Improved Nitrogen Removal Using Modified Sludge Gasification Slag: A Waste-Derived Biofilm Carrier

Sludge gasification slag was utilized as a carrier for wastewater treatment by modification with polyethylenimine (PEI) and ferric chloride (FeCl3) to enhance biofilm growth. The physicochemical properties and nitrogen removal performance of the modified gasification powder (MGP) were evaluated. Modification increased the zeta potential from −2.12 mV to −1.10–1.27 mV and decreased the surface porosity from 51.7% to 33.1–38.3%, enhancing biofilm attachment through combined electrostatic adsorption and void filling. Biofilms on MGPPEI exhibited the highest biomass with a uniform distribution, whereas MGPFeCl3 showed spotty growth, and the original slag mainly trapped the inoculated sludge. Nitrogen removal results indicated that MGPFe0.08M achieved the highest specific nitrification rate due to Fe2+/Fe3+-catalyzed NH4+-N→NO2–-N conversion, while MGPPEI0.75% attained the best simultaneous nitrification-denitrification (SND) efficiency with the highest abundances of Comamonas (7.5%) and Pseudomonas (2.0%). These findings demonstrate the potential of modified sludge gasification slag as an effective carrier in wastewater treatment, providing a novel strategy for resource recovery from sludge disposal.