Comparison of algae cultivation methods for bioenergy production using a combined life cycle assessment and life cycle costing approach

Algae are an attractive energy source, but important questions still exist about the sustainability of this technology on a large scale. Two particularly important questions concern the method of cultivation and the type of algae to be used. This present study combines elements of life cycle analysis (LCA) and life cycle costing (LCC) to evaluate open pond (OP) systems and horizontal tubular photobioreactors (PBRs) for the cultivation of freshwater (FW) or brackish-to-saline water (BSW) algae. Based on the LCA, OPs have lower energy consumption and greenhouse gas emissions than PBRs; e.g., 32% less energy use for construction and operation. According to the LCC, all four systems are currently financially unattractive investments, though OPs are less so than PBRs. BSW species deliver better energy and GHG performance and higher profitability than FW species in both OPs and PBRs. Sensitivity analyses suggest that improvements in critical cultivation parameters (e.g., CO2 utilization efficiency or algae lipid content), conversion parameters (e.g., anaerobic digestion efficiency), and market factors (e.g., costs of CO2 and electricity, or sale prices for algae biodiesel) could alter these results.

► Environmental and economic performance of open ponds and photobioreactors are compared.
► Open ponds deliver better energy return on investment and greenhouse gas performances.
► Open ponds deliver higher profitability index.
► Market forces are key to improved financial outlook for open pond operations.