Case Studies of Nanofiltration and Membrane Distillation Membranes for Desalination Applications

Clean water shortage is one of the most pressing issues for huamkind. In this context, we tested two membrane technologies, namely nanofiltration (NF) and membrane distillation (MD), for desalination in two case studies. For each case study, the performances of commercial polymer membranes and lab-made inorganic membranes wer investigated and comparted in order to obtain information for the construction of pilot-scale facilities.

In the first case study, NF was used for potabilization of the groundwater in a well in Puglia Region, Italy [1]. This groundwater suffers from high salinity, the desalination performance of a commercial polymer membrane (Dow NF90) and a novel lab-made alumina-doped amorphous silica NF membrane were compared. The polymeric membrane modules could reduce the conductivity of the groundwater from 4.6 mS cm-1 to 1.3 mS cm-1 with an average permeability of 2.8 L h-1 m-2 bar-1. Under the same filtration condition, the alumina-doped amorphous silica membrane module can reduce the permeate conductivity to around 2.4 mS cm-1 with an average permeability of 1.2 L h-1 m-2 bar. From these preliminary filtration tests, we calculated that both membrane can operate with a specific energy consumption 0.2 kWh·m−3. Hence, a pilot plant (producting 1m3 of drinking water/day) is under construction next to the well.

In the second case study, MD was used for the desalination of the effluent from an inland mariculture site located in Eilat, Israel. The effluent consists of seawater with high loading of organic resideues from the fish tank. Desalination of such effluent was achieved by MD on a commercial polymeric hollow fiber membrane and wtih a newly developed inorganic membrane. The MD experiments showed that the polymer membrane can achieve an almost complete desalination at 50°C with a permeate flux of around 1 L h-1 m-2. An inorganic MD membrane was specifically developed for this application. Compare with the traditional hydrophobically modified ceramic membranes and the commercial polymeric membranes used in MD, the new inorganic membranes is cheaper and have a lower thermal conductivity. Under the same testing condition, the new inorganic membrane had flux that is almost 3 times higher than the polymer membrane, and maintained the same level of salt rejection