Reusing spent polyaluminum chloride sludge as adsorbent for phosphate removal from secondary wastewater effluent

摘要

This study explored the reuse potential of spent polyaluminum chloride (PAC) sludge as an adsorbent for removing phosphate from secondary wastewater effluent. The adsorption isotherm and kinetics were examined in batch experiments. The effect of temperature, pH, and foreign anions on phosphate adsorption was also investigated. Additionally, continuous column adsorption was employed to evaluate the applicability of the bed-depth-service-time (BDST) model. Experimental results reveal that the adsorption of phosphate onto PAC sludge was rapid in the preliminary 30 min and the adsorption behavior followed a pseudo-second-order model. Langmuir isotherm correlated the experimental data better than Freund-lich isotherm and the maximum value of adsorbed phosphate (q_m) was 2.21 mg P/g SS. Besides, the phosphate adsorption was favored at higher temperature and lower pH and was hardly interfered by the competing anions. Furthermore, the process of phosphate adsorption was spontaneous and endothermic in terms of the thermodynamic parameters, ΔH~0, ΔS~0, and ΔG~0. Finally, the BDST model was appropriate to describe the adsorption of phosphate by PAC sludge in the column mode and could be successfully used in predicting the breakthrough and exhaustion time.