BIOLOGICAL CONVERSION OF SULFIDE TO ELEMENTAL SULFUR

The use of a biological reactor (bioreactor) as a means of removing hy drogen sulfide from waste water and converting it to elemental sulfur has several advantages over conventional physical/chemical treatment p rocesses. A suspended-growth continuous-flow stirred-tank bioreactor u tilizing the green sulfur bacterium Chlorobium limicola was successful ly operated at five different sulfide loading rates and three differen t hydraulic retention times. In all but one of the five experiments, t he rate of consumption of the sulfide was equal to its loading rate. T he separation of elemental sulfur from the bioreactor contents is esse ntial to realize its value as a chemical industry feedstock. Separatio ns of elemental sulfur by plain settling, settling at elevated pH, fil tration and centrifuging were tested at bench scale using the contents of several batch bioreactors.;Under plain settling, elemental, sulfur and bacteria were removed from suspension to the same degree. Raising the pH to 8.6 or 8.8 resulted in some of the sulfur or bacteria settl ing independently of the sulfur-bacteria flocs. Filtration was found t o give conflicting results with different batches of bacteria. Centrif ugation resulted in the best separation between elemental sulfur and b acteria; 90% of the elemental sulfur and 29% of the bacteria could be removed from suspension.