Membrane Based intensification of ammonia removal from wastewater

The aim of this research was to study a novel membrane based oxygen intensification system to enhance a biological wastewater treatment process for ammonia removal. Specifically, this work is concerned with the biological nitrification process which occurs in ion exchange packed columns during ammonia removal from wastewater. Two types of commercial clinoptilolite were used, namely KMI and BIT, as ion exchangers. Removal of ammonium ion by ion exchange offers a number of advantages such as the capability to handle shock loadings and to purify wastewater to a very high specification. Also, ion exchangers can be used to provide a solid surface for bacterial growth which enhances performance. The uptake removal rates of ammonium ions onto KMI and BIT clinoptilolite using DI water, RO water, and filtered tap water were examined. The presence of major metal ions that normally exist in wastewater such as K+, Ca++, and Mg++ and their impact on ammonia adsorption was tested. The experimental data were fitted using Langmuir and Freundlich isotherms and compared to related works done previously. KMI clinoptilolite exhibited the highest uptake capacity, and KMI clinoptilolite preference for the metal ions was found to be in the order Mg++¡ÖK+Ca++. The kinetics of the ammonium ion removal were studied at bench scale using KMI and BIT clinoptilolite. The process variables include: initial ammonia concentration, amount of clinoptilolite in contact with the solution, clinoptilolite particle size, and mixing speed. To model the kinetics removal rates two types of diffusion was assumed to be possible rate limiting steps, namely the external film diffusion and the intraparticle diffusion. Two models were selected to fit the controlled diffusion resistances, Furusawa-Smith to model the external film resistance and McKay model to model the intraparticle film resistance. The values of the external and internal mass transfer coefficients were calculated and tabulated. Five air permeable membranes were used, four porous membranes and a dense membrane. The porous membranes were Polyethersulfone (PES), Polytetrafluoroethylene (PTFE), Polypropylene (PP), and Nylon. The dense membrane was a silicon tube membrane. All membranes were assessed for aeration. The overall mass transfer coefficients were calculated using the two-film theory model. The highest oxygen transfer rate was observed in PTFE membrane, and in the following order of lower performance PP PES Nylon silicon tube. For the column studies, different loading rates were used, 0.96, 0.25, and 0.03 Kg N/(m3day) depending on the type of the experiment. For the bacteria-free silicon membrane column, the inlet ammonia concentration, bed height, and inlet flowrate were examined. Biologically activated silicon membrane column exhibited no difference in the ammonia removal comparing to bacteria-free column under the same operating conditions. The porous membrane columns were designed to enhance the aeration for the combined biologically active ion exchanger packed bed column. It was found that the porous membrane columns were significantly enhanced by introducing the nitrifying bacteria into the columns. For example, the uptake capacity of PP membrane column was increased from 0.43 to 0.67 meq/g by introducing the biological material into the PP column. The breakthrough bed volumes (BVs) were estimated and the uptake column capacities were calculated for all the used columns. The breakthrough curves were modeled using the Bohart-Adams and Thomas models. To assess the bio-regeneration as an alternative to the chemical regeneration, nitrifying bacteria circulated in PP and PES columns to treat exhausted KMI clinoptilolite. The results showed that some regeneration may be achieved, but complete regeneration would require higher concentrations of biomass which is recommended for future study