Long-term anaerobic conversion of lindane by electrochemically generated hydrogen

Lindane (γ‑HCH) persists in many aquifers where electron‑donor scarcity limits reductive dechlorination. Here we present a long‑term (116 d) microbial electrochemical technology (MET) that supplies cathodic H₂ to sustain lindane biotransformation. Sequentially decreasing the graphite‑brush cathode potential from -0.6 to -0.7 and -0.8 V versus SHE raised headspace H₂ from < 0.1% to > 1% (v/v) and accelerated lindane degradation rates. Product inhibition led by the accumulation of monochlorobenzene and benzene stalled the culture. The application of three 15‑min N₂ flushing cycles restored activity each time and boosted the removal rate from 33.3 ± 1.2 (µM/d) to 85.3 ± 4.5 (µM/d) at -0.8 V. The value of the poised cathodic potential also affected the product distribution ratio of monochlorobenzene to benzene. Thus, the MET did not just provide a source of electrons but also seems to have an impact on the transformation pathway of lindane. 16S‑rRNA profiling revealed a biocathode dominated by Shewanella (14.6 ± 5.8%) and Pseudomonas (35.0 ± 8.2%), two genera potentially involved either in the direct transformation of lindane or in establishing an interspecies electron transfer network that enhances its reduction.