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• Passive lipid extraction techniques that skip conventional cell lysis step for microalgal biofuel production. • Energy consumption by passive methods are compared with physical methods. • In-situ transesterification, saponification-acidification, and switchable solvents have low energy consumption. • Passive methods suitable for lipid-based biorefinery is presented. The conventional method of lipid extraction mandatorily includes cell lysis which is considered an essential process for the enhancement of extraction efficiency. However, cell lysis method especially those incorporating mechanical and physical methods such as homogenization, sonication, microwave techniques, etc., are energy intensive and drastically escalates the biofuel production cost. Therefore, the development of an alternate route of extraction skipping the conventional mechanical cell lysis step remains a challenge to be accomplished. In this context, we discuss the reports involving passive techniques that are able to extract lipid from microalgae without significant cell wall shearing. This includes methods such as in-situ transesterification, direct saponification, supercritical fluid extraction, organic solvent extraction, etc. Moreover, the review discusses the employment of passive lipid extraction methods in a biorefinery set-up, outlining the various bioproducts that could be generated along with lipid. The review concludes with the analysis of the economics of microalgal lipid extraction using passive disruption methods and compares with the processes incorporating cell lysis steps. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sodium oleate (NaOL) enhances both biomass and lipid productivity in algae. • Optimum NaOL augmented with light irradiance governed the metabolite accumulation. • Total carotenoid and lipid content were significantly increased. • NaOL ameliorated the antioxidant potential of microalgae during the stationary phase. • NaOL orchestrated the metabolite overproduction in a dose-dependent manner. Microalgal metabolites have emerged as potential commodity components due to their notable beneficial nutritional and economic properties, and thus, their overproduction is of paramount importance to combat the existing ecological and dietary issues. However, the production titer of these metabolites by the algal systems at optimal cultivation conditions is inadequate to meet the burgeoning global demand for those metabolites. Therefore, a pressing demand remains to concurrently co-produce valuable metabolites without compromising cellular biomass production. Here, we report an effective strategy that simultaneously overproduces lipids, biomass and carotenoids in Chlorella vulgaris by providing sodium oleate (NaOL) in the cultivation medium. Supplement of sodium oleate at the optimal concentration (50 µg/mL) at increased light intensity enhances cellular growth rate in a dose-dependent manner. Total lipid content was quantified, which showed that lipid content was significantly increased in the NaOL-treated cells by 2.08-fold than that of the control cells. Interestingly, spectrophotometric determination of total carotenoids showed that carotenoid content was increased by 2.48-fold in the T5 (50 µg/mL) NaOL treated cells compared to the control. Interestingly antioxidant analysis showed that NaOL provision alleviated the antioxidant potential of the algal cells. Together, this report exemplifies the potential strategy to preclude the existing intricacies of co-producing metabolites in C. vulgaris by supplementing NaOL, thereby highlighting the viable chemical engineering approach for the biological production of commercially essential metabolites in microalgae. [ABSTRACT FROM AUTHOR]

• Methyl esterification targets lipids of coccolithophore. • Coccolithophore lipids were methyl-esterified at lower temperature than green alga. • Coccolithophore cell wall, composed of CaCO 3 , acted as a catalyst. • Effect of CaCO 3 on the methyl esterification by supercritical methanol was examined using green alga. • CaCO 3 is more effective than CaSO 4 -0.5H 2 O, which was previously considered effective. The methyl esterification of lipids employing supercritical methanol is an environmentally benign method since it does not produce alkaline wastewater, as is the case with conventional methods employing sodium hydroxide. Previous studies have shown that solid base catalysts are effective in decreasing reaction temperatures in the supercritical methanol methyl esterification. We focused on the coccolithophore Pleurochrysis carterae , which exhibits coccolith, i.e., CaCO 3 cell walls, and confirmed that the coccoliths acted as a catalyst in the methyl esterification of lipids in P. carterae employing supercritical methanol. To confirm the catalytic effect of the coccolith, the results of the supercritical methanol reaction of extracted lipids from P. carterae without coccolith were compared. The results showed that significant differences occurred, confirming that coccolith of P. carterae acts as a catalyst. To confirm the catalytic effect of CaCO 3 , the main component of coccolith, the green alga Chlorella vulgaris with cellulose cell walls was used to compare non-catalyst, addition of CaCO 3 and addition of CaSO 4 –0.5H 2 O, which is reported to be effective. The results revealed that the amount of the product obtained from the methyl esterification of fatty acids in C. vulgaris employing CaCO 3 was more significant than those obtained without any catalyst or with CaSO 4 –0.5H 2 O, indicating the effectiveness of CaCO 3 as a catalyst for methyl esterification by supercritical methanol. Coccolithophores, which exhibit CaCO 3 cell walls, are desirable raw materials for biofuels because they can function as catalysts. [ABSTRACT FROM AUTHOR]

This study focuses on evaluating the effect of residual lipid co-hydroprocessing with a heavy petroleum fraction, towards the production of a hybrid diesel fuel of increased sustainability. Firstly, the effect of Waste Cooking Oil (WCO) co-hydroprocessing with Heavy Atmospheric Gas Oil (HAGO) at different relative ratios (100/0, 95/5, 90/10, 85/15, 80/20 and 70/30 v/v) was evaluated in terms of diesel quality. The experimental results showed explicitly that the addition of WCO did not limit any hydroprocessing reactions targeted. Particularly WCO integration led to a significant diesel content increase which reached 13% for the highest WCO content feedstock (30% v/v), while increasing hydrogen consumption. The study showed that co-hydroprocessing of residual lipids within a refinery can provide an effective and no-risk pathway for integrating residual liquid biomass in transportation fuels, without significant capital investments, while the addition of 5–10% v/v WCO in the hydroprocessing feedstock is considered optimal in terms of H 2 additional requirements (∼6.5%), product quality and WCO availability. [ABSTRACT FROM AUTHOR]

Highlights: [•] Sterol rich lipid was converted to a fuel in a single catalytic cracking step. [•] The cracking of sterol liberates hydrogen, resulting in a reduced olefin content. [•] Cracking over Pd/C gave a fuel with high ratio of linear alkanes & ∼10% aromatics. [•] The resulting hydrocarbon fuel could be blended up to 50% with ULSD. [Copyright &y& Elsevier]

• Chlorella vulgaris grown in the artificial wastewater with different salt concentration. • Effects of ZnO and Fe 2 O 3 nanoparticles on Chlorella vulgaris was tested. • NaCl affects the growth of microalgae and the lipid content. • Optimum dose of the nanoparticles increased the removal efficiency of phosphorus. • Fe 2 O 3 obtained higher lipid content than ZnO. The current investigation highlighted the capability of the Chlorella vulgaris growth in the artificial wastewater with different concentration of NaCl incorporated with difference concentration of nanoparticle ZnO and Fe 2 O 3. Chlorella vulgaris cultured with ZnO and Fe 2 O 3 at the concentration of 5 mg/L, 10 mg/L, 20 mg/L and 50 mg/L. The characterization of the nanoparticles was performed through analytical technique. This study found that, the nutrient removal was effective on ZnO compared to Fe 2 O 3 against total nitrogen and total phosphorous. Further, the NaCl concentration in the wastewater affects the growth of the microalgae and biofuel production. With regard to the biomass concentration, the 20 mg/L ZnO and 50 mg/L Fe 2 O 3 reported highest yield of 2.08 g/L and 2.02 g/L. On the other hand, the maximum lipid accumulation of ZnO and Fe 2 O 3 were 14.25 wt% and 13.8 wt%. Secondly, the procured lipids were processed through transesterification process and characterized by Gas chromatography mass spectrometry (GC–MS). Compelling all the above it is concluded that the Chlorella vulgaris can be the suitable candidate for treatment of wastewater and production of bio-fuel. [ABSTRACT FROM AUTHOR]