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Tratamento terciário de águas residuais urbanas por microalgas: efeito do tempo de retenção hidráulico e suplementação do CO2
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Abstract(s)
O aumento da pressão antrópica sobre os recursos hídricos e ocorrências de
fenómenos relacionados com as alterações climáticas têm causado cada vez mais períodos de
escassez de água. Urge assim a necessidade de encontrar soluções mais económicas e
eficientes para o tratamento de águas residuais, capazes de permitir a sua reutilização. O
tratamento de Águas Residuais Urbanas (ARU) por microalgas é uma das soluções de
tratamento que tem vindo a ser estudada desde há vários anos. É uma alternativa atrativa aos
métodos convencionais de tratamento das ARU, pois fornece uma biomassa com potencial de
valorização para a produção de biocombustíveis como biogás e bioetanol, e biofertilizantes,
entre outros.
Este estudo teve como objetivos: testar a capacidade de tratamento do sistema de
reatores piloto GreenDune®, usando dois TRH (1 e 2d) em duas estações do ano (verão e
outono), e a valorização da biomassa obtida; e à escala laboratorial, testar os benefícios da
suplementação com CO2 no tratamento terciário de ARU. Após o estudo confirmou-se que,
tanto para o TRH 1d como para o TRH 2d em ambas as estações do ano, o sistema conseguiu
cumprir com os parâmetros impostos por lei, com uma remoção de nutrientes de azoto e
fósforo (NH4+, PO43-, NO3-) entre 48 – 85 %, produzindo maior quantidade de biomassa na
campanha de verão. No que diz respeito à valorização da biomassa obtida, a sua elevada
percentagem de cinzas limita a aplicação em processos de transformação, como a produção de
biocombustíveis, sugerindo-se a sua valorização como biofertilizante. À escala laboratorial,
foram realizadas experiências em semi-contínuo suplementadas com diferentes quantidades
de CO2 (6, 12 e 24 ml min-1, durante 1 min). Para a condição de 12 ml min-1, foi possível
verificar um aumento na produção de biomassa em cerca de 50 %, em relação ao controlo.
Para além da maior produção de biomassa, constata-se um aumento significativo nos níveis
de lípidos, hidratos de carbono e proteínas, sendo estes compostos fundamentais na
valorização da biomassa produzida.
Concluindo, o trabalho realizado apresenta informações relevantes para o tratamento
terciário de ARU utilizando blooms naturais de microalgas e para a valorização da biomassa
resultante.
The increase in anthropogenic pressure over the water resources, together with climate change, have increased the periods of water scarcity. Therefore, there is an urgent need to find ecohydrological solutions that are more economical and efficient, capable of allowing the use and reuse of wastewater. The treatment of Urban Wastewater (UWW) by microalgae is one of the treatment solutions that has been studied for several years. They are an alternative to the conventional method of WWT, providing a biomass with potential for recovery as biofuels (biodiesel, biogas or bioethanol) or as biofertilizers. This study aimed, to test the capacity of the pilot GreenDune® photobioreactors, using two TRH (1 and 2d) during two seasons of the year (summer and autumn), for tertiary wastewater treatment and recovery. On a laboratory scale, the benefits of supplementation with CO2 in the tertiary treatment of ARU were assessed. After the study, it was confirmed that, for both TRH 1d and TRH 2d in both seasons, the system was able to remove 48-85% of the nitrogen and phosphorus nutrients (NH4 +, PO43-, NO3 -). The system produced higher amounts of biomass in the summer season although its valorization potential for biofuels was limited by the high percentage of ash. It is, therefore, proposed that the biomass is valued as a biofertilizer. On a laboratory scale, experiments of tertiary treatment of the real wastewater with a microalgal consortia obtained from the WWTP, supplemented with different amounts of CO2 (6, 12 and 24 ml min-1, for 1 min.) were performed using a semi-continuous cultivation mode. Supplementation with 12 ml min-1 of CO2 led to an increase in biomass production of about 50%, compared to the control. In addition to the increased production of biomass, there is a significant increase in the levels of lipids, carbohydrates, and proteins, which are fundamental for the valorization of the biomass. In conclusion, the work carried out presents relevant information for the tertiary treatment of ARU using natural microalgae blooms and for the valorization of the resulting biomass.
The increase in anthropogenic pressure over the water resources, together with climate change, have increased the periods of water scarcity. Therefore, there is an urgent need to find ecohydrological solutions that are more economical and efficient, capable of allowing the use and reuse of wastewater. The treatment of Urban Wastewater (UWW) by microalgae is one of the treatment solutions that has been studied for several years. They are an alternative to the conventional method of WWT, providing a biomass with potential for recovery as biofuels (biodiesel, biogas or bioethanol) or as biofertilizers. This study aimed, to test the capacity of the pilot GreenDune® photobioreactors, using two TRH (1 and 2d) during two seasons of the year (summer and autumn), for tertiary wastewater treatment and recovery. On a laboratory scale, the benefits of supplementation with CO2 in the tertiary treatment of ARU were assessed. After the study, it was confirmed that, for both TRH 1d and TRH 2d in both seasons, the system was able to remove 48-85% of the nitrogen and phosphorus nutrients (NH4 +, PO43-, NO3 -). The system produced higher amounts of biomass in the summer season although its valorization potential for biofuels was limited by the high percentage of ash. It is, therefore, proposed that the biomass is valued as a biofertilizer. On a laboratory scale, experiments of tertiary treatment of the real wastewater with a microalgal consortia obtained from the WWTP, supplemented with different amounts of CO2 (6, 12 and 24 ml min-1, for 1 min.) were performed using a semi-continuous cultivation mode. Supplementation with 12 ml min-1 of CO2 led to an increase in biomass production of about 50%, compared to the control. In addition to the increased production of biomass, there is a significant increase in the levels of lipids, carbohydrates, and proteins, which are fundamental for the valorization of the biomass. In conclusion, the work carried out presents relevant information for the tertiary treatment of ARU using natural microalgae blooms and for the valorization of the resulting biomass.
Description
Keywords
Águas Residuais Urbanas Biofixação de CO2 Bio-remoção de nutrientes Microalgas Tratamento terciário