Removal of Phosphate from Wastewater with a Recyclable La-Based Particulate Adsorbent in a Small-Scale Reactor

Abstract

Tailored La-based particles (La-CZ) sorb phosphate in wastewater. The adsorption capacity of La-CZ particles was 18.2 mg g−1 (PO43−). The adsorbed phosphate mainly existed in a stable state. La-CZ particles were recovered easily in the small-scale reactor designed in this study. Effluent concentrations <0.1 mg/L PO43− were achieved in the reactor when treating river water. Highlights: It is crucial to develop an effective and easily recoverable phosphate absorbent for the control of eutrophication problems in polluted rivers. In this study, a stable particulate adsorbent with a diameter of 5 mm synthesized from lanthanum, activated carbon, and zeolite (La-CZ) was developed, characterized, and tested for the removal of phosphate from wastewater in a small-scale reactor, which was designed to easily recycle La-CZ with a basket. Batch studies showed that La-CZ could reach adsorption equilibrium within 2 h and the maximum phosphate sorption capacity was 18.2 mg g−1. The experimental data showed good compliance with the Langmuir isotherm model and pseudo-second-order kinetic model, implying that chemisorption dominates the phosphate uptake process. La-CZ exhibited a stable adsorption capacity over a wide pH range (3–7), while the adsorption capacity decreased slightly under alkaline conditions. Although Nitrates (NO3−) and Carbonate (CO32−) had some effects, normal coexisting ions such as Chloride (Cl−), Sulfate (SO42−), and Fluorine (F−) had no significant effects on the phosphate adsorption capacity of La-CZ. The main form of phosphate removed from the reaction system was HCl-P (77.68%), as determined through phosphorus fractionation. In particular, this study designed a replaceable filler-type reactor integrating a reflux and aeration system, 98.8% of phosphorus could be removed from actual wastewater, and La-CZ could be reclaimed easily. This work provides an excellent reference for particulate adsorbents that can efficiently remove phosphate in practical applications in the future.