Treatment of industrial wastewater: application of chemical and biological processes
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2017-05-02
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As agroindústrias são um dos setores industriais que causam maior poluição da água, associadas não só ao desperdício de alguma matéria-prima, mas também aos produtos auxiliares adicionados ao longo do processamento que, no seu todo geram as águas residuais. A sua descarga direta nos cursos de água pode, por vezes, apresentar toxicidade para a fauna e flora existente devido às características recalcitrantes dos efluentes gerados. Como consequência, as indústrias têm sido desafiadas para promover um tratamento eficaz previamente à sua descarga. A aplicação de processos biológicos convencionais, frequentemente utilizados pelas vantagens económicas, nem sempre se traduz em resultados satisfatórios, uma vez que em algumas situações as águas residuais podem apresentar resistência à oxidação biológica. A utilização de processos químicos convencionais e em particular de Processos de oxidação avançados (POA) têm surgido como uma tecnologia promissora, de tratamento de águas residuais, principalmente na eliminação de poluentes orgânicos tóxicos/recalcitrantes que, consequentemente, permitem a sua descarga nos cursos de água ou a sua integração com processos biológicos.
O principal objetivo desta tese foi contribuir para o estudo e desenvolvimento de tecnologias oxidativas aplicáveis ao tratamento de águas residuais industriais com potencial impacto na região Norte de Portugal. Foram selecionados os efluentes gerados na produção de azeite, de vinho, de concentrado de sumo de frutas, de frutas cristalizadas, de pasta de papel e celulose, bem como de lixiviados de aterros municipais gerados pela deposição de resíduos sólidos urbanos.
Estruturalmente, a primeira parte do trabalho (capítulo 1) é dedicada à apresentação e revisão da literatura existente para o tratamento das águas residuais alvo de estudo. Neste capítulo, apresenta-se uma breve descrição das etapas envolvidas no processamento, a caraterização das águas residuais geradas e uma seleção de estudos efetuados nos últimos anos, que envolvem processos de oxidação química no tratamento das águas residuais e também quando combinados com outros tratamentos. Dos estudos apresentados verificou-se que a combinação de processos surge como uma proposta muito interessante para o tratamento dos efluentes em estudo. A utilização de
de coagulação/floculação química como tratamento primário desempenha uma etapa essencial na remoção de matéria em suspensão e coloidal para, numa etapa complementar, potenciar a eficiência do tratamento aplicado, seja ele biológico ou químico. Por outro lado, os processos de oxidação avançados, utilizados como pré-tratamento ou tratamento final, removem concentrações de matéria orgânica em efluentes com maior carga poluente, podendo ser complementados com um tratamento biológico.
Na segunda parte do trabalho, onde se inserem os capítulos 2 a 7, são apresentados os trabalhos experimentais efetuados para o tratamento das águas residuais. Todos os estudos apresentaram elevadas percentagens de remoção da fração orgânica, sendo que alguns permitem obter um efluente tratado capaz de ser descarregado num curso de água ou então ser enviado para uma estação de tratamento municipal urbana.
A aplicação do reagente de Fenton com radiação solar, aplicado a um efluente de indústria de pasta de papel, tratado e submetido a um pré-tratamento biológico permitiu atingir remoções de CQO e polifenóis totais acima de 90%. O tratamento solar com reagente de Fenton (foto-Fenton) apresentou maior eficiência quando comparado com os ensaios realizados na ausência de radiação solar nas mesmas condições experimentais. A aplicação de 20 e 50 mg/L de ferro revelou que a reação foto-Fenton solar pode atingir 90% de redução de COT para as duas situações, no entanto, a concentração de H2O2 e o tempo de reação diminuiu com o aumento da concentração de ferro.
No tratamento de um lixiviado de um aterro sanitário estabilizado, a combinação do processo de coagulação/floculação química com reagente de Fenton, permitiu remover 82% de CQO. Inicialmente, a partir do estudo do efeito do processo de coagulação-floculação para diferentes reagentes, foi possível estabelecer as melhores condições operacionais. Assim, a aplicação de 2,0 g/L de FeCl3.6H2O a pH 5, permitiu remover 63% da CQO, 80% de turvação e 74% dos polifenóis totais. Além disso, a combinação do processo de coagulação/floculação seguido do processo foto-Fenton solar revelou maior remoção de COT (75%) quando comparadas com as verificadas apenas no processo foto-Fenton solar (54%).
As águas residuais provenientes de um lagar de azeite foram submetidas ao processo de oxidação por reagente de Fenton combinado com um processo biológico anaeróbio, o que permitiu uma remoção de 58% de CQO. Para as seguintes condições ótimas, H2O2/CQO de 0.20, um valor de pH =3,5 e razão molar de H2O2/Fe2+= 15, o reagente de Fenton traduziu-se numa redução de 17,6% de CQO e 82,5% de polifenóis totais. Por outro lado, o processo biológico anaeróbio por si só, atingiu entre 52% e 74% de redução de CQO, com utilização de microrganismos inoculados em Sepiolite, previamente adaptados. A combinação dos dois processos permitiu obter reduções de CQO entre 64% e 88% e gerar valores de metano entre 281 cm3 e 322 cm3 de CH4/g de CQO removido.
As águas residuais resultantes de uma indústria de fruta cristalizada foram submetidas ao processo reagente de Fenton com radiação em combinação com o processo de coagulação/floculação química. Para as condições ótimas ([H2O2]= 5459 mg/L; [Fe3+]=286 mg/L; tempo > 180 min) previamente determinadas, através da metodologia RSM do modelo de Box-Benhnken, foi possível estabelecer a maior eficiência de tratamento. Assim, as condições definidas atingiram 45, 64 e 74% de remoção de CQO após 360 minutos, para uma irradiância de 23, 70 e 85 W/m2, respetivamente. A combinação do processo UV-A LED foto-Fenton com o processo de coagulação/floculação atingiu 80% de remoção de CQO, 95% de sólidos suspensos, bem como a 99% de turvação.
O tratamento de efluentes vinícolas foi efetuado através da aplicação de um processo oxidativo com base na utilização de reagentes que geram radicais sulfato, catalisados por metais de transição e radiação solar. A aplicação das condições ótimas, previamente determinadas ([HSO5-] = 2,5 mM; [M2(SO4)n] = 1,0 mM; pH = 6.5 e temperatura da reação = 323 K) permitiu obter reduções de CQO de 51, 42 e 35% com aplicação de Fe(II), Co(II) e Cu(II), respetivamente, como catalisadores. Verificou-se que a aplicação de HSO5-/Mn+ em várias doses consecutivas apresenta maior eficiência no início da reação. O processo HSO5-/Fe(II)/UV-A LED demonstrou maior capacidade de remoção de CQO e TOC quando comparado com o processo convencional foto-Fenton.
As águas residuais de uma empresa de concentrados de sumo de frutas foram submetidas a um processo biológico aeróbio seguido do processo de
coagulação/floculação química. Na primeira fase, o processo biológico atingiu remoções de CQO acima de 90%, nos reatores em que se adicionaram 2 g/L de biomassa e 20 g/L de matéria orgânica. Após determinação do coagulante ótimo e respetivas condições operacionais (0,44 g/L de FeCl3.5H2O e pH= 5,5) atingiram-se 94,4% e 99,6% de remoção de CQO e turvação, respetivamente.
Na última parte deste trabalho (Capítulo 8), são apresentadas as principais conclusões que se alcançaram ao longo dos vários estudos efetuados, onde se sugerem também melhorias e ideias complementares ao trabalho já apresentado.
Agro-industries are the main source of water pollution in industrial sector associated not only to depletion of raw materials, but also to additional products used during processing, thus generating wastewater. When it is released directly into natural watercourses, could be toxic to existing fauna and flora due the wastewater characteristics. Consequently, manufacturers have been challenged to promote the wastewater treatment previous to watercourse discharge. Conventional biological treatment processes, often used for it economic benefits do not always represent satisfactory results since in some cases the wastewater may exhibit resistance to biological oxidation. The use of chemical conventional process and advanced oxidation processes (AOP) have emerged as a promising wastewater treatment technology, mainly to the elimination of toxic and recalcitrant organic pollutants, which consequently allow it discharge into watercourse or their integration with biological processes. The main objective of this thesis was contribute to the study and development of oxidative technologies for the treatment of industrial wastewaters with high impact in the north of Portugal. The wastewaters generated in the production of olive oil, wine, fruit concentrate juice, crystallized fruit, pulp and paper, and the municipal landfill leachate generated by waste disposal were selected to be assessed. Structurally, the first part of this work (Chapter 1) is dedicated to the presentation and review of literature in wastewater treatment studied. In this chapter, is presented a brief description of processing, characterization of generated wastewater and a selection of main developed studies in recent years, involving chemical oxidation processes in wastewater treatment and it combination with other treatments (biological and/or chemical). It was found that the combination of processes appears to be the most advantageous for the treatment of effluents in the study. The use of chemical coagulation-flocculation processes as primary treatment plays an essential role in the removal of suspended and colloidal matter, enhancing the efficiency of a complementary treatment. On the other hand, the advanced oxidation processes, used as pre-treatment or final treatment, remove organic matter concentrations in effluents with greater pollutant load to be complemented with biological treatment. In the second part (Chapters 2 to 7) the experimental work performed for the treatment of wastewater is presented. All studies showed high removal rate of the organic fraction, obtaining in some cases a treated effluent that can be discharged into a watercourse or be sent to an urban municipal treatment plant. The application of Fenton reagent with solar radiation, applied to the effluent from pulp mill industry and already subjected to biological pre-treatment reached removals of COD and total polyphenols above 90%. Solar photo-Fenton reaction presented higher efficiency than the respective dark reaction under identical experimental conditions. Using 20 and 50 mg Fe L-1 revealed that solar photo-Fenton can reach the same DOC degradation (90%), however, H2O2 concentration and reaction time decreased with higher iron concentration. In stabilized landfill leachate treatment, the combination of coagulation-flocculation process with Fenton reagent allowed to remove 82% of COD. Firstly, from the study of the effect of coagulation/flocculation with different chemicals, was possible to establish the best operational conditions. Thus, using 2 g L-1 of FeCl3·6H2O at pH 5, allowed removing 63% of COD, 80% of turbidity and 74% of total polyphenols. Moreover, coagulation/flocculation combined with solar photo-Fenton revealed higher DOC (75%) reductions than single solar photo-Fenton (54%). The olive mill wastewater used in the study was submitted to the combination of Fenton reagent with an anaerobic biological to remove the pollutant load. Using a fixed weight ratio H2O2/COD of 0.20, a pH = 3.5 and a H2O2/Fe2+ molar ratio of 15 defined as optimal initial conditions in Fenton process, there was obtained a reduction of 17.6% in COD and 82.5% in the total polyphenol content. On the other hand, anaerobic biological treatment itself allowed conversions from 52% to 74% of COD using microorganisms immobilized in Sepiolite and previously adapted. Both combination allowed COD reductions ranging from 64 to 88% and a yield of methane generation, ranging from 281 cm3 to 322 cm3 of CH4/g COD removed. The candied fruit wastewater was studied by the combination of Fenton reagent subjected to UV radiation with chemical coagulation-flocculation process. Under the optimal conditions ([H2O2] = 5459 mg L-1; [Fe3+] = 286 mg L-1; time >180 minutes) previously determined by a Box-Behnken design of Response Surface Methodology allowed to establish a higher treatment efficiency. Thus, it was achieved a COD removal of 45, 64 and 74% after 360 minutes using an irradiance of 23, 70 and 85 W/m2 respectively. The combination of UV-A LED photo-Fenton with coagulation-flocculation-decantation reached 80 % of COD removal 95% of total suspended solids, as well as almost total removal of turbidity (99%). The treatment of winery wastewater (WW) was studied by the application of oxidative process based on sulfate radicals, catalysed by transition metals and UV radiation. Under determined optimal operational conditions – [HSO5-] = 2.5 mM; [M2(SO4)n] = 1.0 mM; pH = 6.5 and reaction temperature = 323 K – 51%, 42% and 35% of COD removal was achieved using respectively Fe(II), Co(II) and Cu(II) as catalysts. , It was demonstrated that the use of HSO5-/Mn+ in several consecutive doses was more efficient than adding the reagents as a single dose at the beginning of the reaction. The HSO5-/Fe(II)/UV-A LED process demonstrates a high COD and TOC removal efficiency when compared with same conditions conventional photo-Fenton. Wastewater from an industry of fruit juice concentrate was treated by coagulation-flocculation process combined with an aerobic biological process.Firstly in aerobic biological treatment were obtained above 90% of COD removals, in reactors initially loaded with 2 g VSS L−1 of biomass concentration and 20 g COD L−1 of organic matter concentration. After determined coagulation-flocculation optimal conditions in a tertiary treatment (0.44 g L−1 of ferric chloride at pH = 5.5) was achieved 94.4% and 99.6% removal parameters in turbidity and COD, respectively. The last part (Chapter 8) of this work present the main conclusions that were reached during the various studies conducted, which also suggest improvements and additional ideas to the work already presented.
Agro-industries are the main source of water pollution in industrial sector associated not only to depletion of raw materials, but also to additional products used during processing, thus generating wastewater. When it is released directly into natural watercourses, could be toxic to existing fauna and flora due the wastewater characteristics. Consequently, manufacturers have been challenged to promote the wastewater treatment previous to watercourse discharge. Conventional biological treatment processes, often used for it economic benefits do not always represent satisfactory results since in some cases the wastewater may exhibit resistance to biological oxidation. The use of chemical conventional process and advanced oxidation processes (AOP) have emerged as a promising wastewater treatment technology, mainly to the elimination of toxic and recalcitrant organic pollutants, which consequently allow it discharge into watercourse or their integration with biological processes. The main objective of this thesis was contribute to the study and development of oxidative technologies for the treatment of industrial wastewaters with high impact in the north of Portugal. The wastewaters generated in the production of olive oil, wine, fruit concentrate juice, crystallized fruit, pulp and paper, and the municipal landfill leachate generated by waste disposal were selected to be assessed. Structurally, the first part of this work (Chapter 1) is dedicated to the presentation and review of literature in wastewater treatment studied. In this chapter, is presented a brief description of processing, characterization of generated wastewater and a selection of main developed studies in recent years, involving chemical oxidation processes in wastewater treatment and it combination with other treatments (biological and/or chemical). It was found that the combination of processes appears to be the most advantageous for the treatment of effluents in the study. The use of chemical coagulation-flocculation processes as primary treatment plays an essential role in the removal of suspended and colloidal matter, enhancing the efficiency of a complementary treatment. On the other hand, the advanced oxidation processes, used as pre-treatment or final treatment, remove organic matter concentrations in effluents with greater pollutant load to be complemented with biological treatment. In the second part (Chapters 2 to 7) the experimental work performed for the treatment of wastewater is presented. All studies showed high removal rate of the organic fraction, obtaining in some cases a treated effluent that can be discharged into a watercourse or be sent to an urban municipal treatment plant. The application of Fenton reagent with solar radiation, applied to the effluent from pulp mill industry and already subjected to biological pre-treatment reached removals of COD and total polyphenols above 90%. Solar photo-Fenton reaction presented higher efficiency than the respective dark reaction under identical experimental conditions. Using 20 and 50 mg Fe L-1 revealed that solar photo-Fenton can reach the same DOC degradation (90%), however, H2O2 concentration and reaction time decreased with higher iron concentration. In stabilized landfill leachate treatment, the combination of coagulation-flocculation process with Fenton reagent allowed to remove 82% of COD. Firstly, from the study of the effect of coagulation/flocculation with different chemicals, was possible to establish the best operational conditions. Thus, using 2 g L-1 of FeCl3·6H2O at pH 5, allowed removing 63% of COD, 80% of turbidity and 74% of total polyphenols. Moreover, coagulation/flocculation combined with solar photo-Fenton revealed higher DOC (75%) reductions than single solar photo-Fenton (54%). The olive mill wastewater used in the study was submitted to the combination of Fenton reagent with an anaerobic biological to remove the pollutant load. Using a fixed weight ratio H2O2/COD of 0.20, a pH = 3.5 and a H2O2/Fe2+ molar ratio of 15 defined as optimal initial conditions in Fenton process, there was obtained a reduction of 17.6% in COD and 82.5% in the total polyphenol content. On the other hand, anaerobic biological treatment itself allowed conversions from 52% to 74% of COD using microorganisms immobilized in Sepiolite and previously adapted. Both combination allowed COD reductions ranging from 64 to 88% and a yield of methane generation, ranging from 281 cm3 to 322 cm3 of CH4/g COD removed. The candied fruit wastewater was studied by the combination of Fenton reagent subjected to UV radiation with chemical coagulation-flocculation process. Under the optimal conditions ([H2O2] = 5459 mg L-1; [Fe3+] = 286 mg L-1; time >180 minutes) previously determined by a Box-Behnken design of Response Surface Methodology allowed to establish a higher treatment efficiency. Thus, it was achieved a COD removal of 45, 64 and 74% after 360 minutes using an irradiance of 23, 70 and 85 W/m2 respectively. The combination of UV-A LED photo-Fenton with coagulation-flocculation-decantation reached 80 % of COD removal 95% of total suspended solids, as well as almost total removal of turbidity (99%). The treatment of winery wastewater (WW) was studied by the application of oxidative process based on sulfate radicals, catalysed by transition metals and UV radiation. Under determined optimal operational conditions – [HSO5-] = 2.5 mM; [M2(SO4)n] = 1.0 mM; pH = 6.5 and reaction temperature = 323 K – 51%, 42% and 35% of COD removal was achieved using respectively Fe(II), Co(II) and Cu(II) as catalysts. , It was demonstrated that the use of HSO5-/Mn+ in several consecutive doses was more efficient than adding the reagents as a single dose at the beginning of the reaction. The HSO5-/Fe(II)/UV-A LED process demonstrates a high COD and TOC removal efficiency when compared with same conditions conventional photo-Fenton. Wastewater from an industry of fruit juice concentrate was treated by coagulation-flocculation process combined with an aerobic biological process.Firstly in aerobic biological treatment were obtained above 90% of COD removals, in reactors initially loaded with 2 g VSS L−1 of biomass concentration and 20 g COD L−1 of organic matter concentration. After determined coagulation-flocculation optimal conditions in a tertiary treatment (0.44 g L−1 of ferric chloride at pH = 5.5) was achieved 94.4% and 99.6% removal parameters in turbidity and COD, respectively. The last part (Chapter 8) of this work present the main conclusions that were reached during the various studies conducted, which also suggest improvements and additional ideas to the work already presented.
Descrição
Tese de Doutoramento em Ciências Químicas e Biológicas
Palavras-chave
Tratamento de água residual , Indústrias , Resíduos sólidos urbanos