1. Online headspace chromatographic method for measuring VFA in biogas reactors Kanokwan Boe, Damien John Batstone, Irini Angelidaki Environment & Resources Technical University of Denmark Lyngby, Denmark

2. Traditional monitoring

3. Optimal monitoring

4. Good indicator To indicate the actual status of the process To give an early warning To give a secure warning To always predict imbalance

5. Types of disturbances Hydralic overload Organic overload Toxic compounds Temperature changes pH change New substrates

6. Traditional indicators IndicatorPrinciple Biogas productionSpecific gas production Biogas compositionConcentrations of CH 4 and CO 2 pHDecrease in pH due to accumulation of VFA AlkalinityDetects changes in buffer capacity Total VFATotal concentration of VFA (usually determined by titration) Individual VFAAccumulation of different VFA (usually determined by gas chromatography) COD, BOD or VS reduction Degradation efficiency H 2 concentrationAccumulation of hydrogen, a key intermediate CO concentrationAccumulation of CO, a precursor of acetate formate

7. Alternative indicators IndicatorPrinciple Bacterial numbers Bacteria countingNumbers of different groups of bacteria Molecular methods Genetic probingSpecific probes against 16S rRNA for specific groups or individual bacteria Biochemically based indicators Bacterial membrane lipidsSpecial lipids can be used to identify different bacterial groups and their numbers Enzyme activityActivity of specific enzymes can indicate substrate turn in the bacterial ecosystem ATPConcentration of ATP indicates the general microbiological activity F-420F-420 is a characteristic co-enzyme found in methanogens and can quantify active methanogens NADHNADH activity is correlated with bacterial activity Bacterial activity Methanogenic activityMethane production rate during degradation of different substrates can estimate the activity of the corresponding bacterial group

8. Background Co-digestion plants Need of on-line monitoring system VFA as process indicator Digested manure => problem with filtration

9. Concept Gas phase extraction Liquid sample => measure in gas phase High solid sample / slurry waste No pretreatment or filtration needed Individual VFA in liquid phase

10. Strong effect : –pH –Temperature –Salt addition Gas-liquid extraction factor No effect : –Gas/Liquid volume ratio –VFA concentration

11. Concept Equilibrium cell GC pHT AcidSalt Sample H

12. System setup

14. Gas chromatogram of digested manure From liquid sample From gas sample Ac Pr But Iso-val But Iso-but Iso-val Val

15. Test on standard VFA solution Environment & Resources Technical University of Denmark

16. Preliminary test online application Acetic acidPropionic acid Iso-butyric acid Peak area from on-line measurement VFA conc. in liquid phase from off-line measurement

17. Conclusion New online-VFA by gas extraction from liquid sample pH 65 o C Linear calibration curve in application range Measure individual VFA No pretreatment or filtration needed

18. Acknowledgement Technicians : Uwe Albert Walter Majbrit Staun Jensen Students : Elena Fernández Ordáz Mickael Serres