Publicação
Fenton's process applied to wastewaters treatment
| Resumo: | Water resources are not infinite. If even nowadays some people do not have proper access to this vital supply, humanity must do much more effort aiming its preservation in consideration with the future of the generations to come. Avoiding all types of pollutants from contaminating water cycles is currently one of the current utmost matters to be faced by government policies. Research on wastewaters treatment have been dealing this regard over many years now, strongly contributing with solutions to the related problems. The most frequently remediation techniques to several kinds of effluents are the biological treatments, where microorganisms consume the organic charge – thus requiring biomass adaptation when there are changes on substrates composition. Drawbacks emerge when non-biodegradable or toxic effluents must be dealt with. This, sometimes, makes it impossible to treat effluents by activated sludge, especially when the effluent is not available all over the year for bacteria to have time to get acclimated. Therefore, accordingly to the kind or content of the residues requiring remediation before discharge, different approaches may be considered instead. Portugal alone produced 80 kilotons of olive oil in 2012. In the same year, the World’s production exceeded 3.3 megatons, produced from fruits gathered from over 750 million trees spread all over the globe (most of it at the Mediterranean region). This elevated and concentrated production generates huge amounts of different effluents, summing up the so called olive mills wastewaters (OMW). These rejects simultaneously present the two imperative characteristics that renders biological option unsuccessful for environmental legislation achievement: toxicity to microorganisms (due to the presence of phenolic acids) and seasonality (since the crop of the fruits occur for approximately four months of the year). Consequently, it is necessary to find alternative treatments capable of abating these wastewaters’ organic charge at any period for as long as it is necessary. Solution circumventing the mentioned inconveniences are chemical treatment technologies, where the advanced oxidation technologies (AOPs) are included. These last are based on an oxidative reagent able to degrade the aimed compounds, either by complete elimination or by reducing their environmental harmfulness. Parameters such as chemical oxygen demands (COD), total organic carbon levels (TOC), total phenolic content (TPh), biochemical oxygen demand (BOD), eco-toxicity (EC20 and EC50), amongst others, supply key information for these processes’ efficiency assessment, that may be presented as remediation alternatives after proper judgment of experimental results. Hydrogen peroxide (H2O2) is a common reactant when it comes to wastewater oxidative treatments. Although it is a highly oxidative specie, further activation by cleavage into hydroxyl radicals (•OH) can be achieved by the presence of ozone, UV-light or transition metals. In particular, when this excitation is caused by iron ions (usually Fe2+) it is called Fenton’s process, which has several industrial applications involving wastewater treatment with great economic advantages, especially for occurring under normal conditions of pressure and temperature. Besides, the non-selectivity of the Fenton’s radicals assures that several kinds of effluents can be oxidized by these systems. The Fenton’s oxidation of a synthetic solution comprised by a few phenolic acids commonly found in OMW was studied. New results were introduced to the scientific community, obtained by the use of ceramic solids and low cost materials tested as heterogeneous catalysts. The classical process, in homogeneous phase, was also appraised and compared with a different approach of it, achieving interesting results regarding the reduction of sludge formation and reactants yields. Continuous operation modes were also performed in a tubular reactor, reaching good organic charge removals. The operating conditions were planned in a way to allow comparisons amongst several experiments. In this thesis, the calcination temperature of ceramic catalysts is the first subject to be evaluated. Its study shows that the temperature of 300 °C produced the most active solids. An iron-cerium solid at the molar proportion of 70/30 can be highlighted amongst the other ceramic solids by its superior oxidative promotion (which might be related to its higher surface area, 188 m2.g-1): complete phenolic destruction, 49 % COD removal and 45 % TOC abatement. Moreover, the effluent’s biodegradability was greatly enhanced and had its toxicity removed. Other researches using the same methodology of catalyst preparation comprised iron-copper and iron cobalt solids used at the same operation conditions, but without such success. Low cost materials recycling is another theme presented in this document. The attempt of using Fenton’s sludge as catalyst (directly, after calcination and as iron precursor), although resulting in active solids, did not succeed on the biodegradability enhancement, being discarded. On the other hand, zero valent iron (ZVI) gathered from two sources presented outstanding catalytic performances in batch (from 10 minutes to 2 hours) and continuous reactions (stable organic charge removals up to 168 hours of operation). Finally, the homogeneous Fenton’s reaction is appraised in order to generate results linking it to the heterogeneous process. In the same chapter, a different approach for the classical Fenton’s oxidation is performed, showing a great enhancement of the overall efficiency considering the sludge formation reduction and reactants yields augment. |
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| Autores principais: | Rossi, André Fernandes |
| Assunto: | Fenton Chemical engineering Olive mill wastewater Advanced oxidation process |
| Ano: | 2014 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Coimbra |
| Idioma: | inglês |
| Origem: | Estudo Geral - Universidade de Coimbra |
| Resumo: | Water resources are not infinite. If even nowadays some people do not have proper access to this vital supply, humanity must do much more effort aiming its preservation in consideration with the future of the generations to come. Avoiding all types of pollutants from contaminating water cycles is currently one of the current utmost matters to be faced by government policies. Research on wastewaters treatment have been dealing this regard over many years now, strongly contributing with solutions to the related problems. The most frequently remediation techniques to several kinds of effluents are the biological treatments, where microorganisms consume the organic charge – thus requiring biomass adaptation when there are changes on substrates composition. Drawbacks emerge when non-biodegradable or toxic effluents must be dealt with. This, sometimes, makes it impossible to treat effluents by activated sludge, especially when the effluent is not available all over the year for bacteria to have time to get acclimated. Therefore, accordingly to the kind or content of the residues requiring remediation before discharge, different approaches may be considered instead. Portugal alone produced 80 kilotons of olive oil in 2012. In the same year, the World’s production exceeded 3.3 megatons, produced from fruits gathered from over 750 million trees spread all over the globe (most of it at the Mediterranean region). This elevated and concentrated production generates huge amounts of different effluents, summing up the so called olive mills wastewaters (OMW). These rejects simultaneously present the two imperative characteristics that renders biological option unsuccessful for environmental legislation achievement: toxicity to microorganisms (due to the presence of phenolic acids) and seasonality (since the crop of the fruits occur for approximately four months of the year). Consequently, it is necessary to find alternative treatments capable of abating these wastewaters’ organic charge at any period for as long as it is necessary. Solution circumventing the mentioned inconveniences are chemical treatment technologies, where the advanced oxidation technologies (AOPs) are included. These last are based on an oxidative reagent able to degrade the aimed compounds, either by complete elimination or by reducing their environmental harmfulness. Parameters such as chemical oxygen demands (COD), total organic carbon levels (TOC), total phenolic content (TPh), biochemical oxygen demand (BOD), eco-toxicity (EC20 and EC50), amongst others, supply key information for these processes’ efficiency assessment, that may be presented as remediation alternatives after proper judgment of experimental results. Hydrogen peroxide (H2O2) is a common reactant when it comes to wastewater oxidative treatments. Although it is a highly oxidative specie, further activation by cleavage into hydroxyl radicals (•OH) can be achieved by the presence of ozone, UV-light or transition metals. In particular, when this excitation is caused by iron ions (usually Fe2+) it is called Fenton’s process, which has several industrial applications involving wastewater treatment with great economic advantages, especially for occurring under normal conditions of pressure and temperature. Besides, the non-selectivity of the Fenton’s radicals assures that several kinds of effluents can be oxidized by these systems. The Fenton’s oxidation of a synthetic solution comprised by a few phenolic acids commonly found in OMW was studied. New results were introduced to the scientific community, obtained by the use of ceramic solids and low cost materials tested as heterogeneous catalysts. The classical process, in homogeneous phase, was also appraised and compared with a different approach of it, achieving interesting results regarding the reduction of sludge formation and reactants yields. Continuous operation modes were also performed in a tubular reactor, reaching good organic charge removals. The operating conditions were planned in a way to allow comparisons amongst several experiments. In this thesis, the calcination temperature of ceramic catalysts is the first subject to be evaluated. Its study shows that the temperature of 300 °C produced the most active solids. An iron-cerium solid at the molar proportion of 70/30 can be highlighted amongst the other ceramic solids by its superior oxidative promotion (which might be related to its higher surface area, 188 m2.g-1): complete phenolic destruction, 49 % COD removal and 45 % TOC abatement. Moreover, the effluent’s biodegradability was greatly enhanced and had its toxicity removed. Other researches using the same methodology of catalyst preparation comprised iron-copper and iron cobalt solids used at the same operation conditions, but without such success. Low cost materials recycling is another theme presented in this document. The attempt of using Fenton’s sludge as catalyst (directly, after calcination and as iron precursor), although resulting in active solids, did not succeed on the biodegradability enhancement, being discarded. On the other hand, zero valent iron (ZVI) gathered from two sources presented outstanding catalytic performances in batch (from 10 minutes to 2 hours) and continuous reactions (stable organic charge removals up to 168 hours of operation). Finally, the homogeneous Fenton’s reaction is appraised in order to generate results linking it to the heterogeneous process. In the same chapter, a different approach for the classical Fenton’s oxidation is performed, showing a great enhancement of the overall efficiency considering the sludge formation reduction and reactants yields augment. |
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