European Water Chestnut: Invasive Plant or Sewage Treatment Plant?

Typically regarded as a nuisance weed, the European Water Chestnut has an infamous reputation for being an eye sore in natural waters. However, this prolific aquatic plant requires a significant amount of nutrients to grow – nutrients that are readily supplied by wastewater effluent.

Kelsey Hu collects a water sample outside a bed of European Water Chestnut on the Hudson River, south of Denning’s Point in Beacon, NY. Photo: John Cronin

Kelsey Hu collects a water sample outside a bed of European Water Chestnut on the Hudson River, south of Denning’s Point in Beacon, NY. Photo: John Cronin

Discharge from wastewater treatment plants accounts for 53% of the total nitrogen and 77% of the total phosphorus  dumped into the Hudson River every day. The excess nutrients can adversely affect water quality by causing eutrophication which decreases the ecological diversity, aesthetics and navigability of natural bodies of water. By up-taking nutrients from the water column to grow, the water chestnuts actually help to remove the excess nutrients from the wastewater effluent.

Photo: John Cronin

Photo: John Cronin

Based on the standing stock of the water chestnuts near Denning’s Point, we estimate that the plants can hold 2.54 tons of nitrogen in their biomass. If removed before the plants die and release these nutrients back into the water column, these plants could potentially remove 17% of the nitrate and ammonia discharged yearly from the Beacon WWTP. Additionally, if the biomass is then placed in an anaerobic digester, these water chestnuts could yield up to 16,700 m3 of methane gas. That is enough gas to produce 175 MWh of energy.

Extrapolating these findings to include the entire Hudson River, the water chestnuts along the Hudson have the capacity to remove up to 2% of the total nitrogen and 2% of the total phosphorus from the wastewater effluent that is discharged every year. In addition, they have the potential to produce up to 218,000 m3 CH4, which is equivalent to 2.3 GWh of energy every year. These findings show that if the chestnuts are removed and digested annually, they can serve the dual purpose of nutrient removal and biogas production.

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Sustainable Water Chestnut Management: Role of Invasive European Water Chestnut as a Nutrient Bioextractant from Wastewater Outfalls in the Hudson River Estuary  was conducted as part of the ASSETS to Serve Humanity REU Site Program at Clarkson University, sponsored by the National Science Foundation.

Kelsey Hu, the primary author, is studying in the environmental track of civil engineering at the University of Portland. Her co-authors are Nona Jesman and Yujiao Yang, both Ph. D. candidates in Civil and Environmental Engineering at Clarkson.