By Deborah Sullivan Brennan, San Diego Union-Tribune, 6/25/14
Amy Dorman, senior civil engineer with the city of San Diego's Public Utilities Department holds a sample of water purified to the quality level of pure distilled water at the Advanced Water Purification Facility in University City at the North City Water Reclamation Plant. — Howard Lipin
At the North City Water Reclamation Plant in San Diego, senior engineer Amy Dorman drew a flask of cool, colorless water from a tap.
The crystalline liquid had a murky past. It started as sewage, and then passed through a series of treatments that scrubbed it as pure as distilled water.
This water, produced at the city’s 1-million-gallon-per-day demonstration project at the North City facility, is the prototype for what may eventually become a major source of San Diego’s water. And it’s a new way of looking at wastewater for the arid West.
“It is very much cutting-edge,” said San Diego Public Utilities director Halla Razak. “There is a lot of excitement, especially with the drought, that this is a sustainable, locally controlled, drought-proof new water supply that is a great solution for the Southwest.”
With that potential in mind, San Diego plans to construct a water-purification plant that would produce 83 million gallons per day by 2035. At that point, purified water could provide about a third of San Diego’s supplies, Razak said.
Officials estimate the project will eventually cost nearly $2 billion. But that expense could be offset by eliminating the need for $1.8 billion in overdue upgrades to the Point Loma Wastewater Treatment Plant, she said. And it would help San Diego attain the water self-sufficiency that has long eluded the region.
At the North City plant, a demonstration project that was launched in 2011 has fine-tuned the steps that city officials will follow to produce purified water from wastewater. About 80 percent of wastewater is recycled by the end of the process.
It starts with micro-filtration: rows of plastic tubes containing bundles of tiny straws. Microscopic pores on their surfaces allow water molecules in, and then filter out microbes and other contaminants.
From there, the water flows to reverse-osmosis units, which force the water through filters at high pressure to screen out organic material, salts and other solids.
“This is really the workhorse of the whole treatment train,” Dorman said. “This is where 99 percent of what’s in the water is removed.”
It’s the same process used in desalination, but with less salt to remove, it takes only one-sixth of the energy required to treat seawater, Dorman said.
Water from each canister feeds into separate spigots, and workers test each source individually. So if one of the reverse osmosis units fails, they can quickly isolate the malfunctioning part without shutting down the entire system.
By the time the water runs through reverse osmosis, there are almost no impurities left in it. In the final step, workers run the water through a treatment that employs a combination of ultraviolet light and hydrogen peroxide to obliterate any potential contaminants.
“(The UV treatment) does disinfect 99.9999 percent of virus, protozoa and bacteria, but there isn’t expected to be anything in the water” after reverse osmosis, said water research manager Bill Pearce.
The technology isn’t new: Orange County and Los Angeles already use it, along with water districts in Colorado, Texas, Georgia, New Mexico, Arizona and Virginia, according to the Virginia-based Water Reuse Association.
Most of those districts discharge the treated water into groundwater tables, and then draw it up later as needed. But San Diego lacks the large aquifers that many other regions have.
The absence of groundwater is what led San Diego to rely so heavily on imported water. And it held the region back from earlier efforts at water purification, said Ken Weinberg, director of water resources for the San Diego County Water Authority.
“In a groundwater basin, the water filters through with soil,” Weinberg said. “The pathogens can’t survive underground, so that acts as a barrier and you get removal of viruses and pathogens.”
Without that convenient storage option, San Diego had to look at other ways to distribute the purified water. Current plans call for piping it to San Vicente Reservoir, where it would be mixed with other supplies of drinking water. A similar system has been in operation at the Occoquan Reservoir in Virginia since 1978, according to the Water Reuse Association.
But there’s a simpler option.
Instead of mixing the water with supplies in the reservoir — a process called indirect potable reuse — the city could ship it straight to treatment plants to blend with other raw-water supplies before distributing it. That process, known as direct potable reuse, would require a fourth step in purification — ozone treatment - which the city is studying at the North City facility.
The option of direct potable reuse also would need an OK from state health officials. Razak said she’s working on a state committee that’s exploring the possibility, and will report back on its findings by 2016.
In addition, the city is collaborating with federal regulators on legislation that would exempt it from upgrades to the Point Loma Treatment Plant. The upgrades tab has been pegged at $3.5 billion, with interest.
San Diego is one of the last cities in the country without secondary treatment — an additional step in filtering wastewater that’s piped to sea. However, officials said removing water from the waste stream through water purification would be equivalent to secondary treatment. They’re seeking federal approval for the substitution proposal, Razak said.
In the meantime, the city is starting plans for the first phase of its water-purification system beyond the demonstration project. It’s an addition to the North City Plant that would produce 15 million gallons of purified water per day by 2023. Additional facilities would bring that among up to 83 million gallons per day by 2035.
Other water districts in the county are taking a cue from San Diego. The Helix and Padre Dam districts are exploring a plan to expand the reclamation plant at Santee Lakes to produce purified water, said Helix general manager Carlos Lugo.
The city of Escondido recently approved a long-term capital improvement plan that would create more recycled water in coming years, and refine that later to produce up to 12 million gallons of potable water to add to Lake Dixon, said utilities director Christopher McKinney.
As all of these initiatives move forward, the county water authority has flagged purified water as the most important new water source for the thirsty region, Weinberg said.
“One of the things that the drought has brought to the forefront is that our traditional ways of thinking about water just aren’t good enough,” said Melissa Meeker, executive director of the Water Reuse Association. “Historically, we’ve thought of wastewater as a waste product. The reality is that it’s a water resource.”