Effect of sulfide to nitrate ratios on the simultaneous anaerobic sulfide and nitrate removal

Present investigation deals with the effect of sulfide to nitrate (S/N) molar ratio on the simultaneous anaerobic sulfide and nitrate removal on capacity, stability and selectivity of the process. The volumetric sulfide-sulfur and nitrate-nitrogen removal rates at molar S/N ratio of 5:2 were 4.86 kg (m3 d)−1 and 0.99 kg (m3 d)−1, respectively, which were higher than those at S/N molar ratios of 5:5 and 5:8. Moreover, the fluctuations in the effluent at S/N ratio of 5:2 were less than those at the other two tested ratios. During the operation, the ratio of converted sulfide to converted nitrate tended to approach 5:2. The selectivity for elemental sulfur and dinitrogen was improved when the S/N molar ratio was set at 5:2 rather than 5:5 or 5:8. The process became unstable if the influent sulfide surpassed its critical concentration. The electron balance between reactants was also analyzed for different S/N molar ratios.