Biomass-sulfur-based mixotrophic denitrification (BSMD) process for synthetic and real wastewater treatment: Engineering application, applicable scope, and operational strategy

Elemental-sulfur-driven autotrophic denitrification (ESDAD) process is widely used in sewage treatment, while its low denitrification capacity has become the bottleneck of this technology. The biomass-sulfur-based mixotrophic denitrification (BSMD) process is a promising denitrification pathway to improve nitrate removal of sewage. Based on previous research, a comparative analysis of the ESDAD and BSMD processes was adopted in this study. Then, three lab-scale reactors were constructed with various BSMD filters to investigate the characteristics of the BSMD process, and the optimal BSMD filter (F3) with the nitrate removal rate (NRR) of 556 ± 13.6 mg NO3–-N·L−1·d−1 was 3:1:1 by weight ratio of sulfur powder to rice straw powder to shell powder. Additionally, a pilot-scale reactor (volume: 1000 L) filled with filter F3 was designed and operated to treat the effluent of a municipal secondary tank. The feasibility of the BSMD process in engineering application was demonstrated, accompanied by a desirable treatment capacity (hydraulic retention time (HRT) ≤ 1 h) under varying conditions. Moreover, autotrophs and heterotrophs co-existed along the pilot-scale reactor, and the autotrophs remained dominant at seasonal temperatures. In general, the prospect of the BSMD is attractive, and the outcomes of this study could provide guidance for the operation of the BSMD process.