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Abstract(s)
A indústria têxtil é um dos principais setores socioeconómicos a nível mundial. Apesar de suprir algumas necessidades básicas do homem, a indústria têxtil é vista como sendo um setor problemático para o meio ambiente, quer pelo elevado consumo de água, quer por gerar um grande volume de efluentes líquidos. Embora a reutilização de efluentes tratados em novos processos de tingimento tenha vindo a ser abordada para promover a utilização sustentável da água na indústria têxtil, as tecnologias convencionais nem sempre fornecem resultados satisfatórios, isto é, os efluentes tratados com a qualidade necessária para a sua reutilização, principalmente devido à presença de corantes e de uma elevada salinidade. Além disso, muitos dos produtos auxiliares do tingimento das fibras, como agentes igualizadores, dispersantes, humectantes, etc., não são consumidos durante o processo de tingimento, e acabam no efluente final, conferindo-lhe, em alguns casos, elevada toxicidade. Assim, para que o seu reaproveitamento seja economicamente viável, é necessário desenvolver processos de tratamento eficientes, que levem a efluentes tratados com a qualidade mínima necessária para o seu reaproveitamento. Neste contexto, os processos de oxidação eletroquímica (OE) são considerados uma tecnologia de tratamento de águas residuais bastante promissora para o tratamento de efluentes têxteis.
O trabalho apresentado nesta tese teve como objetivo principal avaliar o uso da oxidação eletroquímica, com ânodos de diamante dopado com boro (BDD), para o tratamento de efluentes de processos de tingimento de lã e posterior reutilização em novos processos de tingimento. Foi estudada a reutilização de efluentes de tingimento de lã tratados por OE usando (i) o corante ácido Azul Telon® RR, pertencente à classe das antraquinonas, e (ii) uma mistura tricrómica de corantes Nylosan®: Vermelho N-2RBL, Amarelo N-3RL e Azul N-GL Mix. Para os dois casos foi avaliada a influência do uso de efluentes tratados com diferentes qualidades (elevada e moderada) na qualidade do tingimento de tecidos de lã. No caso em que se usou a mistura tricrómica de corantes Nylosan®, foi também avaliada a ecotoxicidade durante os ciclos de reutilização.
Paralelamente ao estudo de reutilização dos banhos de tingimento, foi determinada experimentalmente, pelo método de equilíbrio, a variação com a temperatura da solubilidade em água de dois corantes usados na indústria têxtil, o corante reativo Vermelho-Brilhante Levafix E-4B e o Azul Telon® RR. Para o Azul Telon® RR, foi ainda estudada a influência, na sua solubilidade, a 25 ºC, da presença dos auxiliares de tingimento sulfato de sódio e Avolan® UL 75.
Os principais resultados obtidos nos estudos de reutilização permitiram concluir que, no caso do corante Azul Telon® RR, os efluentes de tingimento tratados por OE com um ânodo de BDD têm uma influência positiva no processo de tingimento, fazendo aumentar a afinidade entre o corante e a fibra. Assim, mesmo após uma redução de 15% na quantidade de corante necessária para a realização de tingimentos com efluente tratado (60 mA cm−2; 6 h) foi alcançada uma diferença de cor (ΔE*) de 1,19, que cumpre os requisitos menos restritivos para a qualidade do tingimento. Por outro lado, quanto maior o estado de oxidação da matéria orgânica existente no efluente tratado, maior é a adsorção do corante pela fibra. Contudo, para a obtenção de um efluente num estado de oxidação superior é necessário aumentar a intensidade de corrente aplicada ou o tempo de tratamento, o que se traduz num custo energético mais elevado. Em relação à solidez à lavagem dos tecidos tingidos com um banho feito à base de água ou de efluente de tingimento tratado, concluiu-se que não há diferenças significativas no tecido multifibra tingido com os dois tipos de banho.
Em relação aos estudos efetuados com a mistura tricrómica de corantes Nylosan®, o desempenho dos processos de tingimento que utilizaram águas residuais tratadas de qualidade moderada (obtida nos ensaios a 60 mA cm−2) ou elevada (obtida nos ensaios a 100 mA cm−2) conduziram a amostras de tecidos tingidos com valores de ΔE* de 1,0 e com solidez da cor à lavagem semelhante à obtida pelos tecidos do tingimento utilizando água, de onde se retira, mais uma vez, a conclusão que para o reaproveitamento eficiente de efluentes de tingimento têxtil não é necessária uma água de elevada qualidade. Os estudos de ecotoxicidade para Daphnia magna efetuados ao longo destes ensaios mostraram que, durante a reutilização dos efluentes, não há aumento da ecotoxicidade, havendo mesmo uma redução, o que permite uma reutilização mais exaustiva do efluente tratado.
Assim, de um modo geral, e embora sejam necessários mais estudos, tudo aponta para que a OE seja um processo a ter em conta no que concerne à reutilização dos banhos de tingimento pela indústria têxtil.
The textile industry is one of the main socio-economic sectors worldwide. Despite supplying some basic human needs, the textile industry is seen as a problematic sector for the environment, either because of the high consumption of water or because it generates a large volume of liquid effluents. Although the reuse of treated effluents in new dyeing processes has been approached to promote the sustainable use of water in the textile industry, conventional technologies do not always provide satisfactory results, that is, treated effluents with the necessary quality for their reuse, mainly due to the presence of dyes and high salinity. In addition, many of the fiber dyeing auxiliary products, such as equalizing, dispersing, wetting agents, etc., are not consumed during the dyeing process, and end up in the final effluent, giving it, in some cases, high toxicity. Thus, for its reuse to be economically viable, it is necessary to develop efficient treatment processes that lead to treated effluents with the minimum quality necessary for their reuse. In this context, electrochemical oxidation (OE) processes are considered a very promising wastewater treatment technology for the treatment of textile effluents. The work presented in this thesis had as main objective to evaluate the use of electrochemical oxidation, with boron-doped diamond (BDD) anodes, for the treatment of effluents from wool dyeing processes and subsequent reuse in new dyeing processes. The reuse of wool dyeing effluents treated by OE was studied using (i) the acid dye Blue Telon® RR, belonging to the anthraquinone class, and (ii) a trichrome mixture of Nylosan® dyes: Red N-2RBL, Yellow N-3RL and Blue N-GL Mix. For both cases, the influence of the use of treated effluents with different quality (high and moderate) on the quality of the dyeing of wool fabrics was evaluated. In the case where the trichrome mixture of Nylosan® dyes was used, the ecotoxicity during the reuse cycles was also evaluated. Parallel to the study of reuse of dyeing baths, it was studied the variation of the solubility, with temperature, in water of two dyes used in the textile industry, the reactive dye Brilliant Red Levafix E-4B and Telon Blue ® RR. For Azul Telon® RR, the influence, on its solubility, at 25 ºC, of the presence of dyeing aids sodium sulfate and Avolan® UL 75 was also studied. The main results obtained in this work allowed the conclusion that, in the case of the acid dye Blue Telon® RR, the dyeing effluents treated by OE with a BDD anode have a positive influence on the dyeing process, increasing the affinity between the dye and the fiber. Thus, even after a 15% reduction in the amount of dye required for dyeing with treated effluent (60 mA cm−2; 6 h), a color difference (ΔE*) of 1.19 was achieved, which meets the less stringent requirements for dyeing quality. On the other hand, the higher the degree of oxidation of the effluent, the higher is the adsorption of the dye by the fiber. However, to obtain an effluent in a higher oxidation state, it is necessary to increase the intensity of the applied current or the treatment time, which translates into a higher energy cost. Regarding the washing fastness of the fabrics dyed with a bath made with fresh water or treated dyeing effluent, it was concluded that there are no significant differences in the multifiber fabric dyed with the two types of baths. Regarding the studies carried out with the trichrome mixture of Nylosan® dyes, the performance of the dyeing processes that used treated wastewater of moderate quality (obtained in the tests at 60 mA cm−2) or high (obtained in the tests at 100 mA cm−2) led to samples of dyed fabrics with ΔE* values of 1.0 and with color fastness to washing similar to those obtained by dyeing fabrics using fresh water, from which, once again, the conclusion is that, for efficient reuse of textile dyeing effluents, high quality water is not required. The ecotoxicity towards Daphnia magna studies carried out for these tests showed that during the reuse of effluents a reduction in ecotoxicity was observed, which allows a more exhaustive reuse of the treated effluent. Thus, in general, and although more studies are needed, everything points to the OE being a process to be considered regarding the reuse of dyeing baths by the textile industry.
The textile industry is one of the main socio-economic sectors worldwide. Despite supplying some basic human needs, the textile industry is seen as a problematic sector for the environment, either because of the high consumption of water or because it generates a large volume of liquid effluents. Although the reuse of treated effluents in new dyeing processes has been approached to promote the sustainable use of water in the textile industry, conventional technologies do not always provide satisfactory results, that is, treated effluents with the necessary quality for their reuse, mainly due to the presence of dyes and high salinity. In addition, many of the fiber dyeing auxiliary products, such as equalizing, dispersing, wetting agents, etc., are not consumed during the dyeing process, and end up in the final effluent, giving it, in some cases, high toxicity. Thus, for its reuse to be economically viable, it is necessary to develop efficient treatment processes that lead to treated effluents with the minimum quality necessary for their reuse. In this context, electrochemical oxidation (OE) processes are considered a very promising wastewater treatment technology for the treatment of textile effluents. The work presented in this thesis had as main objective to evaluate the use of electrochemical oxidation, with boron-doped diamond (BDD) anodes, for the treatment of effluents from wool dyeing processes and subsequent reuse in new dyeing processes. The reuse of wool dyeing effluents treated by OE was studied using (i) the acid dye Blue Telon® RR, belonging to the anthraquinone class, and (ii) a trichrome mixture of Nylosan® dyes: Red N-2RBL, Yellow N-3RL and Blue N-GL Mix. For both cases, the influence of the use of treated effluents with different quality (high and moderate) on the quality of the dyeing of wool fabrics was evaluated. In the case where the trichrome mixture of Nylosan® dyes was used, the ecotoxicity during the reuse cycles was also evaluated. Parallel to the study of reuse of dyeing baths, it was studied the variation of the solubility, with temperature, in water of two dyes used in the textile industry, the reactive dye Brilliant Red Levafix E-4B and Telon Blue ® RR. For Azul Telon® RR, the influence, on its solubility, at 25 ºC, of the presence of dyeing aids sodium sulfate and Avolan® UL 75 was also studied. The main results obtained in this work allowed the conclusion that, in the case of the acid dye Blue Telon® RR, the dyeing effluents treated by OE with a BDD anode have a positive influence on the dyeing process, increasing the affinity between the dye and the fiber. Thus, even after a 15% reduction in the amount of dye required for dyeing with treated effluent (60 mA cm−2; 6 h), a color difference (ΔE*) of 1.19 was achieved, which meets the less stringent requirements for dyeing quality. On the other hand, the higher the degree of oxidation of the effluent, the higher is the adsorption of the dye by the fiber. However, to obtain an effluent in a higher oxidation state, it is necessary to increase the intensity of the applied current or the treatment time, which translates into a higher energy cost. Regarding the washing fastness of the fabrics dyed with a bath made with fresh water or treated dyeing effluent, it was concluded that there are no significant differences in the multifiber fabric dyed with the two types of baths. Regarding the studies carried out with the trichrome mixture of Nylosan® dyes, the performance of the dyeing processes that used treated wastewater of moderate quality (obtained in the tests at 60 mA cm−2) or high (obtained in the tests at 100 mA cm−2) led to samples of dyed fabrics with ΔE* values of 1.0 and with color fastness to washing similar to those obtained by dyeing fabrics using fresh water, from which, once again, the conclusion is that, for efficient reuse of textile dyeing effluents, high quality water is not required. The ecotoxicity towards Daphnia magna studies carried out for these tests showed that during the reuse of effluents a reduction in ecotoxicity was observed, which allows a more exhaustive reuse of the treated effluent. Thus, in general, and although more studies are needed, everything points to the OE being a process to be considered regarding the reuse of dyeing baths by the textile industry.
Description
Keywords
Efluentes têxteis Oxidação eletroquímica Reutilização de efluentes Ânodo de BDD Lã Processo de tingimento Corantes têxteis Solubilidade