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The aim of this study was to access the efficacy of an enhanced in situ bioremediation technology at a 1,2-dichloroethane (1,2-DCA) polluted site in southern Taiwan. A water-soluble substrate was injected into the groundwater to provide carbon sources for microbial growth. After substrate injection, increased total organic carbon (TOC) concentrations and microbial populations including Dehalococcoides spp. and Desulfitobacterium spp. were observed in the groundwater. Microbial diversity was analyzed using denaturing gradient gel electrophoresis (DGGE) and 16S rDNA sequencing to identify the bacterial strains. The results showed that after 4.5 months of substrate injection, the reduction-oxidation potential (ORP) changed from aerobic to anaerobic conditions. The less oxygen-tolerable 1,2-DCA degrading bacteria Dehalococcoides spp. started to accumulate in groundwater. However, the more oxygen-tolerable Desulfitobacterium spp. didn¡¦t show a prominent change, although the ORP was suitable for Desulfitobacterium spp. to carry out reductive dechlorination. The DGGE results indicate that with the injected carbon sources and mineral nutrients, both the groundwater microbial diversity and the amount of dominant bacteria were increased. The 16S rDNA sequencing demonstrated that the amount and diversity of 1,2-DCA degradation-related bacteria also increased with the injection of substrate. Six groups of 1,2-DCA degradation related reactions were found: dechlorination, chlorinated-compound degradation, denitrification, iron-reduction, sulfate-reduction and methane-utilizing. Four species that can directly degrade 1,2-DCA were found: Dehalobacter sp., Dehalococcoides sp., Nitrosospira sp. and Pseudomonas sp. Moreover, 11 methane-utilizing bacterial species were also discovered. The presence of these methane-utilizing bacteria not only might assist the process of denitrification and sulfate-reduction, but also could diminish the emission of the greenhouse gas. The results of this study confirmed that the addition of substrates could affect the groundwater oxidation-reduction state and enhance the bioremediation at the 1,2-DCA-contaminated site. Thus, enhanced in situ bioremediation is a feasible technology for site remediation.

A new treatment technology, called Advanced Reduction Process (ARP), was developed by combining UV irradiation with reducing reagents to produce highly reactive species that degrade contaminants rapidly. Vinyl chloride (VC) and 1,2-dichloroethane (1,2-DCA) pose threats to humans and the environment due to their high toxicity and carcinogenicity. In this study, batch experiments were conducted under anaerobic conditions to investigate the degradations of VC and 1,2-DCA with various ARP that combined UV with dithionite, sulfite, sulfide or ferrous iron. Complete degradation of both target compounds was achieved by all ARP and the reactions were found to follow pseudo-first-order decay kinetics. The effects of pH, sulfite dose, UV light intensity and initial contaminant concentration on the degradation kinetics were investigated in the photochemical degradation of VC and 1,2-DCA by the sulfite/UV ARP. The rate constants were generally promoted by raising the solution pH. The optimal pH conditions for VC and 1,2-DCA degradation were pH 9 and pH 11,respectively. Higher sulfite dose and light intensity were found to increase the rate constants linearly for both target contaminants. A near reciprocal relation between the rate constant and initial concentration of target compounds was observed in the degradation of 1,2-DCA. The rate constant was observed to be generally independent of VC concentration, but with a slight increase at lower concentrations. A degradation mechanism was proposed that described reactions between target contaminants and reactive species such as the sulfite radical and hydrated electron that were produced in the photolysis of sulfite solution. A mechanistic model that described major reactions in the ARP system was developed and explained the dependence of the rate constant on those experimental factors. Chloride ion and chloroethane were detected as the major degradation products at acid and neutral pH. An increase in pH promoted the extent of dechlorination with complete dechlorination being observed at pH 11 for both VC and 1,2-DCA. Due to the rapid degradation kinetics in these ARPs, this new treatment technology may be applied to remove various contaminants in water and wastewater.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-04-30T16:15:44Z No. of bitstreams: 1 TALLES CAIO LINHARES DE OLIVEIRA - DISSERTAÇÃO PPGEQ 2014..pdf: 2048638 bytes, checksum: 8906a39fa89dff7c77323f97499594a3 (MD5) / Made available in DSpace on 2018-04-30T16:15:44Z (GMT). No. of bitstreams: 1 TALLES CAIO LINHARES DE OLIVEIRA - DISSERTAÇÃO PPGEQ 2014..pdf: 2048638 bytes, checksum: 8906a39fa89dff7c77323f97499594a3 (MD5) Previous issue date: 2014-09 / CNPq / O monômero cloreto de vinila (MVC), matéria prima usada para a obtenção do policloreto de vinila (PVC), é produzido comercialmente em larga escala através da decomposição térmica do 1,2-dicloroetano (EDC) em um reator tubular inserido em um forno industrial. O PVC possui aplicações que vão desde produtos médico-hospitalares e embalagens para alimentos até peças de alta tecnologia como as usadas em equipamentos espaciais. O principal problema enfrentado na operação é a formação de uma camada de coque no interior do reator que limita o tempo de operação. O presente trabalho consiste no desenvolvimento de modelos matemáticos para a previsão do comportamento de um reator de craqueamento térmico de EDC. Um total de três modelos foram formulados, o primeiro modelo serviu para estruturação do algoritmo e para a análise geral da metodologia usada. No segundo modelo uma cinética reacional mais complexa envolvendo composto estáveis e radicais foi implementada, a deposição de coque foi considerada o que possibilitou estimar o seu impacto no tempo de produção e nas variáveis do processo como: pressão, temperatura e conversão. O último modelo foi desenvolvido utilizando técnicas de fluidodinâmica computacional (CFD) e forneceu as distribuições na direção radial e ao longo do reator para as variáveis do processo. Os resultados obtidos de todos os modelos estão em concordância com dados industriais disponíveis. Os modelos I e II podem ser usados para realização de testes no processo sem a necessidade de utilização de unidade piloto e como ponto de partida para a otimização nos fornos de craqueamento, enquanto o modelo em CFD pode contribuir para estudo de melhorias de projeto deste tipo de reator. / The vinyl chloride monomer (MVC) raw material used to obtain the polyvinyl chloride (PVC), is commercially produced on a large scale by thermal decomposition of 1,2dichloroethane (EDC) inserted into a tubular reactor in an oven industrial. PVC has applications ranging from medical products and food containers to high-tech parts like those used in space equipment. The main problem faced in the operation is the formation of a layer of coke inside the reactor which limits the time of operation. The present work is the development of mathematical models for predicting the behavior of reactor thermal cracking of EDC. A total of three models were formulated, the first model was used to structure the algorithm and the overall analysis of the methodology used. In the second model a more complex reaction kinetics involving radicals and stable compound was implemented, coke deposition was found which allowed to estimate their impact on production time and the process variables such as pressure, temperature and conversion. The last model was developed using computational fluid dynamics (CFD) and provided the distributions in the radial direction and along the reactor for the process variables. The results of all the models are in agreement with industrial data available. Models I and II can be used for testing the process without the need of using pilot unit and as a starting point to optimize the cracking furnaces while the CFD model study can contribute to improvements in the design of this type reactor.

A new class of treatment processes called Advanced Reduction Processes (ARP) has been proposed. The ARPs combine activation methods and reducing agents to form highly reactive reducing radicals that degrade oxidized contaminants. Batch screening experiments were conducted to identify effective ARP by applying several combinations of activation methods (ultraviolet light, ultrasound, electron beam, microwaves) and reducing agents (dithionite, sulfite, ferrous iron, sulfide) to degradation of five target contaminants (perchlorate, nitrate, perfluorooctanoic acid, 2,4 dichlorophenol, 1,2 dichloroethane) at 3 pH levels (2.4, 7.0, 11.2). These experiments identified the combination of sulfite activated by ultraviolet light produced by a low pressure mercury vapor lamp as an effective ARP. More detailed kinetic experiments were conducted with nitrate and perchlorate as target compounds and nitrate was found to degrade more rapidly than perchlorate. The effects of pH, sulfite concentration, and light intensity on perchlorate and nitrate degradation were investigated. The effectiveness of the sulfite/UV-L treatment process improved with increasing pH for both perchlorate and nitrate.