Exploration of an innovative approach and its mechanism for the start-up of sulfide-oxidizing autotrophic denitrification in moving-bed biofilm reactors

The Sulfate reduction Autotrophic denitrification Nitrification Integrated (SANI) process has been developed for the treatment of saline sewage which generated from seawater toilet flushing or salt water intrusion. One challenge for full-scale application of this new bioprocess is the start-up required nearly four months - doubled that of the conventional anoxic/aerobic bioprocess. The limiting step is the growth of sulfide-oxidizing autotrophic denitrification (SOAD) biomass on the carriers of moving bed biofilm reactors (MBBR). This study aimed to explore an alternative way to accelerate start-up of SOAD in MBBR by comparing two approaches: i) to cultivate sulfide-based autotrophic denitrifiers by feeding with sulfide and nitrate (MBBR1); ii) to cultivate facultative denitrifiers by switching the feeding substrates from organic carbons/nitrate to sulfide/nitrate (MBBR2). Then the mechanisms behind these two approaches were discussed. The results showed that the cultivated SOAD microbial communities in MBBR2 performs better than MBBR1 in terms of the duration of start-up period, sulfide removal, biomass activity and biomass immobilization. Moreover, a higher proportion of sulfur-oxidizing bacteria (35.0% Paracoccus) was enriched in MBBR2 than MBBR1 (9.7% Sulfurimonas), further legitimizing the hybridized approach for significant SOB enrichment. Therefore, the findings of this study provided some important clues for speeding up and optimizing the development of MBBR-based SOAD bioprocess.