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Bioremediation of swine wastewater with locally isolated microalgal strains
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Abstract(s)
O crescimento exponencial da população humana tem vindo a colocar muita pressão na gestão adequada de recursos hídricos em vários sectores (ex.: agrícolas, domésticos e industriais). Em particular, a agropecuária tem vindo a ter um aumento de recursos hídricos e de nutrientes para tentar acompanhar o desenvolvimento social e económico.
Tendo em conta a complexidade destes problemas, esta tese tem como objetivo melhorar o tratamento de águas residuais de suinicultura, usando microalgas como uma ferramenta de tratamento de águas. A utilização de microalgas permite captar os nutrientes presentes nas águas residuais, podendo depois a biomassa produzida ser usada em diferentes indústrias. Por outro lado, as águas residuais tratadas apresentam uma carga de nutrientes reduzida ou nula, podendo ser reutilizadas ou descartadas em segurança.
Para o desenvolvimento desta tese, foram selecionadas duas microalgas, Chlorella sp. e Scenedesmus sp. Ambas as espécies de microalgas foram produzidas em três sistemas de produção distintos: fotobiorreatores de coluna de 2 L, raceways pilotos de 600 L e um raceway industrial de 110 m3. No decorrer do trabalho, as condições de crescimento foram otimizadas para cada espécie nos sistemas mencionados, e a performance de ambas as microalgas foi comparada a nível de produção de biomassa e da eliminação de nutrientes de um efluente proveniente de uma suinicultura. Ambas as espécies, Chlorella sp. e Scenedesmus sp., cultivadas no efluente com uma diluição de 1:20 (v/v) nos fotobiorreatores de coluna, registaram concentrações de biomassa bastante relevantes, 2,5 ± 0,4 g/L e 4,6 ± 0,3 g/L, respetivamente. Contudo, as melhoras taxas de remoção de 100 % de amoníaco, 82,8 e 80,3 % de nitratos e 73,2 e 100 % de fosfatos, foram observadas em ambas as respetivas microalgas cultivadas neste sistema de produção, no efluente com uma diluição de 1:10 (v/v), num regime de fed-batch.
Nos raceways pilotos, ambas as microalgas foram cultivadas em regime de fed-batch em efluente diluído a 1:40 (v/v), sendo que a Chlorella sp. atingiu uma concentração de biomassa máxima de 0,77 g/L. Por sua vez, a espécie Scenedesmus sp. atingiu valores máximos de peso seco de 0,38 g/L quando cultivada em Nutribloom® Plus (condição controlo) e 0,24-0,33 g/L quando cultivada em efluente de suinicultura com uma diluição de 1:40 (v/v), em regime de fed-batch. Por fim, a microalga com melhor performance, a Chlorella sp., foi cultivada num raceway industrial em regime semi-contínuo, no qual atingiu um peso seco máximo de 0,96 g/L ao fim de 15 dias de ensaio. No decorrer do ensaio, foram obtidas taxas de remoção de amoníaco, nitratos e fosfatos de 71,99 %, 63,81 % e 95,58 %, respetivamente.
Em termos de composição bioquímica, Chlorella sp. cultivada em efluente diluído 1:22 (v/v) no raceway industrial, apresentou 36,31 ± 1,27 % de proteínas, 5,58 ± 1,25 % de lípidos, 10,83 ± 0,37 % de cinzas e 48,34 ± 1,58 % de glícidos. Tendo em conta esta composição bioquímica, sugere-se que a biomassa apresenta potencial para aplicação no setor da agricultura, nomeadamente para a produção de biofertilizantes e bioestimulantes, como também para a produção de bioetanol, bio-hidrogénio e biogás a partir de fermentação alcoólica, fermentação no escuro e digestão anaeróbica, respetivamente.
Em conclusão, esta tese mostrou que o tratamento de efluentes com microalgas permite reduzir significativamente a carga de nutrientes dos efluentes de suinicultura com a produção simultânea de biomassa de microalgas com um perfil bioquímico relevante.
The exponential growth of the human population has put a lot of pressure on water resources management in various sectors, such as agricultural, domestic, and industrial. Particularly, the agriculture and livestock sectors have been experiencing increased water resources and nutrient usage to accompany social and economic development. Considering the complexity of these problems, this thesis aims to improve swine wastewater treatment using microalgae as a wastewater treatment tool. Microalgae are able to capture the nutrients present in wastewater, and the biomass produced can then be used in different industries, such as the agricultural industry. On the other hand, treated wastewater have a reduced or absent nutrient load and can be safely reused or disposed. For the development of this study, two microalgae strains, Chlorella sp. and Scenedesmus sp., were produced in three different production systems: 2 L-bubble column photobioreactors, 600 L-pilot raceways, and 110 m3-industrial raceway. The growing conditions were optimized for each species in the mentioned systems. The performance of both microalgae strains was compared in terms of biomass production and nutrient reduction from the wastewater. Both Chlorella sp. and Scenedesmus sp. cultivated in 1:20 (v/v) wastewater in bubble column photobioreactors had the best biomass concentration results, 2.5 ± 0.4 g/L and 4.6 ± 0.3 g/L, respectively. However, the best removal rates (100 % of ammonium, 82.8 and 80.3 % of nitrates and 73.2 and 100 % of phosphates) in this production system were observed in both microalgae grown in fed-batch under 1:10 (v/v) diluted effluent. In the pilot-scale raceways, both microalgae strains were cultivated in swine wastewater diluted to 1:40 (v/v). In these production systems, Chlorella sp. cultivated in 1:40 (v/v) wastewater in fed-batch regime reached a maximum biomass dry weight of 0.77 g/L. In contrast, Scenedesmus sp. reached a maximum dry weight value of 0.38 g/L when grown in Nutribloom® Plus (control conditions), and 0.24-0.33 g/L in diluted pig wastewater, in the same growth regime. Finally, the best-performing microalga, Chlorella sp., was cultivated in an industrial-scale raceway using 1:22 (v/v) diluted swine wastewater using a semi-continuous growth mode, reaching a maximum dry weight of 0.96 g/L after 15 days. During this period, maximum removal rates of ammonium, nitrates and phosphate of 71.99 %, 63.81 % and 95.58 %, respectively, were obtained. In terms of biochemical composition, Chlorella sp. grown in 1:22 (v/v) wastewater in the 110 m3-industrial raceway presented 36.31 ± 1.27 % of proteins, 5.58 ± 1.25 % of lipids, 10.83 ± 0.37 % of ashes and 48.34 ± 1.58 % of carbohydrates. The obtained biochemical composition suggests that the biomass holds potential for the development of biofertilizers and bio-stimulants, as well as produce bioethanol, biohydrogen and biogas, through alcoholic fermentation, fermentation in dark and anaerobic digestion, respectively. In conclusion, this work showed that the wastewater treatment using microalgae allows to significantly reduce the nutrient load of swine effluents with the simultaneous production of microalgae biomass with a relevant biochemical profile.
The exponential growth of the human population has put a lot of pressure on water resources management in various sectors, such as agricultural, domestic, and industrial. Particularly, the agriculture and livestock sectors have been experiencing increased water resources and nutrient usage to accompany social and economic development. Considering the complexity of these problems, this thesis aims to improve swine wastewater treatment using microalgae as a wastewater treatment tool. Microalgae are able to capture the nutrients present in wastewater, and the biomass produced can then be used in different industries, such as the agricultural industry. On the other hand, treated wastewater have a reduced or absent nutrient load and can be safely reused or disposed. For the development of this study, two microalgae strains, Chlorella sp. and Scenedesmus sp., were produced in three different production systems: 2 L-bubble column photobioreactors, 600 L-pilot raceways, and 110 m3-industrial raceway. The growing conditions were optimized for each species in the mentioned systems. The performance of both microalgae strains was compared in terms of biomass production and nutrient reduction from the wastewater. Both Chlorella sp. and Scenedesmus sp. cultivated in 1:20 (v/v) wastewater in bubble column photobioreactors had the best biomass concentration results, 2.5 ± 0.4 g/L and 4.6 ± 0.3 g/L, respectively. However, the best removal rates (100 % of ammonium, 82.8 and 80.3 % of nitrates and 73.2 and 100 % of phosphates) in this production system were observed in both microalgae grown in fed-batch under 1:10 (v/v) diluted effluent. In the pilot-scale raceways, both microalgae strains were cultivated in swine wastewater diluted to 1:40 (v/v). In these production systems, Chlorella sp. cultivated in 1:40 (v/v) wastewater in fed-batch regime reached a maximum biomass dry weight of 0.77 g/L. In contrast, Scenedesmus sp. reached a maximum dry weight value of 0.38 g/L when grown in Nutribloom® Plus (control conditions), and 0.24-0.33 g/L in diluted pig wastewater, in the same growth regime. Finally, the best-performing microalga, Chlorella sp., was cultivated in an industrial-scale raceway using 1:22 (v/v) diluted swine wastewater using a semi-continuous growth mode, reaching a maximum dry weight of 0.96 g/L after 15 days. During this period, maximum removal rates of ammonium, nitrates and phosphate of 71.99 %, 63.81 % and 95.58 %, respectively, were obtained. In terms of biochemical composition, Chlorella sp. grown in 1:22 (v/v) wastewater in the 110 m3-industrial raceway presented 36.31 ± 1.27 % of proteins, 5.58 ± 1.25 % of lipids, 10.83 ± 0.37 % of ashes and 48.34 ± 1.58 % of carbohydrates. The obtained biochemical composition suggests that the biomass holds potential for the development of biofertilizers and bio-stimulants, as well as produce bioethanol, biohydrogen and biogas, through alcoholic fermentation, fermentation in dark and anaerobic digestion, respectively. In conclusion, this work showed that the wastewater treatment using microalgae allows to significantly reduce the nutrient load of swine effluents with the simultaneous production of microalgae biomass with a relevant biochemical profile.
Description
Keywords
Microalgas Efluente de suinicultura Chlorella Scenedesmus Tratamento de efluentes