Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, No. 1799 Jimei Road, Xiamen City, Fujian, 361021, China; Cluster for Bio-engineering, Department of Microbial and Molecular Systems, Faculty of Engineering Technology, KU Leuven Campus Bruges, Spoorwegstraat 12, 8200, Brugge, Belgium. Electronic address: [Email]
Different from current nutrient recovery technologies of recovering one or two nutrient components (PO43- or NH4+) from wastewater, this study aimed to fractionate various nutrient anions and cations simultaneously, including PO43-, SO42-, NH4+, K+, Mg2+ and Ca2+, into several streams. The recovered streams could be further paired together to produce high-value products. A novel electrodialysis process was developed by integrating monovalent selective anion and cation exchange membranes into an electrodialysis stack. Results revealed that nutrient recovery was achieved effectively by fractionating PO43- and SO42- into the anionic product stream, whereas bivalent cations (Mg2+ and Ca2+) were extracted in the cationic product stream and the monovalent cations (K+ and NH4+) were concentrated in the brine stream. For the permeation capabilities of anions, SO42- and Cl- possessed the higher preference, whereas PO43- permeated the membrane more difficult. As to the cations, the permeation sequence was: NH4+≈K+ >Ca2+>Mg2+≈Na+. Enhancing voltage values not only promoted ion migration rates, but also led to the increase of energy consumption. Although elevating initial phosphate concentration in the anionic product streams from 60 mg/L to 470 mg/L did not influence phosphate fractionation significantly, the current efficiency decreased from 3.55% to 0.65% and a remarkable increased of energy consumption from 29.42 kWh/kg NaH2PO4 to 160.13 kWh/kg NaH2PO4 was observed. Further experiments were conducted for phosphorus recovery by pairing two recovered product streams, which revealed that phosphate precipitation could be achieved by using inherent Ca2+ and Mg2+ in the wastewater without dosing external cation sources.