Combined Chemical Oxidation and Bioremediation for Decabromodiphenyl Ether Degradation in Soil

• Main Authors: Cheng-Chun Lin, 林政君
• Other Authors: Yi-Tang Chang
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/57210768521561988283

碩士 === 東吳大學 === 微生物學系 === 99 === Decabromodiphenyl ether (DBDE) is a flame retardant commonly used in the industry, and its has become an emerging contaminants in recent years. Due to its structural stability and low solubility in water, DBDE has a tendency of accumulating in the sediment, increasing the difficulty of being biodegraded. Thus, DBDE can lead to ecotoxicity and threaten the health of various or organisms. The purpose of this study was to remove DBDE (20 mg/kg) in soil by using Fenton’s reaction pretreatment to accelerate the speed of biodegradation, and to use gas chromatography mass spectrometry (GC/MS), Fourier transform infrared spectroscopy (FT-IR), and ion chromatography (IC) to analyze the degradation pathway of the DBDE decomposition process and the structure of the resulting product. Furthermore, this study used community-level physiological profiling (CLPP), PCR-DGGE, and gene cloning to analyze the bioremediation process of bacterial structure and diversity. In the Fenton’s Process, the soil used in this study contained lower levels of crystalline iron and higher levels of organic matter, so additional ferrous ions were put into the soil to catalytic H2O2. Under these operating conditions and soil type, an optimal treatment efficiency of 43.40% was obtained under the Fenton’s reaction of 44,336 mg/L of H2O2 and 500mg/L of Fe2+ for 30 minutes, and then adding 22,168 mg/L of H2O2 twice for 30 minutes. It was found that Fenton’s oxidation can apply debromination to DBDE, resulting in a pentabrominated diphenyl ether compound, heptabrominated diphenyl ether, and other unknown low molecular weight compounds. For biodegradation, we selected one aerobic mixed culture obtained from the sediment of Daan bridge and two compost mixed cultures. The results showed that the Daan flora had the best degradation rate and can degrade 20 mg/kg of DBDE to 10 mg/kg in 180 days, with a pseudo-first order rate constant (k) of 0.0039 day-1. In contrast, compost in the experimental group may have higher organic matter content, leading to adsorption of DBDE, so the biodegradable ratio in the contribution of the DBDE removal is significantly lower than that of the Daan flora. Microbial structure analysis of Daan flora showed that the system contained 10% of aerobic degrading PBDE bacterium -- Sphingomonas sp., and of aerobic polycyclic compounds degrading a bacterium -- Pseudomonas sp.. This is a possible reason that the flora can degrade DBDE. Combining the chemical and biological experiments, the best processing conditions for Fenton oxidation above were used to treat high concentrations of DBDE contaminated soil, then Daan flora was used for biodegradation. The results show that chemical oxidation pretreatment can degradate 20 mg/kg DBDE to 12.56 mg/kg, and subsequent biodegradation in the following 133 days degraded residual DBDE to 4.99 mg/kg. The overall removal rate of DBDE was 75.05%, and debromination and nitrification occurred at the same time as the biological degradation process. The results also show that Fenton’s reaction pretreatment did not cause too much interference to bacterial physiological status and community structure. The flora was varied significantly between free and attatched bacterium. The study also pointed out that the Fenton’s reaction after pre-treatment was effective in promoting the biodegradation of the DBDE segment growth of bacteria and the biological degradation of the debromination and nitrification. 　　　In the early stage of biodegradation, the proportion of bacteria presented in the flora was comprised mostly of Pseudomonas sp. and Geobacter sp.. With the increase of degradation time, the number of Acidobacteria bacterium, Chlorobi bacterium, and Verrucomicrobia bacterium increased, causing an increase in the bacterial diversity index and the evenness index. As the degradation time increased, the product types increased, and the proportion of the bacteria with a catechol 2,3-dioxygenase gene also increased. Thus the posterior segment of the PBDE products were biodegradable. 　　 The study also separated 10 purified bacteria strains during the degradation of DBDE, and tested the degradation of PBDEs and its metabolites. Results indicat that the majority of strains can oxidize in the presence of DBDE, and strain D2 (Brachybacterium sp.), D3 (Chelatobacter heintzii), B2 (Pseudomonas delhiensis), P5 (Brevibacterium sp.) had the best ability to decompose PBDE and its metabolites. This study shows that physical and chemical treatment can promote the decomposition of DBDE biodegradation, but the ability of ISCO removing organic pollutants would be affected by the chemical structure of pollutants and soil composition, and therefore change the dose of the oxidant. It is recommended that in-situ DBDE remediation should be conducted after the Lab scale pilot test to obtain H2O2 and Fe2+ of the best dose and reaction time. In conclusion, Fenton pre-treatment and post-biodegradation can effectively break down DBDE in soil, and it can be used as a reference of in-situ remediation.