BioCycle November 2010, Vol. 51, No. 11, p. 45
Did you ever watch an engineer try to talk to an English major? This happens at our house every couple of weeks when my step-daughter comes over for dinner. Her dad looks at her like she is some magical alien being that can speak in sentences rather than equations. I have these encounters at work a lot and often think of myself as a facilitator. I tend to think in a mixture of equations and verse, never in a straight line but also not just in circles; curvilinear is the term.
This curvilinear path is often where compost fits in, pleasing to the poets but also of utility to the builders. And I think that very soon, this compost middle ground will be seeing a new, terrific opportunity for infrastructure development. Two things that happened recently at work make me think that there is a soon to be realized use for organics.
A group from the College of Built Environments (CBE, formerly called the Architecture Department) called me awhile back and asked if I would work with them on this grant. The professor from CBE had just gotten back from a sabbatical in New Zealand and a park there had just about changed her life. You see, in this town in New Zealand, the park with its associated skateboard friendly features, plantings and wetland was being used to treat storm water from the city. This nice professor thought this was a fabulous idea, and decided to build park/wetland storm water treatment systems so that specialized and attractive plants can make all of the contaminants go away while people play tennis right next door.
Independently from this encounter, another person called me up. Would I be willing to teach a keystone project class for the Program on the Environment? It is a class about a phytoremediation project, where they will be using willow trees and poplars to clean contaminated storm water on Whidbey Island. The lead on this project wants to make Whidbey Island into a green model for the rest of the Puget Sound. No skateboards but some striking similarities to the New Zealand project. Once again, the plants do all of the work. Never mind that in the Northwest, the storm water season is largely confined to the winter months when the plants are dormant.
I agreed to teach this class, and have also introduced the Whidbey Island guy to the lady in love with New Zealand. First day of class, and 6 out of the 9 students are civil/environmental engineers. I was very happy about this – some lines to go with all of these circles. Everyone in the class likes plants, but all of those engineers were quick to recognize that the soil substrate can have a much more critical role than the plants in binding and or degrading contaminants in storm water. This is particularly true in the winter in the Northwest when the plants aren’t growing.
Preparing for the class identified a few basic realities. First, storm water is not some type of witch’s brew. Contaminants are things like nitrogen, phosphorus, maybe some pathogens, likely some metals, a few PAHs, and maybe soil particles. Nothing exotic here, nothing mysterious (but not necessarily what you want excess of in your lake or stream). Second, compost should be a perfect substrate to treat these contaminants. It can bind metals and phosphorus, has high water holding capacity, a large microbial community, and if you use a carbon rich material, can also absorb nitrogen. I started reading papers to see what work had been done.
Here is a quick summary of what I’ve found. Much of the research on use of compost for protecting water quality is from construction sites. Studies have shown that use of compost on construction sites is as, or more, effective than silt fences at reducing turbidity or movement of soil off site. Same deal for phosphorus movement (most P is transported on particles so this makes sense). Compost also reduced the volume of water moving off site in comparison to both an untreated site and a site with a silt fence. These studies, conducted by Britt Faucette and sponsored by Filtrexx International, involved putting compost in blankets or socks. More power to Filtrexx for sponsoring the research.
But it turns out that the compost works even if it is barefoot. Another study looked at how well cattails remove metals from metal-contaminated water. The cattails were planted in a mix of perlite and biosolids compost. The amount of metals removed was substantial, but it turns out that it was the soil, not the plants, doing the work. In fact, the plants removed less than one percent of the portion of the metals removed from the solution. Compost has also been tested on roadsides. While you can go to Texas and see for yourself, a study I read said that the compost amended soils had reduced soil erosion to only 0.1 to 30 percent as much as a grassy control. The other thing to remember about using compost is that it absorbs so much water, that the actual quantity leaving a site is reduced.
WHY GET JAZZED NOW?
These papers give you a pretty good idea that compost can be an effective tool in cleaning up water. Why all of a sudden, do I think that storm water is going to be such a big opportunity for compost?
Storm water management in urban areas has traditionally involved moving water off of the streets as quickly as possible. Urban areas are known for impervious surfaces, aka sidewalks and streets. So moving water away quickly has not meant moving it off into the neighboring pasture, but rather moving it to the closest water body or combined treatment plant, typically via existing sewer pipes or in specially constructed (and very costly) storm water pipes. Now, with regulations tightening on storm water discharges, water shortages looming, and combined treatment system overflows being frowned upon, alternative storm water technologies are being sought. Many of these systems are based on reversing the traditional approach – slow the water down, not speed the water up. If you slow the water down, many of the suspended particles will fall out, as will much of the phosphorus attached to those particles. Soils will absorb the metals and likely the organic contaminants. If the water moves slowly enough, the pathogens have a chance of staying put and getting eaten by soil bacteria.
Natural treatment systems are becoming all the rage. And King County, Washington where I live is right on top of this trend. The storm water plans for King County, Seattle Public Utilities and the City of Seattle, include a wide range of green management techniques (www.ecy.wa.gov/programs/wq/stormwater/manual.html). Bioswales, greenscapes, rain gardens, green roofs, phytoremediation systems, are just some examples. These offer a pleasing appearance plus low infrastructure costs. To date, most of the emphasis with these systems has been on the type of plants to use. It is thought that the plants themselves, in combination with enhanced microbial activity in the root zone, are the key factors for water management. For example, BMPs on bioswales from the State of Oregon go into great detail on length, depth, width, types of plants, etc. Here is what they say about compost: “Compost or some other organic material must be reintroduced into the soil. The amount of compost additive used should be carefully considered for the desired results.” King County also says using compost is a good thing. Compost is a key component for building soils (www.BuildingSoil.org/tools/Soil_BMP_text.pdf).
For me, it is the soils (with a little help and prettier appearance from the plants) that make the difference. I would argue that these agencies and guidance documents need much greater input and direction on how to use compost. Specifics like how much compost to use per unit of storm water and what types of composts to use. Soil science is a valuable profession and integration of the wealth of information that is already understood into this arena would greatly improve performance. Bring on those engineers – the ones that understand about soils and composts!
We’ll be testing the use of compost as a means to enhance the Whidbey Island phytoremediation project in class. And I would encourage you to test and demonstrate this as well. There is a lot of storm water out there that can use your compost. There are a lot of city planners that wouldn’t mind learning a little bit about soils. Improve performance and save money – now those are good ways to get people interested. And you might ask, what does this have to do climate change? Natural treatment systems offer a means to deal with the more intense storm events that climate change has brought. They require less energy than conventional systems. They also increase soil and plant carbon storage in urban areas, result in improved water conservation…. And the list goes on!
Sally Brown – Research Associate Professor at the University of Washington in Seattle – authors this regular column. E-mail Dr. Brown at firstname.lastname@example.org.