Sewage effect

Pollution movement process:

Various movements occurred immediately after the pollutants entered the water body. Take the ocean as an example for a brief introduction, and the situation of other bodies of water can be analogized.

The residence time of pollutants in seawater τ can be calculated as follows:

τi = Ai/dAi/d t

Where Ai is the total amount of pollutant i discharged into the water body, and dAi/dt is the deposition rate of pollutant i in the ocean. In general, the greater the activity of pollutants in seawater, the shorter the residence time.

The enrichment process of pollutants in the ocean mainly depends on the physical and chemical enrichment settlement such as adsorption and the selective absorption of the food chain, the result is that the pollutants are removed from the sea water, so that the latter is purified, and will be harmful to organisms to varying degrees, and will increase the accumulation of pollutants in the bottom material, which may cause secondary pollution of the sea water.

Hazards to aquatic life

There are many kinds of aquatic animals and plants in nature. There is a complex exchange of matter and energy between living things and water, and between living things and living things, and a dynamic balance relationship is maintained from the quantity. But under the influence of human activities, this balance has been disrupted. When humans discharge pollutants into the water, some beneficial aquatic organisms will be poisoned and die, while some pollution-resistant aquatic organisms will intensify reproduction, consume a large amount of oxygen dissolved in the water, and make beneficial aquatic organisms forced to migrate to other places due to lack of oxygen, or die. In particular, some toxic elements are difficult to dissolve in water and easy to accumulate in living organisms, causing great harm to humans. For example, the content of mercury in water is very low, but the content in aquatic organisms is very high, and the content in fish is surprisingly high. It is assumed that the concentration of mercury in the water body is 1, the concentration of mercury in the benthos of aquatic organisms (refers to the small organisms living in the bottom mud of the water body) is 700, and the concentration of mercury in the fish is as high as 860. It can be seen that when the water body is polluted, on the one hand, the balance between living things and water, living things and living things is destroyed, on the other hand, some toxic substances continue to transfer and enrich, and finally endanger human health and life.

Quartz sand filtration

Quartz sand filtration is one of the most effective means to remove suspended matter in water, and it is an important unit in sewage advanced treatment, sewage reuse and water supply treatment. Its role is to further remove the pollutants that have been flocculated in the water, and it achieves the purpose of water purification through the interception, sedimentation and adsorption of the filter material.

1. For industrial water, domestic water and municipal water supply systems requiring effluent turbidity ≤5mg/L to meet drinking water quality standards;

2. Removal of suspended matter and solid matter in industrial sewage;

3, can be used as ion exchange softening, desalt system in the pretreatment equipment, water quality requirements are not high industrial water raw filtration equipment;

And used in swimming pool circulation treatment system, cooling circulation water purification system, etc.

Water pollution effects:

The harm of water pollution is multifaceted, here is a brief introduction to the impact of water pollution on human health.

● Causes acute and chronic poisoning. Water contaminated by toxic and harmful chemicals can cause poisoning through drinking water or the food chain. The famous Minamata disease and Itamata disease were caused by water pollution.

● Carcinogenic effect. Some carcinogenic chemicals such as arsenic, chromium, nickel, beryllium, aniline, benzo (a) pyrene and other polycyclic aromatic hydrocarbons, halogenated hydrocarbons polluted the water body, can be adsorbed by suspended matter, sediment, can also accumulate in aquatic organisms, long-term drinking water containing such substances, or eating organisms with such substances accumulated in the body (such as fish) may cause cancer.

● Occurrence of water-borne infectious diseases. Human and animal feces and other biological pollutants pollute the water, which may cause bacterial intestinal infectious diseases such as typhoid, dysentery, enteritis, cholera, etc. Common intestinal viruses such as spinal gray matter viruses, Coxsackie viruses, infectious hepatitis viruses, etc., can cause corresponding infectious diseases through water pollution. The "hepatitis A incident" in Shanghai in 1989 was caused by water pollution. In developing countries, about 60 million people die each year from diarrhoea, most of them children.

● Indirect effects. After water pollution, it can often cause the deterioration of sensory properties of water. For example, although some pollutants have no direct harm to human health at a certain concentration, they can cause water to have heteroodor, heterocolor, foam and oil film, etc., which hinder the normal use of water. Copper, zinc, nickel and other substances at a certain concentration can inhibit the growth and reproduction of microorganisms, thus affecting the decomposition and biological oxidation of organic matter in the water, reducing the self-purification capacity of the water body, affecting the health of the water body.

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.

Sewage utilization:

At present, China's sewage resource utilization is still in its infancy, the development is insufficient and unbalanced, the overall utilization level is not high, and there is still a large gap with the requirements of building a beautiful China, and there are also problems such as imperfect standards, imperfect policies, and the level of technical equipment to be further improved.

In January 2021, with the consent of The State Council, the National Development and Reform Commission, together with nine departments including the Ministry of Science and Technology, the Ministry of Industry and Information Technology, the Ministry of Finance, the Ministry of Natural Resources, and the Ministry of Ecology and Environment, jointly issued the Guiding Opinions on Promoting the Resource Utilization of sewage, and deployed the comprehensive promotion of the resource utilization of sewage.

The key areas of sewage resource utilization include urban domestic sewage, industrial wastewater and agricultural and rural sewage.

By 2025, the national sewage collection efficiency has been significantly improved, the sewage treatment capacity of county towns and cities has basically met the needs of local economic and social development, and the sewage treatment in water-sensitive areas has basically been upgraded. The utilization rate of reclaimed water in water-scarce cities at the prefecture level and above has reached more than 25%, and the Beijing-Tianjin-Hebei region has reached more than 35%. The reuse of industrial water, manure of livestock and poultry and the utilization of tail water resources in fishery and breeding have been significantly improved. A policy system and market mechanism for the utilization of sewage resources have been basically established. By 2035, a systematic, safe, environmentally friendly and economical sewage resource utilization pattern will be formed.