Chapter 6 - Techno-economic analysis and life cycle assessment of algal cultivation on liquid anaerobic digestion effluent for algal biomass production and wastewater treatment

Abstract

The purpose of this study was to evaluate techno-economic feasibility and life cycle impact of algal cultivation to produce algal biomass and recover nutrients in liquid anaerobic digestate. Two pretreatment methods, namely chemical addition and electrocoagulation (EC) were applied to prepare the liquid digestate for the cultivation. Techno-economic analysis revealed that for an anaerobic digestion unit with a capacity of 100m3 organic wastes/day, the algal cultivation in the EC-treated digestate has higher biomass production (937kg dry biomass/day) than that in chemical treated digestate (264kg dry biomass/day). The production cost of algal biomass using EC-treated digestate ($3.26/kg dry biomass) was also lower than using chemical treated digestate ($5.78/kg dry biomass). The life cycle analysis further demonstrated the advantages of the algal cultivation with both pretreatment approaches. Algal cultivation results indicated a dramatic reduction (more than 90%) on greenhouse gas emission potential and water eutrophication potential compared to direct land application of the raw liquid digestate. The cultivation on the chemically pretreated digestate resulted in slightly better life cycle impacts due to less electricity demand and more removal of phosphorus and nitrogen. The greenhouse gas emission potential and water eutrophication potential for chemical method and EC treatment were 46 metric ton CO2-e/year and 0.03 metric ton PO4-e/year and 465 metric ton CO2-e/year and 0.06 metric ton PO4-e/year, respectively.