Sulphide and oxygen inhibition over the anaerobic digestion of organic matter:: Influence of microbial immobilization type

Two different types of microbial aggregates (granular sludge and biofilm onto a plastic matrix) were evaluated for their susceptibility to sulphide and dissolved oxygen. Their specific methanogenic and sulphate reducing activities were evaluated separately and simultaneously. Total sulphide concentrations that caused 50% loss of methanogenic activity were 800 and 1250 mg l(-1) and for sulphate reduction 750 and 860 mg l(-1) for the granular sludge and the attached biomass, respectively. Simultaneous methanogenesis and sulphate reduction resulted in an increased tolerance of the sulphate reducing process towards sulphicle. Results suggest that methanogenesis in granular sludge is less resistant to sulphide than in the attached biomass structure, whereas in sulphate reduction the attached biomass exhibited a better tolerance to high concentrations of total sulphide than the granular sludge. The better sulphate reducing capacity in the attached biomass may suggest that biomass was selectively attached. The dissolved oxygen concentration that inhibited 50% the methanogenic activity was 4.9 and 6.4 mg l(-1) for the granular sludge and attached biomass, respectively. When methanogenesis and sulphate reduction were carried out simultaneously, the whole process was not affected by the supplied oxygen, as produced sulphicle was used by sulphicle oxidizing microorganisms thus scavenging oxygen. Results showed that the integration of anaerobic/aerobic conditions in a single bioreactor is quite possible and can be used as a good strategy for the complete transformation of sulphate to elemental sulphur.