Nutrient Adsorption onto Modified Biochar for Stormwater Treatment

Nitrogen (NH3-N, NO2-N, NO3-N) and phosphorus (PO4-P) species are known to be the major dissolved contaminants in stormwater runoff. In this research, a series of batch experiments were conducted to remove nutrients from stormwater using raw and modified biochar with varying initial concentration (1-5mg/L), dosage (2-10g) and pH (4.3-6.5). The raw biochar was modified using NaOH. The results revealed that the removal efficiency was improved using modified biochar by 50%, 10%, 10% and 70% for NH3-N, NO2-N, NO3-N, and PO4-P respectively. Maximum removal was obtained using modified biochar as 92% NH3-N, 40% NO2-N and 100% removal of NO3-N and PO4-P was obtained. The effect of adsorbent dosage and initial concentration was found significant on nutrient adsorption, but pH has insignificant impact. The adsorption isotherm study found Freundlich model explaining the adsorption process better. The adsorption kinetics were studied using intraparticle diffusion, and a pseudo-first order and pseudo-second order model. Most of the kinetic results with modified biochar were found supporting the two-stage intraparticle diffusion. The adsorption data revealed that the pseudo-second order model describes nutrient adsorption better. Modified biochar was found suitable for use in the biochar-augmented bio-filtration system for stormwater treatment.