Ammonium-nitrogen removal from aqueous solution using municipal green waste wood biochars

Abstract

Ammonium (NH4+), one of the most common types of reactive form of nitrogen in wastewater, can cause eutrophication and other environmental problems if released into waterways. This study was conducted to understand NH4+ adsorption mechanism of wood biochar from municipal green waste in an aqueous environment and the factors affecting NH4+ removal. The biochars were produced by pyrolyzing green wood waste at 300°C (WB300), 450°C (WB400), and 600°C (WB600), respectively. Biochar dosage, pH, and contact duration were studied during NH4+ adsorption studies to see how these variables affected the adsorption process. The adsorption process was studied using isotherms and kinetic adsorption models. The batch equilibrium and kinetic studies at 25°C, pH 7, and a contact duration of 240 minutes showed that the WB450 dosage of 0.2 g/L removed the most (NH4+-N) compared to WB600 and WB300. WB450 had higher affinity values and a maximum adsorption capacity of 2.34 mg/g; the ‘Freundlich isotherm’ model had a better fit to the equilibrium experimental data, indicating that heterogeneous sorption was preferable to monolayer sorption. Chemisorption was the dominant (NH4+) adsorption method, as demonstrated by the ‘pseudo-second-order’ kinetic model with an R2 of 0.99. The study concludes that municipal green wood waste-based biochar can be efficient absorbents for NH4+ removal from wastewater. Also, the removal efficiency can be optimized by selecting different feedstocks or the pyrolysis condition for biochar production.

Keywords

• ammonium nitrogen
• adsorption process. municipal green waste
• slow pyrolysis
• wood biochar