Outline 1. Introduction 2. Overview of chlorine disinfection - - PDF document

11/14/2017 1

Joseph Hun-wei Lee Hong Kong University of Science and Technology

Mixing of Chlorine Jets for Sewage Disinfection

Research & Development Forum Drainage Services Department November 14, 2017

Outline

1. Introduction 2. Overview of chlorine disinfection process in Stonecutters Island Sewage Treatment Works 3. Field scale model for study of mixing and rapid chlorine demand in disinfection of primary treated (CEPT) effluent 4. Theoretical modelling of dense chlorine jet – chlorine dosage optimization 5. Conclusions

11/14/2017 2  Chemically-enhanced primary treatment (CEPT) at Stonecutters Island Sewage Treatment Works (SCISTW)  Pollutants removal rate:  70% organics (BOD)  80% suspended solids  60% heavy metals  25% total nitrogen  50% phosphorus  E.coli:

• before disinfection: 50%
• after disinfection: 污水消毒

107 → 105 counts/100mL

HATS Stage 1/2A

Choi et al, Environmental Science and Technology, 2009

Harbour Area Treatment Scheme (HATS) 香港淨化海港計劃

Screening Plants/pumping stations Stonecutters Island Sewage Treatment Work (SCISTW) 昂船洲污水處理廠 Submarine

• utfall

排污口 23.6 km deep tunnels (>100m below ground level)

香港島 九龍 Stonecutters Island STW

Chemically Enhanced Primary Treatment (CEPT) since 2001; 23.6 km of deep tunnels; disinfection since March 2010 Stage 1: Q = 1.4 x 106 m3/d Stage 2A: Q = 1.8 x 106 m3/d

11/14/2017 3

General Layout of ADF

Chamber 15 Dechlorination Dosing Effluent Box Culverts 2 x 2.5 m x 2.5m

Stonecutters Island Sewage Treatment Work (SCISTW)

• Advance Disinfection Facilities – Stage 1

Sedimentation Tanks Main Pumping Station

Flow distribution Chamber Chlorine Dosing

FDC No. 2 Drop Shaft Dechlorination Compound (DC) Riser Shaft Overflow Culvert Chamber 15A Extension of Chamber 15 New Effluent Tunnel

Final Disinfection Facilities at SCISTW

Decommissioned box culvert Flow distribution Chamber (FDC)

• 6 nos. Sodium

Hypochlorite Storage Tanks 6

11/14/2017 4

Motivation for Chlorine Dosage Control

1. Excessive Total Residual Chlorine (TRC) is toxic to aquatic organisms 2. Disinfection by-products (chlorinated organic compounds) are harmful to marine environment 3. Complex interaction between chlorine dosage and CEPT sewage; unknown chlorine demand and disinfection efficiency at high concentration 4. Enhance sustainability: energy and operation costs 5. Environmental protection should be set at an adequate but not unnecessarily severe level Pollution belt resulting from indiscriminate discharge: natural turbulent mixing is slow – Yangtze River, 1995

11/14/2017 5

CEPT Effluent Dosing of sodium hypochlorite Dosing of sodium bisulphite Dechlorinated Effluent Existing box culvert as the chlorine contact system Discharge to Outfall

Chamber 15 Flow Distribution Chamber

SCISTW Chlorine Disinfection

Cl2 conc. (ppm) x (m) 10m 1km 105 10-20

Initial mixing Chlorine decay and 2 order bacterial kill

• Req. Dil.

~ 10000!

after disinfection: 107 → 105 count/100mL

Average chlorine Concentration = 12 mg/L (dry) = 18 mg/L (wet)

What happens actually …

• Most of the chlorine consumption has already taken place before Chamber 9; very low

TRC concentration at Chambers 9 and 15.

• Significant E.coli reduction is observed at Chamber 9; insignificant E.coli reduction

between Chamber 9 and 15

• The 1km culvert does not act as a chlorine contact chamber as expected.

Cl2 conc. (ppm) x (m) 10m 1km

105

10-20 ppm Few E.coli kill TRC << 1 FDC 1km culvert Chamber 15 Chamber 9 80% Chlorine consumed Expected Required Dilution ~ 10000!

11/14/2017 6

Vertical section view

1.7 m opening Submerged flow Free surface flow Dense Jets Dosing Unit 2.65mPD 0.85mPD

Flow Distribution Chamber (Chlorine dosing unit)

• An inclined weir of 1.8m

height in the middle of FDC

• 10% chlorine solution is

injected into the sewage flow through an array of dense jets in two layers

Chlorine dosing unit Weir 2  3.5m  3.5m inlet culvert from sedimentation tanks

Plan view

12.5m

Beaker Test vs Field Dosing

• The mixing processes are very different, inducing very different reaction processes
• Beaker test results may not represent the field condition

Beaker test

• Near-instantaneous mixing
• Limited reactants

Cl2 = 105 mg/L Conc.

CEPT Sewage 20 m3/s

Field Dosing

• Jet mixing, distance and time are required.
• Unlimited reactants

Conc.

11/14/2017 7 A “toy experiment” of chlorine jet in sewage coflow (Qiao et al. 2016)

50.3% 52.9% 44.0%

0% 20% 40% 60% 80% 100% 10% (N=9) 2% (N=8) 1% (N=7) Chlorine demand Source chlorine concentration (% w/w)

Cf = 600mg/L About half of the dosed chlorine is consumed by the chlorinated sewage in 4.5 seconds Similar significant chlorine demand for dosing at 10% or 1% chlorine (same chlorine mass flux) Chlorine jet Uj = 0.3m/s CEPT Sewage Ua = 0.1m/s Δx = 0.45m, Δt = 4.5s Outflow

Chlorine dosing unit Weir 2  3.5m  3.5m inlet culvert from sedimentation tanks

Plan view of FDC

12.5m

1/16 slice of FDC

The objectives are to study:

• the mixing achieved by the dosing unit in the FDC;
• chlorine demand at different key locations in the FDC;
• disinfection efficiency in the FDC; and
• degree of settling of organic solids in the FDC.

The 1:2 physical model represents a “1/16 slice” of the FDC treated sewage flow

1:2 Physical Scale Model (with prototype sewage and chlorine)

11/14/2017 8

1:2 FDC model

CEPT Sewage inflow from sedimentation tank Head tank Dosing unit Discharge of sodium hypochlorite solution Test flume Outlet tank

1:2 Physical Scale Model in SCISTW for study of chlorine mixing (1/16 slice of FDC sewage flow)

Chlorine dosing system (10% NaOCl solution)

Diaphragm pump Air chamber Chlorine Storage tank Safety valve To dosing unit

11/14/2017 9

Discharge of sugar solution in air Jet velocity

Dosing unit

Lower port D = 2.5mm Upper port D = 5mm

Dosing sugar solution ( = 1.168 g/mL) into cross flow in 1:2 model

Initial mixing of upper dosing jet with dyed sugar solution (tap water flow Qs = 60 L/s; Ua = 0.2 m/s; total jet discharge qd = 20 mL/s) Qiao et al. ASCE Journal of Hydraulic Engineering, 2017

11/14/2017 10

Head tank FDC weir Outflow over lateral weirs

Operation of the model flume with CEPT sewage

Flow distribution baffle

Sampling apparatus for TRC and bacteria above the weir (15 points)

0.11 0.11 Measuring point y=0.0 z y Right Center Left Flume bottom z=0.0 Weir plate top (z=0.9 m) Flume side wall Free surface 0.07 0.07 0.05 0.05 0.05 Weir crest

1D motorized vertical traverse for sampling Portable TRC photometer Sampling tube

11/14/2017 11 Summary of experiments on chlorine demand of CEPT sewage (10% NaOCl solution) Oct – Dec 2015

4 key runs with detailed TRC, bacteria and nutrient measurement

CFD modeling of the 1:2 scale FDC model

• 900,000 grid cells
• Free surface determined by

volume of fluid (VOF) method Dosing jet flow = 20mL/s C0 = 100,000 mg/L Δρ/ρ = 0.2

Ua = 0.36m/s Qu = 15.7mL/s Ql = 4.3mL/s

11/14/2017 12

Jet mixing of the chlorine with the sewage co-flow achieves a rapid dilution in the order

• f 1000-2000 in the FDC. This high dilution however falls short of the value required to

achieve full mixing (i.e. a dilution of 5000-10,000). Only approximately 60-80 percent of the sewage flow over the FDC weir is chlorinated.

Flume centreline Cross-sections

0.5 1 1.5 2 2.5 3 3.5 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 Inver level z=0.0 m FDC weir Distance from jet source x(m) Level z(m)  10% chlorine dosage flow 20 mL/s Upper Jet: qu=15.3 (mL/s) and Uj=1.20 (m/s) Low jet: qd=4.7 (mL/s) and Uj=1.50 (m/s) 100 L/s CEPT sewage flow Cm= 12.2 17.7 20.0 10.0 35.0 8.0 58.0 5.8

Measured TRC concentration (mg/L) distribution at the centreline section of FDC

Measured TRC mass flux and average TRC concentration along the flume

Measured cross-section TRC profiles: Qs = 100L/s and qd = 20 mL/s, 10% NaOCl solution

Lee et al. ASCE Journal of Environmental Engineering, 2017

11/14/2017 13

• Approximately 70-80% of the chlorine mass flux is

consumed within a very short distance (0.5-1 m, or a matter of several seconds) from the chlorine dosing unit, well upstream of the weir. Only a small fraction

• f the expected average concentration can be

measured in the sewage outflow from the FDC.

• The chlorine demand appears to be accompanied by

a decrease in ammonia nitrogen of around 4 mg/L.

• No settling and accumulation of chlorine solution or
• rganic solids in the FDC has been observed in the

model. Summary

There is a direct local correlation between TRC and E. coli. Overall there is a

• ne-log E. coli kill above the weir, within a short travel time of about 7-10s from

the chlorine injection. After immediate chlorine demand is satisfied, the residual (> 1.5 mg/L) can effectively disinfect the sewage by 2-log kill within contact time of about 5 minutes.

Correlation between local E. coli and TRC concentration above the weir

• E. coli concentration variation with contact time

at the downstream of the weir

11/14/2017 14

Mixing of dense jet in coflow (Chu & Lee 1996; Lee & Chu 2003)

A top-hat profile (uniform velocity in width B) is assumed in the model Spreading hypothesis of the top-hat half width

𝑒𝐶 𝑒𝑡 = 𝛾𝑡 𝑊−𝑉𝑏 cos 𝜚 𝑊

+ 𝛾𝑜

𝑉𝑏 sin 𝜚 𝑊

+𝛾∗

𝜏 𝑉𝑏

Ua, ρa, S0 U0, C0, ρ0 U(x) W(x) ds B(x) Coflow jet region Shear entrainment Gaussian conc. distribution Advected Line Thermal (ALT) region Vortex entrainment Vortex-pair conc. distribution

𝐺0 = 𝜍0 − 𝜍𝑏 𝜍𝑏 𝑕𝑟𝑒

𝑀𝑐 = 𝐺

0/𝑉𝑏 3 z x

D V(x) C(x), S(x)

𝑟𝑒 = ¼𝜌𝐸2𝑉0

ϕ z(x) s Shear entrainment Vortex entrainment Ambient turbulence σ = RMS velocity fluctuation ≈ 0.15Ua

Integral model of a reacting dense chlorine jet in sewage coflow (Chan et al. ASCE J. Environmental Engineering, 2017)

Spreading hypothesis (top-hat): Excess x-momentum flux:

𝛾𝑡 = 0.16 𝛾𝑜 = 0.4 𝛾∗ = 0.8

𝑒 𝑒𝑡 𝜌𝐶2𝑊 𝑉 − 𝑉𝑏 = 0 (1 + 𝑙𝑜) 𝑒 𝑒𝑡 𝜌𝐶2𝑊𝑋 = 𝐺0 𝑉𝑏 z-momentum flux: 𝑒 𝑒𝑡 ) 𝜌𝐶2𝑊(𝑇𝑏 − 𝑇 = 0 TRC mass flux:

𝑒 𝑒𝑡 𝜌𝐶2𝑊𝐷 = −𝑙𝐷𝑇(𝜌𝐶2)

Sewage “pollutant concentration”: Spreading coeff.: Added-mass coeff.:

𝑙𝑜 = 1

Trajectory: 𝑒𝑦 𝑒𝑡 = 𝑑𝑝𝑡𝜚 𝑒𝑨 𝑒𝑡 = sin 𝜚 Second order reaction

Ua, ρa, S0 U0, C0, ρ0 U(x) W(x) ds B(x) 𝐺0 = 𝜍0 − 𝜍𝑏 𝜍𝑏 𝑕𝑟𝑒 z x D V(x) C(x), S(x) 𝑟𝑒 = ¼𝜌𝐸2𝑉0 ϕ z(x) s

𝑒𝐶 𝑒𝑡 = 𝛾𝑡 𝑊−𝑉𝑏 cos 𝜚 𝑊

+ 𝛾𝑜

𝑉𝑏 sin 𝜚 𝑊

+𝛾∗

𝜏 𝑉𝑏

Solve for B, U, W, C, S and z(x)

11/14/2017 15

Modeling chlorine reaction with sewage

• A second-order reaction model (commonly used in chemical reactions) is used to

simulate the concentration-dependent chlorine reaction with sewage.

• C = TRC concentration (mg/L)
• k is a reaction rate dependent on TRC concentration, based on calibration with

experimental data. 𝜄𝑈−𝑈

0 = temperature dependent factor = 1.1T-20.

• A minimum decay rate of 0.01s-1 is set based on previous decay rate from

beaker tests.

• S is a “pollutant concentration” of sewage, defined as 1 in the ambient and

zero at the chlorine jet nozzle (zero loss of TRC). S represents the availability of reactants in the sewage 𝑒𝐷 𝑒𝑢 = −𝑙𝐷𝑇 𝑙 𝐷, 𝑈 = 𝜄𝑈−𝑈

0 ൝0.2580 ln(𝐷) − 0.7216

0.0044 for 𝐷 > 12.8 𝑛𝑕/𝑀 𝐷 ≤ 12.8𝑛𝑕/𝑀

The relation of k against measured average TRC is obtained from field experiment and further calibrated by comparing model result with measured TRC profile. (T ≈ 29oC)

3D CFD modeling

To predict and interpret the detailed TRC distribution in the FDC flume in the presence of solid boundaries. Solve 3D RANS equations (using VOF) and the advection-diffusion equation for TRC, using the decay coefficient calibrated from field data TRC distribution

11/14/2017 16 Comparison of CFD predicted and measured TRC profiles (10% undiluted chlorine solution, Qs = 100L/s, qc = 20mL/s)

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 20 40 60 80 z (m) TRC (mg/L)

S100C20 x = 0.5m

CFD

• Meas. Oct-30

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 10 20 30 40 50 TRC (mg/L)

S100C20 x = 1.0m

CFD

• Meas. Oct-29

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 10 20 30 40 50 TRC (mg/L)

S100C20 x = 1.5m

CFD

• Meas. Oct-29

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 10 20 30 40 50 TRC (mg/L)

S100C20 x = 2m

CFD

• Meas. Oct-29

0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 10 20 30 40 50 z (m) TRC (mg/L)

S100C20 x = 2.5m, weir

CFD

• Meas. 28-Oct

TRC Mass flux

Flume centerline

Prop roposed solu

• lutio

ion n for for re redu ducin ing g chl hlor

• rin

ine dem demand – pre pre-dilu ilutio ion n of

• f 10%

% chl hlorin rine solut

• lutio

ion

• As demonstrated from the field experiments, the injection of concentrated

10% chlorine solution using a two-jet dosing unit results in high chlorine demand - due to insufficient jet mixing with the ambient flow and fast chemical oxidations processes.

• Based on beaker tests and a bench flume model experiments, it was

suggested that discharging pre-diluted chlorine solution, say ~1%, into the FDC may decrease the extent of chlorine loss.

• Discharging the correspondingly increased dosing flows also led to an
• ptimized design of the dosing unit that uses more jets and resulting in a

much increased sewage contact with the injected chlorine.

• Various alternatives of chlorine dosage optimization are evaluated using the

mathematical models developed and then tested by experimentation in the field-scale model.

11/14/2017 17

Fi Field eld ex experim riment t usi using g pre pre-dil ilut uted d chl hlor

• rin

ine sol

• lut

utio ion n for for re redu ductio tion of

• f chl

hlorin rine dem demand

• A set of 42 experiments were conducted using chlorine solution of 1.25% to

10% chlorine concentration with the same chlorine dosage of 20 mg/L

• All tests were performed with a sewage flow rate of Qs = 100L/s (Ua =

0.36m/s).

• Initial screening of various options based on theory and experiments quickly

pointed to the use of 2.5% chlorine solution; focused tests were performed for this condition with an improved 4-jet (coflow) dosing unit to ensure repeatability over varying sewage conditions and temperatures.

• To determine the chlorine demand of the system, TRC concentration is

measured in the cross-section of the outflow from the FDC, above an end weir (at x = 2.5m) in a total of 21 sampling points in the flow cross-section above the weir.

Dos Dosing unit unit desi design n for for di diluted d chl hlor

• rin

ine sol

• lut

utio ion

Two Jet dosing unit for 10% chlorine solution Four Jet dosing unit for 2.5% chlorine solution

• Diluted chlorine solution with increased dosing flow to maintain the same total

chlorine mass flux (2 g/s)

• Initial jet velocity ~1.0 m/s

0.03 0.125 0.125 0.01 solution from Upper p di z=0.9

Por di z Por di z 0.01 0.125 0.125 0.03 di

qd = 20mL/s qd = 80mL/s 9mm dia. 5mm dia. 6mm dia.

11/14/2017 18

X Z

1 2 3 0.5 1 1.5

10000 5000 1000 500 100 50 10

Weir Dosing Unit

X Z

1 2 3 0.5 1 1.5

10000 5000 1000 500 100 50 10

Weir Dosing Unit

2-jet dosing unit (Du = 10mm, Dl = 9.4mm) 4-jet dosing unit (D = 6mm)

CFD prediction for 2.5% chlorine solution (qc = 80mL/s)

X Z

1 2 3 0.5 1 1.5

10000 5000 1000 500 100 50 10

Weir Dosing Unit

8-jet dosing unit (D = 4mm) Flume centerline Measured TRC profile at centerline above weir (T = 26.5oC) 2 jets 4 jets

Integral model predicted chlorine jet characteristics for 2.5% chlorine solution discharge in CEPT sewage (qd = 80 mL/s).

TRC Concentration TRC Mass flux TRC Concentration

11/14/2017 19

Reduction of chlorine demand by lowering source chlorine concentration: different pre-dilution options

• The dilution of source chlorine solution (maintaining same mass flux) can

effectively reduce the chlorine demand by about 15-20%

• Given site and operational constrains, the results suggest an optimal chlorine

dosing with pre-diluted 2.5% chlorine solution and a four-jet dosing unit.

Predicted (integral model) and meas. chlorine demand above the weir – coflow jets

Summ Summary on

• n re

redu ducin cing chl hlorin rine de demand d by by pre pre-dilu luted chl hlorine solu

• lution
• The dilution of source solution from 10% to 1.25% can effectively reduce the

chlorine demand by about 15-20%, demonstrated by extensive TRC flux measurement above the weir.

• For the case of 2.5% source solution, the chlorine demand can be reduced by

about 10-15% using a 4-jet dosing unit rather than a 2-jet dosing unit.

• The marginal benefit for using 1.25% chlorine solution is not significant

enough to justify a doubling of the flow (to 8qd), given the scarcity of freshwater resources and space constraints in SCISTW.

• The results suggest an optimal chlorine dosing with pre-diluted 2.5%

chlorine solution and a four-jet dosing unit.

• Sewage temperature may also have some effects on reaction kinetics and

thus chlorine demand. However, at a high chlorine condition, the reaction kinetics is mainly dictated by the chlorine level rather than by temperature fluctuations.

11/14/2017 20

Chlorine jet dosing above the weir

Utilize the intensive mixing by the weir overfall to supplement the initial jet mixing of the high concentration chlorine solution to reduce chlorine consumption by the ammonia and organics in sewage. Weir Dosing Jet above weir

x (m) z (m)

2 3 4 5 0.5 1 1.5

10000 1000 100 50 20 10 5 1

Streamlines TRC (mg/L)

Experimental study of chlorine jet dosing above the weir

(d)Downstream of weir (x=6.0 m)

z=0.65 m z=0.9 m

First-point dosing (x=0.0 m) Measuring section at x=6.0 m (a) Sketch of FDC model with second point dosing Measuring section at x=5.0 m Measuring section at x=4.5 m

0.6 m

x=2.5 m

(0,0) x z

CEPT sewage effluent Q0=100 L/s

1.265 m

Second-point dosing (x=2.4 or 2.25 m; z=0.95 or 1.05 m)

(c)Downstream of weir (x=5.0 m)

z=~0.6 m

z=0.5 m 0.4 m 0.3 m 0.2m (b)Downstream of weir (x=4.5 m)

FDC weir

• A two-point dosing system is installed in the 1:2 scale FDC model to

examine the chlorine demand for dosing jet discharging near the weir.

• Detailed measurement of TRC concentration distribution of the chlorinated

sewage flow downstream of the weir. Measurement locations

11/14/2017 21

(Parameters: Sewage flow=102 L/s, sewage temp.=29.5 0C chlorine dosing flow=18.5 mL/s, chlorine dose=18 mg/L)

Chlorine jet dosing close to the weir: supplement initial jet mixing with Turbulent plunging pool mixing: 10% NaOCl solution, August 04, 2017 Higher TRC level downstream of the weir with the chlorine jet discharging close to the weir

Dosing above weir Dosing upstream

5 10 15 20 25 30 35 40 45 5 10 15 20 25 30 35 40 45

Chlorine dose Cd (mg/L) TRC of mixed outflow C3 (mg/L)

Summary of chlorine demand of the FDC model tests (August to October 2017)

1:1

(Sewage flow=100 L/s, sewage temp.=27.5-30.5 0C, chlorine dosing flow=20-40 mL/s, 10% NaOCl solution)

Jet dosing above weir Original jet dosing location

Chlorine demand

11/14/2017 22

Point 1 Point 2 Sewage flow = 100 L/s Dosing flow = 20mL/s C0 = 10%, Ca = 20mg/L

Weir

y = 0.055m

Dosing Unit 2 Q_c = 10mL/s

x (m) z (m)

1 2 3 4 0.5 1 1.5

10000 1000 100 50 20 10 5 1

Two-point dosing

Dosing unit 1 Q = 10mL/s

CFD modeling

Dosing Options

• Pred. Avg TRC (x =

4.5m) Chlorine Demand (%, 25oC) 20oC 25oC 30oC Upstream (Existing) 5.0 3.0 1.8 85.0% One-point above weir 17.4 15.7 14.1 20.9% Two-point dosing U/S = D/S = 10 mL/s 14.9 13.6 12.2 31.9%

Weir

Centerline

Dosing Unit 1 Q_c = 20mL/s

x (m) z (m)

1 2 3 4 0.5 1 1.5

10000 1000 100 50 20 10 5 1

Single point dosing (original design)

Summary of tests on dosing above weir

• A larger portion of the chlorine dose is consumed in the

mixing process by the chemical reactions of chlorine with ammonia and organics, rather than for bacteria inactivation

• By discharging the chlorine jet of 10% NaOCl solution (~20

mg/L chlorine dose) close to the highly turbulent flow region downstream of the FDC weir, the chlorine consumption can be decreased by up to 20 percent.

• Mixing efficiency with second point dosing near the FDC weir

is higher than that with first point dosing; reflecting the additional mixing induced by the plunging pool of the weir

• verfall.

11/14/2017 23

Conclusion

• The chlorine demand of CEPT effluent has been studied in field scale

experiments using prototype sewage and chlorine dosing solution.

• Jet mixing is not able to achieve full mixing of the 10 percent chlorine

solution with the sewage flow in the flow distribution chamber. Only 60-70 percent of the sewage is in contact with chlorine.

• 70-80 percent of the chlorine mass flux is consumed within 5-10 seconds

from the source. The chlorine demand is due to oxidation of organic debris at the high concentrations, and not used in pathogen kill.

• Chlorine demand can be reduced by 10-15% by pre-diluting the sodium

hypochlorite solution to 2.5% or by relocating the chlorine jet to discharge

• ver the weir.
• The performance of chlorine jet discharge over the weir requires further

field experiments and research into chemical kinetics modelling.

46

Research Team Members

• Prof J H W Lee
• Prof Howard Huang
• Prof Stanley Lau
• Dr David K W Choi
• Dr Tree S N Chan
• Dr Q S Qiao
• Ms Mary Anne Borigas
• Mr Daniel Tsang
• Mr J K Yang
• Mr K H Cheng