PubMed · 10109932
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A A Cubley. 1991. Incinerators--avoiding the pitfalls.. https://pubmed.ncbi.nlm.nih.gov/10109932/
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Cutting oils are emulsionable fluids widely used in metalworking processes. Their composition is normally oil, water, and additives (fatty acids, surfactants, biocides, etc.) generating a toxic waste after a long use. Generally, it is a waste too dilute to be incinerated and it is difficult to treat biologically. Other conventional treatment methods currently used are not satisfactory from the environmental point of view. Wet air oxidation (WAO) and supercritical water oxidation (SCWO) are two forms of hydrothermal oxidation that have been proved to be effective processes to treat a wide variety of industrial wastes, but hardly tested for oily wastes. In the case of refractory wastes, WAO process is not efficient enough due to the moderate temperatures used. SCWO is a more powerful process since operating temperatures are usually around 600 degrees C, but the use of severe conditions leads to major disadvantages in the commercialization of the technology. In order to enhance WAO and SCWO efficiency at mild conditions, the use of free radical promoters has been studied in this work. Both normal and promoted hydrothermal oxidation have been tested to treat cutting oil wastes in a continuous flow system operating at 300-500 degrees C. Hydrogen peroxide has been used both as a source of oxygen and as a source of free radicals by introducing it into the reactor with or without previous thermal decomposition, respectively. Organic material is easily oxidized in both cases, obtaining more than 90% TOC reduction in less than 10s at 500 degrees C. At lower temperatures, the use of promoters clearly enhances the oxidation process. Activation energies have been estimated for normal and promoted oxidation processes.
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A model incorporating electrostatic and van der Waals forces was used to predict the wetting behavior of several systems containing a quartz surface, water, and a dense nonaqueous phase liquid (DNAPL). The disjoining pressure between the quartz/water and a water/DNAPL interface as a function of their separation was calculated from a full solution of the nonlinear Poisson-Boltzmann equation allowing for charge regulation. For the pH regime associated with a positive pressure barrier, the quartz surface was predicted to be water wetting. The model takes into account the charging behavior of an isolated DNAPL/water interface as inferred from electrophoretic mobility data. It provides excellent predictions for four coal tar and creosote samples tested, where the quartz was oil-wetting below pH 5 and water-wetting at higher pH values. In a fifth sample, the transition occurred above pH 7, which indicates that mechanisms other than electrostatic interaction control the wetting behavior in this sample.