Digital library

Three species of macroalgae were treated with the aim of reducing nitrogen, sulfur and ash within the biomass prior to hydrothermal processing. The treatments were the nutrient starvation of cultures and post-harvest washing of biomass in freshwater. Subsequently, hydrothermal liquefaction (HTL) of macroalgae was carried out in a batch reactor heated for 8 min with a maximum temperature of 345 °C. Nutrient starvation effectively reduced nitrogen and sulfur levels within the biomass, which led to a reduction in nitrogen by 51–59 wt.% and sulfur by 64–88 wt.% within the biocrude. The yield of biocrude was highest for Derbesia at 38.6–41.7 wt.% and Oedogonium at 35.6–38.8 wt.% when not starved, but was reduced by up to 19 wt.% when the biomass was starved. The washing of biomass consistently reduced the ash content for all species by 7–83 wt.%. The removal of ash affected neither the quality nor the quantity of biocrude produced. The two treatments demonstrate that macroalgal biomass can be effectively manipulated in the production process to modify the composition of the feedstock and, consequently, improve the quality of biocrude. Additionally, reducing the ash content of biomass minimizes its potential impact on HTL processing equipment.

The global aquaculture industry continues to grow rapidly, and it is important to improve sustainability through effective treatment of its waste products. Seaweeds have been used in Integrated Multi-Trophic Aquaculture (IMTA) systems as an effective tool to reduce the nutrient burden of the fish farm effluents. Species of the genus Asparagopsis armata are successful nitrogen biofilters of flow-through fish aquaculture systems because of their high capacity to take up ammonium, the main metabolic waste product of fish. However, the potential of A. armata as a biofilter of recirculating aquaculture systems (RAS), where effluents have higher concentration of nitrate than ammonium, is unknown. In this study, a series of experiments were designed to evaluate the preference and the uptake rates of nitrogen in the forms of ammonium, nitrate and amino acids, as well as the effect of the different nitrogen forms on the growth rates of A. armata. Nitrogen uptake rates were quantified based on the incorporation of 15N-labeled ammonium, nitrate and amino acids in the tissues, during the internally controlled phase, when uptake rates are stabilized and relatively constant. Our results revealed that inorganic and organic nitrogen sources can be simultaneously taken up by A. armata. The species exhibited a clear preference of ammonium over the two other forms of nitrogen (nitrate and amino acids), either when supplied separately or in combination. Notably, in the presence of multiple sources, amino acids were taken up at faster rates than nitrate by A. armata. The species showed a limited capacity to use nitrate when other nitrogen forms were present in the medium. The availability of the different nitrogen forms in the growth medium did not influence the growth rate of A. armata, either when these were supplied alone or in combination, and growth rates did not show an increasing pattern with nutrient concentration. This study confirms that A. armata is a suitable seaweed to be used as a biofilter in IMTA systems. 

In order to investigate the antioxidant properties of the polysaccharides from the brown alga Sargassum fusiforme, the crude polysaccharides from S. fusiforme (SFPS) were extracted in hot water, and the lipid peroxidation inhibition assay exhibited that SFPS possessed a potential antioxidant activity. Hence, two purely polymeric fractions, SFPS-1 and SFPS-2 were isolated by the column of DEAE (2-diethylaminoethanol)-Sepharose Fast Flow, with their molecular weights of 51.4 and 30.3 kDa determined by high performance gel permeation chromatography (HPGPC). They were preliminarily characterized using chemical analysis in combination of infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies and found to contain large amounts of uronic acids and β-glycosidical linkages. The antioxidant activities of these two SFPS fractions were evaluated using superoxide and hydroxyl radical-scavenging assays. The results show that the antioxidant ability of SFPS-2 was higher than that of SFPS-1, probably correlating with the molecular weight and uronic acid content.

Algae are considered as a promising alternative fuel to produce energy due to its advantages such as high production yield, short growth cycle and flexible growing environment. Unfortunately, ash-related issues restrict its thermochemical utilization due to the high ash content and especially the high alkali metal concentration. In this paper, the gasification performance and ash behavior were experimentally analysed for three macro- and micro-algal species. Clear differences in the proximate and ultimate compositions were found between the cultivated algae used in this study and macroalgae (seaweed) harvested from the marine environments. Algal biomass generally contained higher Na and P contents than lignocellulosic biomass. Microalgae also had a relatively high mineral content due to the impurities in the harvesting process which included centrifugal pumping followed by sedimentation. Co-gasification of 20 wt% algae with softwood was investigated using an entrained flow reactor. The addition of both macroalgal species Derbersia tenuissima and Oedogonium to softwood had a limited influence on the gas yields and carbon conversion. On the other hand, the addition of the microalgal species Scenedesmus significantly decreased the main gas yields and carbon conversion. Moreover, the addition of algae clearly changed the residual ash composition of the base fuel. Finally, a preliminary understanding of the ash behavior of the tested algae blends was obtained through the analysis of the fuel ashes and the collected residual ashes. Fouling and corrosion were presumably occurred during the co-gasification of wood/macroalgae blends in view of the high alkali metal content. Microalga Scenedesmus had a high mineral content which could potentially capture the alkali metal in the ash and mitigate fouling when gasified with softwood. The growing environment and harvesting method were found to be significantly affecting the ash behavior implying the need for careful consideration regarding co-gasification process.