Decolourization of dye-containing effluent using mineral coagulants produced by electrocoagulation

摘要

The colour and colour causing-compounds has always been undesirable in water for any use, be it industrial or domestic wastewaters. The discharge of such effluents causes excessive oxygen demand in the receiving water and then a treatment is required before discharge into ecosystems. This study examined the possibility to remove colour causing-compounds from effluent by chemical coagulation, in comparison with direct electrocoagulation. The inorganic coagulants (C|, C_2 and C_3) in the form of dry powder tested, were respectively produced from electrolysis of S_1 = [NaOH (7.5 × 10~(-3) M)], S_2 = [NaCl (10~(2) M)], and S_3 = [NaOH (7.5 × 10~(-3) M) + NaCl (10~(-2) M)] solutions, using sacrificial aluminium electrodes operated at an electrical potential of 12 V. Reactive textile dye (CI Reactive Red 141) was used as model of colour-causing compound prepared at a concentration of 50 mg l~(-1). The best performances of dye removal were obtained with C_2 having a chemical structure comprised of a mixture of polymeric specie (Al_(45)(OH)_(45)Cl) and monomeric species (ArCl(OH)_2·2H_2O and Al(OH)_3). The removal efficiency (R_A) evaluated by measuring the yields of 540 nm-absorbance removal varied from 41 to 96% through 60 min of treatment by imposing a concentration of C_2 ranging from 100 to 400 mg l~(-1). The effectiveness of the treatment increased and the effluent became more and more transparent while increasing C_2 concentration. The comparison of chemical treatment using C_2 coagulant and direct electrocoagulation of CI Reactive Red 141 containing synthetic solution demonstrated the advantage of chemical treatment during the first few minutes of treatment. A yield of 88% of absorbance removal was recorded using C_2 coagulant (400 mg l~(-1)) over the first 10 min of treatment, compared to 60% measured using direct electrocoagulation while imposing either 10 or 15 V of electrical potential close to the value (12 V) required during C_2 production. However, at the end of the treatment (after 60 min of treatment), CI Reactive Red 141 pollutant was completely removed from solution (540 nm-absorbance removal of 100%) using direct electrochemical treatment, compared to 96.4% of absorbance removed while treating dye-containing synthetic solution by means of C_2 coagulant.