An immobilized sludge system model was developed to simulate nitrification (NH4-N → NO3-N) and denitrification (NO3-N → N2) processes in a PEG-pellet (microorganisms entrapped in polyethylene glycol (PEG)) reactor for removing NH4-N from groundwater. The nitrification and denitrification processes were described by modifying the Michaelis-Menten kinetic incorporating the factors of dissolved oxygen, organic carbon and pH. The model consists of seven fixed parameters out of which the maximum velocity of nitrification (Vm,ni) was found to be the most sensitive. The model can be applied to predict the best operating condition (i.e., duration of intermittent aeration period and pellet ratio (PEG-pellet in reactor/reactor volume)) for different NH4-N concentrations. The model predicts that the highest efficiency to remove 45 mg/L of NH4-N can be achieved when the PEG-pellet reactor with 0.2 pellet ratio is operated under 6 h of intermittent aerations and the efficiency is strongly affected by the pellet ratio, especially when NH4-N concentration in the influent is higher than 60 mg/L.

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