The role of phase separation and feed cycle length in leach beds coupled to methanogenic reactors for digestion of a solid substrate (Part 2): Hydrolysis, acidification and methanogenesis in a two-phase system

The effect of phase separation and batch duration on the trophic stages of anaerobic digestion was assessed for the first time in leach beds coupled to methanogenic reactors digesting maize (Zea mays). The system was operated for consecutive batches of 7, 14 and 28 days for ∼120 days. Hydrolysis rate was higher the shorter the batch, reaching 8.5 gTSdestroyed d−1 in the 7-day system. Phase separation did not affect acidification but methanogenesis was enhanced in the short feed cycle leach beds. Phase separation was inefficient on the 7-day system, where ∼89% of methane was produced in the leach bed. Methane production rate increased with shortening the feed cycle, reaching 3.523 l d−1 average in the 7-day system. Low strength leachate from the leach beds decreased methanogenic activity of methanogenic reactors’ sludges. Enumeration of cellulolytic and methanogenic microorganisms indicated a constant inoculation of leach beds and methanogenic reactors through leachate recirculation.

► The effect of feed cycle length on anaerobic digestion’s trophic stages was shown.
► Short feed cycle increased hydrolysis rate and methanogenesis in leach bed reactors.
► Acidogenesis was not affected by feed cycle length.
► Shorter feed cycles resulted in lower methanogenic activity of the sludges.
► Cellulolytic and methanogenic microbes were present in substantial number in both reactors.