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Abstract(s)
O presente trabalho experimental teve como objectivos estudar a tratabilidade dum efluente
lácteo utilizando a técnica de coagulação/floculação e avaliar a possibilidade de utilização do
carvão activado granulado (CAG) Aquasorb 2000 como adsorvente para a remoção de
compostos orgânicos presentes nos efluentes lácteos pré–tratados por
coagulação/floculação, funcionando como um tratamento de polimento.
No estudo da tratabilidade do efluente por coagulação/floculação investigou-se a influência
de determinadas variáveis como o tipo e dose de coagulante e pH, a fim de encontrar as
melhores condições operatórias.
A utilização da referida técnica visou a redução do valor de concentração de alguns
parâmetros: carência química de oxigénio (CQO); fósforo total e turvação, tendo sido
utilizados efluentes desta indústria recolhidos em diferentes datas e após tratamento
biológico, designados por A, B, C e D apresentando características diferentes. Sendo que o
efluente A apresentava valores de CQO, fósforo total e turvação de 500 mg O2/L;32 mg P/L
e 40 NTU respectivamente, o efluente B 1400 mg O2/L; 120 mg P/L e 80 NTU
respectivamente, o efluente C 12300 mg O2/L; 87 mg P/L e 350 NTU respectivamente e o
efluente D 340 mg O2/L; 33 mg P/L e 42 NTU respectivamente. Os coagulantes estudados
foram hidróxido de cálcio (HC), sulfato de alumínio (SA) e tricloreto de ferro (TF).
Verificou-se que o coagulante com maior eficácia nos efluentes estudados foi o TF. As
maiores remoções de CQO, fósforo total e turvação, 89%, 99,9% e 99%, respectivamente,
foram obtidas para o efluente C, com uma dosagem de TF de 4 g/L e com um pH entre 6 e
7. Entre os efluentes estudados este era o que apresentava valores iniciais mais elevados
para qualquer um destes parâmetros.
As melhores percentagens de remoção obtidas com o HC, para a CQO, fósforo total e
turvação foram de 59%, 99% e 91%, respectivamente, com uma dosagem de HC de 1 g/L e
com um pH entre 10 e 11,5 foram conseguidas no tratamento do efluente D, com o qual se
alcançaram também as melhores remoções de CQO, fósforo total e turvação de 65%, 99% e
87%, respectivamente, quando se utilizou o coagulante SA, com uma dosagem de 2 g/L e
com um pH entre 7 e 7,5.
Relativamente ao volume de lamas produzido neste processo pela utilização dos diferentes
coagulantes no tratamento dos efluentes referidos concluiu-se que o coagulante que gera
menor volume de lamas é o HC, sendo o SA aquele que origina um maior volume.
Submeteu-se posteriormente o efluente D, pré-tratado por coagulação/floculação, a um
processo de adsorção em batch utilizando o CAG Aquasorb 2000, onde se conseguiu uma remoção de CQO de 48%, alcançando para este parâmetro o valor de 63 mg O2/L, nas
condições operatórias que correspondem a uma massa de CAG de 12,5 g/L e um tempo de
contacto de 3 horas.
Quanto aos custos associados com os coagulantes, o que menores custos apresenta é o
HC (150 €/ton), seguido pelo TF (250 €/ton) e por ultimo o SA (340 €/ton). Sendo que o
efluente quando tratado com TF e SA é necessário uma correcção do pH do meio para que
estes coagulantes actuem eficazmente, em que essa correcção de pH é realizada com
hidróxido de sódio (540 €/ton).
Realizaram-se ainda estudos de equilíbrio de adsorção com o carvão activado referido e o
azul-de-metileno usando diferentes concentrações deste (50 mg/L; 100 mg/L e 200 mg/L) e
diferentes massas de CAG (0,1g; 0,2g; 0,3g; 0,4g e 0,5g). A temperatura a que se
realizaram estes ensaios foi de 28,7ºC e o volume de azul-de-metileno foi de 200 mL.
Verificou-se que os melhores resultados obtidos foram para uma concentração de adsorvato
de 100 mg/L. Ajustaram-se os modelos de Langmuir e Freundlich às isotérmicas obtidas
tendo correlações mais elevadas para a concentração de 100 mg/L de corante (azul de
metileno), sendo o modelo de Freundlich aquele que melhor se ajustou apresentando uma
correlação quadrática de 0,9744 e os seguintes parâmetros Kf = 6,59 e n = 5,33, enquanto
que o de Langmuir apresentou uma correlação quadrática de 0,9583 e os seguintes
parâmetros qmáx = 83,3 mg/g de adsorvente e K = 20 L/mg de adsorvato..
Verificou-se que a capacidade de adsorção promovida pelo CAG, em relação ao azul-demetileno,
obtida experimentalmente, 83,3 mg/g, é muito inferior à capacidade de adsorção
teoricamente prevista pela ficha técnica deste carvão, 280 mg/g a uma temperatura de 25ºC,
o que pode indiciar que o carvão utilizado não estaria nas melhores condições.
This experimental work has aimed to study the treatability of a dairy wastewater using the technique of coagulation / flocculation and evaluate the possibility of using granular activated carbon (GAC) as adsorbent Aquasorb 2000 for removal of organic compounds in effluent pre-treated milk by coagulation/flocculation, functioning as a polishing treatment. In the study of the treatability of wastewater by coagulation/flocculation investigated the influence of specific variables as the type and dose of coagulant and pH in order to find the best operating conditions. The use of this technique aimed at reducing the concentration value of some parameters: chemical oxygen demand (COD), total phosphorus and turbidity, and were used in this industry effluents collected at different dates and after biological treatment, designated A, B, C and D showing different characteristics. Since the effluent showed values of COD, total phosphorus and turbidity of 500 mg O2/L, 32 mg P/L and 40 NTU respectively, the effluent B 1400 mg O2/L, 120 mg P/L and 80 NTU respectively, the effluent C 12300 mg O2/L, 87 mg P/L and 350 NTU respectively and the effluent D 340 mg O2/L, 33 mg P/L and 42 NTU respectively. The coagulants studied were calcium hydroxide (CH), aluminum sulfate (SA) and iron trichloride (TF). It was found that the coagulant better in the TF effluent was studied. The higher removals of COD, total phosphorus and turbidity, 89%, 99.9% and 99%, respectively, were obtained for the effluent C with a dose of TF 4 g/L and a pH between 6 and 7. Among the studied effluents showed that this was the highest initial values for any of these parameters. The best removal percentages obtained with the HC, for COD, turbidity and total phosphorus were 59%, 99% and 91% respectively, with a dose of HC 1 g/L and a pH between 10 and 11,5 were obtained at the wastewater treatment D, with which it also reached the best removals of COD, total phosphorus and turbidity of 65%, 99% and 87% respectively, when using coagulant SA, with a dosage of 2 g/L and a pH between 7 and 7,5. Regarding the volume of sludge produced by this process using different coagulants in the treatment of these effluents was concluded that the coagulant which generates less sludge volume is the HC, being the one that SA leads to a greater volume. Subsequently underwent the effluent D, pre-treated by coagulation / flocculation, a batch adsorption process using the CAG Aquasorb 2000, which achieved a COD removal of 48% reaching the value for this parameter of 63 mg O2/L, the operating conditions corresponding to a mass of CAG of 12.5 g/L and a contact time of 3 hours. As for the costs associated with the coagulant, which presents the lowest cost is the HC (150 €/ton), followed by TF (250 €/ton) and finally the SA (340 €/ton). Since the effluent when treated with ST and SA is a necessary correction of pH for these coagulants act effectively, that the correction of pH is accomplished with sodium hydroxide (540 €/ton). There were also studies of adsorption equilibrium with the activated carbon and that methylene blue using different concentrations of (50 mg / L, 100 mg / L and 200 mg / L) and different masses of GAC (0,1 g; 0,2 g, 0,3 g, 0,4 g and 0,5 g). The temperature at which it performed these tests was 28.7 ºC and the volume of methylene blue was 200 mL. It was found that the best results were obtained for an adsorbate concentration of 100 mg / L. They set up models of Langmuir and Freundlich isotherms obtained with the highest correlation to the concentration of 100 mg/L of dye (methylene blue), and the Freundlich model that best fit showing a quadratic correlation 0,9744 and the following parameters Kf = 6.59 and n = 5,33, while the Langmuir showed a quadratic correlation 0,9583 and the following parameters qmax = 83.3 mg/g of adsorbent and K = 20 L/mg adsorbate. It was found that the adsorption capacity promoted by the CAG in respect of the methylene blue, experimentally obtained, 83.3 mg / g, well below the theoretical adsorption capacity provided by the sheet of carbon, 280 mg/g temperature of 25 º C, which may indicate that the coal used would not be the best conditions.
This experimental work has aimed to study the treatability of a dairy wastewater using the technique of coagulation / flocculation and evaluate the possibility of using granular activated carbon (GAC) as adsorbent Aquasorb 2000 for removal of organic compounds in effluent pre-treated milk by coagulation/flocculation, functioning as a polishing treatment. In the study of the treatability of wastewater by coagulation/flocculation investigated the influence of specific variables as the type and dose of coagulant and pH in order to find the best operating conditions. The use of this technique aimed at reducing the concentration value of some parameters: chemical oxygen demand (COD), total phosphorus and turbidity, and were used in this industry effluents collected at different dates and after biological treatment, designated A, B, C and D showing different characteristics. Since the effluent showed values of COD, total phosphorus and turbidity of 500 mg O2/L, 32 mg P/L and 40 NTU respectively, the effluent B 1400 mg O2/L, 120 mg P/L and 80 NTU respectively, the effluent C 12300 mg O2/L, 87 mg P/L and 350 NTU respectively and the effluent D 340 mg O2/L, 33 mg P/L and 42 NTU respectively. The coagulants studied were calcium hydroxide (CH), aluminum sulfate (SA) and iron trichloride (TF). It was found that the coagulant better in the TF effluent was studied. The higher removals of COD, total phosphorus and turbidity, 89%, 99.9% and 99%, respectively, were obtained for the effluent C with a dose of TF 4 g/L and a pH between 6 and 7. Among the studied effluents showed that this was the highest initial values for any of these parameters. The best removal percentages obtained with the HC, for COD, turbidity and total phosphorus were 59%, 99% and 91% respectively, with a dose of HC 1 g/L and a pH between 10 and 11,5 were obtained at the wastewater treatment D, with which it also reached the best removals of COD, total phosphorus and turbidity of 65%, 99% and 87% respectively, when using coagulant SA, with a dosage of 2 g/L and a pH between 7 and 7,5. Regarding the volume of sludge produced by this process using different coagulants in the treatment of these effluents was concluded that the coagulant which generates less sludge volume is the HC, being the one that SA leads to a greater volume. Subsequently underwent the effluent D, pre-treated by coagulation / flocculation, a batch adsorption process using the CAG Aquasorb 2000, which achieved a COD removal of 48% reaching the value for this parameter of 63 mg O2/L, the operating conditions corresponding to a mass of CAG of 12.5 g/L and a contact time of 3 hours. As for the costs associated with the coagulant, which presents the lowest cost is the HC (150 €/ton), followed by TF (250 €/ton) and finally the SA (340 €/ton). Since the effluent when treated with ST and SA is a necessary correction of pH for these coagulants act effectively, that the correction of pH is accomplished with sodium hydroxide (540 €/ton). There were also studies of adsorption equilibrium with the activated carbon and that methylene blue using different concentrations of (50 mg / L, 100 mg / L and 200 mg / L) and different masses of GAC (0,1 g; 0,2 g, 0,3 g, 0,4 g and 0,5 g). The temperature at which it performed these tests was 28.7 ºC and the volume of methylene blue was 200 mL. It was found that the best results were obtained for an adsorbate concentration of 100 mg / L. They set up models of Langmuir and Freundlich isotherms obtained with the highest correlation to the concentration of 100 mg/L of dye (methylene blue), and the Freundlich model that best fit showing a quadratic correlation 0,9744 and the following parameters Kf = 6.59 and n = 5,33, while the Langmuir showed a quadratic correlation 0,9583 and the following parameters qmax = 83.3 mg/g of adsorbent and K = 20 L/mg adsorbate. It was found that the adsorption capacity promoted by the CAG in respect of the methylene blue, experimentally obtained, 83.3 mg / g, well below the theoretical adsorption capacity provided by the sheet of carbon, 280 mg/g temperature of 25 º C, which may indicate that the coal used would not be the best conditions.
Description
Keywords
Coagulação/floculação Efluentes lácteos Adsorção CAG Tratamentos de polimento Coagulation / flocculation Dairy effluent Adsorption Polishing treatments
Citation
Publisher
Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto