Evaluation of Performance of Fluidized Bed Bioreactors for On-Site Bioremediation of Water Contaminated with PCE Based on Mass Balance of Pollutants and Gene Expression

摘要

The objective of this study was to evaluate the effect of increasing concentrations of PCE, as well as the effect of using side filters of sand and zero-valent iron (ZVI) on the performance of methanogenic fluidized bed bioreactors. The evaluation was performed in terms of organic chlorine mass balances to determine the PCE dehalogenation and the gene expression in order to confirm the development of microbial dehalogenating capability in our bioreactors. Four methanogenic fluidized bed bioreactors were implemented, two with ZVI-sand side filter (HFBB, for hybrid methanogenic fluidized bed bioreactors) and two without this device (MFBB). All bioreactors were fed with increasing PCE concentrations (80, 165, 278, 393 mg/L; Periods 1 to 4, respectively). The HFBB removed a higher amount of PCE and presented lower concentrations of metabolites than the MFBB in all four periods of operation. In general, mass of metabolites in the effluents, gas trap (volatilized PCE and metabolites) and sorbed onto bed bioparticles represented less than 5% of the input PCE mass. Average PCE removal efficiencies significantly decreased in the periods with highest PCE concentrations, for both types of bioreactors. Average dehalogenating efficiencies were slightly lower than those of PCE, and showed parallel trends with respect to factor type of bioreactor and factor increasing PCE concentration to the variation of PCE efficiency. At the end of each acclimation period qPCR analyses were carried out in samples of bioparticles of the bioreactors in order to show the 16S sRNA DHC gene copies. The general trend showed that the specific gen rate (rg) was higher in the HFBB. The rg in both types of bioreactors improved over periods. The rg increase probably was related to the increase of PCE in the effluent; it is likely that dehalogenating enzymes could be stimulated/induced by the chlorinated aliphatic compounds. We conclude on the one hand that side ZVI-sand filter had a positive effect on PCE removal, although both PCE removal and dehalogenating efficiencies decreased at the highest PCE concentrations. On the other hand, that longterm operation of bioreactors fed with PCE lead to the development of a significant dehalogenating capability in the biomass of reactors.