ENERGY PRODUCTION FROM WASTEWATER
Barış ÇALLI Marmara University, Environmental Engineering Department
Goztepe, Istanbul, TURKEY
http://enve.eng.marmara.edu.tr
Wastewater
o Water carried wastes from residences, institutions,
commercial and industrial establishments.
o When it is allowed to go septic, the decomposition of the
organic matter it contains will lead to nuisance conditions
including the production of malodorous gasses.
o Wastewater also contains nutrients, which can stimulate
the growth of aquatic plants.
o May also contain toxic compounds or compounds that
potentially may be mutagenic or carcinogenic.
MetCalf and Eddy, 2003
Components of domestic wastewater
o Human waste (faeces, tissue paper, urine, etc.)
o Washing water (personal, clothes, floors, etc.)
o Rainfall collected on roofs, yards, etc. Sewage
o Ground water infiltrated into sewage pipes
o General urban rainfall run-off from roads, etc.
o Industrial cooling waters
o Agricultural run-off
o (Pre)treated industrial wastewater
o Water ( > 99.5%)
o Non pathogenic bacteria (>105 / ml)
o Pathogens (bacteria, viruses, protozoa, parasitic worms)
o Organic particles (faeces, hair, food, paper fibres, humus, etc.)
o Soluble organic material (fruit sugars, soluble proteins, drugs, etc.)
o Inorganic particles (sand, grit, metal particles, ceramics, etc)
o Soluble inorganic material (ammonia, sulfides, thiosulfates, etc.)
o Macro solids (sanitary towels, nappies/diapers, etc.)
o Gases (hydrogen sulfide, carbon dioxide, methane)
o Emulsions (oils in emulsion, paints, adhesives, etc.)
o Toxins (pesticides, herbicides, cyanide, etc )
Composition of sewage
SEWAGE
ORGANIC
(70%)
INORGANIC
(30%)
Proteins
(65%)
Carbohydrate
(25%)
Fats
(10%) Grit Salts Metals
Composition of sewage
Characteristics of sewage
Organic matter
Usually measured by BOD (Biological Oxygen Demand) or COD (Chemical
Oxygen Demand) and represents all organic compounds.
Typical BOD level is 250 mg/l.
Suspended solids Includes inert material such as sand and organic solids.
Typical level is 250 mg/l.
Nitrogen
compounds
Present as ammonia or urea and measured as TKN and NH4-N.
Typical TKN is up to 60 mg/l.
Phosphorus
compounds
Present in fecal matters and in detergents.
Typical Total phopshorus is 10-15 mg/l.
Microorganisms Measured by presence of E.coli (a type of bacteria found in intestines).
Typical E.Coli number is 107/100 ml
Heavy metals Present as Hg, Cd, Zn, Cu, Ni, Pb, Cr, Ag in trace amounts
Specific pollutants Compounds like LAS detergents, surfactants and phenols
Conventional WwTP - energy balance
Grit
SCREENS GRIT
REMOVAL
PRIMARY
SEDIMENTATION
FINAL
CLARIFIER
AERATION
TANK
SLUDGE
THICKENER
Primary
sludge
ANAEROBIC
DIGESTER
WAS
Digested
sludge
Discharge Sewage
Biogas
3.4 MJ
Digester
heating
1.2 MJ
Electricity
1.4 MJ
Sludge recycling
CHP unit
+12.5 MJ/kgCOD -1.1 MJ
2.1 MJ
3.8 MJ
8.7 MJ
Heat Loss
-5.5 MJ
5.9 MJ
-2.5 MJ
Imported electricity
+3.2 MJ/kgCOD
Energy loss
-0.5 MJ
Blower
Excess heat
0.3 MJ
1 MJ = 0.278 kWh
Energy consumption in WwTPs
Aeration, pumping and anaerobic sludge digestion operations are typically
the largest energy users.
WEF 2009, Energy Conservation in Water and Wastewater Treatment Facilities. Water Environment
Federation Manual of Practice No 32
Aerobic vs. anaerobic treatment
CODeff
Heat
Organic
matter
Oxidation
Cell synthesis
Energ
y
90%
10%
CH4
Excess
sludge
CODeff
Heat Oxidation
Energ
y
50%
Excess
sludge
Aerobic treatment Anaerobic treatment
CO2
Cell synthesis 50%
CO2
Organic
matter
+ O2
H2O
Energy usage for different aerobic treatment
processes
Logan B., 2009 (Clarke Laureate Lecture)
Aerobic Treatment Anerobic Treatment
Effluent quality GOOD POST TREATMENT
Start-up SHORT LONG
Process control EASY MORE STRINGENT
Sludge production HIGH (~5x) LOW (<1x)
Energy balance NO HEATING
AERATION (-)
HEATING (-)
BIOGAS (+)
Nutrient removal APPLICABLE IMPRACTICAL
Organic Loading RESTRICTED BY
TRANSFER OF O2
VERY HIGH
Aerobic vs. anaerobic treatment
LIMITATIONS
o Moderate BOD removal (80-90%)
o Necessity for nutrient (N and P) removal
o Slow start-up (up to 2-3 months)
o Stringent process control (pH, temp., alkalinity, ORP, etc.)
o Heating requirement (30-35 °C)
o Low efficiency in conversion of biogas to electricity (35-40%)
Anaerobic treatment
OPPORTUNITIES
o Separate collection of black and grey water
o Incorporation of ground-up kitchen wastes in sewage
o Use of membrane bioreactor processes
o Operation at lower temperatures (20-25 °C)
o Progresses in biogas purification/upgrading
o Use of innovative bioelectrochemical systems (BESs)
To increase
organic
load
Anaerobic treatment
Seperate collection and use of kitchen
disposer
Greywater
BATHROOM LAUNDRY WC KITCHEN
Blackwater+
Ground-up kitchen waste
Kitchen
disposer
Waste streams suitable for AD
o Organic fraction of municipal solid waste
o Sewage sludge
o Animal manure
o Fruit and vegetable processing waste
o Slaughterhouse and poultry wastes
o Yard waste and grass/grass silage
o Algae biomass
o Waste paper
o Industrial wastewaters (beverage, brewery, winery, dairy,
petrochemical, pharmaceutical, pulp and paper, textile, etc.)
Converting complex organics in wastewater
to useful energy outputs
Rittmann B. 2008 Biotechol Bioeng.100(2) 203-12
Bio-electrochemical Systems (BESs)
http://mfc-muri.usc.edu/images/public_images/how/how_MFC_animation.gif
Microbial fuel cell (MFC)
Microbial fuel cell (MFC)
Inlet
Outlet
Anode
chamber
Cathode
chamber
Magnetic
Stirrer
230
mL
230
mL
Reference
Electrode
(Ag/AgCl)
Reference
Electrode
(Ag/AgCl)
Proton Exchange Membrane
MEBiG, Marmara University, Environmental Biotechnology Group
http://mebig.marmara.edu.tr
Electron transfer to anode
ANODE
Electrically conductive
pili (nanowires)
(Shewanella)
e-
e-
Substrate CO2 + H2O
e-
Bacteria
e-
Cell-membrane-bound
cytochromes
(Geobacter)
e-
Substrate CO2 + H2O
e-
Bacteria
e-
Direct Transfer
Microbial
mediators
(e- shuttles)
e-
e-
Substrate CO2 + H2O
e-
Bacteria
e-
Bacteria
Medox
Medred
Medox
Medred
Mediator Driven Transfer
MFC electrode reactions
Redox Couple Eo (mV) vs. SHE
CO2/glucose -430
H+/H2 -410
CO2/acetate -280
So/H2S -280
CO2/CH4 -240
SO42-/H2S -220
Fe(CN)63-/Fe(CN)6
4- +360
NO3-/NO2
- +430
MnO2 (s)/Mn2+ +600
NO3-/N2 +740
Fe3+/Fe2+ +770
O2/H2O +820
V = 1.10 V
Eanode
Ecathode
∆G = 847.6 kJ/mol
[CH3COO-]=[HCO3-]=10 mM, pH 7, 298.15 oK, pO2 = 0.2 bar
Theoretical maximum voltage
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Anode: Acetate/CO2 (-0.28 V)
Cathode: O2/H2O (0.82 V)
Redox potential
vs SHE (V)
Theoretical
maximum
VMFC
(1.09 V)
Energy losses in MFCs
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Anode: Acetate/CO2 (-0.28 V)
Cathode: O2/H2O (0.82 V)
Redox potential
vs SHE (V)
VMFC
(0.5-0.6 V)
Energy loss
as a result of
internal
losses
Consumed by
anodophilic
bacteria
Rabaey K, Verstraete W (2005) Trends in Biotechnology 23:291-98
Ohmic losses
Activation losses
Bacterial metabolic losses
Concentration losses
Energy losses in MFCs
• Low Coulombic efficiency and power density
• High internal resistance (losses)
• Limited electrochemical COD removal
• Need for easily biodegradable organic substrate
• High maintenance and material (membrane, anode &
cathode electrodes, catalyst) costs
• Upscaling problems
Limitations of MFC technology
Estimated capital costs of MFCs
Rozendal RA. et al., 2008 Trends in Biotechol. 26(8) 450-59
Comparison of estimated capital costs and product revenues
Rozendal RA. et al., 2008 Trends in Biotechol. 26(8) 450-59
AD, anaerobic digestion; AS, activated sludge; MEC, microbial electrolysis cell;
MFC, microbial fuel cell
ENERGY PRODUCTION FROM WASTEWATER
Barış ÇALLI Marmara University, Environmental Engineering Department
Goztepe, Istanbul, TURKEY
http://enve.eng.marmara.edu.tr