Biotechnologies for bulk production of microalgal biomass: from mass cultivation to dried biomass acquisition

Abstract

Microalgal biomass represents a sustainable bioresource for various applications, such as food, nutraceuticals, pharmaceuticals, feed, and other bio-based products. For decades, its mass production has attracted widespread attention and interest. The process of microalgal biomass production involves several techniques, mainly cultivation, harvesting, drying, and pollution control. These techniques are often designed and optimized to meet optimal growth conditions for microalgae and to produce high-quality biomass at acceptable cost. Importantly, mass production techniques are important for producing a commercial product in sufficient amounts. However, it should not be overlooked that microalgal biotechnology still faces challenges, in particular the high cost of production, the lack of knowledge about biological contaminants and the challenge of loss of active ingredients during biomass production. These issues involve the research and development of low-cost, standardized, industrial-scale production equipment and the optimization of production processes, as well as the urgent need to increase the research on biological contaminants and microalgal active ingredients. This review systematically examines the global development of microalgal biotechnology for biomass production, with emphasis on the techniques of cultivation, harvesting, drying and control of biological contaminants, and discusses the challenges and strategies to further improve quality and reduce costs. Moreover, the current status of biomass production of some biotechnologically important species has been summarized, and the importance of improving microalgae-related standards for their commercial applications is noted.

Keywords: Biological contaminant control; Biomass; Cultivation; Drying; Harvesting; Microalgal biotechnology.

Fig. 1

Milestones in microalgal biotechnology and large-scale cultivation: from natural resources to industrial biomass production and diverse applications

Fig. 2

Schematic diagram of microalgal biomass production. Microalgae are grown in a cultivation unit in an aqueous mineral medium under illumination, and nutrient and carbon source (CO₂, acetate or glucose) supply; subsequently, the biomass is separated from the medium (harvesting) and drying for further application

Fig. 3

Comprehensive evaluation of optimal harvesting techniques for different applications. a Order of suitability of harvesting techniques for various criterions; b order of the most important criterions should be considered for various applications; c order for suitability of harvesting techniques for various applications

Fig. 4

Processes of microalgae harvesting and drying for different end products

Fig. 5

Examples of various biomass production systems for cultivation of commercial microalgae. a, b cultivation facilities (open raceways in greenhouse) of Arthrospira in Erdos (China); c circular ponds for Chlorella cultivation (Sun Chlorella, Japan); d heterotrophic culture facilities for Chlorella; e cultivation of D. salina at Cargill lakes in San Francisco Bay (USA); f D. salina cultivation using open raceway ponds by NBT Co., Ltd. (Eilat, Israel); g open raceways in greenhouse for H. pluvialis cultivation by Green-A (Yunnan, China); h tubular photobioreactors used for H. pluvialis cultivation by Algatech (Israel); i E. gracilis cultivation using circular ponds by Euglena Co., Ltd. (Japan); j a demonstration site for the indoor cultivation of N. sphaeroides in Plateau algal Research Center (China)