In situ control of sulfide emissions during the thermophilic (55°C) anaerobic digestion process

Sulfide volatilization was found to be sensitive to the pH variations expected during normal anaerobic digester operation. As digester pH levels increased from 6.7 to 8.2, gaseous sulfide concentrations decreased from 2900 to 100 ppm H₂S(g). Although gaseous sulfide control through pH adjustment was technically feasible, its practical use was limited by the resulting increase in soluble sulfide concentration. pH adjustment for biogas sulfide control was recommended only under conditions in which the influent sulfur level was well below sulfide inhibitory concentrations.

Control of gaseous sulfide levels through insoluble iron (3+) phosphate addition was an efficient gaseous sulfide control process with no adverse effects on digester performance. By varying the influent FePO₄-Fe:SO₄²⁻-S input ratio from 0.0 to 3.5, gaseous sulfide levels decreased from 2400 to 100 ppm. The availability of iron under anaerobic conditions from an aerobically insoluble compound has been termed reductive solubilization.

Using results from this investigation, a unique anaerobic digestion system is outlined to treat sulfur rich wastes in which sulfide inhibition is minimized while maximizing energy recovery.