Nitrate green removal by fixed-bed columns packed with waste biomass. Modelling and friction parameter estimation

Natural and waste waters pollution by nitrates is considered a major environmental problemdue to the possible consequences on human health and on water bodies through eutrophi-cation phenomenon. Hazelnut shell were employed as packing material in a large lab-scalecolumn for the removal of nitrate from wastewaters, comparing the process performanceswith those obtained in batch system. A nitrate removal efficiency up to about 67% wasobserved in batch mode at low pH and with a sorbent mass concentration of 8 g/L with0.5 mm size. A lower (62%) nitrate removal efficiency was observed at large lab-scale col-umn, though notable volumes of effluents (60–200 L, depending on the inlet flow-rate) weresuccessfully treated with a bed height of 30 cm and a sorbent mass of 590 g. Non-linearregression of batch equilibrium data using Langmuir, Freundlich and SIPS models allowedto estimate the isotherm parameters, subsequently used in a mass transfer dynamic modelto fit the experimental data. The regressed film mass transfer coefficient kf, at six differentinlet flowrate values were elaborated for the estimation of the characteristic parameters ofthe empirical correlation between Sherwood, Reynolds and Schmidt numbers. Furthermore,the pressure drop along the column was calculated and the Ergun and Carman equationswere employed for the estimation of the empirical friction parameters.