Assessment of biofuel production yield using microalgae biomass in cattle wastewater

In this study, cattle wastewater (ARB) was used to cultivate a new mix of microalgae in photobioreactors (FBRs) developed specifically for this research. Over an 8-week period, biomass production collections were conducted, with ARB changes at the beginning of each week. The values presented in this study correspond to the dry biomass results of 4 samples. The dry mass produced ranged from 0.50 to 5.0 g L^− 1, and CO₂ biofixation varied from 0.10 g L^− 1 d^− 1 to 0.90 g L^− 1 d^− 1. The lipid percentages analyzed ranged from 7.3 to 15.7%, while carbohydrate values varied from 22 to 33%, with higher values attributed to the higher concentration of nutrients in ARB. C16:0 fatty acid was detected in higher concentrations in all experiments. Additionally, all samples recorded values greater than 12% for C18:3, failing to meet the requirements of EN14214 (European standard). On the other hand, fatty acids C18:2, C18:3, and C18:1 represented 21% of the sample composition, with lower percentages of these acids implying greater oxidative stability. All samples analyzed had cetane values greater than 45, meeting the requirement of ANP255 (Brazilian standard). Finally, the mass balance to determine biofuel yield from biomass on a real scale yielded values ranging from 131 g kg^− 1 to 223 g kg^− 1. However, the substitution of this production in relation to the national production of diesel and ethanol amounted to only 1% for the case studied. Meanwhile, CO₂ capture from the samples ranged between 2691 kg and 11,145 kg per year from the atmosphere. These results indicate the potential for biofuel production and reduction of greenhouse gas emissions compared to the current scenario of microalgae cultivation in wastewater.