Sewer Scalping – Is the Fresh Coast ready for it?
At a recent Wingspread meeting, David Sedlak of UC-Berkeley made mention of “sewer scalping”. My ears twitched, adjusting to make sure I didn’t miss anything. David is professor of Civil and Environmental Engineering, and co-chairs the NSF-funded center for Re-Inventing Our Nation’s Urban Water Infrastructure, an exciting endeavor (aka ReNUWIt, about which I’ve written previously). David and his colleagues live on the intellectual edge of the very necessary matters surrounding urban water management and I love hearing about their work.
While I’d never heard of sewer scalping per se, I had a mental image of what he meant: diverting sewage from its route to the centralized sewage treatment plant, running it through a small treatment plant, and re-using the water (and sometimes the residuals) locally. But I wanted to know more – was this just a theoretical possibility, or was it being employed in some places? A quick tour around the internet made it clear sewer “mining” as it is also called has been around for quite some time, even if it’s not yet routine.
Not surprisingly, I found a number of articles about the use of sewer mining in Australia. A blog from 2007 is clear indication that it’s been around for awhile, and this easy-to-read overview from Sydney Water makes it seem that for them, at least, it’s beyond the experimental stage.
In the U.S., most of the references I found were on one of the two coasts where water is at a premium either because of low availability or because of a growing population, or both. This undated paper by Kristin Byrne, apparently writing while she was a student at CSU-Long Beach, is a terrific overview of both the technology and the policy development as it has played out in California. I also found a slide deck prepared by Craig Criddle of Stanford, (also part of ReNUWIt, mentioned above) laying out how sewer mining could fit into the existing water management scheme in Palo Alto, including how energy use, resource recovery markets, and legacy infrastructure influence the pros and cons of various scenarios. New York City employs on-site treatment for many of the new high-rise structures in Battery Park; last December I visited some of those buildings and gingerly sipped the treated wastewater.
But does sewer scalping have a place in the Heartland too?
Without going into the exhausting details, suffice it to say that Waukesha, WI sits about twenty miles due west of Lake Michigan. Its main attraction in the late 1890’s was its clean spring water. The water was so highly sought after that it was defended at gunpoint – a scenario engagingly explained in Peter Annin’s 2006 book Great Lakes Water Wars. Fast forward a hundred years and we find the quaint old city of Waukesha surrounded by suburban sprawl with its inevitable large lawns, pools, etc., resulting in over-pumping of the ground water supply. Not only have the springs disappeared, but water from deeper in the aquifer has higher concentrations of radium and now the city needs to find a new source of water.
To the city’s credit, they have enacted water conservation measures in recent years that have obviated some of the need. But it would seem to me that sewer scalping or mining could be an excellent solution for the city to employ, especially for outdoor irrigation of golf courses and lawns, and perhaps for some industrial processes. However, the city is dead set on building a pipeline to Lake Michigan, and another one to carry treated water back to Lake Michigan (estimated to cost $200 million more or less to build, much less to operate), which seems like an awfully expensive, energy-intensive, and inflexible solution.
Milwaukee is trying to make a name for itself as a water innovation hub, so let’s see some innovative solutions to local problems. Milwaukee’s Mayor Tom Barrett likes to call the Great Lakes “America’s Fresh Coast”. In that case, perhaps its time that sewer scalping move beyond just the east and west coasts, and come here to our fresh coast. We deserve nothing less.