Traditionally, destruction of DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] for environmental remediation required high-energy processes such as incineration. Here, the capability of powdered zero-valent iron to dechlorinate DDT and related compounds at room temperature was investigated. Specifically, DDT, DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane], and DDE [2,2-bis(p-chlorophenyl)-1,1-dichloroethylene] transformation by powdered zero-valent iron in buffered anaerobic aqueous solution was studied at 20 °C, with and without the presence of nonionic surfactant Triton X-114. The iron was successful at dechlorinating DDT, DDD, and DDE. The rates of dechlorination of DDT and DDE were independent of the amount of iron, with or without surfactant. The rates with surfactant present were much higher than without. Initial first-order transformation rates for DDT, DDD, and DDE were determined. For example, the initial first-order rate of DDT dechlorination was 1.7 ± 0.4 and 3.0 ± 0.8 day-1 or, normalized by the specific iron surface area, 0.016 ± 0.004 and 0.029 ± 0.008 L m-2 h-1, without and with surfactant, respectively. A mechanistic model was constructed that qualitatively fit the observed kinetic data, indicating that the rate of dechlorination of the solid-phase (crystalline) reactants was limited by the rate of dissolution into the aqueous phase.

The structure of biofilm extracellular polymers (ECPs) was studied by measuring their polysaccharide and protein spatial distributions along biofilm depth. Biofilm was collected from two aerobic heterotrophic biofilm reactors, which were seeded with Sphingomonas sp. and Sphingomonas sp. plus mixed liquor, respectively, and operated under toxic organic (in this case, azo dye) degrading conditions. Complete mixing conditions in the two reactors were verified by measuring water content, and polysaccharide and protein quantities from three vertical sampling positions over time. Experimental results showed that: (1) the biofilm water content of either reactor did not change with sample position or biofilm age, with an average biofilm water content in both reactors of 97%; (2) polysaccharides and proteins in the ECPs did not change with sample position; (3) the profiles of polysaccharides and proteins along the biofilm depth showed a stratified biofilm structure, with their ratio (proteins/polysaccharides) being relatively stable over the depth. Oxygen and substrate transport and interactions among species were considered to be the main reasons for producing such a non-uniform biofilm structure; and (4) Sphingomonas sp. could not compete well with microorganisms derived from the mixed liquor of a wastewater treatment plant aeration basin.

The performance of a soil remediation process can be determined by measuring the reduction in target soil contaminant concentrations and by assessing the treatment's ability to lower soil toxicity. Land treatment of polycyclic aromatic hydrocarbon (PAH)-contaminated soil from a former wood-treating site was simulated at pilot scale in temperature-controlled soil pans. Nineteen two- through six-ring PAHs were monitored with time (initial total PAHs = 2800 mg/kg). Twenty-five weeks of treatment yielded a final total PAH level of 1160 mg/kg. Statistically significant decreases in concentrations were seen in total, two-, three-, and four-ring PAHs. Carcinogenic and five- and six-ring PAHs showed no significant change in concentration. Land treatment resulted in significant toxicity reduction based on root elongation, Allium chromosomal aberration, and solid-phase Microtox bioassays. Acute toxicity, as measured by the earthworm survival assay, was significantly reduced and completely removed. The Ames spiral plate mutagenicity assay revealed that the untreated soil was slightly mutagenic and that treatment may have reduced mutagenicity. The variety of results generated from the chemical and toxicity assays emphasize the need for conducting a battery of such tests to fully understand soil remediation processes.