Application of Aqueous Ammonia Soaking for enhancement of methane potential of swine manure fibers

Purpose: Increasing the methane productivity of manure based biogas plants is challenging because the solid fraction of manure contains lignocellulosic fibers, which are difficult to biodegrade and thus make anaerobic digestion process slow and economically unfavourable. Therefore, pretreatment of the solid fraction is a prerequisite for increasing its digestibility. The purpose of the present study was to evaluate aqueous ammonia soaking (AAS) and subsequent ammonia removal as a pretreatment method for increasing methane potential and biogas productivity of raw and digested manure fibers.
Methods: Manure fibers were pretreated with AAS for 3 days at 22°C and methane production was evaluated in batch experiments (methane potential tests).
Results: It was proven that AAS altered the lignocellulosic structure increasing significantly the concentration of soluble organic material. AAS pretreatment resulted at a 40-80% and 170% increase in methane yield from digested and raw manure fibers, respectively. Moreover, methane potential was evaluated at different organic loadings to test potential inhibition phenomena. Four different TS loadings were tested: 0.16, 0.25, 0.5 and 1 g TS per 10 ml of inoculum. No inhibition was observed for the digested fibers at the loadings tested while raw fibers exhibited slight inhibition only at very high loadings.
Main conclusions: In the present study, AAS was successfully applied as a pretreatment method to increase methane potential of swine manure fibers. Batch anaerobic digestion of AAS-treated digested manure fibers could stand loadings as high as 100 g TS / L inoculum with no inhibition problems.