Browsing by Author "Freitas, Gabriel"
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- Catalytic wet peroxide oxidation of leachate waters using low-cost carbon-based materials as catalystsPublication . Freitas, Gabriel; Roman, Fernanda; Díaz de Tuesta, Jose Luis; Faria, Joaquim; Silva, Adrián; Mambrini, Raquel Vieira; Praça, Paulo; Gomes, HelderThe Directive 2008/98/EC established a hierarchy for management of Municipal Solid Waste (MSW), according to which landfilling should be avoided. In this direction, Mechanical and Biological Treatment (MBT) plants play an important role, since it allows the conversion of the organic fraction of MSW into biogas and compost, with applications as fuel and fertilizer, respectively. However, MBTs generate a wastewater, referred as leachate, with high load of organic matter, that is not properly treated by conventional systems. In addition, the production of compost in MBTs tends to be higher than its demand, resulting in accumulation on landfilling sites. This works aims to address the Catalytic Wet Peroxide Oxidation (CWPO) of a real leachate effluent obtained from a MBT, whose properties are summarized in Table 1. The compost obtained from the MBT was considered to produce the catalyst for the CWPO process. The lowcost catalytic materials were prepared by hydrothermal carbonization at previously optimized operating conditions (230 ºC, 4 h and 130 gcompost/L). Figure 1 shows the profile of H2O2 decomposition, COD and TOC upon time of reaction at 50 °C (solid line) and at 80 °C (dashed lines). At 80 °C, a removal of 40% and 55% for COD and BOD5, respectively, was achieved, increasing BOD5/COD ratio from 0.33 to 0.45, along with a reduction on turbidity (to 12 NTU) and color of the effluent, as observed in Figure 1.
- Desenvolvimento de uma metodologia analítica de monitorização de pesticidas em meios hídricosPublication . Freitas, Gabriel; Queiroz, Ana; Brito, Paulo; Ribeiro, António E.; Patrício, PatríciaO trabalho realizado tem o objetivo de desenvolver uma metodologia analítica para a monitorização de micropoluentes em meios hídricos. Foi selecionado para estudo um grupo de 11 pesticidas tendo por base aqueles mais utilizados na região nordeste de Portugal e no Brasil. Esta metodologia baseia-se numa etapa de extração em fase sólida (SPE) seguida de quantificação por cromatografia gasosa em fase acoplada com espetrometria de massas (GC-MS). Na otimização da etapa de extração utilizam-se cartuchos com adsorvente de poli(divinilbenzeno-co-N-vinilpirrolidona (Chromabond HLB). Optou-se por desenvolver os estudos de SPE utilizando um grupo de pesticidas solúveis em metanol e outro grupo solúvel em hexano. A metodologia de extração proposta obteve recuperações superiores a 78% para uma mistura composta pelos pesticidas dimetoato, terbutilazina e heptacloro. Na identificação e quantificação por GC-MS, os limites de deteção e de quantificação foram estimados através das curvas de calibração obtidas por análise sem extração de soluções padrão de dimetoato, terbutilazina e heptacloro. Os limites de deteção obtidos, são de 0,003 mg/L para o heptacloro, 0,066 mg/L para a terbutilazina e 1,98 mg/L para o dimetoato. Devido à pouca exatidão dos resultados, decidiu-se a utilização do método do padrão interno para melhores resultados. Devido à situação de pandemia e à obrigatoriedade de confinamento imposta pelo governo português, foi possível estudar apenas as condições operatórias de análise utilizando padrões analíticos e sem utilizar a etapa inicial de extração por SPE. Estava prevista a validação do método utilizando amostras recolhidas de 3 rios de Bragança, rio Fervença, Sabor e Onor, contudo, esta não foi realizada.
- Valorization of compost obtained from the mechanical and biological treatment of municipal solid waste: catalysts for wet peroxide oxidation of landfill leachatesPublication . Freitas, Gabriel; Roman, Fernanda; Díaz de Tuesta, Jose Luis; Mambrini, Raquel Vieira; Gomes, HelderSince humanity started living in communities and towns, the generation of solid waste has largely increased and, in 2017, each European citizen generated 480 kg of municipal solid waste (MSW). The main concern with MSW is its management and final destination since in many cases MSW is just thrown in landfills. In mechanical and biological plants, MSW is first sorted into discarded, recyclable, and organic waste streams. This organic fraction goes to the biological treatment stage, generating biogas, and as by-products, leachate, and compost are obtained, the compost being mainly used as an agriculture fertilizer. However, the amount of compost produced is higher than its demand, resulting in an excess that is currently accumulated in landfills. This work deals with the valorization of compost to produce hydrochairs, and pyrochars, through hydrothermal carbonization (HTC) and pyrolysis, respectively, with suitable properties as catalysts for the catalytic wet peroxide oxidation of the landfill leachate. Up to seven catalysts were synthesized under several conditions, 2 from HTC and 5 from pyrolysis. The catalysts were characterized to determine the ash content and elemental analysis. All materials were assessed in the degradation of H 2 O 2 , leading to its complete degradation after 2 h of reaction time. Some selected catalysts were further tested in the CWPO of the landfill leachate (TOC = 27 g L -1 , COD = 60 g L -1 , 38.8 mS/cm, and 5 g L -1 of chloride ions) under the following operating conditions: C Catalyst = 1.8 g L -1 ; T = 80 ºC; C H2O2 = 85.7 g L -1 and pH from 3.0 to 7.3.