Sewage effect

Water pollution can not only seriously harm the ecosystem, but also cause serious economic losses.

Effects of major pollutants:

Lead: harmful to the kidney, nervous system, highly toxic to children, carcinogenicity has been proven;

Cadmium: acute damage to the kidneys;

Arsenic: harm to the skin, nervous system, carcinogenicity has been proven;

Mercury: great harm to the human body, the main organs of harm are kidney, central nervous system;

Selenium: High concentrations can harm the muscles and nervous system;

Nitrite: causes cardiovascular diseases, the most obvious impact on infants (blue baby disease), with carcinogenic;

Total trihalomethanes: Chloroform has the greatest impact on health, and the carcinogen is the most common carcinogen.

Trichloroethylene (organic matter) : excessive inhalation will reduce central nervous system, heart function, long-term exposure is harmful to the liver;

Carbon tetrachloride (organic matter) : It has a wide range of effects on human health, carcinogenic, and has a great impact on liver and kidney function

Classification of water quality index:

Generally divided into physical, chemical, biological three categories.

Physical index

Temperature, chroma, smell and taste, three forms of existence of solid matter: suspended, colloidal, dissolved. Total solids (TS) is used as an indicator for solid substances, and suspended solids (SS) is commonly used in sewage treatment to indicate the content of solid substances (TDS index is higher than 1000).

Chemical index

First, chemical oxygen demand (COD) : refers to the oxygen consumed by the oxidation of organic matter into CO2 and H2O under acidic conditions with a strengthened chemical oxidizer (China's legal potassium dichromate), expressed by CODcr, abbreviated as COD. The higher the chemical oxygen demand, the more organic pollutants in the water, the more serious the pollution.

Determination method of cod:

With the determination of reducing substances in water samples and the different determination methods, the determination values are also different. The most commonly used are acid potassium permanganate oxidation and potassium dichromate oxidation.

1, potassium permanganate (KmnO4) method: the oxidation rate is low, but relatively simple, in the determination of the relative comparative value of organic matter content in water samples, can be used.

2, potassium dichromate (K2Cr2O7) method: high oxidation rate, good reproducibility, suitable for the determination of the total amount of organic matter in water samples. Organic matter is very harmful to industrial water system. Water containing a lot of organic matter will contaminate the ion exchange resin when it passes through the desalting system, and it is especially easy to contaminate the ion exchange resin, so that the resin exchange capacity is reduced. Organic matter can be reduced by about 50% when it is pre-treated (coagulation, clarification and filtration), but it cannot be removed in the desalting system, so it is often brought into the boiler through the make-up water, so that the pH value of the furnace water is reduced. Sometimes organic matter may also be introduced into the steam system and condensate water, reducing the pH and causing system corrosion. High organic content in the circulating water system will promote microbial reproduction.

Therefore, regardless of the desalting, furnace water or circulating water system, the lower the COD is the better, but there is no uniform limit index. When the COD (KmnO4 method) in the circulating cooling water system is >5mg/L, the water quality has begun to deteriorate.

Biochemical oxygen demand (BOD) : The amount of oxygen required when organic pollutants in water are decomposed by aerobic microorganisms is called biochemical oxygen demand (mg/L).

If the sewage composition is relatively stable, in general, COD> BOD5. Generally BOD5/COD is greater than 0.3, it is considered suitable for biochemical treatment.

Third, total oxygen demand (TOD) : the main elements of organic matter are C, H, O, N, S, etc., when the organic matter is all oxidized, it will respectively produce CO2, H2O, NO, SO2, etc., at this time, the oxygen demand is called total oxygen demand (TOD).

Total organic carbon (TOC) : includes the carbon content of all organic pollutants in the water sample, and is also a comprehensive parameter for evaluating the organic substances in the water sample.

Total nitrogen (TN) : nitrogen compounds in sewage are divided into organic nitrogen, ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, and the total amount of four nitrogen compounds is called total nitrogen (TN). Kjeldahl nitrogen (TKN) is the sum of organic nitrogen and ammonia nitrogen.

Total phosphorus (TP) : including organic phosphorus and inorganic phosphorus two categories.

7. pH value.

8. Heavy metals.

Biological index

1, the number of coliform bacteria: the number of coliform bacteria contained in each liter of water sample, measured in 1 /L.

2, the total number of bacteria: is the sum of the number of coliform bacteria, pathogens, viruses and other bacteria, expressed in the total number of bacterial colonies per milliliter of water sample.