Soil and groundwater at many existing and former industrial areas and disposal sites is contaminated by organic solvent compounds that were released into the environment. Organic solvent compounds are heavier than water. When they are released into the subsurface, they tend to adsorb onto the soils and cause the appearance of LNAPL (light nonaqueous phase liquid) and DNAPL (dense nonaqueous phase liquid) pool. The industrial petroleum hydrocarbons (e.g., methyl tertiary-butyl ether, MTBE and benzene) and chlorinated solvent (e.g., trichloroethylene, TCE) are among the most ubiquitous organic compounds found in subsurface contaminated environment. One cost-effective approach for the remediation of the chlorinated solvent and petroleum products contaminated aquifers is the installation of permeable reactive zones or barriers within aquifers. As contaminated groundwater moves through the emplaced reactive zones, the contaminants are removed, and uncontaminated groundwater emerges from the downgradient side of the reactive zones.
The objectives of this study were developed to evaluate the feasibility of applying in-situ chemical oxidation (ISCO) barrier and in-situ slow polycolloid-releasing substrate (SPRS) biobarrier system on the control of petroleum hydrocarbons and chlorinated solvent plume in aquifer. In the ISCO barrier system, it contained oxidant-releasing materials, to release oxidants (e.g., persulfate) contacting with water for oxidating contaminants existed in groundwater. In this study, laboratory-scale fill-and-draw experiments were conducted to determine the compositions ratios of the oxidant-releasing materials and evaluate the persulfate release rates. Results indicate that the average persulfate-releasing rate of 7.26 mg S2O82-/d/g was obtained when the mass ratio of sodium persulfate/cement/sand/water was 1/1.4/0.24/0.7. The column study was conducted to evaluate the efficiency of in situ application of the developed ISCO barrier system on MTBE and benzene oxidation. Results from the column study indicate that approximately 86-92% of MTBE and 95-99% of benzene could be removed during the early persulfate-releasing stage (before 48 pore volumes of groundwater pumping). The removal efficiencies for MTBE and benzene dropped to approximately 40-56% and 85-93%, respectively, during the latter part of the releasing period due to the decreased persulfate-releasing rate. Results reveal that acetone, byproduct of MTBE, was observed and then further oxidized completely. Results suggest that the addition of ferrous ion would activate the persulfate oxidation. However, excess ferrous ion would compete with organic contaminants for persulfate, causing the decrease in contaminant oxidation rates. In the SPRS biobarrier system, the food preparation industry has tremendous experiences in producing stable oil-in-water (W/O, 50/50) emulsions with a uniformly small droplet size. Surfactant mixture (71 mg/L of SL and 72 /L of SG) blending with water could yield a stable and the optimal emulsion was considered the best. The small absolute value of the emulsion zeta potential reduces inter-particle repulsion, causing the emulsion droplets to stick to each other when they collided. Overtime, large masses of flocculated droplets can form which then clog the sediment pores. The results can be used to predict abiotic interactions and distribution of contaminant mass expected after SPRS injection, and thus provides a more accurate estimate of the mass of TCE removed due to enhanced biodegradation. The effect of TCE partitioning to the vegetable oil on contaminant migration rates can be approximated using a retardation factor approach, where 0.28 years through a 3 m barrier. In anaerobic microcosm experiments, result show that SPRS can be fermented to hydrogen and acetate could be used as a substrate to simulate reductive dehalorination. The apparent complete removal of nitrate and sulfate by SPRS addition was likely a major factor that promoted the complete reduction of TCE at later stages of this study. Results from the column experiment indicate that occurrence of anaerobic reductive dechlorination in the biobarrier system can be verified by: (1) the oil: water partition coefficients of dissolved TCE into vegetable oil were be used to predict abiotic interactions and distribution of contaminant mass expected after SPRS injection. (2) The SPRS can ferment to hydrogen and acetate could be used as a substrate to simulate reductive dechlorination. The proposed treatment scheme would be expected to provide a more cost-effective alternative to remediate other petroleum hydrocarbons and chlorinated solvents-contaminated aquifers. Experiments and operational parameters obtained from this study provide an example to design a passive barriers system for in-site remediation.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0906111-225917 |
| Date | 06 September 2011 |
| Creators | Liang, Shu-hao |
| Contributors | Wen Liang Lai, Dheng Di Dong, Liang Ming Whang, Jong Kang Liu, Chih Ming Kao, Ku Fan Chen |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0906111-225917 |
| Rights | user_define, Copyright information available at source archive |
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