Dechlorination of TetrachloroetheneInfluence of Tetrachloroethene and Methane in Batch Cultivation under Methanotrophic Conditions in the Presence of Oxygen

Abstract

The feasibility of combining the reductive dechlorination and oxidative mineralization of tetrachloroethene (PCE) within one system was investigated in non-shaken methanotrophic batch cultivated cell suspensions. In the presence of up to 90% [v/v] methane and 10% [v/v] oxygen in the headspace, 200, 400 and 500 µmol/l PCE were completely dechlorinated over 100 days of incubation with 1% [v/v] activated sludge derived from a municipal wastewater treatment plant (equivalent to 6 mmol/l carbon). Meanwhile nearly 4 mol/l chloride were released to the medium for each mol PCE dechlorinated, indicating that the volatile chlorinated compound was completely dechlorinated in the cell suspensions. Irrespectively of the initial PCE concentration, 40 µmol/l trichloroethene were found temporarily. According to the initial PCE concentration, up to 160 µmol/l cis-dichloroethene were measured in the assays with 500 µmol/l PCE. In the presence of oxygen in the headspace, simultaneously with the dechlorination, methane was oxidized. At 7% [v/v] methane and 10% [v/v] oxygen, 500 µmol/l PCE were dechlorinated to cDCE within 145 days. At PCE concentrations of 600 µmol/l or above, substrate inhibition occurred, and then both the dechlorination and the oxidation of methane were inhibited.

Development of a membrane‐aerated biofilm reactor to completely mineralise perchloroethylene in wastewaters

“…When observed in a static position immediately after the addition of pure oxygen, the bottles contained two layers of biomass; one layer settled to the bottom of the bottles while the other layer was at the biomedium/headspace interface. Similar observations have been made by Klag et al 20 Based on this observation it was thought that the suspended biomass was aerobic bacteria utilising the oxygen added to the bottles, while the bottom layer consisted of anaerobic bacteria shielding from the oxygen. Addition of pure oxygen had a significant effect on PCE degradation (Fig.…”

“…Moreover, in this study oxygen was added intermittently to serum bottles. This was different from the constant 10% (v/v) oxygen concentration maintained in the study carried out by Klag et al 20. In this study, it is possible that the production of methane (results not shown) and ethylene detected in the serum bottles, combined with the addition of oxygen, may have either induced synthesis of methane or alkene monooxygenases, enzymes responsible for the aerobic co‐metabolic degradation of TCE, cis ‐DCE and VC, or promoted autotrophic growth on VC.…”

“…PCE degradation with unacclimated biomasses has, however, been documented; van Eekert et al 7 reported on the constitutive dechlorination of PCE by a non‐acclimated methanogenic consortium. Similarly, Klag et al 20 reported the degradation of high concentrations of PCE under methanotrophic conditions. However, these studies did not compare the degradation rates of PCE with the acclimated sludge and the unacclimated sludge.…”

“…Addition of oxygen to anaerobic serum bottles degrading PCE has been investigated previously; Hirl and Irvine24 described a mixed culture dechlorinating PCE able to survive exposure to 9 mg L −1 of oxygen. Klag et al 20 reported the dechlorination of 500 µmol L −1 of PCE into cis ‐DCE within 145 days in the presence of 90% (v/v) methane and 10% (v/v) oxygen in the headspace. These authors attributed the complete mineralisation of PCE to an interaction between the anaerobic biomass which degraded PCE into TCE and cis ‐DCE, and the aerobic bacteria which subsequently degraded the less‐chlorinated ethenes via aerobic co‐metabolism using methane monoxygenase (MMO).…”

“…These authors attributed the complete mineralisation of PCE to an interaction between the anaerobic biomass which degraded PCE into TCE and cis ‐DCE, and the aerobic bacteria which subsequently degraded the less‐chlorinated ethenes via aerobic co‐metabolism using methane monoxygenase (MMO). Unlike studies by Klag et al ,20 who supplied methane to the headspace to induce aerobic co‐metabolism, methane was not added to our serum bottles. It was expected that methane produced from the anaerobic degradation of glucose would serve as a substrate to induce the synthesis of MMO upon the addition of air.…”