Improvement of Digestate Stability Using Dark Fermentation and Anaerobic Digestion Processes

Elena Albini, Isabella Pecorini and Giovanni Ferrara
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Elena Albini: DIEF—Department of Industrial Engineering, University of Florence, via Santa Marta 3, 50139 Florence, Italy
Isabella Pecorini: DESTEC—Department of Energy, Systems, Territory and Construction Engineering, University of Pisa, via C.F. Gabba 22, 56122 Pisa, Italy
Giovanni Ferrara: DIEF—Department of Industrial Engineering, University of Florence, via Santa Marta 3, 50139 Florence, Italy

Energies, 2019, vol. 12, issue 18, 1-15

Abstract: This paper assessed the effect of dark fermentation, the fermentative phase in a two-stage anaerobic digestion system, in terms of digestate biostabilization efficiency. The digestates analyzed in this study were obtained from a pilot-scale system in which two different substrates were used in order to simulate both the digestion and co-digestion process. Biostabilization performances were evaluated by measuring the specific oxygen uptake rate (SOUR) of the outgoing digestates. This index allowed us to define the degree of effectiveness in terms of stabilization of organic matter, between the traditional anaerobic digestion process and the two-stage configuration. Considering the traditional process as a reference scenario, the results highlighted an increase in biological stability for the two-stage co-digestion process, consisting of a dark fermentation stage, followed by an anaerobic digestion one. Digestates biostabilization efficiency increased up from 6.5% to 40.6% from the traditional one-stage configuration to the two-stage one by improving the anaerobic digestion process through a preliminary fermentative stage. The advantages of the two-stage process were due to the role of dark fermentation as a biological pre-treatment. Considering the partial stability results related to the second stage, biological stability was improved in comparison to a single-stage process, reaching an efficiency of 42.2% and 55.8% for the digestion and co-digestion scenario respectively. The dark fermentation phase allowed for a higher hydrolysis of the substrate, making it more easily degradable in the second phase. Results demonstrated better biostabilization performances of the outgoing digestates with the introduction of dark fermentation, resulting in more stable digestates for both the digestion and co-digestion process.

Keywords: bio-waste; two-stage process; bio-hydrogen; bio-methane; bio-fuels; respirometric test; specific oxygen uptake rate (SOUR) (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2019
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (5)

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