The Effect of Two Plants Grown in Calcined Clay with Activated Alumina on Nitrogen and Phosphorus Removal in Greenhouse Natural Swimming Pool Mesocosms.

Natural swimming pools (NSPs) are recent technological introductions to North America, designed to provide an attractive landscape amenity that also serves as a chemical free swimming pool. Based on constructed wetland technology, natural swimming pools use biological filtration, a designed, intentional hydraulic system, and an impermeable liner to separate the system from the surrounding natural hydrologic cycle. Two ornamental wetland plants, Iris versicolor , blue flag iris, and Canna x generalis, canna sp, were tested for their ability to produce aboveground biomass in the low nutrient environment of an NSP and for their nutrient removal capabilities. Appropriateness of the substrate materials, a mix of calcined clay, sand and alumina, was assessed for plant establishment and nutrient storage capabilities. The experiment included 24 units and 3 treatments 1)blue flag iris, 2) canna sp, 3) unvegetated, with 8 units each. All treatments are divided into 2 conditions, free water surface (FWS) and subsurface flow (SSF), with 4 units in each condition. NO₃ and phosphorus levels in the NSPs water column should be less than 30 mg/l^-1 NO₃ and 0.01 mg/l^-1 P. These are the levels recommended by the 2006 German FLL Guidelines for private NSP design and operation. Treatment effect for plant species and final NO₃ levels in the pool water were highly significant with a p value < .001. Canna removed larger amounts of NO₃ than iris, probably due to greater biomass production. The correlation of biomass and NO₃ removal was highly significant, p<.001, using Pearsons correlation. Above ground biomass was a significant storage compartment in both Canna sp and blue flag iris, demonstrating the importance of harvestable biomass removal. P removal experienced in all three treatments supports the hypothesis that activated alumina combined with calcined clay is an effective media for adsorption of P in a NSP system. All treatments reached treatment goals for P removal and experienced greater than 99% removal of influent P. In all treatments final P measured less than the recommended level of 0.01mg/l^-1. Both vegetated treatments with the calcine clay/alumina/sand substrate supported suitable biomass production and nutrient storage. The unvegetated treatment met the recommended levels of P removal but did not reach the recommended NO₃ level of <30 mg/l^-1.