Anaerobic Digestion of Animal Waste: Effect of Mode of Mixing


Laboratory-Scale Digesters Were Operated to Study the Effect of Mixing (Via Biogas Recirculation, Impeller Mixing, and Slurry Recirculation) on Biogas Production. Three Sets of Experiments Were Performed using Cow Manure Slurry Feed with Either 50, 100, or 150 G/L Total Solids (TS) Concentrations (Referred in the Text as 5%, 10%, and 15% Manure Slurry). the Experiments Were Conducted at a Controlled Temperature of 35°C and a Hydraulic Retention Time of 16.2 Days, Resulting in TS Loadings of 3.1, 6.2, and 9.3 G/L D for 5%, 10%, and 15% Manure Slurry Feeds, Respectively. Results Showed that the Unmixed and Mixed Digesters Performed Quite Similarly When Fed with 5% Manure Slurry and Produced Biogas at a Rate of 0.84-0.94 L/L D. the Methane Yield Was Found to Be 0.26-0.28 L CH4/g Volatile Solids Loaded. However, the Effect of Mixing and the Mode of Mixing Became Important When the Digesters Were Fed Thick Manure Slurry Feeds (10% and 15%). Digesters Fed with 10% and 15% Manure Slurry and Equipped with External Mixing Produced About 10-30% More Biogas Than the Unmixed Digester. While the Mixed Digesters Produced More Biogas Than Unmixed Digesters, Digester Mixing during Start-Up Was Not Beneficial, as It Resulted in Lower PH, Performance Instability and Prolonged Start-Up Time. Mixing using Biogas Recirculation System Was Found Not to Be Effective in the Case of 15% Manure Slurry Feed under the Experimental Conditions Studied. © 2005 Elsevier Ltd. All Rights Reserved.


Chemical and Biochemical Engineering


Office of Energy Efficiency and Renewable Energy, Grant None

Keywords and Phrases

Anaerobic; Biogas; Digestion; Manure; Mixing

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version


File Type





© 2023 Elsevier; IWA Publishing, All rights reserved.

Publication Date

01 Jan 2005

PubMed ID