Thinking outside the infrastructure box
Is there room for modular sewage treatment plants?
IN THE INFRASTRUCTURE WORLD, the past casts a long shadow. Decisions about where to place key public facilities—roads, tracks, and pipes—tend to have a type of permanence. What’s more, they bake in policy decisions of previous eras, inadvertently affecting our own decisions today about how to provide important public services. Disrupting the status quo isn’t easy, or necessarily desirable, but sometimes it’s worth thinking outside the box, as with the issue of sewage treatment.
Back in the late 1800s, Boston and the surrounding communities faced a problem of cholera and typhoid epidemics from untreated sewage being discharged into local streams and rivers and, indeed, into the city streets. The solution that was devised was considered an engineering marvel of that era—even to the point that it was documented in Scientific American. Let’s collect all those local sewer flows into large interceptor pipes and pump all that bad stuff to where it won’t do any harm, Boston Harbor. The pipes and pumping stations led to Nut Island in Quincy and Deer Island, off of Winthrop. In the 1950s and 1960s, the decisions to place the region’s first sewage treatment plants at Nut Island and Deer Island was determined by the location of those pumping stations.
Fast forward to the 1970s, when the Metropolitan District Commission was trying to figure out how to comply with the new federal Clean Water Act, which required a higher level of treatment than what was provided at the two decrepit and outdated wastewater treatment plants. A study was conducted to determine if dispersed treatment plants located throughout the 43 municipalities of the regional sewer district would make sense.
No action was taken to implement the dispersed plan. Part of the problem was that there would be local opposition by communities to siting of wastewater treatment plants along the Charles, Neponset, and Mystic Rivers. Part of the problem, too, was that discharges of wastewater effluent into rivers, as opposed to the harbor, would require more advanced treatment, an expensive proposition.
So, today, about 300 million gallons of water per day are diverted from the Connecticut River basin in western Massachusetts via the Quabbin Reservoir, soiled by residential and commercial use, supplemented by millions of gallons of rainwater runoff from the region’s roads and infiltration of groundwater into the sewers, and put through a $4 billion treatment plant on Deer Island. The cleaned effluent is discharged in Massachusetts Bay through an immense tunnel over nine miles long; and the solids are made into fertilizer in Quincy and sold for agricultural use.
Enter the Charles River Watershed Association, whose executive director Bob Zimmerman has long had the view that ecological needs are better served if water supplies can be extracted and used within their original catchment areas, as opposed to being shipped to other river basins or the ocean. There is a simple logic to Bob’s view. Why not recreate the natural hydrology through stream and wetland restoration at the same time one is cleaning up dirty water?
The problem, though, has been the economics. When you have a huge embedded infrastructure of long pipes headed out to sea, it’s hard to rationalize spending more money on local facilities to do the same treatment work—even if the resulting effluent might be valuable locally.
The association went to work on this problem, and they have come up with an elegant solution, something they call Community Water and Energy Resource Centers, or CWERCs. These centers are modular units handling one to five million gallons a day. They tap the inherent heat of wastewater and the methane-producing capability of solids in the waste stream, while also offering treated water for re-insertion into the local ecology or other non-potable water uses.
More specifically, thermal energy from the water (after treatment) would be captured by a heat pump, available for use locally. Methane from the bioreactor (anaerobic digestion) would be used to produce electricity to sell to the grid or for on-site purposes, and heat would also be recovered from the electric generation process, augmenting the heat energy above. Finally, reclaimed water can be sold under Massachusetts regulations for irrigation, recreational use, industrial or commercial cooling or air conditioning, toilet flushing, agricultural use, carwashes, snowmaking, fire protection, and street cleaning. The water can also be used to create wetlands, recharge aquifers, and the like.
In a recent report, the Charles River Watershed Association investigated two sites to test out the concept, both in downtown Boston. Offering a detailed analysis, Bob and his team assert that CWERCs would be self-sustaining, while charging users only a fraction of current water rates for non-potable reuse water and wastewater treatment. Their economic models posit a distributed network of CWERCs to replace existing centralized systems while remaining cost neutral in the near term and likely profitable over a longer time period. Finally, each CWERC would reduce CO2 emissions by as much as 30 million pounds. And, if global warming raises the sea level and changes the hydraulic flows going to Deer Island, having some inland facilities might be a good insurance policy.It is hard to overstate how disruptive CWERCs would be to the traditional water/wastewater infrastructure model–dispersed modular units strategically located to enhance the ecologic benefits of such installations versus the current massive flows and treatment facilities at “the end of the pipe.”
Paul F. Levy, a Newton resident, is a former CEO of Beth Israel Deaconess Medical Center, a former executive director of the Massachusetts Water Resources Authority, and a former chairman of the Massachusetts Department of Public Utilities.