BIOLOGICAL PRODUCTION OF SULFUR FROM HYDROGEN SULFIDE

ABOUT 100 TRILLION CUBIC FEET OF PROVEN AND FUTURE NATURAL GAS RESERVES ARE EXPECTED TO HAVE HIGH HYDROGEN SULFIDE (H2S) CONCENTRATIONS, REQUIRING TREATMENT AND REMOVAL. CURRENT TREATMENTPROCESSES ARE EXPENSIVE, EMIT LARGE QUANTITIES OF SULFUR GASES TO THE ENVIRONMENT, AND CAN BE APPLIED ONLY TO VERY LARGE RESERVES. TECHNOLOGY THAT CAN BE ECONOMICALLY APPLIED TO SMALL, AS WELL AS LARGE, GAS RESERVES IS NEEDED TO ENSURE CHEAP AND ABUNDANT NATURAL GAS IN THE FUTURE. THIS PROJECT WILL INVESTIGATE A SIMPLE BIOLOGICAL PROCESS FOR THE CONVERSION OF H2S INTO ELEMENTAL SULFUR. CERTAIN ANAEROBIC PHOTOSYNTHETIC BACTERIA METABOLIZE H2S AND CARBON DIOXIDE (CO2) TO PRODUCE SULFUR AND CELL MASS. PRIOR RESEARCH HAS CONCENTRATED ON THE USE OF CHLOROBIUM SPECIES, WHICH DEPOSIT SULFUR OUTSIDE THE CELL MEMBRANE WHERE IT IS EASILY RECOVEREDBY DENSITY DIFFERENCE. THE MICROORGANISMS CAN USE GAS WITH A WIDE RANGE OF H2S CONCENTRATIONS,AND OTHER GASES, SUCH AS NITROGEN, HAVE NO EFFECT UPON THE REACTION. CO2 IS USED IN THE REACTION, REDUCING THE EMISSION OF GREENHOUSE GASES. A SINGLE CELL PROTEIN BY-PRODUCT IS ALSO PRODUCED WHICH HAS A LARGE MARKET AS AN ANIMAL FEED. THE PURPOSE OF THIS THREE-PHASE STUDY IS TO DEMONSTRATE THE CONCEPT AND PERFORM BENCH-SCALE EXPERIMENTS TO DEFINE SCALE-UP PARAMETERS FOR COMMERCIAL DESIGN. IN PHASE I, BACTERIA FOR PRODUCING EXTRACELLULAR SULFUR FROM H2S WILL BE SCREENED, AND THE BEST SELECTED FOR OPTIMIZATION OF SULFUR YEILD AND RATES. REACTOR STUDIESWILL BE PERFORMED TO DEFINE REACTION RATES AND RETENTION TIMES FOR DESIGN AND ECONOMIC PROJECTIONS. PHASE II OF THE PROJECT WILL INVESTIGATE ADVANCED BIOREACTOR CONCEPTS TO MINIMIZE REACTOR VOLUME. METHODS FOR SULFUR AND SINGLE CELL PROTEIN RECOVERY WILL BE DEVELOPED. A BENCH-SCALE UNIT UTILIZING THE BEST BACTERIA AND BIOREACTOR SYSTEM WILL BE OPERATED FOR A PROLONGED PERIOD TO CONFIRM THE VIABILITY OF THE CULTURE. SCALE-UP PARAMETERS WILL BE DEFINED AND A LARGE COMMERCIAL DESIGN AND ECONOMIC ANALYSIS CONDUCTED. PHASE III WILL INVOLVE A FIELD DEMONSTRATION OF THIS PROCESS.