Nitrite and nitrate as electron acceptors for biological sulphide oxidation

Integration of a nitrification bioreactor and an anoxic biotrickling filter for simultaneous ammonium-rich water treatment and biogas desulfurization

A preliminary assessment has been carried out on the integration of an anoxic biotrickling filter and a nitrification bioreactor for the simultaneous treatment of ammonium-rich water and H₂S contained in a biogas stream. The nutrient consumption in the biotrickling filter was as follows (mol^-1 NO₃^--N): 6.3·10^-4 ± 1.2·10^-4 mol PO₄^3--P, 0.04 ± 0.05 mol NH₄⁺-N and 0.04 ± 0.03 mol K⁺-K. Furthermore, it was possible to supply a mixture of biogenic NO₃^- and NO₂^- into the biotrickling filter from the nitrification bioreactor to obtain a maximum elimination capacity of 152 gH₂S-S m^-3 h^-1. The equivalence between the two compounds was 1 mol NO₃^--N equal to 1.6 mol NO₂^--N. The biotrickling filter was also operated under a stepped variable inlet load (30-100 gH₂S-S m^-3 h^-1) and outlet H₂S concentrations of less than 150 ppm_V were obtained. It was also possible to maintain the outlet H₂S concentration close to 15 ppm_V with a feedback controller by manipulating the feed flow (in the nitrification bioreactor). Two stepped variable inlet loads were tested (60-111 and 16-102 gH₂S-S m^-3 h^-1) under this type of control. The implementation of feedback control could enable the exploitation of biogas in a fuel cell, since the H₂S concentrations were 15.1 ± 4.3 and 15.0 ± 3.4 ppm_V. Finally, the anoxic biotrickling filter experienced partial denitrification and this implied a loss of the desulfurization effectiveness related to SO₄^2- production.

Operation performance and microbial community of sulfur-based autotrophic denitrification sludge with different sulfur sources

Operation performance and bacterial community structure of sulfur-based autotrophic denitrification (SAD) based on different sulfur sources served as electron donor was first parallelly compared among three sequencing batch reactors. Sulfur and sodium thiosulfate systems achieved similar operation performance and were superior to that of sodium sulfide. When the influent NO₃^--N concentration ranged from 50 to 150 mg/L, the effluent NO₃^--N concentrations of the sulfur and sodium thiosulfate systems were 0-5.99 mg/L and 0-4.52 mg/L, respectively, without NO₂^--N accumulation. However, when the effluent concentration of NO₃^--N in the sodium sulfide system was 0-10.38 mg/L, that of NO₂^--N in the effluent was 0-39.85 mg/L. In addition, participation of sulfur sources presented obvious pressure on the bacterial community structure based on the high-throughput sequencing. Microbial diversity results indicated that sludge with elemental sulfur as electron donor had the richest microbial diversity, followed by sodium thiosulfate and sodium sulfide. Moreover, sludge with elemental sulfur and sodium thiosulfate as electron donor demonstrated more similar community structure compared with the sludge that denitrified with sodium sulfide according to the microbial similarity analysis. The 9.34%, 24.3% and 29.6% of sequences could be assigned to potential SAD organisms from sludge denitrifying with elemental sulfur, sodium thiosulfate and sodium sulfide, respectively. Furthermore, all sludge denitrifying with different sulfur sources showed an enrichment of separate core functional microorganisms. This study could provide an insight into improving the understanding of SAD in engineering applications.