A year in green tech: Constructed wetlands

A common theme among practical environmentalists centers on the concept that as humans we have no right to shift the consequences of our actions onto another human being.  We point out the injustice of using electricity to maintain a high quality of life, but allowing those who live near coal electricity plants to bear the brunt of the asthma and heart disease that comes from burning coal for energy.  Or letting the residents of West Virginia deal with the water contamination from chemicals associated with coal processing.  Or sitting back while the residents of Colorado wonder if their water is safe to drink after wastewater pits from fracking operations were washed out by floods.  Even with climate change, although it equalizes the impact some through extreme weather events and sea level rise along coastal communities with typically high property values, poorer nations like the Maldives (which just recently grew out of the "least developed country" status in 2011) must deal with the threat that their entire island nation will end up underwater, requiring the relocation of the entire population.  In example after example after example, one segment of our society - and most of the time the poorest and most powerless among us - has to deal with the negative impact of our energy use, while most of us in the highly developed world enjoy only the benefits.

Nowhere do we accept this state of affairs more than with our human waste.  Other than improvements in the medical field associated with child birthing, no single application of technology improved human health and lifespans more than indoor plumbing and wastewater treatment.  Diseases like cholera that commonly affected US urban areas in the late 19th and even early 20th centuries, no longer exist on a mass scale in this country.  When plumbers exclaim that they "protect the health of the nation", that is not over-hype.  Because of this, we accept the entire process as necessary, and even the staunchest environmentalists pay no mind to the process of accumulating and treating that waste.

In Chicago specifically, our "water cycle" involves us draining water from Lake Michigan, using it in our homes and replacing it with various forms of human and chemical waste, then collecting in in large wastewater treatment facilities.  These facilities then remove the solids, phosphorus, nitrogen, and other chemicals, then release that resultant water (also called effluent) into the systems that feed the Mississippi River.  Our output - which also includes almost all of the rainwater that falls on Chicago - travels downstream to the river communities of the Mississippi and gradually to the Delta.  There, it contributes to increased flooding and eutrophication, the process by which a freshwater plume overtakes the saltwater and kills or displaces the naturally occurring ecology of the Caribbean. In this process, we consider the effluent of our treatment plants acceptable to drink, but not by us.  Even these treatment plants have their issues.  The processing of so much human waste produces air quality issues for the communities that surround them.  We all enjoy the increased health benefits of waste management, but only these communities have to deal with the smell.

What if the residents of a block or community had to deal with the odor associated with treating their waste?  Or had to drink the output of the treatment facilities that processed the waste?  Would we have a different approach?

Constructed wetlands treat wastewater while recognizing the importance of placing the consequences of a process on those who benefit from the improved quality of life.  These man-made wetlands provide the benefits of natural wetlands - water purification, flood mitigation, habitat provision - but with the specific purpose of filtering and purifying wastewater from a specific building or community.  The best applications construct them above the water table of naturally occurring wetlands or ground water so that the effluent or outflow naturally finds its way to the local watershed (or land area physically connected to a water source, i.e. Chicago sits mostly in the Lake Michigan watershed) for recycling into the local ecology.  Installing them in this way also keeps them from flooding and prematurely releasing any harmful waste into local streams, rivers, and lakes.

The process works on some basic, natural principles.  The most simple comes from taking a water flowing at measurable velocity out of a pipe and slowing it by spreading it out over a large area.  That action uses the Bernoulli principle to drastically slow the water, which then allows the solids to naturally settle into the wetland.  The wetlands contain plants specifically chosen because of their desire for the likely chemicals present in the waste.  Plants that absorb large amounts of nitrogen, phosphorus, or other chemicals will render the chemical inert or beneficial, cleansing the water in the process.  After working its way through the constructed wetland, the water reaches a level of quality acceptable to return to a natural water source to recycle into our drinking water systems.

Constructed wetlands provide the added benefits of beautifying the local area, and improving the local ecology.  Planted areas lower ambient temperatures, creating more comfortable climates and reducing cooling loads in buildings.  The plants provide a habitat for nature that increases the local biodiversity.  The plants within these systems provide a colorful contrast to "pavement and manicured lawn" look of most urban areas.  Although they work well as somewhat traditional surface-flow wetlands where one can see the water, for areas where people will likely encounter them, a sub-surface-flow application can maintain a typical soil look at the surface with the filtering processes happening out of sight.

I do not believe that most of us, when presented with the facts of a situation, knowingly desire to degrade the life of another to improve our own.  Our natural instincts, however, include both self preservation and ignorance of that which we cannot see.  This combination allows us to accept the damage associated with our choices as long as our quality of life remains high.  As we evolve in this thinking, technologies like constructed wetlands offer us the opportunity to both maintain a high quality of life and accept the consequences of our actions.

P.S. For those that are interested, there is a version of these systems where instead of using land area to construct a wetland, we use tanks in a greenhouse or other indoor environment to accomplish the process.  These are normally prohibitively expensive, and the efficacy still needs improving.  For those who would like more information, follow this link to an example of such a system.

Resources:
EPA A Handbook of Constructed Wetlands
EPA Constructed Treatment Wetlands