Reconsidering the use of ferrous hydroxide for remediation of chlorinated ethylene contaminated groundwater: Ultra-fast trichloroethene dechlorination by ferrous hydroxide and bone char mixture

Abstract

The prevailing view is that dehalogenation of chlorinated ethene by Fe(OH)2 or adsorbed Fe2+ alone is extremely slow or impossible. In this study, a novel composite was prepared by facile mixing of Fe2+, NaOH, and bone char (BC) at room temperature, providing an unprecedented trichloroethene (TCE) dechlorination rate. In the fastest dehalogenation test, 20 μM TCE was removed within 30 min in the presence of 30 mM Fe2+, 4.5 mM NaOH, and 2.0 g/L BC (pH ∼ 5.5), following the pseudo-first-order kinetics with a rate constant of 7.81 h−1. The kinetics feature switched from zero-order to first-order kinetics at increasing BC dosage, indicating that TCE was adsorbed and reduced on BC surface. The major dehalogenation products were non-chlorinated acetylene, while chlorinated products were not detected. Even though the TCE dehalogenation ceased after six reuse cycling tests, a complete recovery of dehalogenation was achieved by the following base injection under excess Fe2+ condition. Moreover, this system could completely remove 20 μM TCE within 6 h in real groundwater at varying pH (5–10). Life cycle assessment (LCA) demonstrated that Fe(OH)2 and BC mixture shows better environmental sustainability in comparison with regular iron based material. In addition, the easy, flexible, and tunable synthesis of Fe(OH)2/BC mixture favors its injection and distribution in the contaminated zone. This study provides evidence to reconsider ferrous hydroxide as an inexpensive and efficient reductant for the remediation of soil and groundwater contaminated with chlorinated ethenes (CEs).