MacRitchie Reservoir

AN OVERVIEW OF PUB SINGAPORE &

OUR WATER QUALITY CHALLENGES

Puah Aik Num

Chief Engineer, Water Supply (Plants) Department

www.pub.gov.sg

Presentation Overview

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1. Brief overview of Singapore & PUB

2. Brief overview of Choa Chu Kang Waterworks

3. Our water quality challenges

4. Feasibility study of the SIX® technology

MacRitchie Reservoir

About Singapore & PUB

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www.pub.gov.sg

Land Area ~719 km2

Population 5.6 mil

Average Annual Rainfall 2.328m

Average Water Demand 430MGD (1.95mil m3/day)

Singapore

Singapore

www.pub.gov.sg

Capture everydrop or water

Reuse water endlessly

Desalinateseawater

Technology & Innovation

Our Key Strategies

www.pub.gov.sg

Our Closed Water Loop

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www.pub.gov.sg

Our Four National Taps

www.pub.gov.sg

Capture Every Drop

• 17 Reservoirs• 2/3 Catchment Area• 8 Waterworks (including Johor River Waterworks)

Local Catchment

Choa Chu Kang Waterworks

MacRitchie Reservoir

Choa Chu Kang Waterworks

www.pub.gov.sg

Capture Every DropChoa Chu Kang Waterworks

Choa Chu Kang Waterworks

KranjiReservoir

PandanReservoir

TengehReservoir

• Serves the western catchment• 3 raw water sources• Capacity of 80 MGD

• 40 MGD Phase 1: Membranes• 40 MGD Phase 2: Sand filters

www.pub.gov.sg

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PHASE 1Completed : 1976 Capacity : 182,000 m3/day (40mgd)Upgraded to UF Membrane Filtration in 2008

PHASE 2Completed : 1981Capacity : 182,000 m3/day (40 mgd)

Kranji

Pandan

Tengeh

www.pub.gov.sg

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To Service

Reservoir

Pumping

Station

Raw water

Reservoirs

To Service

Reservoir

Screening

Immersed Ultra

Filtration

Lime

Alum

Clear Water

Tank

Lime

Sodium

Hypo

Chlorine

Contact Tank

Fluoride

Coagulation

& Flocculation

Sedimentation

CCK Phase 1 (Membranes)

Sodium

Hypo

AmmoniaSodium

Hypo

Raw water

Reservoirs

Sludge Treatment

Plant

Coagulation

& Flocculation

Sedimentation Sand Filtration

Sodium

Hypo

Lime

Fluoride

CCK Phase 2 (Sand Filters)

Ozone

Sodium

Hypo

Pumping

Station

Ammonia

Lime

AlumPolymerSodium

Hypo

Clear Water

TankScreening

Treatment Process

MacRitchie Reservoir

Our Water Quality Challenges

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www.pub.gov.sg

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High TOC in raw water risks the formation of Disinfection By-products

High algae counts, particularly blue-green algae counts, can result in aesthetic issues, e.g.

visual impact (algal scum) and undesirable taste and odour compounds (MIB & geosmin)

Jurong Lake

Tengeh CCKWW

Poyan

Murai

Sarimbun

Pandan• Indirect catchment• Low turnover in dry period• Blue-green algae growth• Higher TOC

Kranji• Nutrient loads from

agricultural catchment • Blue-green algae growth• Higher TOC

Tengeh-Poyan• Blue-green algae

growth• Higher TOC

Kranji

Pandan

Reservoir Water Quality Challenges

www.pub.gov.sg

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1 Jan 2012 1 Jan 2013 2 Jan 2014 3 Jan 2015 4 Jan 2016 4 Jan 2017 5 Jan 2018 6 Jan 2019 7 Jan 2020 7 Jan 2021 8 Jan 2022

TOC

(m

g/L

)

TOC Levels of Raw Water Sources

Kranji Pandan Tengeh Blended

Increasing TOC Levels of our Raw Waters

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2X in 10 years

www.pub.gov.sg

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1 Jan 2012 1 Jan 2013 2 Jan 2014 3 Jan 2015 4 Jan 2016 4 Jan 2017 5 Jan 2018 6 Jan 2019 7 Jan 2020 7 Jan 2021 8 Jan 2022

DO

C (

mg

/L)

DOC Levels of Raw Water Sources

Kranji Pandan Tengeh Blended

Increasing DOC Levels of our Raw Waters

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2X in 10 years

www.pub.gov.sg

Varying Quality of Raw Waters

Unique DOC profiles for each water source

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0 10 20 30 40 50 60 70 80 90 100

Rela

tiv

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ign

al

Resp

on

se

Retention Time (min)

Kranji

Pandan

Tengeh

Blended

Biopolymers

Humics

Building Blocks

LMW

www.pub.gov.sg

Impact of DOCs on CCKWW

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• Increase chlorine demand

• Increase membrane fouling

• Increase DBP / TTHM formation potential

• Higher nitrification potential in distribution network

www.pub.gov.sg

Current Control Measures

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• Operational tweaks

• For e.g. changing blending ratios, enhanced coagulation, maintaining a

narrow band for residual chlorine levels, etc.

• Process upgrading to enhance DOC removal

• Including upgrading of sand filters to ceramic membranes, and a new BAC

and ozone process

MacRitchie Reservoir

Feasibility Study of SIX®

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www.pub.gov.sg

Feasibility of SIX® at CCKWW

DOC removal by SIX®

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• A 6-month bench-scale trial of SIX® was done in CCKWW (Dec 2017 to Jun 2018)

• Results showed the following optimal operating conditions:

Resin concentration 15 – 20 mL/L

Contact time 30 minutes

DOC removal 42% for blended water

UVT increase 17.6% for blended water

www.pub.gov.sg

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Rel

ativ

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gnal

Res

po

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Retention Time (min)

Blended RW (6 Feb 18)

SIX (LL 15mL/L) (6 Feb 18)

Settled Water (1 Feb 18)

Blended RW (1 Feb 18)

LC-OCD Sample Analysis

DOC removal by SIX® vs coagulation

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Biopolymers

Humics

Building Blocks

LMW

SIX and coagulation target different DOC fractions.

www.pub.gov.sg

LC-OCD Sample Analysis

Further DOC removal using coagulation after SIX®

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0 10 20 30 40 50 60 70 80 90 100

Rel

ativ

e Si

gnal

Res

po

nse

Retention Time (min)

Blended RW (6 Feb 18)

SIX (LL 15mL/L) (6 Feb 18)

SIX-FeCl3 (10ppm) (7 Feb 18)

SIX-Alum (15ppm) (7 Feb 18)

Biopolymers

Humics

Building Blocks

LMW

Enhanced DOC removal using lesser coagulant.

www.pub.gov.sg

Feasibility of SIX® at CCKWW

Brine challenges

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• The regeneration process requires ~30 g/L NaCl solution

• A waste brine is generated:

Sewer discharge limits in Singapore:• TDS < 3,000 ppm• Cl- < 1,000 ppm

Amount of salt required 70 tonnes/day

Total amount of brine waste: ~2,346 m3/day

Chloride in the brine waste 6,150 ppm

TDS in the brine waste >6,150 ppm

*Values based on calculations for 80 MGD

www.pub.gov.sg

• Blending of brine with other waste streams

• On-site treatment of brine

• Discharging of brine into sea

• Injection into the ground

Feasibility of SIX® at CCKWW

Brine management options?

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IDEAS?

MacRitchie Reservoir

Thank you