Browsing by Author "Allen, Winthrop C."

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Plant species and temperature effects on the k-C first-order model for COD removal in batch-loaded SSF wetlands
(2006-02) Stein, Otto R.; Biederman, Joel A.; Hook, Paul B.; Allen, Winthrop C.
The modified k–C first-order degradation model proposed by Kadlec and Knight [Kadlec, R.H., Knight, R.L., 1996. Treatment Wetlands. Lewis Publishers, Boca Raton, FL] was fit to 192 data sets of COD concentration versus time measured in batch-loaded wetland microcosms. The time series sets were divided into four replicates of four plant species treatments; Carex utriculata (sedge), Schoenoplectus acutus (bulrush), Typha latifolia (cattail) and unplanted controls housed in a controlled-environment greenhouse in which temperature was cycled in 4 °C increments from 24 to 4 °C and back to 24 °C over a yearlong period. One 20-day batch incubation was conducted at each temperature setting during which seven chemical oxygen demand (COD) samples were drawn from each of 16 wetland columns. Non-linear mixed effects regression was used to fit parameters of the model. Best-fit values of the rate parameter k and the background concentration C* varied significantly by plant species and greenhouse temperature setting. An Arrhenius relationship was used to assess the effect of temperature on these parameters. Species greatly influenced the value of volumetric rate parameter at 20 °C (k20) and ranked Carex > Schoenoplectus > Typha > unplanted control (0.925, 0.743, 0.612 and 0.366 day−1, respectively). All displayed decreasing values for increasing temperature but species variation was much less (θk = 0.945, 0.957, 0.953 and 0.936, respectively). Background COD concentration values at 20 °C (Cx20) ranked Carex < Schoenoplectus < Typha < unplanted control (42, 46, 66, 67 mg L−1, respectively) but seasonal variation was mixed (θC*=1.029, 0.999, 0.958 and 0.935, respectively). The results indicate that (1) seasonal variation of performance is plant-species specific; (2) singly, the rate constant k cannot capture the variation in performance due to temperature as much of the variation is reflected in the C* and (3) there are strong interactions between values of k and C*.
Temperature and wetland plant species effects on wastewater treatment and root-zone oxidation
(2002) Allen, Winthrop C.; Hook, Paul B.; Biederman, Joel A.; Stein, Otto R.
Constructed wetlands are widely used for wastewater treatment, but there is little information on processes affecting their performance in cold climates, effects of plants on seasonal performance, or plant selection for cold regions. We evaluated the effects of three plant species on seasonal removal of dissolved organic matter (OM) (measured by chemical oxygen demand and dissolved organic carbon) and root zone oxidation status (measured by redox potential [Eh] and sulfate [SO2-4]) in subsurface-flow wetland (SSW) microcosms. A series of 20-d incubations of simulated wastewater was conducted during a 28-mo greenhouse study at temperatures from 4 to 24°C. Presence and species of plants strongly affected seasonal differences in OM removal and root zone oxidation. All plants enhanced OM removal compared with unplanted controls, but plant effects and differences among species were much greater at 4°C, during dormancy, than at 24°C, during the growing season. Low temperatures were associated with decreased OM removal in unplanted controls and broadleaf cattail (Typha latifolia L.) microcosms and with increased removal in beaked sedge (Carex rostrata Stokes) and hardstem bulrush [Schoenoplectus acutus (Muhl. ex Bigelow) A. & D. Löve var. acutus] microcosms. Differences in OM removal corresponded to species' apparent abilities to increase root zone oxygen supply. Sedge and bulrush significantly raised Eh values and SO2-4 concentrations, particularly at 4°C. These results add to evidence that SSWs can be effective in cold climates and suggest that plant species selection may be especially important to optimizing SSW performance in cold climates.