Treatment of Photographic Effluents by Electrochemical Method

Abstract

Fixing and bleach/fixing solutions from photographic process were treated in this investigation by an electrochemical reduction process for silver recovery and oxidation process to reduce chemical oxygen demand (COD) levels. The COD oxidation process was undertaken after the silver recovery process. According to these results, silver recovery rate from bleach/fixing solution depends heavily on pHs, whereas the nature of silver deposit from fixing solution is sensitive to cathode potential. The COD, NH4+-N, and total organic carbon (TOC) removal rates from both fixing and bleach/fixing solutions were also examined by electrochemical oxidation at a IrO2 + RuO2/Ti anode with and without the addition of NaCl. In the fixing solution, the oxidation rate of inorganic compounds is faster than that of organic compounds. Under the operating conditions, a current density of 10 A/dm2, and by adding 5% NaCl, about 90% of the COD and NH4+-N in the fixing solution was removed after electrolysis for 10 h. For a bleach/fixing solution, the COD removal rate was independent of the addition of NaCl; meanwhile, the NH4+-N removal rate increased with addition of NaCl. Under the operating conditions of 10 A/dm2 current density and the addition of 5% NaCl, over 95% of COD was removed after electrolysis for 10 h. At the same time, 42,000 mg/L NH4+-N was also completely removed. Key words: Electrochemical oxidation; silver recovery; photographic effluents