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Bioremediation of greenhouse effluents using locally isolated microalgal strains
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Abstract(s)
Dada a escassez de recursos de água devido ao impacto humano, quer para agricultura, uso industrial ou uso doméstico, o tratamento de águas contaminadas é de grande prioridade, de modo a certificar que recursos de água potável não sejam consumidos mais rapidamente do que são recuperados, através da adoção de métodos e tecnologias mais sustentáveis para o planeta. De especial interesse é a poluição de águas doces por nitratos com a principal fonte de contaminação sendo o uso de fertilizantes na agricultura, com cerca de metade do azoto usado globalmente sendo para esse fim. As contaminações de água com nitratos têm como possíveis consequências a perda de biodiversidade e eutrofização. Adicionalmente, os fosfatos são um recurso finito que deve ser reciclado para ser sustentável a longo termo. De modo a reduzir o impacto ambiental da agricultura, novos métodos têm sido adotados de modo a reduzir o consumo de água e aumentar a eficiência da produção de culturas. Um desses métodos é a hidropónica, uma forma de agricultura sem solo em que as raízes das plantas são expostas diretamente a uma solução de nutrientes. O método é mais sustentável, uma vez que há uma maior eficiência no uso de água, espaço e nutrientes. Apesar de haver uma melhor eficiência no uso hidráulico, há ainda uma parte da água usada, rica em nutrientes, que não é usada. Existem vários métodos de tratamento de água, sendo a biorremediação uma deles. A biorremediação foca-se no uso de organismos, por exemplo microalgas, no tratamento de águas, uma vez que usam estes nutrientes em excesso para o seu crescimento
Given increasing scarcity of water resources, the treatment of contaminated waters and its efficiency is of high priority, specially removing pollutants from it. A promising methodology is bioremediation, where microalgae are used for the removal of nutrients, being even considered one of the most promising strategies. Samples from hydroponic drainwater were collected from which seven microalgal strains were isolated and identified by DNA extraction, sequencing and phylogenetic inference. Their growth was compared via competition assay, in which Chlorella sp. (CHL) and Pseudochlorella sp. (PSE) strains were the most effective and were selected for further studies. In terms of growth, we found that the two selected strains showed a significantly higher (p<0.05) growth, assessed through optical density (OD=1.03-1.08 when compared to those of other isolated strains (lowest OD=0.31). Several water pretreatment methods were tested: UV radiation, chlorine treatment and filtering, with UV proving to be the most effective. UV radiation was found to improve growth when compared to control group (p<0.05), showing a peak OD of 0.69 for CHL and of 0.58 for PSE, with a 99% nitrate removal for PSE and 62% for CHL, the highest for each strain in both cases. Additionally, the strains were also co-cultivated with Tetradesmus obliquus, a microalgal strain previously studied regarding nutrient removal. Both novel strains were more effective in the bioremediation process, having a higher growth performance than Tetradesmus obliquus reaching higher cell concentrations. Finally, they were cultivated in photobioreactors for scale-up and biomass production. Both strains presented similar growth and nitrate removal. The produced biomass was evaluated for biochemical composition, with both strains presenting similar protein content (14-15%) and PUFAs (42-47%) relative to other microalgae, which may be useful in feed industries. All this adds to the existing body of evidence for the effectiveness of bioremediation using locally bioprospected microalgal strains.
Given increasing scarcity of water resources, the treatment of contaminated waters and its efficiency is of high priority, specially removing pollutants from it. A promising methodology is bioremediation, where microalgae are used for the removal of nutrients, being even considered one of the most promising strategies. Samples from hydroponic drainwater were collected from which seven microalgal strains were isolated and identified by DNA extraction, sequencing and phylogenetic inference. Their growth was compared via competition assay, in which Chlorella sp. (CHL) and Pseudochlorella sp. (PSE) strains were the most effective and were selected for further studies. In terms of growth, we found that the two selected strains showed a significantly higher (p<0.05) growth, assessed through optical density (OD=1.03-1.08 when compared to those of other isolated strains (lowest OD=0.31). Several water pretreatment methods were tested: UV radiation, chlorine treatment and filtering, with UV proving to be the most effective. UV radiation was found to improve growth when compared to control group (p<0.05), showing a peak OD of 0.69 for CHL and of 0.58 for PSE, with a 99% nitrate removal for PSE and 62% for CHL, the highest for each strain in both cases. Additionally, the strains were also co-cultivated with Tetradesmus obliquus, a microalgal strain previously studied regarding nutrient removal. Both novel strains were more effective in the bioremediation process, having a higher growth performance than Tetradesmus obliquus reaching higher cell concentrations. Finally, they were cultivated in photobioreactors for scale-up and biomass production. Both strains presented similar growth and nitrate removal. The produced biomass was evaluated for biochemical composition, with both strains presenting similar protein content (14-15%) and PUFAs (42-47%) relative to other microalgae, which may be useful in feed industries. All this adds to the existing body of evidence for the effectiveness of bioremediation using locally bioprospected microalgal strains.
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Keywords
Microalgae Bioremediation Bioprospection Hydroponics Nitrates