Two-stage vs single-stage thermophilic anaerobic digestion: Comparison of energy production and biodegradation efficiencies

Andrea Schievano*, Alberto Tenca, Barbara Scaglia, Giuseppe Merlino, Aurora Rizzi, Daniele Daffonchio, Roberto Oberti, Fabrizio Adani

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

151 Scopus citations


Two-stage anaerobic digestion (AD) for integrated biohydrogen and biomethane production from organic materials has been reported to promise higher process efficiency and energy recoveries as compared to traditional one-stage AD. This work presents a comparison between two-stage (reactors R1 and R2) and one-stage (reactor R3) AD systems, fed with identical organic substrates and loading rates, focusing the attention on chemical and microbiological aspects. Contrary to previous experiences, no significant differences in overall energy recovery were found for the two-stage and one-stage AD systems. However, an accumulation in R2 of undegraded intermediate metabolites (volatile fatty acids, ketones, amines, amino acids, and phenols) was observed by GC-MS. These compounds were thought to be both cause and effect of this partial inefficiency of the two-stage system, as confirmed also by the less diverse, and thereby less efficient, population of fermentative bacteria observed (by PCR-DGGE) in R2. The extreme environment of R1 (low pH and high metabolites concentrations) probably acted as selector of metabolic pathways, favoring H2- producing bacteria able to degrade such a wide variability of intermediate metabolites while limiting other strains. Therefore, if two-stage AD may potentially lead to higher energy recoveries, further efforts should be directed to ensure process efficiency and stability.

Original languageEnglish (US)
Pages (from-to)8502-8510
Number of pages9
JournalEnvironmental Science and Technology
Issue number15
StatePublished - Aug 7 2012

ASJC Scopus subject areas

  • General Chemistry
  • Environmental Chemistry


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