Sulfur cycle, a new opportunity for nitrogen removal from textile wastewater: A review

The problem of nitrogen removal from textile wastewater (TW) has plagued for quite a long time. Traditional biological nitrogen removal technology is limited by the complex water quality characteristics, and high concentration of sulfate (over 5000 mg/L) further aggravates its difficulty. After analyzing source and characteristics of nitrogen and sulfur in TW, using miraculous sulfur cycle caused by the existing sulfate to solve the problem of nitrogen removal seems to be a viable option. This review mainly elaborated the heterotrophic sulfate reduction combining with dye removal, which achieved >90 % sulfate reduction and almost complete dye removal, as well as sulfur-driven autotrophic denitrification, with over 85 % total nitrogen removal. The crucial bacteria and key parameters affecting sulfur cycle were summarized. Based on the characteristics of abundant sulfur and nitrogen in TW, the feasibility of relying on sulfur cycle to achieve nitrogen removal in TW is discussed in detail. Furthermore, the sulfur and nitrogen coupled processes, including sulfate reduction, autotrophic denitrification and nitrification integrated process (SANI) and Sulfammox are reviewed. Technology based on sulfur cycle has the advantages of low energy consumption and low sludge production (reduce by 90 %), as well as cutting greenhouse gas emissions (decrease by 90 %). In the context of carbon peaking and carbon neutrality goals, TW treatment based on sulfur cycle is an energy-saving and carbon-reduction technology with development potential.