Green Cities

My sewage is going where?

Did you ever wonder where your poop actually goes? Your sewage-sludge, referred to as “biosolids,” is already being used in cement manufacturing, road construction, and even in baseball diamonds. Some scientists are now saying it could also be mixed with soil for emerging green roofs— technology that could help counteract heat island effects that can lead to deadly summer temperatures. How do green roofs work? Green roofs take an otherwise unused space and transform them into rooftop ecosystems. They can range in their complexity from thinner “extensive” green roofs that generally only a maintain a handful of smaller plants, to greater “intensive” roofs, often supporting bushes, trees, and even walkways. These installations help mimic the natural systems that absorb stormwater and many of the toxins found in the runoff from conventional roofs while simultaneously reducing energy costs for property owners. Conventional roofs are composed of materials like steel, which absorb huge amounts of solar radiation which then emits more heat. Well maintained green roofs, however, are better at handling this heat, with a combination of shade cover and evapotranspiration helping to reduce building heat. Less heat being transferred to your house means lower cooling costs for you. Green roof plants need a solid substrate (soil) base if they are to continue growth, which is where your time on the toilet comes into play. Biosolids, when mixed with more traditional local soils, have been shown to be a highly effective substrate in green roofs, leading to even greater carbon sequestration. Some countries are sending as much as 65 percent of biosolids to landfills. If not properly maintained, these landfill deposits have the potential to leak harmful pollutants like cadmium and arsenic into nearby groundwater. As populations worldwide are expected to continue their exponential growth, existing, risky storage methods could quickly become overwhelmed. Safe green roof applications have the opportunity to not only divert significant amounts of these toxins from landfills, but also have the added benefit of reducing energy costs!   Kegan Gerard, Intern