Toluene induced cometabolism of CIS-1,2-DICHLOROETHYLENE (cas 156-59-2) and vinyl chloride under conditions expected downgradient of a permeable Fe(0) barrier

Add time:09/28/2019    Source:infona.pl

A new approach for groundwater treatment combines a permeable Fe(0) barrier to break down higher chlorinated solvents like PCE and TCE with a downgradient aerobic biological treatment system to biotransform less chlorinated solvents, such as DCE and vinyl chloride (VC), and petroleum hydrocarbons. The expected bacterial performance downgradient of an Fe(0) barrier was evaluated through laboratory batch experiments with a toluene-degrading mixed culture that cometabolically transforms cis-1,2-DCE and VC.The amount of cis-1,2-DCE (initially at 500 ppb) and VC (initially at 250 ppb) transformed was controlled by the initial toluene (0-12,000 ppb) and biomass (0-15μg protein ml - 1 ) concentrations. Cis-1,2-DCE was removed much more effectively than VC, and a higher toluene concentration in comparison to the co-substrate concentrations was needed for complete co-substrate removal. Competitive inhibition was indicated by the sequential degradation of toluene and the co-substrates. When the pH was above 8, the effectiveness of cis-1,2-DCE and VC transformation decreased rapidly for a given toluene concentration. 1,1-DCE, a product of the reduction processes within the Fe(0) barrier, hindered the transformation of toluene, cis-1,2-DCE and VC at concentrations as low as 10 ppb. Acetylene, another chemical reaction product, only marginally inhibited the transformation of the co-substrates in the studied concentration range of 0-1700 ppb.Overall, the coupling of an Fe(0) barrier and subsequent biodegradation appears feasible for remediation of complex mixtures of chlorinated solvents and petroleum hydrocarbons in groundwater. Our results suggest that supplemental toluene or other primary substrate upgradient of the biological process may be required, and that pulsing of this substrate may be advisable. Because passing through a permeable Fe(0) barrier increases the groundwater pH, neutralization with acid may be needed before entering the bioactive zone if the natural buffer capacity of the soil is insufficient. Breakthrough of 1,1-DCE from the Fe(0) barrier could prove a critical factor for the bacterial performance.

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