Green stabilization of nanoscale zero-valent iron (nZVI) with rhamnolipids produced by agro-industrial waste: application on nitrate reduction
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Data
2019-09-13
Autores
Moura, Cinthia Cristine de
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Universidade Estadual Paulista (Unesp)
Resumo
A contaminação ambiental causada por compostos orgânicos é um importante problema que afeta solos e água superficiais. Para reduzir ou remover esses poluentes, os locais contaminados são geralmente tratados com métodos físicos e químicos. No entanto, a maioria dessas técnicas de remediação é custosa e geralmente leva à remoção incompleta e à produção de resíduos secundários. A nanotecnologia consiste na produção e aplicação de estruturas extremamente pequenas, cujas dimensões estão na faixa de 1 a 100 nm, neste cenário a nanopartícula de ferro zero valente representa uma nova geração de tecnologias de remediação ambiental. É não tóxica, abundante, barata, fácil de produzir, e seu processo de produção é simples. No entanto, a fim de diminuir a tendência de agregação, a nanopartícula de ferro zero é frequentemente revestida com surfactantes. A maioria dos surfactantes é quimicamente sintetizado a partir de fontes petroquímicas, eles são persistentes ou parcialmente biodegradáveis, enquanto oferecem baixos riscos à saúde humana, esses compostos podem prejudicar plantas e animais. Para diminuir o uso de métodos químicos, a síntese e estabilização verde de nanomateriais metálicos apresentam-se como uma opção menos perigosa ao meio ambiente. Os biossurfactantes podem potencialmente substituir qualquer surfactante sintético, eles são compostos extracelulares produzidos por microrganismos, como bactérias, e cultivados em diferentes fontes de carbono, podendo ser substratoshidrofílicos. Os biossurfactantes possuem uma grande variedade de estruturas químicas e propriedadesde superfície e entre eles estão os ramnolipídios que já foram intensamente investigados e estudados. Os ramnolipídios podem ser produzidos pela Pseudomonas aeruginosa em diferentes substratos, incluindo o glicerol. Uma produção bem-sucedida de biossurfactantes depende do uso de materiais renováveis e de baixo custo. O glicerol bruto, principal subproduto do processo de transesterificação em uma usina de biodiesel, é um substrato amplamente utilizado para a produção de ramnolipídios. A fim de obter a melhor temperatura e concentração inicial de glicerol, o design rotacional composto central e o método de superfície de resposta foram empregados para delimitar as melhores condições para aumentar a produção de ramnolipídeos e diminuir o glicerol remanescente no meio. Com o auxílio do Método de Superfície e Resposta foi possível verificar a viabilidade do uso do glicerol bruto livre de sal, atingindo uma produção de 2,63 g/L de ramnolipidios e depleção total da fonte de carbono, no meio otimizado contendo 25 g/L de fonte inicial de carbono a 32 ° C. Em seguida, as nanopartículas de ferro zero foram sintetizadas utilizando a redução química com borohidreto de sódio. Foram testadas duas metodologias: (i) adição de ramnolipídios durante a síntese química e (ii) adição após a síntese. As nanopartículas foram subsequentemente testadas quanto à eficiência na redução de nitrato em água subterrânea simulada sob condições anaeróbias em pH 4. A nanopartícula de ferro zero sintetizada adicionando ramnolipídios após a síntese, mostrou a melhor eficiência com uma taxa de remoção de cerca de 78% de remoção de nitrato e concentração inicial de nitrato de 25. mg/L. O método para preparar nanopartícula de ferro zero, usando ramnolipídios como agente estabilizador, mostrou-se uma alternativa promissora para a funcionalização de superfície da nanopartícula, em substituição a surfactantes sintéticos e tóxicos
Environmental contamination caused by organic compounds is the most important challenge that affects a huge number of soils and water surfaces. To reduce or remove these pollutants, contaminated sites are usually treated using physical and chemical methods. However, most of these remediation techniques are expensive and commonly lead to incomplete removal and to the production of secondary wastes. Nanotechnology is the production and application of extremely small structures, whose dimensions are in the range of 1 to 100 nm and Nanoscale zero-valent iron represents a new generation of environmental remediation technologies, is non-toxic, abundant, cheap, easy to produce, and its reduction process requires little maintenance. Nonetheless, in order to diminish the tendency of aggregation, nanoscale zero-valent iron is often coated with surfactants. Most surfactants are chemically synthesized from petrochemical sources, they are slowly or partially biodegradable, while offer low harm to humans, such compounds can influence plants and animals. To decrease the use of chemical methods green synthesis and stabilization of metallic nanomaterials viable option. Biosurfactants can potentially replace virtually any synthetic they are extracellular compounds produced by microbes such as by bacteria and grown on different carbon sources containing hydrophobic/hydrophilic substrates. The biosurfactants have a wide variety of chemical structures and surface properties and among them is the rhamnolipids which have been intensively investigated and extensively reviewed, they can be produced by Pseudomonas aeruginosa from different substrates, including glycerol. Successful production of biosurfactants depends on the use of renewable materials and low cost. Crude glycerol is the primary byproduct of the transesterification process in a biodiesel plant and it is a widely used substrate for rhamnolipid production. To provide the best temperature and initial concentration of glycerol the central composite rotational design and response surface method were employed to increase rhamnolipids yield and lower the glycerol remaining in the medium. The response surface method methodology indicated the viability of the use of crude glycerol, reaching a production of 2.63 g/L of biosurfactant and total depletion of carbon source, at the optimized medium containing 25 g/L of initial carbon source at 32 °C. Then, the iron nanoparticles were synthesized using the chemical reduction of ferric ions with sodium borohydride. Were tested two methodologies: (i) adding rhamnolipids during the chemical synthesis and (ii) adding after the synthesis. The nanoparticles were subsequently tested for their efficiency in nitrate reduction in simulated groundwater under anaerobic conditions at pH 4. The nanoscale zero-valent iron synthetized adding rhamnolipids after the synthesis showed the best efficiency with a removal rate about 78% and initial nitrate concentration of 25 mg/L. The method for preparing nanoscale zero-valent iron using rhamnolipids biosurfactants as stabilizer was found as a promising alternative for the synthesis and surface functionalization of iron nanoparticles, in replacement to toxic synthetic surfactants
Environmental contamination caused by organic compounds is the most important challenge that affects a huge number of soils and water surfaces. To reduce or remove these pollutants, contaminated sites are usually treated using physical and chemical methods. However, most of these remediation techniques are expensive and commonly lead to incomplete removal and to the production of secondary wastes. Nanotechnology is the production and application of extremely small structures, whose dimensions are in the range of 1 to 100 nm and Nanoscale zero-valent iron represents a new generation of environmental remediation technologies, is non-toxic, abundant, cheap, easy to produce, and its reduction process requires little maintenance. Nonetheless, in order to diminish the tendency of aggregation, nanoscale zero-valent iron is often coated with surfactants. Most surfactants are chemically synthesized from petrochemical sources, they are slowly or partially biodegradable, while offer low harm to humans, such compounds can influence plants and animals. To decrease the use of chemical methods green synthesis and stabilization of metallic nanomaterials viable option. Biosurfactants can potentially replace virtually any synthetic they are extracellular compounds produced by microbes such as by bacteria and grown on different carbon sources containing hydrophobic/hydrophilic substrates. The biosurfactants have a wide variety of chemical structures and surface properties and among them is the rhamnolipids which have been intensively investigated and extensively reviewed, they can be produced by Pseudomonas aeruginosa from different substrates, including glycerol. Successful production of biosurfactants depends on the use of renewable materials and low cost. Crude glycerol is the primary byproduct of the transesterification process in a biodiesel plant and it is a widely used substrate for rhamnolipid production. To provide the best temperature and initial concentration of glycerol the central composite rotational design and response surface method were employed to increase rhamnolipids yield and lower the glycerol remaining in the medium. The response surface method methodology indicated the viability of the use of crude glycerol, reaching a production of 2.63 g/L of biosurfactant and total depletion of carbon source, at the optimized medium containing 25 g/L of initial carbon source at 32 °C. Then, the iron nanoparticles were synthesized using the chemical reduction of ferric ions with sodium borohydride. Were tested two methodologies: (i) adding rhamnolipids during the chemical synthesis and (ii) adding after the synthesis. The nanoparticles were subsequently tested for their efficiency in nitrate reduction in simulated groundwater under anaerobic conditions at pH 4. The nanoscale zero-valent iron synthetized adding rhamnolipids after the synthesis showed the best efficiency with a removal rate about 78% and initial nitrate concentration of 25 mg/L. The method for preparing nanoscale zero-valent iron using rhamnolipids biosurfactants as stabilizer was found as a promising alternative for the synthesis and surface functionalization of iron nanoparticles, in replacement to toxic synthetic surfactants
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Palavras-chave
Biossurfactantes, Química verde, Design experimental, Glicerol, Nanopartícula de ferro zero valente, Águas subterrâneas, Biosurfactants, Green chemistry, Experimental design, Glycerol, Nanoscale zero-valent iron, Groundwater