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

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 (Fv/Fm > 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.

Improving the feasibility of producing biofuels from microalgae using wastewater

Biofuels have received much attention recently owing to energy consumption and environmental concerns. Despite many of the technologies being technically feasible, the processes are often too costly to be commercially viable. The major stumbling block to full-scale production of algal biofuels is the cost of upstream and downstream processes and environmental impacts such as water footprint and indirect greenhouse gas emissions from chemical nutrient production. The technoeconomics of biofuels production from microalgae is currently unfeasible due to the cost of inputs and productivities achieved. The use of a biorefinery approach sees the production costs reduced greatly due to utilization of waste streams for cultivation and the generation of several potential energy sources and value-added products while offering environmental protection. The use of wastewater as a production media, coupled with CO2 sequestration from flue gas greatly reduces the microalgal cultivation costs. Conversion of residual biomass and by-products, such as glycerol, for fuel production using an integrated approach potentially holds the key to near future commercial implementation of biofuels production.

BODIPY staining, an alternative to the Nile Red fluorescence method for the evaluation of intracellular lipids in microalgae

In order to develop feasible production processes for microalgal biodiesel, the isolation of high neutral lipid producing microalgae is crucial. Since the established Nile Red (NR) method for detection of intracellular lipids has been successful only for some microalgae, a more broadly applicable detection method would be desirable. Therefore, BODIPY 505/515, a lipophilic bright green fluorescent dye was tested for detection of intracellular lipids in Chlorella vulgaris, Dunaliella primolecta and Chaetoceros calcitrans. An optimum concentration of 0.067 μg ml(-1) was determined for lipid staining in the microalgae. Compared to NR, BODIPY 505/515 was more effective in staining microalgae and showed resistance to photobleaching, maintaining its fluorescence longer than 30 min.