How a wetland can clean equipment-washing water

During the summer of 2011, researchers at the University of Massachusetts Turfgrass Research Center constructed a small artificial wetland (vegetated sand bed) to treat water used to wash the facility’s mowers and spraying equipment following use. The system consists of two parallel trains of wetland cells. The first bed in each cell is coarse gravel with reed canary grass (Phalaris arundinacea). The second bed is coarse sand with a mixture of plants, harlequin blue flag (Iris versicolor), woolgrass (Scirpus cyperinus) and soft rush (Juncus effusus). The beds have vertical flow, with the first bed having down flow and the second bed having up flow. During normal operation, nitrate from equipment washing and clipping degradation entered the system at 2.9 mg/L NO3-N, which dropped to 0.4 mg/L at the outlet to the system — an 86-percent removal.

The system was spiked twice in the fall of 2015 with a 5-10-5 fertilizer (0.15 lb. N/1,000 sq. ft.). Measured influent nitrogen concentrations were 72.8 and 20.5 mg/L of ammonia-N and nitrate-N, respectively. Using the first beds with no addition of water, these concentrations had dropped to less than 5 mg/L within 96 hours of application. A second, larger spike of fertilizer (0.66 lb. N/1,000 sq. ft.) was made later in the fall to allow the calculation of microbial rate constants for both ammonia and nitrate removal.

Fertilizer applications in September 2016 were to measure the levels of nitrate, ammonium and phosphorous through the system following a simulated ‘tank dump’ of fertilizer (application rate 0.15 lb./N/1,000 sq. ft. in a 170-gallon sprayer to cover two acres). Water was added each day to ensure that flow was leaving all four wetland units. Addition of this much water shortened the detention time within the wetland and affected treatment performance. The maximum nutrient level leaving the system never exceeded 8 mg/L ammonia-N, <9 mg=”” l=”” nitrate-n=”” and=”” 6=”” mg=”” l=”” total=”” phosphorous=”” respectively=”” p=””>

This research highlights the effectiveness of artificial wetlands to treat wash water to levels that allow its reuse as irrigation water and/or groundwater return.

Mickey Spokas, Ph.D., is a soil scientist, Michelle DaCosta, Ph.D., is a turfgrass scientist and Scott Ebdon, Ph.D., is a turfgrass scientist at the University of Massachusetts Amherst.

Acknowledgements: Support for this study was provided by the New England Regional Turfgrass Foundation and New England Waste Systems (NEWS-USA).