Craig Criddle, CEE

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Wastewater summit highlights the value of regarding sewage as a rich resource.

Every day in the Bay Area, hundreds of millions of gallons of treated wastewater are dumped into the Bay as if they were worthless. The word “waste” is in the name for a reason, right? What good is sewage?

A lot, says civil and environmental engineering Professor Craig Criddle. With water supplies imperiled by global warming and population growth, and all 40 of the Bay Area’s wastewater treatment facilities reaching the end of their operational design life, he argues, the region faces a combination of imperative and opportunity to begin treating wastewater as a resource for recovery of water, materials, and energy.

To assist with regional planning and to align research activities with those efforts, Criddle and colleagues at the Woods Institute for the Environment at Stanford convened dozens of top regional water officials, regulators, environmentalists, consulting engineers, and entrepreneurs at an “Uncommon Dialogue” conference May 21 in Menlo Park, Calif. Although many water utilities in the Bay Area — and around the country — are experimenting with resource recovery, efforts involving more than a few percent of the gallons they process are rare. In the Bay Area there is no region-wide approach to help the ideas attain greater scale.

“Many key leaders within the Bay Area were at the meeting and contributed to its outcomes and recommendations; these people have the authority and experience to develop a regional vision on resource recovery from wastewater, and I think we can help,” Criddle said. “We agreed that there was a need for a regional vision. We also agreed about the need for a nonprofit entity with a mission of technology R&D and scaling up the technologies and resource recovery implementations. Thats where I think Stanford could have a major impact.”

What a waste

Why bother? For starters it’s a way to keep hundreds of millions of dollars from heading out to sea. Dutch environmental biotechnologist Willy Verstraete has calculated that every 1,000 gallons of wastewater contains the equivalent of $1.88 worth of fertilizer, energy as methane, beneficial organic matter for soils (like compost), and clean water. It doesn’t seem impressive until Criddle points out that the City of Palo Alto’s treatment plant processes an average of 24 million gallons a day. That reflects a potential gross of up to $16.5 million a year.

Were this a purely financial idea, those revenues would have to at least equal the considerable — but not completely understood — cost of adding new equipment for extracting out and refining all these chemicals. But many speakers at the meeting pointed out that the benefits of treating wastewater as a resource extend beyond a simple income statement to include environmental benefits as well.

Former Palo Alto Mayor Peter Drekmeier told the group that the city is already considering a plan to recycle more water in the city (as well as recovering other resources). One of the main reasons is that in a few decades much of the Bay Area could have up to 50 percent less water than it does today because global warming is melting away the mountain snowpack that replenishes California’s reservoirs every spring.

Many experts, including Criddle, argue that water reclamation could be decentralized at the scale of buildings or clusters of buildings. Based on research he’s been doing with Stanford economics Professor Frank Wolack, Criddle told the group that the right combination of technology and economic incentives could feasibly enable such clusters to reclaim 50 percent of their water, dischargeing residual chemicals and solids to the main treatment plant. This would be beneficial for the plant, as it would then have a more concentrated flow of resources to process and sell or re-use.

Several other experts said the needed boost to local supply probably shouldn’t come from desalinating sea water.  To make the point, Bruce Wolfe, executive officer of the San Francisco Bay Regional Water Quality Control Board paraphrased a recent musing by David Nahai, former head of the Los Angeles Department of Water and Power: “Why are we spending big bucks to treat our wastewater just to put it into the ocean and then we are taking about spending big bucks to pull it out of the ocean and desalinate it to just use it again? Why don’t we do a short circuiting there?”

Reusing water locally wouldn’t just ensure that more water remains available. At least in Southern California, it could also cut the energy use and resulting greenhouse gas emissions and costs of moving water downstate. Professor Emeritus Perry McCarty cited figures from the California Energy Commission, showing that 4 percent of the state’s electricity is used by public water systems, and more than half of it is just to transport water from the North to the South.

Trying Technologies

McCarty’s presentation to the group focused on his decades of highly-regarded research on the use anaerobic (no-oxygen) microorganisms to convert organic “waste” to methane, a useful energy source. Most U.S. treatment plants use aerobic reactor treatment methods, which require more energy than they produce. In theory, and in many experiments, anaerobic reactors have produced more energy than they use.

Anaerobic reactors are one of many technologies that can harness energy from wastewater. Robert Hickey, a senior consultant to environmental firms such as Ecolab and Coskata, outlined others as well as improvements to anaerobic processing, most of which are undergoing testing in cities around the country.

Other energy recovery technologies include “gasification” in which organic solids in wastewater are burned to produce energy for an engine that drives a generator, and “microbial fuel cells,” in which a combination of organic and battery chemistry liberates electrons that flow as generated current (materials science and engineering Professor Yi Cui and student Xing Xie are developing one such fuel cell, Criddle said, that boosts power output by coating the anode with carbon nanotubes.)

In yet another idea to harvest energy from wastewater, Criddle is working with aeronautics and astronautics Professor Brian Cantwell on a Woods Institute-funded project to convert the ammonia in wastewater into rocket fuel. Through a microbially-mediated bioreaction that Criddle’s group is still studying, ammonia (NH3) would be converted to nitrous oxide (N2O). Cantwell’s team would break up the N2O in a catalytic decomposition cell they have developed, yielding air (N2 and O2) and energy.

Criddle has separately been working with civil and environmental engineering Associate Professor Sarah Billington on a technology to feed methane extracted from wastewater (or landfills, for that matter) to microorganisms that can create a natural polymer. The polymer could be used as a biodegradable bioplastic or as a key component in a substitute for wood. Because the polymer produces methane when it biodegrades anaerobically, the material can be recycled.

Although there are many encouraging ideas and technologies for extracting energy, materials and clean water from wastewater, the experts at the meeting still sounded a note of frustration that they are developing too slowly, given the urgent need they see.

“Most of these ideas are coming from small technology companies with limited resources,” Hickey said. “The federal government has almost abdicated their role in doing research in water and wastewater. We’re in a situation now where we really don’t have federal or private funding to commercialize the things we need.”

That concern was the impetus for the group’s recommendation for a regional non-profit to encourage technology research and development.

In a sense the conference was the start of a race to make the best case for treating sewage as a valuable raw material — a commodity —before the next round of treatment plants around the Bay Area are built, on average in about 10 years.

“We have a tired infrastructure that’s reaching the end of its 40-year life, so there’s going to be significant money that has to go into that,” Hickey told the group. “I think it is time to pause and think about what we need to do to have an infrastructure that meets our current and future needs. You just can’t view wastewater as a waste anymore.”

For more information:

Could sewage be worth $45 billion?

Last modified Mon, 16 Jul, 2012 at 11:58