In situ production of single-cell protein in microbial electrochemical systems via controlling the operation and CO2 addition

Recovering both energy and nitrogen from livestock wastewater through microbial electrochemical cell (MEC) for the production of single-cell proteins (SCP) represents a promising technology for microbial protein generation. However, the high pH in the MEC cathode restricts the growth of microbial protein. In this study, intermittent operation of MEC and microbial fuel cell (MFC), along with the addition of CO₂, was performed to overcome the limiting factor of high cathode pH, thus achieving the SCP production in situ by recovering both energy and ammonia nitrogen. The removal efficiencies of COD and ammonia nitrogen in wastewater were up to 95 % and 50 %, respectively. The produced protein concentration could reach 67 %, and the dry weight was 168.3 mg·L⁻¹. Seven essential and ten non-essential amino acids were detected, and the essential amino acid richness in the protein was 31 %, surpassing that of meat. After simplified economic evaluation, the economic potential of the electrochemical system is 1.35 €/m³. Additionally, the electron acceptance behavior of Cupriavidus necator H16 from cathode when the pH is around 8.0 was proposed, which supported the production of SCP in MFC. This study provides a new concept for further promoting the resource utilization of livestock wastewater and developing an energy- and resource-efficient process for protein production.