least 4 gram moles of gaseous hydrogen per gram ion of sulfate at least 0 003 gram mole of gaseous co 2 per gram ion of sulfate and an aqueous anaerobic mixed liquor containing group desulfovibrio sulfate reducing bacteria trace nutrients and a suspension of calcium carbonate to maintain a mixed liquor ph of between about 5 5 8 said contacting conducted at a temperature between 0 u00b0 and 60 u00b0 c for a time sufficient to convert the sulfate ions to sulfide ions b removing the sulfide ions from the mixed liquor by transforming them into either a vapor or solid phase and c separating the sulfide containing phase from the mixed liquor the core of the process of the invention is of course the aqueous mixed liquor in which the reduction of the sulfate ions to sulfite ions and then to sulfide ions takes place this mixed liquor uses the calcium carbonate suspension as a buffer the mixed liquor is primarily a vehicle for maintaining the viability of the sulfate reducing bacteria and thus must contain in addition to water as the dispersing medium trace nutrients gaseous hydrogen as the oxygen acceptor for the reduction reaction and gaseous co 2 as a source of bicarbonate ions for biosynthesis cell growth the mixed liquor as well as the sulfate containing stream treated are essentially free of organic materials such as sewage sawduct and other waste carbon materials.