Odor and Corrosion Control Optimization of the North Texas Municipal Water District's Wastewater System

A system-wide master plan was completed to evaluate odor generation and fate within the North Texas Municipal Water District's (NTMWD) wastewater system, assess corrosion related to sulfide, and produce recommendations meant to optimize odor and corrosion mitigation within current expenditures. The master plan focused on achieving a comprehensive characterization of the entire Upper East Fork Interceptor System (UEFIS) plus the two downstream regional wastewater treatment plants (RWWTP). The UEFIS includes over 600,000 feet of piping, 18 lift stations, 7 chemical dosing stations and handles up to 80 MGD during dry weather. Once the current as-operated condition was understood, a coordinated suite of improvements were formulated to improve performance while optimizing expenditures.The project commenced with a comprehensive sampling program during summer 2011. Collection system sampling included deployment of Odalogs at 40 locations within the UEFIS to record diurnal hydrogen sulfide concentrations over the course of two weeks. Additionally, liquid phase grab samples were collected at each location in two rounds: during Odalog deployment and Odalog retrieval. Liquid parameters included dissolved sulfide, dissolved oxygen, BOD, VFA, and nitrate concentrations; pH; and temperature. During collection system sampling, the effectiveness of the current nitrate dosing program was evaluated by turning nitrate off at three of the seven chemical dosing stations.Air sampling of both RWWTPs was completed during Odalog deployment so that the RWWTP sampling efforts corresponded to the collection system sampling. Air samples were collected from every odor source and analyzed for odor concentration, plus specific odorous compounds. Additionally, air ventilation and capture was assessed at all process covers, buildings and ducts using air velocity measurements and smoke testing. Finally, a performance evaluation was completed for every active vapor-phase treatment device including four chemical scrubbers, five bioscrubbers, six carbon scrubbers, and four ozone scrubbers. The sampling effort provided a comprehensive odor assessment of the entire wastewater system.The sampling efforts provided input data needed to complete modeling of sulfide emissions within the collection system and odor dispersion from the RWWTPs. CH2M HILL's INTERCEPTOR model was set up and calibrated for the entire UEFIS and then used to assess scenarios for improving chemical dosing. Bench-scale chemical testing was completed on several wastewater samples to obtain preliminary assessments of the effectiveness of iron salts, pH adjustors and chemical oxidants. The INTERCEPTOR model was used to develop a targeted suite of control options suitable to the needs of different segments within the system A similar comprehensive optimization approach was applied to the RWWTPs using emissions ranking and modeling to prioritize odor sources. Recommendations for the WWTPs focused on targeting sources in order of impact per cost to improve. A group of strategies were recommended for each location, overall resulting in both odor control improvement and cost savings.