High-Rate Biodegradation of Pentachlorophenol by Biofilm Developed in the Immobilized Soil Bioreactor

Abstract

A novel type of bioreactor, the immobilized soil biofilm reactor, was used for the biodegradation of pentachlorophenol (PCP) in aqueous solutions. An extremely high volumetric PCP degradation rate was obtainedsup to 950 mg of PCP L -1 h -1 . The study of the biofilm growth kinetics showed that biofilm mass reached 4 g dry weight/L of reactor volume, which is much higher than values generally reported in the literature. The corresponding yield coefficient was found to be 0.054 g of biomass/g of PCP. The biofilm thickness during the PCP degradation constant rate period was below 100 µm. A mathematical model based on a diffusionreaction mechanism in a cylindrical shell biofilm showed that under these conditions the process is kinetically controlled. Substrate utilization kinetic data showed that the process can be described by a Monod-type model with µ m ) 0.016 h -1 and K s ) 5.74 mg of PCP/L. It was shown that essentially all PCP is degraded within the biofilm, with negligible liquid-phase biodegradation. The effect of different physicochemical parameters of the liquid phase on PCP biodegradation rate was also studied. The optimal temperature range was between 20 and 35 °C, while a 60% rate decrease was observed at 15 °C. The process was inhibited at pH values above 7.7, while the main watersoluble reaction product (chloride ions) affected negatively the process only at concentrations higher than 15.8 g/L. These results show that aerobic biodegradation of PCP is much less affected by variations in the different physicochemical factors when carried out in a biofilm as compared to a free suspended culture. These considerations become the bases for modeling and designing of immobilized soil bioreactors for PCP degradation in aqueous phase (such as groundwater and process water of soil washing).

Microbial degradation of chlorinated phenols

“…The highest rates of PCP biodegradation were observed in a reactor with immobilized biofilms developed on soil retained in geotextiles. The reactor was able to convert 22.8 kg PCP m -3 reactor d -1 (Karamanev and Samson 1998). To obtain these high conversion rates, high effluent PCP concentrations of 10 to 20 mg l -1 were required to overcome biofilm diffusion limitations and thus only partial removal of PCP was achieved.…”

Experimental and modeling approach to study sorption of dissolved hydrophobic organic contaminants to microbial biofilms

“…Therefore, glassware was used wherever possible and tubing made of PTFE. Highporosity polypropylene (Carlson and Silverstein, (1997)), silicone rubber tubes (Zhang et al, 1998) or geotextiles (Karamanev and Samson (1998)), which have been used as solid support in other investigations, were not suitable. For the same reason, no peristaltic pump but a mediumpressure liquid chromatography piston pump with adsorption-resistant materials was used to circulate the solution through the biofilm reactor.…”

On‐line estimation of dissolved methane concentration during methanotrophic fermentations

“…One such reactor is the immobilized soil bioreactor (ISBR) which was originally developed as a membrane bioreactor with a self-contained inoculum (soil) for the mineralization of recalcitrant groundwater contaminants such as pentachlorophenol (Karamanev and Samson, 1998;Karamanev et al, 1999). Its application was then expanded to operation as a methanotrophic bioreactor, for the bioremediation of contaminated groundwater (Ramsay et al, 2001).…”