THE USE OF AQUEOUS HUMIC SUBSTANCES FOR IN-SITU REMEDIATION OF CONTAMINATED AQUIFERS

摘要

This chapter provides a review of the literature on binding of organic contaminants by aqueous humic substances (AHSs). Colloidal dispersions of AHSs are shown to be potential carriers (flushing agents) for enhanced removal of hydrophobic organic contaminants from aquifers. The process involves binding of contaminants by AHSs which can enhance the apparent solubility and mobility of contaminants. Binding, often modelled as linear partitioning, may vary with aqueous concentrations of contaminants and/or AHSs, and other parameters. Evidence is mixed whether aggregation of AHSs at high concentrations increases or decreases their capacity to carry organic contaminants. Sorption of contaminants and AHSs to solid aquifer particles and co-aggregation of AHSs with inorganic colloids/clays are also important, potentially clogging pores and reducing aquifer permeability. Advanced numerical models (e.g., BIONAPL/3D), which include binding/sorption kinetics and in situ biodegradation, can now be used to simulate carrier-assisted transport of contaminants in aquifers. This chapter includes a discussion of a case study: a unique 5-year laboratory test, in which diesel fuel within a pilot-scale model sand aquifer was flushed with water containing 0.8 g/L AHSs (Aldrich® humic acid). AHS flushing increased aqueous concentrations of methylated naphthalenes from diesel two to ten fold. As a direct consequence, in situ biodegradation of the methylated naphthalenes increased. As hydrocarbons were depleted from the diesel, the contaminant plume shrank and disappeared. Numerical simulations using BIONAPL/3D indicated that without AHS flushing, complete diesel dissolution would have taken about 6 times longer. Practical recommendations on use of AHS as flushing agents are given. The use of AHSs at levels > 1 g/L would most effectively flush hydrophobic contaminants (e.g., PAHs). Inexpensive, naturally-derived, non-toxic commercial humic products may offer significant advantages compared to other chemical flushing agents (e.g., surfactants). It may be possible to use AHSs for a combination of flushing, enhanced bioremediation and/or sequestration of organic contaminants in aquifers.