Copper removal from water using a bio-rack system either unplantedor planted with Phragmites australis, Juncus articulatus and Phalarisarundinacea

Abstract

A bio-rack system was developed for treating Cu-contaminated freshwaters. Each pilot constructed wet-land (CW, 110 dm3) contained 15 perforated vertical pipes filled with a mixture of gravel (diorite; 80%)and perlite (20%) and assembled as a rack. The whole experimental device consisted of 12 CW plantedeither with Phragmites australis, Phalaris arundinacea or Juncus articulatus, and unplanted as control (intriplicates). All plants were sampled at a Cu-contaminated site. The CWs were filled with a mix of freshwa-ter (30%) from the Jalle d’Eysines River (Bordeaux, France) and tap water (70%). Water was spiked with Cu(2.5 M, 158.5 g L−1). Three CW batches were carried out, i.e. in early spring (March, S#1), beginning ofthe growing season (May, S#2), and peak growing season (June, S#3). The S#3 water was initially acidifiedto pH 6. For all batches, water was recirculated in the CW during 14 days. Physico-chemical parameters(pH, electrical conductivity, redox potential, BOD5and Cu2+concentrations) were measured every threedays. Water pH of both S#1 and #2 ranged between 7.8 and 8.5 for all treatments during the experi-ment. Initial and final total Cu concentrations were analysed for all CWs and batches. Relative TreatmentEfficiency Index (RTEI) indicated the plant effect compared to the unplanted CW. Free Cu2+removal was<10% for all S#1 treatments (RTEI ranged between 0 and −1) whereas it increased to 77% (RTEI = 0.1) inS#2 for P. arundinacea. In acidic conditions (S#3), Cu2+removal was 99% for all treatments (RTEI = 0). ForS#1 and S#2, highest total Cu removal occurred in CW planted with P. arundinacea (respectively 52% and68%, RTEI = 0.1 and 0.2). For S#3, total Cu removal peaked up to 90% in the unplanted CW. The RTEI valuessuggested no beneficial effect of macrophytes on Cu removal at short term. Conversely, the CW plantedwith J. articulatus generally displayed a lower efficiency. The lowest value for total Cu concentration inwater after the 14-day period was 13 g L−1in S#3 unplanted and planted with P. arundinacea. The roleof the biofilm as a key-player of Cu removal in such bio-racks is discussed.