The methanogenic archaea characteristics and efficacy of aerobic waste sludge in the start-up of anaerobic hybrid reactors treating cassava wastewater

Abstract

Inoculum is a crucial factor influencing the success of an anaerobic digester start-up. This study evaluated the efficacy of aerobic waste activated sludge (WAS) to start-up anaerobic hybrid reactors (AHR) treating cassava wastewater. The start-up performance and stability of five 6.2 L AHRs inoculated differently by WAS (AHR1) and WAS co-inoculated with pig manure (AHR2), cow dung (AHR3), chicken manure (AHR4), and anaerobic pond sludge (AHR5) were investigated. The results depicted the potential of WAS as starter seed for AHR's start-up. This sludge contained methanogenic populations, mainly Methanomicrobials, Methanosarcinales, and Thermoplasmatales, for 1.5 × 107 MPN/g VS compared to 4.0 × 103-6.0 × 107 MPN/g VS in manures and anaerobic sludge. Co-inoculation of WAS with cow dung (AHR3) and anaerobic sludge (AHR5) promoted a rapid start-up, achieved 4.0 kg COD/m3.d within 1.5-1.7 months, while about 2.5-3.3 months needed for the others. A satisfying performance, stability, microbial development and activity, depicted as high COD removal (CODrem) efficiency and methane productivity, were achieved in all digesters. About 0.32 and 0.21 m3/kg CODrem for biogas and methane yielded in AHR1, whereas 0.41-0.49 m3-biogas/kg CODrem and 0.25-0.32 m3-CH4/kg CODrem obtained in other reactors. This finding confirmed that inoculum's quality is critical for productive gas productivity and system stability maintenance.