( a ) microbial nutrition
The nutrients required by microorganisms must include various raw materials and energy-generating substances that make up the cells, including: water, carbon nutrient sources, nitrogen nutrient sources, inorganic salts, and growth factors.
The molecular formula of the cell: C 5 H 7 O 2 N ( or C 60 H 87 O 23 N 12 P) . Nutritional requirements: aerobic microorganisms: BOD 5 : N: P = 100: 5: 1 ; anaerobic microorganisms: BOD 5 : N: P = 400: 5:1 .
1. Water: a component, a solvent for metabolic processes. About 80% of the bacteria are made up of water.
2. Carbon source: The carbon content accounts for about 50 % of the cell dry matter. The carbon source mainly constitutes the carbonaceous material of the microbial cells and the energy required for the growth, reproduction and movement of the microorganisms. Generally, the sewage contains sufficient carbon source.
3. Nitrogen source: A substance that provides microbial synthesis of cellular proteins.
4. Inorganic elements: mainly phosphorus, sulfur, potassium, calcium, magnesium and trace elements. Role: constitutes cellular components, components of enzymes , maintains enzyme activity, regulates osmotic pressure, and provides energy for autotrophic microorganisms. Phosphorus: nucleic acid, phospholipid, ATP conversion. Sulfur: a protein component, aerobic sulfur bacteria energy. Potassium: Activates the enzyme. Calcium: Stabilizes the cell wall and activates the enzyme. Magnesium: an activating enzyme, an important component of chlorophyll
5. Growth factors: amino acids, proteins, vitamins, etc.
( 2 ) Temperature
The temperature range in which various microorganisms grow varies from about 5 °C to 80 °C. This temperature range can be divided into the lowest growth temperature, the highest growth temperature and the optimum growth temperature (the temperature at which the microbial growth rate is the fastest ) . Microorganisms can be classified into medium temperature (20 to 45 °C ) , good heat ( high temperature ) ( above 45 °C ) and good cold ( low temperature ) ( below 20 °C ) depending on the temperature range in which the microorganisms are adapted. When the temperature exceeds the maximum growth temperature, the microbial protein is rapidly denatured and the enzyme system is destroyed and inactivated. In severe cases, the microorganism can be killed. Low temperature will reduce the metabolic activity of microorganisms, and then stop growing and reproduction, but still retain its vitality.
( three ) pH
Different microorganisms have different pH adaptation ranges. The pH range of bacteria, actinomycetes, algae and protozoa is between 4 and 10 . Most bacteria are suitable for environments that are neutral and alkaline (pH = 6.5 to 7.5) . The optimum pH range should be maintained during the biological treatment of wastewater. When the pH of the wastewater changes greatly, a conditioning tank should be provided to keep the wastewater entering the reactor ( such as the aeration tank ) at a suitable pH range.
( 4 ) Dissolved oxygen
Important factors affecting the effectiveness of biological treatment. The dissolved oxygen treated by aerobic microorganisms is generally 2~4mg/L .
( 5 ) Toxic substances
In industrial wastewater, there are sometimes chemical substances that inhibit and kill microorganisms. These substances are called toxic substances. Its toxic effect is mainly manifested in the destruction of the normal structure of the cells and the deterioration of the enzymes in the bacteria, and the loss of activity. In the biological treatment of wastewater, these toxic substances should be strictly controlled, but the allowable range of toxic concentration needs to be analyzed.
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