Recycling of acetate and ammonium from digestate for single cell protein production by a hybrid electrochemical-membrane fermentation process

Digestate is a potential substrate for yeast to produce single cell protein (SCP), but its complex matrix constrains applications. This study developed a hybrid electrochemical-membrane fermentation process to recover nutrients from synthetic digestate and produce yeast SCP. Electrodialysis (ED) was first employed to recover acetate and ammonium. More nutrients were recovered at a higher voltage but with lower current efficiency. At 2 V, 42.2% and 60.1% of acetate and ammonium were reclaimed, and further concentrated by 14- and 10-fold via a forward osmosis (FO) process. Due to the complexity of real digestate, the recovery efficiency of ED in practical applications should be further investigated. Saccharomyces cerevisiae fed on raw and concentrated recovery achieved similar SCP productions of 0.76–0.86 g/L, with amino acid concentrations above the FAO recommendation by 1.5–4.2-fold. The total production cost was estimated to be €20.4/kg-SCP by single ED, while the hybrid ED-FO process cost 40 times more.