精华 移民应该知道的事情: 核污染的遗产, 知道为什么当地人不吃从河里钓的鱼吗？
- 主题发起人 reine02
- 开始时间
- 注册
- 2012-02-27
- 消息
- 9,440
- 荣誉分数
- 2,120
- 声望点数
- 273
The City of Ottawa operates two treatment plants to supply drinking water – Lemieux Island Water Purification Plant (capacity: 400 ML/d; constructed 1931) and Britannia Water Purification Plant (capacity: 360 ML/d; constructed 1961). The source water for both plants is the Ottawa River. Both plants use identical water treatment processes and have undergone significant expansion and modernization over the years.
Raw water enters the treatment plants through large intake pipes that extend into the main flow of the river. The treatment process makes use of the “multiple barrier” principle. A series of treatment steps successively remove undesirable substances such as colour, suspended particles, algae, bacteria, and viruses from the water. The purification process in Ottawa consists of the following steps:
- coagulation (alum and sulphuric acid)
- flocculation (activated silica as a coagulant aid)
- sedimentation
- filtration (sand/anthracite)
- primary disinfection (sodium hypochlorite)
- pH correction (sodium hydroxide)
- secondary disinfection (chloramine)
- fluoridation (HFS)
http://ottawa.ca/sites/ottawa.ca/files/2012_annual_report_britannia.pdf
Drinking Water - Regulations
Environmental Protection Agency sets Maximum Contaminant Levels (MCLs) for inorganic chemicals such as arsenic, cadmium and mercury and synthetic organic chemicals such as benzene (an industrial chemical), PCBs, atrazine (an herbicide). Municipal drinking water supplies cannot contain any microorganisms which may originate in fecal matter (e.g. Escherichia coli , a species of bacteria found in the guts of humans and other warm blooded animals) because fecal contamination may carry pathogens and spread disease. Recent concerns relating to drinking water include the presence of protozoan pathogens (e.g. Giardia) and the creation of cancer-causing chemicals (trihalomethanes, THMs) when drinking water is chlorinated.
Drinking Water Treatment
At its simplest level, drinking water treatment seeks to remove turbidity (solids) and pathogens. Additional treatment may be applied to deal with specific problems, e.g. hardness and chemical contamination. The description of drinking water treatment which follows addresses the turbidity and pathogen issues and includes five steps: coagulation, flocculation, sedimentation, filtration and disinfection. Each of these terms will be defined and described in the following pages.
Drinking Water Treatment - Coagulation
Solids are removed by sedimentation (settling) followed by filtration. Small particles are not removed efficiently by sedimentation because they settle too slowly; they may also pass through filters. They would be easier to remove if they clumped together (coagulated) to form larger particles, but they don't because they have a negative charge and repel each other (like two north poles of a magnet).
In coagulation, we add a chemical such as alum which produces positive charges to neutralize the negative charges on the particles. Then the particles can stick together, forming larger particles which are more easily removed.
The coagulation process involves the addition of the chemical (e.g. alum) and then a rapid mixing to dissolve the chemical and distribute it evenly throughout the water.
[MEDIA]http://techalive.mtu.edu/meec/module03/documents/Coagulation.swf[/MEDIA]
Drinking Water Treatment - Flocculation
Now that the particles have a neutral charge and can stick together. The water flows into a tank with paddles that provide slow mixing and bring the small particles together to form larger particles called flocs. Mixing is done quite slowly and gently in the flocculation step. If the mixing is too fast, the flocs will break apart into small particles that are difficult to remove by sedimentation or filtration.
[MEDIA]http://techalive.mtu.edu/meec/module03/documents/Flocculation.swf[/MEDIA]
Drinking Water Treatment - Sedimentation
Next, the water flows to a tank called a sedimentation basin where gravity causes the flocs to settle to the bottom. Large particles settle more rapidly than small particles. It would take a very long time for ALL of the particles to settle out and that would mean we would need a VERY large sedimentation basin. So the clarified water, with most of the particles removed, moves on to the filtration step where the finer particles are removed.
[MEDIA]http://techalive.mtu.edu/meec/module03/documents/Sedimentation.swf[/MEDIA]
Drinking Water Treatment - Filtration
The filtration apparatus is a concrete box which contains sand (which does the filtering), gravel (which keeps the sand from getting out) and an underdrain (where the filtered water exits). After the filter is operated for a while, the sand becomes clogged with particles and must be backwashed. Flow through the filter is reversed and the sand and particles are suspended. The particles are lighter than the sand, so they rise up and are flushed from the system. When backwashing is complete, the sand settles down onto the gravel, flow is reversed and the process begins again.
[MEDIA]http://techalive.mtu.edu/meec/module03/documents/Filtration.swf[/MEDIA]
Drinking Water Treatment - Disinfection
With particles removed, it only remains to provide disinfection so that no pathogens remain in the water. Protozoan pathogens are large in size and have been removed with other particles. Bacteria and viruses are now destroyed by addition of a disinfectant, chlorine (the same chemical present in bleach). Enough chlorine is added so that some remains to go out in the water distribution system, protecting the public once the water leaves the plant.
[MEDIA]http://techalive.mtu.edu/meec/module03/documents/Disinfection.swf[/MEDIA]
Drinking Water Treatment - Softening
In areas where water comes into contact with limestone, there may be high levels of calcium and magnesium present. These chemicals make the water "hard", producing scale and soap scum. Hardness is removed by a process called softening. Two chemicals (lime, CaO and soda ash, Na2CO3 ) are added to the water, causing the calcium and magnesium to form a precipitate. This solid substance is then removed with the other particles by sedimentation and filtration.
The City of Ottawa operates two treatment plants to supply drinking water – Lemieux Island Water Purification Plant (capacity: 400 ML/d; constructed 1931) and Britannia Water Purification Plant (capacity: 360 ML/d; constructed 1961). The source water for both plants is the Ottawa River. Both plants use identical water treatment processes and have undergone significant expansion and modernization over the years.
Raw water enters the treatment plants through large intake pipes that extend into the main flow of the river. The treatment process makes use of the “multiple barrier” principle. A series of treatment steps successively remove undesirable substances such as colour, suspended particles, algae, bacteria, and viruses from the water. The purification process in Ottawa consists of the following steps:
During the final treatment step, fluoride is added for prevention of dental cavities, and chloramine (mixture of chlorine and ammonia) is added to preserve water quality as it travels through the vast water distribution system. The pH level is adjusted in order to minimize corrosion effects in the distribution system.
- coagulation (alum and sulphuric acid)
- flocculation (activated silica as a coagulant aid)
- sedimentation
- filtration (sand/anthracite)
- primary disinfection (sodium hypochlorite)
- pH correction (sodium hydroxide)
- secondary disinfection (chloramine)
- fluoridation (HFS)
http://ottawa.ca/sites/ottawa.ca/files/2012_annual_report_britannia.pdf
Drinking Water - Regulations
Environmental Protection Agency sets Maximum Contaminant Levels (MCLs) for inorganic chemicals such as arsenic, cadmium and mercury and synthetic organic chemicals such as benzene (an industrial chemical), PCBs, atrazine (an herbicide). Municipal drinking water supplies cannot contain any microorganisms which may originate in fecal matter (e.g. Escherichia coli , a species of bacteria found in the guts of humans and other warm blooded animals) because fecal contamination may carry pathogens and spread disease. Recent concerns relating to drinking water include the presence of protozoan pathogens (e.g. Giardia) and the creation of cancer-causing chemicals (trihalomethanes, THMs) when drinking water is chlorinated.
Drinking Water Treatment
At its simplest level, drinking water treatment seeks to remove turbidity (solids) and pathogens. Additional treatment may be applied to deal with specific problems, e.g. hardness and chemical contamination. The description of drinking water treatment which follows addresses the turbidity and pathogen issues and includes five steps: coagulation, flocculation, sedimentation, filtration and disinfection. Each of these terms will be defined and described in the following pages.
Drinking Water Treatment - Coagulation
Solids are removed by sedimentation (settling) followed by filtration. Small particles are not removed efficiently by sedimentation because they settle too slowly; they may also pass through filters. They would be easier to remove if they clumped together (coagulated) to form larger particles, but they don't because they have a negative charge and repel each other (like two north poles of a magnet).
In coagulation, we add a chemical such as alum which produces positive charges to neutralize the negative charges on the particles. Then the particles can stick together, forming larger particles which are more easily removed.
The coagulation process involves the addition of the chemical (e.g. alum) and then a rapid mixing to dissolve the chemical and distribute it evenly throughout the water.
http://techalive.mtu.edu/meec/module03/documents/Coagulation.swf
Drinking Water Treatment - Flocculation
Now that the particles have a neutral charge and can stick together. The water flows into a tank with paddles that provide slow mixing and bring the small particles together to form larger particles called flocs. Mixing is done quite slowly and gently in the flocculation step. If the mixing is too fast, the flocs will break apart into small particles that are difficult to remove by sedimentation or filtration.
http://techalive.mtu.edu/meec/module03/documents/Flocculation.swf
Drinking Water Treatment - Sedimentation
Next, the water flows to a tank called a sedimentation basin where gravity causes the flocs to settle to the bottom. Large particles settle more rapidly than small particles. It would take a very long time for ALL of the particles to settle out and that would mean we would need a VERY large sedimentation basin. So the clarified water, with most of the particles removed, moves on to the filtration step where the finer particles are removed.
http://techalive.mtu.edu/meec/module03/documents/Sedimentation.swf
Drinking Water Treatment - Filtration
The filtration apparatus is a concrete box which contains sand (which does the filtering), gravel (which keeps the sand from getting out) and an underdrain (where the filtered water exits). After the filter is operated for a while, the sand becomes clogged with particles and must be backwashed. Flow through the filter is reversed and the sand and particles are suspended. The particles are lighter than the sand, so they rise up and are flushed from the system. When backwashing is complete, the sand settles down onto the gravel, flow is reversed and the process begins again.
http://techalive.mtu.edu/meec/module03/documents/Filtration.swf
Drinking Water Treatment - Disinfection
With particles removed, it only remains to provide disinfection so that no pathogens remain in the water. Protozoan pathogens are large in size and have been removed with other particles. Bacteria and viruses are now destroyed by addition of a disinfectant, chlorine (the same chemical present in bleach). Enough chlorine is added so that some remains to go out in the water distribution system, protecting the public once the water leaves the plant.
http://techalive.mtu.edu/meec/module03/documents/Disinfection.swf
Drinking Water Treatment - Softening
In areas where water comes into contact with limestone, there may be high levels of calcium and magnesium present. These chemicals make the water "hard", producing scale and soap scum. Hardness is removed by a process called softening. Two chemicals (lime, CaO and soda ash, Na2CO3 ) are added to the water, causing the calcium and magnesium to form a precipitate. This solid substance is then removed with the other particles by sedimentation and filtration.
自来水主要就是做了去悬浮物和杀菌
但是去悬浮物和杀菌对于吃鱼的作用好像不是很大，除非是打算吃生鱼，我觉得吃鱼的最大的担心是重金属和有害化学物质，但是这个问题在自来水饮用上同样存在，所以与其担心鱼能不能吃，不如担心水能不能喝。话说鱼能吃多少，还有超市鱼可以选择，但是水就逃不掉了。
- 注册
- 2012-02-27
- 消息
- 9,440
- 荣誉分数
- 2,120
- 声望点数
- 273
mi123
新手上路
- 注册
- 2013-05-26
- 消息
- 13
- 荣誉分数
- 0
- 声望点数
- 11
谢谢楼主的知识普及。那这个地区的核实验室现在是关闭了还是一直在运行？ 我看了google地图，这个地区离ottawa是在是太太太的近了。那个下雨啥的，都能把核污水冲到ottawa river里，那在ottawa市里的桥上看到的波涛汹涌的河水，真的是有核污染的水？真的很震惊也~~~~~~~~~
- 注册
- 2012-02-27
- 消息
- 9,440
- 荣誉分数
- 2,120
- 声望点数
- 273
一直在运行。全世界所有医院放射科使用的放射同位素，几乎都是这里生产的。http://www.ottawacitizen.com/health...shipments+Chalk+River+near/8446302/story.html
渥太华属于核污染高危区，所以，大概10年前，建立了核污染实时监控系统，安装了探测器，24小时不间断遥测数据。下图是放射物探测器的安装位置分布图。圆圈内有!号的是在核设施区域和沿CHALK RIVER和Ottawa River的探测器，圆圈内有实心三角符号的，在渥太华市区。
让人担心的，主要是CHALK LAKE核设施经费不足，还有就是核废料储箱年代太久老化，已经有锈蚀，且处于地震带上。
