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.
