principles of anaerobic wastewater treatment and sludge treatment jan bartáček ict prague...
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Sustainable approach to wastewater treatment Not only to dispose, but to reuse water raw materials energyTRANSCRIPT
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Principles of anaerobic wastewater treatment and sludge treatment
Jan BartáčekICT PragueDepartment of Water Technology and Environmental [email protected]
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Anaerobic digestion technology•Wastewater
▫wastewater treatment▫sludge stabilization
•Solid waste▫biogas plants▫landfilling with biogas collection
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Sustainable approach to wastewater treatmentNot only to dispose, but to reuse•water •raw materials •energy
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Transformation of pollution into biogas
aerobicWWT
BM anaerobicstabilization
WWWWT
BGanaerobic
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AD milestones•end of 19th century: beginning
(septic tank, biogas use)•mid-20th century : sludge stabilization •1970s oil crisis: interest in new
energy sources
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Anaerobic digestion (AD)• CxHyOz + a H2O b CH4 + c CO2 +
biomass• (S) H2S / S2-
• (N) NH3 / NH4+
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Anaerobic conditions
O2
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Oxidation-Reduction potential (ORP)•A measure of the tendency of chemical
species to acquire electrons and thereby be reduced
•Nernst equation
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Oxidation-Reduction potential (ORP)•Standard half-cell potential (E0)
▫ V▫F2(g) + 2e- 2F-
(aq) +2.87▫O3(g) + 2H+
(aq) + 2e- O2(g) + H2O(l)
+2.08▫AgCl(s) + e- Ag(s) + Cl-
(aq)
+0.22▫2 H+
(aq) + 2e- H2(g) 0.00
▫Fe2+(aq) + 2e- Fe(s) –0.44
▫Na+(aq) + e- Na(s) –2.71
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Oxidation-Reduction potential (ORP)•Standard half-cell potential (E0)
▫ V▫F2(g) + 2e- 2F-
(aq) +2.87▫O3(g) + 2H+
(aq) + 2e- O2(g) + H2O(l)
+2.08▫AgCl(s) + e- Ag(s) + Cl-
(aq) +0.22▫2 H+
(aq) + 2e- H2(g) 0.00▫Fe2+
(aq) + 2e- Fe(s) –0.44▫Na+
(aq) + e- Na(s) –2.71
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Oxidation-Reduction potential (ORP)•Standard half-cell potential (E0)
▫ V▫F2(g) + 2e- 2F-
(aq) +2.87▫O3(g) + 2H+
(aq) + 2e- O2(g) + H2O(l)
+2.08▫AgCl(s) + e- Ag(s) + Cl-
(aq) +0.22▫2 H+
(aq) + 2e- H2(g) 0.00▫Fe2+
(aq) + 2e- Fe(s) –0.44▫Na+
(aq) + e- Na(s) –2.71
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Processes at Biological WWTP
DenitrificationAnoxic oxidation
Oxic oxidation
Nitrification
Phosphate depolymerisationDesulphatation
Acidogenesis
Acetogenesis
Methanogenesis
ORPH
(mV)
-300
270
170
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Processes at Biological WWTP
DenitrificationAnoxic oxidation
Oxic oxidation
Nitrification
Phosphate depolymerisationDesulphatation
Acidogenesis
Acetogenesis
Methanogenesis
ORP’ (mV)
-500
+50
-50
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Anaerobic degradation of organic compounds
Proteins Polysaccharides Lipids
Alcohols, VFA
Acetic acids Hydrogen
Methane
Aminoacids Monosaccharides Fatty acidshydrolysis
acidogenesis
acetogenesis
methanogenesis
Hydrolytic bacteria
Synthrophic bacteria
Acidogenic bacteria
Methanogenic bacteria
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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
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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
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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.
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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)
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Anaerobic degradation of organic compounds
Proteins Polysaccharides Lipids
Alcohols, VFA
Acetic acids Hydrogen
Methane
Aminoacids Monosaccharides Fatty acidshydrolysis
acidogenesis
acetogenesis
methanogenesis
Hydrolytic bacteria
Synthrophic bacteria
Acidogenic bacteria
Methanogenic bacteria
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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
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Methanogenesis in nature
Methanogens in biofilm
Methanosarcina sp.
Methanosaeta sp.
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Anaerobic granular sludge
Sekiguchi et al. 1999 Applied And Environmental Microbiology, 65(3), 1280-1288.
Fernández, et al 2008. Chemosphere, 70(3), 462-474.
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Role of Hydrogen•Inhibition –
thermodynamic effect
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Role of Hydrogen•Inhibition –
thermodynamic effect▫C6H12O6 + 2H2O 2CH3COOH + 2CO2 +4H2 ▫C6H12O6 CH3CH2CH2COOH + 2CO2 +2H2 ▫C6H12O6 + 2H2 2CH3CH2COOH + 2H2O
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Role of Hydrogen•Inhibition –
thermodynamic effect▫C6H12O6 + 2H2O 2CH3COOH + 2CO2 +4H2 ▫C6H12O6 CH3CH2CH2COOH + 2CO2 +2H2 ▫C6H12O6 + 2H2 2CH3CH2COOH + 2H2O
Hard to degrade
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Role of Hydrogen
Reaction possible
Reaction impossible
Methanogenicniche
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Effect of temperature•Each species has its own optimum
psychrophilicmesophilic
thermophilichyperthermophilic
37 °C 55 °C
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Effect of pH•Most vulnerable are methanogens
•Extremely important buffering systems▫H2CO3 HCO3
- + H+ CO32- + 2 H+
▫NH3 ·H2O NH4+ + OH- NH3(aq) + H2O
Optimum pH
Methanogens 6.5 – 7.5Acidogens (e.g. Clostridium sp.)
4.5 – 7.5
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Effect of pH – buffering capacity
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Effect of pH – buffering capacity
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Acidification of anaerobic reactors•Frequent result of process instability
Methanogenic capacity exceeded
VFA increase
pH decreaseUnionized VFA increase
Toxicity increasePropionate increase
H2 pressure increase
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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
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COD Balance
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Comparison of the COD balance during anaerobic and aerobic treatment of wastewater containing organic pollution
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BiogasCH4 60 - 80 %CO2 20 - 40 %
( H2O, H2, H2S, N2, higher hydrocarbons, … )
Heat value 17 – 25 MJ/m3
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Biogas composition•Depends on Mean Oxidation State of
Carbon▫CnHaObNd + ¼(4n+1-2b-3d)O2 nCO2 +
(a/2-3d/2)H2O + dNH3
▫Cox.= (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
= 8/3-2/3Cox.
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Advantages of anaerobic WWT( in comparison with aerobic )
low energy consumption low biomass production high biomass concentration high organic loading rate low nutrients demand
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Limits of anaerobic WWT( in comparison with aerobic )
longer start-up higher sensitivity to change of conditions minimum nutrients removal need of post-treatment
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Principles of anaerobic wastewater treatment and sludge treatment
Jan BartáčekICT PragueDepartment of Water Technology and Environmental [email protected]