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

Microalgae has been identified as a potential feedstock for biodiesel production since its cultivation requires less cropland compared to conventional oil crops and the high growth rate of microalgae. Research on microalgae oils often are focused on microalgae oil extraction and biomass harvesting techniques. However, energy intensive and costly lipid extraction methods are the major obstacles hampering microalgae biodiesel commercialisation. Direct biodiesel synthesis avoids such problems as it combines lipid extraction techniques and transesterification into a single step. In this review, the potential of direct biodiesel synthesis from microalgae biomass was comprehensively analysed. The various species of microalgae commonly used as biodiesel feedstock was critically assessed, particularly on high lipid content species. The production of microalgae biodiesel via direct conversion from biomass was systematically discussed, covering major enhancements such as heterogeneous catalysts, the use of ultrasonic and microwave- techniques and supercritical alcohols that focus on the overall improvement of biodiesel production. In addition, this review illustrates the cultivation conditions for biomass growth and lipid productivity improvement, the available harvesting and lipid extraction technologies, as well as the key challenges and future prospect of microalgae biodiesel production. This review serves as a basis for future research on direct biodiesel synthesis from modified microalgae biomass to improve profitability of microalgae biodiesel.

Sustainability of direct biodiesel synthesis from microalgae biomass: a critical review.

Biodiesel production from algal biomass is widely considered a sustainable alternative to petroleum fuels, especially in the transportation sector. However, the high energy consumption associated with the harvesting phase poses a significant impediment to the substantial commercialization of algal biodiesel. Centrifugation is among those harvesting methods that have a high efficiency close to 100% but can consume more energy than it produces. This review aims to address possible solutions for the issue of the high energy cost of centrifugation as an efficient harvesting technique. In addition, a detailed overview of the potential types of centrifugation that can be used to harvest microalgae with their pros and cons is provided. The most prevalent centrifugal devices that have been identified to be effectively useful to harvest algal biomass include disc-stack centrifuge, solid-bowl centrifuge, hydrocyclone, tubular centrifuge, and multi-chamber centrifuge. Overall, the analysis showed that centrifugation alone is not suitable for the harvesting of microalgae for biodiesel production. Nevertheless, coupling centrifugation with other harvesting technologies, e.g. with flocculation, as a primary pre-concentration step, can increase the energy output significantly thus, reducing the production cost.

Harvesting of microalgae by centrifugation for biodiesel production: A review

Critical processes and variables in microalgae biomass production coupled with bioremediation of nutrients and CO2 from livestock farms: A review.

The burning of fossil fuels is an unsustainable activity, which is leading to an increase in greenhouse gases (GHGs) emissions and related global warming. Among sustainable energy sources, microalgae represent a promising alternative to fossil fuel and contribute to the achievement of important Sustainable Development Goals (SDGs). In particular, the potential contribution of marine microalgae to sustainable development is large as, among other benefits, they represent a carbon negative energy source and may be applied in many coastal areas around the world. Despite this, significant economic and technological improvements are needed in order to make microalgae biofuels viable on a large scale. This review aims to explore how and to what extent third-generation biofuels (marine microalgae, but also the latest advances in freshwater microalgae) can benefit the realization of these SDGs. From this study we concluded that the production of large-scale marine microalgae biofuels is not yet feasible from the economic perspective at a large scale. However, the cultivation of microalgae in seawater holds great potential for increasing the small to medium viability of this biofuel source. The possibilities for improvement along with the contributions to sustainable development lay the groundwork for continuing to study and apply the potential of sustainable production of microalgae bioenergy.

https://www.mdpi.com/2073-4441/13/10/1373/pdf

Marine Microalgae Contribution to Sustainable Development

Mass harvesting of marine microalgae using different techniques

The production of high-value bioproducts from microalgae biomass has been widely investigated However, their 
production is hindered by the expensive harvesting process To date, flocculation followed by DAF process has been 
accepted as one of the affordable harvesting approaches In this study, the use of DAF technique was attempted to 
harvest marine microalgae Nannochloropsis sp Batch DAF harvesting was carried out using fabricated DAF unit 
equipped with several compartments including separation column, product collecting vessel and rotary skimmer 
Tannin-based biopolymer flocculant, AFlok-BP1 at pH 5 with a concentration of 160 mg/L was used to facilitate the 
flocculation of particles The effects of different saturator pressure at 18, 2, and 22 bar were then evaluated at a 
constant volume of 6 L microalgae culture The effects of different microalgae culture volumes (6, 8 and 10 L) were 
also evaluated at a fixed saturator pressure of 22 bar The highest pressure at 22 bar yielded the best result with the 
highest total solid of 319 ± 001% and a maximum yield of 170 ± 005 g/g (wet basis) The microalgae concentration 
was the lowest (0027 g/L) when 6 L of culture volume was used However, the values were significantly higher when 
the culture volume was increased to 8 and 10 L to approximately 0035 and 0050 g/L, respectively As a conclusion, 
the study provided evidence for the feasibility of DAF technique in harvesting marine microalgae Nannochloropsis sp

/pdf/harvesting-marine-microalgae-nannochloropsis-sp-using-18xvcokji9.pdf

Wan Azlina W.A.K.G.

Papers

Mass harvesting of marine microalgae using different techniques

Harvesting marine microalgae Nannochloropsis sp. using Dissolved Air Flotation (DAF) technique