Eutrophication, the process through which a nutrient-rich body of water begins to produce unwanted plant life at an outsize rate is a problem in many lake and coastal areas. The resulting growth, typically caused by fertilizer runoff, can deplete water bodies of the oxygen necessary to sustain other forms of life. It can also lead to the formation of toxic organisms such as the photosynthesis-powered cyanobacteria, whose name derives from its blueish color.
Researchers at the University of Southern Denmark (USD) have found a potential solution to eutrophication in the form of a common building material: crushed concrete sourced from demolition sites. The cement in concrete attracts phosphorous—a primary ingredient in fertilizers—due to its high concentrations of calcium, aluminum, and iron. According to Melanie Sønderup (left), an environmental engineer and a USD Ph.D. candidate, filtering water through crushed concrete can remove up to 90 percent of its phosphorous content.
But it is neither sufficient nor desirable to line lake embankments with concrete walls, as the binding process requires contact with pulverized concrete—and the smaller the cement particles, the better the binding. Moreover, exposed concrete is less effective because the process of weathering depletes its calcium content. The concrete also requires periodic replenishing, as its effectiveness at filtration declines over time.
Nevertheless, this finding suggests a new and environmentally beneficial application of recycled concrete, which could be reused in road-bed construction once it is depleted of its phosphorous-binding capacity. This research may also contribute to a new market for gabions filled with crushed concrete whose small particles are contained within a filtration cloth. These gabions could be located in areas with concentrated runoff, thus benefiting a seemingly intractable problem with a surgical-material strategy.
Blaine Brownell, AIA, is a regularly featured columnist whose stories appear on this website each week. His views and conclusions are not necessarily those of ARCHITECT magazine nor of the American Institute of Architects.
Opening photo courtesy Flickr user Pelle Sten via a Creative Commons license.
