Treatment of tannery industry wastewater by advanced oxidation and electrochemical advanced oxidation processes

Abstract

Tanneries are typically characterized as pollution-intensive industrial complexes that generate widely varying, high- strength wastewaters. The variability of tannery wastewaters arises not only from the fill and draw-type operation associated with tanning processes, but also from the different procedures used for hide preparation, tanning and finishing. One of the refractory groups of chemicals in tannery wastewater derives mainly from tannins. Tannins are characterized by complex chemical structures, because they are composed of an extended set of chemicals such as phenol, naphthalene, formaldehyde and melamine-based syntans, and acrylic resins. The BOD5/COD ratio of tanning is also lower than other compounds. However, it is worth noting that no one of these compounds showed a BOD5/COD ratio higher than 0.4, indicating a very low biodegradability for each of them. The activated sludge process has been the most common wastewater treatment process for the removal of organics in our country; however, it is inefficient for the removal of recalcitrant organics and micro pollutants in tannery wastewater. The high concentrations of pollutants with low biodegradability in tannery wastewater represent a serious and actual technological and environmental challenge. Therefore, many researchers have attempted to develop new technologies for complementing or even replacing some of these treatments. Advanced Oxidation Processes (AOP) can be considered an effective alternative and have become the most widely used treatment technologies for organic pollutants not treatable by conventional technologies due to their high chemical stability and/or low biodegradability. Tanneries generate wastewater in the range of 30 35 litre per kilogram of skin/ hide processed with variable pH=7.5±0.5, colour (at 465nm)=0.98± 0.100, COD=2370±70 mg/L, BOD5 = 985± 15 mg/L, Chromium (III)=16± 0.1mg/L. The advanced oxidation process were carried out in the bench scale reactor which is made of acrylic material and hopper bottom of dimensions of 21.5 cm × 15 cm × 25 cm with a working volume of 5 L. The electrochemical advanced oxidation process experiments were carried out in the bench scale reactor with a working volume of 5 L. The reactor had an iron plate cathode (218 cm2 ) and iron plate anode (218 cm2 ). To provide desired current, the electrodes were connected to DC power supply newline