Start-up of novel pilot-scale plant based on two-stage expanded granular sludge bed reactors for pig slurry treatment: Performance and microbial dynamics

Abstract

Pig manure management is an environmental challenge that can be improved through high-rate anaerobic digestion, enabling efficient biogas production and resource recovery. This study evaluated a pilot-scale two-stage expanded granular sludge bed (EGSB) system treating real pig slurry over a 150-day start-up. The reactors, operated in series with different working volumes (100 and 500 L), underwent progressive hydraulic retention times (HRT) reductions (R1: 3–1 d; R2: 12–7 d), increasing organic loading rates (OLR) (R1: 7.6–21.4 kg COD m−3 d−1; R2: 1.0–2.5 kg COD m−3 d−1). General chemical oxygen demand (COD) removal reached 68%, with system sensitivity to high solids, while biogas production and methane yield (MY) remained stable, reaching 264 L/d and 352 L CH4/kg COD removed. Microbial analysis identified Clostridium sensu stricto_1, Methanosarcina, and Methanoculleus as key taxa supporting process stability. These results demonstrate the potential of two-stage EGSB systems for sustainable pig manure valorisation.