Anaerobic Digestion of Pig Slurry in Fixed-Bed and Expanded Granular Sludge Bed Reactors

Abstract

Anaerobic digestion of animal manure is a potential bioenergy resource that avoids greenhouse gas emissions. However, the conventional approach is to use continuously stirred tank reactors (CSTRs) with hydraulic retention times (HRTs) of greater than 30 d. Reactors with biomass retention were investigated in this study in order to increase the efficiency of the digestion process. Filtered pig slurry was used as a substrate in an expanded granular sludge bed (EGSB) reactor and fixed-bed (FB) reactor. The highest degradation efficiency (ηCOD) and methane yield (MY) relative to the chemical oxygen demand (COD) were observed at the minimum loading rates, with MY = 262 L/kgCOD and ηCOD = 73% for the FB reactor and MY = 292 L/kgCOD and ηCOD = 76% for the EGSB reactor. The highest daily methane production rate (MPR) was observed at the maximum loading rate, with MPR = 3.00 m3/m3/d at HRT = 2 d for the FB reactor and MPR = 2.16 m3/m3/d at HRT = 3 d for the EGSB reactor. For both reactors, a reduction in HRT was possible compared to conventionally driven CSTRs, with the EGSB reactor offering a higher methane yield and production rate at a shorter HRT.

The Role of Biogas and Biomethane as Renewable Gases in the Decarbonization Pathway to Zero Emissions

“…Hernández and co-authors present a techno-economic assessment of biogas treatment plants for the agro-industrial sector, optimizing the design and operation of these plants to reduce greenhouse gas emissions and improve the circular use of nitrogen [7]. Häner and colleagues explore the use of fixed-bed and expanded granular sludge bed reactors for the anaerobic digestion of pig slurry, aiming to increase efficiency by using reactors with biomass retention [8]. Mukawa and co-authors examine the energy potential of biogas from sewage sludge treated with thermal hydrolysis, providing detailed energy balance calculations and evaluating thermal energy demand coverage [9].…”