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Microalgae showcase an extraordinary capacity for synthesizing high-value phytochemicals (HVPCs), offering substantial potential for diverse applications across various industries. Emerging research suggests that subjecting microalgae to abiotic stress during cultivation and the harvesting stages can further enhance the accumulation of valuable metabolites within their cells, including carotenoids, antioxidants, and vitamins. This study delves into the pivotal impacts of manipulating abiotic stress on microalgae yields, with a particular focus on biomass and selected HVPCs that have received limited attention in the existing literature. Moreover, approaches to utilising abiotic stress to increase HVPCs production while minimising adverse effects on biomass productivity were discussed. The present study also encompasses a techno-economic assessment (TEA) aimed at pinpointing significant bottlenecks in the conversion of microalgae biomass into high-value products and evaluating the desirability of various conversion pathways. The TEA methodology serves as a valuable tool for both researchers and practitioners in the quest to identify sustainable strategies for transforming microalgae biomass into high-value products and goods. Overall, this comprehensive review sheds light on the pivotal role of abiotic stress in microalgae cultivation, promising insights that could lead to more efficient and sustainable approaches for HVPCs production. • Abiotic stresses are crucial for phytochemicals secretion in microalgae. • Impacts of various stresses on HVPCs production are examined. • Possibilities for one-pot production of biomass and HVPCs are discussed. • Techno-economic constraints were gauged and addressed. • Future directions to improve microalgae industry are elucidated. [ABSTRACT FROM AUTHOR]

Derivation of biofuel from microalgae biomass has been widely researched in the past few decades. Microalgae is capable of producing 58,700 litres oil per hectare that can generate 121,104 litres biodiesel per hectare, which seemingly a promising transition over conventional fossil fuels. Nevertheless, economic sustainability of commercial scale production of microalgae biomass is still in shadows of doubt, especially the cultivation and harvesting process. Apparently, the microalgae cultivation system has evolved from traditional open pond to various modern photobioreactor (PBR) designs. However, with regards to tubular and flat panel PBRs as the most ubiquitous systems for biofuel production at commercial level, extensive discussion on reactor configurations and design betterment was presented in this review, along with precise technical comparison on cost and energy requirements for the cultivation systems. This review intended to serve as guideline for long term adoption of these well-established cultivation technologies in biofuel plants given the numerous economic benefits. Besides that, in attempt to lower the harvesting cost, potential use of various waste biomass as bioflocculants to recover microalgae biomass was introduced in this review. This article also deliberates direction on potential policy interventions to produce microalgae biofuel in a more sustainable and cost-effective manners in near future. • Microalgae-derived biofuel is the potential substitute over fossil fuel. • Cultivation and harvesting steps are the bottlenecks to produce microalgae biofuel. • Wise selection of cultivation technology ensures sustainable biofuel production. • Bioflocculants from waste biomass are cheap, non-toxic, easily extracted. • Suitable policy framework ensures successful microalgae biofuel commercialization. [ABSTRACT FROM AUTHOR]

Microalgae have been recognized as a potential feedstock for biodiesel production due to their fast growth rate and ability to accumulate lipid within their cells. However, high lipid content and biomass productivity are usually difficult to achieve simultaneously. Instead of stressing the microalgae during cultivation stage, the stress environment such as nutrient starvation, salinity and light effect were introduced to Chlorella vulgaris after harvesting to study the effect on their lipid content. From the results attained, one day of nutrient starvation with 6.0 g/L of salinity stress under dark room condition had shown the highest lipid content of 38.8% (dry weight basis). The lipid content was recorded at 40.28% (dry weight basis) when the working volume was scaled up. In addition, the fatty acids identified in the extracted microalgae lipid were mainly consisted of linoleic, linolenic and palmitic acid, which were commonly found in corn oil, soybean oil and sunflower oil. • High biomass productivity and lipid are difficult to achieve simultaneously. • The stress towards the lipid content of microalgae after harvesting was studied. • Triple stress condition resulted the highest lipid content of microalgae. • Fatty acids of microalgae has similar profile as corn, soybean and sunflower oil. [ABSTRACT FROM AUTHOR]

Changing the growth environment for microalgae can overall lead to the fundamental alteration in cellular biochemicals whilst attaching onto palm kernel expeller (PKE) waste to form adhesion complex in easing harvesting at stationary growth phase. This study had initially optimized the PKE dosage, light intensity and photoperiod in maximizing the attached microalgal productivity being attained at 0.72 g/g day. Lipid content increased progressively from pH 3 to pH 11, with the highest value observed at pH 11. Meanwhile, in terms of protein and carbohydrate contents, the highest values were obtained by cultivation medium of pH 5 with 9.92 g and 17.72 g, respectively followed by pH 7 with 9.16 g and 16.36 g, respectively. Moreover, the findings also suggested that the low pH mediums utilized polar interactions in the formation of complexes between PKE and microalgae, whereas at higher pH levels, the non-polar interactions became more significant. The work of attachment was thermodynamically favourable towards the attachment formation with values greater than zero which was also aligned with the microscopic surface topography, i.e., revealing a clustering pattern of microalgae colonizing the PKE surface. These findings contribute to comprehensive understanding of optimizing growth condition and harvesting strategy of attached microalgae in attaining the cellular biochemical components, facilitating the development of efficient and sustainable bioresource utilization. [Display omitted] • Attached microalgae onto palm kernel expeller in producing cellular biochemicals. • PH factor positively militated biochemical components of attached microalgae. • Low dispersive and polar energy surface yielded optimal microalgal productivity. • Microalgae biolayer formed cluster upon reaching stationary growth phase. [ABSTRACT FROM AUTHOR]