In Part 1 of this series, I left off comparing a natural forest “water system” with our urbanized centralized water/wastewater systems. I also noted the value forest systems find in waste, and began describing the potential for similar value in large urban water infrastructure systems. There is energy in the organics in wastewater, thermal energy in the water itself, and value in the cleaned water we discharge as “waste” someplace far away from where that water was first collected as potable drinking water.
Urban water system managers are pursuing the energy generation opportunities that organics in wastewater and food waste contain, capturing what we discharged as waste and turning it into a resource. But this step forward has its limits, because contained in the same wastewater is significant thermal heat energy, and enormous volumes of re-usable water. For example, cleaning one million gallons of wastewater requires approximately 4,000 kilowatts of energy, but because that same chunk of wastewater is warm, it contains approximately 36,500 kilowatts of thermal energy.
As my wastewater engineer friend David del Porto always says, “It’s only wastewater if we waste it.” The water treated at wastewater treatment plants is a very valuable resource.
Everyday approximately 300 million gallons, or enough water to fill 450 Olympic swimming pools, is treated and thrown away... In other words, a lot of water we throw away as inconsequential.
In Boston’s case, water is stored in huge reservoirs in central Massachusetts, and then distributed via aqueduct to 2.2 million people in eastern Massachusetts. Once used, it is collected, treated at our Deer Island wastewater plant on Massachusetts Bay, and then discharged 9.5 miles out into the ocean. Everyday approximately 300 million gallons, or enough water to fill 450 Olympic swimming pools, is treated and thrown away. Four hundred and fifty Olympic swimming pools lined up would be 14 miles long, a little over 25 yards wide, and a little over six feet deep. In other words, a lot of water we throw away as inconsequential.
The other important thing to consider about the wastewater we collect and treat in Boston every day is that approximately 30 percent is actually clean groundwater leaking into the pipes (water leaks from groundwater into sewer pipes as it seeks the path of least resistance); annually another 10 percent is rainwater flowing into the same pipes. Leaking pipes in our vast centralized wastewater collection systems are stealing water that rightfully belongs in streams and rivers, wetlands, and lakes and ponds. The leaks contribute significantly to low river flow, and low river flows concentrate contaminants. This problem is not unique to the Charles River watershed; it is a problem common to virtually all urban centralized systems.
In other words, in the wastewater we are throwing away lies potential sources of renewable electric energy, thermal heating and cooling energy, and large volumes of clean, fresh water, all at serious consequence to the environment and ourselves.
While I’m at it, I should point out that our current urban water infrastructure faces a number of additional challenges that will only magnify as our climate continues to change. First, the system is finite and inflexible. Each system element has an absolute upper limit on the amount of water it can carry. In Boston’s case, the upper limit is about 1.2 billion gallons per day of groundwater, stormwater and sewage mixed together. As the system approaches its capacity, mixed sewage and stormwater are allowed to blow into surface waters like the Charles River and Boston Harbor – called combined sewer overflows (CSOs) – to prevent the system from overloading and backing up into people’s homes. Boston’s system has been updated over the past 20 years to reduce the volume of CSOs in the Charles by 98%, however, we still experience between nine and twelve activations annually – that is, in a “typical” year. More rain than average results in more overflows. Though Boston has one of the best strategies for reducing CSOs of any city in the nation, as climate change intensifies rainstorms, activations will begin to increase. CSOs discharge partially, or untreated wastewater into our waterways, closing beaches, limiting recreational activities, impacting natural habitats and degrading the beauty of our rivers and coasts.
With finite capacity comes the inability of the system to handle flooding. We depend on our stormwater and wastewater systems to handle water in volume, but with an upper limit to piped capacities, they are mostly inadequate to the task.
Compare our finite piped systems to the groundwater, vernal pool, wetland, flood plain, and river systems of the natural environment: in flood conditions, the capacity of each is lent to all others in an intimately connected system that allows for great flexibility and adaptability. Conversely, in a drought, groundwater storage, reuse, and interconnectedness allows for deep resilience. And remember, the forest wastes nothing and generates tremendous energy.
Image graphic source: Jamestown, NY Board of Public Utilities