Introduction into Digester Biology

Transcription

1 Introduction into Digester Biology Workshop for international experts Oberschleißheim, 12 October 2015 Katrin Kayser 1

2 Conversion process 1. biochemical 2. physical Organic matter Digester biogas CHP Electricity Heat dependent on efficiency factors! - Efficiency factor of the inputs Yield [m³ CH 4 /t ots] - Efficiency factor of the digester Productivity [m³ CH 4 /(m³rv d)] - Electrical efficiency factor [%] - Thermal efficiency factor [%] 2

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

4 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 H 2 /CO 2 Carbon dioxide CO 2 Biomass Polysaccharides Sugar, Amino acids, Biogas Methane CH 4 Proteins, Fats fatty acids Fatty acids ( acid (propionic alcohols Acetic acid acetic acid H2 H2 CH 4 /CO 2 Hydrolytic bacteria Acidogenic bacteria Acetogenic bacteria Methanogenic bacteria 4

5 Generation time of different bacteria Anaerobe Microorganisms Acid producing bacteria Bacterioides < 24 h. Clostridien 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. 5

6 The different degradation processes occur at the same time simultaneously In agricultural biogas plants the separation of the degradation stages plays a minor role strongly depend on 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 hydrolysis is the fastest, methane formation the slowest biogas digestate 6

7 Environment conditions of anaerobic degradation Measured variable Temperature ph value C:N-Relation Solid content Redox - potential Nutrient demand C:N:P:S Trace elements Hydrolysis/acidification 25 35º C 5,2 6, < 40 % DM mv 500 : 15 : 5 : 3 No specific requirements Methane formation Mesophilic: ºC Thermophilic: ºC 6,7 7, < 30 % DM < -250 mv 600 : 15 : 5 : 3 Essential: Ni, Co, Mo, Se FAL TB Environmental requirements for the fermentation of raw and residual substrates W CDR 7

8 The most important requirements for the biogas process Temperature ph-value Salt content Trace elements 8

9 Temperature ranges Thermophil (50-60 C) high gas yield after short retention time sensitive biocoenosis caution with rapid degradable substrates, (hydrolysis develops too fast) Mesophil (32-45 C) stable biocoenosis satisfying gas yield with acceptable retention time common, particularly in wet fermentation processes Psychrophil (< 25 C) low growth rate long retention times inefficient for biogas production no longer in use 9

10 ph-value and CO 2 -solubility outside 0,03 Vol-% CO 2 sampling inside approx. 40 Vol-% CO 2 Immediately after taking a sample, outside the digester CO 2 begins to escape. ph-value rises ph-value in the digester is lower than measured outside the digester! 10

11 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: Carbonate buffer, Ammonium buffer,... ph-value as sole parameter is not suited to evaluate the process It s a question of buffer! 11

12 Säure in [g / l FMI] Acidity in [g/l FM] ph-stability through buffer systems 10 Acidity Säureanalyse analysis 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 12

13 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 Correction on a temperature of 25 C If value is critical: add water 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) 13

14 Principles of the biogas process 1 The biogas process 2 Environmental conditions 3 Engineering process parameter 14

15 Functional principle Through hydrostatic pressure, liquid level is at the same height in the connecting pipe Overflow system communicating vessels Liquid levels balance themselves Overflow works 15

16 Fundamental process engineering parameters Dry Matter; DM (odm) Hydraulic retention time; T (HTR) Organic loading rate; B R Input Output 16

17 Solids Wet/ Fresh mass (FM) Solid matter content Solid content = Dry Matter [DM] Water content = organic Dry Matter or Volatile solids [odm; VS] (FM = fresh matter) Organic solids = Volatile solids [from % FM or % DM ] Mineral solids = ash (minerals) 17

18 (Hydraulic) Retention time T, HRT Digester volume = Work volume (gross volume without gas storage space) 18

19 (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 19

20 Organic loading rate B R Solids (DM, odm) load per m³ work volume and day Tendency for higher load 20

21 Example for calculation: Organic loading rate B R Substrate Substrate [t/a] odm [%FM] odm [t/a] odm [kg/d] Cattle manure ,0% Leftovers ,0% Chicken dry manure ,0% Grease waste ,0% Total Daily feeding of organic DM = 1926 kg Work volume = 800 m³ Process sensitivity increases with a larger organic loading rate 21

22 Gas productivity [m³ Gas /(m³ Fer. * d)] Gas yield [m³ Gas /kg odm] Critical organic loading rate and retention time Hydraulic retention time [d] 1 2 Critical hydraulic retention time and organic loading rate 2 Organic loading rate [kg odm/(m³*d)] 1 22

23 Be curious! Any questions? 23

24 Thank you for your attention! Speaker: Dipl.-Ing. Katrin Kayser IBBK Fachgruppe Biogas GmbH, Am Feuersee Kirchberg / Jagst, Germany k.kayser@biogas-zentrum.de Credentials: Birgit Pfeifer, bioreact GmbH 24

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