Abstract
This review presents the extractions, characterisations, applications and economic analyses of natural coagulant in separating pollutants and microalgae from water medium, known as microalgae harvesting. The promising future of microalgae as a next-generation energy source is reviewed and the significant drawbacks of conventional microalgae harvesting using alum are evaluated. The performances of natural coagulant in microalgae harvesting are studied and proven to exceed the alum. In addition, the details of each processing stage in the extraction of natural coagulant (plant, microbial and animal) are comprehensively discussed with justifications. This information could contribute to future exploration of novel natural coagulants by providing description of optimised extraction steps for a number of natural coagulants. Besides, the characterisations of natural coagulants have garnered a great deal of attention, and the strategies to enhance the flocculating activity based on their characteristics are discussed. Several important characterisations have been tabulated in this review such as physical aspects, including surface morphology and surface charges; chemical aspects, including molecular weight, functional group and elemental properties; and thermal stability parameters including thermogravimetry analysis and differential scanning calorimetry. Furthermore, various applications of natural coagulant in the industries other than microalgae harvesting are revealed. The cost analysis of natural coagulant application in mass harvesting of microalgae is allowed to evaluate its feasibility towards commercialisation in the industrial. Last, the potentially new natural coagulants, which are yet to be exploited and applied, are listed as the additional information for future study.
Highlights
The fast-developing countries rely heavily on large-scale industrialisation to improve their global economic competitiveness
The usage of natural coagulants derived from plant, animal and microbial sources in industry is a trend of sustainable environmental development in the 21st century
The extraction processes differ for each type of natural coagulant
Summary
The fast-developing countries rely heavily on large-scale industrialisation to improve their global economic competitiveness. Natural coagulant has emerged as a promising solution in microalgae harvesting as it will not create by-product, such as suspended alum residual in microalgae biomass, which is needed to be further removed before lipid extraction. A non-suspended mode of cultivation allows microalgae to grow on the surface to form a biofilm It is more commercially feasible because the harvesting process of microalgae biomass will be easier. Natural coagulant is an emerging solution to green and sustainable water treatment Besides microalgae harvesting, it has been utilised on various new sectors, for example, electro-coagulation in microbial fuel cell system to precipitate heavy metals for self-power system [5]. Natural coagulants derived from plants, microorganism and animals are reviewed for their extractions, characterisations and applications in microalgae harvesting. Cost analysis of natural coagulant for large scale application in industrial is carried out to provide an appropriate platform for future researchers to intensify on microalgae harvesting by using these natural materials
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