Assessing the viability of using membrane distillation for the reclamation of clean water from nutrient-reduced municipal wastewater : A zero-liquid-discharge approach

Here, membrane distillation (MD) was used to reclaim clean water from municipal wastewater after advanced nutrient removal process (struvite synthesis/recovery effluent). Two hydrophobic membranes, i.e., polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), were comprehensively compared. PTFE was more favorable, while the effect of lower permeate/distillate temperature was found marginal. Pre-treating (sand filtration, activated carbon adsorption, and acidification/neutralization) the struvite synthesis supernatant before membrane distillation grossly enhanced the flux of the membrane and minimized the permeation of ammonia, thus, to a great extent, preventing scaling, and aiding in an increase in pH of the solution. Furthermore, after pretreatment, the PTFE membranes achieved an average mass flux of 1.4 g/cm2/h over an extended and prolonged period, thus suggesting the durability of this type of membrane. A high quality product water (permeate/distillate) was reclaimed, which can be used in agriculture, industry, or even for drinking water, but remineralization is required. Based on the obtained results, it can be concluded that integrating nutrient recovery with clean water reclamation using membrane distillation can be a feasible option that not only valorises municipal wastewater but also partially addresses the water scarcity concerns in South Africa and further afield. This will go a long way in validating the applicability of this technology in clean water reclamation, thus, to a notable extent, demostrating the feasibility of bridging the gap between brine-rich technologies and the zero-liquid discharge (ZLD) systems.