Removal of the Selected Pesticides from a Water Solution by Applying Hollow Fiber Liquid–Liquid Membrane Extraction

A supported liquid membrane extraction of different pesticides (acetamiprid, dimethoate, imidacloprid, linuron, and tebufenozide) from an aqueous solution containing 20 mg dm –3 of each pesticide by 5% TOPO (tri- n -octylphosphine oxide) in DHE (di- n -hexyl ether) has been investigated in a hollow fiber contactor having an aqueous feed/organic interfacial area of 15.4 cm 2 . In a single-pass operation, the maximum removal efficiency of 95% was achieved for the most nonpolar (log P = 4.38) pesticide tebufenozide at the feed flow rate of 0.5 cm 3 min –1 . The diffusion through the boundary layer of the feed stream was a rate-controlling step in the extraction of nonpolar pesticides (linuron and tebufenozide) with a mass-transfer coefficient in the feed stream being proportional to the feed flow rate raised to the power of 0.51–0.57. The maximum overall mass-transfer coefficient based on the feed phase of K F = 0.18 cm min –1 was obtained for tebufenozide at the feed flow rate of 1.8 cm 3 min –1 . The organic phase entrapped in the membrane pores offered a major resistance to the mass transfer of polar pesticides (log P < 1) and accounted for 85% of the overall mass-transfer resistance for imidacloprid at 1.8 cm 3 min –1 . The pesticides removed from the feed solution were almost completely accumulated in the organic phase but were recovered from the membrane pores to a large extent (50–90%) by rinsing the membrane with methanol after extraction.