Transcript Document
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 Traditional monitoring Gas Optimum Brave Careful Time Suppliers Pre-storage Reactor After-storage Operatør Optimal monitoring Gas optimum Time Suppliers Pre-storage After-storage Reactor Datareg. Model PLC Operator Good indicator • To indicate the actual status of the process • To give an early warning • To give a secure warning • To always predict imbalance Types of disturbances • Hydralic overload • Organic overload • Toxic compounds • Temperature changes • pH change • New substrates Traditional indicators Indicator Principle Biogas production Specific gas production Biogas composition Concentrations of CH4 and CO2 pH Decrease in pH due to accumulation of VFA Alkalinity Detects changes in buffer capacity Total VFA Total concentration of VFA (usually determined by titration) Individual VFA Accumulation of different VFA (usually determined by gas chromatography) COD, BOD reduction or VS Degradation efficiency H2 concentration Accumulation of hydrogen, a key intermediate CO concentration Accumulation of CO, a precursor of acetate formate Alternative indicators Indicator Principle Bacterial numbers Bacteria counting Numbers of different groups of bacteria Molecular methods Genetic probing Specific probes against 16S rRNA for specific groups or individual bacteria Biochemically based indicators Bacterial membrane lipids Special lipids can be used to identify different bacterial groups and their numbers Enzyme activity Activity of specific enzymes can indicate substrate turn in the bacterial ecosystem ATP Concentration of ATP indicates the general microbiological activity F-420 F-420 is a characteristic co-enzyme found in methanogens and can quantify active methanogens NADH NADH activity is correlated with bacterial activity Bacterial activity Methanogenic activity Methane production rate during degradation of different substrates can estimate the activity of the corresponding bacterial group Background • Co-digestion plants • Need of on-line monitoring system • VFA as process indicator • Digested manure => problem with filtration 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 Gas-liquid extraction factor • Strong effect : – pH – Temperature – Salt addition • No effect : – Gas/Liquid volume ratio – VFA concentration Concept Sample GC Acid Salt H pH T Equilibrium cell System setup System setup Gas chromatogram of digested manure Iso-but Pr Ac But Iso-val Val But Iso-val Iso-but Pr Ac From liquid sample From gas sample Val Test on standard VFA solution Peak area 250000 Acetic 200000 Propionic 150000 Iso-butyric Butyric 100000 Iso-valeric 50000 Valeric 0 0 10 20 30 VFA concentration (mM) 40 120000 Acetic Peak area 100000 Propionic 80000 Iso-butyric 60000 Butyric 40000 Iso-valeric 20000 Valeric 0 0 1 2 3 4 VFA concentration (mM) 5 Environment & Resources Technical University of Denmark Preliminary test online application 25000 85 20000 80 15000 75 10000 70 5000 65 0 07May 08May 09May 10May 11May 12May 34 33 20000 32 15000 31 28 07May 6.1 5.6 5.1 07May 08May 09May 10May 11May 12May 13May Peak area 14000 12000 10000 8000 6000 4000 2000 0 0 08May 09May 10May 11May 12May 13May Peak area from on-line measurement Iso-butyric acid 6.6 5000 29 13May 7.1 10000 30 VFA conc. in liquid phase from off-line measurement Peak area 90 Peak area 30000 Propionic acid (mM) Propionic acid 95 Iso-butyric acid (mM) Acetic acid (mM) Acetic acid Conclusion • New online-VFA by gas extraction from liquid sample • pH < 2, Temperature > 65oC • Linear calibration curve in application range • Measure individual VFA • No pretreatment or filtration needed Acknowledgement • Technicians : Uwe Albert Walter Majbrit Staun Jensen • Students : Elena Fernández Ordáz Mickael Serres