August 2013, Vol. 25, No.8

What took us so long?

news Direct potable-water reuse debuts in Texas 

News that several drought-plagued Texas cities are planning to turn treated wastewater into drinking water has got Texans talking. And the conversation may not be exactly what you might expect. 

Rather than wringing their hands over the “yuck factor” and “toilet-to-tap” concerns, a majority are expressing relief, according to officials in two affected communities.  

“You always get one or two who say they won’t drink it [recycled water],” said John Grant, general manager of the Colorado River Municipal Water District (CRMWD; Big Spring, Texas). “But people here have more appreciation for water than you might see in an area where the supply is plentiful. Most are asking why we haven’t done this before.”  

This is good news to CRMWD, which supplies untreated water to five West Texas cities, including Odessa and Midland. Faced with dwindling supplies, the district recently completed the first direct potable-water reuse (DPR) project in the U.S., a 7600-m3/d (2-mgd) water-reclamation and reuse plant built next to the existing wastewater resource recovery facility (WRRF) in Big Spring. Today, reclaimed water produced there is blended with the untreated water from the city’s reservoir and distributed to CRMWD member cities for conventional water treatment and use.  

  

Water shortage concerns accelerate acceptance  

CRMWD customers aren’t alone in their increasing acceptance of DPR. Some 400 km (250 mi) to the northeast in Wichita Falls, Texas, residents are anxious for the completion next spring of a 19,000-m3/d (5-mgd) DPR project, said Daniel Nix, the city’s utilities operations manager. Wichita Falls provides water and wastewater services to about 120,000 residents of the city and the surrounding region, which is also in the midst of a lengthy drought.  

“People here realize that technology exists to make our wastewater effluent reusable, and they know it is now going downstream for someone else to use,” Nix said. “The question on their minds is whether the plant will be up and operating before we run out of water in the lake.” 

This is a legitimate concern in a community that saw lake levels drop below 40% of capacity earlier this year.  

Could Wichita Falls run out of water? “If we have another year [in terms of rainfall] like 2011, it will be very close,” Nix said. “If it’s more like 2012, it will extend our supply by 8 to 9 months.” 

The current drought is hardly a first in this part of the country.  

“Every decade, we’ve needed more water,” Grant said. Since the 1950s, CRMWD has constructed a series of reservoirs to hold water from the Colorado River, in addition to developing Ward County groundwater supplies.  

DPR is one of the few viable options that remain, Grant said. It’s an approach the district began considering in 2002.  

“We made the decision at that time that we were not going to build any more lakes or reservoirs,” Grant said. “And the good-quality groundwater is already taken.”  

If the region were to grow, it needed alternative water sources. “That’s when we began asking if there was a way to reuse the water we were already sending to these cities, rather than developing a new source,” Grant said.  

  

Economics drive decision-making  

CRMWD spent the next several years determining its next step. It considered three possible sites for a water-reclamation plant: a large WRRF plant in Odessa and two smaller ones in Snyder and Big Spring. 

In its research, the district made an important discovery. “Whatever location we chose, it would take the same basic process and technologies to treat the effluent to drinking water standards,” Grant explained. “It’s how all the parts came together — where the water comes from, where the output goes — that drove economic feasibility.” 

In Odessa or Snyder, for example, reclaimed water would have to be transported 48 km (30 mi) to injection wells for discharge, Grant explained. In Big Spring, all it would take was a 90-m-long (300-ft-long) pipeline to discharge the treated effluent into a nearby creek.  

Those differences were reflected in the projects’ estimated costs. In Big Spring, a water-reclamation plant could produce about 7600 m3 (2 mgd) at a cost of about $0.92/m3 ($3.48/1000 gal), compared to a larger-scale plant in Odessa that could produce 30,000 m3/d (8 mgd) — but at a cost of $0.26 more per 1 m3 ($0.98 more per 1000 gal).  

By comparison, untreated water in the region today costs about $0.71/m3 ($2.69/1000 gal). “No matter what new water supplies we develop, the cost is going up,” acknowledged Grant. “If you think otherwise, you are dreaming.”  

  

In Wichita Falls: Same song, next verse  

Wichita Falls, where interest in alternative water sources dates back to the late 1990s, tells a similar economics-driven story.  

At that time, utility leaders identified two projects to offset the shrinking reservoir supply: a reverse-osmosis system to treat water in a previously untapped brine lake and a pilot microfiltration system to treat effluent leaving the WRRF.  

When the drought ended a year or two later, the infrastructure was in place, but demand waned for the water that was produced. By the time water shortages returned in 2011, environmental regulations had grown more stringent, and the water the projects produced no longer met permitting requirements.  

The additional nutrient-removal requirements for the brine lake were especially onerous, Nix said. “It was too much to get our arms around in the short term,” he said. 

The city instead began working with the Texas Commission on Environmental Quality to determine how it might adapt the microfiltration and the reverse-osmosis systems already in place to treat its wastewater effluent to drinking water standards.  

“If we were starting from scratch, the economics wouldn’t have worked,” Nix said. Instead, it became a matter of providing additional treatment to address three areas of deficiency and adding a pipeline between the WRRF and reclamation plants.  

  

Ensuring water quality  

To allay any lingering public misgivings, officials in Big Spring and Wichita Falls point to multiple backup systems and strict testing regimens.  

In Big Spring, water quality is monitored as it goes through each phase of treatment — microfiltration, reverse osmosis, and ultraviolet disinfection. Testing begins even before it reaches the reclamation plant. “If chlorine levels aren’t high enough, we won’t take it,” Grant said. “If it doesn’t meet our parameters at any step along the way, we send it back to the beginning.” 

After it leaves the plant, the reclaimed water is blended with untreated water, with the reclaimed water comprising 15% or less of the initial blend, before it is distributed to CRMWD member cities for conventional water treatment. When the pipeline connects with other raw-water pipelines, it is diluted even further, Grant said.  

When its operation comes on-line next spring, Wichita Falls will follow a similar process but without the ultraviolet disinfection, Nix said. Plans are to blend the reclaimed water with water from two reservoirs at a 50:50 ratio prior to conventional water treatment.  

There is no “magic” ratio of reclaimed to raw water, Nix said. “These projects need to be considered on a site-by-site basis, with the understanding that each project must be evaluated on its own merit,” he said. 

From a regulatory standpoint, reclaimed water is no different from groundwater or river or lake water, Nix said. “You have to look at the water quality and see what you have, and then put a treatment process in place that brings it to regulatory standards,” he said.  

DPR involves a learning curve for utilities and regulators alike, Nix said.  

Because few rules and regulations exist, it’s important to confer with your regulatory agency from Day 1, Nix said. It’s also critical to understand the quality of the effluent leaving the WRRF, which, in many cases, is remarkably good.  

“Forty years ago, when there were rivers on fire, direct potable reuse was not doable,” Nix said. “But the Clean Water Act changed all that. It has helped make wastewater effluent a high-quality resource. We need to start treating it that way.” 

                                                            — Mary Bufe, WE&T