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@ U S T . H K
But it is a hugely complex task. How
to forecast the mixing and turbulent
vortices generated when, for example, a
discharge of treated sewage is expelled
into a tidal current or moving seawater
(described as a buoyant jet because
fresh water is lighter than seawater
and the discharge has momentum)?
And to predict turbulent buoyant shear
flow not only for one buoyant jet but for
hundreds of interacting buoyant jets?
World-leading
Predictive Modeling
In
seeking
to
expand
such
understanding, Prof Lee has contributed
a rigorous body of knowledge to
the fluid mechanics of buoyant jets,
publishing over 40 articles in leading
international journals to date and
authoring
Turbulent Jets and Plumes – A
Lagrangian Approach
(Springer 2003).
Prof Lee and his team have
also developed powerful tools to
assist global research and practice
in this area, including the JETLAG
mathematical model to predict the
initial mixing of an arbitrarily inclined
buoyant jet in a current over a wide
range of environmental conditions.
From this, the researchers went on to
develop VISJET computer ocean outfall
modeling and visualization software.
JETLAG/VISJET, now in use in
50 countries, is the only model in
the world that integrates accurate
predictions of multiple jets with three-
dimensional trajectories, including
multiple plume merging and interaction,
and advanced visualization technology.
It is particularly suited for application
in the heavily utilized shallow coastal
waters in Asia. The related basic
research received a prestigious 2010
State Scientific and Technological
Progress Award (Second Class) from
China's State Council.
Treated Effluent,
Chlorine Optimization
More recently, Prof Lee and his
researchers
have
utilized
their
expert knowledge of buoyant jets to
tackle a complex problem involving
chlorination of treated effluent. Since
2010, the treated effluent at Hong
Kong’s Stonecutters Island Sewage
Treatment Works, the world’s largest
chemically enhanced centralized
primary treatment (CEPT) plant, has
been disinfected by chlorination to
reduce the bacterial (
E. coli
) level and
protect the water quality of nearby
bathing beaches. The plant serves a
population of around 3.5 million, with a
daily average sewage flow of 1.8 million
CITY
~10 km
BEACH
Initial mixing
Turbulent dispersion,
bacterial decay
SEWAGE
PLUME
Harbor
Tidal current
Solar
radiation
Deep tunnels
Submarine outfall
SEWAGE
TREATMENT
WORKS
10-20 m
Sewage from 3.5 million people is conveyed to Stonecutters Island Sewage Treatment Works, the largest of its kind in the world, via a 23.6 km-long deep tunnel
system and is centrally treated by chemically enhanced primary treatment (CEPT). The treated effluent is discharged into the harbor in the form of multiple
rosette buoyant jet groups from an ocean outfall. VISJET provides a realistic simulation for the trajectory and dilution of such a complex diffuser.
Bacteria/pathogen loads are carried in the trapped sewage plume below the surface (in summer stratification) and transported by the tidal current while
undergoing turbulent mixing and decay before arriving at a bathing beach.
Rosette diffuser
VISJET simulation
How you formulate
a problem is very important
in engineering. We don’t
make a problem more
complicated than necessary.
We take a complex issue and
find a simple way of
solving it effectively
PROF JOSEPH HUN-WEI LEE
Elman Family Professor of
Engineering and Public Policy
Hong Kong Harbour AreaTreatment Scheme (HATS)
