A modeling study on the effects of pH and partial wetting on the removal of ammonia nitrogen from wastewater by membrane contactors

A one-dimensional mass transfer model, which includes two vital parameters on the performance of the membrane contactors for the ammonia nitrogen removal from wastewater, namely wastewater pH and membrane partial wetting, was developed. The degree of membrane wetting was estimated as a function of wastewater velocity and included in the determination of the overall mass transfer coefficient based on the resistance-in-series model. A modified Henry's law constant was employed to take into account the effect of pH on the mass transfer. The calculated overall mass transfer coefficients based on the proposed model fitted well with experimental results in various ranges of wastewater inlet pH and velocities. The contribution analysis of resistance in each phase to the overall mass transfer resistances showed that the wastewater phase was still the dominant phase, although the partial wetting was included in the consideration. Comparing with the carbon dioxide and methane desorption, the membrane phase resistance of the ammonia desorption was much more significant to the mass transfer. The determination of the membrane area required to remove the dissolved ammonia revealed that the area was greatly influenced by the wastewater inlet pH. The K-ov along the length of membrane module was gradually decreased due to the NH3 desorption. Thus, the membrane area could be significantly much lower when the wastewater pH was adjusted to the initial value in between the membrane modules connected in the series.