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Process diagnosis using methanogenic Archaea in maize-fed, trace element depleted fermenters.
Bernhard Munk1, Michael Lebuhn1
1Bavarian State Research Center for Agriculture, Central Department for Quality Assurance and Analytics, Lange Point 6, 85354 Freising, Germany.
Anaerobe
|April 22, 2014
Summary
Trace element deficiency, particularly cobalt and selenium, caused acidification in a pilot-scale fermenter. Supplementation improved stability, with metabolic quotient serving as an early warning for process acidification.
Area of Science:
- Biotechnology and Bioengineering
- Environmental Microbiology
- Anaerobic Digestion
Background:
- Trace element (TE) deficiency, specifically cobalt, selenium, and sodium, led to severe acidification in a mesophilic maize-fed pilot-scale fermenter.
- Micronutrient deficiencies can significantly impact the stability and performance of anaerobic digestion processes.
Purpose of the Study:
- To investigate the impact of specific trace element deficiencies (cobalt, selenium) on fermenter stability and microbial community dynamics.
- To analyze methanogen population dynamics and activity at DNA and mRNA levels under varying organic loading rates (OLRs).
- To evaluate the Metabolic Quotient (MQ) and cDNA/DNA ratio as early warning indicators of process acidification.
Main Methods:
- Operated three lab-scale flow-through fermenters using inoculum from a deficient pilot-scale fermenter, with supplementation of selenium, cobalt, or no supplementation (control).
- Increased organic loading rate (OLR) and monitored fermenter stability.
- Quantified methanogen populations and composition using Real-Time PCR (DNA and mRNA) and amplicon sequencing.
- Calculated Metabolic Quotient (MQ) and cDNA/DNA ratio to assess microbial activity and stress.
Main Results:
- The control fermenter acidified at an OLR of 4.0 kg VS * m(-3) * d(-1), while selenium and cobalt supplementation improved stability up to 4.5 and 5.0 kg VS * m(-3) * d(-1), respectively.
- Methanogen communities shifted, with Methanosarcina spp. becoming dominant and active during acidification in TE-supplemented fermenters, while Methanobacteriaceae dominated the acidified control.
- The MQ indicated metabolic stress approximately one month before critical acidification (TVA/TIC ratio of 0.7), and the cDNA/DNA ratio reflected increasing methanogenic activity with OLR.
Conclusions:
- Cobalt and selenium are critical trace elements for maintaining the stability of mesophilic maize-fed anaerobic digestion.
- Methanogen community composition and activity, particularly the dominance of Methanosarcina spp. during stress, are key indicators of process health.
- Metabolic Quotient (MQ) is a reliable early warning parameter for detecting impending process acidification in anaerobic digesters.
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