Nitrate removal from aqueous solution by direct contact membrane distillation using two different commercial membranes

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Abstract
In the present work, the removal of nitrate from aqueous solution by direct contact membrane distillation (DCMD) using flat sheets polypropylene (PP) and polyvinylidene fluoride (PVDF) membranes was studied. Effect of operating parameters, such as feed temperature, feed flow rate, initial nitrate concentration, feed ionic strength, and competing co-existing anions on permeate flux and nitrate rejection, was investigated. In all DCMD experimental runs, an almost complete nitrate rejection was achieved (higher than 99.90%) and the permeate nitrate concentration was largely below the maximum permissible level in potable water. Under the same operating conditions, PVDF hydrophobic membrane showed a higher permeate flux of 37.21 L/m2h than PP membrane with a permeate flux of 4.12 L/m2h. For both the membranes, feed temperature is the important operating parameter which enhanced exponentially the permeate flux. Likewise, a positive effect on permeate flux was found when feed flow rate was increased. However, no significant effect was found by varying initial nitrate concentration, feed ionic strength, and the presence of co-existing anions on DCMD permeate flux or nitrate rejection efficiency.

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