De-ammonification using direct contact membrane distillation – An experimental and simulation study

Abstract

In this study, a mathematical model was developed to simulate the ammonia recovery behaviour in a Direct Contact Membrane Distillation (DCMD) system. The developed model successfully predicted the binary mass transfer phenomenon (water and ammonia vapour) across the PTFE membrane under different operating conditions, including non-traditional DCMD operating conditions that the permeate temperature is the same or higher than the feed temperature. The developed model suggests that ammonia mass transfer increases as a function of feed inlet temperature, achieving 90% of the ammonia removal at 70 °C feed inlet temperature only requires less than half of the time at 20 °C feed inlet temperature. It was also found that pH value difference between the feed and permeate sides plays the most significant role in ammonia recovery compared to other operating conditions. The developed model demonstrates that, for ammonia removal, it is not necessary to create (1) temperature difference between the feed and permeate sides, or (2) higher feed inlet temperature compared to permeate inlet temperature for DCMD system. This potentially makes the MD-based ammonia recovery system more economically viable as no external heat energy is required.