Biodegradation of pentachlorophenol : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Environmental Engineering at Massey University

Abstract

Three isolates previously isolated from pentachlorophenol (PCP) contaminated soil as a consortium were tested for their ability to remove PCP from a minimal mineral salts medium with and without vitamin supplementation. Only one of the isolates, designated Bradyrhizobium sp. strain ET01, could utilise PCP as a sole source of carbon and energy. The other two isolates designated Pseudomonas putida strain ET02 and formerly Pseudomonas aureofaciens strain ET03 could grow in the presence of PCP but could not utilise it as a sole source of carbon and energy. The effects of various initial PCP concentrations and vitamin supplementation on the kinetics of PCP removal and the cell numbers for ET01 and culture combinations was tested. An increasing initial PCP concentration affected the PCP removal rate, the lag period, the cell yield, cell numbers and specific growth rate. PCP removal by ET01 ceased at a concentration of 175mg/1. The PCP removal rate increased for ET01 in pure culture through the course of the experiments. The rate of removal at 150mg/1 initial PCP concentration improved from 1.48mg/1/hr to 1.85mg/1/hr. The rate of removal at 120mg/1 initial PCP concentration improved from 1.38mg/1/hr to a maximum of 2.10mg/1/hr. The shortest lag period was 4 hours for ET01 in pure culture on 20mg/1 initial PCP concentration. The lag period for ET01 in pure culture was 0.30 of the initial PCP concentration. The size of the inoculum of ET01 had an effect on the lag period and the rate of PCP removal. Cell yield was extremely low for ET01 and the culture combinations at all initial PCP concentrations tested. Measurable PCP removal was observed when the cell density of ET01 reached approximately 1x10 7 cells/m1. The final number of cells for ET01 for initial PCP concentrations over the range of 20mg/1 to 150mg/1 was approximately 5.5x107 cell per m1 (0.09mg/1). The highest specific growth rate for ET01, 0.06hr-1, occurred in media containing yeast extract and at an initial PCP concentration of 40mg/1. Continuous subculturing under the selective pressure of PCP as the sole carbon and energy source in media containing yeast extract led to an increased PCP removal rate and a decreased lag period for ET01. There was a slight increased rate effect of combining ET01 and ET02, but generally ET01 in pure culture removed PCP at a higher rate than any of the culture combinations.