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 harvesting techniques: A review.

Membrane technology in microalgae cultivation and harvesting: a review.

In recent years, biodiesel production has grabbed significant attention due to the awareness of fossil fuel exhaustion. Microalgae become interested feedstock candidate of biodiesel production as they have rapid growth rate and high oil content compared to crops. Efforts have been made to increase microalgae productivity and oil content. To investigate the potential of microalgae for biodiesel production, it is essential to knowledge if the microalgae oil is qualified as possible feedstock oil. Moreover, what would be the energy and environmental effect of the production? And whether the production cost would be reasonable? This paper compared the properties of microalgae oil with traditional biodiesel production oils (vegetable oils); the properties of the biodiesel produced from microalgae and vegetable oils; reviewed the net energy ratio (energy output to energy input), GHG emissions, and economic analysis of the process of biodiesel production from microalgae; as well as discussed the factors which would influent the energy, environment, and cost of the process.

The potential of microalgae in biodiesel production

Microalgae are a promising renewable feedstock for a diverse number of products such as fuels, fine chemicals, nutraceuticals, and cosmetics. The extraction and processing of biochemicals from microalgae require the handling of large volumes of feedstock, largely due to the small biomass to liquid ratio, typically This work reviews the developments in microalgae harvesting and details the underlying phenomena of each technology in relation to key physical parameters such as: size, morphology, surface charge, and density. A critical appraisal of each method is given in relation to biomass concentration, biomass recovery, energy consumption and integration into a biorefinery approach. Finally, we detail four microalgae harvesting case studies from pilot-plants across Northwest Europe. The case studies are: (1) membrane filtration of Scenedesmus sp. used for protein, carbohydrate and lipid extraction; (2) synergetic harvesting of cyanobacteria by autoflocculation and passive capillary dewatering for the production of bioactive extracts; and, (3) bioflocculation and filtering of wastewater-grown microalgae for the production of shrimp feed, biogas and fertilizer. Overall, this review highlights that there is considerable scope for further innovation in harvesting processes, especially with synergistic interactions that exploit multiple physical and chemical properties simultaneously.

Harvesting of microalgae within a biorefinery approach: A review of the developments and case studies from pilot-plants

https://www.tpbin.com/Uploads/Subjects/02af3fca-54c0-44d0-bd0e-e7ec3cee0858.pdf

Benchmark study on algae harvesting with backwashable submerged flat panel membranes

The environmental sustainability of microalgae as feed for aquaculture: a life cycle perspective.

The environmental sustainability of microalgae production for aquaculture purposes was analyzed using exergy analysis (EA) and life cycle assessment (LCA). A production process (pilot 2012, 240 m(2)) was assessed and compared with two upscaling scenarios (pilot 2013, 1320 m(2) and first production scale 2015, 2.5 ha). The EA at process level revealed that drying and cultivation had the lowest efficiencies. The LCA showed an improvement in resource efficiency after upscaling: 55.5 MJ(ex,CEENE)/MJ(ex) DW biomass was extracted from nature in 2012, which was reduced to 21.6 and 2.46 MJ(ex,CEENE)/MJ(ex) DW in the hypothetical 2013 and 2015 scenarios, respectively. Upscaling caused the carbon footprint to decline by factor 20 (0.09 kg CO2,eq/MJ(ex) DW in 2015). In the upscaling scenarios, microalgae production for aquaculture purposes appeared to be more sustainable in resource use than a reference fish feed (7.70 MJ(ex,CEENE) and 0.05 kg CO2,eq per MJ(ex) DW).

The environmental sustainability of microalgae as feed for aquaculture: a life cycle perspective

Bulk cultivation of microalgae in large scale production systems is subject to high production costs. Recycling of growth medium contributes to reducing water, nutrient and salt expenditure, and hence to increase both the economic viability and sustainability of microalgae production systems. In this study it was shown that, upon algae harvesting by means of centrifugation, spent broth from a Nannochloropsis sp. production system can be treated by means of microfiltration and reapplied as rejuvenated growth medium without negatively influencing subsequent growth. During recirculation of growth medium, nutrients consumption rates were documented and used to adjust the medium recipe to enable long term medium recirculation. An 80% recycle rate could be maintained for 167 days during a course of ten production runs, translating into a decrease in nutrient, salt and water expenditure of 44%, 74% and 80%, respectively. The potential for long term reuse of medium for monocultures of multiple economically interesting species should be assessed in future research to evaluate the broad applicability of medium re-use in microalgae cultivation.

Reuse of rejuvenated media during laboratory and pilot scale cultivation of Nannochloropsis sp.

Reuse of growth medium after biomass harvesting is a cost-saving approach to improve the economic feasibility of algae mass cultivation. Algal exudates, cell debris and varying amounts of residual nutrients, impose challenges to the recycling of spent medium. In this study, the potential of combining reused medium from different algae species for growing monocultures of other algal strains was evaluated by making use of three successive cultivation setups with increasing volume; 400 mL in turbidostat mode, 2.6 L and 220 L in semi-continuous mode. Cultivation on replenished medium derived from Nannochloropsis sp. and Tisochrysis lutea, had no adverse effect on the productivity of either of the strains, regardless of whether they were grown in their own recycled medium or that of the other alga. Microfiltration of the reused medium proved to be sufficient to avoid cross-contamination. Moreover, a substantial average reduction in water footprint (77%) and nutrient cost (68% or 9 €·kg−1 dry biomass) was achieved. Extension and validation of the medium recycling approach to other economically interesting algae species can contribute to improving the economic feasibility of large scale microalgae production systems.

Luc Roef

Papers

Benchmark study on algae harvesting with backwashable submerged flat panel membranes

The environmental sustainability of microalgae as feed for aquaculture: a life cycle perspective.

The environmental sustainability of microalgae as feed for aquaculture: a life cycle perspective

Reuse of rejuvenated media during laboratory and pilot scale cultivation of Nannochloropsis sp.

Combining medium recirculation with alternating the microalga production strain: a laboratory and pilot scale cultivation test