Phosphate removal from simulated wastewater using industrial calcium-containing solid waste

Anthropogenic solid waste can serve as a reactive substrate to adsorb and immobilize PO43- to enhance the sustainability of the water-energy-food nexus due to nutrient streams being recovered and recycled into the food chain as slow-release fertilizers. However, the structural complexity of solid waste presents significant hurdles identifying its ultimate potential to efficiently adsorb PO(4)(3-)from wastewater streams while its rich chemical composition - obtaining usable, heavy metal-free products to be reused in a highly regulated environment. In this study, two types of calcium-rich solid waste, biomass combustion bottoms ash (BA) and lime kiln dust (LKD), were evaluated for their propensity to adsorb PO43- from simulated wastewater streams. Batch adsorption studies showed maximum adsorption (PO43- removal) taking place at 2200 ppm of BA and 1800 ppm LKD with the sorption kinetics obeying well second order behavior. Estimated sorption capacity was 55.6 and 35.3 mg P/g LKD and BA, respectively, comparable or higher than for other natural Ca-containing natural minerals reported in the literature. PO43- ion adsorption was shown to be inhibited to below 50% as organic acid concentration increased in simulated wastewater solution. Importantly, heavy metal release into the simulated wastewater was assessed and it was concluded that only BA released Zn concentrations which were higher than those regulated by EPA. Mechanistically, the underlying metal release phenomena were observed and explained by the significant initial material dissolution rather than by any competing processes, such as organic acid competitive adsorption with PO43- ion.