Co-Design of Cyanobacteria Mutant Strains and Processes for Phosphorus Recovery from Livestock Wastewater

Livestock agriculture generally operates as a linear economy, consuming large quantities of nonrenewable energy and nutrients while generating waste that often pollutes the environment. In this work, we propose approaches to help mitigate nutrient pollution via the development of cyanobacteria-based processes that capture phosphorus from dairy manure. Using engineered strains of cyanobacteria, we were able to increase biomass phosphorus density 8.5-fold with no impact on growth rate, producing biomass that contained 14% phosphorus by mass. Techno-economic modeling revealed that the dramatic increase in phosphorus density leads to a significantly more cost- and resource-efficient process, with over a 2-fold reduction in total annualized cost (TAC), 8-fold reduction in required land use, 3-fold reduction in energy usage, and fully eliminating the use of freshwater. Further analysis showed that combining the mutant strain with a simplified nutrient recovery process resulted in a phosphorus recovery charge (PRC) of 9.2 USD per kg P, which is 88% lower than an estimated socioeconomic cost of P runoff (75 USD per kg P) and equivalent to a service charge of 0.015 USD/gal of manure processed. By using cyanobacteria biomass as a P-dense biofertilizer, the proposed approach can help facilitate nutrient transportation and the transition to a more circular agricultural economy.