Effects of nitrate on methane production, fermentation, and microbial populations in in vitro ruminal cultures

Effects of N/S Molar Ratio on Product Formation in Psychrophilic Autotrophic Biological Removal of Sulfide

“…The imposed increase in feed NO 3 − concentration had, as expected, an impact on the presence of the four different sulfur components, HS − , SO 4 2− and two fractions of S 0 : accumulated (S 0 acc ) and suspended (S 0 ss ) ( Figure 5). The initially tested N/S ratio revealed that around 11% (0.34 ± 0.07 mM/L) of influent sulfur remained unreacted as HS − .…”

“…The NO 3 − removal was equal to 96.8 ± 3.9% at the highest N/S ratio and 99.3 ± 2.3% at the lowest ratio. It has been reported that NO 3 − removal can be significantly inhibited at N/S ratios much higher than derived from stoichiometry [17] but this was not the case here.…”

“…Excess effluent compared to influent sulfur must have a temporary nature until the S 0 acc in granules is exhausted but the experiment did not last long enough to reach such a steady state. The slight increase in N/S ratio from 0.35 to 0.40 (equivalent to catabolic reaction in simultaneous NO 3 − and HS − removal to yield S 0 ) was imposed to supply sufficient NO 3 − such to obtain the complete removal of HS − , it however led to less HS − oxidation. The presence of S 0 fractions also decreased from 67 to 54%, reducing the concentration of S 0 acc by 23% and S 0 ss by 18% in comparison to the previous (N/S = 0.35) period ( Table 2).…”

“…It has been reported that concentrations of dissolved HS − in the 100-800 mg/L range can inhibit anaerobic digestion [2]. Additionally, the presence of NO 3 − can inhibit volatile fatty acids (VFAs) production, methanogens, and consequently methane production [3]. Due to the wide diversity of sulfur reducing bacteria (SRB) the production of H 2 S can occur also in psychrophilic conditions [4].…”

Targeting methanogenesis with a nitrooxypropanol bullet

“…However, monensin is relatively nonspecific and impairs beneficial processes, like acetic acid formation by acetogenic bacteria (7,8). Other antimethanogenesis compounds that have been developed include 2,4-bis (trichloromethyl)benzo [1,3] dioxins (9), an inhibitor of methanopterin biosynthesis (10), and nitrogen oxides (nitrate, nitrite, NO, and N 2 O) (11)(12)(13)(14). Whereas the former two compounds have complex structures, the third is simple.…”