Comprehensive Planning for DPR in Colorado: A Precedent Setting Project Putting New Regulations To Good Use

This presentation will describe the key considerations and elements for implementing DPR, particularly in the context of the recently approved DPR regulations in Colorado. Although the project approach was tailored to meet the Colorado DPR regulations, the concepts for treatment, public outreach, enhanced source water control plan, and TDS management broadly apply to all system considering the implementation of DPR. An in-depth evaluation of Aurora's water reclamation facility was conducted as an early task to determine the availability of DPR supply. Key water quality considerations such as nitrate, TOC, and TDS as well as the control of pathogens and trace organics were evaluated as part of the multitude of treatment scenarios evaluated. The costs and benefits associated with wastewater treatment facility improvements compared to (or in addition to) advanced treatment processes alternatives at the existing IPR purification facility were evaluated. Several combinations of scenarios for improvements at each and both facilities were evaluated to determine the optimal DPR scheme. Figure 1. Available DPR flow from SCWRF Developing a framework and implementing a comprehensive Enhanced Source Water Control Plan (ESWCP) is an essential component of DPR. The project team started this process prior to initiating the project by identifying the legal authority for implementing a pretreatment program in parallel to analyzing the inventory of industries previously cataloged within the sewershed. Regional coordination is an essential element of the development of the ESCWCP since Aurora's WRF is a scalping plant so the regional authority for treating wastewater flows as well as industrial pre-treatment mostly falls within the Metro Water Recovery's (a.k.a. Denver Metro) purview. Aurora has established an internal task force to manage long-term ESWCP implementation. Another early data analysis included extensive pathogen and chemical data, which were analyzed to assess log reduction values and removal of indicator compounds. Establishing the appropriate treatment goals for pathogen and chemical removal were fundamental components of developing optimal treatment alternative approaches. The comprehensive treatment alternatives were paired down to a short list of DPR alternatives based on implementation feasibility, capital and O&M costs, and residuals production/disposal considerations. Critical control points for pathogen and chemical control were defined for the short listed alternatives. The preliminary pathogen sampling results suggested that the Colorado minimum pathogen targets of 8 log virus, 6 log Cryptosporidium, and 7 log Giardia may be acceptable, however these minimal LRVs targets may not provide a sufficient buffer in the event of a key process failure such UV system failure. In the event of a power loss, 6 log pathogen reduction for each pathogen would be lost while water would continue to flow through the process. To account for this likely potential scenario, and based on the initial pathogen sampling data, more robust pathogen LRVs of 10.5/9.5/9.5 for virus/Cryptosporidium/Giardia were identified as safe targets. Prior to determining the final pathogen LRVs, the project team determined that additional pathogen sampling to provide a statistically relevant data set. Figure 2. Preliminary Pathogen Statistical Analysis Reverse osmosis is not required by Colorado's DPR regulations, but systemwide salinity management is important because the current system relies on blending to achieve the target total dissolved solids (TDS) concentrations. To prevent accumulation of salinity in the system, a sustainable blending strategy and/or treatment necessary to remove TDS from the system was evaluated. Treatment alternatives include an emerging suspended ion exchange process compared to RO. Capital and O&M costs for treatment and disposal were evaluated to determine the life cycle cost associated with these alternatives. Aurora's direct potable reuse (DPR) project will blaze a path as the first DPR application in Colorado. Leveraging an existing reclamation and advanced treatment system with a proactive and comprehensive approach positions Aurora Water to implement the new state regulations and set a precedent for carbon-based DPR. This presentation will demonstrate the methodology to plan and execute a comprehensive potable reuse scheme.