Treatment for soil contaminated with dioxin using nano assisted photodegradation and biological technologies | |
| Author | Nguyen Duy Binh |
| Call Number | AIT Diss. no.EV-14-02 |
| Subject(s) | Soil pollution Dioxins--Environmental aspects |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Environmental Engineering and Management |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. EV-14-02 |
| Abstract | The overall goal of the study is to find appropriate technologies to deal with dioxin contaminated soil, which can eventually be applied in the dioxin hotspots in Vietnam. The research aimed to test the hypothesis that nanoparticles can enhance the photodegradation and biological degradation of dioxins in soil. Based on the hypothesis, two treatment approaches, including photodegradation treatment and biological treatment were implemented in order to investigate the feasibility of the developed treatment methods for application in the dioxin hotspots in Vietnam. For the nano assisted photodegradation approach, decomposition of 2,3,7,8-TCDD present in soil at 11.7 ppb under UV illumination (350-400 nm) was investigated using a novel combination of nontoxic solvents (1-butanol, tetradecane, and water) mixed in soil and nanoscale anatase TiO2 (nTiO2) distributed on 2mm soil surface. Solvents were added in order to desorb and mobilize dioxins upward for photodegradation reactions. Three types of UV-exposure experiments were conducted: intermittent exposure (8h/day) for 90 days and 120 days, sequential intermittent (120 days) and continuous (24h/day) for the next 55 days, and continuous exposure for 55 days. The influence of several factors on dioxin photodegradation efficiency was investigated, including UV absorption by the targeted dioxin, presence of catalytic nTiO2 on soil surface, the solvent evaporation rate as well as the vertical gradients of solvents added into the soil columns. Results of dioxin analysis for the soil samples collected at the end of experiments showed that mixture of solvents desorbed and mobilized dioxin from bottom soil layers to top soil layers for photodegradation reactions. It was observed that the photodegradation enhanced by nTiO2present on the soil surface considerably increased the dioxin degradation. Higher removal efficiencies were found for treatments with 15% by wt of nTiO2 mixed in surface soil as compared to the 5%wt nTiO2 treatments. The highest removal efficiency (79.6%) was for the sequential intermittent-continuous UV exposure experiment with nTiO2. Continuous UV exposure experiment yielded low removal efficiencies, which was probably due to an extremely high solvent evaporation rate that hindered the dioxin mobilization through the soil column to the surface for photodegradation. Dechlorinated products of 2,3,7,8-TCDD were generally not detected which suggests the degradation of the targeted dioxin by C-Cl cleavage was negligible. Further modifications to improve the removal efficiency were proposed. Large scale engineered systems may employ this integrated treatment approach which can also incorporate the recovery of nTiO2 contained surface soil and solvent vapor. For the nano assisted biodegradation approach, the sequentially anaerobic-aerobic biodegradation (17 weeks under anaerobic condition and 6 weeks under aerobic condition) of 2,3,7,8-TCDD contaminated soil (at 12.5 ppb) was implemented under different scenarios. The sequential anaerobic-aerobic biodegradation was conducted to investigate the potential of dechlorination in anaerobic conditions and oxidation of the less chlorinated dioxin in the aerobic condition. The treatments included Bio alone, Bio and Carboxymethyl cellulose (CMC) coated nanoscale zero valent iron (CMC-nZVI), Bio and surfactant (Tween-80), Bio and CMC-nZVI and Tween-80. In Bio alone treatments, dioxin contaminated soil was contained into 120ml serum bottles with the addition of nutrient solution as well as minimal salts medium solution containing microorganisms from a native dioxin hotspot in Vietnam (Bien Hoa airbase). The native microorganisms were enriched from Bien Hoa sediment under anaerobic condition for 1 month before use. With Bio and CMC-nZVI, Bio and surfactant (Tween-80), Bio and CMC-nZVI and Tween-80, the preparation of microcosms was similar with Bio alone treatment, the only difference iv was the adding of synthesized CMC-nZVI solution, or Tween-80 solution, or combination of both of them, respectively. The pH of the microcosms was adjusted to 7.5 in all treatment units. The results showed that enriched microorganisms collected from Bien Hoa airbase were quite effective in dioxin removal. Under sequential anaerobic-aerobic conditions, approx. 60% of dioxin removal was achieved, even in severe low pH condition (below 4.0) at the end of each treatment. Surfactant Tween-80 seemed to biostimulate methanogens rather than dechlorinators as the measured methane production was the highest while the dioxin removal efficiency was the lowest, compared with other bio-treatments. The CMC coated on the nZVI particle surface could prevent the direct contact between bacterial cell surface and nZVI hence prevented cell death and lysis which lead to a high dioxin removal efficiency. The presence of CMC-nZVI in bio-treatments could gradually provide H2 required for microbiological processes. However, it seemed that the amount of CMC-nZVI added into bio-treatment was higher than required which provided a high release rate of H2 that would benefit (biostimulate) methanogens than dechlorinators. Suggestions for enhancing dioxin removal efficiency were discussed including controlling pH variations during the treatment and optimize the CMC-nZVI amount. More dioxin congeners should also be analyzed especially for lower chlorinated congeners than 4 to examine the effects of anaerobic and then aerobic biodegradation processes. Feasibility of the newly developed laboratory scale treatment methods for application in hotspots in Vietnam was investigated. It is expected that by considering all of the influencing factors, the nano-photodegradation as well as the bio-treatment approaches could be promisingly apply for in situ remediation of soil contaminated with dioxin or dioxin-like compounds due to its treatment efficiency, low cost, and no impact to environment. Overall, the photodegradation system would be promisingly suitable for tropical conditions by utilizing the natural sunlight especially in the hot climate of southern Vietnam. However, an engineering system may be more suitable to provide the artificial UV source during the rainy and dark conditions. Gradient solvent injection and reuse of solvent and nanoparticles can also be considered in such an engineering system. The biodegradation experiments should be further optimized and more laboratory scale tests should be conducted to final optimal conditions. |
| Year | 2014 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-14-02 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering (EV) |
| Chairperson(s) | Nguyen Thi Kim Oanh ;Preeda Parkpian (Co-Chairperson) |
| Examination Committee(s) | Karstensen, Kare ;Pham Huy Giao |
| Scholarship Donor(s) | Ministry of Education and Training (Vietnam) ;Asian Institute of Technology Fellowship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2014 |