Evaluation of the biomethane potential from multiple waste streams for a proposed community scale anaerobic digester

Abstract

This paper examines the biomethane potential from organic waste for a proposed community scale anaerobic digester in a rural town. The biomethane potential test is used to assess the suitability of waste streams for biomethane production and to examine the variation in biomethane potential between waste sub-streams. A methodology for accurately estimating the biomethane potential from multiple heterogeneous organic waste substrates is sought. Five main waste streams were identified as possible substrates for biogas production, namely Abattoir waste (consisting of paunch and de-watered activated sludge); cheese factory effluent; commercial and domestic food waste; pig slurry and waste water treatment sludge. The biomethane potential of these waste streams ranged from as low as 99 L CH₄ kg VS⁻¹ for pig slurry to as high as 787 L CH₄ kg VS⁻¹ for dissolved air floatation (DAF) sludge from a cheese effluent treatment plant. The kinetic behaviour of the biomethane production in the batch test is also examined. The objective of the paper is to suggest an optimum substrate mix in terms of biomethane yield per unit substrate for the proposed anaerobic digester. This should maximize the yield of biomethane per capital investment. Food waste displayed the highest biomethane yield (128 t⁻¹) followed by cheese waste (38 t⁻¹) and abattoir waste (36 t⁻¹). It was suggested that waste water sludge (16 t⁻¹) and pig slurry (4 t⁻¹) should not be digested. However, the biomethane potential test does not give information on the continuous operation of an anaerobic digester.

Keywords:

• anaerobic digestion
• biogas
• biomethane potential test
• waste to energy

Acknowledgements

Researchers were funded by Science Foundation Ireland (SFI), the Irish Research Council for Science, Engineering and Technology (IRCSET) and Bord Gais Energy (BGE). Laboratory equipment was funded by Bord Gais Networks (BGN).