Investigation on sulfide-oxidizing autotrophic denitrification in moving-bed biofilm reactors: An innovative approach and mechanism for the process start-up

Abstract

This study aims to explore an alternative way to accelerate the start-up of sulfide-oxidizing autotrophic denitrification (SOAD) in moving-bed biofilm reactors (MBBRs). Two approaches were tested: i) cultivating sulfide-based autotrophic denitrifiers with sulfide and nitrate (MBBR1); and ii) cultivating facultative denitrifiers by switching the feed from organic carbon/nitrate to sulfide/nitrate (MBBR2). The mechanisms behind these two approaches are discussed. The results showed that both MBBRs could achieve stable nitrate removal (≥90%) after 20 days, while the SOAD microbial communities cultivated in MBBR2 performed better than those cultivated in MBBR1 in terms of the sulfur oxidation activity (0.47 ± 0.03 vs. 0.21 ± 0.07 kg SO42--Sgenerated/(m3·d)), biomass activity and immobilization (540 mg attached volatile solids (AVS)/L vs. 390 mg AVS/L, respectively). Moreover, the proportion of sulfur-oxidizing bacteria (SOB) enriched was higher in MBBR2 (35.0% Paracoccus) than in MBBR1 (9.7% Sulfurimonas and 5.2% Thauera), further legitimizing the hybridized approach for significant SOB enrichment. The findings of this study provide important clues for accelerating and optimizing the development of the MBBR-based SOAD bioprocess.