Combining Compost and Phosphorus Sorption Media into a Homogenized "Mix" for Stormwater Treatment

Focus Area

Water Quality/Wetlands


Natural Resources






Over 3 years

Research Idea Scope

This study will develop a compost blended with phosphorus sorption media mix (Mix), which will treat highways stormwater runoff while limiting phosphorus leaching. Compost effectively removes metals and other pollutants from stormwater, increases infiltration on highways embankments, and increases planted vegetation. Best Management Practices (BMPs) like Compost Amended Vegetated Filter Strips incorporate compost to treat highways runoff. However, compost amendments export phosphorus. In receiving water bodies phosphorus is a major water quality pollutant, contributing to hypoxic zones unable to support aquatic life, cyanobacteria toxicity affecting drinking water, and others. As a result, compost amendments are generally not applied where runoff discharges to waterbodies. Finding a practical method of substantially reducing phosphorous leaching from compost might allow broader use of compost based BMPs on highway projects. Additionally, since compost is widely used in agriculture, finding ways to reduce compost phosphorus exports may have wide scale positive impacts on water quality. Since phosphorus is a primary water quality pollutant, reducing it is a common water quality goal, and many studies have explored and demonstrated the ability of various media to remove phosphorus from water. The primary treatment mechanism in these studies is sorption, where phosphorus adheres to the media. Media with proven phosphorus sorption capabilities include lime and aluminum water treatment residuals, limestone, oyster shells, dolomite, gypsum, and others. Blending phosphorus sorption media with compost may produce a stormwater treatment Mix with minimal phosphorous export. Ascertaining the ideal Mix requires controlled comparison studies. The proposed research consists of an extensive literature review to determine ideal sorption media(s) for testing, column tests of Mix(s) in a laboratory setting, and field tests of promising Mix(s). In addition to determining the test media via literature review, this proposal posits testing at least three particular media: limestone, dolomite and gypsum. Limestone is composed primarily of calcium carbonate; dolomite of calcium magnesium carbonate; and gypsum of calcium sulfate dehydrate. The calcareous nature of these media adsorb phosphorus, and all three have demonstrated significant phosphorus removal from water. All three are readily available in a form, such as powdered or pelleted, that feasibly mixes and homogenizes with compost. All three media are large-scale agricultural amendments and have the benefits of the existing agricultural infrastructure. These benefits include: availability in most areas, established transport systems for large volumes, large scale spreading, mixing and application techniques, and competitive cost and economic structures. The objectives of this research are to: 1) Develop a practical Mix that effectively limits phosphorous export while maintaining the stormwater pollutant removal and hydrologic capabilities of standard compost. 2) Develop guidance on the use, limitations, design and implementation of the Mix. Achieving the research’s objectives involves the following tasks: 1) Conduct a survey and synthesis of existing literature related to phosphorus sorption media, as well as monitor for potential negative impacts from said media. 2) Design and implementation testing of one or more compost and phosphorus sorption media Mix(s) (including laboratory column tests and real world field testing). 3) Develop guidance for the use, design and implementation of the Mix. This guidance would include design criteria, taking into account varying facility operations and climate.

Urgency and Payoff

Compost applications have the ability to effectively and affordably treat stormwater runoff, such as from highway sheetflow. Reducing phosphorus exports from compost may dramatically increase the applicability of the technique, and help to mitigate the effects of stormwater pollutants in areas sensitive to phosphorus pollution. Additionally, reducing phosphorus exports from compost may inform agricultural applications, which often impact downstream receiving waters.

Suggested By

Brandon Slone Washington State Department of Transportation 360-570-2458

[email protected]