Harmful substances in sewage

Harmful substances in sewage can be divided into three categories: heavy metals, pathogenic microorganisms and organic chemicals.

Heavy metals: including rust, sediments, lead, mercury, zinc, chromium, etc. Drinking water with excessive heavy metals can easily cause diseases such as bone pain, dementia and stones;

Pathogenic microorganisms: drinking water with excessive bacteria can easily cause cholera, hepatitis A, cold, SARS, avian influenza, infectious diseases, etc.

Organic chemicals: Organic chemicals such as chemical fertilizers, pesticides and residual chlorine in tap water can easily cause human cell mutation, tumor, deformity and other diseases.

Heavy metal wastewater refers to wastewater containing heavy metals discharged in industrial production processes such as mining and metallurgy, machinery manufacturing, chemical industry, electronics, instruments and meters. Wastewater containing heavy metals (such as cadmium, nickel, mercury and zinc). ) is one of the most serious industrial wastewater that pollutes the environment and harms human beings, and its water quality and quantity are related to production technology. In general, heavy metals in wastewater can not be decomposed and destroyed, but can only transfer their existing positions and change their physical and chemical forms. The treatment method is to reform the production process first, without using or using less toxic heavy metals. Chemical precipitation method and ion exchange method are often used for local treatment in the production site (if not discharged from the production workshop), and the treated heavy metals in the water can be discharged or reused if they are lower than the discharge standard. The new concentrated products of heavy metals should be recycled or treated harmlessly as much as possible.

Domestic sewage, sewage from livestock and poultry farms and wastewater from tanning, wool washing, slaughter and hospitals often contain various pathogens, such as viruses and germs. Pathogenic microorganisms refer to microorganisms that can invade the human body and cause infections and even infectious diseases, or pathogens. Among pathogens, bacteria and viruses are the most harmful. Pathogenic microorganisms refer to prions, parasites (protozoa, worms and medical insects), fungi, bacteria, spirochetes, mycoplasma, rickettsia, chlamydia and viruses.

Organic chemical wastewater is easy to cause eutrophication and is more harmful. Domestic sewage, food processing, papermaking and other industrial wastewater contain carbohydrates, protein, oil, lignin and other organic substances. These substances exist in sewage in suspended or dissolved state and can be decomposed by biochemical action of microorganisms. In the process of its decomposition, it needs to consume oxygen, so it is called oxygen-consuming pollutant. This pollutant will reduce the dissolved oxygen in water and affect the growth of fish and other aquatic organisms. After the dissolved oxygen in water is exhausted, the organic matter is decomposed anaerobically, which produces unpleasant smells such as hydrogen sulfide, ammonia and mercaptan, which makes the water quality worse. The composition of organic matter in water is very complex, and the concentration of oxygen-consuming organic matter is usually expressed by the amount of oxygen consumed by biochemical decomposition of oxygen-consuming substances in unit volume of water.

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