Reduction of trichloroethylene and nitrate by zero-valent iron with peat

Abstract

The feasibility of using zero-valent iron (ZVI) and peat mixture as in situ barriers for contaminated sediments and groundwater was investigated. Trichloroethylene (TCE) and nitrate (NO₃ ⁻), redox sensitive contaminants were reduced by ZVI and peat soil mixture under anaerobic condition. Peat was used to support the sorption of TCE, microbial activity for biodegradation of TCE and denitrification while TCE and nitrate were reduced by ZVI. Decreases in TCE concentrations were mainly due to ZVI, while peat supported denitrifying microbes and further affected the sorption of TCE. Due to the competition of electrons, nitrate reduction was inhibited by TCE, while TCE reduction was not affected by nitrate. From the results of peat and sterilized peat, it can be concluded that peat was involved in both dechlorination and denitrification but biological reduction of TCE was negligible compared to that of nitrate. The results from hydrogen and methane gas analyses confirmed that hydrogen utilization by microbes and methanogenic process had occurred in the ZVI-peat system. Even though effect of the peat on TCE reduction were quantitatively small, ZVI and peat contributed to the removal of TCE and nitrate independently. The 16S rRNA analysis revealed that viable bacterial diversity was narrow and the most frequently observed genera were Bacillus and Staphylococcus spp.

Keywords:

• Trichloroethylene
• nitrate
• zero-valent iron
• peat
• dechlorination
• biodegradation
• reduction
• 16S rRNA

Acknowledgments

This work was supported by the Korea Science and Engineering Foundation (KOSEF) (Grant M07-2003-000-20253-0) and Korea Research Foundation (KRF).

This paper was presented at the SETAC Asia/Pacific 2006 conference held at Peking University, China on September 18–20, 2006.

Notes

^a All background solution consisted of KCl 10 mM and CH₃COOK 40 mM.

^b Amendment concentrations were KNO₃ (20 mM) and TCE (1.4 mM).

^c Peat slurry was made to have 1 : 1.5 (peat : background solution) mass ratio.

^d 4 mL of formaldehyde was injected (3.33 vol. %) to the serum bottle for inactivation of microbes.