Nutrients Adsorption onto Biochar and Alum Sludge for Treating Stormwater

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Abstract
In this study, Eucalyptus wandoo (EW) biochar and alum sludge and their mixture are used in batches to remove nutrients (ammonium-nitrogen (NH3-N), nitrate-nitrogen (NO3-N), nitrite-nitrogen (NO2-N), and phosphate-phosphorus (PO4-P)) from synthetic stormwater. First, batch tests were conducted using biochar and alum sludge separately with varying concentration (0.5–5 mg/L); dosage (2–10 g); pH (4–9); and contact time (0–24 h). The results revealed that the EW biochar alone could remove 100% of NO2-N and NH3-N while the alum sludge alone could remove 100% of PO4-P. Next batch tests were carried out with the mixture of EW biochar and alum sludge of different proportions and the results revealed that the mixture of 8 g biochar and 2 g alum sludge gave the best combination for removing all nutrients (NH3-N = 98.2%; NO2-N = 99.4%; PO4-P = 99.8%) except NO3-N. The adsorption kinetics of mix-medium were studied for Intraparticle diffusion, liquid film diffusion and Lagergren pseudo first and second-order models. The nutrient adsorptions onto mix-medium show two-stage adsorption process following Intraparticle diffusion and liquid film diffusion. The results revealed that the pseudo-second order kinetic models fitted better with high R2 (0.98–1.00) and small normalized standard deviation, Δq (0.00–0.62). The isotherm results revealed that the NH3-N adsorption followed both Langmuir and Freundlich model while NO2-N and PO4-P adsorption followed Langmuir model better.

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