Water resource shortage and water pollution
Causes of water resource shortage
(1) The development of science and technology relies on the excessive plundering of resources and excessive emissions. The total global population is increasing year by year, resulting in excessive water consumption, which makes water pollution increasingly serious and the existing resources unsustainable.
(2) Severe natural climate change and uneven rainfall have caused long-term drought in some areas, making production and life very difficult. On the contrary, in some areas, floods will occur during the flood season, which may endanger the property and life safety of the people.
(3) The urbanization process is speeding up, and the urban area accounts for less than 1% of the total area of the earth. So many people are concentrated on a small area of land, making the scarce water resources more difficult in the process of centralized supply.
Classification of water pollution
(1) Physical pollution is typically suspended solid pollution, which is the pollution caused by some wastes mixed with water and suspended in water. Secondly, there is thermal pollution caused by wastewater discharged by the factory for circulating cooling, and radioactive pollution caused by smelting and mining radioactive materials, etc.
(2) Chemical pollution is mainly divided into organic pollution and inorganic pollution. Organic pollution is the pollutant decomposed by oxygen consumption, which consumes the oxygen-rich in water and makes the animals and plants in the water unable to survive. Inorganic pollution is mainly acid-base pollution and heavy metal pollution, causing damage to body functions. Some plants will produce excessive nutrient element pollution, resulting in the eutrophication of water.
(3) Biological pollution comes from urban sewage, wastewater from biological products, etc. Most microorganisms in wastewater and sewage are harmless, but there are also pathogens that cause harm to the human body. If viruses and pathogenic microorganisms are produced, the water area will become the carrier of bacteria and a variety of infectious diseases will occur.
Common sewage treatment methods
Sewage treatment methods can be divided into physical treatment, chemical treatment, and biological treatment from the perspective of the reaction principle. Among them, the physical treatment method is more targeted at the pollution of suspended solids, and its applicability is relatively narrow. The chemical treatment method can only be applied to intractable wastewater with high concentration and high salinity. It is difficult to reach the discharge standard. After treatment, it will not work, and the cost is high. The biological treatment method is the most widely used method at present. It is very effective to treat wastewater with low concentration and can meet the discharge standard as required. Biological treatment mainly adopts the activated sludge method and biofilm method.
Activated sludge method
This method is similar to the natural self-purification process, but the effect is better. It has the best effect on industrial wastewater, urban sewage, etc. The activated sludge process includes three elements: microorganisms required for oxidation, decomposition, and adsorption, organic substances of sewage treatment objects, and the presence of dissolved oxygen in the treatment process. This method can be continuously adjusted and recycled according to the needs so that the content of sludge and microorganisms can maintain a moderate proportion, and the effect of organic matter decomposition can be achieved with the help of dissolved oxygen.
The biofilm process is comparable to the activated sludge process described above in terms of treatment technology. It mainly aims at colloid and dissolved organic pollutants. As the name implies, the biofilm method is to form a layer of biofilm on the surface. When this layer of biofilm contacts sewage, it will absorb the organic pollutants therein, and generate water, ammonia, carbon dioxide, and other substances after conversion, so as to achieve the effect of purifying water. The surface and interior of the biofilm are aerobic and anaerobic microorganisms respectively. When the biofilm thickness gradually increases, the anaerobic layer exceeds the aerobic layer, and this biofilm will fall off to form a new biofilm, completing a life cycle, and then maintaining the operating state.
Automation instruments in the sewage treatment process
In the process of sewage treatment, the control of pH value is more important. In the process of acid-base neutralization, the flow interference of incoming water should be controlled to achieve the control effect. Therefore, in the process of sewage treatment, a variety of automatic instruments should be used to coordinate the whole control process.
Level control instrument
At present, there are many kinds of liquid level control instruments, and the common one is the floating ball level gauge, which shows high reliability in actual operation and is very intuitive to observe, but it cannot be remotely controlled. In order to achieve remote control, the ultrasonic level gauge can be used, with low cost and a wide application range. After the liquid level signal is transmitted back, the height of the liquid level can be successfully displayed by connecting the display instrument.
Flow control instrument
Among the flow control instruments for sewage treatment, the electromagnetic flowmeter has the highest accuracy, with strong reliability and high accuracy. However, when the flow is not saturated and the pipeline is not full, the electromagnetic flowmeter will produce certain errors. The ultrasonic open channel flowmeter is used to measure the liquid level and then obtain the flow through the data processing of the internal microcontroller.
The pH index plays an important role in the sewage treatment process, which directly determines whether the process can be stable and smooth and whether the treatment effect can meet the discharge standard. The working principle of the pH meter is to calculate the pH value of the object to be treated through potential difference, that is, the measuring electrode in the object to be measured has a certain functional relationship with the reference electrode of constant potential, and the pH value of the object to be measured can be calculated by obtaining the potential difference. The electrode has many choices, and the glass electrode is the most widely used in sewage treatment.