VEGETATED SUBMERGED BEDS WITH ARTIFICIAL SUBSTRATES .2. N AND P REMOVAL

Settled wastewater was batch fed into 22-L microcosms containing monocultures of the emergent aquatic plants, Sagittaria latifolia, Scirpus pungens, Phragmites australis, and Typha latifolia. Plants were cultured in 1.25 cm gravel and 2.5 and 5.0 cm plastic trickling filter media with specific surface areas of 394, 279, and 138 m2/m3 respectively. Nitrogen (N) and phosphorus (P) removal rates [i.e., grams removed per meter square per day] were compared at three target hydraulic loading rates (HLR): 4.7, 9.4, and 18.8 cm/day. N removal increased linearly for all plants over an N loading range of 0.6-4.4 g/(m2.day), with percent N removal greater than 75% for Typha and Sagittaria. Nitrogen removal rate was independent of the specific surface area of the substrate. Vegetated pots removed more N than the nonvegetated pots at the higher N loading rates. Phosphorus removal rate increased in proportion to P loading over the range of 0.14-0.92 g/(m2.day). At the HLR of 18.8 cm/day, Typha, Sagittaria, and nonvegetated systems removed more P[> 0.43 g/(m2.day)] than Scirpus and Phragmites [< 0.26 g/(m2.day)].