Innovative Treatment of Digestate and Biogas Upgrade Using Chlorella Vulgaris

In the era of energy transition, the research efforts are devoted to find sustainable solutions to enable the transition to a decarbonised energy and production system, by renewable energy sources promoting products circularity, green technologies and safer processes. Anaerobic digestion is a bioprocess involving organic substrate breakdown by various microbial species in the oxygen absence. It yields two valuable products: digestate and biogas. Digestate can be used as fertilizer after stabilization and reduction of its polluting load. Through an upgrading process, biogas can be converted into biomethane, a widely utilized resource in energy and transportation. In this study, a non-conventional method has been investigated to achieve simultaneous biomethane production and reduction of digestate polluting power using Chlorella vulgaris, resulting in two valuable products. A 6-liter anaerobic digester was fed with simulated municipal organic waste every 3 days. Biogas was fed into a photobioreactor, where C. vulgaris was cultivated under mixotrophic conditions, utilizing CO2 from biogas as a carbon source. Biogas was converted into biomethane with over 90% methane content, while digestate was treated in the same photobioreactor, reducing its chemical oxygen demand (COD) by up to 80%. Using CO2 from biogas, maximum cell concentration of 1.332 g/L, maximum specific growth rate of 0.091 day-1 and biomass productivity of 0.057 gBS/L d were obtained at 70 µmol/m2 s. Biogas was analyzed by gas chromatography, and digestate was assessed for suspended solids, total solids, and COD. After cultivation, biomass was harvested, dehydrated, and characterized for total lipids and calorific value. Combining both approaches transforms waste into valuable biomethane and microalgal biomass, supporting the zero-waste objective

Effect of Tetracycline and Ciprofloxacin on Growth and Biochemical Composition of Chlorella Vulgaris

This research aimed to evaluate the impacts of Tetracycline (TC) and Ciprofloxacin (CIP) on the growth and biochemical composition of Chlorella vulgaris. In this regard, TC and CIP were added to C. vulgaris culture media at concentrations of 5, 10, 30, and 50 mg L-1. The effects on growth, antibiotic removal efficiency, and biochemical composition of microalgal cells in terms of chlorophyll, carotenoid, protein, and lipid contents were investigated over a 14-day period. Using both TC and CIP, the highest removal efficiencies (92.0 and 82.2 %, respectively) were observed at an antibiotic concentration of 5 mg L-1, while the highest final biomass concentrations (0.43 and 0.54 g L-1) were obtained at TC and CIP concentrations of 10 and 30 mg L-1, respectively. It is noteworthy that, despite the growth limitation at high concentrations of the antibiotics, the microalga exhibited resilience and survival. As the TC and CIP concentration was raised in the medium, a decrease in chlorophyll, carotenoid, and protein contents occurred compared to the control medium. Conversely, at a TC and CIP concentration of 50 mg L-1, the lipid content increased up to 28.68 and 27.51 %, respectively. This study provides valuable insights into the response of C. vulgaris to specific antibiotic-induced stress, shedding light on both growth patterns and biochemical composition of this microalga under such conditions

Fibrinolytic enzyme from Arthrospira platensis: Kinetic and thermodynamic investigation

Fibrinolytic enzymes from microorganisms have been investigated by their potential application as thrombolytic agents. Previous studies show that the fibrinolytic enzyme from Arthrospira platensis (FEAP) is stable at human physiological temperature (<50 ◦C) and pH (6.0–10.0). Understanding of the kinetic/thermodynamic characteristics is important to make the advances for industrial applications feasible. Therefore, a kinetic/thermodynamic analysis of FEAP was performed on the fibrin hydrolysis and enzyme thermoinactivation. Results showed two Michaelis-Menten-type profiles with two plateaus, revealing high affinity for the substrate with low Michaelis constant values (0.02 and 6.37 μg•mL-1). The activation energy of the hydrolysis catalyzed by FEAP and the standard enthalpy variations of reversible enzyme unfolding were 49.65 and 107.01 kJ•mol-1, respectively. When the temperature increased from 40 to 70 ◦C, the deactivation rate constant increased from 0.0050 to 0.0134 min- 1, while the half-life decreased from 138.62 to 51.72 min. These results allowed to estimate the activation energy (E*d = 27.50 kJ•mol-1), enthalpy (24.64 ≤ ΔH*d ≤ 24.89 kJ•mol-1), entropy (-209.86 ≤ ΔS*d ≤ -210.10 J•mol-1•K-1), and Gibbs free energy (90.61 ≤ ΔG*d ≤ 96.74 kJ•mol-1) of thermal denaturation. The data suggest that FEAP is a promising and thermostable biocatalyst that could be exploited for industrial applications