Water treatment by enhanced ultrafiltration

The efficiency of removal of copper ions from aqueous solutions was investigated by means of ultrafiltration enhanced with chitosan. The different experimental parameters such as initial concentration of metal ions, background electrolytes, pH solutions, ultrafiltration membranes of different molecular weight cut-offs on the kinetic of copper extraction as well as polymer rejection were studied. Presence of chitosan in feed solution provided effective removal of metal ions from an aqueous medium because of formation of complexes and their consequent deposition on the membrane surface and pores. The metal rejection increased with pH growth, exceeding 90% in neutral/alkaline solutions. The same tendency was observed at the different ratio values between chitosan and copper. The effectiveness of metal rejection improved with the increase in this ratio due to intensification of the entire metal–biopolymer interaction.

Efficiency of Cu2+ ion removal from water solutions was explored by an enhanced UF method based on the formation of complexes of metal with the biopolymer chitosan and their further filtration. Interaction of metal and chitosan amino groups constitutes the coordinating bonds. The presence of chitosan in feed solution results in an increase of copper extraction, which is multiplied 5–7 times in comparison with solutions without a biopolymer. Consequently, the rejection coefficient of copper reached almost 100%. It is shown that the pH of the solution has the greatest influence on permeate flux and metal rejection, independent of the presence of inorganic salts in solution. To achieve process efficiency, it is necessary to consider the complex effect of the chitosan/copper ratio (β) on Сu2+ ion rejection coefficient and on permeate flux (Jv/Jw.). The most effective removal of copper ions (RCu = 98%) can be achieved at pH 6 with β = 10 on a UAM-300 membrane at a pressure of 0.1 MPa, and the nominate permeate flux still equals 0.86. NaCl (1-1 type electrolyte) introduction into the solution does not practically influence copper ion retention, whereas in the presence of CaCl2 (2-1 type electrolyte), copper removal from the solution becomes worse. This is the result of squeezing a double-electric layer of chitosan aggregates and the reduction of the electrostatic interaction of metals ions with a biopolymer.