Mechanism of ozone decomposition in aqueous solutions Reaction Rate constants in M, s units Ref.

Advanced oxidation processes (AOPs) for water and wastewater treatment are often handicapped by their inability to completely eliminate total organic carbon (TOC). In order to explore the capability of the combination of ultrasonic irradiation with ozone for the rapid removal of TOC, we examined the degradation rates of dissolved phenol (C6H5OH) in water with high-frequency ultrasound over the range of 200-1000 kHz, with ozone and with the combined application of sonication and ozonation. When ozone and ultrasound are applied simultaneously, a pronounced synergistic effect is observed that leads to the complete and rapid elimination of TOC at enhanced reaction rates. At longer reaction times, phenol oxidation by 03 leads to oxalate and formate, which accounts for the majority of the residual TOC. However, the combination of US (ultrasound) and ozone together readily oxidizes HCO2- and C2O4(2-) to CO2 while they prove to be relatively resistant to further oxidation to CO2 by O3 alone.

A novel pilot-plant scale sonochemical reactor (UES 4000 C Pilotstation) has been specifically developed for degrading a variety of water contaminants in large-scale applications. We report here the sonochemical degradation of three chemical compounds in aqueous solution: the chlorinated volatile contaminants dichloromethane (DCM) and trichloroethylene (TCE) and the nonvolatile azo dye methyl orange (MO). The flow-through reactor in the Pilotstation consists of four 612 kHz piezoelectric transducers which are driven by a power source operating at 3kW. The sonochemical reaction chamber has a volume of 6 L, while the total capacity of the Pilotstation, including a heat-exchanger unit and a reservoir tank varies from a minimum volume of 7.25 L to a maximum over 45 L. The observed reaction rates for the degradation of these contaminants in the Pilotstation were compared with values determined under similar conditions in small-scale bench reactors in order to evaluate its performance over a wide range of power densities. The pseudo-first-order degradation rate for TCE in the Pilotstation was found to be more than 4 times higher than corresponding smaller values measured in lab-scale reactors. Furthermore, the observed rates for DCM degradation also exceeded those of the small-scale reactors by factors from 3 to 7. The degradation rate of these two chlorinated compounds was faster with decreasing initial concentration in all cases. Experiments with 10 µM MO (aq) in the Pilotstation operating at different total volumes exhibited a linear dependence between the observed rate constants for sonolysis and the applied power density (PD), in the range 67 < PD (W/L) < 414. Steady-state •OH (aq) radical concentrations in each reactor were calculated and were shown to correlate with the applied power density in the vessel. A power budget analysis for the Pilotstation indicates that nearly one-third of the applied power is converted in sonochemical activity.

Recently, a new fiber-laden, self-diverting, and viscoelastic acid has been successfully used for matrix acidizing of highly heterogeneous carbonate formations The fibers have been designed to be inert under surface and pumping conditions, and their geometry allows them to form strong and stable fiber networks that can effectively bridge across natural fractures, wormholes, and perforation tunnels. Eventually, the fibers degrade into a water-soluble organic liquid that is produced back to the surface during flowback.In the case of perforated wells, experiments suggest that diversion with fibers operates in three phases. First, as the early volumes of fiber-laden acid reach the perforations, the acid penetrates the reservoir as if no fibers were present. Second, as the fibers bridge, they accumulate inside the perforations and form a fiber cake. Third, the fibers plug the perforation, and the injectivity decreases locally, promoting diversion into other perforations. The pressure drop through a plugged perforation was analyzed by performing 340 separate fine-scale 3D simulations. The original work was based on theoretical and laboratory-based experiments, considering typical perforation schemes and for various permeability ratios between the generated fiber cake and the formation's original permeability. The results were compiled, and a correlation was made to model the resulting skin. The model was implemented into an acid placement simulator and was extensively tested and validated in the field.In this paper, we present the model that describes the effect of fiber accumulation within perforations and explain how some of the model parameters such as formation-permeability contrast, fiber-cake permeability, and total permeability thickness (kh) may affect diversion efficiency. Case studies from field testing of the model illustrate methods of pressure history matching, job design, and treatment history evaluation.

Ultrasonic irradiation in the presence of ozone is demonstrated to be effective for the rapid oxidation of oxalic acid, bioxalate, and oxalate (H(2)C(2)O(4)/HC(2)O(4)(-)/C(2)O(4)(2-)) in aqueous solution to CO(2) and H(2)O. The degradation rate of bioxalate exposed to "sonozone" (i.e., simultaneous ultrasonication and ozonolysis) was found to be 16-times faster than predicted by the linear addition of ozonolysis and ultrasonic irradiation rates. The hydroxyl radical (*OH) is the only oxy-radical produced that can oxidize oxalate on a relevant time-scale. Thus, plausible *OH production mechanisms are evaluated to explain the observed kinetic synergism of ultrasonication and ozonolysis toward bioxalate decomposition. *OH production via decomposition of O(3) in the cavitating bubble vapor and via the reaction of O(3) and H(2)O(2) are considered, but kinetic estimations and experimental evidence indicate neither to be a sufficient source of *OH. A free-radical chain mechanism is proposed in which the HC(2)O(4)(-) + *OH reaction functions as a primary propagation step, while the termination occurs through the O(3) + CO(2)(*-) reaction via an O-atom transfer mechanism. Kinetic simulations confirm that ozone reacts efficiently with the superoxide (O(2)(*-)) ion that is produced by the reaction of O(2) and CO(2)(*-) to form *OH radical, and that the reaction of O(3) + CO(2)(*-) must be chain terminating. Oxalate is also readily oxidized by "peroxone" treatment (i.e., H(2)O(2) and O(3)). However, the addition of H(2)O(2) during the course of the sonolytic ozonation of oxalic acid does not appear to increase the observed degradation rate and decreases rates at millimolar levels.