Biodegradation of low aqueous concentration pentachlorophenol (PCP) contaminated groundwater

Bioremedial treatment to remove low level organic contamination to regulatory standards has met with limited success. In this study source water from a contaminated surficial aquifer at a former wood treatment facility was used to evaluate the potential for indigenous microorganisms to degrade low level (<1.0 mg) pentachlorophenol (PCP) to a regulatory drinking water standard of 0.001 mg/L. PCP degradation was evaluated in series of batch reactors in a two phase study to (a) determine the rate and extent of PCP removal and (b) evaluate the impact of nutrient amendment (N and P) on removal rate. All reactors with the exception of the abiotic control demonstrated PCP removal to a level < 0.002 mg/L within a maximum period of 32 d with and without nutrient amendment. A regression analysis of reactive phosphate (ortho-P) concentration versus removal rate produced an R2 of 0.94 (p= 0.006) indicating a significant correlation between the level of available phosphate and PCP degradation rate. Selective bacterial enumeration (for PCP degrading bacteria) revealed PCP-degrading bacteria increased in abundance prior to and in conjunction with the degradation phase to a density of between 103 to 104 CFU/ml. Isolates were also analyzed for total fatty acids using Fatty Acid Methyl Ester (FAME) methodology and the results indicated that PCP degrading bacteria were present in the aquifer and consisted of predominately fluorescent, oxidase positive Pseudomonas species. Overall, data indicate that autochthonous microbes are capable of removing low level PCP (<1.0 mg/L) to approach if not reach the regulatory standard of 0.001 mg/L with the addition of oxygen, with or without nutrient amendment. Results of this research can be applied to full-scale implementation of in-situ or ex-situ bioremediation of groundwater at former wood treatment facilities.