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Infrastructures for Phosphorus Recovery from Livestock Waste Using Cyanobacteria: Transportation, Techno-Economic, and Policy Implications

Abstract:

This work presents a computational framework for investigating the economics of phosphorus (P) recovery infrastructures in the dairy sector based on cyanobacterial (microalgal) cultivation. Our framework integrates supply chain and techno-economic analysis to assess the potential of large- and small-scale open pond raceways (OPRs) and bag photobioreactors (PBRs). We explore the integration of these cultivation systems with anaerobic digestion, dry algal biomass production, and biofuel/biogas production units. To guide our assessment, we propose three economic indicators that we call the "social milk incentive"(SMI), "social animal incentive"(SAI), and "social phosphorus incentive"(SPI). The SMI is defined as the revenue necessary to achieve a zero net present value (NPV) for the infrastructure, relative to the total amount of milk produced in the studied region. The SAI is the revenue required relative to the number of cows in the region, and the SPI is the revenue required relative to the total P recovered by the infrastructure. These indicators facilitate comparisons between alternative infrastructure layouts, highlight incentives needed, and can help communicate hidden costs of dairy farming to the public. We use our framework for analyzing infrastructures that recover P in the Upper Yahara watershed region in Wisconsin, which currently faces severe nutrient pollution. Our results show that an infrastructure comprising a single, centralized OPR coupled with a dry algal production unit requires the lowest SMI (0.33 USD/gal) and that this incentive represents 17% of the current price of milk (1.85 USD/gal). Our framework also reveals that increasing the growth rate of algae by 20% (e.g., via metabolic engineering) can potentially eliminate the need for incentives (SMI of 0 USD/gal). Moreover, we found that the best SPI achievable (22 USD/kg P) is below a recent estimate of the economic impact of P pollution (74.5 USD/kg P); as such, the proposed infrastructure provides a viable avenue to mitigate nutrient pollution and associated environmental costs.