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Virtual laboratory: investigating water
qualities of local lake in CU campus
Water Quality in
CUHK
Data Analysis Skill
Environmental Science Module of Science &
Technology Curriculum
Location of 4 Sites for Collection of Water Samples
In CUHK a natural stream runs into an artificial lake called Weiyuan Lake. The
domestic sewage from the campus may contaminate the lake. Rain water serves as a
diluting agent. Water is then discharged to Tolo Harbour or recycled as flushing water.
Site description
Site A: Little bridge & flowing water
A natural stream comes from the hill and passes this site. Surrounded by
vegetation, the area is damp, moist and shady. Sewage from a nearby student
hall is discharged into this water body. Water flow was comparatively fast.
Site B: The exit of a drainage pipe from a nearby canteen
The pipe collects rainwater from the hills, but it may be contaminated by
wastewater discharged from a library, offices and a canteen. Patches of floating
green algae could be found but no fishes or shrimps were observed.
Site C: Bridge
Trees in the coast were not tall leaving the area as exposed and open. An oily layer
was found covering the water surface, making the water grey. But there were still
many fishes found.
Site D: Ditch near Fung Shu Cheun Building
Trees and bushes were planted near the site.
Via two main pipes water from the Weiyuan Lake is discharged into Tolo Harbour.
Ducks could be seen near the site. Their feces further contaminated this site.
Results of the samples quality
Site
Parameter
Light intensity (kilolux)
Temperature (OC)
pH
Dissolved oxygen
(mg/L)
Total bacteria count
(cfu/ml)
Coliform bacteria count
(cfu/ml)
A
1.877
18.1
6.81
6.48
B
5.213
17.3
6.95
5.57
C
7.537
19.2
5.84
5.00
D
7.111
18.8
6.91
5.68
1630
10100
800
1800
60
3900
20
800
cfu* ：colony forming unit
Light intensity difference: reflects the shadiness of the 4 sampling points.
Temperature: not much difference: no industrial activity around to discharge hot water.
pH: acceptable range. Not suffered from acid rain. Not hard water.
Standard pH value for Clean River: 6.0 – 9.0
The total bacteria count:
Site B > Sites D & A > Site C
Fecal coliform bacteria counts:
Site B > Site D > Site A > Site C
•
•
Site B: daily discharge of domestic sewage rich in nutrients
from a nearby canteen supports high population sizes of many
bacteria.
Site B: the high usage of toilets in the surrounding area
contributes to the high fecal coliform bacteria count.
Why is the highest total bacterial count in Site B?
Reasons show as follows:
Site B: Lots of organic pollutants are discharged from canteen and
offices and accumulate under slow stream condition. The pollutants
are food of bacteria.
Site C: Open and large water system. Rainwater and runoff
from a nearby stream will have a diluting effect on the sewage
collected from the campus.
Hong Kong Drinking Water Standard: <180 coliform bacteria/100mL
water (=<1.8 cfu/mL)
If for beach seawater grading system:
This water body could
NOT be used directly for
drinking.
Water Quality according to
Coliform bacterial counts:
Site A: Very poor
Site B: Very poor
Site C: Very poor
Site D: Very poor
NOR this water be used for
swimming sports.
Dissolved oxygen at 4 sites (5.00 – 6.48 mg/L):
Site A > Sites B & D > Site C
Reasons for the differences：
Site A : Fast stream. Less pollutants accumulate.
Site B : Large organic pollutants discharged and accumulate
under slow stream condition. Bacteria grows easily.
Site C : Oxygen cannot dissolve in water where oil floats on the
surface.
Site D : Watershed before discharging to Tolo Harbour. Large
organic pollutants accumulate.
Reasons for decline of dissolved oxygen
• In site B, the Total bacterial count is the highest.
• The water run out from canteen.
• High nutrient content  higher amount of bacteria decreased in DO
Standard D.O value for Clean River: ≧ 4
Dissolved oxygen (DO) represents the water quality. The range is
acceptable as found in natural unpolluted river water.
Recycle the flushing water in the campus
Is it a good method to recycle the flushing water ?
Sewage has high amount of bacteria which is not safe to
recycle. Well water can be used as flushing water in
Hong Kong.
In CUHK, this lake water is recycled for flushing as the
wastewater has been diluted with rain and incoming
river water. Further, primary treatment has been
implemented, and artificial aeration has been applied to
degrade the organic load in this lake water.
Contrast and compare ‘reuse’ and ‘recycle’. Reuse: use for the same purpose.
Recycle: use a waste as a raw material for another process.
Action taken: add primary treatment to the water before recycling.
Methods for improving the water quality:
• filter – remove the big substance and bacteria
• UV – kill bacteria
Methods not applicable to open water system.
The best solution is to deal with the source of the organic pollutants especially
nutrients. e.g. by introducing a predator-prey food web/chain.
Keep fishes and operates fishing activities. The fishes caught are not for food for
for leisure.
Dredging to remove the sediment which is a source of pollutants readily leaking
out pollutants.
Increase water flow or implement an aeration system.
Make a water lily pond to consume the nutrients in the aquatic system, and grow
water hyacinth to remove nutrients from water.
References
• 環境保護署 - 近期的河溪水質
http://www.info.gov.hk/epd/tc_chi/environmentinhk/water/
river_quality/rwq_recent.html
• 環境保護統計名詞定義
http://www.twdep.gov.tw/statistics/term/term03.htm
• Fecal Coliform and Escherichia coli.htm
http://www.geocities.com/RainForest/5055/fc.html
• Fecal coliforms
http://oh.water.usgs.gov/micro/fc.html
• Water quality
http://www.grc.nasa.gov/WWW/K12/fenlewis/Waterquality.html