Photobioreactor configurations in cultivating microalgae biomass for biorefinery

Microalgae, highly prized for their protein, lipid, carbohydrate, phycocyanin, and carotenoid-rich biomass, have garnered significant industrial attention in the context of third-generation (3G) biorefineries, seeking sustainable alternatives to non-renewable resources. Two primarily cultivation methods, open ponds and closed photobioreactors systems, have emerged. Open ponds, favored for their cost-effectiveness in large-scale industrial production, although lacking precise environmental control, contrast with closed photobioreactors, offering controlled conditions and enhanced biomass production at the laboratory scale. However, their high operational costs challenge large-scale deployment. This review comprehensively examines the strength, weakness, and typical designs of both outdoor and indoor microalgae cultivation systems, with an emphasis on their application in terms of biorefinery concept. Additionally, it incorporates techno-economic analyses, providing insights into the financial aspects of microalgae biomass production. These multifaceted insights, encompassing both technological and economic dimensions, are important as the global interest in harnessing microalgae's valuable resources continue to grow.

Pyrolysis of azolla, sargassum tenerrimum and water hyacinth for production of bio-oil

Pyrolysis of azolla, sargassum tenerrimum and water hyacinth were carried out in a fixed-bed reactor at different temperatures in the range of 300-450°C in the presence of nitrogen (inert atmosphere). The objective of this study is to understand the effect of compositional changes of various aquatic biomass samples on product distribution and nature of products during slow pyrolysis. The maximum liquid product yield of azolla, sargassum tenerrimum and water hyacinth (38.5, 43.4 and 24.6wt.% respectively) obtained at 400, 450 and 400°C. Detailed analysis of the bio-oil and bio-char was investigated using 1H NMR, FT-IR, and XRD. The characterization of bio-oil showed a high percentage of aliphatic functional groups and presence of phenolic, ketones and nitrogen-containing group. The characterization results showed that the bio-oil obtained from azolla, sargassum tenerrimum and water hyacinth can be potentially valuable as a fuel and chemicals.

Sustainability assessment of water hyacinth fast pyrolysis in the Upper Paraguay River basin, Brazil

Fast pyrolysis of naturally produced water hyacinth was assessed through Emergy accounting approach. Two analyses were carried out to evaluate the influence of additional services and externalities on Emergy indicators for a pyrolysis plant unit able to process 1000 kg of dry biomass per hour. The initial approach was a traditional Emergy assessment in which financial fluxes and externalities were not considered. The second approach included taxes and fees of the Brazilian government, interests related to financing operations and assumes a reserve financial fund of 5% of the total investment as externalities cost. For the first evaluation, the renewability of 86% indicates that local and renewable resources mainly support the process and the Emergy Yield Ratio of 3.2 shows that the system has a potential contribution to the regional economy due to the local resources use. The inclusion of financial fluxes and externalities in the second evaluation reduces both renewability and Emergy Yield Ratio, whereas it increases the Emergy Investment Ratio which means a higher dependence on external resources. The second analysis allows portraying significant forces of the industrial and financial systems and the evaluation of the externalities' impact on the general system Emergy behavior. A comparison of the renewability of water hyacinth fast pyrolysis with other biofuels like soybean biodiesel and sugarcane ethanol indicates that the former is less dependent on fossil fuel resources, machinery and fertilizers. To complement the sustainability assessment provided by the Emergy method, a regular financial analysis for the second defined system was done. It shows that the system is financially attractive even with the accounting of additional costs. The results obtained in this study could be used as the maximum and minimum thresholds to subsidize regulatory policies for new economic activities in tropical wetlands involving natural resources exploitation and bio-industrial systems.

Catalytic hydrothermal liquefaction of water hyacinth

Thermal and catalytic hydrothermal liquefaction of water hyacinth was performed at temperatures from 250 to 300 °C under various water hyacinth:H2O ratio of 1:3, 1:6 and 1:12. Reactions were also carried out under various residence times (15-60 min) as well as catalytic conditions (KOH and K2CO3). The use of alkaline catalysts significantly increased the bio-oil yield. Maximum bio-oil yield (23 wt%) comprising of bio-oil1 and bio-oil2 as well as conversion (89%) were observed with 1N KOH solution. (1)H NMR and (13)C NMR data showed that both bio-oil1 and bio-oil2 have high aliphatic carbon content. FTIR of bio-residue indicated that the usage of alkaline catalyst resulted in bio-residue samples with lesser oxygen functionality indicating that catalyst has a marked effect on nature of the bio-residue and helps to decompose biomass to a greater extent compared to thermal case.

Pyrolysis characteristics and kinetics of aquatic biomass using thermogravimetric analyzer

The differences in pyrolysis process of three species of aquatic biomass (microalgae, macroalgae and duckweed) were investigated by thermogravimetric analysis (TGA). Three stages were observed during the pyrolysis process and the main decomposition stage could be divided further into three zones. The pyrolysis characteristics of various biomasses were different at each zone, which could be attributed to the differences in their components. A stepwise procedure based on iso-conversional and master-plots methods was used for the kinetic and mechanism analysis of the main decomposition stage. The calculation results based on the kinetic model was in good agreement with the experimental data of weight loss, and each biomass had an increasing activation energy of 118.35-156.13 kJ/mol, 171.85-186.46 kJ/mol and 258.51-268.71 kJ/mol in zone 1, 2 and 3, respectively. This study compares the pyrolysis behavior of various aquatic biomasses and provides basis for further applications of the biomass thermochemical conversion.