Introduction to sewage

(1) Additive effect, that is, when two or more poisons coexist, the total effect is roughly the sum of the effects of each component.

(2) Synergistic effect, that is, when more than two poisons coexist, one component can promote a sharp increase in the toxicity of another component. For example, when copper and zinc coexist, their toxicity is 8 times that of when they exist alone.

3, antagonism, when more than two poisons coexist, their toxicity can offset part or most of it. For example, zinc can inhibit the toxicity of cadmium; For example, selenium can have antagonistic effect on mercury under certain conditions. In short, in addition to considering the content of toxic pollutants, it is also necessary to consider its existence and comprehensive effects, so as to fully understand the impact of pollutants on water quality and human health.

Toxic pollutants mainly fall into the following categories:

1. Heavy metals. Such as mercury, cadmium, chromium, lead, vanadium, cobalt, barium, etc., of which mercury, cadmium and lead are more harmful; Arsenic, selenium and beryllium are also more toxic. Heavy metals are generally not easy to disappear in nature, they can be enriched through the food chain; In addition to directly acting on the human body to cause disease, some metals may also promote the development of chronic diseases.

2, inorganic anions, mainly NO2-, F-, CN- ions. NO2- is a carcinogen. Cyanide, a highly toxic substance, mainly comes from industrial wastewater discharge.

3, organic pesticides, polychlorinated biphenyls. There are about 6,000 kinds of organic pesticides in the world, and about 200 kinds are commonly used. Pesticides sprayed in farmland, through leaching and other effects into the water, resulting in pollution. Organic pesticides can be divided into organophosphorus pesticides and organochlorine pesticides. Although the toxicity of organophosphorus pesticides is high, it is easy to degrade and accumulation is not strong, so the impact on the ecosystem is not obvious. The vast majority of organochlorine pesticides have high toxicity, almost no degradation, and high accumulation, which have a significant impact on the ecosystem. Polychlorinated biphenyls (PCB) is a general term for various isomer mixtures formed after some or all of the hydrogen in the biphenyls molecule is replaced by chlorine. Polychlorinated biphenyls are highly toxic, fat soluble, easy to be absorbed by biology, chemical properties are very stable, difficult to and acids, bases, oxidants and other effects, have a high degree of heat resistance, in 1000 ~ 1400℃ high temperature to completely decompose, so it is difficult to degrade in water and biology.

4. Carcinogens. Carcinogens are generally divided into three categories: thick cyclic aromatic hydrocarbons (PAHs), such as 3, 4-benzopyrene; Heterocyclic compounds, such as aflatoxin; Aromatic amines, such as methyl, ethylaniline, benzidine, etc.

5. General organic matter. For example, there are more than 2000 kinds of phenolic compounds, the simplest is phenol, which are highly toxic substances; Nitrile compounds are also toxic, of which acrylonitrile has the most notable environmental impact.

Petroleum pollutant

Oil pollution is one of the important types of water pollution, especially in estuarine and offshore waters. The impact of oil pollution [4] on people is also gradually far-reaching. Oil pollution of the sea has become a serious problem in the world... Petroleum Petroleum, also known as crude oil, is a brown-black flammable viscous liquid extracted from deep underground. The amount of oil released into the ocean is estimated to be between millions and tens of millions of tons per year, or about five-thousandths of the world's total oil production. Oil pollutants mainly come from industrial discharge, which can be caused by cleaning the cabins and machinery of oil transport vessels, accidents and offshore oil production. The accident of oil tanker is a concentrated source of explosive pollution, and the harm is devastating.

Petroleum is a mixture of alkanes, alkenes and aromatic hydrocarbons, and its harm after entering the water body is manifold. If the oil film is formed on the water, it can hinder the reoxygenation of the water body, and the oil adheres to the gills of the fish, which can asphyxiate the fish. It sticks to algae and plankton and kills them. Oil can inhibit the laying and hatching of water birds, and in severe cases, cause a large number of bird deaths. Oil pollution can also reduce the quality of aquatic products.

Radioactive contaminant

Radioactive contamination is caused when radioactive materials enter the water. Radioactive pollutants mainly come from cooling water discharged from nuclear power plants, radioactive waste thrown into the sea, nuclear explosions falling into the water body, nuclear fuel accident leakage; When mining, refining and using radioactive materials, if not handled properly, it can also cause radioactive contamination. Radioactive pollutants in the water can be attached to the surface of organisms, can also enter the accumulation of organisms, and can also produce internal irradiation through the food chain.