The Role of Microbial Biofilm in Removing Ammonia in Floating Treatment Wetlands

Abstract

Laboratory experiments were conducted under controlled conditions to quantify the potential of microbial transformation associated with floating matrix of floating treatment wetland (FTW) in ammonia removal and nitrification kinetics. The effect of different design parameters on ammonia removal from synthetic medium was investigated to optimize system performance. Effects of surface area of mat material, range of ammonia concentrations, and aeration on ammonia removal kinetics were studied using microcosm systems. A simple dynamics model of mineral nitrogen transformation was used as a framework for interpreting the experimental results. 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. The higher ammonia removal efficiency was caused by a larger surface area, which could support the growth of more microbes. Removal rate constants for treatments were 0.011, 0.015, 0.026, 0.035, and 0.033 day–1 for T1, T2, T3, T4, and T5, respectively. There was also a clear inhibitory effect of NH3 on second-stage nitrification manifested as low production of NO3–. Quantitative index of optimized knit/calibrated knit indicated high inhibition effects of NH3 at high concentration of total ammonia (60 mg N L–1). There was no major effect of oxygen saturation on NHx removal using aerated and nonaerated conditions. Better mechanistic understanding of the fundamental processes operating in FTWs should provide the basis for improving FTW design and efficacy.

Keywords

• nitrification
• biofilm
• kinetics
• inhibition
• ftw
• dynamics modeling