Comparative study of thiosulfate and elemental sulfur-driven autotrophic denitrification: Startup process, extracellular electron transfer pathways and microbial community evolution

Sulfur-driven autotrophic denitrification (SAD) is a promising biological nitrogen removal process from wastewater. However, the slow growth of sulfur oxidation bacteria (SOB) results in a long start-up process. In this study, inoculating anaerobic granular sludge shortened the start-up process of thiosulfate-driven autotrophic denitrification (TAD) granular process to 7 days. The electron donor was successfully transferred to the element sulfur within 23 days under the nitrogen loading rate of 176.2 g N m-3 d-1. The indirect electron transfer pathway was dominant in TAD, while SAD preferred to direct pathway. Thiobacillus and Sulfurimonas were dominant SOB in TAD, but transferred to Longilinea in SAD. Furthermore, thiosulfate addition upregulated NADH, glutamate and cytochrome c-related enzyme, which enhanced extracellular electron transfer ability. SBR1031 and Bacteroidales were categorized as keystone populations. Collectively, this study provides a method for rapidly starting up a SAD granular process and upgrading our understanding about T/SAD.