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Evaluation of Strategies to Treat and Reuse Vactor Truck Wastewater
AuthorO'Hair, Brett Casey George
AdvisorDennett, Keith E.
Civil and Environmental Engineering
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The treatment of vactor truck wastewater (VTWW) for the purpose of reuse in vactor truck maintenance operations has been explored by the Nevada Department of Transportation (NDOT) and other states’ departments of transportation (DOTs) alike. VTWW is typically characterized by total suspended solids (TSS) concentrations greater than 10,000-mg/L and turbidities greater than 4,000 nephelometric turbidity units (NTU). NDOT has explored the treatment of VTWW by filtration, but these filters clogged rapidly, and final water quality was unsuitable for reuse. Methods used by other DOTs to treat VTWW along with current literature regarding physicochemical treatment using aluminum sulfate (alum) were reviewed to perform bench-scale and pilot-scale experiments to determine how to effectively treat VTWW for reuse during maintenance operations. Bench-scale experiments including sieve analyses and settling column experiments for determining the size distribution and settling characteristics of TSS in VTWW. Jar testing was performed to determine favorable alum dosages, mixing times, mixing intensities, and final pH conditions. Water quality suitable for vactor truck reuse was determined to be when 80 to 95% of TSS were removed and when final turbidity was reduced to 20 to 50 NTU. For each of the pilot system trials, desirable dosages of alum were targeted from 150-mg/L to 200-mg/L and final pH conditions ranged from about pH 5 to pH 6.5. System parameters like initial raw water pH, slow mixing speeds, and the routine removal of settled solids from the clarifier sludge basin were recognized to have significant impacts on the effluent water quality from the pilot-scale treatment system. Once these parameters were identified and stabilized, the pilot-scale system performance was more predictable and capable of achieving water quality suitable for vactor truck reuse.