Autotrophic denitrification filter prepared using gasification coarse slag and pyrite: Physicochemical characteristics and performance removal of nitrogen

Abstract

Conventional heterotrophic denitrification processes face challenges in achieving the requirements of sustainable development goals due to their dependence on external organic carbon sources and the risk of secondary pollution. In this study, the nitrogen removal performance of a sulfur autotrophic denitrification filter prepared from gasification coarse slag (GCS) and pyrite was evaluated, and its underlying mechanisms were elucidated using microbial community, EDS-SEM, BET, and FT-IR analyses. Pyrite and GCS were combined at a 4:6 mass ratio, followed by the addition of Silica fume (7%), NaOH (4%), and Portland cement (10%) all expressed as percentages relative to the total mass of GCS and pyrite mass). The resulting mixture was granulated to form 10-mm GCS-PRFM particles and steam-cured at 80 °C. The GCS-PRFM exhibited a compressive strength of 3.0 MPa, bulk density of 1272 kg/m³, water absorption rate of 13.5%, specific surface area of 17.00 m²/g, and total pore volume of 0.048 cm³/g. Its specific surface area and total pore volume were 10.3-fold and 16-fold greater, respectively, than those of the pyrite filter (PRFM). The nitrate removal efficiency of GCS-PRFM (81.23%) was approximately double that of PRFM (40.92%). GCS-PRFM supported a higher abundance of Thiobacillus, Rhodanobacter, Ferruginibacter, and Sulfurimonas than PRFM. Following wastewater treatment, sulfur content decreased by 77.19% in GCS-PRFM compared with only 6.23% in PRFM, indicating greater sulfur utilization by autotrophic microorganisms. These findings demonstrate that the higher surface area, pore volume, and sulfur availability of GCS-PRFM promote microbial growth and enhance nitrate removal efficiency. The study provides a novel approach for preparing sulfur autotrophic denitrification filters using pyrite and industrial solid waste.