Evaluating the integration of nanofiltration membranes in advanced water reclamation schemes using synthetic solutions: From phosphorous removal to phosphorous circularity

Abstract

The more stringent regulations related to the reduction of residual phosphorous concentration in treated wastewater and the consideration of phosphorous as a critical raw material are boosting new technologies towards its recovery from waste effluents. The concentration of phosphate in these effluents can be easily increased using nanofiltration (NF) due to its high phosphate rejections (>99%) in order to recover it as a raw material for the fertilizer industry. In this work, different model solutions were used to characterise the transport of phosphate species across a semi-aromatic polyamide membrane (NF270) using the Solution-Electro-Diffusion-Film coupled with reactive transport (SEDFRT) model. Experiments were carried out with waters containing one dominant salt (NaCl or Na2SO4) and one trace salt (dihydrogen or hydrogen phosphate salts) to easily determine membrane permeances to species without simulating the complexity of real solutions. Besides, for the first time the transport of H+ and OH– was also modelled. Results showed a high performance of NF270 when separating phosphate (rejections higher than 90%). Finally, the obtained permeances were used to evaluate the recovery capacity of phosphate as struvite from a model secondary treatment effluent through the SEDFRT model. Results demonstrate the potential of NF as a step forward towards closing the urban phosphorus cycle.