Development and validation of an adsorption process for phosphate removal and recovery from municipal wastewater based on hydrotalcite-related materials
Carla Maggetti, Davide Pinelli, Vittorio Di Federico, Laura Sisti, Tommaso Tabanelli, Fabrizio Cavani, Dario Frascari
Abstract
In the current international context characterized by the tendency to stricter limits for P concentration in treated wastewater and a strong drive towards phosphate recovery, it is crucial to develop cost-effective technologies to remove and recover phosphate from municipal wastewater (MWW). In this study, an initial screening of the phosphate adsorption performances of 9 sorbents including several hydrotalcites led to the selection of calcined pyroaurite - an innovative material composed of mixed Mg/Fe oxides - as the best-performing one. The assessment of calcined pyroaurite by means of isotherms and continuous-flow adsorption/desorption tests conducted with actual MWW resulted in a high P sorption capacity (12 mg P g −1 at the typical phosphate concentration in MWW), the capacity to treat 730 BVs at the 1 mg P L −1 breakpoint imposed by the current EU legislation, and a 93 % phosphate recovery. Calcined pyroaurite resulted in satisfactory performances also in a test conducted with a saline MWW deriving from a hotspot of seawater intrusion, a rapidly increasing phenomenon as a result of climate change. Five consecutive adsorption/desorption cycles conducted in a 20-cm column at a 5-min empty bed contact time resulted stable in terms of P adsorption/recovery performances, specific surface area and chemical structure of calcined pyroaurite. In the perspective to apply phosphate recovery with calcined pyroaurite at full scale, the process scale-up to a 60-cm packed bed - close to the column heights of industrial applications - resulted in stable performances. Calcium phosphate, widely used to produce phosphate-based fertilizers, can be obtained from the desorbed product by precipitation with Ca(OH) 2 . These results point to calcined pyroaurite as a very promising material for phosphate removal and recovery from MWW and from other P-rich effluents in a circular economy perspective. • Calcined pyroaurite effectively removed and recovered phosphate from wastewater. • It resulted in high phosphate adsorption selectivity and high operational capacity. • Performances resulted stable during 6 consecutive adsorption/desorption cycles. • Suitable results obtained also with wastewater from hotspot of seawater intrusion. • Scale-up from 20-cm to 60-cm column led to constant adsorption performances.