The adverse effects of ammonia and related compounds commonly found in wastewater streams have promoted the development of more efficient methods for their removal. In this study, polypropylene hollow-fiber membranes were used to achieve this purpose. A dilute solution of sulfuric acid was used as a stripping solution to accelerate the removal of the ammonia from aqueous solutions. The effects of several factors such as the initial concentrations of the ammonia and sulfuric acid solutions, the pH of the ammonia feed, the velocity of the feed streams and the presence of excess ions in the ammonia feed solution on the overall mass transfer of the ammonia were investigated. The Taguchi method was used to design the experiments and analyze the results. Polypropylene hollow-fiber membranes were found to be very effective in separating ammonia from the waste waters, in proper conditions, ammonia removal of over 99% was achieved. Results show that the initial concentrations and velocities of the ammonia and sulfuric acid solutions had negligible effects on the ammonia removal in the range studied. Increasing the pH value of ammonia feed solution up to 10 improved the removal of ammonia significantly while further increasing the pH to the higher values resulted in insignificant improvements. Raising the ammonia feed velocity enhanced the ammonia removal in the range studied. (C) 2010 Elsevier B.V. All rights reserved.