Waterjet injection of powdered activated carbon for sediment remediation

In situ sediment remediation through waterjet-activated carbon amendment delivery is an innovative means to mitigate the dangers posed by hydrophobic organic compounds. Ease of use and applicability to inundated environments makes this technique valuable. This work made feasible low-pressure injections of a 15% (by dry weight) carbon/water slurry through a pulsating piston pump waterjet. The project fabricated nozzle tips and a unique injection apparatus comprising a quantitative system for the evaluation of bench scale models. Based on a series of iterative processes, injections of carbon were analyzed for depth and concentration. Injections varied in duration and they were made into a white kaolinite surrogate sediment. The carbon concentration throughout the target area was analyzed using a spectroradiometer that plotted wavelength against the reflectance of each sample. To confirm the impact of carbon placement, soil contaminated with polyaromatic hydrocarbons (PAHs) was used during testing to quantify the reduction in the bioavailable portion of the contaminant. The performance of carbon liquid injections into the sediment was evaluated using solid phase microextraction fibers and high-performance liquid chromatography. Testing showed that, when used in a kaolinite sediment the customized waterjet is capable of delivering a carbon/water slurry at depths up to 30 cm with a uniform concentration averaging 3.0%. Further testing in the contaminated sediment showed reductions of over 90% in the bioavailable portion of PAHs at depths of 30 cm or greater. The unique features of waterjets and their proven performance make them a viable remedial technique in subaqueous applications --Abstract, page iv

Waterjet Injection of Powdered Activated Carbon for Sediment Remediation

Purpose: In situ contaminated sediment remediation through the addition of activated carbon has been proven to be an effective remediation technique. An amendment delivery system was developed to accurately place and inject a powdered activated carbon slurry. The system was set up to deliver a series of discrete injections over a rectangular grid with the objective to deliver 3% carbon (C) by dry weight to an inundated saturated sediment at a maximum sediment depth of 30 cm. Materials and methods: In situ conditions have been researched and small bench-scale models have been developed to provide valuable data for future field-scale models. Experiments were performed using kaolinite as a surrogate sediment because the color contrast between the clay and the C permitted the delivered C concentration to be quantified using a spectroradiometer. The experiments showed that a set of operational parameters for the injection system could be identified that provided relatively complete mixing of the C and clay at the desired depths. The experiments were repeated using soil samples contaminated with polyaromatic hydrocarbons (PAHs) and polydimethylsiloxane coated solid-phase microextraction fiber analyses to quantify pore water concentrations. Results and discussion: Several different combinations of pressure, injection duration, and nozzle diameter were evaluated during the initial phase of the characterization of powdered activated C penetration in the surrogate sediment. Iterative approach tactics were conducted that concluded specifically placed, short-duration injections were necessary to deliver meaningful amounts of C in the test sediment. Analysis of these injections found that an average amended C concentration of 14% was achieved up to 26.7 cm deep in the surrogate sediment by a 9.5-s injection, whereas a 7.5-s injection at the same depth yielded an average concentration of 9.3%. The reduction in pore water PAHs concentrations through C injection was achieved in excess of 90% at all sampled locations within the injected perimeter. Conclusions: Reduction in contaminant pore water concentrations within the soil/sediment appeared to be less dependent on the duration of the individual waterjet injections, and the effective depth of penetration appeared to be greater than that observed during the surrogate sediment experiments. The empirical nature of the waterjet work and the expected heterogeneity of contaminated soils/sediments suggest that it is appropriate to conduct site-specific bench-scale treatability testing prior to full-scale remediation using waterjet-delivered activated C