Efficient removal of ammonia nitrogen using biochar derived from the co-fermentation residue of waste activated and orange peel waste: Linking structure properties and reaction kinetics

Elevating ammonia nitrogen (NH4+-N) levels pose substantial threats to both human health and ecological systems. Employing adsorption as a strategic approach for NH4+-N removal is appealing due to its operational simplicity and high efficiency. Prior studies have successfully harnessed valuable volatile fatty acids through the anaerobic co-fermentation of waste activated sludge (WAS) and orange peel waste (OPW). Nevertheless, the proper disposal of the resulting fermentation residue remains a critical concern. This study highlights the effectiveness of biochar derived from WAS/OPW co-fermentation residue in adsorbing NH4+-N in aquatic environments. The highest NH4+-N removal rates were attained at 9.76, 44.1, 76.0, and 97.8% for biochar dosages of 3, 5, 8, and 10 g/L, respectively. The adsorption of NH4+-N by biochar closely aligns with the Langmuir model and exhibits compatibility with both pseudo-first and pseudo-second kinetic models. This implies a single-layer adsorption process with the simultaneous occurrence of physical and chemical adsorption. Subsequent analysis revealed that, relative to fermentation residue, biochar exhibited a more porous structure post-pyrolysis, with a specific surface area 3.43 times larger, increased pore volume, and additional mesopores. Furthermore, the biochar displayed a higher abundance of functional groups and metal oxides after pyrolysis, collectively contributing to its robust adsorption capability for NH4+-N. This research introduces a promising approach for mitigating NH4+-N pollution in aquatic environments while concurrently enhancing the resource utilization of organic solid waste.