Harvesting techniques applied to microalgae: A review

Abstract

Research studies on microalgae have increased in the last decades due to the wide range of applications associated to these photosynthetic microorganisms. Microalgae are an important source of oils and other biomolecules that can be used in the production of biofuels and high-valued products. However, the use of microalgae in these green processes is still not economically viable. One of the main costs associated to microalgal production is related to the harvesting process, as it usually accounts for about 20-30% of total cost. Therefore, this review focuses on the main harvesting processes applied to microalgae, presenting the main advantages and disadvantages of each method, to allow the selection of an appropriate procedure to effectively separate microalgal biomass from the culture medium. To reduce the associated costs, it is common to harvest microalgae in a two-step separation: (i) thickening procedures, in which microalgal slurry is concentrated to about 2-7% of total suspended solids; and (ii) dewatering procedures, which result in the concentration of microalgal slurry to 15-25% of total suspended solids. Selection of the adequate harvesting methods depends on the characteristics of the target microorganism and also on the type and value of the end product.

Recycling Nannochloropsis oceanica culture media and growth inhibitors characterization

“…Although sedimentation and flotation are commonly used as algae harvesting methods on a large scale, valuable nutrients are removed with the algal biomass in these processes, which lowers the value of the recycled media. The residual coagulants in the recycled media are also problematic for algae growth [18]. Membrane separation could successfully avoid the above disadvantages [19] and provides purified media which is the most suitable for reuse for the subsequent cultivation of microalgae [20].…”

Research on Harvesting of Microalgae Chlorella Sp. By Electrochemical Flotation Method Using Corrosive Electrodes

“…Microalgae can be used as feedstock for the production of biofuels such as biodiesel, biomethane, bioethanol, biohydrogen and biobutanol [1,2] also can be used in the synthesis of different high-valued compounds, such as supplements for animal and aquaculture feed, cosmetics and pharmaceuticals [2]. Regarding the environment, microalgae can play an important role in treatment of wastewater also carbon dioxide sequestration [3,4].…”

“…However, the use of microalgae in these green processes is still not economically viable. One of the main costs associated to microalgal production is the harvesting one, as it usually accounts for about 20-30 % of total cost [1]. Microalgae can be harvested by a number of methods such as sedimentation, flocculation, flotation, centrifugation and filtration or a combination of any of these [1,5].…”

“…Centrifugation is an efficient technique but the high energy consumption makes it unsuitable for microalgal products of a low cost. Chemical flocculation and filtration are inefficient and time consuming methods for harvesting of small size microalgae [1].…”

Biofuels from Microalgae, A Promising Alternative

“…Barros et al showed in their investigation that biomass recovery efficiency above 90% of Dunaliella tertiolecta microalgae was reached when the pH was brought to values of 10.5 by adding of NaOH. It can be due to neutralization of the charges present at the microalgae surface with consequent formation of large aggregates and subsequent sedimentation [3]. Furthermore, this low cost harvesting method allows reuse the culture medium by pH neutralization.…”