Bioremediation of Trichloroethylene and cis-1,2-Dichloroethylene-Contaminated Groundwater by Methane-Utilizing Bacteria.

Abstract

ABSTRACT. Experimental studies on the bioremediation of groundwater contaminated with low concentration trichloroethylene (TCE) and cis1,2-dichloroethylene (DCE) were performed with two sets of bioreactors. Reactors No. 1 and No. 2 were operated without and with methane supplement, respectively. No inoculum was used. The concentrations of TCE and DCE in the effluent and the off gas from reactor No. 2 were much lower than those from reactor No. 1. When air and an H 2 O 2 solution were supplied to reactor No. 2, concentrations of TCE and DCE in the effluent and the off gas were lower than the lowest detectable limit. The population of methaneutilizing bacteria in reactor No. 2 was 1,000 times higher than that in groundwater or in the effluent from reactor No. 1. These methaneutilizing bacteria were apparently attributable to the treatment of TCE.-KEY WORDS: bioreactor, methane-utilizing bacteria, trichloroethylene.J. Vet. Med. Sci. 61 (7): [861][862][863] 1999 Two bioreactors were packed with 1,000 ml (an effective volume of 500 ml) cylindrical (4 mm OD , 3 mm ID , 5 mm L ) carriers made of polypropylene [18]. No inoculum was used. These reactors were operated in a single-pass mode with a hydraulic retention time of 8 hr. The influent groundwater flow rate was 1 ml/min, the air flow rate of reactor No. 1 5 ml/min, the air flow rate of reactor No. 2 4 ml/min and the methane flow rate of reactor No. 2 1 ml/ min. The concentration of H2O2 supplied was 0.3% and a 0.3% H2O2 solution flow rate was 5 ml/hr. An experiment which used H2O2 as the oxygen source of supply of the bioreactor was reported by Gerhard et al. [8]. The concentration of H2O2 was so set as to make 13 ppm oxygen in the reactors based on the field experiment made by Semprini et al. [17]. The number of heterotrophic bacteria was calculated by counting colonies, which appeared on standard agar plates (Eiken Co., Tokyo, Japan) incubated at 25°C for 7 days. The methanotrophic bacteria were counted by the most probable number (MPN) method after 8 weeks of incubation in nitrate mineral salts (NMS) medium [26] under an atmosphere of methane-air (1:4) in a desiccator at 30°C. Samples for determination of TCE and DCE concentrations in liquids were prepared by the head-space method [1] and gas samples were analyzed with a gas chromatograph (Type GC-311, HNU Co., U.S.A.). Dissolved oxygen (DO) was analyzed with a DO meter. Groundwater contaminated with about 0.6 ppm of TCE and 0.2 ppm of DCE was used as influent. There were 1 × 10 3 MPN/ml of methane-utilizing bacteria in this groundwater.At first, oxygen was supplied to reactors by aeration. Methane-utilizing bacterial flocculation, a substantial growth of salmon-pink-colored biomass, was seen in the whole reactor No. 2 in two weeks after the beginning the experiment, and then, decrease in TCE became apparent and DO in effluent dropped from 7.5 ppm to 1.0 ppm in reactor No. 2. Finally, more than 90% of TCE and more than 70% of DCE were removed from reactor No. 2 in 3 weeks. However, in reactor No.

Stable isotope probing in the metagenomics era: A bridge towards improved bioremediation

“…Methane and other one-carbon (C 1 ) compounds are of global ecological significance because they can affect climate change, influence atmospheric and marine chemistry, and impact cloud formation. In the context of bioremediation, methanotrophs and/or methylotrophs have been implicated in the degradation of trichloroethylene and cis -1,2-dichloroethylene (Little et al, 1988, Arai et al, 1999, Shigematsu et al, 1999, Takeuchi et al, 2005), insecticides (Topp et al, 1993), nitro-substituted explosives (Van Aken et al, 2004), methyl halides (Warner et al, 2005), methyl tert -butyl ether (Nakatsu et al, 2006, Kane et al, 2007), and other xenobiotic compounds. Therefore, investigating the metabolism of C 1 compounds is also potentially valuable for bioremediation.…”