Removal of ammonia from wastewater by air stripping process in laboratory and pilot scales using a rotating packed bed at ambient temperature

In this study, a continuous-flow rotating packed bed (RPB), functioning as an efficient gas-liquid contactor, was employed for the ammonia stripping from wastewater in laboratory-scale and pilot-scale systems at ambient temperature. The effects of major operating variables, such as rotational speed (omega), liquid flow rate (Q(L)), and gas flow rate (Q(G)) on the volumetric liquid mass-transfer coefficient (K(L)a) and stripping efficiency (eta) were elucidated. The results show that the K(L)a values demonstrate the greatest increase with increasing gas flow rate (Q(G)), followed by liquid flow rate (Q(L)) and rotating speed (omega). Although changes in K(L)a would be expected to directly reflect in the eta values, the increased Q(L) results in considerable compensation effects leading to the decreased eta, predominantly due to the decreased liquid hydraulic retention time. The dimensionless models used in this study describe the relationships of K(L)a and eta with the major parameters for ammonia stripping in the RPB, and demonstrate good agreement with the experimental data. Moreover, in the continuous-flow pilot-scale RPB, an eta of 95% was achieved at 4.6 min. while K(L)a values of approximately 0.017-0.027 1/s and height transfer unit (HTU) values of 2.2-4.8 cm were obtained at a Q(L) of 5 L/min, Q(G) of 1,500 L/min, and omega of 480-1000 rpm, suggesting that the RPB is a viable alternative technology for stripping large loadings of ammonia from wastewater. (C) 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.