A hybrid adsorption/ultrafiltration process for perchlorate removal

A hybrid adsorption/ultrafiltration (UF) process for perchlorate removal using chitosan as an adsorbent was investigated in this work. Chitosan was introduced into the ultrafiltration process due to its widespread availability, good adsorptivity, nontoxicity and biodegradability. The retention efficiency of perchlorate was discussed by considering the factors of pH, adsorbent concentration, perchlorate concentration, membrane pore size and solution anions. The experimental results showed that perchlorate ions could be bounded by chitosan molecules and the adsorption equilibrium was reached within 3 min. The optimum pH for perchlorate removal was 4.3 and the removal efficiency was about 92% with the initial perchlorate concentration and adsorbent dosage of 10 mg/L and 0.8 g/L, respectively. The presence of other anions in the solution caused a decrease in the perchlorate removal efficiency due to their competition with perchlorate for the adsorption sites. Raman spectra indicated that perchlorate was adsorbed by chitosan mainly due to electrostatic attraction between perchlorate and the positively charged -NH3+ on chitosan. Scanning electron microscope (SEM) and Energy Dispersive X-ray Spectrometer (X-EDS) analysis demonstrated that the colloidal layer of chitosan deposited on the membrane surface resulted in membrane blocking during the ultrafiltration process. But the colloidal layer could be effectively removed by soaking the fouled membrane in 0.1 M NaOH solution for 15 min followed by water washing. The mechanism of perchlorate retention was dependent on the electrostatic interaction between perchlorate and chitosan and the filter cake structure. The application of the chitosan adsorption/ultrafiltration process showed high practical potential for perchlorate removal. (C) 2010 Elsevier B.V. All rights reserved.