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Algae biomass has been recognized as one of the most suitable, efficient, and reliable feedstocks for bio-oil production. Among the different processes, hydrothermal liquefaction (HTL) is emerging as an effective technology for the valorization of various types of wet or dry biomass. Several factors, including temperature, retention time, and catalyst, significantly influence the overall efficiency of HTL products. The temperature ∼280 ± 40 °C is reported to be the most suitable range to achieve maximum bio-oil. Both homogeneous and heterogeneous catalysts have been used to improve bio-oil yield. For several advantages, heterogeneous catalysts are the preferred choice due to improved bio-oil generation, easy recovery, and uses. The eco-friendly approach and the reduction of heteroatoms in bio-oils make heterogeneous catalysts an ideal choice to be fortified. Alkaline catalysts have been considered most suitable to improve HTL yield. Variations in temperature and catalysts not only influence the yield of the bio-oil but also influence the characteristics of the bio-oil (e.g. high heating value, oxidative stability, gaseous emission, etc.) simultaneously. This review reveals interesting features including HTL temperature vs. yield, catalysts vs. yield, and the effect of wet and dry biomass on bio-oil properties, and finally, observations, remarks/limitations are presented for future studies.

Utilization of harmful algal blooms (HABs) for the cultivation of oleaginous microorganisms can provide dual benefits of mitigating the toxicity from the aquatic reservoirs and generation of copious media for biodiesel production. In the present investigation, microwave-assisted dilute alkali-freeze pretreatment was optimized to develop a low-cost growth medium from HAB dried biomass. The electron micrographs along with the elemental analysis confirmed the efficient breakage of HABs after the microwave-assisted hydrolysis treatment as compared with the acid hydrolysis. Moreover, the sugar analysis revealed ~ 46% higher carbohydrate content in microwave-assisted hydrolysate as compared with acid hydrolysate. The microwave-assisted hydrolysate and conventional dilute acid hydrolysate were then used to cultivate microalga (Chlorella minutissima) and yeast (Trichosporon cutaneum) for biomass and lipid accumulation and compared to artificial media. Microalga showed ~ 1.3- and 2-fold higher dry cell weight (DCW) and lipid content, respectively, while the yeast growth increased by ~ 27% with lipid content of 30%. The fatty acid profiles and biodiesel properties were also amenable to the international biodiesel standards. Hence, the present study provides a proof-of-concept of utilizing HAB hydrolysate for culturing oleaginous microorganisms for potential biodiesel production.

Waste material generated from food sources contributes a significant percentage of the waste generated worldwide. However, it is believed that about two-thirds of food is wasted globally. Anaerobic digestion methods have established important prospects in the field of food waste treatment. Obviously, it can produce significant amounts of energy and can remove a significant proportion of the organics. Microalgae represent a promising option for recycling waste nutrients from different types of food waste that can reduce the cost of producing different value-added products. The process of cultivating microalgae in anaerobic digestate from food waste fulfills the two objectives of environmental policy, i.e., treatment and recovery. This review focuses on the cultivation of microalgae in wastewater from the anaerobic digestate of food waste and the extraction of different value-added products from the biomass of microalgae.

The hydrothermal liquefaction of municipal sludge was investigated under isothermal conditions (255 °C, 45 min) with TiO2 as a catalyst. In this study, we used two separation methods (an organic solvent-assisted extraction method and the Soxhlet extraction method) for the production of bio-crude oil. The maximum yield of bio-crude oil was 20.7 wt. % reported with the Soxhlet extraction method. The aqueous phase was examined for TN, TP, COD, and TOC to determine the suitability of this phase for microalgae cultivation. Four strains of oleaginous microalgae were cultivated in the aqueous phase. The results show that the growth of microalgae in the aqueous phase was lower compared to the control medium; this may be due to the high COD value. Microalgae and yeast co-cultivation increases biomass and lipid productivity using nutrients in the aqueous phase.

The effect of UV light on growth, biomass, lipid accumulation and biodiesel properties of microalgae was studied. A Microalgae strain Chlorella sorokiniana UUIND6 was cultivated for 14 days as unde...

The present study describes an integrated method that can be used to sequentially extract five economically important fractions viz., essential oil, organic acids, resin, cellulose, and residual carbon from biomass of pine needles. It is a simple but very effective approach which can give consistent yields from the residual biomass with every successive extraction step. For example, aqueous extracts 0.2 ± 0.5 ml/g, essential oil 0.03 ± 0.1 ml/g, resin 64.125 ± 0.2 mg/g, and 302.20 ± 04 mg/g of sugar and 1 ± 0.3 g of residual carbon. Sugars were further fermented under optimized conditions for the production of ethanol (18.2 ± 0.4 g/l). These yields were compared to direct processing of the individual components. Residual carbon obtained after hydrolysis was used for the preparation of activated carbon. This combined ethanol production and chemical extraction approach may provide a compelling model for a biorefinery and increasing commercial viability.

In this study, an integrated biomass conversion concept of producing liquid biofuels from fresh water macroalgal biomass was investigated. The algal biomass was collected from the Song river, Dehradun, Uttarakhand, India and processed under laboratory. 0.650 g dry wt m−2of algal biomass was harvested from the freshwater river. The collected algal biomass contained mainly 2 macroalgae species. Lipid extraction was done by soxhlet extraction method using chloroform: methanol (2:1) as solvent. 18.6% of lipid was obtained from macroalgae biomass. Blends of algae biodiesel with, butanol and diesel fuel (A5B25D70 and A10B30D60) were prepared by Inline blending method on a volume basis. Oil extracted algal biomass was further hydrolyzed for release of fermentable sugar. The theoretical yield of conversion of fermentable sugars to bioethanol was estimated and found to be 61.0%.

The declining reserves of fossil fuels and fossil fuel-related environmental issues, especially greenhouse gas (carbon dioxide, methane) emissions, have posed a great threat and challenge to the sustainability of the world economy, the global environment, and hence the quality of life of human beings. Biomass pyrolysis could help reduce both the world’s dependence on oil and CO2 production. These bio-oils have the potential to cut CO2 emission because they are made up of plants that use CO2 for growth. There is a need to integrate process operation and reactor design to improve the effectiveness of different processes used for biomass to produce multiple products using a combination of technologies.

Fuels derived from biomass are essential in order to overcome the excessive dependence on petroleum. They also minimize the emissions of greenhouse gases. Pretreatment in biofuel production is a very important step. Pretreatment is not only costly in its own right but also has a pervasive impact on the cost of virtually all other processing operations. The present study investigates the effect of bacterial amylase pretreatment on ethanol production from different kinds of starch-based solid waste (SBSW). For this purpose four amylase-producing bacterial isolates were obtained from samples collected from municipal waste dumping sites. The isolated bacteria were then used for the pretreatment of SBSW for ethanol production. After bacterial amylase pretreatment, 13% yield of ethanol was obtained.

A number of different pretreatments involving biological, chemical, physical, and thermal approaches have been investigated over the years to reduce the cost of biofuel production. This study investigates the effect of bacterial amylase pretreatment on bioethanol production from different kinds of starch-based solid waste. We have isolated one strain (Xenorhabdus japonica) of amylase-producing bacteria from municipal waste dumping site's soil. Maximum ethanol yield was obtained after bacterial amylase pretreatment from wheat bread and rice (132 g/L), while the minimum was obtained from potato (99 g/L). Bacterial amylase pretreatment shows the best results as compared to the acid pretreatment.

A low-cost small-scale high-rate algal pond (HRAP) was constructed to investigate the synergistic potential of a novel oleaginous microalga, Chlorella sorokiniana for phyco-mitigation, and biodiesel production using raw urban wastewater. An enhanced nutrient removal (97%), total organic carbon (74%), alkalinity (70%) and hardness (75%) from the wastewater was obtained. The microalga dominated in the HRAP as ~90% increase in the dissolved oxygen with high biomass (1.13 g/L) was noted. The microalga biomass showed sufficient lipid content (~31% of dry cell weight) as compared to control (Bold’s Basal media). The total lipid profiling of the microalga cultivated in wastewater showed augmentation in the levels of both storage and neutral lipids with good quality fatty acids composition. Moreover, the sucker fishes grew healthy in the treated wastewater with an increase in body weight.

In order to increase microalgal biomass productivity efficient cultivation and harvesting methods are needed against the available traditional methods. The present study focuses on the same by harvesting microalgae using agar gel. Agar medium containing bold's basal medium (BBM) undergoes a thermoreversible gel transition. As compared to the traditional protocols, this gel is used to cultivate microalgae without even affecting the total productivity. To develop the gel for microalgae cultivation, agar was boiled in BBM. Then the agar was cooled to 35°C and microalgae culture was added to it. After seeding the microalgae the temperature of the agar was further decreased by 10°C to induce gelation. Instead of isolated cells microalgae were grown in clusters within the agar gel. Microalgal clusters gravimetrically settle at the bottom within 2h. In this method agar can be reused.