Simultaneous nitrate and phosphate abatement using calcium silicate hydrate adsorbent: Fixed bed column adsorption study

Nitrate and phosphate are the main nutrients that cause eutrophication and thus remedial measures have to be taken. In this work, Calcium Silicate Hydrate (CSH) synthesized from Alum Factory solid waste residue was used to simultaneously remove nitrate and phosphate by fixed-bed column adsorption. The effect of fixed-bed column operating parameters, namely flow rate (5, 7.5, and 10 mL/min.) and bed depth (6, 9, and 12 cm) on the breakthrough curves were examined. Fixed-bed column adsorption models namely Thomas, Yoon-Nelson, Adams-Bohart, and bed depth service time (BDST) were fitted to the experimental data. The observed data demonstrated that Thomas and BDST models were fitted well with the experimental data and thus are suitable to predict the breakthrough curve parameters for both nitrate and phosphate. The column adsorption capacity estimated by the Thomas model for binary-component, mono-component, and municipal wastewater were 1.74 mg/g, 2.13 mg/g and 1.63 mg/g for nitrate, and 4.93 mg/g, 5.61 mg/g, and 3.37 mg/g for phosphate, respectively. The high R2 value of 0.973-0.997 for nitrate and 0.917-0.999 for phosphate indicated that the BDST model could be used to estimate the breakthrough time required for selected depth without conducting extra experiments. Moreover, the fractional value of 0.82 and 0.88 for nitrate and phosphate, respectively calculated using (qm binary)/(qm mono) for simultaneous adsorption of nitrate and phosphate indicated the antagonism (competitive) nature of adsorption. The observation of this work concluded that CSH could be used for the simultaneous removal of nitrate and phosphate from an aqueous solution.