Mechanistic understanding of ammonia removal kinetics in floating treatment wetlands
2019-08-01T11:28:17Z (GMT) by
The role of Floating Treatment wetlands (FTWs) in nitrogen removal from natural water is reasonably well documented, however their function as a polishing technique in domestic wastewater treatment systems is poorly defined. Specifically, develop design criteria for optimal system performance in removing ammonia from sewage is not well addressed. The contribution of this research is to develop a mechanistic understanding of ammonia dynamics in FTWs to improve design and operation. A scaled-up methodology of different experimental FTW systems associated with modelling based-approach were employed to investigate kinetics of ammonia removal under different design criteria. Effects of surface area of mat material, plant density and water depth on ammonia removal kinetics were investigated using microcosm, mesocosm and field pilot-scale systems. The results revealed that ammonia removal was enhanced in FTWs and the magnitude of removal was controlled by the design factors examined. Removal by nitrification was directly proportional to mat surface area. Vegetated treatments with higher plant density exhibited higher ammonia removal by uptake. Field observations showed that ammonia removal was inversely proportional to water depth. Findings presented in this thesis suggest that a design code of full coverage of water surface with mat material, high plant density, and shallow water depth can be considered a critical design for FTW system to remove ammonia from domestic wastewater. This design promoted nitrification as principal ammonia removal process even when plants were present. The contribution of nitrification to overall ammonia removal in the vegetated treatments was estimated to be between 59–83 % in mesocosms and between 81 - 85% in the pilot-scale system. Plant uptake contributed to 16–40% of the total N loss in mesocosms and 19-14 % in the pilot system. Ammonia loss via volatilization was determined to be negligible in all examined systems. Estimated kinetics parameters in the examined systems revealed close agreement between microcosm and pilot-scale system performance in treating ammonia (0.03 and 0.14 day-1). The results suggest that supplementing field study with a well-controlled laboratory microcosm study was useful for confirming kinetics parameters derived from field data. The use of kinetics parameters obtained from such approach could be useful to estimate ammonia removal and establish design criteria in a broader perspective including full-scale wastewater treatment systems.