Efficient nitrogen removal and elemental sulfur recovery through sulfide-driven partial denitrification coupled with anammox: Strategies based on N/S ratio and HRT.

Abstract

Sulfide-driven partial denitrification is emerging as one of the most efficient solutions to provide nitrite without carbon addition for anammox system. In this study, the sulfide-driven partial denitrification coupled with anammox (SPDA) process was constructed in one reactor and high nitrogen removal and sulfur recovery efficiencies were realized by optimizing the N/S ratio and hydraulic retention time (HRT). The results of short-term per-experiment showed that the reactor with a N/S ratio of 1 could achieve the best performance, with total nitrogen removal efficiency (TNRE) and elemental sulfur accumulation efficiency (ESAE) up to 88.0% and 53.4%. Subsequently, a long-term experiment was constructed in an up-flow anaerobic sludge blanket reactor (UASB) to determinate optimum HRT. The results indicated that when the HRT was shortened to 6 h (the nitrogen and sulfur load of 0.7 kg N/(m³·d) and 0.8 kg S/(m³·d)) at a N/S ratio of about 1.0, TNRE and ESAE reached 87.0 ± 3.4% and 60.6 ± 2.2%. At that point, the anammox process was the dominant nitrogen removal pathway with an average contribution of 97.7 ± 2.2% to total nitrogen removal. High-throughput sequencing analysis identified Thiobacillus and Sulfurovum as the dominant genera of sulfur-oxidizing bacteria in the SPDA system, and CandidatusKuenenia and CandidatusBrocadia as the dominant anammox bacteria. In addition, the abundance of genes encoding cytochrome bc1 complex and electron transport complex proteins increased after shortening the HRT to 6 h. It was hypothesized that enrichment of genes encoding electron transport may improve nitrite and ammonium transport, thereby increasing nitrogen removal efficiency.