Influence of composition on the biomethanation potential of restaurant waste at mesophilic temperatures

doi:10.1016/j.wasman.2007.03.031

Waste Management

Volume 28, Issue 6, 2008, Pages 965-972

https://doi.org/10.1016/j.wasman.2007.03.031 Get rights and content

Abstract

A synthetic waste was used to study the effect of waste composition on anaerobic degradation of restaurant waste. It was made by blending melted pork lard, white cabbage, chicken breast, and potato flakes, to simulate lipids, cellulose, protein, and carbohydrates, respectively. Four blends of the four constituents with an excess of each component were assayed and compared with a fifth blend containing an equal amount of chemical oxygen demand (COD) of each of the four components. The methane production and the time course of soluble COD and volatile fatty acids were assessed in batch assays. A high reduction of volatile solids (between 94% and 99.6%) was obtained in all the assays. The methane yield was between 0.40 m³ CH₄/kg VS_initial (excess of carbohydrates) and 0.49 m³ CH₄/kg VS_initial (excess of lipids). The degradation of the lipid-rich assays differed from the others. Fifty percent of the biochemical methane potential was obtained after 3–6 days for all of the assays, except for the one with excess of lipids which achieved 50% methanation only after 14.7 days of incubation. In the assay with excess of lipids, a considerable fraction of COD remained in the liquid phase, suggesting an inhibition of the methanogenic process that was likely due to the accumulation of long chain fatty acids. The hydrolysis rate constants, assuming first order kinetics, over the first 6 days were between 0.12 d⁻¹ (excess of lipids) and 0.32 d⁻¹ (excess of carbohydrates). The results indicate that anaerobic digestion facilities with large variations in lipid input could have significant changes in process performance that merit further examination.

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/gCOD_added).

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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Influence of composition on the biomethanation potential of restaurant waste at mesophilic temperatures

Abstract

Introduction

Section snippets

Waste characterization

Results and discussion

Conclusions

Acknowledgements

Process Biochem.

J. Biol. Chem.

Methods Enzymol.

Effects of free long-chain fatty acids on thermophilic anaerobic digestion

Appl. Microbiol. Biotechnol.

Standard Methods for the Examination of Water and Wastewater

Will anaerobic digestion of solid waste survive in the future?

Water Sci. Technol.

Reactor sizing process kinetics and modelling of anaerobic digestion of complex wastes. Biomethanisation of the organic fraction for municipal solid wastes