SESSION 1 – WASTEWATER MANAGEMENT

Innovative Sewage Infrastructure for Reinforcing

Sustainable Urban Development

- Largest Cavern STW in Hong Kong

Ir Echo LEONG

Executive Director, AECOM

2015.11.11

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Project Benefits

Relocated STSTW

Existing STSTW

Release premium river-front land for other

beneficial uses – As part of HK’s pursuit of

sustainable development

Currently, the project is at Investigation stage

The construction is scheduled in Q3 2017 for

commissioning in 2027

Existing STSTW

Footprint: 28 hectares

Treatment Level: Secondary

Treatment Capacity: 340,000 m3/d

Catchment Population: ~700,000

Nui Po Shan

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Design Considerations of Cavern STW

Special Attentions:

• System Hydraulics

• Cavern Configuration

• Fire Safety – access,

ventilation, protection

measures etc.

• Operation Safety – H2S,

aerosol, confined space etc.

• Construction Programme –

excavation volume, C&D waste

transport etc.

• Sewage and Sludge Treatment

Processes – reliability, cost

effectiveness, energy efficiency

etc.

Preliminary Layout

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Impact on Construction Programme

Cost Effectiveness – Life Cycle Cost

Tender Competition

Suitability for Cavern Installation

Technological Innovation

Process Reliability

Sludge Handling Requirements

O&M Requirements

Flexibility to Meet Future Design

Requirements

Energy Consumption and Carbon

Footprint

• Evaluation criteria and respective criterion weighting have

been discussed with relevant departments for a balance

view on the selection of the treatment processes for the

cavern STW

• Evaluation criteria for sewage treatment processes:

Process Evaluation Criteria

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Pilot Test Finish

Cavern Detailed Design

Cavern Construction Start for Commissioning

in 2027

Pilot Test Start

IDC Consultancy

Start

Project Programme

Q2‘15 Q3‘16 Q4 ‘16 Q2 ‘17 Q3 ‘17

• Updated technology review

• Updated life-cycle cost analysis

Interim Process Review 1

Treatment

Process

Confirmation

STW Layout Confirmation and Cavern

Requirements

Cavern Construction

Oct ‘14

First-hand operating experience in local conditions, including start-up and stabilization.

Pilot Study 3

Better understanding of process performance and O&M requirements

Technical Visit 2

Pilot test result will help optimizing process design

Design & Construction of Pilot Plants

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Potential Sewage Processes

• During the Feasibility Study stage, Compact Activated Sludge

(CAS) selected as preferred process for establishing the

baseline design

• Large footprint / cavern volume and potential high CAPEX could

be a key constraint to the Project

• Alternative compact treatment technologies identified for further

evaluation based on latest technological development and

requirements of the Project:

• Integrated Fixed-film Activated Sludge (IFAS)

• Moving Bed Biofilm Reactor (MBBR)

• Aerobic Granular Sludge (AGS)

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IFAS Process

Suspended Biomass

• BOD removal and denitrification

• MLSS: ~2,000 mg/L

• SRT: ~4 days

Attached Biomass

• Biofilm carriers in nitrification zone only

• Carrier fill rate – up to 65%

• Specific surface area of carriers: 500-1,200 m2/m3 (typical)

• Reduce the size of nitrification zone and have more stable

nitrification performance

Similar Operation

Requirements as

Activated Sludge

Process

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IFAS Process

• Commonly adopted for upgrading existing STWs with

conventional activated sludge

• Over 200 installations worldwide

Example: Marquette-Lez-Lille, France

• ADWF: 246,000 m3/d

• Population: 620,000 PE

• Start-up year: 2013

BioFilmChipTM M (1,200 m2/m3, 51% Fill)

• Compact design + Enhanced nitrification

• Flexibility for future expansion

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MBBR Process

• Attached growth for both C and N removal - compact reactor

• No sludge return – smaller energy use

• Max. allowed approaching velocity of 30 m/h – limit the reactor configuration

• Post solids removal (~200mg/L in MBBR reactor effluent) by dissolved air

flotation (DAF), high-rate clarification, sand filtration, disk filter etc.

Anoxic Zone

• Carrier fill rate – 50%

Aerobic Zone

• Carrier fill rate – 60%

• DO set point – 2 mg/L in BOD removal zone / 5 mg/L in nitrification zone

MBBR Process

SET AS

SET AS

MBBR Process

Example: Ytre Sandviken WWTP, Norway

• ADWF: 33,600 m3/d

• Population: 44,000 PE

• Start-up year: 2014

• AnoxKaldnes™ K3 Media (500

m2/m3) for BOD removal (42% Fill)

• First full-scale installation in early 1990s in Norway

• Over 400 installations worldwide

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AGS Process

• Simultaneous BOD, P and N-removal

• Simple one-tank concept - No sludge return, no

internal recycle, no clarifier, no moving

decanter, no mixer – lower energy demand,

smaller footprint

• Cycle time: 1 hr fill & decant / 1.5 hr reaction /

0.5 hr settle

• Hydraulic loading limit: 3.5 m/hr

• Good settling property (> 0.2 mm) & high

MLSS concentration (up to 15,000 mg/L) –

smaller reactor size

13 Courtesy Delft University of Technology

Aerobic Granular Biomass Activated Sludge

AGS Process

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AGS Overview

• First municipal installation in 2010 (Epe STP)

• 10+ full-scale municipal system in operation, with over 40

in design or under construction globally

Example: Garmerwolde WWTP, the Netherlands

• Population: 375,000 PE

• ADWF: 24,000m3/d; PWWF: 100,000m3/d

(AGS)

• Start-up year: 2013

• Compact footprint and energy efficiency

2 nos. 9,500m3 Nereda reactors

handle ~40% of the influent

A/B system handles

~60% of the influent

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Pilot Study at Existing STSTW

Study Objective

Assess the performance of two potential processes (MBBR and AGS)

under local conditions e.g. saline sewage and collect operation data for

process selection and full-scale design, if applicable

1. Proven Process - MBBR

• Verify treatment performance and energy consumption

• Optimize reactor configuration

• Identify O&M requirements

2. Emerging Process - AGS

• Verify treatment performance and energy consumption

• Assess granule stability and digestibility

• Identify O&M requirements

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SANI (Sulfate-reduction, Autotrophic-denitrification, and Nitrification

Integrated) process is a unique process, which makes use of the sulfate

ion available in the saline sewage from seawater toilet flushing in Hong

Kong to purify wastewater.

Source: HKUST

SANI® Process

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SANI® Process

Potential Benefits

• ~80% less biological sludge production

• ~35% energy saving

• No carbon requirement for Denitrification

Included in the Pilot Study

Objective for SANI

• To understand and collect more data of SANI

• Verify treatment performance and potential savings

• Identify design and O&M requirements for future implementation, if the

pilot study results are promising.

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Pilot Study at Existing STSTW

• Three pilot plants for MBBR, AGS and SANI processes will be

installed at the existing STSTW

• Approximate capacity of each pilot plant: 800-1,000 m3/day

• Tendering completed; currently at design stage

THANK YOU Relocation of Sha Tin Sewage Treatment Works to Caverns