Application of electrodialysis for nutrient recovery from manure digestate: A long-term investigation of membrane fouling

• Long-term membrane fouling behavior was investigated using real manure digestate. • The anti-fouling performance of homogeneous and heterogeneous membranes was compared. • ED maintained high nutrient recovery and perm-selectivity, with high potential in resource recovery. • Progressive membrane fouling was evaluated. • AM fouling was more severe, and the homogeneous membrane was more suitable for digestate treatment. Nutrient recovery from wastewater is pivotal for sustainable development, particularly in mitigating resource scarcity and environmental pollution. This study investigated the potential of long-term electrodialysis (ED) for nutrient recovery from pig manure digestate with a focus on membrane fouling, which is often overlooked in short-term operations. ED reactors were operated over 1100 hours using both heterogeneous and homogeneous ion exchange membranes (IEMs), with a treatment loading of 5000 L of digestate /m². The ED system demonstrated effective desalination, achieving over 80% recovery of ammonium (NH₄⁺) and 90% recovery of phosphate (PO₄³⁻), while maintaining high perm-selectivity (>95%). Membrane analysis revealed significant color darkening and structural deterioration, particularly in heterogeneous anion exchange membranes (AM), which exhibited increased resistance and reduced ion exchange capacity (IEC) after a treatment loading of 3472 L/m². Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) confirmed the accumulation of organic matter and the formation of hydrogen bonds on fouled membranes. Cation exchange membranes (CM) demonstrated greater stability and resistance to fouling than AM, with homogeneous CM outperforming their heterogeneous counterparts in maintaining IEC and structural integrity. Despite the increased membrane resistance, the ED system led to efficient nutrient recovery, highlighting the resilience of membrane perm-selectivity. This study highlights the potential of ED for resource recovery and emphasizes the critical role of effective fouling mitigation strategies in ensuring its long-term feasibility in nutrient recovery from high-solid wastewater streams, thereby providing a strong foundation for its practical application.