Residual phosphorus supply for methanotrophic cultivation and microbial protein production

Microbial protein (MP) is a promising alternative protein source with several economic and environmental advantages. Currently, there is a research trend investigating the use of residual sources for the inputs of the production process, so it becomes more circular and efficient. In this study, the residual phosphorus (P) sources struvite and precipitated calcium phosphate (PCP), recovered from wastewater, were evaluated as P sources for the production of MP using methane oxidising bacteria (MOB). The study aims to understand the P requirements of bacteria in order to optimise P dosing in the culture medium. Since phosphate is provided in excess as a buffer, its optimal supply for assimilation will have an impact on pH control. Thus, pH and buffer capacity are also monitored. Both nitrate and ammonium were used as nitrogen sources, as they have different impacts on pH. Additionally, strategies for the dissolution of struvite and PCP were assessed, as were their implications on process design. MOB were capable of growing with both PCP and struvite as a phosphorus source. However, PCP shows lower growth rates and is more difficult to dissolve efficiently. Struvite was thus the best candidate for P recovery via MP from MOB.