Improved sulphate removal rates at increased sulphide concentration in the sulphidogenic bioreactor

Abstract

The product of the biological sulphate reduction is sulphide. High concentrations of molecular H 2 S (g) can be inhibitory for microbial activity, especially at a reactor pH of 6 to 7. This paper focuses on the effect of high sulphide concentrations on the sulphate reduction rates. The results of three investigations operating a continuous reactor, a column reactor and batchtest reactors have shown that increased sulphide concentrations have resulted in improved biological sulphate reduction. In all instances the reactor pH was kept at 7.5 to 8.5. It was shown that when the sulphide concentration was 700 mg/ℓ in a continuously operated reactor, the sulphate reduction rate was 12 gSO 4 /ℓ•d. When operating batch-test reactors the results showed that when the sulphide concentration increased, to 1 400 mg/ℓ, the volumetric and specific sulphate reduction rates correspondingly increased to 4.9 gSO 4 /ℓ•d and 1.5 gSO 4 /gVSS, respectively. Thirdly, operating a tall column reactor using H 2 and CO 2 as the energy source, showed that when the initial sulphide concentration of the feed water was 0, 100 and 268 mg/ℓ, the average biological sulphate removals were 650, 1 275 and 1 475 mg/ℓ, respectively. These obtained results indicated that the addition of sulphide to the feed water to the reactor had a positive effect on sulphate removal. Improved sulphate removal results in increased alkalinity production and in an increased reactor pH, which in turn is favourable for a decrease in the redox potential, when a dominant redox couple, like sulphate: sulphide, is present in a reactor.

Molybdate to prevent the formation of sulfide during the process of biogas production

“…Sulfate-reducing bacteria (SRB) reduce sulfate (SO 4 2- ) to sulfide by transferring electrons obtained by the degradation of organic matter such as lactate and acetate. The presence of SRB decreases the final biogas production by competing with methanogen for acetate and by generating toxic H 2 S 5–8 . Values higher than 500 ppmv of sulfide in the biogas, produce a dangerous corrosive effect, significantly reducing the lifetime of pipes and other metallic hardware 9 .…”

Advances in the biological removal of sulphides from aqueous phase in anaerobic processes: A review

“…From the above studies, it is evident that there are difficulties involved when setting sulphide concentrations so no inhibition of the anaerobic process occurs, however, there is a general consensus that anaerobic inhibition begins to occur at values of 50-250 mg sulphur/L. Although, there have been studies that not only obtain good performances from anaerobic reactors operating at higher concentrations than those identified above (Iza et al 1986), but it has also been suggested that increased concentrations of sulphur can enhance the biological sulfate reduction (Greben et al 2005).…”

Performance of a sulfidogenic bioreactor and bacterial community shifts under different alkalinity levels

“…Besides NaHCO 3 , other types of alkalinity might also improve the SRE. Greben et al (2005) found that the addition of sulfide to the influent had a positive effect on sulfate removal, and resulted in improved biological sulfate reduction. Hence, in the acidogenic sulfidogenic system, the functional microbes, especially the SRB, favored higher alkalinity regardless of type.…”

“…In addition to neutralizing the acid generated by the biochemical process, carbonate alkalinity might be necessary to meet the inorganic carbon requirement of ammonia-oxidizer (Biesterfeld et al, 2003). Greben et al (2005) even found that addition of sulfide to the feed water had a positive effect on sulfate removal; however, excessive alkalinity negatively affected process performance. This fact was confirmed by Majumder and Gupta (2009) in anaerobic-aerobic reactor systems containing chlorophenols, where an alkalinity/ COD ratio in the influent of >1.1 caused gradual decrease in the chlorophenol removal in UASB reactors.…”