Minimizing effects of chloride and calcium towards enhanced nutrient recovery from sidestream centrate in a decoupled electrodialysis driven by solar energy

To advance nutrient recovery from waste streams by electrodialysis (ED), a decoupled ED system with separated anode/cathode units was developed in this study. The use of an additional cation exchange membrane in the anode unit was designed to prevent chloride oxidation and collect phosphate at a higher concentration. The results show that the decoupled ED removed 92 +/- 2% of ammonia and 81 +/- 3% of phosphate from a synthetic solution, or 75 +/- 4% (ammonia) and 62 +/- 2% (phosphate) from a real centrate. Both current generation and nutrient removal could be improved with increasing the applied voltage from 3 to 5 V, and a higher voltage of 6 V did not pose positive effects on removal efficiency but resulted in higher energy consumption. A shorter electrodes distance benefited the decoupled ED operation with a lower internal resistance. The solar energy was successfully applied to power the decoupled ED that exhibited comparable performance (removing 74 +/- 4% of ammonia and 60 +/- 2% of phosphate) to that by a power supply, although the use of solar energy would depend on the illumination condition. The quality of the recovered struvite was enhanced by either a pre-treatment step to precipitate calcium ions or using a small quantity of the catholyte for struvite formation. These results have demonstrated a promising approach to recover nutrients from sidestream centrate as struvite and ammonium sulphate, encouraging further exploration of ED application towards enhancing flexibility and utilizing clean energy. (C) 2020 Elsevier Ltd. All rights reserved.