Browsing by Author "Stein, Otto R."

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Ammonium removal in constructed wetland microcosms as influenced by presence and species of plants and organic carbon load
(2005-06) Riley, Kate Alexis; Stein, Otto R.; Hook, Paul B.
We evaluated ammonium nitrogen removal and nitrogen transformations in three-year-old, batch-operated, subsurface wetland microcosms. Treatments included replicates of Typha latifolia, Carex rostrata, and unplanted controls when influent carbon was excluded, and C. rostrata with an influent containing organic carbon. A series of 10-day batch incubations were conducted over a simulated yearlong cycle of seasons. The presence of plants significantly enhanced ammonium removal during both summer (24 degrees C, active plant growth) and winter (4 degrees C, plant dormancy) conditions, but significant differences between plant species were evident only in summer when C. rostrata outperformed T. latifolia. The effect of organic carbon load was distinctly seasonal, enhancing C. rostrata ammonium removal in winter but having an inhibitory effect in summer. Season did not influence ammonium removal in T. latifolia or unplanted columns. Net production of organic carbon was evident year-round in units without an influent organic carbon source, but was enhanced in summer, especially for C. rostrata, which produced significantly more than T. latifolia and unplanted controls. No differences in production were evident between species in winter. COD values for C. rostrata microcosms with and without influent organic carbon converged within 24 hours in winter and 7 days in summer. Gravel sorption, microbial immobilization and sequential nitrification/denitrification appear to be the major nitrogen removal mechanisms. All evidence suggests differences between season and species are due to differences in seasonal variation of root-zone oxidation.
Evapotranspiration crop coefficients for cattail and bulrush
(2004-05) Towler, Brett William; Cahoon, Joel; Stein, Otto R.
Accurate estimates of evapotranspiration from constructed wetlands are required to establish design flow estimates and to assess the effectiveness of wetland water quality amelioration. Water consumption by two wetland plant species, Typha latifoilia (broadleaf cattail) and Scoenoplectus acutus (hardstem bulrush), was measured in a greenhouse for eight months. Measurements of actual evapotranspiration (ETC) from replicates of both plant treatments were related to potential evaporation (ET0) as approximated by evaporation from saturated gravel beds. Ratios of ETC to ETO used to develop crop coefficients (KC) for each plant species. The relationship between cattail ETC/ET0 and the ratio of vegetative to open water surface area (SV/S0) agreed with previous investigations. A linear relationship was used to account for advective energy fluxes due to peripheral canopy area. Cattail crop coefficients were scaled according to this relationship. The resulting scaled crop coefficient curve may be transferable to constructed wetlands of a known SV/S0.
Floating treatment wetlands for domestic wastewater treatment
(2011-11) Faulwetter, J. L.; Burr, Mark D.; Cunningham, Alfred B.; Stewart, Frank M.; Camper, Anne K.; Stein, Otto R.
Floating islands are a form of treatment wetland characterized by a mat of synthetic matrix at the water surface into which macrophytes can be planted and through which water passes. We evaluated two matrix materials for treating domestic wastewater, recycled plastic and recycled carpet fibers, for chemical oxygen demand (COD) and nitrogen removal. These materials were compared to pea gravel or open water (control). Experiments were conducted in laboratory scale columns fed with synthetic wastewater containing COD, organic and inorganic nitrogen, and mineral salts. Columns were unplanted, naturally inoculated, and operated in batch mode with continuous recirculation and aeration. COD was efficiently removed in all systems examined (>90% removal). Ammonia was efficiently removed by nitrification. Removal of total dissolved N was ∼50% by day 28, by which time most remaining nitrogen was present as NO3-N. Complete removal of NO3-N by denitrification was accomplished by dosing columns with molasses. Microbial communities of interest were visualized with denaturing gradient gel electrophoresis (DGGE) by targeting specific functional genes. Shifts in the denitrifying community were observed post-molasses addition, when nitrate levels decreased. The conditioning time for reliable nitrification was determined to be approximately three months. These results suggest that floating treatment wetlands are a viable alternative for domestic wastewater treatment.
Influence of season and plant species on the abundance and diversity of sulfate reducing bacteria and ammonia oxidizing bacteria in constructed wetland microcosms
(2013-01) Faulwetter, J. L.; Burr, Mark D.; Parker, Albert E.; Stein, Otto R.; Camper, Anne K.
Constructed wetlands offer an effective means for treatment of wastewater from a variety of sources. An understanding of the microbial ecology controlling nitrogen, carbon and sulfur cycles in constructed wetlands has been identified as the greatest gap for optimizing performance of these promising treatment systems. It is suspected that operational factors such as plant types and hydraulic operation influence the subsurface wetland environment, especially redox, and that the observed variation in effluent quality is due to shifts in the microbial populations and/or their activity. This study investigated the biofilm associated sulfate reducing bacteria and ammonia oxidizing bacteria (using the dsrB and amoA genes, respectively) by examining a variety of surfaces within a model wetland (gravel, thick roots, fine roots, effluent), and the changes in activity (gene abundance) of these functional groups as influenced by plant species and season. Molecular techniques were used including quantitative PCR and denaturing gradient gel electrophoresis (DGGE), both with and without propidium monoazide (PMA) treatment. PMA treatment is a method for excluding from further analysis those cells with compromised membranes. Rigorous statistical analysis showed an interaction between the abundance of these two functional groups with the type of plant and season (p<0.05). The richness of the sulfate reducing bacterial community, as indicated by DGGE profiles, increased in planted vs. unplanted microcosms. For ammonia oxidizing bacteria, season had the greatest impact on gene abundance and diversity (higher in summer than in winter). Overall, the primary influence of plant presence is believed to be related to root oxygen loss and its effect on rhizosphere redox.
Nitrogen Removal via Ammonium Adsorption to Gravel Sized Particles in Constructed Wetlands
(2013-03) Hafla, Erin C.; Stein, Otto R.
Constructed wetlands are currently used as an alternative to conventional waste-water treatment systems throughout the world. However, several of the chemical processes involved are still in the process of being understood. The removal of ammonium from waste-water is one of these processes. Two mechanisms by which constructed wetlands remove ammonium from the system is by ammonium adsorption or through ammonium volatilization. The focus of this study was to discover the reasons behind abnormally high adsorption rates recorded in a previous study conducted in 2005 for a gravel currently used in one of Montana State University’s constructed wetland projects. This sorption study consisted of five experiments. The first experiment was meant to determine the Cation Exchange Capacity (CEC) of the gravel to further define the ability of the gravel to sorb ammonium in a constructed wetland system. The second addresses the basic physical properties that are involved in determining whether the amount of ammonium adsorption occurring in the gravel. The third and fourth experiments sought to establish which of the two main processes involved in the removal of ammonium was the reason behind the overall loss of ammonium from this particular constructed wetland system, and complete a mass balance of a specific amount of ammonium through an adsorption and desorption experiment. These two experiments also looked at the ability of gravel to sorb variable initial concentrations of ammonium over a period of 24 hours. The fifth experiment was meant to determine the maximum sorptive capacity of the gravel of interest. Results of this analysis showed that the gravel’s CEC was below the detectable limit of the methodology that was being used, which was calibrated for a soil. An X-ray Powder Diffraction machine was used to determine the components of the gravel, which were revealed to be mainly a type of quartz and a silica based compound as well as 10 to 20% calcium mica. Mica increased the CEC of the gravel dramatically, thus increasing the adsorption ability of the gravel. Adsorption was found to be the single cause of ammonium loss from the system and a concentration of around 500 mg/L of NH4Cl as N was discovered to saturate the system allowing for all of the adsorption sites to be filled. The pH of the solution never rose above 6.5, effectively preventing chemical reactions from converting ammonium to ammonia and disallowing volatilization to begin. The maximum a sorptive capacity was determined to be approximately 180 mg/L of NH4 as N, which is about 232 mg/L of NH4. These results are consistent with the amount of adsorption calculated in the previous research. Overall, sorption may still be affected by factors acting on the system; research opportunities to discover the extent that these factors may change the absorbance of ammonium are many.
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*.
Polar organic solvent removal in a microcosm constructed wetlands
(2005-10) Kowles-Grove, J. L.; Stein, Otto R.
Three polar organic solvents, acetone, tetrahydrofuran (THF) and 1-butanol, were added at 100 mg/l each to post-primary municipal wastewater in order to simulate a mixed waste stream. This mixture was applied to an experimental microcosm subsurface constructed wetland system consisting of replicates of Juncus effusus, Carex lurida, Iris pseudacorus, Pondeteria cordata and unplanted controls in a series of 14-day batch incubations over a yearlong period simulating a summer and winter season. 90% removal of 1-butanol typically took less than 3 days. 90% removal of acetone required from 5 to 10 days in summer and 10 to 14 days in winter. 90% removal of THF required at least 10 days and was frequently not achieved during the 14-day incubations. Initial experiments confirmed that the majority of solvent removal was via microbial bioremediation. Solvent removal was typically better in planted replicates, especially Juncus, regardless of season. The removal rate of all solvents was slower in winter, but the seasonal effect was most pronounced in the unplanted control replicates and least in the Carex and Juncus replicates. Plant and seasonal effects are believed to be due, in part, to variation in metabolic pathways induced by plant and seasonal variation in available root-zone oxygen. Variation in transpiration also influenced species and seasonal effects on THF removal, but not the other more biodegradable solvents. A model based on a prediction of plant uptake of nonionic dissolved chemicals suggests that as much as 39% of the THF in solution could have been removed through plant transpiration.
Seasonal effects of 19 plant species on COD removal in subsurface treatment wetland microcosms
(2011-05) Taylor, Carrie R.; Hook, Paul B.; Stein, Otto R.; Zabinski, Catherine A.
Plants have many well-documented influences in treatment wetlands, but differences in individual species’ effects on year-round and seasonal performance are poorly understood. In this study, we evaluated plant effects on seasonal patterns of organic carbon removal (measured as COD) and sulfate concentration (used as an indicator of rootzone oxidation) in replicated, batch-loaded, greenhouse microcosms simulating subsurface treatment wetlands. Microcosms were planted with monocultures of 19 plant species or left unplanted as controls, dosed every 20 days with synthetic secondary wastewater, and operated over 20 months at temperatures from 4 to 24 °C. Study-long COD removal averaged 70% for controls and 70–97% for individual species. Most species enhanced COD removal significantly and the benefits of plants were greatest at 4–8 °C because COD removal decreased at low temperatures in controls but displayed limited seasonal variation in planted microcosms. Removal was significantly better at 24 °C than 4 °C with two species (Panicum virgatum and Leymus cinereus), significantly poorer with two species (Carex utriculata and Phalaris arundinacea), and did not differ with 15 species. Only one species showed a significant positive correlation between temperature and COD removal (Iris missouriensis, r = 0.67), while two species showed significant negative correlations (better when colder: Carex nebrascensis, r = −0.67; C. utriculata, r = −0.93). High COD removal throughout the study was strongly associated with high SO4 concentrations at low temperatures, suggesting that plant performance is related to rootzone oxidation and species’ abilities to promote aerobic over anaerobic microbial processes, particularly in winter. Results indicate that improved year-round and cold-season COD removal is common across diverse wetland plant species and novel species can be as good or better than those typically used. Better performing species were largely in the sedge and rush families (Cyperaceae and Juncaceae), while poorer performing species were largely in the grass family (Poaceae).
Seasonal influence on sulfate reduction and metal sequestration in sub-surface wetlands
(2007-08) Stein, Otto R.; Borden-Stewart, Deborah J.; Hook, Paul B.; Jones, Warren L.
To characterize the effects of season, temperature, plant species, and chemical oxygen demand (COD) loading on sulfate reduction and metals removal in treatment wetlands we measured pore water redox potentials and concentrations of sulfate, sulfide, zinc and COD in subsurface wetland microcosms. Two batch incubations of 20 day duration were conducted in each of four seasons defined by temperature and daylight duration. Four treatments were compared: unplanted controls, Typha latifolia (broadleaf cattail), and Schoenoplectus acutus (hardstem bulrush), all at low COD loading (267 mg/L), plus bulrush at high COD loading (534 mg/L). Initial SO4-S and zinc concentrations were 67 and 24 mg/L, respectively. For all treatments, sulfate removal was least in winter (4 °C, plant dormancy) greatest in summer (24 °C, active plant growth) and intermediate in spring and fall (14 °C), but seasonal variation was greater in cattail, and especially, bulrush treatments. Redox measurements indicated that, in winter, plant-mediated oxygen transfer inhibited activity of sulfate reducing bacteria, exacerbating the reduction in sulfate removal due to temperature. Doubling the COD load in bulrush treatments increased sulfate removal by only 20–30% when averaged over all seasons and did not alter the basic pattern of seasonal variation, despite tempering the wintertime increase in redox potential. Seasonal and treatment effects on zinc removal were broadly consistent with sulfate removal and presumably reflected zinc-sulfide precipitation. Results strongly suggest that interactive effects of COD loading rate, temperature, season, and plant species control not only sulfate reduction and zinc sequestration, but also the balance of competition between various microbial consortia responsible for water treatment in constructed wetlands.
Simulation of batch-operated experimental wetland mesocosms in AQUASIM biofilm reactor compartment
(Journal of Environmental Management, 2014-02) Mburu, N.; Rousseau, D. P.; Stein, Otto R.; Lens, Piet N. L.
In this study, a mathematical biofilm reactor model based on the structure of the Constructed Wetland Model No.1 (CWM1) coupled to AQUASIMâ€™s biofilm reactor compartment has been used to reproduce the sequence of transformation and degradation of organic matter, nitrogen and sulphur observed in a set of constructed wetland mesocosms and to elucidate the development over time of microbial species as well as the biofilm thickness of a multispecies bacterial biofilm in a subsurface constructed wetland. Experimental data from 16 wetland mesocosms operated under greenhouse conditions, planted with three different plant species (Typha latifolia, Carex rostrata, Schoenoplectus acutus) and an unplanted control were used in the calibration of this mechanistic model. Within the mesocosms, a thin (predominantly anaerobic) biofilm was simulated with an initial thickness of 49 mm (average) and in which no concentration gradients developed. The biofilm density and area, and the distribution of the microbial species within the biofilm were evaluated to be the most sensitive biofilm properties; while the substrate diffusion limitations were not significantly sensitive to influence the bulk volume concentrations. The simulated biofilm density ranging between 105,000 and 153,000 gCOD/m3 in the mesocosms was observed to vary with temperature, the presence as well as the species of macrophyte. The biofilm modeling was found to be a better tool than the suspended bacterial modeling approach to show the influence of the rhizosphere configuration on the performance of the constructed wetlands.
Simulation of carbon, nitrogen and sulphur conversion in batch-operated experimental wetland mesocosms
(2012-05) Mburu, N.; Sanchez-Ramos, D.; Rousseau, D. P.; van Bruggena, J. J. A.; Thumble, G.; Stein, Otto R.; Hook, Paul B.; Lens, Piet N. L.
A simulation model based on Constructed Wetland Model No. 1 (CWM1) using the AQUASIM mixed reactor compartment as a platform was built to study the dynamics of key processes governing COD and nutrient removal in wetland systems. Data from 16 subsurface-flow wetland mesocosms operated under controlled greenhouse conditions with three different plant species (Typha latifolia, Carex rostrata, Schoenoplectus acutus) and an unplanted control were used for calibration and validation in this mechanistic model. Mathematical equations for plant related processes (growth, physical degradation, decay, and oxygen leaching), physical re-aeration, as well as adsorption and desorption processes for COD and ammonium were included and implemented alongside CWM1 in the AQUASIM software, while some CWM1 parameters were adjusted to better fit the model predictions to experimental data during calibration. The simulation results showed that the model was able to describe the general trend of COD (R2 = 0.97–0.99), ammonium (R2 = 0.85–0.97) and sulphate (R2 = 0.71–0.93) removal in the wetland mesocosms and also in their controls (unplanted) through the experimental temperature range of 12–24 °C. Oxygen transfer by physical re-aeration was found to be 0.05 and 0.09 g m−2 d−1 at 12 °C and 24 °C, respectively. The amount of root oxygen transfer was the highest for the planted mesocosms at 12 °C at rates of 1.91, 0.94, and 0.45 g m−2 d−1 in the Carex, Schoenoplectus and Typha mesocosms, respectively, indicating that COD of the bulk wastewater was removed mainly by anaerobic processes under the specific experimental situations. Measured COD removal was better in the planted mesocosms than in the control; differences were effectively modelled by varying the bacteria concentration. The sorption process was found to be important in simulating COD and ammonia removal under these experimental conditions.
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.
Temperature, plant species and residence time effects on nitrogen removal in model treatment wetlands
(2013-12) Allen, Christopher Robert; Stein, Otto R.; Hook, Paul B.; Burr, Mark D.; Parker, Albert E.; Hafla, Erin C.
Total nitrogen (TN) removal in treatment wetlands (TWs) is challenging due to nitrogen cycle complexity and the variation of influent nitrogen species. Plant species, season, temperature and hydraulic loading most likely influence root zone oxygenation and appurtenant nitrogen removal, especially for ammonium-rich wastewater. Nitrogen data were collected from two experiments utilizing batch-loaded (3-, 6-, 9- and 20-day residence times), sub-surface TWs monitored for at least one year during which temperature was varied between 4 and 24 Â°C. Synthetic wastewater containing 17 mg/l N as NH4 and 27 mg/l amino-N, 450 mg/l chemical oxygen demand (COD), and 13 mg/l SO4-S was applied to four replicates of Carex utriculata, Schoenoplectus acutus and Typha latifolia and unplanted controls. Plant presence and species had a greater effect on TN removal than temperature or residence time. Planted columns achieved approximately twice the nitrogen removal of unplanted controls (40â€“95% versus 20â€“50% removal) regardless of season and temperature. TWs planted with Carex outperformed both Typha and Schoenoplectus and demonstrated less temperature dependency. TN removal with Carex was excellent at all temperatures and residence times; Schoenoplectus and Typha TN removal improved at longer residence times. Reductions in TN were not accompanied by increases in NO3, which was consistently below 1 mg/l N.
Temperature, plants and oxygen: How does season affect constructed wetland performance?
(2005-06) Stein, Otto R.; Hook, Paul B.
The influence of temperature and plant-mediated oxygen transfer continues to draw attention from researchers, practitioners and regulators interested in the use of constructed wetlands for wastewater treatment. Because the vast majority of research on constructed wetland performance has been conducted during periods of active plant growth, the true influence of temperature, season, and plant species selection on constructed wetlands performance has not yet been evaluated adequately. In this article, we briefly summarize changes in the understanding of these influences on wetland performance, and suggest that effects of temperature and oxygen transfer are not readily separable because both factors respond to seasonal cycles and because effects of one can offset the other. We further speculate that the net effect of seasonal variation in these factors is such that plant-mediated oxygen transfer affects water treatment most in winter. Results of controlled-environment experiments conducted at Montana State University support these perspectives. Different plant species' capacities to oxidize the root zone responded differently to seasonal cycles of growth and dormancy, and species' effects on wastewater treatment were most pronounced in winter.