Adsorptive removal of nitrate from wastewater using modified lignocellulosic waste material

Waste lignocellulosic material, namely brewers' spent grain (BSG), was modified by quaternisation, where amino groups were introduced into BSG via the reaction with N, N-dimethylformamide (DMF) and epichlorohydrin. The applicability of the modified BSG (MBSG) for the removal of nitrate ions from model solutions and wastewater was evaluated in batch adsorption experiments. Adsorption of nitrate to the MBSG was confirmed by FTIR analysis of the saturated/spent adsorbent. Fixed bed adsorption column and regeneration studies were performed to determine the regeneration capacity of MBSG. The MBSG had a maximum nitrate adsorption capacity of 22.65mgg−1 for model nitrate solution, 18.22mgg−1 for model wastewater and 14.4mgg−1 for the real wastewater effluent generated from dairy industry. The analysis of the equilibrium data showed that the Freundlich isotherm model provided a slightly better fit to the obtained data than the Langmuir model, indicating multilayer sorption. The data were further analysed by pseudo-first- order and pseudo-second-order kinetic models, and the results revealed that the adsorption followed pseudo-second-order kinetics. The intraparticle diffusion model was used to interpret the mechanism of adsorption, and the results suggest that intraparticle diffusion was not the only process that controlled the adsorption. The adsorption- desorption studies in fixed bed column indicated that MBSG could be regenerated and reused for more than three cycles when model nitrate solutions were used. However, when real dairy industry effluent was used in the fixed bed experiments, the clogging of the column occurred. The applied modification technique was found to be appropriate yielding an effective adsorbent for selective nitrate removal from water.