Student Research Projects

Chemical Amendments as a Means of Controlling Phosphate Levels in the Leachate of Green Roofs

Student John Maravich
Faculty Mentor(s)
Department Earth and Environmental Sciences


Green roofs are growing in popularity as a way of beautifying buildings, reducing energy needs, and retaining rain runoff from buildings. All of these are laudable purposes but there are some draw backs to green roofs that need to be addressed. Because most clients of green roof companies want a “green” roof, many companies add commercial fertilizer to the soil in order for the plants to grow faster and look lusher. While this improves the aesthetics of the green roof, it does not help the environment. There is often an overload of nutrients that the plants cannot possibly absorb. This excess is in turn washed out of the soil during strong rain events and ends up in local water ways if the drainage does not connect to a waste water treatment facility. Nutrient overload is all too often the cause of severe algal blooms that damage waterways. Most often, phosphorous is the limiting nutrient that holds the algae in check (Lewandowski et al. 2003). It is therefore, the purpose of this study to explore ways of reducing the phosphorous content of the runoff through an effective chemical agent that can be added to the soil. In this study, Potassium Carbonate (K2CO3), Aluminum potassium sulfate dodecahydrate (alum AlKSO4 * 12H2O), Sodium Bicarbonate (NaHCO3), Ferric Oxide (Fe2O3), Calcium Carbonate (CaCO3), and a proprietary substance, Phosfilter, were all employed as phosphorous retaining agents. Most of the chemicals were identified through a review of the literature in controlling phosphorous in waste water. To test these chemicals, a simulated green roof soil plot was created for each of the chemical treatments plus a control. Rain water was poured on the plots and collected for testing. The asorbic acid method of phosphorous testing was employed in this study. The results indicated that alum had the greatest potential for lowering the amount of phosphorous in the runoff.