Biotechnological treatment of chlorophenol-contaminated water

Abstract: Widespread presence of toxic and persistent pollutants in the environment, even at low concentrations, causes risks of adverse effects to human health and the ecosystem. Biological methods for treatment of water streams and removal of persistent pollutants are of great interest due to their simplicity, low cost, and mild operational conditions without harmful by-products. The purpose of this research was to improve high-performance bioprocesses for treatment of water streams contaminated with toxic organic pollutants. Chlorophenols were chosen as model toxic organic pollutants to degrade. Biological treatment processes are usually inhibited by the presence of toxic pollutants. Photolysis pretreatment was successfully used to detoxify the chlorophenols-contaminated water followed by mineralization in biological step, which was not observed using individual biological treatment. Two-liquid phase partitioning bioreactor was also used for mineralization of pentachlorophenol, at high concentrations, without accumulation of metabolites. Biphasic system was optimized by investigating the influence of type of the solvent, phase ratio, agitation speed, and substrate concentration. Integrated physicochemical-biological processes presented high potential for treatment of toxic pollutants by providing the potential to prevent accumulation of hazardous by-products in chemical treatment, reduce the toxicity of effluent for biological processes, and control the delivery of pollutants to the microorganisms. Fixed-biofilm reactors were used for degradation of chlorophenols under different operational conditions including suboptimal environment. These reactors were studied under different organic and hydraulic loading rates, temperatures, and substrate feedings. High removal efficiencies were obtained even at low temperatures down to 4?C. However, different patterns and removal efficiencies were observed for different chlorophenols fed to the reactors. The performance of fixed-biofilm reactors was limited neither by the bacterial activity nor by the inhibition effect of substrate at high loading rates, but by the limited solubility of oxygen in water to provide dissolved oxygen for the microorganisms. An essential issue for improvement of biological processes is in situ monitoring of the hydrodynamic and biological parameters in relating to operational conditions and process efficiency. The biological treatment processes were investigated in situ by monitoring the bacterial community profile using fluorescence in situ hybridization technique and the concentration of toxic pollutants using a cell-based biosensor. Biofilms from different reactors were dominated by ?- and then ?-proteobacteria. Bacterial community of biofilm was not influenced by organic loading rate. However, reduction of the working temperature caused significant increase in the population of ?-proteobacteria and Pseudomonas based on total community. Two bacteria were isolated from biofilms and identified as Ralstonia basilensis and Alcaligenes sp. able to degrade 50 mg chlorophenol l-1 under a wide range of temperature 5-30?C. Beside to this, a cell-based biosensor was developed able to detect and monitor the concentration of dichlorophenol. The performance of biosensor was improved by integrating within a flow injection system for continuous analysis of target pollutant.