Abstract
In this study, loading of optimum leather fleshings was investigated with four identical batch reactors with different fleshings and treatment sludge ratios (0:1, 0.25:1, 0.35:1, 0.50:1) to contribute to the state of art of the biogas production from tannery solid wastes. Results showed that lipids-containing leather fleshings boosted the methane production potential. However, H2S inhibition and volatile fatty acids accumulation were the main concern in the anaerobic digestion of these wastes. The modified Gompertz model was applied to the batch tests data to determine the kinetic constants of anaerobic digestion of tannery solid wastes. It was calculated with the model outputs that the ultimate methane production potential and maximum methane production rate in reactors having mixing ratio of 0.35:1 and 0.5:1 (dry basis) were highly similar. 0.35 was found to be an optimum leather fleshing and treatment sludge ratio with a 54% more methane production potential than that of control reactor in this study.
Highlights
Tanning industry is one of the oldest sectors in the history of human beings
It was calculated with the model outputs that the ultimate methane production potential and maximum methane production rate in reactors having mixing ratio of 0.35:1 and 0.5:1 were highly similar. 0.35 was found to be an optimum leather fleshing and treatment sludge ratio with a 54% more methane production potential than that of control reactor in this study
In addition to lipids and protein, tannery solid wastes contain residual chemicals such as lime and sulfide, which are used in beam house operations for the purpose of hair removal [16]
Summary
Tanning industry is one of the oldest sectors in the history of human beings. Because of the severe environmental problems related to leather production process and the increasing labor prices, the production sector has been declining in developed regions and become widespread mostly in the far east countries such as China, Vietnam, Endonesia [1],[2].Leather making process is basically divided into three steps: pre-tanning including soaking, unhairing and liming, fleshing, splitting, deliming, bating and pickling; tanning process; and the finishing process [1]. Tanning industry is one of the oldest sectors in the history of human beings. Substantial amount of solid waste is generated during pre-tanning operations such as skin trimmings, keratin wastes and fleshings, which consist of mainly protein and lipids [3]. The fleshing operation is performed in order to remove flesh and fats from the skin so that the rapid skin degradation can be prevented and chemicals used in the subsequent steps can penetrate to the raw skin [4]. Fleshing wastes are the major portion of the solid waste caused by tanning industry [5]. As a result of the production of one ton of raw hide, up to 250 kg of fleshings and 200 kg of treatment sludge are generated [4],[6]
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