Orthophosphate Adsorption Equilibrium and Breakthrough on Filtration Media for Storm-Water Runoff Treatment

Abstract

Total phosphorus (TP) in storm-water runoff is a common regulatory target for maintaining the quality of receiving surface water. Previous storm-water treatment studies show that it is difficult to consistently achieve TP removal higher than 40%, whereas regulatory goals of 50–65% removal are becoming common. To meet these goals, storm-water filtration technologies utilizing an expanding array of filtration media are being deployed, especially in areas with protected water bodies such as Puget Sound and Chesapeake Bay. One challenge is that if the media has no adsorption capacity, particulate phosphorus can redissolve into solution and form liberal orthophosphate (Ortho-P), resulting in lower overall TP removal. Therefore, effective Ortho-P adsorption capacity in filtration media is crucial to meet more stringent TP removal goals. Additional media characteristics that should be considered include gradation, permeability, surface area, morphology, cost, and toxicity. In response to these requirements, an engineered media (EM) was developed and evaluated by Ortho-P adsorption isotherms and breakthrough in typical storm-water runoff conditions. Three other media, perlite, zeolite, and granular activated carbon (GAC), widely used in storm-water treatment, were also investigated under the same experimental conditions. With adsorption isotherms, EM showed the highest adsorption capacity of