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Electro-reactor for the removal of PPCPs and microorganisms from effluent: feasibility assessment
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A visão da água residual tem vindo a mudar ao longo dos anos, à medida que as estações de tratamento de águas residuais (ETAR) começaram a ser consideradas fontes de recursos valiosos que podem ser recuperados. O uso de água residual tratada para fins não-potáveis como irrigação agrícola representa uma opção viável, capaz de dar resposta a situações de escassez hídrica permitindo tirar pressão na exploração de fontes de água doce. No entanto, a água residual tratada pode possuir riscos químicos e microbiológicos, visto que as tecnologias de tratamento secundário e terciário atualmente utilizadas não permitem atingir uma remoção completa de contaminantes emergentes, como fármacos e produtos de cuidado pessoal.
Tecnologias electrocinéticas constituem soluções para o tratamento de água residual para fins de reutilização. A presente dissertação explora a aplicação do processo electrocinético num reator electroquímico para estudar a degradação de cinco compostos orgânicos emergentes: cafeína (CAF), sulfametoxazol (SMX), carbamazepina (CBZ), diclofenaco (DCF) e oxibenzona (OXY). De forma complementar, o efeito do campo elétrico na comunidade microbiológica total do efluente foi avaliado através da contagem de unidades formadoras de colónias que cresceram em meio de agar dextrose de batata, passadas 24 h. Os reatores foram dopados com a mistura de contaminantes com uma concentração de 0.2 mg/L, e foi aplicada uma densidade de corrente fixa de 8 mA/cm² entre elétrodos de óxido de metal misto. No primeiro conjunto de experiências, o processo electrocinético foi aplicado em efluente desinfetado por radiação UV-C à escala laboratorial e três tempos de degradação foram testados: 2 h, 4 h e 6 h. A electrodegradação variou entre 17 ± 6% para CAF após 2 h de tratamento electrocinético, tendo o SMX ficado abaixo do limite de deteção do método, ao fim de 4 h de tratamento. Microrganismos totais cultiváveis do efluente foram reduzidos em cerca de 1.0 unidade logarítmica (Redução em 90%), no primeiro conjunto de experiências. No segundo conjunto de experiências, realizadas em efluente fresco e pelo período de 6 h, verificou-se uma maior inativação dos microrganismos totais cultiváveis, até 3.7 unidades logarítmicas (Redução em 99.98%). Testou-se em paralelo a fotólise por meio de UV-C dos compostos como termo de comparação com o processo eletrocinético. Electrodegradação em efluente fresco permitiu obter para SMX e OXY degradações superiores a 95%.
Tanto os fármacos e os produtos de cuidado pessoal em estudo como os microrganismos presentes no efluente podem ter sofrido oxidação anódica direta e oxidação indireta por espécies intermédias formadas em meio aquoso. Ao permitir remover PPCPs e microrganismos, o processo eletrocinético provou ser viável enquanto tecnologia de remediação e desinfeção para efluente secundário de ETAR.
The vision of wastewater has been changing over the years, as wastewater treatment plants (WWTPs) are now considered supplies of valuable resources that can be recovered. The use of reclaimed water for non-potable uses such as agriculture irrigation, represents a viable option capable of dealing with water scarcity and allowing to alleviate the exploration of freshwater supplies. However, reclaimed water may enclose chemical and microbiological risks, as the currently used secondary and tertiary treatment technologies do not allow a complete removal of emergent contaminants, such as pharmaceuticals and personal care products (PPCPs). Electrokinetic (EK) technologies are available solutions for wastewater treatment aiming reclamation purposes. This dissertation explores the application of the EK process in one-compartment (1c-cell) electrochemical reactor to study the degradation of five target emergent organic contaminants (EOCs): caffeine (CAF), sulfamethoxazole (SMX), carbamazepine (CBZ), diclofenac (DCF) and oxybenzone (OXY). In addition, the effect of the electric field generated by the low-level direct current (DC) in the effluent total microbial community was also assessed by performing counts of colonies forming units grown in potato dextrose agar media after 24 h of incubation. Reactors were spiked with a mixture of the target PPCPs at a concentration of 0.2 mg/L and a fixed current density of 8 mA/cm² was applied between mixed metal oxide electrodes. In Set 1, the EK process was applied in bench scale UV-C treated effluent and three treatment times were tested: 2 h, 4 h and 6 h. Electrodegradation ranged from 17 ± 6% for CAF after 2 h of EK treatment, to removal below the method detection limit for SMX after 4 h of EK treatment. Total culturable microorganisms were reduced by ≈ 1.0 Log10 unit (90% removal), in Set 1. In Set 2 experiments, performed in fresh effluent and for a period of 6 h, total culturable microorganisms achieved a higher inactivation, up to 3.7 Log10 units (99,98% removal). UV-C photolysis of PPCPs was also tested in Set 2, in comparison to EK treatment. Electrodegradation of PPCPs in fresh effluent was higher than 95% for both SMX and OXY. Both PPCPs and total microorganisms from secondary effluent can suffer direct anodic oxidation and indirect oxidation by generated intermediate species in aqueous media. By allowing PPCPs and microorganisms removal, the EK process proved to be a viable remediation and disinfection technology for secondary effluent from WWTPs.
The vision of wastewater has been changing over the years, as wastewater treatment plants (WWTPs) are now considered supplies of valuable resources that can be recovered. The use of reclaimed water for non-potable uses such as agriculture irrigation, represents a viable option capable of dealing with water scarcity and allowing to alleviate the exploration of freshwater supplies. However, reclaimed water may enclose chemical and microbiological risks, as the currently used secondary and tertiary treatment technologies do not allow a complete removal of emergent contaminants, such as pharmaceuticals and personal care products (PPCPs). Electrokinetic (EK) technologies are available solutions for wastewater treatment aiming reclamation purposes. This dissertation explores the application of the EK process in one-compartment (1c-cell) electrochemical reactor to study the degradation of five target emergent organic contaminants (EOCs): caffeine (CAF), sulfamethoxazole (SMX), carbamazepine (CBZ), diclofenac (DCF) and oxybenzone (OXY). In addition, the effect of the electric field generated by the low-level direct current (DC) in the effluent total microbial community was also assessed by performing counts of colonies forming units grown in potato dextrose agar media after 24 h of incubation. Reactors were spiked with a mixture of the target PPCPs at a concentration of 0.2 mg/L and a fixed current density of 8 mA/cm² was applied between mixed metal oxide electrodes. In Set 1, the EK process was applied in bench scale UV-C treated effluent and three treatment times were tested: 2 h, 4 h and 6 h. Electrodegradation ranged from 17 ± 6% for CAF after 2 h of EK treatment, to removal below the method detection limit for SMX after 4 h of EK treatment. Total culturable microorganisms were reduced by ≈ 1.0 Log10 unit (90% removal), in Set 1. In Set 2 experiments, performed in fresh effluent and for a period of 6 h, total culturable microorganisms achieved a higher inactivation, up to 3.7 Log10 units (99,98% removal). UV-C photolysis of PPCPs was also tested in Set 2, in comparison to EK treatment. Electrodegradation of PPCPs in fresh effluent was higher than 95% for both SMX and OXY. Both PPCPs and total microorganisms from secondary effluent can suffer direct anodic oxidation and indirect oxidation by generated intermediate species in aqueous media. By allowing PPCPs and microorganisms removal, the EK process proved to be a viable remediation and disinfection technology for secondary effluent from WWTPs.
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Pharmaceuticals and Personal Care Products Electrokinetic process Total culturable microorganisms Electrochemical disinfection