Water pollution substances and hazards (1)

The basic sources of pollution in various water bodies in China are point sources and non-point sources
.

Point sources include industrial wastewater, urban domestic sewage, and livestock and poultry farm wastewater and waste; non-point sources include farmland runoff (including pesticides, fertilizers, toxic substances, etc.

The water quality of the 192 monitored sections of rivers entering the sea is generally poor, and the amount of river pollutants entering the sea is greater than the amount of pollutants directly discharged into the sea
.

The total amount of pollutants from rivers in the East China Sea into the sea is much higher than other sea areas

The total sewage discharge of 461 direct sea industrial pollution sources, domestic pollution sources and comprehensive sewage outlets with daily sewage discharge greater than 100t is 5.
092 billion tons, and the total discharge of various pollutants is: chemical oxygen demand of 219,400 tons, and petroleum products of 1215 tons.
, Ammonia nitrogen 22870t, total phosphorus 2901t, mercury 244.
6kg, hexavalent chromium 1076kg, lead 1064kg, cadmium 392kg
.

The status of wastewater discharge and treatment in China from 2008 to 2010 is shown in Table 1-3
.

Good results have been achieved through energy conservation, emission reduction and increased governance.

Table 1-3 Status of Wastewater Discharge and Treatment in my country (2008～2010)

There are many types of water pollutants.

According to the different harms caused by environmental pollution, the pollutants are divided into the following categories

1.
2.
1 Solid pollutants

The existence of solid pollutants in water has three forms: suspended state, colloidal state and dissolved state
.

Substances in a suspended state are usually called suspended matter, which refers to impurities with a particle size greater than 100nm, which cause significant turbidity in the water

The so-called colloidal substance refers to impurities with a particle size of approximately 1-100 nm
.

Most of the colloidal impurities are clay inorganic colloids and polymer organic colloids

Substances in a dissolved state, whose particles are approximately below 1 nm, mainly exist in the state of low molecules or ions
.

This impurity will not produce the appearance of turbid water

Solid pollutants in water mainly refer to suspended solids
.

Suspended pollutants are contained in industrial wastewater and domestic sewage such as hydraulic ash washing, coal washing, metallurgy, slaughter, fertilizer, chemical industry, construction, etc.

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2.
2 Organic Pollutants

Most of the polluted rivers in China are characterized by organic pollution, which is manifested by the increase in the concentration of COD and BOD in water bodies
.
Organic pollutants refer to natural organic substances in the form of carbohydrates, proteins , amino acids, and fats, and certain other biodegradable synthetic organic substances
.
These organics mainly come from domestic sewage and part of industrial wastewater
.
After the organic pollutants are discharged into the water body, the material composition in the water body changes and the original material balance is destroyed
.
At the same time, they are also involved in the material transformation and recycling process in the water body.
They are decomposed or separated through a series of physical, chemical, physical chemical and biochemical reactions, so that the water body basically or completely restores to its original state, that is, the original ecology.
The balance is restored
.
This process is the self-purification of the water body
.
The surface water body has a certain self-purification ability for organic matter.
After the wastewater is discharged into the water body, if there is sufficient dissolved oxygen in the water, and it can be continuously replenished from the atmosphere, the dissolved oxygen can be maintained above a certain level, indicating the organic pollution entering the water body The material does not exceed the self-purification capacity of the water body
.
At this time, the organic matter undergoes aerobic decomposition in the water body
.

If there is too much organic matter discharged into the water body, a large amount of dissolved oxygen in the water will be consumed, and the oxygen supplemented from the atmosphere will not be enough.
This means that the discharged organic pollutants exceed the self-purification capacity of the water and soil, and the water body will appear due to lack of oxygen.
Some phenomena
.
When the dissolved oxygen is below 4~5mg/L for a long time, ordinary fish cannot survive.
If the oxygen is completely depleted, organic pollutants will be transferred to anaerobic decomposition, producing reducing gases such as hydrogen sulfide and methane , which will cause a large number of plants and animals in the water Death, and can make the water body black and muddy, produce foul odor, and destroy the environment
.

1.
2.
3 Oil pollutants

The oily pollutants mainly come from oily wastewater.
The oil content of 0.
01mg/L in the water body can make the fish have a special smell and cannot be eaten
.
When there is a little more oil, an oil film is formed on the water surface, which isolates the atmosphere from the water surface, destroys the normal oxygenation conditions, and results in hypoxia in the water body.
At the same time, the degradation of oil under the action of microorganisms also requires oxygen consumption, resulting in hypoxia in the water body; the oil film can also attach On the gills, it makes it difficult to breathe, and even suffocates to death; during the spawning period of the fish, most of the fry hatched in the oily wastewater waters are deformed, with low vitality and easy to die
.
Oily wastewater also has an impact on plants, hindering photosynthesis and aeration, and reducing the production of rice and vegetables; after the oily wastewater enters the ocean, the harm caused is also self-evident
.