Evaluation of greenhouse gas emissions from municipal …Evaluation...emissions from municipal UASB...

Evaluation of greenhouse gas

emissions from municipal UASB

wastewater treatment plants

Original authors: B. Heffernan, J. Blanc, H. Spanjers

Jan Pereboom

Biothane Systems InternationalTel: +31.(0).15.27.00.121E-Mail: [email protected]

Contents

1. Introduction

2. Methods

3. Carbon footprint

4. OPEX

5. Conclusions

2

Introduction

1

4

Municipal UASB reactor

Sludge withdrawal pipe

Influent distribution pipes

GashoodInfluent distribution box

Gas Deflector

Sludge blanket

Effluent collection

Typical UASB process diagram

5

Sludge thickener Anaerobic digester Centrifuge

Sludge disposal

Biogas holder Electricity

Treated waterFinal settlerActivated sludgeUASB reactor

Raw wastewater

Influent pumping Coarse and fine screens Aerated grit chamber

Biogas scrubber Biogas flare

COD Conversion – Anaerobic vs Aerobic

Carbon Dioxide

Biomass

BODAir (O2)

Aerobic100 kg COD

Sludge, 30-40 kg COD

Heat loss

2-10 kg COD

BOD(25OC – 35OC)

Anaerobic100 kg COD

Biogas50-60 kg COD

Sludge 15-20 kg COD

30-40 kg COD

Advantages of municipal UASB

Capable of removing between 60 – 80% of COD, BOD and TSS

Very low operational costs

Low energy demand

Energy production in the form of biogas

Low sludge production

Low or no chemical consumption

7

Example – Top view of UASB reactor Onca, Brazil

SouthAmerica

Europe

North Asia

EastAsia

Southeast Asia

Oceania

South Asia

NorthAmerica

North America

South America

Africa

Middle East

12-56-50

Central Asia

Countries with municipal UASB treatment plants

The municipal UASB market

8Largest plant constructed to date 340 MLD (2009 India)

Countries with municipal UASB treatment plants

The municipal UASB market

9

74%

17%

3%

2%

1%1%

1%1%

India Brazil Mexico Columbia UAE Pakistan Honduras Indonesia Egypt

Largest plant constructed to date 340 MLD (2009 India)

10.012.014.016.018.020.022.024.026.028.030.0

5 10 15 20 25 30 35 40Dis

solv

ed

met

han

e c

on

cen

trat

ion

(m

g/l)

Temperature

Dissolved methane concentration as a function of temperature

Methane has a low solubility

Dissolved Methane estimations by Henry’s Law• Methane conc. (70 – 80%); Atmospheric 1 Bar; “Ambient” Temperature

Dissolved methane in effluent of municipal UASBs

COD determines Methane in effluent

11

Parameter Sewage Brewery Units

Flow 50,000 6,000 m3/d

COD 500 3,000 mg/l

Temperature 20 35 °C

Dissolved CH4 20 17 mg/l

Digested COD 55% 80% mg COD/l

Effluent COD 20% 15% mg COD/l

Sludge COD 25% 5% mg COD/l

Dissolved Methane in UASB effluents

COD determines Methane in effluent

12

Dissolved Methane in UASB effluents

29%

71%

Sewage

CH4 effluent CH4 gas phase

3%

97%

Brewery

CH4 effluent CH4 gas phase

Dissolved Methane in municipal UASB effluents

Up to 25 – 40% of the produced Methane in effluent• CH4 is a potent green house gas

• Valuable Energy is lost

13

Methods

2

Basis for carbon footprint analysis

Municipal plant for 1.0 mln population equivalents

Design sewage temperature was 25°C

Parameter Value

Flow (m3/d) 130,000

COD (mg/l) 600

BOD5 (mg/l) 300

TSS (mg/l) 315

NH4-N (mg/l) 35

Parameter Value

Flow (m3/d) -

COD (mg/l) 125

BOD5 (mg/l) 10

TSS (mg/l) 10

NH4-N (mg/l) 2

Influent characteristics Effluent requirements

15

Treatment options

UASB is pre-treatment • Aerobic post-treatment needed to meet effluent limits

1. Primary clarification• Primary clarification + activated sludge + digester

2. UASB with methane recovery• UASB + activated sludge + digester

3. UASB without methane recovery• UASB + activated sludge + digester

16

Treatment options

1. Primary clarification• Primary and secondary sludge are digested anaerobic

• Biogas is used for energy production

SettlerAerobic reactor

Screened and degritted sewage

Biogas engine

Primary clarifier

Dewatering unit

Sludge digester

17

Treatment options

2. UASB with methane recovery• UASB surplus sludge digested

• Methane in effluent recovered and utilised

18

Sludge digester



Biogas engine

UASB

Dewatering unit

Pre-aeration

reactor

Combustion gas

Treatment options

3. UASB without methane recovery• UASB surplus sludge digested

19

Sludge digester



Biogas engine

UASB

Dewatering unitCombustion gas

Emissions considered in carbon footprint

Upstream activities:

• The electricity emissions factor is country specific

• The emission factor for the UAE is 0.82 kg CO2 eq/kWh

• Electricity is used on site – excess is sent to grid

Chemical consumption (polymer)

Onsite activities:

• Distributed CH4 loss estimated at 1% for all three configurations

Downstream

• Sludge disposed to landfill with no CH4 recovery

20

Emissions not considered in carbon footprint

Upstream activities :

• Plant construction ; usually > 5% of emissions over lifetime

• CO2 produced in the treatment process (short cycle)

• N2O emissions (Ahn et al., 2010)

21

Direct and avoided emissions

Direct emissions are all green house gas emissions from STP:• Electricity generation

• Chemical consumption

Avoided emissions by sold by-products• Excess electricity that is sold to the grid

• Fertilizer based on removed N+P

Direct emissions are a positive number avoided are negative

22

Results

3

GHG emissions

UASB with CH4 recovery has the lowest carbon footprint

22,400

6,900

25,500

0 -4,200 -200

-10,000

-5,000

0

5,000

10,000

15,000

20,000

25,000

30,000

Primary clarification UASB with CH4 recovery UASB without CH4 recovery

To

ns

CO

2 e

q/y

GHG emissions for the three configurations

-10,000

-5,000

0

5,000

10,000

15,000

20,000

25,000

30,000


To

ns C

O2

eq

/y

India - High carbon power (0.994 kg CO2 eq/kWh)

Energy Process Reagents Sludge Avoided Emissions

Influence of electrical emission factor

25

-5,000

0

5,000

10,000

15,000

20,000

25,000

30,000


To

ns C

O2

eq

/y

Brazil - low carbon power (0.081 kg CO2 eq/kWh)



26

OPEX cost estimation

4

Basis for cost comparison

Cost price of electricity 0.12 $/kWh

Sales price of electricity 0.06 $/kWh

Sludge disposal cost 120 $/ton dry solids

Polymer dosing rate 10 kg PE/ton dry solids

Polymer cost 4500 $/ton PE

Technology Development

Energy production/consumption

29

0

500

1,000

1,500

2,000

2,500

3,000


Ele

ctri

city

pro

du

ctio

n/c

om

sum

pti

on

(kW

)

Electricity produced Electricity consumed

OPEX

30

$2,390,385

-$92,528

$222,833

-$500,000

$0

$500,000

$1,000,000

$1,500,000

$2,000,000

$2,500,000

$3,000,000


OP

EX (

US$

/yr)

Total Electricity cost Sludge disposal cost Polymer cost

Conclusions

4

Conclusions

The carbon footprint of a municipal UASB is worse than a conventional aerobic treatment plant

Methane recovery can make municipal UASB systems better than conventional aerobic treatment plants

Sludge disposal is an important consideration for the carbon footprint of a treatment plant

Methane recovery is also cost effective

32

Conclusions

Thank you for your attention

Questions

33

Limitations of municipal UASB

COD/SO4 ratio below 3 –Organic COD is converted to inorganic COD (H2S) in the UASB.

Strict nitrogen limits

Temperature –Below 15°C, the rate of anaerobic digestion is very low

Methane dissolved in effluent

34

Example – Top view of UASB reactor Onca, Brazil

SouthAmerica

NorthAmerica

UASB applicable

UASB non-applicable

Carbon constraint

Resource depletion:• As fossil fuels becomes scarcer

the cost of energy is likely to increase

35

Carbon taxes/Carbon credits:• As temperatures rise

governments are/will take action to reduce GHGs emissions

Detailed GHG emissions

Detailed breakdown of sources of CO2 emissions

43%

2% 2%

53%

0

22,370

-5,000

0

5,000

10,000

15,000

20,000

25,000

30,000


Total

Ton

s C

O2

eq

/y

Primary clarification

0% 20.5% 2%

77.5%

-4,200

6,850

-5,000

0

5,000

10,000

15,000

20,000

25,000

30,000


Total

Ton

s C

O2

eq

/y

UASB with CH4 recovery



0

79%

0.5%

20.5%

-200

25,450

-5,000

0

5,000

10,000

15,000

20,000

25,000

30,000


Total

To

ns C

O2

eq

/y

UASB without CH4 recovery



0.79

0.24

0.90

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

PC+AS UASBre+AS UASBno+AS

kg C

O2

eq

/kg

CO

D

Present study Keller and Hartely

Comparison with literature results

39

0.79

0.24

0.90

1.58

1.04

1.46

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

PC+AS UASBre+AS UASBno+AS

kg C

O2

eq

/kg

CO

D

Present study Keller and Hartely


40

SouthAmerica

NorthAmerica

Country Emission factor (kg CO2/kWh) Carbon power

Mexico 0.541 Medium

Brazil 0.081 Low

India 0.944 High

Egypt 0.470 Medium

UAE 0.820 High

Countries where municipal UASBs plants are in operation


Electrical emission factor• Varies depending on how electricity is produced

Country fuel mix determines the electrical emission factor

Three Electrical emission factor categories:• High carbon power

• Medium carbon power

• Low carbon power

41


42

-5,000

0

5,000

10,000

15,000

20,000

25,000

30,000


To

ns C

O2

eq

/y

Egypt - medium carbon power (0.447 kg CO2 eq/kWh)


Excess sludge production

43

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000


Exce

ss s

lud

g p

rod

uct

ion

(kg

TSS

/d)

Excess sludge production

Polymer dosing

44

0

10

20

30

40

50

60

70


Po

lym

er

do

sin

g (T

on

/y)

Polymer use

Evaluation of greenhouse gas emissions from municipal …Evaluation...emissions from municipal UASB...

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