DETOXIFICATION OF TANNERY WASTE LIQUORS WITH AN ELECTROLYSIS SYSTEM

This paper describes an electrochemical treatment and detoxification o f tannery waste liquors (TWL). In this technique, TWL was passed throu gh an electrolytic cell using a Ti/Pt anode and a stainless steel 304 cathode. Owing to the strong oxidizing potential of the chemicals prod uced (chlorine, oxygen, hydroxyl radicals and other oxidants) the orga nic and inorganic pollutants (ammonia, sulfides and chromium) were wet oxidized to carbon dioxide, nitrogen oxides and sulfur dioxide. In ad dition, chromium was precipitated as Cr-2(SO4)(3). Experiments were ru n in a batch, laboratory-scale, pilot-plant, and the results are repor ted herein. After 30 min and 3 h of electrolysis at 0.26 A cm(-2), 45 degrees C and pH 9, total chemical oxygen demand (GOD) was reduced by 52 and 83% and biochemical oxygen demand (BOD5) was reduced by 35 and 66%, respectively. Additionally, total suspended solids (TSS) were red uced by 8.6 and 26%, total phenolic compounds were reduced by 95.6 and 99.4%. Ammonia, sulfides and soluble chromium were reduced by 100% in both cases, while the mean anode efficiency was 81 g h(-1) A(-1) m(-2 ) and 1.9 g h(-1) A(-1) m(-2). Also, the mean energy consumption was 4 .8 kwh kg(-1) of COD reduced and 200 kwh kg(-1) of COD reduced for 0.5 and 3 h, respectively. These results strongly indicate that this elec trolytic method of total oxidation of TWL cannot be cost effective for wide use. However, it can be used as an effective pretreatment stage for detoxification of the wastewater, owing to great efficiency especi ally with respect to COD and toxicity (phenolics) reduction. (C) 1997 Elsevier Science Ltd.