Enhancing the bioavailability of sulfur for denitrification in integrated floating-film and activated sludge (IFFAS) system filled with modified carriers under mixotrophic and autotrophic conditions

Abstract

Sulfur autotrophic denitrification (SAD) holds application prospect in carbon-limited wastewater due to no additional carbon source, less sludge yield, and lower costs. However, the poor bioavailability of sulfur (S0) and the slow development of sulfur oxidizing bacteria (SOB) limit its wide application. Tween 80 is a nonionic surfactant with low toxicity and can regulate interface action between S0 and microorganisms. In this study, integrated floating-film and activated sludge (IFFAS) filled with graphene oxide (GO)-modified carriers was adopted and Tween 80 was introduced to enhance bioavailability of S0. When the influent C/N was below 0.7 and nitrogen loading was 0.24 Kg/(m3∙d), the total nitrogen removal efficiencies in reactors filled with GO-modified carriers and Tween 80 were above 90% while that of reactors filled with high density polyethylene (HDPE) carriers and 0.5 wt% GO-modified carriers was74.08 ± 12.8% and 81.87 ± 11.51%. Microbial analysis revealed that Tween 80 could enhance autotrophic denitrification bacteria relative abundance in biofilm at C/N ratios of < 0.7, such as Sulfurisoma (21.21%), Dechloromonas (8.42%) and Ignavibacterium (14.68%). Furthermore, predicted microbial functions analysis by PICRUSt showed that denitrification, sulfide oxidation, electron transfer and biofilm formation pathways were enhanced in reactors added Tween 80. This study demonstrated Tween 80 was able to improve the bioavailability of S0 and enhance the efficiency of SAD.