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Aplicação de processos biológicos para a remoção de microplásticos de águas residuais
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Abstract(s)
A presente dissertação explora estratégias inovadoras para a remoção de microplásticos de
águas residuais urbanas, em conformidade com a Diretiva Europeia UE 2024/3019, que impõe
a sua monitorização nas estações de tratamento de águas residuais e a implementação de
medidas que reduzam a sua presença nas águas residuais e lamas. O estudo centrou-se na
biodegradação de microplásticos usando a enzima lacase, uma multicobre oxidase produzida
por fungos de podridão branca e reconhecida pela sua elevada versatilidade biocatalítica.
Foram estudados três tipos de microplásticos: poliamida 6 (PA6), com tamanho de 10–
20 μm; polietileno de baixa densidade (LDPE), com partículas de 300 μm e 600 μm; e
politereftalato de etileno (PET), com tamanho de 300 μm. Cada tipo foi analisado em duas
condições distintas: sem envelhecimento e com envelhecimento artificial, realizado durante 33
dias sob exposição a luz fluorescente branca, a uma temperatura de 22 °C e com 70% de
ventilação. Ao longo dos ensaios, foi feita a monitorização da atividade enzimática, através do
substrato cromogénico ácido 2,2′-azino-bis(3-etilbenzotiazolina-6-sulfónico (ABTS). No final do
período experimental (7 dias), avaliaram-se os parâmetros físico-químicos pH, condutividade e
sólidos suspensos totais. Adicionalmente, procedeu-se à caraterização dos microplásticos,
através das técnicas analíticas de espectroscopia no infravermelho com transformada de
Fourier (FTIR) e espectroscopia de micro-Raman, com o objetivo de identificar possíveis
alterações estruturais nos polímeros.
Nos estudos com microplásticos virgens, a lacase demonstrou interações superficiais. No
ensaio com LDPE de 300 μm, observaram-se alterações no pH e condutividade, mas sem
evidência de degradação estrutural. O PA6 apresentou formação de subprodutos e
modificações espectrais ligeiras identificadas por micro-Raman. No PET, observaram-se sinais
de oxidação superficial, evidenciados pelo aumento da intensidade das bandas associadas aos
grupos carbonilo e hidroxilo; contudo, não tendo sido identificadas alterações da estrutura
polimérica principal.
Nos ensaios com microplásticos envelhecidos, verificou-se que o envelhecimento aumentou
a suscetibilidade do PA6 à ação da lacase, refletida numa redução nos sólidos suspensos totais
e por alterações nas bandas caraterísticas do grupo amida detetadas por FTIR. O PET
envelhecido evidenciou uma fragilidade acrescida da matriz polimérica e sinais de oxidação
superficial detetados por FTIR, sugerindo que o envelhecimento favoreceu a atuação da lacase
a nível da superfície do microplástico. Em contraste, o LDPE manteve-se altamente resistente,
não evidenciando alterações estruturais relevantes, mesmo após envelhecimento.
Conclui-se que a eficácia da lacase é influenciada pela natureza química, granulometria e
estado de envelhecimento dos microplásticos. Embora não tenham sido observadas alterações
relevantes, a lacase demonstrou potencial para induzir modificações superficiais nos
microplásticos.
This dissertation explores innovative strategies for the removal of microplastics from urban wastewater, in accordance with the European Directive EU 2024/3019, which mandates monitoring at wastewater treatment plants and the implementation of measures to reduce their presence in wastewater and sludge. The study focused on the biodegradation of microplastics using laccase, a multi-copper oxidase produced by white-rot fungi and recognised for its high biocatalytic versatility. Three types of microplastics were studied: polyamide 6 (PA6), with a size of 10–20 μm; lowdensity polyethylene (LDPE), with particles of 300 μm and 600 μm; and polyethylene terephthalate (PET), with a size of 300 μm. Each type was analyzed under two distinct conditions: without aging and with artificial aging, the latter performed over 33 days under white fluorescent light exposure, at a temperature of 22 °C and 70% ventilation. Throughout the experiments, enzymatic activity was monitored using the chromogenic substrate 2,2′-azinobis( 3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). At the end of the experimental period (7 days), the physicochemical parameters pH, conductivity, and total suspended solids were evaluated. Additionally, the microplastics were charaterised using Fourier Transform Infrared Spectroscopy (FTIR) and micro-Raman spectroscopy to identify potential structural changes in the polymers. In studies with virgin microplastics, laccase showed surface-level interactions. In the LDPE 300 μm assay, changes in pH and conductivity were observed, but without evidence of structural degradation. PA6 showed the formation of by-products and slight spectral modifications detected via micro-Raman. Signs of surface oxidation were observed in PET, indicated by an increase in the intensity of the bands associated with carbonyl and hydroxyl groups; however, the main polymer structure remained intact. In the assays with aged microplastics, ageing was found to increase the susceptibility of PA6 to laccase activity, reflected in a reduction in total suspended solids and alterations in characteristic amide group bands detected by FTIR. Aged PET showed an increased fragility of the polymer matrix and signs of surface oxidation identified by FTIR, suggesting that ageing favored laccase action at the microplastic surface. In contrast, LDPE remained highly resistant, showing no significant structural changes even after ageing. In conclusion, laccase effectiveness is influenced by the chemical nature, granulometry, and ageing state of microplastics. Although relevant degradation was not observed, laccase demonstrated potential to induce surface-level modifications in the microplastics.
This dissertation explores innovative strategies for the removal of microplastics from urban wastewater, in accordance with the European Directive EU 2024/3019, which mandates monitoring at wastewater treatment plants and the implementation of measures to reduce their presence in wastewater and sludge. The study focused on the biodegradation of microplastics using laccase, a multi-copper oxidase produced by white-rot fungi and recognised for its high biocatalytic versatility. Three types of microplastics were studied: polyamide 6 (PA6), with a size of 10–20 μm; lowdensity polyethylene (LDPE), with particles of 300 μm and 600 μm; and polyethylene terephthalate (PET), with a size of 300 μm. Each type was analyzed under two distinct conditions: without aging and with artificial aging, the latter performed over 33 days under white fluorescent light exposure, at a temperature of 22 °C and 70% ventilation. Throughout the experiments, enzymatic activity was monitored using the chromogenic substrate 2,2′-azinobis( 3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). At the end of the experimental period (7 days), the physicochemical parameters pH, conductivity, and total suspended solids were evaluated. Additionally, the microplastics were charaterised using Fourier Transform Infrared Spectroscopy (FTIR) and micro-Raman spectroscopy to identify potential structural changes in the polymers. In studies with virgin microplastics, laccase showed surface-level interactions. In the LDPE 300 μm assay, changes in pH and conductivity were observed, but without evidence of structural degradation. PA6 showed the formation of by-products and slight spectral modifications detected via micro-Raman. Signs of surface oxidation were observed in PET, indicated by an increase in the intensity of the bands associated with carbonyl and hydroxyl groups; however, the main polymer structure remained intact. In the assays with aged microplastics, ageing was found to increase the susceptibility of PA6 to laccase activity, reflected in a reduction in total suspended solids and alterations in characteristic amide group bands detected by FTIR. Aged PET showed an increased fragility of the polymer matrix and signs of surface oxidation identified by FTIR, suggesting that ageing favored laccase action at the microplastic surface. In contrast, LDPE remained highly resistant, showing no significant structural changes even after ageing. In conclusion, laccase effectiveness is influenced by the chemical nature, granulometry, and ageing state of microplastics. Although relevant degradation was not observed, laccase demonstrated potential to induce surface-level modifications in the microplastics.
Description
Keywords
Ageing Enzymatic biodegradation Microplastics Laccase Quaternary treatment Urban wastewater Águas residuais urbanas Biodegradação enzimática Envelhecimento Microplásticos Lacase Tratamento quaternário