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Sludge Treatment and Disposal in Singapore

KAN LOCK MENGSenior Manager

WATER RECLAMATION (PLANTS) DEPARTMENTSep 2011

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AGENDA

• Introduction

• Brief History

• Used Water System & Water Reclamation Process

• Sludge Thickening

• Sludge Dewatering

• Thermal Drying

• Sludge Disposal

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“To deliver and sustain a clean and healthy

environment and water resources for all in

Singapore.”

“To ensure an efficient,

adequate & sustainable

supply of water”

� Clean Water

“To ensure a sustainable quality

environment in Singapore”

� Clean Land

� Clean Air

� Public Health

Introduction - PUB

A Statutory Board constituted under the

Public Utilities Act 2001 to provide

integrated water supply, sewerage and

drainage services

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From sourcing, collection, purification and supply of drinking water, to treatment of used water and turning it into NEWater, drainage of storm water

Collection

of Rainfall

in Drains

&

Reservoirs

Treatment

of Raw to

Potable

Water

Collection

of Used

Water in

Sewers

Treatment

of Used

Water

Production

of

NEWater

SEARAINStormwater

Management

Supply of

Water to

Population &

Industries

Desalination

Introduction – Closing the Water Loop

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SingaporeSingaporeSingaporeSingapore

Land AreaLand AreaLand AreaLand Area 710 km710 km710 km710 km2222

PopulationPopulationPopulationPopulation 5.08 mil5.08 mil5.08 mil5.08 mil

Average Annual RainfallAverage Annual RainfallAverage Annual RainfallAverage Annual Rainfall 2,400 mm2,400 mm2,400 mm2,400 mm

Average Water DemandAverage Water DemandAverage Water DemandAverage Water Demand 1.6 mil m1.6 mil m1.6 mil m1.6 mil m3333/day/day/day/day

Singapore

Introduction – Singapore

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Sanitation

What’s Next?

Land Water

Reclamation

Energy

Key Drivers to Used Water Treatment

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Brief History

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Sanitation

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Year

Population

('000)

Population('000) Population served by night soil

Population served by modern sanitation

1987: Nightsoil

phased out

1997: 100%

modern sanitation

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• 1917 – First Trickling Filter Plant

• 1948 – First Activated Sludge Plant

• 1961 to 1981 – 5 additional Activated Sludge Plants

built to cater to:

• Rapid Industrialisation

• Development of New Towns (Public Housing)

• 1987 – Nightsoil bucket system totally phased out

Used Water System – Brief History

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Physical Evolution of Water Reclamation Plants

Albert

Street

P.Station

Park

Road

P.Statio

n

River Valley

P.Station

Alexandra

Sewage

Disposal

Works

1st sewers – 1910s

Alexandra Sewage Disposal Works

1st Water Reclamation Plant – Kim Chuan WRP

Covering up of WRPs – Ulu Pandan

Changi WRP -Compact Design

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Used Water Infrastructure before DTSS

Jurong WRP

Ulu Pandan WRP

Kranji WRP

Seletar WRP

Kim Chuan WRP

Bedok WRP

Water Reclamation Plants

Used Water Pumping StationsUsed Water Pumping Stations

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• Used water superhighway to meet needs for the future

• Sustainable solution to Singapore’s long-term needs for used

water collection, treatment, disposal and reclamation

• Integral part of Singapore’s water supply strategy

Phase 1

Phase 2

Used Water Infrastructure

- Deep Tunnel Sewerage System (DTSS)

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• Used water superhighway to meet needs for the future

• Sustainable solution to Singapore’s long-term needs for used

water collection, treatment, disposal and reclamation

• Integral part of Singapore’s water supply strategy

Kranji WRPSeletar WRPDecommissioned

Kim Chuan WRPDecommissioned

Bedok WRPDecommissioned

Changi WRP

Ulu Pandan WRP

Jurong WRP

Jurong Island

Transforming water management in Singapore –the Deep Tunnel Sewerage System

Present Used Water Infrastructure

- Completion of DTSS Phase 1

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Used Water System and

Water Reclamation Process

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Pumping

Pipes carry final effluent to the sea

SEWERlkw/jstw/98

Drains&

Rivers

Used Water System

PTP

Manhole

Households

Industries

Public Places Water Reclamation

Plants

Station

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Activated Sludge Process

Liquid Treatment

Solid Treatment

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Used Water and Sludge Treatment

CoarseScreen

InletPump

FineScreen

Vortex GritChamber

Grit

Primary SettlementTank

AerationTank

Final SettlementTank

ThickeningCentrifuge

Digester

Dual FuelGenerator

DewateringCentrifuge

DewateredSludge

Storage Bin

SludgeIncineration

Returned ActivatedSludge

ToSea

PrimarySludge

Waste ActivatedSludge

ThickeningCentrate

(To Inlet Works)

Primary & ThickenedSludge

BioGas

DigestedSludge

DewateringCentrate

(To Inlet Works)

Inlet Works

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Liquid Treatment

• Screens

• Primary Clarifiers

• Aeration Tanks

• Final Clarifiers

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Inlet Pump

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Screens

• Screen off large objects eg. rags,

stringy materials to

protect downstream

equipment

Fine Screen

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Primary Clarifiers

• Allow solids to

settle

• Solids are

removed as

sludge

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Aeration Tanks• Aerobic micro-organisms

break down organic matter

in used water

• Air is supplied to micro-

organisms

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Final Clarifiers

• Allow culture of

micro-organisms to

settle

• Treated used water is

� discharged to the

sea or

� reclaimed

• Settled solids are

removed as sludge

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Effluent Standard

• Activated Sludge Process

• Effluent standards for discharge to the sea:

BOD5 = 20 mg/L; SS = 30 mg/L

• Effluent standards for feed to NEWater:

Lower BOD5 & SS with NH3< 5 mg/L

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Solid Treatment

• Sludge Thickening

• Anaerobic Digestion

• Sludge Dewatering

• Thermal Drying

• Sludge Incineration

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Sludge Treatment Diagram

Thickening

Digestion Dewatering

Drying

Ultimate

DisposalDilute

Sludge

Typical Sludge Treatment Flow Diagram

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What is Sludge Treatment

• What is Sludge Treatment ?

– Treat to a stable form to render it safe for disposal

– Reduce moisture content to reduce handling cost

– Stabilise and reduce organic content

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Definition of Sludge

• also known as solids or biosolids

• generated from the process of purifying liquid waste/wastewater

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Anaerobic Digestion

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Digesters

• Anaerobic micro-

organisms break down

organic matter in sludge

• Biogas is produced

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Dual Fuel Generators

• Biogas is used as

fuel to generate

electricity

• Can provide

about 20% of

plant’s need

• Supplement to

electricity

imported from

the grid

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Benefits of Sludge Thickening

• Smaller capacity of tanks and

equipment required

• Lesser chemicals required for sludge

conditioning

• Lower piping and pumping costs for

sludge transferring

Thickening

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Sludge Dewatering

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Benefits of Dewatering

• The costs of transportation of sludge to the ultimate disposal site

become substantially lower when volume is reduced by dewatering.

• Dewatered sludge is easier to handle. Dewatered sludge can be

shoveled, moved about with tractors, fitted with buckets and blades,

and transported by belt conveyors.

• Enhance incineration by removing excess moisture and hence

increasing its calorific value.

• Dewatering is required prior to landfilling sludge to reduce leachate

production at the landfill site.

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Plate Press

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Dewatering Centrifuges

• Water is removed

from digested

sludge

• For ease of handling

and disposal

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Sludge Storage Silos

Dewatered Sludge

Send to

incineration

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Thermal Drying

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Thermal Drying

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Thermal Drying

• Thermal drying involves the application of heat to

evaporate water to reduce moisture content of the

biosolids (sludge).

• High level of drying is achievable with production of dried

sludge of up to 90 % dry solids content. Some heat

drying systems are able to produce dense and dried

sludge pellets which are easy to handle and to dispose

of.

• The advantages of heat drying include reduced

transportation cost, further pathogen reduction, and

improved storage capacity.

Products of heat drying:Dried and dense sludge pellets

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95%1000 m³ Sludge/day 150 m³/d 50m³/dDS = 3.0% DS = 20% DS = 92%

Volume Reduction:78%

Volume Reduction:85%

DEWATERING DRYING

Total Volume Reduction: 95 %

VOLUME REDUCTION BY SLUDGE DRYING

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Loads

10

Loads

2

Loads

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Sludge Disposal

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Land Application

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Options for Sludge Disposal

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SLUDGE INCINERATION

• Sustainable method

• Only incombustible ash remains

after sludge is incinerated

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MINERGY GLASS AGGREGATE

• Sludge is melted at temperatures >1500o C

• Toxic organic compounds are destroyed

• Produces an environmentally inert product

• Approved for use in US as construction material

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CRYSTALLISATION

• Patented crystallisation

process that converts sludge

to aggregates for land

reclamation

SYNTHETIC STONES/AGGREGATES

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PRODUCTION OF BIOFUEL

• Converts wood waste to

charcoal

• Waste heat can be used

to dry sludge

• Charcoal and dried

sludge is used to

produce electricity

Picture to be inserted

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SLURRY FRACTURE INJECTION

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Sludge Incineration

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Sludge Incineration at ECO

• Design:

To incinerate a combination of dried (90 to 95% DS) and

dewatered sludge (20 to 25% DS).

• Incineration process:

Step 1: The dried and dewatered sludge is premixed

Step 2: Premixed sludge is sent for drying

Step 3: After drying, it is incinerated.

The heat from the incineration process is recycled for

the drying process.

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Sludge Incineration Process

Sludge Drying

Sludge Incineration

Flue Gas Treatment

Wastewater Treatment

To environment

To public

sewer

PremixDried

Sludge

Dewatered Sludge

Ash:

1. Disposal at Pulau Semakau

2. Working on ash reuse

Recycling of Heat

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ECO Special Waste Management

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Future

• Use Green technology to reduce carbon dioxide emission.

• Convert sludge to recycle materials

• Tap on new emerging technoloy.

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Thank You