How on earth is tap water polluted?

In the past few years, with the occurrence of water pollution events, such as water pollution, yellow water quality, odor and toxic equipment, the safety of tap water has become a personal concern.

In addition to the deterioration of water quality in water sources and the backward treatment technology in waterworks, there are also phenomena such as damaged water distribution network, aging secondary water supply facilities of water users and irregular cleaning. After these steps, the tap water with qualified water quality will be greatly polluted. Statistics show that there are about 1700 water pollution incidents in China every year, and how to ensure the safety of drinking water has become the focus of the whole society.

For example, at the end of May, 2065438+2004, blue-green algae pollution broke out again in Taihu Lake, which caused a large area of tap water in Wuxi to stink, and residents' domestic water was seriously tense, and bottled water in supermarkets and shopping malls was snapped up. The main cause of pollution is the accumulation of cyanobacteria near the water source, and a large number of malodorous substances such as NH3, mercaptan, sulfide and hydrogen sulfide are produced during anaerobic decomposition.

First, the water pollution situation

Surface water runoff and rivers are the main characteristics of material transport in the basin, water movement is the carrier of pollutant migration, and the main way for pollutants to reach the lake from the source is the water system in the basin. Mastering the hydrodynamic characteristics of river basins is the key and foundation of water environment management in river basins.

Several years, such as the Ministry of Science and Technology? 973? Scientific and technological breakthroughs have been made in key projects such as lake eutrophication process and cyanobacteria outbreak mechanism, water quality improvement, pollution source control and ecological reconstruction of heavily polluted lakes. However, the pollution of water sources is not optimistic.

The Ministry of Environmental Protection previously released a message saying: 4,929 monitoring stations in 198 prefecture-level administrative regions across the country show that nearly 60% of groundwater is? Poor? 16.8% monitoring points have extremely poor water quality. In China, 250 million residential areas are close to key sewage enterprises or main roads, and 280 million residents use unsafe drinking water. ? This result is shocking, but it is also expected. ? Fu Tao, director of Tsinghua University Water Policy Research Center, said that under the constraints of declining water quality, treatment technology of waterworks and aging pipe network, although the water quality of waterworks has reached the national standard, it does not mean that it is healthy water.

In June, 20 14, China Beverage reported that the upstream and coastal red lines of the Beijing-Tianjin water source area were not effectively protected, which led to littering around some water sources, indiscriminate mining and excavation of mines, water surface development and tourism, fish culture in cages, and serious water pollution, which led to the continuous relaxation of drinking water source standards.

Only one or two types of water can no longer meet people's drinking needs, and three types of water have also begun to be used as tap water sources. ? The water conservancy department announced that at present, the water quality of reservoirs 1 1% is not up to standard, the water quality of lakes is poor, only about 30% is up to standard, and the water quality of groundwater is only 40%.

Second, tap water purification treatment

The polluted water source is likely to contain a variety of toxic and harmful substances, such as microorganisms, radionuclides, nitrates, nitrites and heavy metals.

Chlorine in tap water is one of the pollution killers. At present, chlorine disinfection is widely used in the treatment of urban tap water in China, but the by-products of chlorine disinfection will form polymers harmful to human body, so the water treatment process is not suitable. Dirty? It is also worrying.

Scientists have proved that chlorine is the main factor leading to human cancer, heart disease and other diseases. Almost all water plants use traditional sedimentation and chlorination processes to treat tap water. In this process, chlorine combines with organic matter and humus to produce trihalomethane, haloacetic acid and so on. These are all more toxic pollution than chlorine.

On the basis of conventional water treatment, activated carbon adsorption is an economical and effective traditional process to remove various micro-pollutants in water. Common water treatment processes are:

Raw water (with coagulant) is clarified and filtered, and then purified water is adsorbed by activated carbon before leaving the factory.

Activated carbon mainly relies on its high adsorption capacity to effectively remove chlorine, abnormal color, odor, miscellaneous bacteria and heavy metals in water. Activated carbon is made of coconut shell, with uniform particles and a large number of micropores on the surface, forming a huge specific surface area. 1 g activated carbon can absorb dust particles, which is equivalent to 1.400 square meters. Activated carbon water filter is also the core of the most widely sold water purification products on the market.

Aluminum sulfate is a coagulant widely used in tap water treatment, and it is an economical method to remove suspended matter, colloid and chromaticity.

The water quality and safety index of the purified tap water can meet the national standards, but it is difficult to avoid secondary pollution in the process of delivery to the end users.

Third, the secondary pollution of tap water

The pollution sources of tap water secondary pollution mainly include water distribution network and secondary water supply system in residential areas.

After the tap water leaves the factory, it must pass through a long water distribution network and high-rise pools (boxes) and other intermediate facilities. In the process of transmission, there is a lot of pollution in the water. Rust, dirt, miscellaneous bacteria and heavy metals all directly affect the quality of tap water at the user's end. They interact and produce more toxic chemicals at the same time.

According to a statistical data, from 2000 to 2003, the water quality of pipe networks in 184 large and medium-sized cities in China was polluted 4323 times. Although the frequency of secondary pollution in urban pipe network has decreased in recent years, the pollution in suburban and rural areas has increased.

The common causes of secondary pollution are: first, pipeline aging and corrosion, miscellaneous bacteria breeding, pipe network leakage. If it is too close to the broken sewage pipe, it is more susceptible to pollution. Second, the pool (tank) is not cleaned and disinfected in time, sediment deposition, microbial growth, dead insects floating and so on. , once again aggravated the pollution of tap water. Among these secondary pollutions, the pollution of secondary water supply equipment is the most prominent.

Fourth, the pollution situation of secondary water supply equipment is worrying.

What does secondary water supply mean? Units or individuals use storage and pressurization equipment to store and pressurize urban public water supply before supplying it to users? .

In order to ensure the water supply of high-rise buildings, a reservoir (box) is set for secondary pressurization, and tap water stops here. The normal monitoring of health disease control departments does not include this link, and the sanitary conditions of some secondary water supply facilities are unsightly, which may easily lead to illness of drinkers.

Water supply enterprises will add a proper amount of chlorine to the factory water to achieve a certain sterilization effect in the municipal pipe network. However, people in the industry said that tap water is supplied to residents' homes from the factory. The last mile? Blind spot of pollution control.

Qiu Wenxin, chief engineer of Wuhan Water Group, who has investigated the secondary water supply facilities, said that the sanitary conditions of some secondary water supply facilities are unsightly. The secondary water supply facilities belong to property management, and the secondary water supply storage tanks in some communities are not cleaned all the year round, which has potential safety hazards. The pool with secondary water supply is easy to become a breeding ground for microorganisms, producing silt, moss and even red worms. This tap water smells bad, and drinking it directly is comparable to taking poison.

Five, the faucet heavy metal exceeds the standard.

Excessive heavy metals in faucets are also secondary pollution sources.

Did you use the first glass of water in the tap in the morning to brush your teeth and rinse your mouth? The quality spot check conducted by Shanghai Quality Supervision Department found that there were serious quality problems such as excessive precipitation of lead, manganese or hexavalent chromium in batch 10. Drinking the first glass of water in the morning is not recommended.

The results of the quality supervision and spot check of the water faucet products announced this time show that 23 of the 62 batches of products are unqualified, of which 10 contains lead, manganese or hexavalent chromium precipitation exceeding the standard.

Another monitoring result of basin, bathtub and shower head is not optimistic. The samples of 29 faucets sampled are not clearly marked on the outer packaging or instructions whether they can be used as drinking water. 19 samples exceeded the standard by 0.005 mg/L for lead, 0.0 1mg/L for manganese, and 0.005mg/L for hexavalent chromium in two samples. Is this faucet off? Water? , but poison.

Studies have shown that long-term use of faucets with excessive precipitation of heavy metals such as lead, manganese and hexavalent chromium as drinking water appliances will do harm to human health. If the faucet with too much heavy metal precipitation is mistakenly used in drinking water appliances, there will be greater safety hazards.

Six, tap water pollution control and solutions

The industry believes that solving the problem of drinking water pollution is not a one-off event. The whole society needs to participate, increase investment in environmental protection and governance, and let residents drink clean and healthy tap water as soon as possible.

1, water source protection, water source protection and isolation, to a certain extent, can ensure that the water quality of water source is not polluted, but it can not fundamentally solve the secondary pollution of water distribution network and high-rise water tanks.

2. Technical transformation of the water plant has optimized the water treatment technology and equipment of the water plant. At present, the investment in transformation is large, and it is difficult in many cities in a short time, especially the transformation of water distribution network.

3. Pipeline water supply and pipeline drinking water and graded non-drinking water. Domestic conditions are not yet mature and can only be limited to new residential areas. The construction of water supply by quality is difficult, the maintenance of pipe network is troublesome, and the investment is high, which is difficult for water price users to accept.

4. The home terminal water purifier can be directly installed on the pipes or faucets in residents' homes, so that tap water can be purified again, which is convenient to install and use, with obvious effect and low cost. Therefore, home terminal water purification equipment may be the most effective way for the public to solve tap water pollution.