Influence of composition on the biomethanation potential of restaurant waste at mesophilic temperatures
Introduction
Although anaerobic digestion of organic solid wastes is an established technology in Europe with 120 full scale plants treating about 4 million tons per year, it represents, on average, only 27.5% of all of the biological waste treatment processes (De Baere, 2006).
Kitchen waste is a large fraction of municipal solid waste (20–65%) (Tchobanoglous et al., 1993). The biomethanation potential of the waste depends on the relative amounts of the four main components – proteins, lipids, carbohydrates, and cellulose. Kitchen and restaurant waste are not homogeneous in day-to-day composition. It is important to have data to predict how these fluctuations may influence the anaerobic digestion process.
This work aims to study how variations of the major components of restaurant waste influence the methane yield and the process kinetics.
Section snippets
Waste characterization
A synthetic restaurant waste, representing the major components of waste from a real restaurant prepared by mixing melted lard of pork, white cabbage, chicken breast, and potato flakes, to simulate lipids, cellulose, protein and carbohydrates, respectively. A preliminary assay was done in order to assess the adequacy of the synthetic waste to simulate a real restaurant waste. The restaurant waste was a composite sample (1 week based) from the waste produced in the restaurant of the University
Results and discussion
In the first experiment, the cumulative methane production obtained from the real restaurant waste was compared with the methane production obtained from the synthetic waste (Fig. 1). This experiment was planned to indicate the adequacy of the synthetic waste to represent the real waste. Only the initial cumulative methane production was considered, which in eight days reached 56% of the theoretical methane yield for both wastes (196 mL CH4/gCODadded).
The similar initial methane production
Conclusions
Batch degradation of restaurant waste under methanogenic conditions depends on waste composition. If lipids are in excess a slower methane production, a higher concentration of COD in the liquid, and a lower hydrolysis rate constant is observed in comparison with a waste with equivalent amounts of COD of proteins, carbohydrates, lipids, and cellulose. One waste with an excess of carbohydrates and proteins presented hydrolysis rate constants higher (0.32 and 0.22 d−1, respectively) than the
Acknowledgements
The authors thank to FCT for the financial support given to Lúcia Neves through the Project POCTI/1999/CTA/36524 and SFRH/BD/18174/2004. The English revision provided by A.S. Danko is gratefully acknowledged.
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