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Title: Phosphorus retention in lab and field-scale subsurface-flow wetlands treating plant nursery runoff

Author
item WHITE, SARAH - Clemson University
item TAYLOR, MILTON - Foreign Agricultural Service (FAS, USDA)
item Albano, Joseph
item WHITWELL, TED - Clemson University
item KLAINE, STEVE - Clemson University

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2011
Publication Date: 9/1/2011
Citation: White, S.A, Taylor, M.D., Albano, J.P., Whitwell, T., Klaine, S.J. 2011. Phosphorus retention in lab and field-scale subsurface-flow wetlands treating plant nursery runoff. Ecological Engineering. 37:1968-1976.

Interpretive Summary: Constructed wetland systems built to handle nutrient contaminants are often efficient at removing nitrogen, but ineffective at reducing phosphorous (P). Incorporating clay-based substrate can enhance P removal in subsurface-flow constructed wetland systems. Crushed brick, a recycled building product, and two particle sizes of calcined clay were evaluated for their capacity to bind P from simulated nutrient-rich plant nursery runoff. The three substrates were screened for P sorbing behavior using sorption, desorption, and equilibration experiments. The coarse calcined clay bound the highest percentage of P supplied. Phosphorous-saturated clay was found to serve as a slow-release source of P for fertilization purposes. This study demonstrated the viability of using course calcined clay as root bed substrate in subsurface-flow treatment wetlands remediating phosphorous from plant nursery runoff.

Technical Abstract: Constructed wetland systems built to handle nutrient contaminants are often efficient at removing nitrogen, but ineffective at reducing phosphorous (P) loads. Incorporating clay-based substrate can enhance P removal in subsurface-flow constructed wetland systems. We evaluated the potential of crushed brick, a recycled building product, and two particle sizes of palygorskite-bentonite industrial mineral aggregate (calcined clay) to sorb P from simulated nutrient-rich plant nursery effluent. The three substrates were screened for P sorbing behavior using sorption, desorption, and equilibration experiments. We selected one substrate to evaluate in an 8-month field trial to compare field sorption capacity with laboratory capacity. In the laboratory, coarse calcined clay average sorption capacity was 497 mg/kg and it sorbed the highest percentage of P supplied (76%), except at exposure concentrations >100 mg/L where the increased surface area of fine clay augmented its P sorption capacity. Subsurface-flow mesocosms were filled with course calcined clay and exposed to a four and seven day hydraulic retention time treatment. Phosphorous export was reduced by 60 to 74% for both treatments until substrate P-binding sites began to saturate during month seven. During the eight month experiment, the four and seven day treatments fixed 1273 +/- 22 mg/kg P and 937 +/- 16 mg/kg, respectively. Sequential extractions of the P saturated clay indicated that P could desorb slowly over time from various pools within the calcined clay; thus if the calcined clay were recycled as a soil amendment, most P released would be slowly available for plant uptake and use. This study demonstrated the viability of using course calcined clay as root bed substrate in subsurface-flow treatment wetlands remediating phosphorous from plant nursery runoff.