Recycling Water in US Cities: Potable Reuse

Event Date

Wed, 10/19/2016

3:00pm - 4:00pm

Ames Hall 234
Johns Hopkins University, Homewood Campus

The Earnest and Agnes Gloyna Distinguished Lecture in Environmental Engineering presents R. Rhodes Trussell. In the 20th Century we were short on technology but long on resources and dual systems for non-potable reuse made the most sense. Today we are short on resources and long on technology and integrating water recycling with our traditional potable water systems is becoming more attractive. Potable reuse avoids the cost of new distribution infrastructure, matches supply and demand through the seasons and does not commit water to the support of low priority uses. It is consistent with the densification of U.S. Cities in the decades ahead. In its 2013 report on Water Reuse: Potential for Expanding the Nation’s Water Supply through Reuse of Municipal Wastewater, the National Research Council (NRC) estimated that recycling the used water discharged to the ocean could supply early 1/3rd the nation’s urban water use.

Potable reuse is not new. It has been commonplace for a city to draw water downstream of the discharge of used water from another city, a practice the NRC called “de facto potable reuse”. Recent studies demonstrate that de facto is on the rise. Planned potable reuse is also increasing. By the end of the 20th century, 150 mgd of capacity was online and today that number is 400 MGD. Several more projects are in planning.

Existing projects use an environmental buffer - a groundwater aquifer or a surface water reservoir where the recycled water loses its identity. The benefits of these buffers, while real, are poorly defined and inconsistent in nature. Many emerging schemes make use of new technologies to substitute for the environmental buffer. This has stimulated a debate on the benefits of the environmental buffer. California, is discussing regulation of several forms of potable reuse. In 2014, regulations for the augmentation of groundwater with recycled water were promulgated.

Regulations on surface water augmentation, are on the way and the State is assessing of the feasibility of eliminating the environmental buffer. Effectively planned, potable reuse can play an important role in the Nation’s municipal water supply in the decades ahead. Throughout the U.S., both de facto and planned reuse are regulated individually at the state level. At the Federal level, today’s CWA and SDWA regulations address chemicals in potable reuse more effectively than they do pathogens. The types of planned potable reuse projects and their associated treatment approaches are diverse. California has developed the most formal regulations addressing both chemicals and pathogens for potable reuse scenarios.