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.

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Harvesting techniques applied to microalgae: A review

The present hype in microalgae biotechnology has shown that the topic of photobioreactors has to be revisited with respect to availability in really large scale measured in hectars footprint area, minimization of cost, auxiliary energy demand as well as maintenance and life span. This review gives an overview about present designs and the basic limiting factors which include light distribution to avoid saturation kinetics, mixing along the light gradient to make use of light/ dark cycles, aeration and mass transfer along the vertical or horizontal main axis for carbon dioxide supply and oxygen removal and last but not least the energy demand necessary to fulfil these tasks. To make comparison of the performance of different designs easier, a commented list of performance parameters is given. Based on these critical points recent developments in the areas of membranes for gas transfer and optical structures for light transfer are discussed. The fundamental starting point for the optimization of photo-bioprocesses is a detailed understanding of the interaction between the bioreactor in terms of mass and light transfer as well as the microalgae physiology in terms of light and carbon uptake kinetics and dynamics.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/elsc.200900003

Design principles of photo-bioreactors for cultivation of microalgae.

Due to diminishing petroleum reserves and deleterious environmental consequences of exhaust gases from fossil-based fuels, research on renewable and environment friendly fuels has received a lot of impetus in the recent years. However, the availability of the non-edible crops serve as the sources for biofuel production are limited and economically not feasible. Algae are a promising alternative source to the conventional feedstocks for the third generation biofuel production. There has been a considerable discussion in the recent years about the potential of microalgae for the production of biofuels, but there may be other more readily exploitable commercial opportunities for macroalgae and microalgae. This review, briefly describes the biofuels conversion technologies for both macroalgae and microalgae. The gasification process produces combustible gases such as H2, CH4, CO2 and ammonia, whereas, the product of pyrolysis is bio-oil. The fermentation product of algae is ethanol, that can be used as a direct fuel or as a gasohol. Hydrogen can be obtained from the photobiological process of algal biomass. In transesterification process, algae oil is converted into biodiesel, which is quite similar to those of conventional diesel and it can be blended with the petroleum diesel. This study, also reviewed the production of high value byproducts from macroalgae and microalgae and their commercial applications. Algae as a potential renewable resource is not only used for biofuels but also for human health, animal and aquatic nutrition, environmental applications such as CO2 mitigation, wastewater treatment, biofertilizer, high-value compounds, synthesis of pigments and stable isotope biochemicals. This review is mainly an attempt, to investigate the biorefinery concept applied on the algal technology, for the synthesis of novel bioproducts to improve the algal biofuels as even more diversified and economically competitive. The employment of a high-value, co-product strategy through the integrated biorefinery approach is expected to significantly enhance the overall commercial implementation of the biofuel from the algal technology.

Macroalgae and microalgae as a potential source for commercial applications along with biofuels production: A biorefinery approach

Biodiesel production using enzymatic transesterification – Current state and perspectives

Closed photobioreactors for production of microalgal biomasses.

One of the most important dilemmas of the modern world is to supply enough energy with minimal environmental impact. On this demand bioenergy from renewable biofuels is of growing public and private interest. Recent developments in the scientific researches show that microalgae have potential as a source of bioenergy. With their exception of being one of the oldest residents of the Earth and playing a vital role in building up the atmosphere, microalgae have a variety of diversified strains, biochemical routes and products that can be used for biofuel processing. An increasing number of researchers, academics, entrepreneurs and investors are now working on new technologies to adapt microalgae originated energy into our daily life. The aim of this review is to focus on microalgae based biofuels under the main titles of biodiesel, biohydrogen, bioethanol and biomethane. For evolution in bioenergy that started with the first generation way through the third generation and today stepping on the concept of fourth generation, microalgae will be a good candidate for an alternative energy source.

Microalgae for a macroenergy world

Potential of microalgal compounds in trending natural cosmetics: A review

Exosomes: Large-scale production, isolation, drug loading efficiency, and biodistribution and uptake.

Comparison of tubular and panel type photobioreactors for biohydrogen production utilizing Chlamydomonas reinhardtii considering mixing time and light intensity.

Suphi S. Oncel

Papers

Microalgae for a macroenergy world

Potential of microalgal compounds in trending natural cosmetics: A review

Exosomes: Large-scale production, isolation, drug loading efficiency, and biodistribution and uptake.

Comparison of tubular and panel type photobioreactors for biohydrogen production utilizing Chlamydomonas reinhardtii considering mixing time and light intensity.

Comparison of two different pneumatically mixed column photobioreactors for the cultivation of Artrospira platensis (Spirulina platensis)