By Peter Chawaga
The advent of potable reuse has not been easy. Widely considered within the treatment industry to be a viable alternative to increasingly-strained freshwater supplies, the concept has struggled to shed a negative reputation among consumers. However, even those who are in favor of recycled drinking water don’t always have the chance to provide it.
A major obstacle still stands in the way of potable reuse in some of the areas most severely plagued by drought. Many of the driest regions in the U.S. are landlocked and as such, they cannot realistically pursue the method that has typically allowed for potable reuse: reverse osmosis (RO).
To come up with alternatives to RO and accommodate potable reuse projects in such regions, the Water Environment & Reuse Foundation (WE&RF) underwent a study in Tucson, AZ.
“One of the hallmarks of RO is the brine that is produced during the treatment process,” said Justin Mattingly, research manager with WE&RF, who headed the project. “The disposal of this brine isn’t too difficult to manage at a coastal location that has access to the ocean, where a brine disposal pipeline can be relatively easy to permit and construct. In Tucson, the nearest outfall for a brine disposal line would be well over 100 miles away, making that option and other brine disposal options difficult and cost prohibitive.”
Tucson Water, the city’s water department, has been exploring ways to implement potable reuse as a means to expand its water supply, but found the RO treatment scheme — RO with microfiltration and UV advanced oxidation — to be unsustainably expensive because of the required capital investment, energy demand, and the environmental challenges posed.
To vet methods that might prove to be viable alternatives, a pilot facility was constructed at Tucson Water’s Sweetwater Recharge Basins, which receive secondary effluent from the Agua Nueva Water Reclamation Facility. WE&RF and Tucson Water teamed up with engineering company CH2M and the University of Arizona to put everything together. CH2M provided a principal investigator to oversee pilot design and the testing plants, and the University of Arizona conducted data and laboratory analysis and operated the pilot facility.
The pilot system operated for six months and utilized multiple barriers to filter out pathogens and organics, including soil aquifer treatment, sidestream nanofiltration, ozone, and granular activated carbon. The research team conducted water quality analysis, operations monitoring, and specialized testing like membrane autopsy to thoroughly understand how the treatment system was doing.
“Results from the research showed that this treatment approach should receive consideration as an alternative potable reuse strategy,” said Mattingly. “Water produced during the six months of pilot testing was excellent with total organic carbon below detection limits, no detectable compounds of emerging concern, and disinfection byproduct production well below U.S. EPA standards. Through the use of multiple treatment barriers, there is significant pathogen log reduction with no detectable pathogens measured during testing.”
Mattingly hopes that the success of the pilot testing offers a new route for potable reuse to those that found previously vetted methods prohibitive for any reason. The results clear another roadblock in the way of potable reuse and as more consumers come around to the idea, perhaps these alternatives will get it to them.