A newly built zero-liquid discharge industrial wastewater treatment plant for the treatment of groundwater flow from a railroad tunnel provides an excellent example of an elegant solution to a highly constrained challenge. The lessee of the one-hundred-year-old Moffat Tunnel in the Rocky Mountains was newly required to treat the water flowing from the tunnel to meet a NPDES permit for discharge to the Fraser River. An industrial treatment plant was designed, built and, starting May 1st, 2017, operated to treat the groundwater flow from the tunnel (190 gpm) containing variable solids loading and dissolved metals. The treatment plant design was constrained by the high elevation of Winter Park, CO, a lack of space available for the structure on an existing maintenance yard located adjacent to a resort community, the difficulty to connect to a domestic water supply or sewer, and very low allowable levels of metals in the treated water. To meet the proposed NDPES permit, UF membranes were recommended for the facility. A UF pilot study was performed to identify feasibility of thickening the backwash with a dissolved air flotation (DAF) system and identifying the impacts on the membranes from the required coagulant/thickening aids. Using the UF pilot data, the facility was designed to nearly eliminate membrane cleaning requirements by selecting a conservative flux, direct coagulation, and utilizing excess recirculation with the membrane feed flow. This approach results in less chemical use, and allows for recirculation of typical clean in place (CIP) waste flows. During start-up, initial challenges with a high frequency of the 100-micron UF strainer backwash cycle was negatively impacting the backwash recovery system. System operating data evaluation with the membrane supplier and the UF system integrator resulted in an increase in the strainer mesh size. The replacement had no impact on the transmembrane pressure (TMP) or cleaning requirements of the membranes while still increasing the overall UF system recovery from less than 80% to over 90%. The system was further constrained as the backwash recovery system (DAF thickening and a centrifuge for dewatering) must be recycled into the process flow. This constraint requires thickening of the backwash solids without use of a polymer. Addition of detergent to the DAF whitewater saturation recirculation process proved successful in floating the solids without the use of a polymer. The combination of the small amount of detergent and the robust design of the UF system has allowed the system to operate for four months with very little TMP accumulation and no need to perform a chemical cleaning on the membranes. Ultimately, the UF membrane design has allowed the plant to operate with low chemical costs and with zero-liquid discharge.
This presentation is available to AMTA Members only.
- Tim Rynders, PE
- CDM Smith Inc.
- AMTA/SWMOA Technology Transfer Workshop, Keystone, CO
- AMTA/SWMOA Technology Transfer Workshop
- zero liquid discharge, crossflow filtration, dissolved air flotation