Sludge reduction and cost saving in removal of Cu(II)-EDTA from electroplating wastewater by introducing a low dose of acetylacetone into the Fe(III)/UV/NaOH process

Cu(II)-EDTA is highly stable in a wide pH range (3.0∼12.0) and hard to be removed by the conventional precipitation method. Fe(III) displacement/UV photolysis/alkaline precipitation [Fe(III)/UV/NaOH] has been proposed as a promising method for the removal of Cu(II)-EDTA. Nevertheless, a high dose of Fe(III) is needed in this combined process, resulting in the production of a large amount of hazardous sludge. The photochemistry of Fe(III) is known to be ligand-dependent. Fe(III)-oxalate complexes are strongly photoactive. However, the addition of oxalic acid to the Fe(III)/UV/NaOH process was of little help. Acetylacetone (AA) is a good chelating ligand for many metals and has been proved as an efficient photo-activator. By introducing a low dose of AA ([AA]/[Cu] = 1.5) into the Fe(III)/UV/NaOH process, the Fe(III) dosage ([Fe]/[Cu]) was reduced from 10.4 to 3.2. As a result, the chemical cost was reduced from 13.9 to 7.6 kW h/m³. Meanwhile, the energy cost in the UV photolysis was reduced from 1066.5 to 752.4 kW h/m³. Most importantly, the sludge yields were reduced from 8.3 to 2.7 kg/m³ in a simulated wastewater and from 101.8 to 30.8 kg/m³ in a real electroplating wastewater. Such a sludge reduction is of great significance in mitigating the load of landfill.