Recycling air conditioner-generated condensate water for microalgal biomass production and carbon dioxide sequestration

Abstract

Air conditioners alleviate the discomfort of human beings from heat waves that are consequences of climate change caused by anthropogenic activities. With each passing year, the effects of global warming worsen, increasing the growth of air conditioning industry. Air conditioning units produce substantial amounts of non-nutritive and (generally) neglected condensate water and greenhouse gases. Considering this, the study explored the potential of using air conditioner condensate water (ACW) to cultivate Chlorella sorokiniana, producing biomass, and sequestering carbon dioxide (CO₂). The maximum biomass production was obtained in the BG11 medium (1.45 g L^-1), followed by ACW-50 (1.3 g L^-1). Similarly, the highest chlorophyll-a content was observed in the BG11 medium (11 μg mL^-1), followed by ACW-50 (9.11 μg mL^-1). The ACW-50 cultures proved to be better adapted to physiological stress (F_v/F_m > 0.5) and can be suitable for achieving maximum biomass with adequate lipid, protein, and carbohydrate production. Moreover, C. sorokiniana demonstrated higher lipid and carbohydrate yields in the ACW-50 medium, while biomass production and protein yields were comparable to the BG11 medium. The lipid, protein, and carbohydrate productivity were 23.43, 32.9, and 23.19 mg L^-1 d^-1, respectively for ACW-50. Estimation of carbon capture potential through this approach equals to 9.5% of the total emissions which is an added advantage The results indicated that ACW could be effectively utilized for microalgae cultivation, reducing the reliance on freshwater for large-scale microalgal biomass production and reduce the carbon footprints of the air conditioning industry.

Keywords: Carbohydrate; Greenhouse gases; Lipid; Photosynthesis; Protein; Sustainable development goals.