Optimization of flocculation with tannin-based flocculant in the water reuse and lipidic production for the cultivation of Acutodesmus obliquus

Morphology, molecular phylogeny and biomass evaluation of Desmodesmus abundans (Scenedesmaceae-Chlorophyceae) from Brazil

Abstract The biotechnological potential of microalgae has been the target of a range of research aimed at using its potential to produce macromolecules with high added value. Particular focus has been given to biofuels' production, such as biohydrogen, biodiesel, and bioethanol from lipids and carbohydrates extracted from microalgal biomass. Bioprospecting and accurate identification of microalgae from the environment are important in the search for strains with better performance. Methodologies that combine morphology and molecular techniques allow more precise knowledge of species. Thereby, this work aimed to identify the new strain LGMM0013 collected at Iraí Reservoir, located in Paraná state, Brazil, and to evaluate the production of biomass, carbohydrates, and lipids from this new microalgal strain. Based on morphology and phylogenetic tree from internal transcribed spacer (ITS), strain LGMM0013 was identified as Desmodesmus abundans. D. abundans accumulated 1500 mg L-1 of dried biomass after 22 days of cultivation in autotrophic conditions, 50% higher than Tetradesmus obliquus (LGMM0001) (Scenedesmaceae-Chlorophyceae), usually grown in photobioreactors located at NPDEAS at the Federal University of Paraná (UFPR) to produce biomass. Analysis of the D. abundans biomass from showed an accumulation of 673.39 mg L-1 of carbohydrates, 130% higher than T. obliquus (LGMM0001). Lipid production was 259.7 mg L-1, equivalent to that of T. obliquus. Nitrogen deprivation increased the production of biomass and carbohydrates in D. abundans LGMM0013, indicating this new strain greater biomass production capacity.

Innovative microalgae biomass harvesting methods: Technical feasibility and life cycle analysis

In order to ease one of the main challenges of biomass production in wastewater, the harvest stage, this study proposes as main innovations: the comparison of technical and environmental performance of different methods of harvesting biomass which have not been addressed in the literature and the projection of an optimal environmental scenario for biomass harvesting. For this, three harvesting methods were evaluated and compared, namely the gravitational sedimentation (GS) via settling tank, coagulation with tannin followed by gravitational sedimentation (TC/GS), and a biofilm reactor operated in parallel with a settling tank (BR/GS). TC/GS required less time to concentrate the biomass (121.13 g/day); however, the biomass had a higher moisture content (99.02%), which may compromise its direct application for production of most bioproducts and bioenergy, only a dewatering step is recommended. The harvesting methods interfered in biomass characterisation, mainly in carbohydrate content, which was higher in biomass concentrated over time (28-37%) than biomass concentrated in a single day by coagulation (13.8%). The results of the life cycle assessment revealed that in scenarios which included TC/GS methods and the BR/GS presented less environmental impact in relation to only GS. Additionally, the combination of these two methods comprises the best scenario and promises to optimise the harvest of biomass grown in wastewater.

Up-scaling of tannin-based coagulants for wastewater treatment: performance in a water treatment plant

Tannin extracts from the bark of Acacia mearnsii and wood of Schinopsis balansae, commonly known as Quebracho, were employed. These were modified at laboratory sale via the Mannich aminomethylation with formaldehyde and dimethylamine hydrochloride. Some reaction conditions were varied, namely the formaldehyde dosage and reaction time, while keeping the Mannich solution activation time constant, and their influence on the shear viscosity of the created bio-coagulants was evaluated. The effect of the final pH of the products on their shear viscosity was also analyzed. Up-scaling of the Mannich reaction for tannin from South Africa was performed and the procedure developed at 1-L scale was reproducible in upscaled conditions. One example of a modified South Africa tannin and the modified Quebracho tannin was subsequently selected for the treatment of an industrial wastewater and tested for color and turbidity reduction in jar tests. The effluent treatment was carried out in a single and dual system with cationic synthetic flocculation agents of different charge degree. Good turbidity and decoloration results (93 and 89% reduction, respectively) were obtained with the simultaneous introduction of a cationic, 40% charged polyacrylamide, with minimal dosage (5 ppm) of the latter additive. The tannin-based coagulant from Acacia mearnsii was successfully applied in dual system with cationic polyacrylamide flocculant for industrial wastewater treatment at pilot plant scale. It was shown to satisfactorily treat the water and generate less sludge.

Reused Cultivation Water Accumulates Dissolved Organic Carbon and Uniquely Influences Different Marine Microalgae

Reusing growth medium (water supplemented with nutrients) for microalgae cultivation is required for economical and environmentally sustainable production of algae bioproducts (fuels, feed, and food). However, reused medium often contains microbes and dissolved organic matter that may affect algae growth. While the accumulation of dissolved organic carbon (DOC) in reused medium has been demonstrated, it is unclear whether DOC concentrations affect algae growth or subsequent rates of algal DOC release. To address these questions, lab-scale experiments were conducted with three marine microalgae strains, Navicula sp. SFP, Staurosira sp. C323, and Chlorella sp. D046, grown in medium reused up to four times. Navicula sp. and Chlorella sp. grew similarly in reused medium as in fresh medium, while Staurosira sp. became completely inhibited in reused medium. Across the three algae, there was no broad trend between initial DOC concentration in reused medium and algae growth response. Navicula sp. released less DOC overall in reused medium than in fresh medium, but DOC release rates did not decrease proportionally with increased DOC concentrations. Net DOC accumulation was much lower than gross DOC released by Navicula sp. and Staurosira sp., indicating the majority of released DOC was degraded. Additionally, biodegradation experiments with reused media showed no further net decrease in DOC, suggesting the accumulated DOC was recalcitrant to the associated bacteria. Overall, these results suggest that taxa-specific factors may be responsible for algae growth response in reused medium, and that DOC release and accumulation are insensitive to prior cultivation rounds. Choosing an algae strain that is uninhibited by accumulated DOC is therefore critical to ensure successful water reuse in the algae industry.