Bioremediation of Pentachlorophenol and Bleach Plant Effluent by Trametes versicolor and its Extracellular Fluid, Focused on Intermediates and Products Formed and the Role of Protein Binding of Chlorinated Compounds in a Two-stage Reactor System

Abstract

Bioremediation of pentachlorophenol (PCP) from aqueous solutions can provide valuable methods to remove other toxins from aqueous solutions, those that are more or less persistent or toxic than PCP. Understanding the mechanisms of remediation of PCP from aqueous solutions can provide information on the reactions involved in removing PCP from solution and the products resulting from the removal reactions. It is important to recognize if the products formed are less toxic or less bioavailable than the original compound being removed if the remediation technique is to be feasible and practical to use. There were several objectives of this study. One objective was to develop and optimize a novel two-stage bioreactor system that utilizes the white-rot fungus Trametes versicolor and its extracellular fluids to effectively remove PCP from aqueous solutions. Use of this bioreactor system to treat an industrial significant effluent, bleach plant effluent, was another goal of this investigation. Throughout the study, an objective was to identify the reactions that were involved in remediation of PCP, other than direct action of the fungal material. Realizing the types of products formed by removing PCP from solutions was an important objective to determine if the products formed were either more or less harmful to the environment.

The extracellular fluid of two-stage bioreactor system developed was determined to remove over 96.6% of PCP from a feed containing of 2.56mg/L at 8 hours retention time. Long-term effectiveness and robustness to environmental fluctuations were found to be useful characteristics of the two-stage bioreactor system. Tetrachlorohydroquinone (TCHQ) was identified as an oxidative product of PCP, and was present in untreated BPE. When the bioreactor system was used to treat BPE about 90% of the PCP and TCHQ present was removed. Non-enzymatic reactions were found to proceed in reactor resulting in the formation of addition products, probably 2,3,4,5,6-pentachloro-4-(pentahchlorophenoxy)-2,5-cyclohexadien-1-one and 2,3,5,6-tetrachloro-4-(pentachlorophenoxy)-phenol. Protein produced by the immobilized Trametes versicolor was determined to be important in removing PCP and TCHQ from solution. PCP and TCHQ were removed from aqueous solution by reactor protein as a result of binding with the sulfhydryl groups in the protein.