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The Capacity of Duckweed to Treat Wastewater

Ecological Considerations for a Sound Design

^a Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, Germany
^b Institute for Environmental Studies, Vrije Universiteit, De Boelelaan 1087, 1081 HV Amsterdam, the Netherlands
^c Water Company Overijssel WMO, Oude Veerweg 1, 8000 GW Zwolle, the Netherlands

View larger version (121K): [in a new window]   Fig. 1. Isopleth contour map of relative growth rates of fat duckweed (in kg kg-1 dry wt. d-1) as a function of pH and total ammonia concentrations in domestic wastewater at 23°C (y axis starting at 10 mg L-1 total ammonia). Data from Körner et al. (2001).

View larger version (26K): [in a new window]   Fig. 2. Exponential chemical oxygen demand (COD) removal curves in differently treated wastewater. Multiple comparisons of fitted curves were made across all possible combinations. The COD removal was significantly faster in treatments containing duckweed compared with the control, whereas treatments with artificial duckweed, air bubbling, or both were not significantly different from either the control or the duckweed treatment. For curve fit parameters see Körner et al. (1998). Data points represent means of four replicates; for clarity, standard errors were omitted. Data from Körner et al. (1998).

View larger version (26K): [in a new window]   Fig. 3. Nitrogen and phosphorus removal coefficients of duckweed-covered wastewater in dependence of the initial nutrient concentrations (85, 72, 46, 25, and 12 mg Kjeldahl N L-1 and 14, 10, 4, 2, and 1 mg total P L-1). One data point was excluded for the curve fit of Kjeldahl N. Data from Körner and Vermaat (1998).

View larger version (42K): [in a new window]   Fig. 4. Contribution of the different components and processes of a duckweed-covered system to the total N and P loss in shallow duckweed-covered batch systems. The terms Ndw and Pdw are uptake by duckweed; Nad and Pad are uptake by biofilm attached to duckweed; Naw and Paw are uptake by biofilm attached to the walls and/or sediment; and Nnd and Nnw are N loss due to nitrification–denitrification by biofilm attached to duckweed (nd) and walls (nw). Data from Körner and Vermaat (1998).

View larger version (22K): [in a new window]   Fig. 5. Nitrogen and phosphorus removal rates of fat duckweed, biofilm (uptake by attached algae and bacteria), and coupled nitrification–denitrification (n/d) of attached bacteria in duckweed-covered domestic wastewater dependent on the initial nutrient concentrations. Removal rates of duckweed refer to the surface of the system whereas those of the biofilm and nitrification–denitrification refer to the growth surface available on duckweed and walls of the system. For the curve fit of the N removal by duckweed, one data point (Experiment 1 without duckweed growth) was excluded. Data from Körner and Vermaat (1998).