Discharge Avoidance: Emerging Driver for Potable Reuse In The West

APPLICABILITY
In the arid west, water reuse has historically been driven predominantly by water supply needs. Because wastewater discharge permit constituents and concentrations are becoming more stringent, agencies are considering implementing potable reuse to not only address increasing water supply needs but also help reduce the massive capital expenditures necessary to meet the new discharge permit constituents and concentrations. Three Colorado case studies demonstrate how new direct potable reuse (DPR) regulations and challenging parameters in discharge permits (e.g., chlorides, sulfates, temperature) are changing the cost-effectiveness equation for DPR that increasingly favors potable reuse.

DEMONSTRATED RESULTS AND OUTCOMES
Methodology and Result
What drives a community to implement water reuse? In the arid west, the answer has predominantly been water supply needs for growing populations. New discharge permit constituents and concentrations are driving some utilities to consider potable reuse to reduce or avoid massive capital expenditures necessary to meet discharge limits. The advent of DPR regulations could help some utilities adopt a 'zero discharge' approach that might not otherwise have been feasible.

This represents a major shift in how our industry considers DPR. DPR has often been perceived as a treatment-intensive, costly approach for local water supply. The potential to offset discharge permit compliance costs is reframing the cost-effectiveness equation. In less-arid portions of the country, discharge avoidance has long been a driver for reuse. For example, the passage of Florida Senate Bill 64 in 2021 is accelerating Florida utilities' consideration of implementing of DPR.

Newly-adopted DPR regulations in Colorado and California are also spurring interest in DPR. With DPR regulatory certainty, utilities can accurately assess DPR cost and benefits, illustrated by three Colorado case studies.

The City of Aurora, CO, initiated a comprehensive DPR evaluation in 2023. Aurora could leverage existing treatment assets to fully use treated effluent from its Sand Creek Water Reuse Facility (SCWRF) by directly piping it to the Binney Water Purification Facility, adding advanced treatment to fill any gaps. The latest SCWRF wastewater discharge permit includes new parameters (e.g., chloride) that would drive major capital investments. Rather than invest tens of millions of dollars in discharge compliance, Aurora is considering reusing all of the SCWRF flow for seasonal nonpotable uses and year-round DPR.

Similarly, the Plum Creek Water Reclamation Authority (Castle Rock, Colorado) is anticipating new limits in its next discharge permit that would drive major capital projects. Estimated capital costs to remove chloride at this facility exceed $100 million. Cooling towers to reduce water temperatures add another $14 million. All told, the 20-year master plan anticipates upwards of $300 million for wastewater discharge permit compliance. Abandoning its wastewater discharge permit would add operating risk and costs for storing off-spec water during process upsets, and a portion of the capital costs would still be necessary. However, the cost savings of zero discharge could help offset the costs of advanced water purification for DPR.

In Denver, Metro Water Recovery (Metro), Denver Water, and the City of Aurora are jointly evaluating the potential for regional DPR. While Aurora and Denver Water stand to realize water supply benefits, Metro could benefit from reducing an anticipated $1 billion capital investment in additional treatment processes at its Hite and Northern Treatment Plant facilities. Offsetting even a fraction of this cost through discharge reduction or avoidance could tilt the scales in favor of DPR.

Conclusions/Outcomes
This presentation will show how DPR regulations and discharge permit conditions together can 'turn the tide' toward reuse through accelerating consideration of DPR through zero discharge or reductions in discharges from water reclamation facilities, while understanding potential risks and the extent of investments still necessary at water reclamation facilities. This fosters balanced consideration of DPR as an option for offsetting discharge costs.

RELEVANCE TO AUDIENCE
Attendees will:
- Learn how cost avoidance can be factored into an assessment of the cost-effectiveness of DPR, especially in states that have advanced the adoption of DPR regulations.
- Benefit from insights gained from three case studies in Colorado where stringent discharge permit conditions are accelerating consideration of DPR through zero discharge or reductions in discharges from water reclamation facilities.
- Understand potential risks of zero discharge and consideration of investments still necessary at water reclamation facilities, allowing a balanced consideration of DPR as a way of offsetting discharge costs.