Simultaneous harvesting and cell disruption of microalgae using ozone bubbles: optimization and characterization study for biodiesel production

Effect mechanism of metal cations on the interface interaction of cell-collector-bubble for microalgal foam flotation

Foam flotation is generally recognized as a low-cost and efficient technology for the harvesting of microalgae for food, feed and fuel production, as well as environmental remediation. However, the harvesting efficiency of microalgae using foam flotation is restricted by the residual metal cations in the medium, and the corresponding inhibition mechanism has not yet been revealed. This study investigated the effects of metal cations in the medium on the harvesting efficiency and concentration factor during the foam flotation of Scenedesmus acuminatus. The interface interaction of cell-collector-bubble effected by metal cations was revealed by quantifying the amount of collector (cetyl trimethylammonium bromide, CTAB) between cells and bubbles, as well as the response of bubble interface characteristics. Results showed that the harvesting efficiency dropped linearly as the increase of cationic concentrations. Under the CTAB dose of 20 mg L-1, the harvesting efficiency decreased from 98.65% to 56.77% with a decrease of concentration factor from 25.41 to 9.05 in the presence of metal cations. The Na+ and Mg2+ in the medium were the major inhibitors. The inhibitory mechanisms revealed that metal cations obviously impeded the adsorption of CTAB onto the cells by competing adsorption site, resulting in a low harvesting efficiency. The presence of metal cations also inhibited the bubble coalescence and slowed down drainage velocity in the plateau channel of foam layer, forming foam with higher water content, thus reducing the concentration factor. A schematic illustration is proposed to better understand the effect mechanism of metal cations on microalgal foam flotation. This study might facilitate the process development in an effort to overcome the inhibition of cations during microalgal foam flotation.

A biphasic photobioreactor system for consecutive extraction of lipids and carotenoids from pre-hydrolysed microalgae and evaluation of its biodiesel potential

A green extraction method is developed using partially hydrolysed microalgal cells grown in biocompatible solvent for simultaneous cultivation and extraction of bioproducts from a highly efficient permeabilized microalgal cell with enhanced biomass and lipid content for potential use in biodiesel production. Incomplete digestion of cell wall was achieved by regulating the incubation time of the enzymatic pretreatment of the microalgal cells. 15.77% increase in lipid content was seen when untreated cells were cultured with biocompatible solvent, while cultivation of these enzymatically pretreated cells with biocompatible solvent, the lipid content increased by 53.33% and 22% higher carotenoid content was observed as compared to conventional extraction. The total fatty acids obtained after 1st and 2nd extractions in untreated samples were 67.82%, while those in enzymatically partially digested samples were 91.94%. The untreated and partially enzymatically predigested strain showed suitable properties for quality biodiesel production as per international recommendations. The cost benefit analysis of the overall process showed the use of biocompatible solvent coupled to enzymatically predigested biomass was a favorable option as compared to conventional extraction.

Efficiency and mechanism of ozonated microbubbles for enhancing the removal of algae and algae-derived organic matter

The effective control of eutrophication caused by algae blooms is still the focus of global attention. The traditional dissolved air floatation process for algae removal has a low adhesion efficiency between bubbles and algal cells and a low removal efficiency of organic pollutants. Aiming to address these defects, this study set up an ozone microbubble-enhanced air flotation experiment to explore the removal trends of algal cells and algal organic matter (AOM) pollution. In contrast to traditional air flotation, this approach targets the removal of various forms of AOM after algal cell damage. The highest removal rates of algal cells, extracellular microcystin (Mc), intracellular Mc-lr and total Mc-lr were 96.6%, 60.1%, 95.2% and 93.7%, respectively. Compared with the traditional process, the absorption rate and utilization rate of ozone were increased by 41.9% and 46.2%, respectively. The removal effect of AOM was also greatly improved, and ozone microbubbles enhanced the removal of aromatic protein-like substances and high-molecular-weight fulvic acid, humic acid and humic substances. The advantageous synergistic effect of ozone and microbubbles on algae removal was analyzed by exploring the enhanced air flotation removal mechanism of ozone microbubbles' enhanced air floatation removal. Good vacuole adhesion and strong oxidation caused by ozone microbubbles jointly guaranteed a good removal rate of AOM. The enhanced air flotation process with ozone microbubbles has high feasibility and a good effect, can effectively remove algal cells and algal pollutants, and has great potential in algal removal and control of water eutrophication.

Performance indicators for the optimal BTE of biodiesels with additives through engine testing by the Taguchi approach

Biodiesel commercialization is questionable due to poor brake thermal efficiency. Biodiesel utilization should be improved with the addition of fuel additives. Hydrogen peroxide is a potential fuel additive due to extra hydrogen and oxygen content, which improves the combustion process. In this experimental study, biodiesel has been produced from Jatropha oil employing catalyzed transesterification homogeneously to examine its influence on the performance and emissions at engine loads with 1500 rpm utilizing a four-stroke single-cylinder diesel engine. D60B40 (having 60% diesel and 40% biodiesel) and D60B30A10 (60% diesel, 30% biodiesel and 10% hydrogen peroxide (H2O2)), are the fuel mixtures in the current study. The addition of H2O2 reduces emissions and enhances the combustion process. This effect occurred due to the micro-explosion of the injected fuel particles (which increases in-cylinder pressure and heat release rate (HRR)). An increase of 20% in BTE and 25% reduction in BSFC for D60B30A10 was observed compared to D60B40. Significant reduction in emissions of HC up to 17.54%, smoke by 24.6% CO2 by 3.53%, and an increase in NOx was noticed when the engine is operated with D60B30A10. The HRR increased up to 18.6%, ID reduced by 10.82%, and in-cylinder pressure increased by 8.5%. Test runs can be minimized as per Taguchi's design of experiments. It is possible to provide the estimates for the full factorial design of experiments. Exhaust gas temperature standards are evaluated and examined for all fuel blends.