As population, sewer use go up, so do energy costs

2013-06-09T00:00:00Z 2014-07-15T17:48:56Z As population, sewer use go up, so do energy costsTony Davis Arizona Daily Star Arizona Daily Star
June 09, 2013 12:00 am  • 

When it comes to water, energy and the environment, there is no free ride.

Cleaner wastewater from sewage plants needs much more energy than dirty wastewater. So does renewable water for drinking and watering golf courses, compared to the energy used by groundwater pumping. But that groundwater pumping had for decades threatened to hollow out the aquifer under Tucson's core.

These tradeoffs resonate clearly in a recent study of greenhouse gas emissions and energy use in the Tucson area, done by the Pima Association of Governments, a regional planning agency.

First, the study showed that more people and better sewage treatment requires more electricity to run the air blowers, clarifiers, fans and odor scrubbers that do the work.

Energy use and emissions of heat-trapping greenhouse gases from Pima County's wastewater treatment system soared from 2000 to 2010, the study showed. Those increases occurred at a faster rate than in any other major area of local government, it said.

Since 2000, "the Wastewater Department in Pima County has gone through a tremendous transformation, from minimally treated sewage to sophisticated advanced processes," said Jackson Jenkins, the county's wastewater chief, explaining the steep increase in energy use and greenhouse gas emissions.

Moreover, with a new Roger Road sewage plant and a vastly upgraded one at Ina Road due to go on line next year, the wastewater system's energy use and gas emissions are due for another big boost, county figures show. These sewage plant upgrades are aimed largely at improving the quality of sewage effluent discharged into the Santa Cruz River to meet federal water quality standards.

Within city government, meanwhile, the only area where energy use and greenhouse gas emissions rose significantly during the 2000s was at Tucson Water. That was due mainly to the city's efforts to replace groundwater pumping with environmentally friendlier Central Arizona Project and reclaimed water.

Clean effluent costly

What caused the surge in the sewer system's energy demand?

Among other reasons were upgrades to several plants, including the county's Randolph Park, Green Valley and Corona de Tucson plants so they could produce high-quality effluent for golf course reuse, Jenkins said.

At the same time, countywide population growth from 843,000 in 2000 to nearly 1 million in 2010 required a 50 percent boost in the sewer system's treatment capacity at the Ina Road plant.

"That took a lot more energy to clean the sewage than it did in 2000," he said.

Yet the sewer system's electricity and natural gas use dropped slightly from 2008-10, a sign that the depressed economy of that period was even reducing sewage discharges from homes and businesses.

Overall, modern wastewater treatment is very energy intensive, said Laura Fairbanks, a wastewater department spokeswoman. "We do a lot of automation, and we have a lot of things built into our facilities to lower our energy use. But it takes a lot of energy to run these plants."

Pumping expensive, too

Tucson Water's energy use, meanwhile, rose during the 2000s even as total customer water use declined about 6 percent, city records show.

The higher energy use stems largely from the city's actions a decade ago to start recharging and pumping out Central Arizona Project water in the Avra Valley west of Tucson and pumping it uphill into the city, said Tucson Water spokes-man Fernando Molina.

Until then, Tucson was one of the largest if not the largest U.S. city totally dependent on groundwater. By the end of the last decade, however, the city was using more than twice as much CAP water as groundwater.

The city now pumps out water from the Avra Valley at 600 feet deep, far deeper than most wells in the center of Tucson where water had been pumped heavily and the water table had been falling since World War II.

Then, the city pumps the CAP water uphill to the Hayden-Udall treatment plant in the Tucson Estates area west of the Tucson Mountains for disinfection and other treatment. From there, the federal Bureau of Reclamation pumps the water into the city.

The city's reclaimed water system's energy use also rose, by 35 percent. Its contribution to CO2 emissions jumped 38 percent, due to a 51 percent increase in reclaimed water demand over the decade, Tucson Water figures show. That happened as more and more parks and golf courses around the city and county switched from groundwater to reclaimed water.

Costs to go up

Looking to the future, the Pima County Regional Wastewater Reclamation Department predicts that electricity use at the Roger and Ina Road plants will rise by nearly another 50 percent between fiscal years 2011-12 and 2014-15, as the upgrades at the plant kick in.

In part, the upgrades, costing more than $600 million total, are aimed at removing nitrogen and ammonia from the plants' effluent before it lands in the Santa Cruz.

That effluent, starting at Roger Road, becomes the only stretch of the river within the Tucson metro area to carry any water except immediately after big storms.

Separately, the county is boosting its capacity to treat sewage at Ina another 33 percent or so, up to 52 million gallons daily, to handle expected growth.

The U.S. Environmental Protection Agency and the Arizona Department of Environmental Quality ordered the upgrades years ago.

Immediately, the improved water quality could make that stretch of river hospitable to fish, biologists have said. In the long term, the improved quality will make it easier to treat the wastewater further to drinking-water quality if an additional supply is ever needed.

"You can take water from sewage to drinking water, but it takes a lot of energy - it's just a factor of how much energy you want to put into it," the county's Jenkins said.

The wastewater department has taken some steps toward renewable energy, having installed one megawatt worth of solar panels at the Roger and Ina sewage plants in 2010 and 2011, respectively. The City of Tucson has also installed a megawatt of solar in 2011 at its Avra Valley-CAP recharge facility.

In time, the county most likely will look at larger solar projects serving wastewater plants and other facilities, he said.

The county will also look for additional opportunities to save energy at the plants, said Terry Finefrock, the county's contracts and procurements manager.

BY THE NUMBERS

• Electricity and natural gas use rose 97 percent from 2000 to 2010 at the county wastewater plants at Ina and Roger roads on the northwest side, the Randolph Park plant in midtown Tucson and far-flung suburban plants in Green Valley, Corona de Tucson and Marana. Greenhouse gas emissions of carbon dioxide from those plants rose 178 percent.

• Pima County government's total energy use rose 51 percent during that period. Its total CO2 emissions rose 55 percent.

• The city of Tucson's total energy use rose about 2.7 percent. Its total greenhouse gas emissions dropped 4 percent. But Tucson Water's total energy use jumped 30 percent while its greenhouse gas emissions rose 13 percent.

Source: Pima Association of Governments study

ANOTHER TRADEOFF

Cleaner water from the Pima County sewer system has also had a cost in dollars and cents.

The average homeowner's sewer bill rose more than 300 percent from $11.04 in fiscal year 2001-02 to $37.48 in fiscal year 2012-13.

Source: Pima County Regional Wastewater Reclamation Department

Contact reporter Tony Davis at tdavis@azstarnet.com or 806-7746.

Copyright 2014 Arizona Daily Star. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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