Effect of optical panel distance in a photobioreactor for nutrient removal and cultivation of microalgae

Agricultural biowaste, rice bran, as carbon source to enhance biomass and lipid production: analysis with various growth rate models

As a byproduct of agriculture, rice bran can be a good alternative carbon source to mass-produce microalgae and increase lipid content. The purpose of this study was to investigate the effects of rice bran extract (RBE) on the mass culture and oil content of microalgae. Various parameters were applied to the growth rate model to explain the dynamics of substrate inhibition and growth of microalgae. The rice bran contains 46.1% of carbohydrates, in which is 38.3% glucose, and is very suitable as a carbon source for microalgae growth. The culture with RBE had a four times higher biomass production than microalgae cultured on Jaworski's medium (JM) with a small amount of 1 g/L. In addition, for RBE, the lipid content was three times higher and saturated fatty acid was 3% lower than were those of JM. According to the above results, when Chlorella vulgaris is cultured using RBE, a high amount of biomass and high lipid content can be obtained with a small amount of RBE. RBE is a discarded waste and has a high content of glucose, so it can be replaced by an organic carbon source to increase microbial biomass growth and lipid content at low cost.

Valorization of waste eggshell-derived bioflocculant for harvesting T. obliquus: Process optimization, kinetic studies and recyclability of the spent medium for circular bioeconomy

Waste eggshell-derived bioflocculant was used for harvesting T. obliquus in a circular bioeconomy approach. It was found that 120 mg L^-1 bioflocculant can flocculate 98.62 ± 0.43% of T. obliquus cells within 25 min at optimal pH 4.0 and temperature 35 °C. The influence of bioflocculant concentration, pH and temperature on zeta potential was evaluated to understand the flocculation mechanism. Microscopic and FESEM-EDX images were analyzed to evaluate the microalgal structural changes. Adsorption mechanism of bioflocculant over the microalgal cells was determined by performing adsorption kinetic studies. Pseudo-second order kinetic model was a suitable fit for the data obtained from the experiments, which indicated chemisorption as the probable mechanism. The spent medium recovered after harvesting process was successfully recycled for subsequent cultivation of T. obliquus, thus reducing the dependency on fresh medium. The FAME composition of the biomass treated with bioflocculant was not altered.

Microalgae Chlorella vulgaris biomass harvesting by natural flocculant: effects on biomass sedimentation, spent medium recycling and lipid extraction

BACKGROUND

Microalgal biomass harvesting using traditional chemicals is costly for the production of biofuels, hindering the scale-up process of the technology. Thus, the search for a cost-effective microalgal harvesting method is extremely important. Using chitosan as a natural flocculant to harvest microalgal biomass seems to be an efficient and convenient solution. Although microalgal biomass flocculation by chitosan has been reported in some previous studies, literature on the harvesting of microalgae C. vulgaris biomass using such polymer is scanty. In addition, there is limited information available on whether the usage of chitosan during the harvesting will affect downstream lipid extraction. Still, whether microalgae can be re-grown with the spent medium after chitosan flocculation is still unknown.

RESULTS

In this study, microalgal biomass harvesting using chitosan as a natural flocculant and aluminum sulfate as a traditional flocculant was compared and evaluated. Optimal doses and effects on biomass sedimentation, spent medium recycling and lipid extraction were investigated. The results showed that the optimal doses for chitosan and aluminum sulfate to achieve more than 90% biomass recovery were 0.25 and 2.5 g/L, respectively. The sedimentation time of 10 min was found to be the most appropriate to remove over 90% biomass from culture. The spent medium after chitosan flocculation could be potentially recycled for the re-cultivation of microalgae, which demonstrated robust growth in comparison with those grown in the recycled medium from aluminum sulfate flocculation. The lipid content of microalgae harvested by chitosan reached 32.9, 4.6% higher than that of those harvested by aluminum sulfate, indicating that the application of the natural flocculant would not impact the downstream extraction of microalgal lipids.

CONCLUSION

The results herein presented, demonstrated that chitosan is applicable for microalgal harvesting during the upscaling process. Flocculation method developed by using chitosan as a natural flocculant is a worthy microalgal harvesting method for microalgae-based biofuel production. There is hope that chitosan can be reasonably and technically realistically applied in a full-scale process for the harvesting of microalgal biomass.

A novel method to harvest Chlorella sp. via low cost bioflocculant: Influence of temperature with kinetic and thermodynamic functions

In this study, harvesting efficiency (HE) of bioflocculant (egg shell) was observed with variation in flocculent concentrations (0-100mgL^-1), temperature (30°C, 35°C 40°C, 45°C and 50°C) and variable contact time (0-50min). It was found maximum (≈95.6%) with 100mgL^-1 bioflocculant concentration whereas influence of temperature was also observed with optimized concentration of bioflocculant (100mgL^-1) at 40°C (≈98.1%) and 50°C (≈99.3%), in 30min of contact time. Significant changes in algal cell structures were also analyzed after exposure to various temperatures with microscopy, SEM (Scanning electron microscopy) and EDS (Energy dispersive X-ray spectroscopy) images with and without bioflocculant. The experimental data was found to be a good fit with pseudo-second order kinetic model. The thermodynamic functions such as ΔG (Gibbs free energy), ΔH (enthalpy), ΔS (entropy) were also determined. The negative value of ΔG and positive value of ΔH and ΔS shows the spontaneous and endothermic nature of flocculation process.

Heavy metal removal from acid mine drainage by calcined eggshell and microalgae hybrid system

This study investigates the use of calcined eggshells and microalgae for the removal of heavy metals from acid mine drainage (AMD) and the simultaneous enhancement of biomass productivity. The experiment was conducted over a period of 6 days in a hybrid system containing calcined eggshells and the microalgae Chlorella vulgaris. The results show that the biomass productivity increased to ~8.04 times its initial concentration of 0.367 g/L as measured by an optical panel photobioreactor (OPPBR) and had a light transmittance of 95 % at a depth of 305 mm. On the other hand, the simultaneous percent removal of Fe, Cu, Zn, Mn, As, and Cd from the AMD effluent was found to be 99.47 to 100 %. These results indicate that the hybrid system with calcined eggshells and microalgae was highly effective for heavy metal removal in the AMD.