Substrate and operational conditions as regulators of fluid properties in full-scale continuous stirred-tank biogas reactors - implications for rheology-driven power requirements

• Published in: Water science and technology Vol. 78; no. 3-4; pp. 814 - 826
• Main Authors: Björn, Annika, Šafarič, Luka, Karlsson, Anna, Danielsson, Åsa, Ejlertsson, Jörgen, Svensson, Bo H, Yekta, Sepehr Shakeri
• Format: Journal Article
• Language: English
• Published: England IWA Publishing 01.09.2018
• Subjects: Agricultural production; Alternative energy sources; Anaerobiosis; Anatomical structures; Biofuels; Biogas; Bioreactors; Continuously stirred tank reactors; Digesters; Engineering; Fluids; Hydraulic retention time; Load distribution; Loading rate; Methane; Municipal solid waste; Non-Newtonian fluids; Organic loading; Particle size; Principal components analysis; Profiles; Properties; Properties (attributes); Reactors; Regulators; Retention time; Reynolds number; Rheological properties; Rheology; Sewage; Sewage sludge; Shear stress; Sludge; Sludge digestion; Substrates; Temperature requirements; Viscosity; Waste Disposal, Fluid; Water treatment; Yield stress; viscosity; continuous stirred-tank biogas reactor; rheology; anaerobic digestion; power requirement; biogas
• ISSN: 0273-1223; 1996-9732; 1996-9732
• DOI: 10.2166/wst.2018.352

Understanding fluid rheology is important for optimal design and operation of continuous stirred-tank biogas reactors (CSTBRs) and is the basis for power requirement estimates. Conflicting results have been reported regarding the applicability of total solid (TS) and/or total volatile solid (TVS) contents of CSTBR fluids as proxies for rheological properties. Thus, the present study investigates relationships between rheological properties of 12 full-scale CSTBR fluids, their substrate profiles, and major operational conditions, including pH, TS and TVS contents, organic loading rate, hydraulic retention time, and temperature. Rheology-driven power requirements based on various fluid characteristics were evaluated for a general biogas reactor setup. The results revealed a significant correlation only between the rheological fluid properties and TS or TVS contents for sewage sludge digesters and thermophilic co-digesters (CD), but not for mesophilic CD. Furthermore, the calculated power requirements for pumping and mixing, based on the various fluid characteristics of the studied CSTBRs, varied broadly irrespective of TS and TVS contents. Thus, this study shows that the TS and/or TVS contents of digester fluid are not reliable estimators of the rheological properties in CSTBRs digesting substrates other than sewage sludge.