ANAEROBIC-DIGESTION OF HIGH-SULFATE-CONTENT WASTE-WATER FROM THE INDUSTRIAL-PRODUCTION OF CITRIC-ACID

The start-up and steady-state operation of a full-scale fixed bed dige ster treating citric acid production wastewater with an estimated COD/ sulphate ratio of approximately 4 are described. Parallel studies at l aboratory-scale with two reactors, one of which received the same high influent sulphate concentration as the full-scale plant, confirmed th e finding that methanogenesis was not inhibited by the level of sulpha te reduction shown to occur. After long-term operation on a high sulph ate influent, the retained biomass in the laboratory and full-scale re actors displayed a very low specific methanogenic activity against pro pionate and butyrate. Since propionate and butyrate were barely detect able in the effluents at steady-state, their oxidation under high infl uent sulphate conditions may be completely or incompletely mediated by fatty-acid-utilising SRB.