Complete dechlorination of tetrachloroethylene by use of an anaerobic Clostridium bifermentans DPH-1 and zero-valent iron

Effect of sudden addition of PCE and bioreactor coupling to ZVI filters on performance of fluidized bed bioreactors operated in simultaneous electron acceptor modes

The present work evaluated the effects of (i) feeding a water contaminated with 80 mg/L PCE to bioreactors seeded with inoculum not acclimated to PCE, (ii) coupling ZVI side filters to bioreactors, and (iii) working in different biological regimes, i.e., simultaneous methanogenic aeration and simultaneous methanogenic-denitrifying regimes, on fluidized bed bioreactor performance. Simultaneous electron acceptors refer to the simultaneous presence of two compounds operating as final electron acceptors in the biological respiratory chain (e.g., use of either O₂ or NO₃^- in combination with a methanogenic environment) in a bioreactor or environmental niche. Four lab-scale, mesophilic, fluidized bed bioreactors (bioreactors) were implemented. Two bioreactors were operated as simultaneous methanogenic-denitrifying (MD) units, whereas the other two were operated in partially aerated methanogenic (PAM) mode. In the first period, all bioreactors received a wastewater with 1 g chemical oxygen demand of methanol per liter (COD-methanol/L). In a second period, all the bioreactors received the wastewater plus 80 mg perchloroethylene (PCE)/L; at the start of period 2, one MD and one PAM were coupled to side sand-zero valent iron filters (ZVI). All bioreactors were inoculated with a microbial consortium not acclimated to PCE. In this work, the performance of the full period 1 and the first 60 days of period 2 is reported and discussed. The COD removal efficiency and the nitrate removal efficiency of the bioreactors essentially did not change between period 1 and period 2, i.e., upon PCE addition. On the contrary, specific methanogenic activity in PAM bioreactors (both with and without coupled ZVI filter) significantly decreased. This was consistent with a sharp fall of methane productivity in those bioreactors in period 2. During period 2, PCE removals in the range 86 to 97 % were generally observed; the highest removal corresponded to PAM bioreactors along with the highest dehalogenation efficiency (94 %). Principal component analysis as well as cluster analysis confirmed the trends mentioned above, i.e., the better performance of PAM over MD, and the unexpected no effect of the ZVI side filters on PCE removal and dehalogenation efficiencies. To the best of our knowledge, this is the first report on the combined treatment ZVI-biological of a water polluted with PCE, where the biological operation relied on simultaneous electron acceptors.

Investigation of the decomposition mechanism of hexachlorobenzene on gamma-Al2O3

Decomposition of hexachlorobenzene (HCB) on high surface area y-alumina was comprehensively studied using in situ Fourier transform infrared spectroscopy, gas chromatography/mass spectrometry (GC-MS) and ion chromatography. Monitoring of the temperature-dependent decomposition by Fourier transform infrared spectroscopy showed that HCB decomposed as the temperature increased and phenolate species and other decomposition products formed. Pentachlorophenol (PeCP) and pentachlorobenzene were identified as the main decomposition products by GC-MS, and the time dependence of the formation of PeCP and pentachlorobenzene suggested that PeCP was the main intermediate. A trace analytical method based on derivatization and GC-MS revealed the presence of 3,4,5,6-tetrachloro-1,2-benzenediol and tetrachloro-hydroquinone. A small amount of inorganic chlorine ions produced by dechlorination of HCB was detected by ion chromatography. PeCP was the main intermediate and was transformed to 3,4,5,6-tetrachloro-1,2-benzenediol and tetrachloro-hydroquinone on the alumina surface. These compounds then decomposed to small molecules via cracking of their aromatic rings.

A field comparison of two reductive dechlorination (zero-valent iron and lactate) methods

Two parallel pilot experiments were performed at Kurivody (Czech Republic) in order to compare two reductive remedial technologies for chlorinated ethenes - microbial dehalogenation assisted by lactate and chemical dehalogenation with zero-valent iron (nZVI) nanoparticles. The methods were applied at a site contaminated by tetrachlorethylene (PCE) and trichlorethylene (TCE), with total concentrations from 10 to 50 mg/l. Concentrations of chlorinated ethenes, inorganic components of interest, pH and oxidation reduction potential (ORP) were monitored at the site for a period up to 650 days. The method of biological reductive dechlorination supported by lactate showed a considerable removal of PCE and TCE, but temporary accumulation of transient reaction product 1,2-cis-dihloroethene. Reductive dechlorination with nZVI showed a significant reduction in the concentration of chlorinated ethenes without a formation of intermediate products. The development of pH showed only small changes due to the high buffering capacity of the aquifer. Both methods differ in the initial development of ORP, but over the long term showed similar values around 100 mV. Significant differences were observed for chemical oxygen demand, where groundwater after the application of nZVI showed no change in comparison to the application of lactate. The reductive effects of both agents were verified by changes in inorganic compound concentrations.