The humic substance analogue antraquinone-2, 6-disulfonate (AQDS) enhanced zero-valent iron based autotrophic denitrification: Performances and mechanisms

Abstract

Zero-valent iron based autotrophic denitrification (ZVI-AD) has attracted increasing attentions in nitrate removal due to saving organic carbon budget in wastewater treatment, but limited by the low reaction speed, poor electron transfer efficiency as well as the compaction/blocking by iron hydrolysis products. Humic substances (HS) were promising to regulate iron cycle and accelerate electron transfer by serving as electron mediators. In this study, HS analogue, antraquinone-2, 6-disulfonate (AQDS), was added to enhance ZVI-AD process. Results showed that the dosage of AQDS led to a NO3−-N removal efficiency of 83.37 ± 3.98% within 96 h, which was 32.28 ± 1.25% higher than that in ZVI-AD system. The corrosion of ZVI and microbially nitrate reduction were both improved at the presence of AQDS. The addition of AQDS enriched the functional species, including autotrophic denitrobacteria namely Thauera and Hydrogenophaga, iron redox-related species namely Ferruginibacter and HS respiration related species namely Flavobacterium. The genes napA and napB related to electron transfer, nirK and nosZ related to the accumulation of intermediate products were also enriched by the addition of AQDS. AQDS addition boosted the electrons flowing to both abiotic and biotic nitrate reduction. Nitrate removal mechanism involved in ZVI-AQDS coupled system was proposed. This study provided an alternative strategy for improving ZVI-AD by HS.