Biogenie H2so4 corrosion of concrete in pure oxygen activated sludge bioreactors

Significant concrete corrosion has occurred within the headspace of a pure oxygen activated sludge treatment (OAS) bioreactor treating pulp mill effluent. The severity of damage required extensive and expensive repair, which comprised rehabilitation of the concrete and installation of a protective coating. It also caused a loss of production. A review of the relevant literature was conducted to validate the suspected mechanism of biogenic H2SO4 corrosion. Of the various factors required to sustain that mechanism, a reasonably constant H2S (TRS) concentration within the headspace atmosphere was found to be most critical for OAS bioreactors treating pulp mill effluent. Bioreactor input effluent solutions were then compared to identify the process condition(s) most likely responsible for the biogenic H 2SO4 corrosion. It was found that the inputs to the corroded OAS bioreactor contained a significant concentration of dissolved TRS, particularly in the primary clarified effluent, which is the major input on a volume basis. It is believed that this dissolved TRS component, when stripped from the effluent during biotreatment, is the source of H2S (TRS) required to sustain corrosion. Anaerobic activity within the primary clarifier has been identified as the likely root source of dissolved TRS in primary clarified TMP/newsprint effluent. A change in, or improved control of the TMP/newsprint primary clarifier operating conditions to minimize septicity may be the best way forward to tackle the problem.