Stimulation of conversion rates and bacterial activity in a silage-fed two-phase biogas process by initiating liquid recirculation |
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Authors: | Åsa Jarvis Åke Nordberg Berit Mathisen Bo H Svensson |
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Institution: | (1) Department of Microbiology, Swedish University of Agricultural Sciences, P.O. Box 7025, S-750 07 Uppsala, Sweden;(2) Swedish Institute of Agricultural Engineering, P.O. Box 7033, S-750 07 Uppsala, Sweden;(3) Department of Water and Environmental Studies, Linköping University, S-581 83 Linköping, Sweden |
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Abstract: | The effects of liquid recirculation on a liquefaction-acidogenic reactor in an anaerobic two-phase digesting system operating with grass-clover silage was studied during 40 days after initiating recirculation of effluent from the methanogenic reactor to the liquefaction-acidogenic reactor. An increase in alkalinity and, thus, an increase in pH from 5.2 to 6.0 occurred in the liquefaction-acidogenic reactor. During the same period, a 10-fold increase (from 0.2 to 1.9 g·l–1·h–1) in the degradation rate of mannitol and an almost 9-fold increase in the activity of hydrogenotrophic methanogens was observed. The estimated number of these bacteria increased by one order of magnitude. The average degradation rate of lactate increased 3-fold, probably as a consequence of the more efficient hydrogen consumption by the hydrogenotrophic methanogens. An observed increase in net mineralization of organic nitrogen compounds was probably the main reason for an enhanced net production of organic acids (from 0.2 to 0.9 g·l–1·d–1). The liquefaction of cellulose and hemicellulose was low from the start of recirculation (3% and 20% reduction, respectively) and did not seem to be affected by the liquid recirculation. This was in accordance with the low number of cellulose degraders (4.0·102 counts·ml–1) observed. The results from this investigation show that the initiation of liquid recirculation in silage-fed two-phase biogas processes will stimulate the activity of hydrogenotrophic methanogens in the liquefaction-acidogenic reactor. This will lead to more thermodynamically favourable conditions for acidification reactions which are dependent upon interspecies transfer of reducing equivalents.Abbreviations COD
chemical oxygen demand
- CSTR
completely stirred tank reactor
- HRT
hydraulic retention time
- LA-reactor
liquefaction-acidogenic reactor
- M-reactor
methanogenic reactor
- MPN
most probable number
- OLR
organic loading rate
- SMA
specific methanogenic activity
- SRT
solids retention time
- TKN
total Kjeldahl nitrogen
- ts
total solids
- tss
total suspended solids
- vs
volatile solids
- vss
volatile suspended solids |
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Keywords: | Hydrogen consumption lactate liquid recirculation mannitol silage two-phase anaerobic digestion |
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