Bianca Mella

CHAPTER 16:Chromium in Tannery Wastewater

Chromium is found naturally in the environment in rocks, animals, plants, soil, volcanic dust and mists. Chromium is not found free in the most important deposits of the planet, it is found in elemental form or in the trivalent oxidation state. The conversion from trivalent to hexavalent oxidation state of chromium is an important feature, where hexavalent chromium predominates under highly oxidizing conditions. The majority of the chromium in the surface water may be in the form of particulate matter or deposited sediment. Industrial effluents containing chromium are discharged into rivers, soil and air. The results of several studies point to the need to control wastewater, considering that the improper disposal of chromium contributes to contamination of water resources and groundwater. The main human activities in which the chromium and its compounds are released into the environment result from the manufacture of cement and construction materials, welding alloys, foundries, manufacturing steel and alloys, electroplating industry, lamps, mines, urban waste and industrial waste incineration, coal ash, tanneries, fertilizers and wood preservatives. Solid wastes and wastewaters from leather manufacturing contain chromium. The use of chrome in the tanning process occurs with the trivalent chromium, usually in the form of basic chromium sulfate. The effects of chromium in the environment, water contamination by chromium, the process management and technologies of chromium usage in tanneries, the wastewater treatment operations and the chromium recovery will be addressed in this chapter.

Treatment of Leather Dyeing Wastewater with Associated Process of Coagulation-Flocculation/Adsorption/Ozonation

ABSTRACT This study is based on the investigation of performance of associated wastewater treatments of coagulation-flocculation/adsorption (CF-ADS) and coagulation-flocculation/ozonation (CF-OZ) for the removal of pollutants from tannery wastewater. The chemical dosage was optimized and the use of waste from the tannery process was tested as a low-cost alternative adsorbent for wastewater treatment plants. For the CF-ADS the removal of TOC, COD, Na+ and color were 50.04%, 53.13%, 17.05% and 61.13%, respectively, and for the CF-OZ the removal were 46.50%, 56.25%, 11.10% and 85.34%. Also, BOD/COD and COD/TOC ratios were studied to verify the oxidation efficiency of the wastewater.

REMOÇÃO DE CROMO DE BANHOS RESIDUAIS DE CURTIMENTO ATRAVÉS DE PRECIPITAÇÃO QUÍMICA E ELETROCOAGULAÇÃO

RESUMO – Curtumes empregam grandes volumes de agua no processamento das peles, bem como, em sua maioria, utilizam sais de cromo como agente curtente, metal que possui seus efeitos nocivos conhecidos quando disposto inadequadamente no ambiente. Este trabalho visa a remocao do cromo presente nos banhos de curtimento atraves de precipitacao quimica e eletrocoagulacao como uma alternativa ambientalmente correta e economicamente viavel, pois testa sua reutilizacao como materia-prima no processo. Nos ensaios de precipitacao quimica obteve-se remocao de ate 99,74% nas amostras. Nos ensaios de eletrocoagulacao observou-se 97,76% de remocao com eletrodos de aluminio, 69,91% com eletrodos de cobre e 90,27% com eletrodos de ferro. Apos estes testes o cromo foi empregado novamente como agente curtente, onde as peles curtidas com o cromo recuperado por precipitacao quimica e eletrocoagulacao com eletrodos de cobre apresentaram resultados satisfatorios se comparados ao curtimento com sal de cromo comercial.