Effect of air gap membrane distillation parameters on the removal of fluoride from synthetic water

As freshly available water around the world becomes scarcer, schemes to reuse and rectify contaminated water sources are becoming a necessity. The implementation of conventional treatment processes increases stress on existing infrastructure resources, requiring significant quantities of energy and/or chemicals, including pre-treatment processes and ongoing maintenance. An unconventional alternative to these processes is air-gap membrane distillation (AGMD), an emerging technology delivering excellent rejection of contaminants over a broad range of operating conditions. While showing great promise, the size of membrane distillation systems in existing literature is not readily scaled to industrial levels. In this paper, we present the results of our research in terms of permeate quality, rejection efficiency and scalability of a large laboratory scale AGMD system, with effective area of approximately 25 times larger than those presented in previous studies. This study found a large discrepancy in flux production when compared with small scale results, with experimental data analysed using normality and residual analysis tests. Statistical analysis of the AGMD process data provides insight into the key driving forces and interactions of feedwater temperature, concentration and flowrate on flux production. Results showed excellent rejection of contaminants (>98%) along with some fouling evident after approximately 25 h of operation.