Towards efficient sulfur autotrophic denitrification for saline wastewater treatment: Mechanistic insights and available strategies.
AI summary
75% confidenceThis MEC study investigates Autotrophic nitrogen removal, Denitrifying sulfur-oxidizers, Inhibition responses. The research focuses on system optimization and characterization.
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Abstract
Sulfur autotrophic denitrification (SADN) process is cost-effective and carbon-free for treating nitrate-containing wastewater, but the salt in industrial and municipal (coastal cities) wastewaters typically affects its stability. To address this challenge, an in-depth understanding of the inhibitory mechanisms of salt stress on functional bacteria (denitrifying sulfur-oxidizers) in the SADN process is crucial. By comparing the existing research on the SADN process for saline wastewater treatment, this review identifies the heuristic salinity reference points (i.e., causing irreversible inhibition) of 3.1%-4.8% for the SADN process based on the micro and macro response characteristics. Low salinity levels (0.1%-2.0%) stimulate the SADN process by intensifying the metabolic activity of the salt-tolerant denitrifying sulfur-oxidizers and microbial interactions. In high salinity scenarios, a range of 2.0% to 3.1% or 4.8% (reference points) causes transient inhibition, while salinity exceeding approximate 3.1%-4.8% results in severe inhibition (difficult to recover within a short-term of 8-20 days). High salinity scenario leads to diminished microbial activity, reduced relative abundance of salt-tolerant functional bacteria, and superimposed stress from by-products (nitrite and sulfate), thereby blocking the nitrate removal. Moreover, this review discusses three effective strategies (e.g., addition of exogenous regulators, integration of heterotrophic denitrification, and bio-electrochemical enhancement) for alleviating SADN salt stress and their underlying mitigation mechanisms. Lastly, further research directions on electron transfer response mechanisms and interdisciplinary disinhibition strategies are proposed to broaden the applicability of SADN systems for saline wastewater treatment. This review expands the knowledge of salt inhibitory mechanisms on denitrifying sulfur-oxidizers and provides a theoretical foundation for optimizing SADN systems in saline wastewater treatment.