Biofuel recovery from microalgae biomass grown in dairy wastewater treated with activated sludge: The next step in sustainable production.

Microalgae biofuel could be the next step in avoiding the excessive use of fossil fuels and reducing negative impacts on the environment. In the present study, two species of microalgae (Scenedesmus obliquus and Chlorella vulgaris) were used for biomass production, grown in dairy wastewater treated by activated sludge systems. The photobioreactors were operated in batch and in continuous mode. The dry biomass produced was in the range of 2.30 to 3.10 g L-1. The highest volumetric yields for lipids and carbohydrates were 0.068 and 0.114 g L-1 day-1. Maximum CO2 biofixation (750 mg L-1 day-1) was obtained in continuous mode. The maximum values for lipids (21%) and carbohydrates (39%) were recorded in the batch process with species Scenedesmus obliquus. In all of the experiments, the Linolenic acid concentration (C18:3) was greater than 12%, achieving satisfactory oxidative stability and good quality. Projected biofuel production could vary between 4,863,708 kg and 9,246,456 kg year-1 if all the dairy wastewater produced in Brazil were used for this purpose. Two hectares would be needed to produce 24,99 × 109 L year-1 of microalgae bioethanol, a far lower value than used in cultivating sugar cane. If all dairy wastewater generated annually in Brazil were used to produce microalgae biomass, it would be possible to obtain approximately 30,609 to 53,647 barrels of biodiesel per year. These data show that only by using dairy wastewater would biofuels be produced to replace 17% to 40% of the fossil fuels currently used in Brazil.

Enhanced Arthrospira platensis Biomass Production Combined with Anaerobic Cattle Wastewater Bioremediation.

Microalgae biomasses offer important benefits regarding macromolecules that serve as promising raw materials for sustainable production. In the present study, the microalgae Arthrospira platensis DHR 20 was cultivated in horizontal photobioreactors (HPBR), with and without temperature control, in batch mode (6 to 7 days), with anaerobically digested cattle wastewater (ACWW) as substrate. High dry biomass concentrations were observed (6.3-7.15 g L-1). Volumetric protein, carbohydrate, and lipid productivities were 0.299, 0.135, and 0.108 g L-1 day-1, respectively. Promising lipid productivities per area were estimated between 22.257 and 39.446 L ha-1 year-1. High CO2 bio-fixation rates were recorded (875.6-1051 mg L-1 day-1), indicating the relevant potential of the studied microalgae to mitigate atmospheric pollution. Carbon concentrations in biomass ranged between 41.8 and 43.6%. ACWW bioremediation was satisfactory, with BOD5 and COD removal efficiencies of 72.2-82.6% and 63.3-73.6%. Maximum values of 100, 95.5, 92.4, 80, 98, and 94% were achieved concerning the removal of NH4 +, NO3 -, Pt, SO4 2-, Zn, and Cu, respectively. Total and thermotolerant coliform removals reached 99-99.7% and 99.7-99.9%. This microalgae-mediated process is, thus, promising for ACWW bioremediation and valuation, producing a microalgae biomass rich in macromolecules that can be used to obtain friendly bio-based products and bioenergy. Supplementary Information: The online version contains supplementary material available at 10.1007/s12155-021-10258-4.