Crude proteins and pigments were extracted from different microalgae strains, both marine and freshwater. The effectiveness of enzymatic pre-treatment prior to protein extraction was evaluated and compared to conventional techniques, including ultrasonication and high-pressure water extraction. Enzymatic pre-treatment was chosen as it could be carried out at mild shear conditions and does not subject the proteins to high temperatures, as with the ultrasonication approach. Using enzymatic pre-treatment, the extracted proteins yields of all tested microalgae strains were approximately 0.7 mg per mg of dry cell weight. These values were comparable to those achieved using a commercial lytic kit. Ultrasonication was not very effective for proteins extraction from Chlorella sp., and the extracted proteins yields did not exceed 0.4 mg per mg of dry cell weight. For other strains, similar yields were achieved by both treatment methods. The time-course effect of enzymatic incubation on the proteins extraction efficiency was more evident using laccase compared to lysozyme, which suggested that the former enzyme has a slower rate of cell disruption. The crude extracted proteins were fractionated using an ion exchange resin and were analyzed by the electrophoresis technique. They were further tested for their antioxidant activity, the highest of which was about 60% from Nannochloropsis sp. The total phenolic contents in the selected strains were also determined, with Chlorella sp. showing the highest content reaching 17 mg/g. Lysozyme was also found to enhance the extraction of pigments, with Chlorella sp. showing the highest pigments contents of 16.02, 4.59 and 5.22 mg/g of chlorophyll a, chlorophyll b and total carotenoids, respectively.

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The present study investigated the growth, harvesting, biocrude conversion, and recycling of the HTL aqueous phase for one self-settling (i.e., Chlorocystis sp.) and another non-settling (i.e., Picochlorum sp.) marine microalgae. Both the strains were grown simultaneously in 2 identical 25,000-L raceway ponds in the Qatari desert. The cell size of Picochlorum sp. was small (2-3 µm), and its biomass was harvested using a centrifuge. Cells of Chlorocystis sp. (6-9 µm) formed flocs that settled spontaneously in a sedimentation chamber. Harvested biomass of these two strains was then converted to biocrude oil, using a 500-mL Parr reactor. The biocrude yield of Picochlorum sp. and Chlorocystis sp. was 39.6 ± 1.15% and 34.8 ± 1.65%, respectively. The energy content of the biocrude oil was 32.78 and 33.38 MJ/kg for Chlorocystis sp. and Picochlorum sp., respectively. Both the strains were capable of efficiently utilizing more than 95% nitrogen of the HTL aqueous phase. Although lower biocrude yield was obtained from Chlorocystis sp., compared to Picochlorum sp., harvesting of Chlorocystis sp. would require much lower energy compared to Picochlorum sp. Therefore, a self-settling microalgae (e.g., Chlorocystis sp.) could potentially be a better candidate, over non-settling microalgae, for producing biofuel feedstock.

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Due to increase in environmental pollution and decline in petroleum reserves, there is an increase in the demands of developing alternative renewable bio-based products. Petroleum and lubricant manufacturing companies are searching for alternative renewable bio-based products since environmental protecting agencies, all over the world, are putting stringent environmental regulation in practice. Especially, there is a lot of ongoing research to find an alternative and renewable fuels and lubricants. One such alternative for mineral oil based lubricants are biolubricants as they have minimal impact on the environment and human health; furthermore, they have lesser toxicity, excellent lubricating properties, and a higher biodegradability index. Recent research is primarily focused on the synthesis of biolubricants from vegetable oils or animal fats either by chemically modifying the structure of oil or by blending of additives. The aim of this study was to develop biolubricants from renewable feedstocks, found in Qatar, by blending a viscosity modifier additive to meet the existing lubricant standard specifications. We selected 3 renewable feedstocks from Qatar: (i) Waste cooking oil, (ii) Jojoba seeds, and (iii) Waste date seeds. Unlike waste cooking oil and date seeds, jojoba oilseeds need to be collected from the plant. Jojoba plants can be irrigated with brackish water and can be grown in arid region. Oil-rich jojoba seed, therefore, can be considered as the base oil for biolubricants. Waste cooking oil was procured from a local restaurant in Doha, Qatar. Both the Jojoba seeds and the waste date seeds were collected from the Qatar University Biology farm in Zubarah. Initially, the seeds were sun-dried and grounded using a kitchen grinder. Next, oil from jojoba seeds and waste date seeds was extracted using a soxhlet extractor; hexane was used as extraction solvent. Soxhlet extractor was operated for 8 hrs to extract oil from jojoba seeds and waste date seeds. Oil yields from jojoba seeds and waste date seeds were found to be 55% and 10.2% (wt/wt basis) respectively. Waste cooking oil (WCO), jojoba oil (JO) and waste date seed oil (WDSO) were further blended with a viscosity modifier additive, i.e., ethylene vinyl acetate (EVA) in concentrations of 2%, 3% and 4% to formulate biolubricants from all three vegetable oil feedstocks. Addition of viscosity modifier-Ethylene vinyl acetate to WCO, jojoba oil and waste date seed oil increased the kinematic viscosities to maximum values for WCO from 70 mm2/s to 197 mm2/s at 30°C; similarly for jojoba oil it increased 27 mm2/s to 154 mm2/s at 30°C for Waste date seed oil it increased from 29 mm2/s to 160 mm2/s at 30°C. Viscosity for commercial oil (Mobil 20W40 Engine oil) was 190 mm2/s at 30°C. Viscosity index for all biolubricant formulations was calculated and it was found to be above 180. Thermogravimetric analysis of biolubricants revealed that formulated biolubricants were thermally more stable in order of WCO>DSO>JO>CO (Commercial oil). Biodegradability index was calculated BOD/COD ratio it was found to greater than 0.5. In this study, we found that biolubricants formulated from waste cooking oil, jojoba oil, waste date seed oil using viscosity modifier additive and all these biolubricants exhibited increased viscosity, higher viscosity index, better thermal stability and high biodegradability when compared with conventional mineral oil-based lubricant.