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