Effect of feeding gas type and nitrogen : Sulfur ratio on a novel sulfide-driven denitrification methane oxidation (SDMO) system

To save treatment costs of nitrogen-polluted water, a novel sulfide-driven denitrification methane oxidation (SDMO) system, which integrated autotrophic denitrification (AD) and denitrification anaerobic methane oxidation (DAMO) to simultaneously realize wastewater denitrification and biogas utilization in situ, has been operated. In this work, nine groups V0—V8 were derived from a mature SDMO reactor which already enriched AD and DAMO microorganisms. Batch tests about them were proceeded to investigate the effect of feeding gas type and N/S ratio on kinetic performance, microorganism community structure, and functional genes. Results showed as N/S rising up from 2.3 to 23.3, the nitrate removal efficiency decreased from 100 % to 15.4 % but its contribution by DAMO/AD ratio increased from 0.5 to 2.2. Biogas serving as feeding gas enhanced nitrate removal efficiency to 100 % at most in group V3 (N/S = 2.3, H₂S = 1.5 %) whereas DAMO and AD contribution for nitrate removal was 33.1 % and 65.6 % respectively. Low H₂S content gave little effect on microorganism community structure but high hydrogen sulfide content decreased the abundance of DAMO bacteria Candidatus Methylomirabilis to ∼ 4 % and increase abundance of AD bacteria Thiobacillus to > 20 %. Comparing with V1 feeding with methane, nitrate reduction genes napA, narG, nirK, nirS, cnorB and sulfide oxidation gene soxB up-regulated to > 3.0 × 10⁹ copies/g in HS groups (biogas with high H₂S content > 1 %) while gene pmoA up-regulated to ∼ 1.0 × 10⁹ copies/g in LS groups (biogas with low H₂S content < 1 %). This study provided more comprehensive understanding for the effect of feeding gas type and N/S ratio on SDMO system.