3. Biogas-Training Introduction into Digester Biology Birgit Pfeifer, International Biogas and Bioenergy entre of ompetence (IBBK) Nesta Boutique Hotel Ankara, 12.-13.09.2011 13.09.2011 initiative on the basis of a decision adopted by the German Bundestag.
onversion process 1. biochemical 2. physical Organic matter Digester biogas HP Electricity Heat dependent on efficiency factors! - Efficiency factor of the inputs Yield [m³ H 4 /t ots] - Electrical efficiency factor [%] - Efficiency factor of the digester Productivity [m³ H 4 /(m³rv d)] - Thermal efficiency factor [%]
Principles of the biogas process 1 The biogas process 2 Environmental conditions 3Engineering process parameter
Biogas formation H OH 2 B H H OH 2 OH O O H H 2OH OH H O OH H O O H H OH 2 OH H O OH H O H OH H O OH Biomass: H O H E OH H carbohydrate, fats, proteins H H H H H OH 2 OH O H Methane biogas O H arbon dioxide H OH Intermediate products: Sugar, fatty acids, amino-acids acids Fatty acid production: butyric acid propionic acid acetic acid
The 4 stages of the fermentation gas formation Acidification Biogas formation 1. Stage Hydrolysis 2. Stage Acidogenesis 3. Stage Acetogenesis 4. Stage Methanogenesis Hydrogen H 2 Biomass Polysaccharides Sugar, Amino acids, H 2 /O 2 Biogas arbon dioxide O 2 Methane H 4 Proteins, Fats fatty acids Fatty acids (propionic acid) alcohols Acetic acid acetic acid H2 H2 H 4 /O 2 Hydrolytic bacteria Acidogenic bacteria Acetogenic bacteria Methanogenic bacteria
Generation time of different bacteria Anaerobe Microorganisms Acid producing bacteria Bacterioides < 24 h. lostridien 24-36 h. Acetogenic bacteria 80-90 h. Methanogenic bacteria Methanococcus ca. 10 d Methanosarcina barkeri 5-15 d! Aerobe microorganisms Escherichia coli 20 Min. Activated sludge bacteria 2 h.
The most important reactions 1. Degradation of Acid Propionic H 3 H 2 OOH + 2 H 2 O H 3 OOH + O 2 + 3 H 2 3. Stage Propionic acid Acetic acid Hydrogen 2. Acetic acid degradation and methane formation O 2 + 4 H 2 H 4 + 2 H 2 O ((30%(? of the methane) H 3 OOH H 4 + O 2 (70% of the methane) 4. Stage
The different degradation processes occur at the same time simultaneously In agricultural biogas plants the separation of the degradation stages plays a minor role one-stage process biogas digestate
The different degradation processes occur at the same time simultaneously In agricultural biogas plants the separation of the degradation stages plays a minor role are strongly dependent from each other Intermediate products are needed for following processes one-stage process can cause mutual inhibition Intermediate products may not accumulate Product inhibition develop slowly in advanced stages Hydrolysis is the fastest, methane formation the slowest biogas digestate
Environment conditions of anaerobic degradation Measured variable Temperature ph value :N-Relation Solid content Redox - potential Nutrient demand :N:P:S Trace elements Hydrolysis/acidification 25 35º 5,2 6,3 10-45 < 40 % DM +400 300 mv 500 : 15 : 5 : 3 No specific requirements Methane formation Mesophilic: 32 42 º Thermophilic: 50 58 º 6,7 7,5 20-30 < 30 % DM < -250 mv 600 : 15 : 5 : 3 Essential: Ni, o, Mo, Se FAL TB Environmental requirements for the fermentation of raw and residual substrates W0104124DR
ircumstances of the anaerobic degradation onditions Start-up ph-value Milieubedingungen - Inbetriebnahme ph-wert onditions Milieubedingungen - Inbetriebnahme Start-up Temperatur temperature ph-wert 6,5 6 5,5 5 4,5 4 19.05.2007 ph 5 21.05.2007 23.05.2007 25.05.2007 Zeitraum 27.05.2007 29.05.2007 ph 6,5 Parameter Hydrolysis Methanogenesis Temperature 25 35 Methanogenic: 32-42 Thermophilic: 50-58 ph 5,2 6,3 6,7 7,5 Temperatur in ph-wert 42 40 38 36 34 32 30 34 19.05.2007 21.05.2007 23.05.2007 25.05.2007 Zeitraum 27.05.2007 40 29.05.2007 Source: Novatech GmbH Support program
The most important requirements for the biogas process Temperature ph-value Salt content Trace elements
Temperature ranges Thermophil (50-60 ) high gas yield after short retention time sensitive biocoenosis caution with rapid degradable substrates, (hydrolysis develops too fast) Mesophil (32-45 ) stable biocoenosis satisfying gas yield with acceptable retention time common, particularly in wet fermentation processes Psychrophil (< 25 ) low growth rate long retention times inefficient for biogas production no longer in use
Temperature range Influence of temperature on bacteria activity % relative acivity 160 140 120 100 80 60 40 20 mesophilic Frequently temperature range in practice thermophilic 0 20 30 40 50 60 Temperature in bp Prozessbetreuung, Pfeifer based on Source: Biogas-Praxis, Eder-Schulz, 3. Auflage 2006
Range of temperature - mesophilic Range of temperature - mesophilic - 48 47 46 temperature of digester 45 44 43 42 41 BGA 1 BGA 2 BGA3 BGA4 BGA5 BGA6 BGA7 40 39 38 20.05.2008 03.06.2008 17.06.2008 01.07.2008 15.07.2008 29.07.2008 12.08.2008 Date
Temperature gradient in german biogas facilities! Is the right temperature a philosophical question? Source: bioreact, Dr. Udo Hölker, 2010
Is the right temperature a philosophical question? No! Mesophilic biogas facilities have a better substrate utilization (in average) Source: bioreact, Dr. Udo Hölker, 2010
ph-value and O 2 -solubility outside 0,03 Vol-% O 2 sampling inside approx. 40 Vol-% O 2 Immediately after taking a sample, outside the digester O 2 begins to escape. ph-value rises ph-value in the digester is lower than measured outside the digester!
ph-value Hydrogen ion (H+)- concentration (Attention: H + H 2 ) Metabolites would reduce the ph-value, but: Plants with manure have normally good buffering systems: arbonate buffer, Ammonium buffer,... ph-value as sole parameter is not suited to evaluate the process It s a question of buffer!
Without buffer: water Acidification by H + - Ions Acetic acid Ions dissolved in water
With buffer: An overdose off free H + -ions will be bound alcium carbonate Propionic acid alcium carboate Acetic acid ph-value remains stable
ph stability through buffer systems 10 Acidity Säureanalyse analysis Säure in [g / l FMI] Acidity in [g/l FM] 9 8 7 6 5 4 3 ph 7,7 ph 7,6 ph 7,6 ph 7,8 Acidification n-valeriansäure n-buttersäure Propionsäure Essigsäure 2 1 0 KW 51/05 KW 01 / 06 KW 06 / 06 KW 07 / 06 Source: Novatech GmbH Support program
Salt content or electric conductivity Simple measurement Should be always included in case of inexplicable changes High salt content dry up the bacteria Osmotic pressure Unit: ms/cm Values > 60 ms/cm are critical orrection on a temperature of 25 Usually no problem during fermentation of energy crops, BUT You have to analyse during fermentation of food-waste (e.g. canteens, grease separator, salted matter) If value is critical: add water
Principles of the biogas process 1 The biogas process 2 Environmental conditions 3Engineering process parameter
3. Fundamental process engineering parameters Dry Matter; DM (odm) Hydraulic retention time; T (HTR) Organic load; B R Rate of Degradation; ŋ rel., ŋ abs. Specific gas production; A biogas, A H4 Input Output
Solid matter content Solid content = Dry Matter [DM] Wet/ Fresh mass (FM) Water content = organic Dry Matter or Volatile solids [odm [ odm] (FM = fresh matter) Solids Mineral solids = ash (minerals)
Solid matter content Solid content = Dry Matter [DM] Wet/ Fresh mass (FM) Solids Water content = organic Dry Matter or Volatile solids [odm [ odm] (FM = fresh matter) Organic solids = Volatile solids [from % FM or % DM ] Mineral solids = ash (minerals)
(Hydraulic) Retention time T, HRT Digester volume = Work volume (gross volume without gas storage space)
(Hydraulic) Retention time T, HRT Digester volume = Work volume (gross volume without gas storage space) central parameter in the case of liquid manure plants less important in the case of plants operating with energy crops
Organic loading rate B R Solids (DM, odm) load per m³ work volume and day Tendency for higher load
Example for calculation: Organic loading rate B R Work volume = 800 m³ Substrate Substrate [t/a] odm [%FM] odm [t/a] odm [kg/d] attle manure 2200 9,0% 198 542 Leftovers 700 17,0% 119 326 hicken dry manure 500 34,0% 170 466 Grease waste 800 27,0% 216 592 Total 4200 703 1926 Daily feeding of organic DM = 1926 kg Process sensitivity increases with a larger organic loading rate
ritical organic loading rate and retention time Gas productivity [m³ Gas /(m³ Fer. * d)] 2 2 Hydraulic retention time [d] 1 ritical hydraulic retention time and organic loading rate Organic load [kg odm/(m³*d)] Gas yield [m³ Gas /kg odm] 1
Source: bioreact, Dr. Udo Hölker, 2010
Relative utilization rate from substrat (of 1.000 biogas facilities) Here: as a function of the organic loading rate (BR) (small squares: single plants; big squares: mean score) Relative utilization rate of substrate [%] Organic loading rate (kg odm / m3 * d] Source: bioreact, Dr. Udo Hölker, 2010
Organic loading rate vs. Hydraulic retention time 4,0 300 3,5 250 3,0 2,5 2,0 1,5 1,0 0,5 200 150 100 50 RB F1 VZ F1 Organic Raumbelastung loading rate [kg otr/m³ d] Hydraulic retention Verweilzeit time [d] 0,0 0 28.04.06 05.05.06 12.05.06 19.05.06 26.05.06 02.06.06 09.06.06 16.06.06 23.06.06 30.06.06 07.07.06 14.07.06 21.07.06 28.07.06 04.08.06 11.08.06 18.08.06 25.08.06 01.09.06 08.09.06 15.09.06 22.09.06 Support Betreuungszeitraum time frame Source: Novatech GmbH Support program
Relative and absolute degree of degradation odm Input degradated odm Input Output - Reduction of the material contents related to the input (relative) or the work volume (absolute) - Sink and floating layers forged the degradation rate
Degradation - Formulas Layers of sedimentation and floating particles effect the grade of decomposition Extremely dependent on the substrate used
3. Fundamental process engineering parameters Dry Matter Hydraulic retention time Organic load Rate of Degradation Specific gas production Input Output
Specific biogas or methane yield: -With reference to the feeded ODM, DM, FM -Better is... Standard conditions: 0 = 273 K 1013 mbar 0 % moisture Biogas per kg fresh matter (input): (FM = fresh matter)
Methods to determine the gas yield alculation Out of OD, TO Out of fodder analyses Problem: Estimation of the degradation rate Analyses are needed Fermentation test ommon method Problem: Long and error susceptible
Fermentation test Batch-tests in different magnitudes ontinuous experiment
Biogas capability of substrates Is determined by: Ingredients of the substrate Organic content, organic dry matter content, odm Proportion of fat, protein and carbohydrates Retention time in the digester Form of preparation Process temperature Methane production Maize silage Organic constituents Gas yield [m 3 /kg] Methane content [%] Raw protein 0,7 71 Raw fat 1,25 66 Raw fiber 0,79 50 Free N extract materials 0,79 50 Methane production Process time [d] Source: Roediger Source:. Tidjen, FAL
Thank you for your attention! Turkish-German Biogas Project Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH And Sokak No: 8/11 06680 ankaya/ankara, TURKEY T +90 312 466 7056 T +49 6196 79830 007 E biogas-tr@giz.de I www.giz.de I www.biyogaz.web.tr Author: Birgit Pfeifer, International Biogas and Bioenergy entre of ompetence (IBBK) 43