4-消毒副产物

清华大学环境科学研究所
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Theory of Disinfection
Criteria
Applicable to Small Utilities Operator Skill (5 highest) Secondary Disinfectant Produce THM’s
Storage
清华大学环境科学研究所
Sedimentatio n basin
Sludge
To Distribution System
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Forms of Chlorine
Chlorine gas - preferred for medium to large disinfection systems Sodium Hypochlorite (liquid) - typically used for small disinfection systems and large swimming pools Calcium Hypochlorite (powder, tablet) typically used for private swimming pools
Alternative Disinfectants
Ozone (O3)
– very powerful oxidant – potent bactericide and viricide, kills cysts – no taste and odor problems – widely used in Europe – no residual – more expensive than chlorine (more economical when chlorine must be used with activated carbon)
清华大学环境科学研究所
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Consumers Guide to Drinking Water Quality
“The likelihood of such by-products forming can be greatly reduced by treating the water to lower levels of dissolved organic matter before chlorine is added for disinfection purposes”
清华大学环境科学研究所 http:// www.china-pops.net/, http:// www.china-popsorg/
Disinfection By-Products (DBPs)
Most concern is for bladder cancer Some concern for rectal cancers Suggested link with spontaneous abortions
“o ”表示为列入我国“水中优先控制污染物黑名单”的有 机物 “x”表示为列入美国“水中优先控制污染物黑名单”[2]
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Consumers Guide to Drinking Water Quality
Chlorine Reactions in Water
HOCl = H+ + OCl0 0 2 4 5
pK = 7.54 at 25oC
pH
10 15
HOCl
OCl-
pC
6 8 10 12
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前沿知识(4)
消毒副产物 Disinfection By-Products (DBPs)
清华大学环境科学研究所
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Surface Water Treatment
Screen Surface water from supply Rapid Flocculation Rapid Mix Basin Sand Filter Disinfection
清华大学环境科学研究所 http:// www.china-pops.net/, http:// www.china-popsorg/
某城市自来水中的DBPs
ox氯仿，ox四氯化碳，一溴二氯甲烷，1，1－ 二氯丙烷，ox溴仿六氯乙烷，o四氯乙烯，一 溴三环(4,3,1,1)+－烷，1－氯－2,3－二氢－ 1H－茚，1－氯基－2硝基苯，ox1,2－二氯苯 ，x1,3－二氯苯ox1,4－二氯苯，1,2,3－三氯 苯，1,2,4－三氯苯
Consumers Guide to Drinking Water Quality
“Chlorine’s main disadvantage is a tendency to react with naturally occurring dissolved organic matter to form chlorinated organic compounds” “The substances formed by the disinfectant reacting with the natural organic matter in the water are referred to as disinfection by- products”
Chlorine Ozone Chlorine Dioxide
Permanganate Chloramine
Peroxide
Ultraviolet
1
5
5
1
2
5
3
Produce Oxidised Organics Produce Halogenated Organics Produce Inorganic By-Products
清华大学环境科学研究所
http:// www.china-pops.net/, http:// www.china-popsorg/
清华大学环境科学研究所
http:// www.china-pops.net/, http:// www.china-popsorg/
Chlorine Reactions in Water
Cl2 (g) + H2O = HOCl + H+ + Cl– pH dependent – essentially complete within a few milliseconds
HOCl = H+ + OCl– HOCl is about 80 - 100 times more effective than is OCl- for E. Coli – [HOCl] + [OCl-] = free available chlorine
清华大学环境科学研究所 http:// www.china-pops.net/, http:// www.china-popsorg/
清华大学环境科学研究所
http:// www.china-pops.net/, http:// www.china-popsorg/
Chlorine dioxide (ClO2)
– potent bactericide and viricide – may produce toxic chlorate and chlorite – provides residual disinfection
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清华大学环境科学研究所 http:// www.china-pops.net/, http:// www.china-popsorg/
Alternative Disinfectants
Ultraviolet radiation
– effective bactericide and viricide – water must be free of turbidity and lamps free of slime and precipitates – no residual protection
“The risk of death from pathogens is at least 100 to 1000 times greater than the risk of cancer from disinfection byproducts” “The risk of illness from pathogens is at least 10 000 to 1000 000 times greater than the risk of cancer from disinfection byproducts”
清华大学环境科学研究所 http:// www.china-pops.net/, http:// www.china-popsorg/
Biblioteka Baidu
Disinfection By-Products (DBPs)
Trihalomethanes (THM’s) - first reported in drinking water in 1974 45 currently known DBP’s - 15 of which are potentially associated with Chlorine Countless DBPs have been identified and will continue to be identified ox氯仿，ox四氯化碳，一溴二氯甲烷，1，1－ 二氯丙烷，ox溴仿六氯乙烷，o四氯乙烯，一 溴三环(4,3,1,1)+－烷，1－氯－2,3－二氢－ 1H－茚，1－氯基－2硝基苯，ox1,2－二氯苯 ，x1,3－二氯苯ox1,4－二氯苯，1,2,3－三氯 苯，1,2,4－三氯苯
Other Forms of Chlorine
Hypochlorite salts
– NaOCl – Ca(OCl)2
Advantages/Disadvantages
– chlorine gas: cheaper, tends to decrease pH, reduces alkalinity – hypochlorite salts: more expensive, saver, always contain alkali to enhance stability, tend to raise pH
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Alternative Disinfectants
Chloramines (NH2Cl, NHCl2, NCl3)
– longer lifetimes in water – less effective oxidant – usually used in combination with other disinfectants