Biogenic H2so4 corrosion of concrete in oxygen activated sludge bioreactors

Significant concrete corrosion has occurred within the head space of a pure oxygen activated sludge treatment (OAS) bioreactor treating pulp and paper mill effluent. Bioreactor input effluent solutions were characterized and compared to identify the process conditions most likely responsible for the biogenic H2SO4 corrosion and the damage mechanism. The results suggest that dissolved hydrogen sulfide (H2S), total reduced sulfur (TRS), or both, when stripped from the effluent during biotreatment, are the critical factors required to sustain corrosion. Anaerobic activity within the primary clarifier has been identified as the likely root source of dissolvedTRS in primary clarified TMP/newsprint effluent. Changing, or improving control of, TMP/newsprint primary clarifier operating conditions to minimize septicity may be the best way to tackle the problem. Application: Mills should inspect bioreactors for biogenic corrosion and avoid process conditions that elevate levels of total reduced sulfur compounds (particularly hydrogen sulfide) in input effluents, which the bacteria need to live.