Fabrication of a Sulfur/Steel Slag-Based Filter and Its Application in the Denitrification of Nitrate-Containing Wastewater

To solve the problems of deep nitrogen removal in wastewater treatment plants and the high value utilization of steel slag in the metallurgical industry, this work aims to prepare a sulfur/steel slag-based filter using the melting method. The melt granulation method and the utilization of metallurgical waste were the main innovations of this work. On this basis, the nitrogen removal performance of the filter media in simulated wastewater and actual wastewater were systematically investigated. Furthermore, the factors affecting the nitrogen removal performance of the filter media were studied, and pilot experiments were carried out. The microbial community in the reactor was also analyzed. The results showed that when the mass ratio of sulfur and steel slag was 9:1, the filter media could remove up to 90% of TN in simulated wastewater at room temperature, with a hydraulic retention time (HRT) of 5–20 h and an influent TN of 21 mg/L. In the simulated wastewater, the effluent NO3−-N was less than 2 mg/L, the SO42− was less than 200 mg/L, and the pH was between 6 and 8. The removal of TN from actual wastewater was also greater than 90% at room temperature under a hydraulic retention time (HRT) of 8–20 h and an influent TN of 8 mg/L. Influence factor experiments were conducted at room temperature, with a C/N of 2:1, a DO of 0.9–1 mg/L, and an HRT of 4 h. The results of the pilot experiment confirmed that the effluent TN was stable below 10 mg/L. The filter media was compounded for practical engineering applications. Microbial community analysis showed that the sulfur autotrophic denitrifying bacterial species Thiobacillus accounted for 3.69% and 5.55% of the simulated and actual wastewater systems, respectively. This work provides a novel strategy for the application of solid metallurgical waste in the field of nitrate-containing wastewater treatment.