Electricity-driven microbial protein production: Effect of current density on biomass growth and nitrogen assimilation

Abstract

Conventional agro-systems are characterised by low nitrogen conversion efficiencies, primarily due to excessive loads and limited plant nitrogen assimilation into grains by plants. Therefore, it is crucial to explore technologies that can achieve higher nitrogen assimilation efficiencies in food production. This study shows the development of a sustainable bioelectrochemical platform for ammonium recovery and upgrading into bacterial protein-rich biomass. Electrochemically-assisted batch fermenters were operated in galvanostatic mode to examine the impact of current density (0.0 – 1.0 mA·cm−2) on bacterial growth. The results revealed a linear increase in volumetric biomass productivity rate with the increment in current density. At the high current densities tested (1.0 mA·cm−2), the more elevated growth and ammonium removal rates were achieved (473 ± 164 mgTSS·L−1·d−1 and 93 ± 39 mgN·L−1·d−1, respectively). Adjusting the current density allowed for the production of biomass with high hydrogen (H2) and nitrogen yields, indicating the influence of H2 availability on these values (up to 2.6 gTSS·gH2−1 and 6.9 gTSS·gN−1, respectively). This study confirms the potential of the electro-microbial platform in recovering and transforming nutrients, particularly nitrogen, into microbial biomass that can be utilised as edible protein or organic fertiliser. The findings highlight the viability of this approach for achieving efficient nitrogen assimilation and biomass production, offering promising prospects for addressing nitrogen utilisation challenges in conventional agro-systems.