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
Principles of anaerobic wastewater treatment and sludge treatment
Jan BartáčekICT PragueDepartment of Water Technology and Environmental [email protected]
Anaerobic digestion technology•Wastewater
▫wastewater treatment▫sludge stabilization
•Solid waste▫biogas plants▫landfilling with biogas collection
Sustainable approach to wastewater treatmentNot only to dispose, but to reuse•water •raw materials •energy
Transformation of pollution into biogas
aerobicWWT
BM anaerobicstabilization
WWWWT
BGanaerobic
AD milestones•end of 19th century: beginning
(septic tank, biogas use)•mid-20th century : sludge stabilization •1970s oil crisis: interest in new
energy sources
Anaerobic digestion (AD)• CxHyOz + a H2O b CH4 + c CO2 +
biomass• (S) H2S / S2-
• (N) NH3 / NH4+
Anaerobic conditions
O2
Oxidation-Reduction potential (ORP)•A measure of the tendency of chemical
species to acquire electrons and thereby be reduced
•Nernst equation
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
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
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
Processes at Biological WWTP
DenitrificationAnoxic oxidation
Oxic oxidation
Nitrification
Phosphate depolymerisationDesulphatation
Acidogenesis
Acetogenesis
Methanogenesis
ORPH
(mV)
-300
270
170
Processes at Biological WWTP
DenitrificationAnoxic oxidation
Oxic oxidation
Nitrification
Phosphate depolymerisationDesulphatation
Acidogenesis
Acetogenesis
Methanogenesis
ORP’ (mV)
-500
+50
-50
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
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
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
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.
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)
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
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
Methanogenesis in nature
Methanogens in biofilm
Methanosarcina sp.
Methanosaeta sp.
Anaerobic granular sludge
Sekiguchi et al. 1999 Applied And Environmental Microbiology, 65(3), 1280-1288.
Fernández, et al 2008. Chemosphere, 70(3), 462-474.
Role of Hydrogen•Inhibition –
thermodynamic effect
Role of Hydrogen•Inhibition –
thermodynamic effect▫C6H12O6 + 2H2O 2CH3COOH + 2CO2 +4H2 ▫C6H12O6 CH3CH2CH2COOH + 2CO2 +2H2 ▫C6H12O6 + 2H2 2CH3CH2COOH + 2H2O
Role of Hydrogen•Inhibition –
thermodynamic effect▫C6H12O6 + 2H2O 2CH3COOH + 2CO2 +4H2 ▫C6H12O6 CH3CH2CH2COOH + 2CO2 +2H2 ▫C6H12O6 + 2H2 2CH3CH2COOH + 2H2O
Hard to degrade
Role of Hydrogen
Reaction possible
Reaction impossible
Methanogenicniche
Effect of temperature•Each species has its own optimum
psychrophilicmesophilic
thermophilichyperthermophilic
37 °C 55 °C
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
Effect of pH – buffering capacity
Effect of pH – buffering capacity
Acidification of anaerobic reactors•Frequent result of process instability
Methanogenic capacity exceeded
VFA increase
pH decreaseUnionized VFA increase
Toxicity increasePropionate increase
H2 pressure increase
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
COD Balance
Comparison of the COD balance during anaerobic and aerobic treatment of wastewater containing organic pollution
BiogasCH4 60 - 80 %CO2 20 - 40 %
( H2O, H2, H2S, N2, higher hydrocarbons, … )
Heat value 17 – 25 MJ/m3
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.
Advantages of anaerobic WWT( in comparison with aerobic )
low energy consumption low biomass production high biomass concentration high organic loading rate low nutrients demand
Limits of anaerobic WWT( in comparison with aerobic )
longer start-up higher sensitivity to change of conditions minimum nutrients removal need of post-treatment
Principles of anaerobic wastewater treatment and sludge treatment
Jan BartáčekICT PragueDepartment of Water Technology and Environmental [email protected]