Groundwater contamination by petroleum hydrocarbons has become one of the serious environmental problems in many countries. The sources of petroleum-hydrocarbon contaminants may be released from above ground and underground storage tanks, and pipelines. Petroleum hydrocarbons are mainly composed of benzene, toluene, ethyl- benzene, and xylems (BTEX), and other constituents such as methyl-tert-butyl ether (MTBE), naphthalene, 1,3,5-trimethylbenzene (1,3,5-TMB), and 1,2,4-trimethylbenzene (1,2,4-TMB). It is generally recognized that petroleum hydrocarbons have high risks to environmental receptors when hydrocarbon releases occur. Various biological, physical, and chemical remediation technologies (e.g. pump and treat, air sparging, enhanced bioremediation, and chemical oxidation) can be used to remediate petroleum-hydrocarbon contaminated groundwater. However, many of these techniques are typically costly or have limited applications.
Permeable reactive barriers (PRBs) are a promising technology for the passive and in situ treatment of contaminated groundwater. A PRB can be defined as ¡§an emplacement of reactive materials in the subsurface designed to intercept a contaminant plume, provide a preferential flow path through the reactive media, and transform the contaminant(s) into environmentally acceptable forms to attain remediation concentration goals at points of compliance.¡¨ The oxygen release materials can be emplaced in the PRBs to passive increase dissolved oxygen (DO) in the subsurface to enhance the intrinsic biodegradation of dissolved hydrocarbons.
In the first part of this study, guidelines for PRBs installation have been developed for the remediation of petroleum hydrocarbons, heavy metals, and organic solvents contaminated groundwater. PRB is a cost-effective approach for the remediation of contaminated aquifers. As contaminated groundwater moves through a permeable reactive barrier, the contaminants are scavenged or degraded, and uncontaminated groundwater emerges from the downgradient side of the reactive zone. The permeable reactive barrier concept has several advantages over other remediation technologies currently in use (e.g., pump and treat, air sparging), including absence of mechanical facilities and the electric power, no groundwater extraction and reinjection, treatment in situ, and cost-effective. The first part of this study presents the designs, applications, and case studies of PRB systems on groundwater remediation.
In the second part of this study, oxygen release materials have been constructed and evaluated for the appropriate components in batch experiments. Microbial degradation of petroleum hydrocarbons in groundwater can occur naturally. Since the petroleum-hydrocarbons are generally degraded faster under aerobic conditions, aerobic bioremediation can be applied to enhance the biodegradation of petroleum-hydrocarbons within of the plume if oxygen can be provided to the subsurface economically. Batch experiments were conducted to design and identify the components of the oxygen-releasing materials. Cement and gypsum were used as a binder in this mixtures experments.
(1) using cement as the binding material
The mixtures of the oxygen release material were prepared by blending cement, peat, sand, ethylene-vinyl acetate copolymer(EVA), calcium peroxide (CaO2), and water together at a ratio of 1.0¡G0.18¡G0.20¡G0.10¡G1.12¡G1.74 by weight. Cement was used as a binder and regular medium filter sand was used to increase the permeability of the mixture. Calcium peroxide releases oxygen upon contact water. The designed material with a density of 1.9 g/cm3 was made of 3.5 cm cube for the batch experiment. Results show that the oxygen release rate of the material is 0.046 mg O2/day/g rock. The oxygen release material was able to remain active in oxygen release for more than three months.
(2) using gypsum as the binding material
The mixtures of the oxygen release material were prepared by blending gypsum, CaO2, sand, and water together at a ratio of 1¡G0.5¡G0.14¡G0.75 by weight. Gypsum was used as a binder and regular medium filter sand was used to increase the permeability of the mixture. Calcium peroxide releases oxygen upon contact water. The designed material with a density of 1.1 g/cm3 was made of 3.5 cm cube for the batch experiment. Results show that the oxygen release rate of the material is 0.031 mg/day/g. The oxygen release material was able to remain active in oxygen release for more than three months.
In the third part of this study, immobilization technology was applied to produce the low permeability wrapping film for the construction of oxygen-releasing granular materials. The mixtures of the oxygen release material were prepared by blending alginate, CaO2, and sand together at a ratio of 8.3¡G1.0¡G1 by weight. The low permeability wrapping film of the oxygen release material was able to remain active in oxygen release for two months.
In the fourth part of this study, a laboratory-scale column experiment was conducted to evaluate the feasibility of this proposed system on the bioremediation of petroleum-hydrocarbon contaminated groundwater. This system was performed using a series of continuous-flow glass columns including four consecutive soil columns. Simulated petroleum-hydrocarbons contaminated groundwater with a flow rate of 0.263 m/day was pumped into this system. In the column experiment, the samples of column influent and specified sampling ports were collected and analyzed for pH, DO, BTEX, MTBE, and microbial populations. Results show that up to 99% of BTEX removal was observed in this passive system.
Results from this study would be useful in designing an efficient and cost-effective passive oxygen-releasing and bioremediation system to remediate petroleum- hydrocarbon contaminated aquifer.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0121108-031517 |
| Date | 21 January 2008 |
| Creators | Chen, Ting-yu |
| Contributors | Jong-kang Liu, Mun-she Lee, Long-chem Wu, Ting-nien Wu, Chih-ming Kao, Cheng-di Dong |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0121108-031517 |
| Rights | not_available, Copyright information available at source archive |
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