Domestic sewage is the wastewater discharged from residents' daily life, mainly from residential buildings and public buildings, such as residences, institutions, schools, hospitals, shops, public places and industrial enterprise toilets. The pollutants contained in domestic sewage testing are mainly organic matter (such as protein, carbohydrate, fat, urea, ammonia nitrogen, etc.) and a large number of pathogenic microorganisms (such as parasite eggs and intestinal infectious viruses, etc.). The organic matter present in domestic sewage is extremely unstable and easily rots to produce stench. Bacteria and pathogens reproduce in large numbers using organic matter in domestic sewage as nutrients, which can lead to the spread of infectious diseases. Hazards of domestic sewage 1. Pathogen pollution mainly comes from urban domestic sewage, hospital sewage, garbage and surface runoff. The characteristics of pathogenic microorganisms are: ① large number; ② wide distribution; ③ long survival time; ④ rapid reproduction; Some pathogenic microorganisms and viruses can still survive in large numbers; such pollutants actually enter the human body through various channels and survive in the body, causing human diseases. 2. The common feature of aerobic organic pollutants is that these substances directly enter the water body and are decomposed into simple inorganic substances carbon dioxide and water through the biochemical action of microorganisms. During the decomposition process, dissolved oxygen in the water needs to be consumed. The lower pollutants will be corrupted and decomposed, and the water quality will deteriorate. These organic substances are often called aerobic organic substances. The more aerobic organic matter in the water body, the more oxygen consumption, and the worse the water quality, indicating that the water body is more polluted. 3. Eutrophication pollution is a phenomenon of water pollution caused by excessive plant nutrients such as nitrogen and phosphorus. Eutrophication of aquatic ecosystems through chemical pollutants? Depend on? Two pathways occur: one through the increase in the amount of inorganic nutrients that normally limit the plant; the other through the increase in organic matter that acts as a decomposer. 4. Odor Odor is a common pollution hazard, and it also occurs in polluted water bodies. There are more than 4,000 kinds of stench that people can smell, and dozens of them are more harmful. The hazards of stench are as follows: ① hinder normal respiratory function and reduce digestive function; mental irritability, reduced work efficiency, reduced judgment and memory; working and living in a foul smelling environment for a long time will cause olfactory disturbance, damage the central nervous system and cerebral cortex ② Some aquatic products are contaminated with stench and cannot be eaten or sold; ③ Smelly water cannot be used for swimming, fish farming or drinking, which destroys the use and value of water; ④ It can also produce hydrogen sulfide, formaldehyde, etc. Toxic hazard. 5. Acid, alkali, and salt pollution Acid and alkali pollution change the pH of the water body, destroy its buffering effect, eliminate or inhibit the growth of microorganisms, hinder the self-purification of the water body, and corrode bridges, ships, and fishing gear. Acids and alkalis often enter the same water body at the same time, and some salts can be produced after neutralization. From the perspective of pH value, acid and alkali pollution are self-purified due to neutralization, but various salts are produced, which become new pollutants in the water body. pollutants. Because the increase of inorganic salt can increase the osmotic pressure of water, which has adverse effects on the growth of freshwater organisms and plants. In salinized areas, the salt in surface water and groundwater will further harm the soil quality. 6. The hardness of groundwater increases. The hazards of high-hard water, especially permanent high-hardness water, are manifested in many aspects: it is unpalatable; it can cause digestive tract dysfunction, diarrhea, abortion of pregnant animals; it is inconvenient for people's daily use; it consumes a lot of energy; it affects the kettle , Boiler life; scaling in boiler water can easily cause explosion; softening and purification treatment is required, and the loss of acid, alkali and salt into the environment will cause the hardness of groundwater to increase, forming a vicious circle. 7. Pollution of toxic substances Domestic sewage detection Toxic substance pollution is a particularly important category of water pollution. There are many types, but the common feature is the toxicity and harm to biological organisms.