System Performance in UASB Reactors Receiving Increasing Levels of Sulfate

Abstract

Glucose-fed high-rate UASB reactors were tested at three COD/SO 4 ratios and hydraulic retention times to promote sulfate reducing activity and observe the effects on reactor performance. Different COD/SO 4 ratios (20, 10, and 5) resulted in changes in organic matter removal, methane production, alkalinity, dissolved sulfide and biomass concentrations and profile. The COD removal dropped from 95 to 80-84 % at the lowest COD/SO 4 ratio. Sulfate was removed at 79 to 89 % at the highest ratio and dropped to 72 to 74 % with increasing sulfate loading. Alkalinity was produced at higher levels with increasing sulfate loading. Specific methane production dropped with decreasing hydraulic retention times. Sulfate-reducing activity used a maximum of 11.7 % of organic matter at the highest sulfate loading level, producing a slight shift to sulfate-reducing activity in the substrate competition between sulfate-reducing bacteria and methanogens. Increased sulfate loading at COD/SO 4 ratios of 10 and 5 caused deterioration of the concentration profile of the sludge, resulting in biomass washout and decreased volatile fraction of biosolids in the reactors.

Microbial community dynamics reflect reactor stability during the anaerobic digestion of a very high strength and sulfate‐rich vinasse

“…). Sulfate removal efficiencies (not shown) in the same order of magnitude (80–85%) were obtained at the SO 4 2‐ /COD ratios of 0.05 and 0.10, as reported earlier , …”

“…Towards the end of the experiments, the increase in SLR during E‐8 and E‐9 caused an increase in the average fraction of organic matter converted by SRB to 20.3 ± 0.8% and 27.1 ± 0.6%, respectively. These results were in between the lower (11.7%) and the higher values (58%) reported by Erdirencelebi et al and Annachhatre and Suktrakoolvait, when similar and higher SLR values were applied at a SO 4 2‐ /COD ratio of 0.20.…”

“…at a higher sulfate loading rate (SLR)). A similar reduction [(20 mL CH 4 g COD removed ) −1 ] of the methane yield was obtained by Erdirencelebi et al, 17 when the SO 4 2-/COD ratio increased from 0.05 to 0.10 during the treatment of a synthetic wastewater.…”

“…Consequently, a remarkable decrease (up to 30%) in the methane production rate was observed in E-4, E-5 and E-6 with respect to E-1, E-2 and E-3, respectively. In contrast, Erdirencelebi et al 17 showed similar COD removal efficiencies at SO 4 2-/COD ratios of 0.05 and 0.10, when OLR and SLR increased in the same order as this experiment. It was likely because they used a medium strength synthetic wastewater (6000 mg COD L -1 ), which decreased the concentrations of [H 2 S] free and H 2 S aq (both are known inhibitors of anaerobic digestion [9][10][11] ) in the experiment of Erdirencelebi et al, 17 leading to a higher COD removal efficiency in comparison with this experiment.…”

“…and reactor efficiencies. 10,11,[15][16][17] Only few studies have focused on microbial community characteristics. 18,19 Knowledge on the characteristics of the microbial community is essential to control and/or enhance process efficiency.…”