Degradação de poluentes de preocupação emergente empregando processos mediados por persulfato

Orientador: Prof. Dr. Patricio Peralta-ZamoraCoorientador: Prof. Dr. Ronny Rocha RibeiroDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Química. Defesa : Curitiba, 27/10/2020Inclui referências: p.83-89Resumo: Nas últimas décadas surgiram novas preocupações envolvendo um grupo de poluentes que se apresenta em baixas concentrações e para os quais, em geral, não existe previsão na legislação ambiental. Trata-se de poluentes orgânicos considerados de preocupação emergente (CECs), os quais são recalcitrantes frente aos sistemas convencionais de tratamento de resíduos. Em função dos efeitos tóxicos apresentados por este tipo de poluentes, muitos esforços têm sido dedicados ao estudo de novas alternativas de tratamento, incluindo processos de oxidação avançada (POAs) que envolvem a formação de espécies radicalares altamente oxidantes. Um dos reagentes utilizados como precursor de radicais é o persulfato, agente que apresenta elevado potencial padrão de redução e, portanto, alta capacidade oxidativa, porém que pode ser ativado de diversas formas para produzir espécies radicalares ainda mais oxidantes, como os radicais sulfato e hidroxila. Em função destes argumentos, o presente estudo objetivou avaliar a potencialidade de três formas de ativação do persulfato (térmica, por radiação visível e ultravioleta e por formas iônicas de ferro), em relação à degradação de poluentes modelo, fenol e um azo corante (preto reativo 5). Os estudos envolveram a avaliação do efeito de variáveis de relevância por meio de sistemas de planejamento fatorial de experimentos, o cálculo de parâmetros cinéticos associados à degradação dos substratos modelo, a investigação de formas radicalares por espectroscopia de ressonância paramagnética eletrônica (EPR) e a verificação da participação de cada radical no processo de degradação, utilizando-se sequestrantes de radicais. Para as ativações térmica e por radiação, a otimização das variáveis experimentais mostra que a concentração de persulfato é positivamente relevante na degradação dos substratos modelo, porém a energia fornecida ao sistema tem maior importância na formação das espécies radicalares. O sistema ativado por calor apresentou melhor eficiência de degradação em elevadas temperaturas (Cps 300 mg L-1, T 80 °C, pH 4,00), enquanto o sistema ativado por radiação requereu uma energia alta (ultravioleta, lâmpada vapor de Hg) para promover a quebra da ligação peróxido do persulfato (Cps 300 mg L-1, pH 4,00). O pH se mostrou relevante frente às espécies radicalares formadas, sendo que soluções ácidas (pH 4,00) favorecem a formação de radical sulfato e soluções alcalinas (pH 8,00), radical hidroxila. A ativação térmica se mostrou mais eficiente no que diz respeito à capacidade de formação de radicais em solução aquosa, sendo possível fazer essa comparação por meio dos espectros de EPR normalizados, que mostraram sinais com maior intensidade para esse tipo de ativação. Nos testes com formas solúveis de ferro, a ativação com ferro livre (Cps 300 mg L-1, CFe 1,11 mmol L-1, pH 3,00) não promoveu a ativação do persulfato, o que pode ser comprovado pela mínima capacidade de degradação observada, bem como pela ausência de sinal nos espectros de EPR. Por outro lado, nos ensaios com ferro complexado (Cps 300 mg L-1, CFe 1,11 mmol L-1, Cedta 1,11 mmol L-1, pH 7,00) foi possível observar formação de espécies radicalares, porém em pequena concentração. Para esse tipo de ativação, é necessário otimizar as proporções entre os reagentes. Os resultados obtidos neste trabalho poderão contribuir com futuras pesquisas na área de degradação por processos envolvendo persulfato ativado, principalmente no direcionamento de otimização de sistemas e entendimento dos mecanismos de reação frente às espécies radicalares mais ativas em cada condição experimental. Palavras-chave: Persulfato ativado. Degradação. Radicais oxidantes. EPR.Abstract: In the past few decades new concerns about a specific group of pollutants has arrived. These compounds are found in low concentrations and there is no environmental regulation for most of them. The so-called contaminants of emerging concern (CECs) are recalcitrant to conventional waste treatment and, as a result of the toxicity of them, huge efforts have been made in the developing of new treatment alternatives, including advanced oxidation processes (AOPs), which involve the production of radical species highly oxidants. One of the reagents used as a radical precursor is the persulfate ion that is a strong oxidant agent per se; however, when it passes through activation reactions, it promotes the formation of species with higher standard reduction potential, such as sulfate and hydroxyl radicals. Considering these statements, the objective of this work was to evaluate the potentiality of three persulfate activation processes (thermal, radiation and iron ions), in face of the degradation of pollutants substrates, phenol and a dye (reactive black 5). The studies involved the evaluation of the effects of experimental variables employing full factorial design experiments, the kinetics parameters associated to degradation of model compounds, the investigation of radical species by electron paramagnetic resonance (EPR) and assays employing radical scavengers were conducted in order to evaluate the contribution of each species during the degradation reactions. For both thermal and radiation (visible and ultraviolet) activation, the optimization of experimental variables has shown that the concentration of persulfate influences the degradation positively; however, the energy provided to the system is more relevant in the formation of radical species. The thermally-activated system has shown better results - in terms of degradation percentage - in higher temperatures (Cps 300 mg L-1, T 80 °C, pH 4.00), while the radiation-activated system required high energy - ultraviolet - to break the persulfate-peroxide bond (Cps 300 mg L-1, pH 4.00). The pH showed to be a relevant variable front of the formation of radical species: acidic medium (pH 4.00) favored the formation of sulfate radical, while in alkaline conditions (pH 8.00) the hydroxyl radical was the main oxidant species. The thermally-activated system proved to be the most effective way to produce radicals in aqueous solution, which could be conclude by comparing the EPR normalized spectrums that showed the highest intensity for this type of activation. In the ironactivated systems, free iron (Cps 300 mg L-1, CFe 1.11 mmol L-1, pH 3.00) could not activate persulfate in the experimented conditions, which can be proved by the small degradation percentage as well as the absence of signal in EPR spectrum. On the other hand, the reaction between persulfate and iron complexed with EDTA Cps 300 mg L-1, CFe 1.11 mmol L-1, Cedta 1.11 mmol L-1, pH 7.00) resulted in oxidant radicals, yet in lower concentrations. In a nutshell, for this type of activation is necessary to optimize the ratio between the reactants. The findings of this work may contribute for futures studies in activated-persulfate reactions in the degradation of contaminants, especially in the direction to optimization and better understanding of the contribution of each species in reaction mechanisms. Keywords: Activated persulfate. Degradation. Oxidant radicals. EPR

Modulation of crude glycerol fermentation byClostridium pasteurianum DSM 525 towards theproduction of butanol

High production yields and productivities are requisites for the development of an industrial butanol production process based on biodiesel-derived crude glycerol. However, impurities present in this substrate and/or the concentration of glycerol itself can affect the microbial metabolism. In this work, the effect of crude glycerol concentration on the production of butanol and 1,3-propanediol (1,3-PDO) by Clostridium pasteurianum DSM 525 is studied. Also, the effect of acetate and butyrate supplementation to the culture medium and the culture medium composition are evaluated. The results showed a marked effect of crude glycerol concentration on the product yield. The competitive nature of butanol and 1,3-PDO pathways has been evident, and a shift to the butanol pathway once using higher substrate concentrations (up to 35 g l 1) was clearly observed. Butyrate supplementation to the culture medium resulted in a 45% higher butanol titre, a lower production of 1,3-PDO and it decreased the fermentation time. Acetate supplementation also increased the butanol titre but the fermentation was longer. Even though glycerol consumption could not be increased over 32 g l 1, when the concentrations of NH4Cl and FeCl2 were simultaneously increased, the results obtained were similar to those observed when butyrate was supplemented to the culture medium; a 35% higher butanol yield at the expense of 1,3-PDO and a shorter fermentation. The results herein gathered suggest that there are other factors besides butanol inhibition and nutrient limitation that affect the glycerol consumption.The authors acknowledge the financial support from the Strategic Project PEst-OE/EQB/LA0023/2013; the project ref. RECI/BBB-EBI/0179/2012 (project number FCOMP-01-0124-FEDER-027462); and the PhD grant given to R. Gallardo (ref SFRH/BD/42900/2008) funded by Fundacao para a Ciencia e a Tecnologia. The authors thank the MIT-Portugal Program for the support given to R. Gallardo

Social Media, Gender and the Mediatisation of War: Exploring the German Armed Forces’ Visual Representation of the Afghanistan Operation on Facebook

Studies on the mediatisation of war point to attempts of governments to regulate the visual perspective of their involvements in armed conflict – the most notable example being the practice of ‘embedded reporting’ in Iraq and Afghanistan. This paper focuses on a different strategy of visual meaning-making, namely, the publication of images on social media by armed forces themselves. Specifically, we argue that the mediatisation of war literature could profit from an increased engagement with feminist research, both within Critical Security/Critical Military Studies and within Science and Technology Studies that highlight the close connection between masculinity, technology and control. The article examines the German military mission in Afghanistan as represented on the German armed forces’ official Facebook page. Germany constitutes an interesting, and largely neglected, case for the growing literature on the mediatisation of war: its strong antimilitarist political culture makes the representation of war particularly delicate. The paper examines specific representational patterns of Germany’s involvement in Afghanistan and discusses the implications which arise from what is placed inside the frame of visibility and what remains out of its view