Cultivation of Scenedesmus dimorphus with air contaminants from a pig confinement building

The continual consolidation and concentration of animal feeding operations (AFOs) raises various environmental challenges, including air pollutant emission. Cost-effective mitigation technologies are pursued to protect the health and wellbeing of animals and farmers as well as the environment. Previous lab studies utilized ammonia (NH₃) and carbon dioxide (CO₂), two major air pollutants in AFOs, for microalgal cultivation. However, the field performance of this algae-based mitigation approach has yet to be investigated. In this study, two photobioreactors (PBRs) were tested in a nursery pig barn to mitigate NH₃ and CO₂ while growing Scenedesmus dimorphus (S. dimorphus). Pit air was fed into the PBRs where the two pollutants were adsorbed by S. dimorphus as nutrients to produce algal biomass and oxygen gas (O₂). The cleaned air then recirculated back to the room space. S. dimorphus reached its maximum cell count on the 17th day of the experiment when NH₃ and CO₂ concentrations in the pit air were 25.6 ppm and 3150 ppm, respectively. The maximum biomass concentration occurred on the 11th day when the NH₃ and CO₂ concentrations were 14.6 and 2250 ppm, respectively. The average mitigation efficiency was 31-50% for NH₃ and 1-1.7% for CO₂. The costs for removing 1 g NH₃ and CO₂ were estimated to be $3.77 and $0.20, respectively. This study shows that an integrated PBR system is technically feasible for reducing pig barn air pollutant emission while producing microalgae as a valuable product.