On-line microdialysis-ion chromatographic determination of inorganic anions in olive-oil mill wastewater

A fully automated method is presented for the determination of inorganic an ions in olive-oil mill effluents using on-line dialysis-ion chromatography. The wastewater is first of all sonicated at room temperature to make it ho mogeneous, then diluted and microdialized. Most of the organic load of the effluents is removed in a few minutes without using reagents, while soluble anion quantitation remains unaffected. The clear solution is analyzed for the inorganic anions content by direct injection on to an ion chromatograph equipped with a conductivity detector. In the absence of standards, the se paration efficiency of microdialysis has been investigated by spiking waste water samples as well as standard oil emulsions with varying amounts of ino rganic anions and subjecting them to microdialysis for different periods of time prior to performing instrumental analysis. Excellent spike recoveries and low relative standard deviations are obtained for all the anions if a 10 min microdialysis time is overcame. Chloride, nitrite, nitrate, phosphat e and sulphate are not affected by the microdialysis procedure and their re covery is between 96 and 104% in wastewater as well as in standard oil emul sion. Calibration plots are linear over about two orders of magnitude. The dialysis membrane has been replaced after more than 100 analyses. The UV ph otolysis pre-treatment of the same sample evidences the different informati on that can be obtained by the two sample pre-treatment procedures. (C) 200 0 Elsevier Science B.V. All rights reserved.