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Abstract(s)
A presente dissertação apresenta dois grandes objetivos, a análise e otimização da estação de tratamento de águas residuais (ETAR) de uma empresa da indústria dos curtumes, Dias Ruivo Lda., e a redução do consumo de água da mesma, durante a produção. Com o propósito de se analisar a ETAR da empresa teve-se em consideração vários aspetos, nomeadamente os valores limite de emissão (VLE) exigidos por lei no que toca
à descarga de águas residuais nos solos. Assim, numa fase inicial foi necessário proceder à caracterização do efluente em estudo avaliando diferentes parâmetros como: pH, sólidos suspensos totais (SST), carência química de oxigénio (CQO), azoto total e carbono orgânico total (COT). Para este estudo foram recolhidas amostras semanais do efluente bruto e tratado, verificando-se que a eficiência de remoção para os quatro últimos parâmetros foi de 95%, 57%, 37% e 65%, respetivamente. Os parâmetros pH e SST, em comparação com os VLE presentes no TUA – Título Único Ambiental -, que a empresa possui, apresentam valores dentro do esperado, para o efluente tratado. Já no que diz respeito ao valor final da CQO, do azoto total e do COT estes foram de 957 mg O2/L, 62 mg N/L, e 298 mg/L, respetivamente, não sendo possível comparar estes últimos com nenhum valor estabelecido por lei. Para a otimização da ETAR recorreu-se ao estudo de tratamentos adicionais tais como a oxidação com reagente de Fenton, adsorção com carvão ativado e melhoria do arejamento do efluente inicial. No que diz respeito ao tratamento com reagente de Fenton,
este mostrou-se mais eficaz no tratamento da água bruta (água à entrada do tanque 1 da ETAR), do que para a água já tratada pelos processos físico-químicos implementados. Desta forma, obteve-se valores para a eficiência de remoção da CQO e do COT de 70% e 74%, respetivamente, para um pH inicial da reação de 3,5, [H₂O₂] estequiométrica e razão mássica [Fe²⁺ : H₂O₂] = 1:5, que se verificou ser, das condições operatórias testadas, a que conduziu aos melhores resultados. Já no que toca ao tratamento de adsorção com carvão ativado, obteve-se resultados superiores com recurso ao carvão Norit RX 3 do que utilizando o carvão ativado
granulado, sendo a eficiência de remoção da CQO para este tratamento de 95%, referente a 48h de contacto entre o carvão e o efluente tratado na ETAR. Por outro lado, melhorando as condições de arejamento do efluente à entrada da ETAR, verificou-se que em 3h a diminuição da CQO e dos SST já demonstra ser elevada, com valores de 47% e 40%, respetivamente, ao passo que após 48h de arejamento os valores obtidos para a eficiência de remoção foram de 55% para a CQO e 45% para os SST. Por fim, realizou-se uma análise económica para a implementação do tratamento com reagente de Fenton e com carvão ativado. Assim, concluiu-se que para o tratamento usando carvão ativado a máxima eficiência de remoção da CQO é de 95% correspondendo a um gasto de implementação do tratamento de 195 €/ m3 de efluente, enquanto o tratamento com reagente de Fenton apresenta uma eficiência de remoção da CQO de 70% e a necessidade de menores gastos económicos para a sua implementação, necessitando de 11,18 €/m3 de efluente, no que diz respeito aos gastos com reagentes. Analisado o consumo mensal de água da empresa, e com o objetivo de diminuir o elevado consumo verificado, estudou-se a viabilidade de utilização de água tratada na ETAR para a obtenção de couro, selecionando-se três artigos de alta taxa de produção (Natur Batido, Slide e Crust para verniz). Nas etapas de produção correspondentes ao final da 1ª lavagem, final da neutralização e final do tingimento, verificou-se que os ensaios que recorreram à água recirculada da ETAR apresentavam valores de pH semelhantes aos que utilizaram água do poço (procedimento habitual). No entanto, para os valores de SST e CQO, as diferenças foram significativas. Por fim testou-se o couro produzido com os dois tipos de água referida, em termos da distensão da camada de flor e de resistência à tração. Todos os resultados obtidos nos
testes físico-mecânicos encontram-se conforme o mínimo exigido para calçado em pele de bovino, exceto o alongamento na rutura do artigo Crust para verniz, obtido no ensaio que utiliza a água do poço no processo de produção, que demonstra ser inferior ao pretendido. Posto isto, verificou-se que é viável a reutilização da água da ETAR, diminuindo assim o consumo de água utilizado pela empresa e não comprometendo a qualidade e as características do couro produzido.
This dissertation has two main objectives: to analyze and optimize the wastewater treatment plant (WWTP) of a company in the leather industry, Dias Ruivo Lda, and to reduce its water consumption during production. In order to analyze the company's wastewater treatment plant, several aspects were taken into consideration, including the emission limit values (ELVs) required by law for discharging wastewater into the ground. Thus, initially it was necessary to characterize the effluent under study by evaluating different parameters such as: pH, total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen and total organic carbon (TOC). For this study, weekly samples were taken of the raw and treated effluent, and the removal efficiency for the last four parameters was 95%, 57%, 37% and 65%, respectively. The pH and TSS parameters, in comparison with the ELVs contained in the company's Single Environmental Permit, showed values within the expected range for the treated effluent. The final values for COD, total nitrogen and TOC were 957 mg O2/L, 62 mg N/L and 298 mg/L, respectively, and it was not possible to compare these with any values established by law. In order to optimize the WWTP, additional treatments were studied, such as oxidation with Fenton's reagent, adsorption with activated carbon and improved aeration of the initial effluent. With regard to treatment with Fenton's reagent, this proved to be more effective in treating the raw water (water entering tank 1 of the WWTP) than the water already treated by the physical-chemical processes implemented. This resulted in COD and TOC removal efficiencies of 70% and 74%, respectively, for an initial reaction pH of 3.5, a stoichiometric [H₂O₂] and a mass ratio [Fe²⁺: H₂O₂] = 1:5, which, of the operating conditions tested, led to the best results. As for the adsorption treatment with activated carbon, better results were obtained using Norit RX 3 carbon than using granulated activated carbon, with a COD removal efficiency of 95% for this treatment, referring to 48 hours of contact between the carbon and the effluent treated at the WWTP. On the other hand, by improving the aeration conditions of the effluent at the entrance to the WWTP, it was found that in 3 hours the reduction in COD and TSS was already high, with values of 47% and 40% respectively, while after 48 hours of aeration the values obtained for removal efficiency were 55% for COD and 45% for TSS. Finally, an economic analysis was carried out for the implementation of treatment with Fenton's reagent and activated carbon. It was concluded that the maximum COD removal efficiency for treatment using activated carbon is 95%, corresponding to a cost of 195 €/m3 of effluent to implement the treatment, while treatment using Fenton's reagent has a COD removal efficiency of 70% and requires less economic expenditure to implement, requiring 11.18 €/m3 of effluent in terms of reagent costs. Once the company's monthly water consumption had been analyzed, and with the aim of reducing the high consumption, the feasibility of using water treated at the WWTP to produce leather was studied, selecting three articles with a high production rate (Natur Batido, Slide and Crust for varnish). In the production stages corresponding to the end of the 1st wash, the end of neutralization and the end of dyeing, it was found that the tests using recirculated water from the WWTP had pH values similar to those using well water (the usual procedure). However, the differences in TSS and COD values were significant. Finally, the leather produced with the two types of water was tested in terms of the ball burst method and tensile strength. All the results obtained in the physical-mechanical tests were in line with the minimum required for bovine leather footwear, except for the elongation at break of the Crust article for varnish, obtained in the test using well water in the production process, which proved to be lower than desired. That said, it was found that it is feasible to reuse the water from the WWTP, thus reducing the water consumption used by the company and not compromising the quality and characteristics of the leather produced.
This dissertation has two main objectives: to analyze and optimize the wastewater treatment plant (WWTP) of a company in the leather industry, Dias Ruivo Lda, and to reduce its water consumption during production. In order to analyze the company's wastewater treatment plant, several aspects were taken into consideration, including the emission limit values (ELVs) required by law for discharging wastewater into the ground. Thus, initially it was necessary to characterize the effluent under study by evaluating different parameters such as: pH, total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen and total organic carbon (TOC). For this study, weekly samples were taken of the raw and treated effluent, and the removal efficiency for the last four parameters was 95%, 57%, 37% and 65%, respectively. The pH and TSS parameters, in comparison with the ELVs contained in the company's Single Environmental Permit, showed values within the expected range for the treated effluent. The final values for COD, total nitrogen and TOC were 957 mg O2/L, 62 mg N/L and 298 mg/L, respectively, and it was not possible to compare these with any values established by law. In order to optimize the WWTP, additional treatments were studied, such as oxidation with Fenton's reagent, adsorption with activated carbon and improved aeration of the initial effluent. With regard to treatment with Fenton's reagent, this proved to be more effective in treating the raw water (water entering tank 1 of the WWTP) than the water already treated by the physical-chemical processes implemented. This resulted in COD and TOC removal efficiencies of 70% and 74%, respectively, for an initial reaction pH of 3.5, a stoichiometric [H₂O₂] and a mass ratio [Fe²⁺: H₂O₂] = 1:5, which, of the operating conditions tested, led to the best results. As for the adsorption treatment with activated carbon, better results were obtained using Norit RX 3 carbon than using granulated activated carbon, with a COD removal efficiency of 95% for this treatment, referring to 48 hours of contact between the carbon and the effluent treated at the WWTP. On the other hand, by improving the aeration conditions of the effluent at the entrance to the WWTP, it was found that in 3 hours the reduction in COD and TSS was already high, with values of 47% and 40% respectively, while after 48 hours of aeration the values obtained for removal efficiency were 55% for COD and 45% for TSS. Finally, an economic analysis was carried out for the implementation of treatment with Fenton's reagent and activated carbon. It was concluded that the maximum COD removal efficiency for treatment using activated carbon is 95%, corresponding to a cost of 195 €/m3 of effluent to implement the treatment, while treatment using Fenton's reagent has a COD removal efficiency of 70% and requires less economic expenditure to implement, requiring 11.18 €/m3 of effluent in terms of reagent costs. Once the company's monthly water consumption had been analyzed, and with the aim of reducing the high consumption, the feasibility of using water treated at the WWTP to produce leather was studied, selecting three articles with a high production rate (Natur Batido, Slide and Crust for varnish). In the production stages corresponding to the end of the 1st wash, the end of neutralization and the end of dyeing, it was found that the tests using recirculated water from the WWTP had pH values similar to those using well water (the usual procedure). However, the differences in TSS and COD values were significant. Finally, the leather produced with the two types of water was tested in terms of the ball burst method and tensile strength. All the results obtained in the physical-mechanical tests were in line with the minimum required for bovine leather footwear, except for the elongation at break of the Crust article for varnish, obtained in the test using well water in the production process, which proved to be lower than desired. That said, it was found that it is feasible to reuse the water from the WWTP, thus reducing the water consumption used by the company and not compromising the quality and characteristics of the leather produced.
Description
Keywords
Keywords: Leather WWTP Fenton reagent Activated carbon Aeration Water consumption Curtumes ETAR Reagente Fenton Carvão ativado Arejamento Consumo de água