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Abstract(s)
O consumo de produtos farmacêuticos tem aumentado nos últimos anos. Parte dos
fármacos consumidos são excretados e permanecem nas águas residuais como substâncias
bioativas. A deteção de alguns fármacos nos efluentes das estações de tratamento de águas
residuais, indica que a tecnologia e os processos utilizados não têm sido eficazes na
remoção destes compostos. Estes fármacos são denominados de poluentes emergentes e
estão associados a efeitos negativos nos ecossistemas aquáticos e na saúde humana
mesmo na ordem dos ng/L. Tendo em conta o problema apresentado, este trabalho
consistiu no estudo da adsorção de poluentes emergentes, nomeadamente, ciprofloxacina
e carbamazepina, em carvão ativado produzido a partir de resíduos de pinha.
O carvão ativado foi produzido por ativação química com hidróxido de potássio, tendose
obtido um material com uma distribuição de tamanho de partícula alargada. A
caracterização textural indica que o material é microporoso (volume de microporos de
0,483 cm3/g) com uma área superficial específica de 1224 m2/g. Verificou-se que
partículas com diâmetro inferior a 0,710 mm possuem uma estrutura porosa mais
desenvolvida do que as partículas com diâmetro superior a 2,0 mm, com valores das áreas
superficiais de 1315 e 971 m2/g, respetivamente.
Para o estudo do equilíbrio de adsorção de ciprofloxacina, verificou-se que o modelo de
Freundlich proporciona um bom ajuste aos dados experimentais, com capacidades de
adsorção experimentais da ordem de 180 mg/g.
No estudo do equilíbrio de adsorção para a carbamazepina, verificou-se que o modelo
que melhor ajusta os dados experimentais é o modelo de Sips, obtendo-se uma capacidade
de adsorção máxima para as partículas menores de 176 mg/g e de 62 mg/g para as
partículas maiores. Na adsorção de carbamazepina em leito fixo foi obtido um tempo de
ruptura baixo, 4 minutos, o que originou uma curva de ruptura com uma forma assimétrica
e atípica, sugerindo que a adsorção da carbamazepina em leito fixo pode ser limitada por
limitações difusionais intraparticulares.
Nos ensaios cinéticos efetuados verificou-se que os dados experimentais foram bem
ajustados pelo modelo de difusão intraparticular de Weber e Morris. Os resultados
sugerem que a adsorção de carbamazepina nas partículas com diâmetro superior a 2,0 mm
é controlada pela difusão intraparticular e para as partículas com diâmetro inferior a 0,710
mm a cinética de adsorção é mais rápida e não é controlada exclusivamente pela difusão
intraparticular. A velocidade de difusão intraparticular de carbamazepina foi maior nas
partículas de diâmetro inferior a 0,710 mm, visto que o valor do coeficiente de difusão
intraparticular foi de 0,79 mg/(g.min2), enquanto que nas partículas mais pequenas o valor
deste coeficiente foi 5,93 mg/(g.min2), ou seja 6,74 vezes superior. Os resultados sugerem
que as características texturais do carvão ativado influenciaram fortemente a adsorção da
carbamazepina. Concluiu-se que a utilização do carvão ativado à base de resíduos de
pinha, com diâmetro de partícula superior a 2,0 mm não é viável para o tratamento de
efluentes em maior escala, devido às limitações difusionais internas e velocidades de
adsorção baixas.
The consumption of pharmaceutical products has increased in recent years. A portion of the consumed pharmaceuticals is excreted and remains in wastewater as bioactive substances. The detection of some pharmaceuticals in the effluents of wastewater treatment plants indicates that the technology and processes used have not been effective in removing these compounds. These pharmaceuticals are referred to as emerging pollutants and are associated with negative effects on aquatic ecosystems and human health at concentrations in the order of ng/L. Considering this issue, this work focused on the study of the adsorption of emerging pollutants, namely ciprofloxacin and carbamazepine, on activated carbon produced from pine cone waste. The activated carbon was produced by chemical activation with potassium hydroxide, resulting in a material with a wide particle size distribution. Textural characterization indicates that the material is microporous (micropore volume of 0.483 cm³/g) with a specific surface area of 1224 m²/g. It was found that particles with a diameter less than 0.710 mm have a more developed porous structure than particles with a diameter greater than 2.0 mm, with specific surface areas of 1315 and 971 m²/g, respectively. For the adsorption equilibrium study of ciprofloxacin, it was found that the Freundlich model provides a good fit to the experimental data, with experimental adsorption capacities of around 180 mg/g. In the adsorption equilibrium study for carbamazepine, the Sips model best fits the experimental data, with a maximum adsorption capacity for the smaller particles of 176 mg/g and 62 mg/g for the larger particles. In the fixed-bed adsorption of carbamazepine, a low breakthrough time of 4 minutes was obtained, resulting in an asymmetric and atypical breakthrough curve, suggesting that the fixed-bed adsorption of carbamazepine may be limited by intraparticle diffusion limitations. Kinetic tests showed that the experimental data were well fitted by the Weber and Morris intraparticle diffusion model. The results suggest that the adsorption of carbamazepine on particles with a diameter greater than 2.0 mm is controlled by intraparticle diffusion, while for particles with a diameter less than 0.710 mm, the adsorption kinetics are faster and not exclusively controlled by intraparticle diffusion. The intraparticle diffusion rate of carbamazepine was higher in particles with a diameter less than 0.710 mm, as the intraparticle diffusion coefficient value for the larger particles was 0.79 mg/(g.min²), while for the smaller particles this coefficient was 5.93 mg/(g.min²), which is 6.74 times higher. The results suggest that the textural characteristics of the activated carbon strongly influenced the adsorption of carbamazepine. It was concluded that the use of activated carbon from pine cone waste, with a particle diameter greater than 2.0 mm, is not feasible for larger-scale wastewater treatment due to internal diffusion limitations and low adsorption rates.
The consumption of pharmaceutical products has increased in recent years. A portion of the consumed pharmaceuticals is excreted and remains in wastewater as bioactive substances. The detection of some pharmaceuticals in the effluents of wastewater treatment plants indicates that the technology and processes used have not been effective in removing these compounds. These pharmaceuticals are referred to as emerging pollutants and are associated with negative effects on aquatic ecosystems and human health at concentrations in the order of ng/L. Considering this issue, this work focused on the study of the adsorption of emerging pollutants, namely ciprofloxacin and carbamazepine, on activated carbon produced from pine cone waste. The activated carbon was produced by chemical activation with potassium hydroxide, resulting in a material with a wide particle size distribution. Textural characterization indicates that the material is microporous (micropore volume of 0.483 cm³/g) with a specific surface area of 1224 m²/g. It was found that particles with a diameter less than 0.710 mm have a more developed porous structure than particles with a diameter greater than 2.0 mm, with specific surface areas of 1315 and 971 m²/g, respectively. For the adsorption equilibrium study of ciprofloxacin, it was found that the Freundlich model provides a good fit to the experimental data, with experimental adsorption capacities of around 180 mg/g. In the adsorption equilibrium study for carbamazepine, the Sips model best fits the experimental data, with a maximum adsorption capacity for the smaller particles of 176 mg/g and 62 mg/g for the larger particles. In the fixed-bed adsorption of carbamazepine, a low breakthrough time of 4 minutes was obtained, resulting in an asymmetric and atypical breakthrough curve, suggesting that the fixed-bed adsorption of carbamazepine may be limited by intraparticle diffusion limitations. Kinetic tests showed that the experimental data were well fitted by the Weber and Morris intraparticle diffusion model. The results suggest that the adsorption of carbamazepine on particles with a diameter greater than 2.0 mm is controlled by intraparticle diffusion, while for particles with a diameter less than 0.710 mm, the adsorption kinetics are faster and not exclusively controlled by intraparticle diffusion. The intraparticle diffusion rate of carbamazepine was higher in particles with a diameter less than 0.710 mm, as the intraparticle diffusion coefficient value for the larger particles was 0.79 mg/(g.min²), while for the smaller particles this coefficient was 5.93 mg/(g.min²), which is 6.74 times higher. The results suggest that the textural characteristics of the activated carbon strongly influenced the adsorption of carbamazepine. It was concluded that the use of activated carbon from pine cone waste, with a particle diameter greater than 2.0 mm, is not feasible for larger-scale wastewater treatment due to internal diffusion limitations and low adsorption rates.
Description
Keywords
Carbamazepine Ciprofloxacin Adsorption Isotherm Adsorption kinetics Carbamazepina Ciprofloxacina Isotérmica de adsorção Cinética de adsorção