Transcript PPT
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