Water Treatment
11.75 In general treatment at waterworks comprises coagulation with alum and lime followed by rapid gravity filtration, sterilization using chlorine, pH value correction and fluoridation. At stations designed to treat water from the more polluted sources filtration is preceded by sedimentation and chlorination. At Sha Tin treatment works, activated carbon for control of taste and odour and poly-electrolytes to assist the clarification and filtration processes can also be dosed as and when required.
11.76 At Sha Tin and certain other stations, the replacement of part of the sand in the filters by a layer of graded crushed anthracite successfully increased filtration rates, and a report on performance was prepared.
11.77 Consumption of principal chemicals used in treatment was as follows:
Long tons Average dose in parts per million (p.p.m.) Alum 3,526 10.6 Hydrated lime 3,420 10.3 Liquid chlorine 537 1.6 Sodium silicofluoride 380 0.7 (as fluoride)11.78 The purity of treated water achieved, both chemically and bacteriologically, continued to be considerably higher than target standards recommended by the World Health Organization.
11.79 Generally, the supply is classified as soft, and low to moderate in salt content. The chemical quality in most areas is subject to some fluctuation according to the proportion of water abstracted from Plover Cove reservoir, which has a higher mineral content than water from other sources. Principal characteristics given in parts per million (p.p.m.) were as follows:
Average (1971-72 figures in brackets) Range Hardness (as CaCO3) 32 (43) 14-74 Salinity (as NaCl) 42 (100) 10-220 Total dissolved salts 101 (158) 42-314 ... 56 (...) 155Water Treatment
11.75 In general treatment at waterworks comprises coagulation with alum and lime followed by rapid gravity filtration, sterilization using chlorine, pH value correction and fluoridation. At stations designed to treat water from the more polluted sources filtration is preceded by sedimentation and chlorination. At Sha Tin treatment works activated carbon for control of taste and odour and poly- electrolytes to assist the clarification and filtration processes can also be dosed as and when required.
11.76 At Sha Tin and certain other stations the replacement of part of the sand in the filters by a layer of graded crushed anthracite successfully increased filtration rates and a report on performance was prepared.
11.77 Consumption of principal chemicals used in treatment was as follows:
Average dose
Alum
Hydrated lime Liquid chlorine
Sodium silicofluoride
Quality of Supply
...
Long tons
in parts per million (p.p.m.)
3,526
10.6
3,420
10.3
537
1.6
G
380
...
0.7 (as fluoride)
11.78 The purity of treated water achieved, both chemically and bacteriologically, continued to be considerably higher than target standards recommended by the World Health Organization.
11.79 Generally the supply is classified as soft, and low to moderate in salt content. The chemical quality in most areas is subject to some fluctuation according to the proportion of water abstracted from Plover Cove reservoir which has a higher mineral content than water from other sources. Principal characteristics given in parts per million (p.p.m.) were as follows:
Hardness (as CaCO3)
Salinity (as NaCl)
Total dissolved salts
Average (1971-72 figures in brackets)
32 (43)
Range
14 74
10-220
42-314
56 (100)
101 (158)
155
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