A new, closed loop process for the disinfection, stabilisation and removal of heavy metal from sewage sludge (consisting of a sludge/sulfuric acid reactor, hybrid H2S generator and H2S bioscrubber) is described. Preliminary results for total solids (TS), volatile suspended solids (VSS), chemical oxygen demand (COD), acetate and propionate destruction in the hybrid H2S generator have shown that digestion efficiency is not compromised in a hybrid reactor generating H2S compared to a methanogenic reactor. 70% of the electron flow in the hybrid H2S generator was diverted to methane at a COD:SO4 ratio of 5.45:1. Enough H2SO4 could be generated from the H2S emitted at this ratio to effect sufficient metal solubilisation and pathogen removal from primary sludge.

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