From The Denver Post (Bruce Finley):
Colorado water providers facing a shortfall…are turning to a long-ignored resource: wastewater.
They’re calculating that, if even the worst sewage could be cleaned to the point it is safe to drink — filtered through super-fine membranes or constructed wetlands, treated with chemicals, zapped with ultraviolet rays — then the state’s dwindling aquifers and rivers could be saved.
Colorado officials at work on the first statewide water plan to sustain population and industrial growth recognize reuse as an option.
“We need to go as far and as fast as we can on water-reuse projects,” Colorado Water Conservation Board director James Eklund said.
But there’s no statewide strategy to do this.
Other drought-prone states, led by Texas, are moving ahead on wastewater conversion to augment drinking-water supplies.
Several obstacles remain: huge costs of cleaning, legal obligations in Colorado to deliver water downstream, disposal of contaminants purged from wastewater, and safety.
Local water plans recently submitted by leaders in five of Colorado’s eight river basins all call for reuse, along with conservation and possibly capturing more snowmelt, to address the projected 2050 shortfall.
Front Range utilities will “push the practical limit” in reusing water, according to the plan for the South Platte River Basin, which includes metro Denver. The Arkansas River Basin plan relies on reuse “to the maximum potential.”
Western Slope authorities in the Gunnison, Yampa and Colorado river basins contend Front Range residents must reuse all available wastewater as a precondition before state officials consider new trans-mountain projects.
The emerging Colorado Water Plan, to be unveiled Dec. 10, remains a general guide, lacking details such as how much water is available. Nor does this 358-page draft plan specify how much of Colorado’s shortfall can be met by reuse.
Water industry leaders urge an aggressive approach. Colorado officials should determine how much water legally can be reused and analyze how this could boost supplies, WateReuse Association director Melissa Meeker said in a letter to the CWCB. Colorado’s strategy “should be crafted to encourage innovation and creativity in planning reuse projects.”
Cleaning up wastewater to the point it can be reused as drinking water long has been technically feasible. Water already is recycled widely in the sense that cities discharge effluent into rivers that becomes the water supply for downriver communities.
Cleaning systems
In 1968, utility operators in Windhoek, Namibia, a desert nation in Africa, began cleaning wastewater and pumping it into a drinking-water system serving 250,000 people.
Denver Water engineers in the 1980s pioneered a multiple-filter cleaning system at a federally funded demonstration plant. From 1985 to 1991, Denver Water used wastewater to produce 1 million gallons a day of drinking water, which proved to be as clean as drinking water delivered today.
Delegations of engineers from Europe and the Soviet Union visited.
“There was a sense we were ahead,” said Myron Nealey, a Denver Water engineer who worked on the project.
But utility leaders scrapped it, partly out of fear that customers would object to drinking water that a few hours earlier might have been flushed from a toilet. They also were struggling to dispose of thousands of gallons a day of purged contaminants — a super-concentrated salty mix that must be injected into deep wells or buried in landfills. [ed. emphasis mine]
So Denver Water has focused instead on recycling wastewater solely for irrigation, power-plant cooling towers and other nonpotable use. An expanding citywide network of separate pipelines distributes this treated wastewater — 30 million gallons a day.
“Reuse is definitely a way to maximize the use of the water we have,” said Jim Lochhead, manager of Denver Water and former natural resources director for the state.
“We’re in the exploration stage of trying to analyze what are the options for various types of reuse,” Lochhead said. “What’s the most effective? What’s the least costly? What’s the most secure?”
Meanwhile, drought and population growth in Texas have spurred construction of water-cleaning plants at Wichita Falls and Big Spring. Engineers have installed water-quality monitoring and testing systems sensitive enough to track the widening array of pathogens, suspended particles and hard-to-remove speciality chemicals found in wastewater.
A Texas state water plan calls for increasing reuse of wastewater eightfold by 2060. The New Mexico town of Cloudcroft is shifting to reuse as a solution to water scarcity. And California cities hurt by and vulnerable to drought, including San Diego, are considering wastewater conversion for drinking water.
Costs can be huge, depending on the level of treatment. Water industry leaders estimate fully converted wastewater costs at least $10,000 per acre-foot (325,851 gallons).
By comparison, increased conservation, or using less water, is seen as the cheapest path to making more water available to prevent shortages. The most costly solution is building new dams, reservoirs and pipelines that siphon more water from rivers.
Colorado also faces legal constraints. The first-come-first-serve system of allocating water rights obligates residents who rely on diverted water from rivers to return that water, partially cleaned, to the rivers to satisfy rights of downriver residents and farmers.
However, much of the Colorado River Basin water diverted through trans-mountain pipelines has been deemed available for reuse. Western Resource Advocates experts estimate more than 280,000 acre-feet may be available. In addition, water pumped from underground aquifers — the savings account that south Denver suburbs have been tapping for decades — is available for reuse.
Indirect reuse
While nobody in Colorado has embarked on direct reuse of treated wastewater, Aurora and other cities have begun a form of indirect reuse that involves filtering partially treated wastewater through river banks. This water then is treated again at Aurora’s state-of-the-art plant. Cleaned wastewater then is blended with water from rivers to augment municipal supplies.
The most delicate challenge has been dealing with safety — making sure engineered water-cleaning systems are good enough to replace nature’s slow-but-sure settling and filtration.
While industry marketers focus on semantics to try to make people feel more comfortable — rejecting phrases such as “toilet to tap” to describe reuse — engineers are honing the systems.
They envision early-detection and shut-off mechanisms that quickly could stop contaminants left in water from reaching people. They aim for filtration and other advanced treatment sufficient to remove the multiplying new contaminants found in urban wastewater. Cleaning water increasingly entails removal of plastic beads used in personal-care products; mutating viruses; resistent bacteria; synthetic chemicals such as herbicides; ibuprofen; birth control; anti-depressants; and caffeine.
“That’s the whole job of treatment and monitoring, to remove pathogens and other contaminants to where it is safe to drink,” said John Rehring of Carollo Engineers, a Denver-based expert on water reuse.
“It’s not a question of ‘Can we do it?’ We can do it,” he said. “And because of growing affordability and public acceptance, we’re starting to see it implemented.”
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