Under anaerobic conditions, humic acids (HA) may act as terminal electron acceptors, allowing facultative anaerobic bacteria to obtain energy from anaerobic respiration. Structural and electrochemical changes due to biological oxidation and reduction were investigated on HA extracted from a peat sample, incubated under controlled aerobic and anaerobic conditions. Coulometry showed the increase of the electron donating capacity (EDC) of HA after biological reduction. Coherent structural changes were confirmed by FTIR. This experiment showed that transfer of electrons from microbially reduced moieties is slow and most of their EDC persists under oxic conditions.
