United States Department of Transportation
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Abstract:The limited availability of water and stringent wastewater effluent standards at rest areas led to the development of a water recycle-reuse system to treat flush water from water closets. Flush fluid for rest area water closets accounts for 95% to 97% of the rest area water requirements. For a flush fluid to be acceptable it must have no objectionable odors, no objectional color, no substantial foaming, and no apparent suspended solids, and it must be low in bacterial count and chemically and biologically stable. Prior research with a bench-scale system confirmed the application of extended aeration biological treatment followed by granular media filtration as a water recycle-reuse concept. This prior work led to the installation of a full-scale field system at a rest area to develop data for implementation of the recycle concept. The treatment system at an existing rest area was modified to provide a closed loop return of water to and from the water closets. A water balance was achieved by wasting an amount of recycle water equal to the water input from sewered potable water. Data from the field recycle-reuse system were obtained during its operation from November 15, 1976, to August 31, 1977. During this time start-up was evaluated and equilibrium was achieved and evaluated at 95% recycle. The biological system and filtration system provided flush water of a quality that met standards set for flush water and was accepted by the users. Operation of the closed loop extended aeration and granular filter system for flush water recycle and reuse was similar to the conventional operation of these processes. The influence of nitrogen accounted for the most significant operating difference. Ammonia nitrogen transformation to nitrite and nitrate nitrogen resulted in an operating pH of 5.5 to 6.0 and, as a result, incomplete nitrification occurred. Nitrogen buildup in the form of ammonia, nitrite, and nitrate was experienced but the concentrations did not cause a reduction in the organic biological oxidation efficiency. The biological system functioned under conditions suitable for the utilization of organics by fungi. The biological solids were threadlike; however, they readily separated through gravity settling. The quality of the water in the recycle-reuse system varied between winter and summer operation, but it remained acceptable as a flush fluid. The variability in quality can be attributed mainly to nitrogen. Nitrogen in the recycled water greatly influences biochemical oxygen demand results and renders this test useless as a measure of organic stability. Storage requirements for recycle flush water are dictated by the resident time of the users in the building that houses the water closets, the resident time of users in the parking facility, and the physical layout of the water closet facility. Average daily and maximum daily water use based on resident times and gallons (litres) per user establishes storage, biological treatment, and filter requirements. Instantaneous peak flow establishes pipe sizes and integration of system requirements for storage and use sets pump requirements.
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