Partial Sulfur-Driven Denitrification: A Promising Pathway to Break Through the Nitrite Bottleneck in the Anammox Process

The anammox technology, as an efficient and energy-saving denitrification method, has been widely used in the field of wastewater treatment. Nevertheless, this process faces two key challenges in actual operation, namely the fluctuation of nitrite substrate supply and the residual nitrate, which greatly limits its promotion and application in a wider range. Although the traditional combined process of partial denitrification/anammox (PD/A) can generate nitrite substances, the coexistence of heterotrophic microorganisms and organic carbon sources in the system may have a significant inhibitory effect on the proliferation of Anammox bacteria. The sulfur-oxidizing bacteria (SOB) involved in the sulfur autotrophic denitrification process (SAD) have overlapping ecological niches with Anammox microorganisms and have stable nitrite enrichment characteristics. In view of this, sulfur-oxidizing bacteria are regarded as a potential candidate for combining with the Anammox process. However, the denitrification efficiency of this process is often restricted by the low solubility and poor bioavailability of substrates. At the same time, there are significant research gaps and data deficiencies regarding the key operating parameters for autotrophic short-range denitrification using elemental sulfur to achieve nitrite accumulation and the coupling application of this process with other wastewater treatment technologies. In view of this, this study is committed to comprehensively sorting out and evaluating the existing optimization methods of the elemental sulfur autotrophic denitrification process, while providing an in-depth analysis of its mechanism of action and environmental control factors. At the same time, this study also carried out innovative exploration on the modification process of the sulfur element from the frontier perspective of materials science and pointed out the key directions for subsequent optimization of the construction path of the elemental sulfur autotrophic denitrification system and for improving the denitrification process efficiency. In summary, this study systematically discusses the mechanism of action, practical application, and improvement scheme of PS0AD.