Factors controlling the efficiency of bio-enhanced PCE NAPL dissolution.

摘要

Theoretical studies have shown that the dissolution rate of non-aqueous phase liquids (NAPLs) containing tetrachloroethene (PCE) can be accelerated due to the activity of PCE-dehalogenating bacteria. Even after this phenomenon was observed experimentally, the factors that may affect the efficiency of bio-enhanced dissolution are not well understood. In this work, a numerical model was developed to evaluate the performance of the bio-enhanced PCE NAPL pool dissolution. It was found that the active biomass self-concentrates over time as biomass grows on substrate fluxes from different directions and advection between the NAPL and the biomass decreases. When the electron donor is the limiting factor, active biomass accumulates away from the interface, diminishing the concentration gradient. Such adverse impacts may significantly decrease the enhancement in comparison with predictions by models that do not consider bio-clogging.; Next, the model was extended to evaluate several factors that may control the dissolution enhancement for a residual NAPL source zone. It was found that dehalogenating kinetics, electron donor levels, NAPL configuration, and ED competition among microorganisms all affect the extent of dissolution. The key to the significant enhancement depends on how deep the dehalogenating activity can develop in the source zone. The inhibitory effects of PCE and it transformation products, such as 1,2-cis-dichloroethene (cDCE), may restrict the dehalogenating activity only at the upgradient part of the source zone, and thus are considered as the most likely factors that limit the enhancement in field applications.; A pure culture of Dehalospirillum multivorans and a mixed dehalogenating culture were tested to examine the cDCE inhibition effects on PCE dehalogenatinn. The inhibition effect on both cultures was similar. The maximum cDCE concentration achievable for both cultures was about 8.3 mM. The loss of dehalogenating activity under high cDCE concentrations over a month is well represented by a first order decay process. The lost dehalogenating activity was recoverable and the degree of recovery was proportional to the amount of PCE consumed. Data suggest that the likely cause of toxicity is the partition of PCE and its products into the bacterial membrane.