H₂ production with anaerobic sludge using activated-carbon supported packed-bed bioreactors

Packed-bed bioreactors containing activated carbon as support carrier were used to produce H₂ anaerobically from a sucrose-limiting medium while acclimated sewage sludge was used as the H₂ producer. The effects of bed porosity (ε_b) and substrate loading rate on H₂ fermentation were examined using packed beds with ε_b of 70-90% being operated at hydraulic retention times (HRT) of 0.5-4 h. Higher ε_b and lower HRT favored H₂ production. With 20 g COD 1^-1 of sucrose in the feed, the optimal H₂ production rate (7.4 1 h^-1 1^-1) was obtained when the bed with ε_b = 90% was operated at HRT = 0.5 h. Flocculation of cells enhanced the retention of sludge for stable operations of the bioreactor at low HRTs. The gas products resulting from fermentative H₂ production consisted of 30-40% H₂ and 60-70% CO₂. Butyric acid was the primary soluble product, followed by propionic acid and valeric acid.