Biotechnology Techniques 13: 533–538, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands. 533 Metal removal by immobilised and non-immobilised Azolla filiculoides R.V. Fogarty 1 , P. Dostalek 2 , M. Patzak 2 , J. Votruba 3 , E. Tel-Or 4 & J.M. Tobin 1,∗ 1 School of Biotechnology, Dublin City University, Dublin 9, Ireland 2 Dept. of Fermentation and Bioengineering, Institute of Chemical Technology, Prague 6, Czech Republic 3 Academy of Sciences, Prague, Czech Republic 4 Department of Agricultural Botany, The Hebrew University of Jerusalem, Rehovot 76100, Israel ∗ Author for correspondence (Fax: 353-1-7045412; E-mail: John.Tobin@dcu.ie) Received 29 April 1999; Revisions requested 19 May 1999; Revisions received 17 June 1999; Accepted 18 June 1999 Key words: biosorption, metals, immobilised, Azolla, columns Abstract Milled-sieved and epichlorhydrin-immobilised Azolla biosorbed ca. 363 and 320 μmol Cu 2+ g −1 from a 100 mg l −1 solution. Efficiency of Cu 2+ removal by columns was in the order epichlorohydrin-immobilised Azolla>milled-sieved Azolla>untreated Azolla. The 2.5 g epichlorohydrin-immobilised Azolla column demon- strated complete metal sequestration from ca. 12 l of influent 5 mg Cu 2+ l −1 and was still at less than 75% saturation even after ca. 22 l had passed through the column. EDTA effectively desorbed Cu 2+ with a ca. 55-fold decrease in volume. Introduction In recent years there has been considerable interest in the area of metal accumulation from aqueous solution by yeasts, fungi and plant biomass (Leusch et al. 1995, Tel-Or et al. 1996). Due to their non-biodegradability, metals cannot be treated biologically in-situ and must instead be extracted from contaminated streams (Sa- hoo et al. 1992). Conventional chemical methods for treating metal-bearing effluents, such as chemi- cal precipitation, electrolysis and ion-exchange, may be economically non-viable at low metal ion concen- trations and this, together with increasing concerns over the amounts of trace metals entering the envi- ronment, has spurred research towards the develop- ment of alternative processes for the removal and/or recovery of toxic and precious metals. Most metal ion-sequestering processes using microbial or plant biomass involve either a ‘batch’ or ‘column’ configu- ration (Bedell & Darnall 1990). Batch systems involve the mixing of free or immobilized cells with the metal ion solution while column configuration systems per- mit the metal ion solution to be pumped through a column packed with cells. Azolla filiculoides is a floating water fern common in many parts of the world. It has recently gained at- tention as a potential metal biosorbent for use in the treatment of metal-bearing effluents (Sela et al. 1989, 1990, Tel-Or et al. 1996). The aim of the present study was to investigate the effects of a range of immobil- ising techniques on the metal uptake characteristics of Azolla biomass. Initial screening of different met- als and immobilisation methods was performed in batch systems. Biomass types exhibiting greatest up- take were selected for use in column studies with a copper-containing feed. A novel desorption protocol using EDTA was tested for Cu 2+ recovery. Materials and methods Azolla filiculoides Lamarck: Preparation for batch studies Azolla filiculoides Lamarck used was obtained from the Department of Agricultural Botany, The Hebrew University of Jerusalem, Rehovot 76100, Israel. This biomass was used in a range of different forms ei- ther in its untreated state or following immobilisa-