Title: Anaerobic digestion of grass-cuttings under mesophilic and regulated digester pressure

Authors: Ishmael M. Ramatsa; Esther T. Akinlabi; Robert Huberts

Addresses: Department of Chemical Engineering, University of Johannesburg, Cnr Joe Slovo and Beit St 2001 Doornfontein, Johannesburg, Gauteng, South Africa ' Department of Chemical Engineering, University of Johannesburg, Cnr Joe Slovo and Beit St 2001 Doornfontein, Johannesburg, Gauteng, South Africa ' Department of Chemical Engineering, University of Johannesburg, Cnr Joe Slovo and Beit St 2001 Doornfontein, Johannesburg, Gauteng, South Africa

Abstract: The successful functioning and stability of an anaerobic digester depends on the interplay of several factors, each of which is very important to the success of the system as a whole. pH is central to the whole system as it dictates the survival for the bacteria. In this study the effect of digester pressure was investigated at a fixed temperature of 36°C. The digester pressure was manipulated using back pressure regulator. Grass cuttings were used as feed material to the digester. Three pressures of 2bar, 4bar and 6bar were investigated for a period of ten days. The characteristics and methane yield achieved when digesting grass cuttings under constant digester pressure (gauge pressure) suggested that it is possible to produce biogas that has minimal amount of CO₂. The highest methane compositions at 0bar, 2bar, 4bar and 6bar were 55.77, 62.2, 65.8 and 71.2% and carbon dioxide compositions were 58.85, 35.2, 32.5 and 26.2%. The amount of CO₂ decreased significantly with increased pressure and the pH values dropped to 7.01, 6.96 and 6.78 respectively with increase in pressure.

Keywords: regulated pressure; pH; ammonia-nitrogen; methane; inert gases.

DOI: 10.1504/IJRET.2018.090102

International Journal of Renewable Energy Technology, 2018 Vol.9 No.1/2, pp.28 - 38

Received: 15 Dec 2016
Accepted: 10 Jul 2017
Published online: 28 Feb 2018 *

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