Process synthesis and economic analysis of cyanobacteria biorefineries: A superstructure-based approach

In this study, we develop, synthesize, and evaluate a cyanobacteria biorefinery incorporating all relevant subsystems including: (1) supply of CO2, water, and nutrients, (2) production at cultivation ponds, and (3) products separation and purification. A superstructure-based approach is proposed to evaluate technical and economic feasibility of cyanobacteria biorefineries to produce biochemicals. Supply subsystems include a wastewater treatment (WWT) facility and a power plant to provide water, nutrients, and CO2. In the production subsystem, an approach to model cultivation ponds is developed based on production requirements and cyanobacteria characteristics i.e. residence time and productivity. In the purification subsystem, optimal separation technologies are selected based on product attributes and concentration to recover products and recycle water and nutrients, while minimizing costs. Later, all subsystems are integrated and system-wide optimization is performed. Impacts of key parameters such as cyanobacteria productivity and performance for a cellular level analysis; and CO2 transportation phase, distances, and product titers for a systems level analysis are investigated. Results indicate that depending on product attributes, the production cost could vary between $2.74−$34/kg ($0.7−$2.65/kg) at product concentrations of 0.5 g/L (10 g/L), highlighting the importance of achieving higher product titers. Analyses for the base-case show that for a titer of 0.5 g/L, reducing productivity from 30 to 5 g m−2 day−1 while increasing residence time from 5 to 30 days increases the production cost by about 22% in the system with water and nutrients supply form WWT, respectively. Results show that providing water and nutrients from a WWT facility improves the economics. The present study provides critical insights for future research and development and successful commercialization of cyanobacteria biorefineries.