Multifunctional colloidal particles for in situ remediation of dense non-aqueous phase liquids.

摘要

This research is aimed at the design of novel adsorptive-reactive particles that are effective in the environmental treatment of dense non-aqueous phase liquids (DNAPLs) such as trichloroethylene (TCE). The attainable multifunctional particles have the ability to transport through soil, target contaminants directly, adsorb contaminants and break them down, holding a promising to be efficiently applied for in situ injection remediation technology.;The widespread occurrence of DNAPLs in groundwater and in soil is of serious environmental concern. Compared to traditional remediation technology, the in situ injection remediation technology using nanoscale zerovalent iron (NZVI) particles is the preferred method because it will not only potentially reduce the remediation cost and time substantially, but it may also directly access and target the contaminants. However, neat NZVI particles have a strong tendency to form aggregates, rendering them undeliverable to the specified contaminant zone. Additionally, the hydrophilicity of NZVI particles makes them hard to target contaminants directly, lowering the remediation efficiency.;To improve the performance of NZVI in in situ injection remediation technology, three different novel composites based on NZVI were developed successfully in this study, i.e. NZVI/silica, (carboxymethyl cellulose + NZVI)/carbon and NZVI/aerosol-carbon. In these composites, NZVI particles were incorporated in the silica matrix or supported on the carbon surface, respectively. Meanwhile, the following beneficial characteristics of these composites have been proved: (1) they are reactive to dechlorination of TCE due to the presence of reactive nanoscale zerovalent iron; (2) the supports (silica or carbon) exhibit hydrophobic property and thus serve as adsorbents for TCE, lowering bulk dissolved TCE concentrations without limiting the remediation rate and bringing TCE to the proximity of the zerovalent reduction sites. Adsorption coupled with reaction is an important concept in this research; (3) hydrophobic supports allow the nanocolloids to effectively partition into TCE phase upon encountering regions of bulk TCE after they transport through the saturated zone; (4) the nanocolloids are of the optimal size range for effective transport through groundwater; (5) the preparation processes are environmentally benign and economical and (6) the aerosol-assisted technology involved in the preparation of composites process is conducive to scale up, as it is a virtually continuous process.;In this thesis, the preparation and characterization of such systems are presented. The characteristics of adsorption, reaction, transport and partitioning relevant to the problem of TCE remediation are studied.