Enhancement of nitrate removal and recovery from municipal wastewater through single- and multi-batch electrodialysis: Process optimisation and energy consumption

The vast volume of nutrients discharging from municipal wastewater (MWW) into water resources, along with the stringent limitations of their discharge, can be addressed via the recovery of nutrients from this stream. Hence, the purpose of this study is to optimise and enhance nitrate recovery from MWW using single and two-stage electrodialysis processes. Furthermore, the chemical quality of the recycled water was comprehensively tested and compared with the standards. Better nitrate recovery was obtained at the flow rate of 60 Lh⁻¹, with four cell pairs, diluted-to-concentrated volume ratio (VD/VC) of 2/0.5 and using Na₂SO₄ as the electrolyte. Under these conditions, the nitrate concentration in the diluted part was near zero with a concentration ratio of 4.6 and energy consumption of 1.44 kWh kg NO₃⁻. Two-stage batch electrodialysis enhanced nitrate concentration ratio to 19.2 with energy consumption of 4.34 kWh kg NO₃⁻. The volumes of 2 L and 8 L of water could be recovered per 0.5 L of concentrated solution by applying single- and two-stage batch electrodialysis respectively. The pH, permeation sequence, membrane fouling and water transfer were also investigated. These results indicated that the electrodialysis system has the potential to provide functional nutrient recovery and drinking water source alternatives.