Effects of recovered exogenous nitrogen addition on pilot-scale single-cell protein production from soybean soaking...

The valorization of nutrient-rich food-processing wastewater through single-cell protein (SCP) production offers a sustainable route to simultaneously reduce pollution and supplement protein supplies. However, the frequent nitrogen deficiency in such wastewater limits efficient microbial protein synthesis. This study demonstrates the pilot-scale production of SCP from real soybean-soaking water (SSW) using ammonium sulfate recovered from chicken manure as a sustainable nitrogen supplement. Without supplementation, the nitrogen-limited SSW yielded only 0.18 ± 0.03 grams SCP per gram chemical oxygen demand removed (COD_R) with a crude protein content of 42.0 ± 1.0%. Adding recovered nitrogen at a carbon‑to‑nitrogen ratio of 33 significantly improved performance, raising SCP yield to 0.34 ± 0.04 g/g COD_R and protein content to 47.7 ± 1.0%. However, excessive nitrogen addition led to sulfides accumulation and the precipitation of potentially toxic elements in SCP. This integrated approach effectively couples wastewater treatment with the production of high-value SCP, advancing a circular bioeconomy in the food industry.