Removal of the selected pesticides from a water solution 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 cm2. 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 cm3 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 KF = 0.18 cm min–1 was obtained for tebufenozide at the feed flow rate of 1.8 cm3 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 cm3 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.