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

Abstract

Natural and waste waters pollution by nitrates is considered a major environmental problem due to the possible consequences on human health and on water bodies through eutrophication phenomenon. Hazelnut shell were employed as packing material in a large lab-scale column for the removal of nitrate from wastewaters, comparing the process performances with those obtained in batch system. A nitrate removal efficiency up to about 67% was observed in batch mode at low pH and with a sorbent mass concentration of 8 g/L with 0.5 mm size. A lower (62%) nitrate removal efficiency was observed at large lab-scale column, though notable volumes of effluents (60–200 L, depending on the inlet flow-rate) were successfully treated with a bed height of 30 cm and a sorbent mass of 590 g. Non-linear regression of batch equilibrium data using Langmuir, Freundlich and SIPS models allowed to estimate the isotherm parameters, subsequently used in a mass transfer dynamic model to fit the experimental data. The regressed film mass transfer coefficient kf, at six different inlet flowrate values were elaborated for the estimation of the characteristic parameters of the empirical correlation between Sherwood, Reynolds and Schmidt numbers. Furthermore, the pressure drop along the column was calculated and the Ergun and Carman equations were employed for the estimation of the empirical friction parameters.