1. Principles of anaerobic wastewater treatment and sludge treatment Jan Bartáček ICT Prague Department of Water Technology and Environmental Engineering Jan.bartacek@vscht.cz

2. Anaerobic digestion technology Wastewater ▫wastewater treatment ▫sludge stabilization Solid waste ▫biogas plants ▫landfilling with biogas collection

3. Sustainable approach to wastewater treatment Not only to dispose, but to reuse water raw materials energy

4. Transformation of pollution into biogas aerobic WWT BM anaerobic stabilization WW WWT BG anaerobic

5. AD milestones end of 19th century: beginning (septic tank, biogas use) mid-20th century : sludge stabilization 1970s oil crisis:interest in new energy sources

6. Anaerobic digestion (AD) C x H y O z + a H 2 O  b CH 4 + c CO 2 + biomass (S)  H 2 S / S 2- (N)  NH 3 / NH 4 +

7. Anaerobic conditions O2O2

8. Oxidation-Reduction potential (ORP) A measure of the tendency of chemical species to acquire electrons and thereby be reduced Nernst equation

9. Oxidation-Reduction potential (ORP) Standard half-cell potential (E 0 ) ▫ V ▫F 2(g) + 2e -  2F - (aq) +2.87 ▫O 3(g) + 2H + (aq) + 2e -  O 2(g) + H 2 O (l) +2.08 ▫AgCl (s) + e -  Ag (s) + Cl - (aq) +0.22 ▫2 H + (aq) + 2e -  H 2(g) 0.00 ▫Fe 2+ (aq) + 2e -  Fe (s) –0.44 ▫Na + (aq) + e -  Na (s) –2.71

10. Oxidation-Reduction potential (ORP) Standard half-cell potential (E 0 ) ▫ V ▫F 2(g) + 2e -  2F - (aq) +2.87 ▫O 3(g) + 2H + (aq) + 2e -  O 2(g) + H 2 O (l) +2.08 ▫AgCl (s) + e -  Ag (s) + Cl - (aq) +0.22 ▫2 H + (aq) + 2e -  H 2(g) 0.00 ▫Fe 2+ (aq) + 2e -  Fe (s) –0.44 ▫Na + (aq) + e -  Na (s) –2.71

11. Oxidation-Reduction potential (ORP) Standard half-cell potential (E 0 ) ▫ V ▫F 2(g) + 2e -  2F - (aq) +2.87 ▫O 3(g) + 2H + (aq) + 2e -  O 2(g) + H 2 O (l) +2.08 ▫AgCl (s) + e -  Ag (s) + Cl - (aq) +0.22 ▫2 H + (aq) + 2e -  H 2(g) 0.00 ▫Fe 2+ (aq) + 2e -  Fe (s) –0.44 ▫Na + (aq) + e -  Na (s) –2.71

12. Processes at Biological WWTP Denitrification Anoxic oxidation Oxic oxidation Nitrification Phosphate depolymerisation Desulphatation Acidogenesis Acetogenesis Methanogenesis ORP H (mV) -300 270 170

13. Processes at Biological WWTP Denitrification Anoxic oxidation Oxic oxidation Nitrification Phosphate depolymerisation Desulphatation Acidogenesis Acetogenesis Methanogenesis ORP ’ (mV) -500 +50 -50

14. Anaerobic degradation of organic compounds Proteins Polysaccharides Lipids Alcohols, VFA Acetic acidsHydrogen Methane Aminoacids Monosaccharides Fatty acids hydrolysis acidogenesis acetogenesis methanogenesis Hydrolytic bacteria Synthrophic bacteria Acidogenic bacteria Methanogenic bacteria

15. Hydrolysis Polymeric substances  Oligomers Products of hydrolysis are suitable for transport into bacterial cells where they can be utilized. Extracellular hydrolytic enzymes Rate-limiting step for solid substrates Temperature sensitive

16. Acidogenesis Production of ▫volatile fatty acids (VFA) – namely acetic acid, propionic acid, butyric acid, valeric acid etc.) ▫alcohols – ethanol, butanol Large number of acidogenic bacteria (~1% of all known species), e.g. Clostridium, Enterobacter or Thermoanaerobacterium

17. Acetogenesis Specific functional groups – ▫Syntrophic acetogens ▫Homoacetogens Important part of the anaerobic microbial community VFA  acetic acid, hydrogen and carbon dioxide Homoacetogens ▫heterogenic group of bacteria ▫produce acetic acid from a mixture of low-carbon (mostly mono-carbon) compounds and hydrogen. ▫Carbon dioxide, carbon monoxide and methanol are the most important substrates.

18. Methanogenesis Methanogens - strictly anaerobic Archaea  (Methanococcus, Methanocaldococcus, Methanobacterium, Methanothermus, Methanosarcina, Methanosaeta and Methanopyrus) ▫Hydrogenotrophic m.  H2 + CO2  CH4+H2O ▫Acetotrophic m. (Acetoclastic m.)  CH3COOH  CH4 + CO2 Extremely sensitive (temperature, pH, toxicity)

19. Anaerobic degradation of organic compounds Proteins Polysaccharides Lipids Alcohols, VFA Acetic acidsHydrogen Methane Aminoacids Monosaccharides Fatty acids hydrolysis acidogenesis acetogenesis methanogenesis Hydrolytic bacteria Synthrophic bacteria Acidogenic bacteria Methanogenic bacteria

20. Methanogenesis in nature Probably the oldest mode of life Any organics-rich environment with low ORP ▫Sediments (freshwater or marine) ▫Wetlands/swamps ▫Guts of animals ▫Hot springs Able to adapt to extreme conditions ▫~15 – 100 °C ▫pH 3 – 9 ▫From halophiles to freshwater

21. Methanogenesis in nature Methanogens in biofilm Methanosarcina sp. Methanosaeta sp.

22. Anaerobic granular sludge Sekiguchi et al. 1999 Applied And Environmental Microbiology, 65(3), 1280-1288. Fernández, et al 2008. Chemosphere, 70(3), 462-474.

23. Role of Hydrogen Inhibition – thermodynamic effect

24. Role of Hydrogen Inhibition – thermodynamic effect ▫C 6 H 12 O 6 + 2 H 2 O  2CH 3 COOH + 2CO 2 +4H 2 ▫C 6 H 12 O 6  CH 3 CH 2 CH 2 COOH + 2CO 2 +2H 2 ▫C 6 H 12 O 6 + 2H 2  2CH 3 CH 2 COOH + 2H 2 O

25. Role of Hydrogen Inhibition – thermodynamic effect ▫C 6 H 12 O 6 + 2 H 2 O  2CH 3 COOH + 2CO 2 +4H 2 ▫C 6 H 12 O 6  CH 3 CH 2 CH 2 COOH + 2CO 2 +2H 2 ▫C 6 H 12 O 6 + 2H 2  2CH 3 CH 2 COOH + 2H 2 O Hard to degrade

26. Role of Hydrogen Reaction possible Reaction impossible Methanogenic niche

27. Effect of temperature Each species has its own optimum 37 °C55 °C

28. Effect of pH Most vulnerable are methanogens Extremely important buffering systems ▫H 2 CO 3  HCO 3 - + H+  CO 3 2- + 2 H + ▫NH 3 ­·H 2 O  NH 4 + + OH -  NH 3(aq) + H 2 O Optimum pH Methanogens6.5 – 7.5 Acidogens (e.g. Clostridium sp.)4.5 – 7.5

29. Effect of pH – buffering capacity

31. Acidification of anaerobic reactors Frequent result of process instability Methanogenic capacity exceeded VFA increase pH decrease Unionized VFA increase Toxicity increase Propionate increase H 2 pressure increase

32. COD Balance organic pollution is measured by the mass of oxygen needed for its chemical oxidation ▫“Chemical Oxygen Demand” (COD) COD expresses the amount of energy contained in organic compounds Can be used to asses energy flow

33. COD Balance

34. Comparison of the COD balance during anaerobic and aerobic treatment of wastewater containing organic pollution

35. Biogas CH460 - 80 % CO2 20 - 40 % ( H2O, H2, H2S, N2, higher hydrocarbons, … ) Heat value17 – 25 MJ/m3

36. Biogas composition Depends on Mean Oxidation State of Carbon ▫C n H a O b N d + ¼(4n+1-2b-3d)O 2  nCO 2 + (a/2- 3d/2)H 2 O + dNH 3 ▫C ox. = (2b-a+3d)/n ▫COD=8(4n+a-2b-3d)/(12n+a+16b+14d) ▫TOC=12n/(12n+a+16b+14d) ▫COD/TOC = 8/3+2(a-2b-3d)/3n = 8/3-2/3C ox.

37. Advantages of anaerobic WWT ( in comparison with aerobic )  low energy consumption  low biomass production  high biomass concentration  high organic loading rate  low nutrients demand

38. Limits of anaerobic WWT ( in comparison with aerobic )  longer start-up  higher sensitivity to change of conditions  minimum nutrients removal  need of post-treatment

39. Principles of anaerobic wastewater treatment and sludge treatment Jan Bartáček ICT Prague Department of Water Technology and Environmental Engineering Jan.bartacek@vscht.cz