Effect of anaerobic digestion on chrome sludge – A by-product of tanned leather waste

Abstract

The leather industry is environmentally important as a user of a by-product of the meat industry. It is perceived as a consumer of resources and a producer of pollutants. The most serious problem is chrome tanned solid wastes, which are now under control through alkali-enzymatic hydrolysis treatment of chrome shavings. The main products of this hydrolytic reaction are gelable protein hydrolysate, enzymatic hydrolysate, and chrome sludge. In chrome sludge, the rest of the biomaterial is collagen protein. Approximately 20-40 % (on free moisture basis) is strongly bound as co-ordinate complex with chromium, which creats serious problems for further treatment of it to recover tanning salt. One possible solution is to decrease the content of collagen protein by anaerobic digestion, which is presented in this paper. The effect of anaerobic digestion on chrome sludge was observed under controlled conditions using different fermentation compositions of broth at 50degreesC for a 15 day incubation period. Sludge, inoculum and water at 3: 1:1 ratio was determined to be the optimum fermentation composition from the bioconversion point-of-view. During anaerobic digestion, the content of biomaterial associated with the chrome sludge decreased while the quantity of free chromium increased. These observations were confirmed by attenuated total reflectance (ATR) using FTIR spectophotometric and scanning electron microscopic (SEM) analysis.