Browsing by Author "Hafla, Erin C."

Now showing 1 - 2 of 2

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.
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.