Introduction into Digester Biology

Transcription

1 3. Biogas-Training Introduction into Digester Biology Birgit Pfeifer, International Biogas and Bioenergy entre of ompetence (IBBK) Nesta Boutique Hotel Ankara, initiative on the basis of a decision adopted by the German Bundestag.

2 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 [%]

3 Principles of the biogas process 1 The biogas process 2 Environmental conditions 3Engineering process parameter

4 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

5 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

6 Generation time of different bacteria Anaerobe Microorganisms Acid producing bacteria Bacterioides < 24 h. lostridien h. Acetogenic bacteria h. Methanogenic bacteria Methanococcus ca. 10 d Methanosarcina barkeri 5-15 d! Aerobe microorganisms Escherichia coli 20 Min. Activated sludge bacteria 2 h.

7 The most important reactions 1. Degradation of Acid Propionic H 3 H 2 OOH + 2 H 2 O H 3 OOH + O H 2 3. Stage Propionic acid Acetic acid Hydrogen 2. Acetic acid degradation and methane formation O H 2 H H 2 O ((30%(? of the methane) H 3 OOH H 4 + O 2 (70% of the methane) 4. Stage

8 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

9 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

10 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, < 40 % DM mv 500 : 15 : 5 : 3 No specific requirements Methane formation Mesophilic: º Thermophilic: º 6,7 7, < 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 W DR

11 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, ph Zeitraum ph 6,5 Parameter Hydrolysis Methanogenesis Temperature Methanogenic: Thermophilic: ph 5,2 6,3 6,7 7,5 Temperatur in ph-wert Zeitraum Source: Novatech GmbH Support program

12 The most important requirements for the biogas process Temperature ph-value Salt content Trace elements

13 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

14 Temperature range Influence of temperature on bacteria activity % relative acivity mesophilic Frequently temperature range in practice thermophilic Temperature in bp Prozessbetreuung, Pfeifer based on Source: Biogas-Praxis, Eder-Schulz, 3. Auflage 2006

15 Range of temperature - mesophilic Range of temperature - mesophilic temperature of digester BGA 1 BGA 2 BGA3 BGA4 BGA5 BGA6 BGA Date

16 Temperature gradient in german biogas facilities! Is the right temperature a philosophical question? Source: bioreact, Dr. Udo Hölker, 2010

17 Is the right temperature a philosophical question? No! Mesophilic biogas facilities have a better substrate utilization (in average) Source: bioreact, Dr. Udo Hölker, 2010

18 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!

19 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!

20 Without buffer: water Acidification by H + - Ions Acetic acid Ions dissolved in water

21 With buffer: An overdose off free H + -ions will be bound alcium carbonate Propionic acid alcium carboate Acetic acid ph-value remains stable

22 ph stability through buffer systems 10 Acidity Säureanalyse analysis Säure in [g / l FMI] Acidity in [g/l FM] ph 7,7 ph 7,6 ph 7,6 ph 7,8 Acidification n-valeriansäure n-buttersäure Propionsäure Essigsäure KW 51/05 KW 01 / 06 KW 06 / 06 KW 07 / 06 Source: Novatech GmbH Support program

23 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

24 Principles of the biogas process 1 The biogas process 2 Environmental conditions 3Engineering process parameter

25 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

26 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)

27 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)

28 (Hydraulic) Retention time T, HRT Digester volume = Work volume (gross volume without gas storage space)

29 (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

30 Organic loading rate B R Solids (DM, odm) load per m³ work volume and day Tendency for higher load

31 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 ,0% Leftovers ,0% hicken dry manure ,0% Grease waste ,0% Total Daily feeding of organic DM = 1926 kg Process sensitivity increases with a larger organic loading rate

32 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

33 Source: bioreact, Dr. Udo Hölker, 2010

34 Relative utilization rate from substrat (of 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

35 Organic loading rate vs. Hydraulic retention time 4, , ,0 2,5 2,0 1,5 1,0 0, RB F1 VZ F1 Organic Raumbelastung loading rate [kg otr/m³ d] Hydraulic retention Verweilzeit time [d] 0, Support Betreuungszeitraum time frame Source: Novatech GmbH Support program

36 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

37 Degradation - Formulas Layers of sedimentation and floating particles effect the grade of decomposition Extremely dependent on the substrate used

38 3. Fundamental process engineering parameters Dry Matter Hydraulic retention time Organic load Rate of Degradation Specific gas production Input Output

39 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)

40 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

41 Fermentation test Batch-tests in different magnitudes ontinuous experiment

42 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

43 Thank you for your attention! Turkish-German Biogas Project Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH And Sokak No: 8/ ankaya/ankara, TURKEY T T E biogas-tr@giz.de I I Author: Birgit Pfeifer, International Biogas and Bioenergy entre of ompetence (IBBK) 43