Impact of ultrasonication of hog manure on anaerobic digestability

Abstract

The efficiency of ultrasonication as a pretreatment method for hog manure prior to anaerobic digestion is evaluated at specific energies of 250–30,000 kJ/kgTS. This study confirmed that COD solubilisation from particulates correlated well with the more labor and time intensive degree of disintegration test. The particle size distribution for hog manure was bimodal (0.6–2500 μm), while ultrasonication primarily impacting particles in the 0.6–60 μm range. Hog manure was found to be more amenable to ultrasonication than waste activated sludge, as it took only 3000 kJ/kgTS to cause 15% more solubilization as compared to 25,000 kJ/kgTS for waste activated sludge. Bound protein degradation during sonication was 13.5% at 5000 kJ/kgTS and remained constant thereafter for higher energy input. It was noted that biomass cell rupture occurred at specific energy of 500 kJ/kgTS. An economic evaluation indicated that only a specific energy of 500 kJ/kgTS was economical, with a net energy output valued at $4.1/ton of dry solids, due to a 28% increase in methane production.