OPTIMIZATION OF A PURIFICATION METHOD FOR METAL-CONTAINING WASTE-WATER BY USE OF A TAGUCHI EXPERIMENTAL-DESIGN

A procedure for purifying waters polluted with metal ions has been des igned. The method is based on the precipitation of metals as magnetic ferrite from the alkalinised solution containing iron(II). The working conditions were optimised by using a Taguchi L(9)(3(4)) experimental design in order to minimise the total residual concentration (TRC) of metal ions in solution. A statistical analysis of the experimental dat a revealed the most influential factor to be the Fe(II)/metal concentr ation ratio (F), with a 29.5% contribution, followed by pH (P, 5.2%) a nd time (H, 2.3%). On the other hand, temperature (T) had little effec t on the purification efficiency (1.0%), whereas noise (N, KMnO4) was found to contribute by as much as 22.1%. Maximal purification efficien cy (99.99%) is achieved when wastewater samples are treated for 3 h at 50 degrees C and pH 10 in the presence of iron(II) in a ratio Fe(II)/ total metal of 15. In these conditions, the process efficiency is also the least influenced by variability in the sample composition, which validates the proposed procedure. Copyright (C) 1996 Elsevier Science Ltd