Reductive debromination of bromo‐substituted C2 aliphatics using a biochar–iron(II) composite

BACKGROUND: Tribromoethylene (TrBE), dibromoethylenes (DBEs) and 1,2‐dibromoethane (DBA) are widespread, toxic and persistent contaminants found in anaerobic soil and groundwater. The abiotic debromination of TrBE, DBEs and DBA using a layered iron(II)–iron(III) hydroxide (green rust, GR) with biochars acting as electron mediators was studied. A screening of biochar substrates was conducted. Reactive biochars were chosen for debromination of TrBE, DBEs and DBA in deionized water and groundwater. Post‐pyrolysis activation with CO₂ was tested for reactivity enhancement. RESULTS: Bone meal (BM) and shrimp shell (SS) biochars resulted in 60% and 90% debromination of TrBE, respectively. The SS biochar catalyzed debromination by elimination reactions of TrBE and DBEs resulting in formation of acetylene, while DBA was reduced to ethylene. All debrominations in deionized water followed pseudo‐first‐order kinetics with half‐lives t₁/₂ of 5.1, 1.3, 2.6 and 9.5 h for TrBE, cDBE, tDBE and DBA, respectively. For similar experiments in moderately hard groundwater, removal t₁/₂ values were on average 2.6 times slower, but still considered fast. Compared to removal t₁/₂ in deionized water, post‐pyrolysis activation with CO₂ of an acid‐treated SS biochar produced a t₁/₂ 11 times shorter for removal of TrBE and two times shorter for DBA. CONCLUSIONS: Biochars are efficient mediators of reductive debromination of TrBE, DBEs and DBA. TrBE, DBEs and DBA can be effectively debrominated in deionized water and groundwater samples using a GR–SS biochar composite. The mediating ability of the SS biochar can be further improved by post‐pyrolysis CO₂ activation. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).