Polycaprolactone-Modified Biochar Supported Nanoscale Zero-Valent Iron Coupling with Shewanella putrefaciens CN32 for 1,1,1-Trichloroethane Removal from Simulated Groundwater: Synthesis, Optimization, and Mechanism

Abstract

1,1,1-Trichloroethane (1,1,1-TCA) is a typical organochloride solvent in groundwater that poses threats to human health and the environment due to its carcinogenesis and bioaccumulation. In this study, a novel composite with nanoscale zero-valent iron (nZVI) supported by polycaprolac-tone (PCL)-modified biochar (nZVI@PBC) was synthesized via solution intercalation and liquid-phase reduction to address the 1,1,1-TCA pollution problem in groundwater. The synergy effect and improvement mechanism of 1,1,1-TCA removal from simulated groundwater in the presence of nZVI@PBC coupling with Shewanella putrefaciens CN32 were investigated. The results were as follows: (1) The composite surface was rough and porous, and PCL and nZVI were loaded uniformly onto the biochar surface as micro-particles and nanoparticles, respectively; (2) the optimal mass ratio of PCL, biochar, and nZVI was 1:7:2, and the optimal composite dosage was 1.0% (w/v); (3) under the optimal conditions, nZVI@PBC + CN32 exhibited excellent removal performance for 1,1,1-TCA, with a removal rate of 82.98% within 360 h, while the maximum removal rate was only 41.44% in the nZVI + CN32 treatment; (4) the abundance of CN32 and the concentration of adsorbed Fe(II) in the nZVI@PBC + CN32 treatment were significantly higher than that in control treatments, while the total organic carbon (TOC) concentration first increased and then decreased during the culture process; (5) the major improvement mechanisms include the nZVI-mediated chemical reductive dechlorination and the CN32-mediated microbial dissimilatory iron reduction. In conclusion, the nZVI@PBC composite coupling with CN32 can be a potential technique to apply for 1,1,1-TCA removal in groundwater.

Environmental remediation approaches by nanoscale zero valent iron (nZVI) based on its reductivity: a review

“… 138 The combination of nZVI with microorganisms has also been applied in the bio-nano-dechlorination of TCE, bisphenol A, bisphenol S, pentachlorophenol, dichloromethane and 1,2-dichloroethane. 139–143 The major removal improvement mechanisms involve chemical reduction by nZVI and dehalogenation bacterium-mediated microbial dissimilatory iron reduction ( Longilinea and Desulfofustis , Dechloromonas sp., Shewanella putrefaciens CN32, Terrimonas , Lysobacter , Acidovorax , Dehalococcoides mccartyi , and Burkholderia ambifaria strain L3). 138,139,141,142,144,145 Xu et al proposed a removal mechanism of organic halides as: (i) organohalide-respiring bacteria utilize H 2 generating from nZVI corrosion to enhance dechlorination in the short term; (ii) the adsorption of nZVI materials and the promotion of dechlorination by attached biofilm in long-term.…”

Biochar, microbes, and biochar-microbe synergistic treatment of chlorinated hydrocarbons in groundwater: a review

“…However, when the compound addition amount exceeds 1:100, the increase in removal rate slows down; In addition, when the dosage ratio of composite materials and Shewanella putrefactive bacteria CN32 is 1:100, as the concentration gradient of 1,1,1-trichloroethane increases (25, 50, 100, and 200 mg/L), the degradation rate gradient decreases, and the degradation effect also gradually decreases (50 h, 90–38%). The reason for this is that 1,1,1-trichloroethane reacts strongly with nZVI when the initial concentration is relatively high, and a dense passivation layer consisting of Fe(III) oxides/hydroxides is rapidly formed on the BC surface, which hinders the reaction ( Ye et al, 2023 ).…”