Report
Teaser, summary, work performed and final results
Periodic Reporting for period 1 - TASAB (TOWARDS A SUSTAINABLE ALGAL BIOREFINERY)
Teaser
Today, the world’s energy supply is largely based on fossil fuels which represent 80 % of the primary energy consumed. The combustion of fossil fuels contributes to global environmental pollution and climate change. Therefore, investments in renewable energy will lead the...
Summary
Today, the world’s energy supply is largely based on fossil fuels which represent 80 % of the primary energy consumed. The combustion of fossil fuels contributes to global environmental pollution and climate change. Therefore, investments in renewable energy will lead the way out of the economic, energetic and environmental crises that Europe and the world are facing. By promoting renewable energy technologies, we will be able to tackle both the security of energy supply and climate change, while at the same time creating a future-oriented sustainable economy. In this context, the development of a bio-refinery for producing biofuels from algae has received much attention. Algae are considered to be a futuristic raw material for establishing a bio-refinery because of their rapid growth, high biomass yields and their potential to produce multiple products. In addition, their ease of harvest from ponds or closed photobioreactor systems gives them excellent commercial potential as sustainable environmentally-friendly carbon-neutral fuel sources. However, algal biorefineries must overcome a number of hurdles before they can compete in the fuel market and be broadly deployed. These challenges include increasing energy yield, nutrient and resource allocation and use, and the production of co-products to improve the economics of the entire system.
TASAB project aims to maximize energy production and generate value-added products from algae as well as nutrient recovery for microalgae cultivation in order to overcome the techno-economic issues facing the European algal biofuel companies to produce cost-competitive biofuels.
To achieve these challenging goals, TASAB proposes, for the first time, a novel bio-refinery concept, offering an environmentally-sustainable closed system integrating both anaerobic fermentation processes and pyrolysis to increase energy yield and upgrade bio-oil, while recovering high value products and producing activated carbon from biochar. As well, TASAB proposes a closed loop nutrient recycling system to recover nutrients from aqueous phases to be used as alternative fertilizer for algae culture.
Work performed
During the first stage of the project, six commercially grown macroalgae and two microalgae ( were selected to be used as feedstock for dark fermentation, anaerobic digestion and pyrolysis.
The different algae were firstly characterized for their ultimate, proximate and biochemical composition and then used as feedstock for bio-methane and bio-hydrogen production using BMP and BHP, respectively. The results showed that Chlorella vulgaris and Sargassum polycystum had the highest biomethane and biohydrogen potential among the algal biomasses tested.
Secondly, in order to maximize energy recovery from these algae, the solid fraction of digestate derived from anaerobic fermentation processes were separated and used as feedstock for pyrolysis. Firstly, the solid digestate were analyzed to determine their ultimate and proximate composition. Then, thermogravimetric analysis (TGA) was carried out in order to determine the thermal degradation and to understand the chemical and physical properties of algal biomass before and after anaerobic fermentation. The results revealed that TGA of raw algal biomasses and their derived digestate were completely different indicating that the fermentation processes affected strongly the structure and the composition of algae.
In order to investigate the effect of fermentation processes on bio-oil quality, Pyrolysis-Gas Chromatography/Mass-Spectrometry (Py-GC/MS) was used to identify potential high value products from raw algae and their derived digestate. The chemical products obtained during the pyrolysis of the raw algae were mainly composed of anhydro-sugars and furans. However, after dark fermentation the bio-oil of the fermented algae was rather rich in organic acids with acetic acid as the main product. Interestingly, the results of the pyrolysis of the algal digestate resulting from the anaerobic digestion processes showed a high proportion of aromatic compounds which hold a significant use within different industries, from food, cosmetics, pharmaceuticals to petrochemicals.
In addition, the biochar produced from algal biomass were also analyzed and used to recover nutrient from the liquid digestate fraction. The results showed high adsorption efficiencies of the derived macroalgae biochars to remove nitrate and phosphorus due to their high ash content and their mineral composition.
Through the TASAB project we have also aimed to recover more energy from downstream effluents of the integrated process of anaerobic fermentation and pyrolysis. The high soluble organic load in these effluents could be converted into energy using bio-electrochemical systems. Accordingly, these effluents were used as substrate for microbial electrolysis cells.
In addition to energy recovery from wastewater streams, we have also succeeded in recovering nutrients as struvite. In fact, the liquid digestate from both dark fermentation and anaerobic digestion were analyzed to determine the concentration of nutrients. The recovered struvite was analyzed using XRD, FTIR and EDAX to confirm its composition and morphology.
Finally, the recovered struvite, liquid digestate and biochar were used to culture Chlorella and Chlamaydomonas under both mixotrophic and heterotrophic conditions. The microalgae gown using these alternative fertilizers had a high lipid content in comparison to algae grown in TAP medium. Furthermore, different nutrient concentrations, carbon sources and bio-stimulants were used to increase lipids and high value products in these two microalgae. The harvested algae under these different culture conditions represented a good source for biodiesel production.
Final results
TASAB project, is an innovative sustainable algal bio-refinery concept which will tackle environmental, energetic and economic issues covering the restoration of eutrophic surface water, climate change mitigation and waste treatment, to the sustainable production of different biofuels chemicals and fertilizer. TASAB will help to increase the potential of commercialization of European algal bio-refinery by adding new unit operations to the current algal bio-refineries to maximize the energy yield recovered from the organic fraction of algae and to recover the whole mineral fraction as nutrients for algae cultivation. TASAB will generate a new chemical fertilizer industry from algal bio-refineries which will reduce greatly the costs and the environmental concerns associated with the use of external chemical fertilizer. Adding a downstream electrolysis unit is also very innovative to recover energy from the soluble organic fraction contain in the liquid digestate and bio-oil aqueous phase. This unit will maximize the energy yield recovered in comparison to a conventional algal bio-refinery in which the soluble organics are lost in the effluents with potential risk of environmental pollution. Furthermore, TASAB will improve the economic viability of algal bio-refineries by producing high value commodities from pyrolysis that could be sold at a premium and would offset production costs for energy generation. Finally, TASAB will reduce the input costs of the algal bio-refinery while increasing the output energy with high commercial potential and less environmental impact.