Microalgae dewatering is a major obstruction to industrial-scale processing of microalgae for biofuel prodn. The dil. nature of harvested microalgal cultures creates a huge operational cost during dewatering, thereby, rendering algae-based fuels less economically attractive. Currently there is no superior method of dewatering microalgae. A technique that may result in a greater algal biomass may have drawbacks such as a high capital cost or high energy consumption. The choice of which harvesting technique to apply will depend on the species of microalgae and the final product desired. Algal properties such as a large cell size and the capability of the microalgae to autoflocculate can simplify the dewatering process. This article reviews and addresses the various technologies currently used for dewatering microalgal cultures along with a comparative study of the performances of the different technologies.

Dewatering of microalgal cultures : a major bottleneck to algae-based fuels

Extensive and improper utilization of water from industrial, municipal, and agricultural activities generate 380 trillion L/y of wastewater worldwide. Wastewaters from different sources contain enormous amounts of nutrients such as carbon, nitrogen, and phosphorus. Thus, the recovery of these nutrients via appropriate sustainable process becomes a necessity. Among various processes microalgae-based technologies has attracted considerable attention and its strategies for sustainable and low-cost treatment of wastewater has allowed removal of over 70% nutrient loads from the wastewater. After the treatment of wastewater, the harvested microalgae biomass contains value-added biomolecules which can used for bioenergy production and nanoparticle synthesis. At present, high operational costs represent a major limitation for the development of microalgae-based biorefineries. Thus, the main aim of the review is to provide the knowledge about the potential of low-cost microalgae-based integrated biorefinery for wastewater treatments and resource recovery. Also, this review provides the insight of microalgae biomass-based bioenergy products, nanoparticles synthesis their application within the concept of circular bioeconomy. Furthermore, this review also provides information on different established industries which used microalgae for wastewater treatment.

Microalgae-based biorefineries for sustainable resource recovery from wastewater

Global issues such as environmental problems and food security are currently of concern to all of us Circular bioeconomy is a promising approach towards resolving these global issues The production of bioenergy and biomaterials can sustain the energy–environment nexus as well as substitute the devoid of petroleum as the production feedstock, thereby contributing to a cleaner and low carbon environment In addition, assimilation of waste into bioprocesses for the production of useful products and metabolites lead towards a sustainable circular bioeconomy This review aims to highlight the waste biorefinery as a sustainable bio-based circular economy, and, therefore, promoting a greener environment Several case studies on the bioprocesses utilising waste for biopolymers and bio-lipids production as well as bioprocesses incorporated with wastewater treatment are well discussed The strategy of waste biorefinery integrated with circular bioeconomy in the perspectives of unravelling the global issues can help to tackle carbon management and greenhouse gas emissions A waste biorefinery–circular bioeconomy strategy represents a low carbon economy by reducing greenhouse gases footprint, and holds great prospects for a sustainable and greener world

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Waste biorefinery towards a sustainable circular bioeconomy: a solution to global issues

Microalgae for high-value products: A way towards green nutraceutical and pharmaceutical compounds.

Waste based hydrogen production for circular bioeconomy: Current status and future directions.

Microalgal bioenergy production under zero-waste biorefinery approach: Recent advances and future perspectives

Microalgae are considered as a potential and sustainable feedstock for the production of biofuels, fine chemicals, nutraceuticals, and cosmetics. This is accredited to their high lipid and carbohydrate content, fast growth and rapid CO2 sequestration ability. However, large volumes of feedstock are required to extract and process biochemicals from microalgal biomass due to the small biomass to liquid ratio. This produces substantial challenges in attaining a sustainable energy balance in microalgae-based products process operations. Additionally, the small size of microalgal cells along with their negatively charged cell surface and cell density similar to the growth medium produces challenges in microalgae harvesting. The high cost associated with microalgae harvesting is a major bottleneck for commercialization of algae-based industrial products. Hence, microalgae harvesting is recognized as an area that needs to be explored and developed. This article aims to collate and present an overview of current harvesting strategies such as physical, chemical, biological, electrical and magnetic methods along with their future prospects. This review also highlights the evolution of microalgal harvesting and elucidates the fundamental phenomena of each technology in relation to key physical parameters such as morphology, size, density and surface charge. Besides throwing widespread light on various harvesting methods, this review article has also presented their advantages and disadvantages. Life cycle assessment (LCA) and technoeconomic analysis (TEA) was reviewed to assess the feasibility of various harvesting system for commercial application based on the environmental and technoeconomic impacts. Hence, the vital proposals provided in this review article would undeniably pave the way for choosing the appropriate harvesting strategy.

A comprehensive review on microalgal harvesting strategies: Current status and future prospects

Valorization of waste eggshell-derived bioflocculant for harvesting T. obliquus: Process optimization, kinetic studies and recyclability of the spent medium for circular bioeconomy.

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Identification of lipase producing fungus isolated from dairy waste contaminated soil and optimization of culture conditions for lipase production by the isolated fungus

A two-stage cultivation approach was employed to investigate the effect of nitrogen and/or phosphorus starvation on the morphology, biomass yield, photosynthetic activity, biochemical, and fatty acid composition of Tetradesmus obliquus KMC24. A two-day nitrogen-starved cells (-N2) were able to accumulate the maximum amount of lipid (39.93 ± 0.44%) without affecting the biomass yield (2.15 ± 0.04 g L−1). During nitrogen (-N) and phosphorus (-P) starvation, photosynthetically fixed carbon pool was diverted to lipid biosynthesis. Pearson’s correlation analysis suggested that stress-induced lipid accumulation is associated with an increased intracellular reactive oxygen species (ROS) level. The ROS fluorescence intensity was highest in -N2 cultures (17,051.49 ± 93.15 a.u.), suggesting highly oxidative stress-tolerant cells. A high degree of fatty acid saturation was obtained under nitrogen starvation as compared to other culture conditions. Biodiesel properties such as cetane number, saponification number, and iodine value improved under nitrogen starvation.

Madonna Roy

Papers

Microalgal bioenergy production under zero-waste biorefinery approach: Recent advances and future perspectives

A comprehensive review on microalgal harvesting strategies: Current status and future prospects

Valorization of waste eggshell-derived bioflocculant for harvesting T. obliquus: Process optimization, kinetic studies and recyclability of the spent medium for circular bioeconomy.

Identification of lipase producing fungus isolated from dairy waste contaminated soil and optimization of culture conditions for lipase production by the isolated fungus

Nutrient starvation-induced oxidative stress-mediated lipid accumulation in Tetradesmus obliquus KMC24