The U.S. Army is evaluating recycle of field shower water as a conservation practice in arid regions and is seeking to define appropriate technologies and health criteria. Shower wastewaters at a military installation have been characterized in terms of physical, chemical and microbiological parameters. Two treatment technologies have been investigated. Microfiltration cartridges with a nominal pore size of 0.2 µm achieved consistent removals of 75±15% of total organic carbon (TOC) and better than 99% of turbidity from synthetic shower water containing 50 to 100 mg/L of TOC as soap. An alternative treatment technology utilized powdered activated carbon and coagulation/flocculation/sedimentation followed by diatomaceous earth filtration. A TOC reduction of 70±15% was achieved in three separate studies, although at a cost of 1 g/L or more of powdered activated carbon. Revised quality criteria for recycled shower water have been developed with guidance from the National Research Council. Parameters which can practically be measured in the field are primarily associated with microbiological safety. Therefore, the safety of recycled shower water with respect to chemical contamination must depend on design considerations.
The rate constant for the title reaction was redetermined using discharge flow technique and mass spectrometric measurements of HOCl consumption. The overall rate constant k = (1.7±0.3)×10−13 cm3 molecule−1 s−1 was obtained and found to be practically independent of temperature in the range 213 K≤T≤298 K. In experiments using 18O atoms the time dependence in the formation of the products 18O16O, HC1 and Cl2 was determined. Based on the experimental data available it is proposed that the reaction occurs via an intermediate complex mechanism but it could not be decided by which primary steps the reaction is initiated.
Ab initio model calculations were carried out in an attempt to quantify conceived reaction pathways. Structures and energetics of the intermediates were computed. On the basis of these calculations it is suggested that Cl abstraction from HOC1 should be regarded as the preferred initiation step. The O‐atom attack leads to the formation of an intermediate HOClO. Alternative reaction pathways, like H abstraction from HOCl by O‐atom attack, or a mechanism in which HO2 and Cl are formed were found to be less probable. In the present calculations no support could be found for the thermodynamically most preferred reaction route to contribute to product formation. Structure and energy of the intermediate HOC1O are computed.
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