Nutrient removal from secondary wastewater effluent by adsorption with hydrotalcite: effect of calcination temperature and co-existing ions

Abstract

Hydrotalcites have been investigated as adsorption systems for water treatment. However, there is a notable gap in the literature regarding studies analyzing their simultaneous removal of ammonium and phosphate pollutants. This work presents an analysis of the ammonium and phosphate adsorption process in real wastewater by commercial hydrotalcite calcined at different temperatures. In addition, an analysis of the effect of co-ions in the medium is performed, studying synergies and interferences between them. Optimal nutrient adsorption is achieved by calcining the adsorbent at 550 °C, facilitating a crystalline restructuring. During adsorbent hydration, the chemical memory effect allows phosphate to be incorporated into the interlamellar space, while ammonium is adsorbed mainly by electrostatic attraction when the zero-charge point is exceeded. The alkaline nature of water decreases adsorption capacities due to interference with the adsorbent’s crystalline reestablishment process and a buffer effect. The latter effect favors the loss of magnesium from the adsorbent, which results in a lower phosphate adsorption capacity. By contrast, calcium in the medium improves phosphate adsorption but inhibits ammonium adsorption. In real wastewater, the removal performance of phosphate and ammonium reached 90 and 50%, respectively, with standardized doses of 150 mgads/mg PO4 3 and 80mgads/mg N-NH4