Microalgae systems - environmental agents for wastewater treatment and further potential biomass valorisation.

Water is the most valuable resource on the planet. However, massive anthropogenic activities generate threatening levels of biological, organic, and inorganic pollutants that are not efficiently removed in conventional wastewater treatment systems. High levels of conventional pollutants (carbon, nitrogen, and phosphorus), emerging chemical contaminants such as antibiotics, and pathogens (namely antibiotic-resistant ones and related genes) jeopardize ecosystems and human health. Conventional wastewater treatment systems entail several environmental issues: (i) high energy consumption; (ii) high CO2 emissions; and (iii) the use of chemicals or the generation of harmful by-products. Hence, the use of microalgal systems (entailing one or several microalgae species, and in consortium with bacteria) as environmental agents towards wastewater treatment has been seen as an environmentally friendly solution to remove conventional pollutants, antibiotics, coliforms and antibiotic resistance genes. In recent years, several authors have evaluated the use of microalgal systems for the treatment of different types of wastewater, such as agricultural, municipal, and industrial. Generally, microalgal systems can provide high removal efficiencies of: (i) conventional pollutants, up to 99%, 99%, and 90% of total nitrogen, total phosphorus, and/or organic carbon, respectively, through uptake mechanisms, and (ii) antibiotics frequently found in wastewaters, such as sulfamethoxazole, ciprofloxacin, trimethoprim and azithromycin at 86%, 65%, 42% and 93%, respectively, through the most desirable microalgal mechanism, biodegradation. Although pathogens removal by microalgal species is complex and very strain-specific, it is also possible to attain total coliform and Escherichia coli removal of 99.4% and 98.6%, respectively. However, microalgal systems' effectiveness strongly relies on biotic and abiotic conditions, thus the selection of operational conditions is critical. While the combination of selected species (microalgae and bacteria), ratios and inoculum concentration allow the efficient removal of conventional pollutants and generation of high amounts of biomass (that can be further converted into valuable products such as biofuels and biofertilisers), abiotic factors such as pH, hydraulic retention time, light intensity and CO2/O2 supply also have a crucial role in conventional pollutants and antibiotics removal, and wastewater disinfection. However, some rationale must be considered according to the purpose. While alkaline pH induces the hydrolysis of some antibiotics and the removal of faecal coliforms, it also decreases phosphates solubility and induces the formation of ammonium from ammonia. Also, while CO2 supply increases the removal of E. coli and Pseudomonas aeruginosa, as well as the microalgal growth (and thus the conventional pollutants uptake), it decreases Enterococcus faecalis removal. Therefore, this review aims to provide a critical review of recent studies towards the application of microalgal systems for the efficient removal of conventional pollutants, antibiotics, and pathogens; discussing the feasibility, highlighting the advantages and challenges of the implementation of such process, and presenting current case-studies of different applications of microalgal systems.

Potential of Microalgae Extracts for Food and Feed Supplementation-A Promising Source of Antioxidant and Anti-Inflammatory Compounds.

Microalgae are known producers of antioxidant and anti-inflammatory compounds, making them natural alternatives to be used as food and feed functional ingredients. This study aimed to valorise biomass and exploit new applications and commercial value for four commercially available microalgae: Isochrysis galbana, Nannochloropsis sp., Tetraselmis sp., and Phaeodactylum tricornutum. For that, five extracts were obtained: acetone (A), ethanol (E), water (W), ethanol:water (EW). The antioxidant capacity (ABTS•+/DPPH•/•NO/O2•-/ORAC-FL) and anti-inflammatory capacity (HBRC/COX-2) of the extracts were screened. The general biochemical composition (carbohydrates, soluble proteins, and lipids) and the main groups of bioactive compounds (carotenoids, phenolic compounds, and peptides) of extracts were quantified. The results of antioxidant assays revealed the potential of some microalgae extracts: in ABTS•+, Nannochloropsis sp. E and Tetraselmis sp. A, E, and P; in DPPH•, Tetraselmis sp. A and E; in •NO, P. tricornutum E and EW; in O2•-, Tetraselmis sp. W; and in ORAC-FL, I. galbana EW and P. tricornutum EW. Concerning anti-inflammatory capacity, P. tricornutum EW and Tetraselmis sp. W showed a promising HBRC protective effect and COX-2 inhibition. Hence, Tetraselmis sp. and P. tricornutum extracts seem to have potential to be incorporated as feed and food functional ingredients and preservatives.

Gloeothece sp. as a Nutraceutical Source-An Improved Method of Extraction of Carotenoids and Fatty Acids.

The nutraceutical potential of microalgae boomed with the exploitation of new species and sustainable extraction systems of bioactive compounds. Thus, a laboratory-made continuous pressurized solvent extraction system (CPSE) was built to optimize the extraction of antioxidant compounds, such as carotenoids and PUFA, from a scarcely studied prokaryotic microalga, Gloeothece sp. Following "green chemical principles" and using a GRAS solvent (ethanol), biomass amount, solvent flow-rate/pressure, temperature and solvent volume-including solvent recirculation-were sequentially optimized, with the carotenoids and PUFA content and antioxidant capacity being the objective functions. Gloeothece sp. bioactive compounds were best extracted at 60 °C and 180 bar. Recirculation of solvent in several cycles (C) led to an 11-fold extraction increase of ß-carotene (3C) and 7.4-fold extraction of C18:2 n6 t (5C) when compared to operation in open systems. To fully validate results CPSE, this system was compared to a conventional extraction method, ultrasound assisted extraction (UAE). CPSE proved superior in extraction yield, increasing total carotenoids extraction up 3-fold and total PUFA extraction by ca. 1.5-fold, with particular extraction increase of 18:3 n3 by 9.6-fold. Thus, CPSE proved to be an efficient and greener extraction method to obtain bioactive extract from Gloeothece sp. for nutraceutical purposes-with low levels of resources spent, while lowering costs of production and environmental impacts.