Pollution control and biodiesel production with microalgae: new perspectives on the use of flat panel photobioreactors regarding variation in volume application rate.

In the present study, the microalga Arthrospira platensis DHR 20 was cultivated in vertical flat-plate photobioreactors (FPBRs) to bioremediate anaerobically digested cattle wastewater (ACWW) and used as a growth substrate. The final objective was to evaluate the properties of the oil extracted from this biomass to determine its potential for biodiesel production. The process was divided into five phases, varying the volume of the applied substrate: 1 L (Phase I), 5 L (Phase II), 10 L (Phase III), 15 L (Phase IV), and 20 L (Phase V). Dry biomass reached a maximum of 5.7 g L-1, and productivity peaked at 0.74 g L-1d-1. The highest rate of CO2 biofixation was 1213.5 mg L-1 day-1, showing good potential for purifying the air. The highest specific maximum growth rate (µmax) and the shortest doubling time (Dt) were found during Phase I. The removal of pollutants and nutrients during the experimental phases ranged from 65.8% to 87.1% for chemical oxygen demand (COD), 82.2% to 85.8% for total organic carbon (TOC), 91% to 99% for phosphate (PO43-), 62.5% to 93% for nitrate (NO3-), 90.4% to 99.7% for ammoniacal nitrogen (NH4+), and 86.5% to 98.5% for total nitrogen (TN). The highest lipid production recorded was 0.172 g L-1 day-1. The average cetane number recorded in Phase IV of 51 suggests that the fuel will ignite efficiently and consistently, providing smooth operation and potentially reducing pollutant emissions. The analysis of fatty acids revealed that the produced biodiesel has the potential to be used as an additive for other low-explosive biocombustibles, representing an innovative and sustainable approach that simultaneously offers bioremediation and carbon sequestration.

Potential of Chlorella fusca LEB 111 cultivated with thermoelectric fly ashes, carbon dioxide and reduced supply of nitrogen to produce macromolecules.

Fly ashes present several minerals that along with carbon dioxide (CO2) represent a promising nutrient source and an alternative to reduce environmental problems. Thus, the objective of this study was to investigate if CO2, thermoelectric fly ashes and reduction in nitrogen supply alters the production of macromolecules in Chlorella fusca LEB 111. For this purpose, 1.5 or 0.75 g L-1 of NaNO3, injection of 10% (v v-1) of CO2 as well as 0, 40 and 120 ppm of fly ashes were studied. The protein content was not impaired in cultivations with 0.75 g L-1 of NaNO3 since nitrogen was not fully consumed. Nevertheless, this cultivation strategy increased carbohydrate content by up to 25%, which could be fermented to produce bioethanol. Therefore, Chlorella fusca presented not only potential for CO2 biofixation and assimilation of nutrients from fly ashes but also for enhancement of carbohydrates accumulation when the nitrogen supply was reduced.

CO2 conversion by the integration of biological and chemical methods: Spirulina sp. LEB 18 cultivation with diethanolamine and potassium carbonate addition.

The aim of this work was to evaluate if the addition of the chemical absorbents diethanolamine and potassium carbonate affects the CO2 biofixation, growth and biomass composition of Spirulina sp. LEB 18. The association of the diethanolamine (DEA) and potassium carbonate (K2CO3) absorbents increased the dissolved inorganic carbon concentration in the cultivation medium, allowing greater CO2 biofixation by the Spirulina. Higher biomass concentration (2.1 g L-1) and maximum productivity (174.2 mg L-1 d-1) were observed with the mixture of 1.64 mmol L-1 of DEA and 0.41 mmol L-1 of K2CO3. In this cultivation condition, Spirulina sp. LEB 18 showed high protein content (58.8 w w-1) and an increased carbohydrate concentration (23.7% w w-1). The addition of these absorbent concentrations may be applied in the cultivation of Spirulina sp. LEB 18 to increase CO2 biofixation and cell growth.

Chlorella minutissima cultivation with CO2 and pentoses: Effects on kinetic and nutritional parameters.

CO2 emissions and the large quantity of lignocellulosic waste generated by industrialized nations constitute problems that may affect human health as well as the global economy. The objective of this work was to evaluate the effects of using CO2 and pentoses on the growth, protein profile, carbohydrate content and potential ethanol production by fermentation of Chlorella minutissima biomass. CO2 and pentose supplementation can induce changes in the microalgal protein profile. A biomass production of 1.84g.L-1 and a CO2 biofixation rate of 274.63mg.L-1.d-1 were obtained with the use of 20% (v.v-1) CO2. For cultures with 20% (v.v-1) CO2 and reduced nitrogen, the carbohydrate content was 52.3% (w.w-1), and theoretically, 33.9mL.100g-1 of ethanol can be produced. These results demonstrate that C. minutissima cultured with the combined use of CO2 and pentoses generates a biomass with high bioenergetic potential.