Microalgal Cultivation Using Animal Production Exhaust Air: Technical and Economic Feasibility

Fixing airborne nutrients from animal feeding operations (AFOs) into microalgal biomass could alleviate AFOs air emissions and reduce microalgal production cost. The aim of this study was to conduct a technical and economic assessment of integrating air emissions mitigation with microalgal cultivation. Experiments were conducted to determine technical feasibility for three air emission scenarios of exhaust gases, dust (particulate matter), and exhaust air. In the first scenario, microalgal Scenedesmus and Desmodesmus growing on the nutrients from exhaust gases had 92.7 and 71.0% of NH3 mitigation efficiency with biomass productivities of 11.2 and 21.5 g/m2 per day, respectively. In the second scenario, particulate matter from AFOs provided essential nutrients for Desmodesmus cultivation. The nutrient recoveries were 0.08 mg NH4+-N/mg biomass, 0.13 mg NO3−-N/mg biomass, and 0.03 mg PO43−-P/mg biomass. The biomass productivity was 21.4 g/m2 per day. In the third scenario, exhaust air from AFOs was the nutrient source to culture three microalgae of Scenedesmus, Chlorella, and Chlamydomonas. The corresponding microalgal biomass productivities were 14.5, 9.7, and 8.7 g/m2 per day. Four conceptual cases were applied to assess the economic feasibility of the integrated air emission mitigation and microalgae cultivation. The results demonstrated that using the recovered CO2 and nutrients in exhaust air could significantly reduce the cost of microalgal culture systems, and a net revenue of $0.0005/egg could be achieved by the integrated system with improved microalgal biomass productivity of 20 g/m2 per day.