Routine treatment of tap water quality inspection(2)

- Dec 11, 2019-

Turbidity tester3. The huge threat caused by pollution

3.1 Threats from raw water pollution

Today, most water plants that use surface water as the source of water mostly use conventional processes for coagulation, sedimentation, filtration, and disinfection. This classic physical and chemical treatment process has lasted for more than a hundred years, and all the changes are improvements in details such as the pool type. With the continuous increase of organic pollution in raw water, the conventional treatment process has obviously not adapted to the current state of raw water quality.

Because some organic pollutants are attached to the surface of the impurity particles such as clay in water, the hydrophilicity of the impurity particles is increased, the negative charge of the impurity colloid particles is improved, and it is more stable in the water. Therefore, most water purification plants generally use pre-chlorination methods to directly add a large amount of chlorine to raw water to oxidize organic pollutants in the water and make the water easy to coagulate and clarify. In order to obtain turbidity, color, phenol, iron, Indicators such as manganese meet the drinking water quality standards. However, during the pre-chlorination process, organic carbon such as humic acid and fulvic acid in the raw water is easy to be chlorinated and decarbonized, and forms trihalomethanes and other potential carcinogens such as chloroform, which will threaten people's health and safety. A large increase in trihalomethanes and other organic compounds such as chloroform in tap water must be highly vigilant.

3.2 Threats from water pollution caused by pipelines

3.2.1 Pipe material

 Due to the corrosive nature of water on metal pipe walls, it is easy to form scale mainly composed of iron oxide. Microorganisms and organic matter in the pipeline will adhere to the inner wall of the pipeline, which is prone to breed anaerobic bacteria, make the bacteria content exceed the standard, and pollute the water quality.

3.2.2 Pipeline auxiliary facilities and pipeline design and construction

 The auxiliary facilities such as control valves, drain valves, and fire hydrants in the pipeline network are often damaged by rain or other sewage due to being placed underground or in the open air for a long time. Once the pipeline network loses pressure, it will suck nearby underground sewage into the pipeline network, causing secondary pollution.

3.3.3 Pipeline velocity and network pressure are unstable

水 The velocity of water in the pipeline is too low, or the diameter of the pipe is too thick and there are few users. The residence time of water in the pipeline is too long, which promotes the oxidation deposition of iron and manganese, which accumulates more and affects the water quality.

4. Measures to control water pollution

4.1 Strict control over turbidity

 The purified water treated by the conventional treatment process may not meet the drinking water standards. Pretreatment and concentration treatment processes can be increased, such as the ozone method, activated carbon method, biological activated carbon method, contact oxidation method, and photooxidation method. For groundwater with high iron content, oxidation method, alkalization method, oxygenation and algae return method can be adopted; for high fluorine content, precipitation method and ion exchange method can be used. At the same time, the overall quality control of the water purification process should be strengthened, rational dosing, and automatic betting and dosing to improve the quality of water supply.

4.2 Deepening Pipe Network Management

Pipes should be selected from manufacturers with better product quality, and the pipes must have better inner walls, which can resist corrosion and do not precipitate harmful substances. In the design and construction, the water supply engineering design and construction specifications should be strictly adhered to, such as when the pipeline crosses other pipes, the minimum distance required by the specification should be guaranteed; when connecting with self-provided water sources or non-potable water pipelines, air blocking devices should be adopted, etc. Measures to prevent the pollution of drinking water; Because the ring pipe network has better water quality conditions than the tree-like pipeline, if economic conditions permit, the pipeline should be as circular as possible. Even if the tree is used, the pipeline should not be too long to avoid water stagnation at the end; The pipeline extension is too long, you should consider adding chlorine and regular flushing midway; the installation position of the drain valve should be reasonable, not to be submerged in water; it is forbidden to pump directly from the pipe network with a pump. In order to avoid negative pressure generated by the pipe network and infiltrate the dirt; in terms of maintenance and management, the water supply pipeline with a long service life shall be renovated or scraped and lined, and the pipe shall be flushed regularly, and the end of the pipe network shall be flushed at least once a year. The entire system is carried out every two years. Through reasonable management measures, water quality will no longer be polluted.

4.3 Improve the design and construction of secondary water supply facilities

In terms of design and construction, improve the technological structure of the pool, avoid the emergence of dead water zones, make the water form a push flow state, and maintain a certain flow rate; the volume of the living pool should not be too large to meet 40-60% of the daily water consumption. The inlet and outlet pipes should be set reasonably, and the water level control valve should be installed in the inlet pipe, and the overflow pipe should not be installed as much as possible. In terms of materials, pools are generally made of cement, and the inner wall and bottom should be smooth and flat. In terms of management, formulate administrative rules and regulations for urban secondary water supply management, establish a secondary water supply management system, and work with health and epidemic prevention departments to strengthen water quality monitoring and supervision. Users clean and disinfect water tanks and pools at least once a year, establish secondary water supply facility files, and improve the cycle supervision and management system. Measures to effectively solve the problem of water pollution in secondary water supply.

4.4 Reasonable chlorination

On the premise of ensuring the elimination of bacteria, viruses and other microorganisms in water, the dosage of chlorine should be minimized. The chlorination point should be moved to the next process as much as possible to achieve as many chlorination points as possible at the facility. In order to help maintain the residual chlorine in the pipe network, the residual chlorine in the factory water can be in the chloramine state, and it can be fully mixed with the factory water to maintain a contact time of more than 30 minutes. At the same time, it is necessary to strengthen water quality detection methods and strengthen continuous monitoring of the chlorine content in the factory water and the residual chlorine content of the pipe network. If the pipeline is too long and the residual chlorine is insufficient, consider adding chlorine midway. In addition, when the content of iron and manganese in the water is high, it should not be disinfected with chlorine, so as to avoid the precipitation of black-brown water. Improving the degree of chlorination automation is the key to achieve reasonable chlorination.

4.5 Strengthening the measurement and prediction of water quality in pipe networks

 In order to grasp the dynamic changes of the water quality of the pipe network, the water company should set up a continuous chlorine analyzer, a turbidity meter, and a bacterial analyzer at the sampling points of the pipe network. At present, the water quality forecasting software has been released. Based on the relationship between biodegradable organic matter, bacteria, residual chlorine, pH value, water temperature and other parameters and water quality changes, it can predict changes in residual chlorine and bacteria in the pipe network. Water quality provides the basis for decision-making.

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