Comprehensive indicators of organic pollution and nutrients

(1) Dissolved oxygen The dissolved oxygen content of natural water depends on the balance of oxygen in the water body and the atmosphere
.

The saturation content of dissolved oxygen is closely related to the partial pressure of oxygen in the air, atmospheric pressure, and water temperature

(2) Chemical oxygen demand (COD) refers to the amount of oxidant consumed to oxidize oxidizable substances in a water sample under specified conditions
.

The chemical oxygen demand reflects the degree of pollution in the water by reducing substances.

(3) Permanganate index refers to the amount consumed when processing water samples with potassium permanganate as the oxidant in acidic or alkaline media
.

Both the permanganate index and COD _cr are called chemical oxygen demand, which are just values ​​measured under different conditions

(4) Biochemical Oxygen Demand (BOD) Domestic sewage and industrial wastewater contain a large amount of various organic matter
.

When it pollutes waters, these organic substances consume a large amount of dissolved oxygen when they decompose in the water body, thereby destroying the oxygen balance of the water body, deteriorating the water quality, and causing the death of fish and other aquatic organisms due to lack of oxygen

Table 1-5 Advantages and disadvantages of BOD and COD

Note: COD is more oxidizing than BOD.

For COD»BOD of the same water quality, the difference can roughly indicate the organic matter that cannot be degraded by microorganisms.

(5) Total Organic Carbon (TOC) is a comprehensive index that expresses the total amount of organic matter in a water body by carbon content
.

Because TOC is measured by combustion method, it can oxidize all organic matter.

(6) Phosphorus The mass fraction of phosphorus in the earth's crust is about 0.
118%
.

Phosphorus appears in the form of various phosphates in nature

(7) Total Phosphorus In natural water and wastewater, almost all phosphorus exists in the form of various phosphates, which are divided into orthophosphate , condensed phosphate ( pyrophosphate , metaphosphate and polyphosphate) and organic combination The phosphorus (such as phospholipids, etc.
), they exist in solution, humic particles or aquatic organisms
.

Generally, the content of phosphate in natural water is not high, and industrial wastewater and domestic sewage from industries such as fertilizers, smelting, and synthetic detergents often contain relatively large amounts of phosphorus

(8) Kjeldahl nitrogen refers to the content measured by Kjeldahl method
.
It includes ammonia nitrogen and organic nitrogen compounds that can be converted into ammonium salts under these conditions
.
Such organic nitrogen compounds mainly refer to proteins, amino acids, nucleic acids, urea and a large number of synthetic organic nitrogen compounds with negative trivalent nitrogen
.
It does not include nitrogen-containing compounds such as azide, hydrazine, azo, nitrate, nitrite, nitro, nitroso, oxime, and hemicarbopeptone
.
Since most of the organic nitrogen compounds existing in water are the former, after measuring Kjeldahl nitrogen and ammonia nitrogen, the difference is called organic nitrogen
.
The measurement of organic nitrogen or Kjeldahl nitrogen is mainly to understand the pollution status of water bodies, especially when evaluating the eutrophication of lakes and reservoirs, it is an important indicator
.

(9) Total nitrogen There are four types of nitrogen in sewage, namely organic nitrogen, ammonia nitrogen, nitrite nitrogen and nitrate nitrogen
.
A large amount of domestic sewage, farmland drainage or nitrogen-containing industrial wastewater is discharged into the water body, which increases the content of organic nitrogen and various inorganic nitrogen compounds in the water, and the mass reproduction of organisms and microorganisms consumes dissolved oxygen in the water and deteriorates the quality of the water body
.
When lakes and reservoirs contain excessive amounts of nitrogen and phosphorus, it will cause phytoplankton to reproduce vigorously and appear eutrophication
.
Therefore, total nitrogen is one of the important indicators to measure water quality
.

(10) Nitrate Nitrogen Nitrate nitrogen in water is the most stable nitrogen compound in various forms of nitrogen-containing compounds such as nitrous nitrogen and ammonia nitrogen in an aerobic environment.
It is also the final decomposition product of nitrogen-containing organic matter through inorganic action
.
Nitrite can be oxidized to produce nitrate.
Nitrate can also be reduced to nitrite under the action of microorganisms in an oxygen-free environment
.
The content of nitrate nitrogen in water varies greatly, ranging from tens of micrograms per liter to tens of milligrams per liter.
The content of clean groundwater is very low, and the content of polluted water bodies and some deep groundwater is relatively high
.
Tannery wastewater, pickling wastewater, effluent from certain biochemical treatment facilities and farmland drainage can contain a large amount of nitrate
.
Ingestion of nitrate or through the action of microorganisms in the intestinal tract can be transformed into nitrite, and poisoning occurs
.
When the nitrate nitrogen content in water reaches tens of milligrams per liter, it can cause infant poisoning
.

(11) Nitrite nitrogen is an intermediate product of the nitrogen cycle and is unstable
.
Depending on the water environment, it can be oxidized to nitrate or reduced to ammonia
.
Nitrite can oxidize the body's normal hemoglobin (hypo-hemoglobin) into methemoglobin, and methemoglobin will lose the ability of hemoglobin to transport oxygen in the body, and symptoms of tissue hypoxia will appear
.
Nitrite can react with secondary amines to form carcinogenic nitrosamines.
Under acidic conditions with low pH, it is beneficial to the formation of nitrosamines
.

(12) Ammonia nitrogen refers to compound ammonia in the form of ammonia or ammonium ions
.
The composition of the two depends on the pH and temperature of the water
.
When the pH is high, the proportion of free ammonia is higher
.
On the contrary, the proportion of ammonium salt is high, and the water temperature is the opposite
.
The sources of ammonia nitrogen in water are mainly the decomposition products of nitrogen-containing organic matter in domestic sewage by the action of microorganisms, certain industrial wastewater, such as coking wastewater and synthetic ammonia fertilizer plants, and farmland drainage
.
In addition, in an anaerobic environment, nitrite present in water can also be reduced to ammonia by the action of microorganisms
.
In an aerobic environment, ammonia in water can also be converted into nitrite, and even continue to be converted into nitrate
.
The determination of various forms of nitrogen compounds in water helps to evaluate the pollution and "self-purification" of water bodies
.
Fish are more sensitive to ammonia nitrogen in water, and high levels of ammonia nitrogen will cause fish death
.