The Effects of Biochar on the Revival and Performance of an Organohalide-Respiring Mixed Culture

Anaerobic reductive dechlorination of chlorinated ethenes (CEs) in groundwater, driven by bioaugmentation of organohalide-respiring bacteria (OHRB), can stall when OHRB abundance and activity are low, leading to incomplete dechlorination and daughter-product accumulation. Pyrogenic carbonaceous matter (PCM), increasingly applied as CE sorbents in groundwater, may enhance OHRB performance. We evaluated how poplar biochars pyrolyzed from 350 to 900 °C influence ethene formation and methanogenesis in an anaerobic tetrachloroethene (PCE)─dechlorinating consortium with initially low OHRB activity. The stressed consortium accumulated cis-dichloroethene and produced no ethene in controls without biochar (no materials and sand), but completely dechlorinated PCE to ethene in all biochar treatments. Compared to controls, OHRB in biochar treatments more strongly expressed genes for biofilm formation, resuscitation, cobalamin transport and salvage, and pilus formation, indicating their involvement in OHRB revival in the presence of biochar. Ethene production rates were higher with less apolar biochars produced at 350-500 °C (5.1-5.6 μmol/bottle/day) than with more apolar biochars produced at 700-900 °C (3.2-3.7 μmol/bottle/day). A positive correlation between ethene formation rate and biochar pore size suggests that CE pore-filling and desorption hysteresis affect ethene production. These results identify material properties that can be tuned to enhance targeted biological activity and inform PCM-based CE bioremediation strategies.