds, chlorinated phenols have been chosen for this study because of their wide spread into the environment, affecting both soil and groundwater. Chlorophenols especially mono- and dichlorophenols are formed during the chlorination of water and waste water, in the presence of some pollutants. Several techniques are available for the removal of contaminants from waste water, although not all are efficient enough to reduce to acceptable limits. Biological treatment by use of microorganisms is especially attractive because it has the potential to almost completely degrade Chlorophenol while producing innocuous end products. In addition, it has the advantage of reduced capital and operating cost because of operating at ambient conditions. A pure culture of chlorophenol degrading bacteria used in this study was isolated from soil near waste water treatment tank of an industry manufacturing compounds using chlorophenols. Colonies of 2, 4-DCP and PCMX degrading organism were obtained from the highest dilutions on nutrient agar plates containing 10 ppm of 2, 4- DCP and PCMX. The bacteria were identified by genotype and phenotypic characterization as Bacillus cereus. Comparative analysis of the 16S rDNA sequence in the Gene Bank database revealed that these bacteria are related to Bacillus cereus. Growth of Bacillus cereus was optimized in concentrations ranging from 0.5 mg/L to 50mg/L of both 2, 4-DCP and PCMX. Degradation of Chlorophenol was studied using this culture in defined salt media under various ambient conditions of pH values (pH 2,3,4,5,6,7 and 8) and different temperature (250C, 300C, 350C, 400C). The residual 2, 4-DCP estimation revealed that maximum degradation of 28 % occurred in cultures placed at 30oC in 7pH for 264 hour with 10 mg/L of 2,4-DCP. The maximum degradation was 28.76 % at 30oC in 7 pH for 216 hour with 50 mg/L of PCMX. In 264 hour 64.6 % 2, 4-DCP was removed at pH 3. The acidic pH influence the efficiency of degradation of 2,4-DCP. The maximum percentage degradation of PCMX is at 7pH (28 %) when compared to other pH. The parent strains where subjected to two types of mutation for enhancement of degradation as per the protocols reported in literature and the mutated strain have exhibited higher potential degradation for 2,4-DCP compared to PCMX, were parent strain could effectively degrade instead of mutated organism. The statistical tools to understand the interaction of the process variables by use of RSM has been carried out. The experimental results closely match the predicted values. Application studies by treating the effluent contain chlorinated organic compound was carried out by parent strain and mutated strain. Chlorinated organic compound in the effluent was effectively degraded.