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Why does high-concentration saline wastewater have a great impact on microorganisms in industrial wastewater treatment?

2023-01-05

Use a semi-permeable membrane to separate two different concentrations of salt solution, and the water molecules of the low concentration salt solution will enter the high concentration salt solution through the semi-permeable membrane, and the water molecules of the high concentration salt solution will also enter the low concentration salt solution through the semi-permeable membrane, but the quantity is small, so the liquid level on the side of the high concentration salt solution will rise, and the permeation will stop when the height difference of the liquid level on both sides produces enough pressure to prevent the water from flowing again, At this time, the pressure generated by the height difference of the liquid level on both sides is the osmotic pressure. Generally speaking, the higher the salt concentration, the greater the osmotic pressure. The situation of microorganism in saline solution is similar to that of osmotic pressure test. The unit structure of microorganism is cell, and the cell wall is equivalent to semi-permeable membrane. When the concentration of chloride ion is less than or equal to 2000mg/L, the osmotic pressure that the cell wall can withstand is 0.5-1.0 atmospheric pressure. Even if the cell wall and the cell plasma membrane have certain toughness and elasticity, the osmotic pressure that the cell wall can withstand will not be greater than 5-6 atmospheric pressure. However, when the concentration of chloride ion in the aqueous solution is more than 5000mg/L, the osmotic pressure will increase to about 10-30 atmospheric pressure. Under such a high osmotic pressure, the water molecules in the microbial body will penetrate into the solution in vitro in a large amount, resulting in water loss of the cell and the separation of the plasma wall, and in serious cases, the microbial death. In daily life, people use salt (sodium chloride) to pickle vegetables and fish, and sterilize and preserve food. The engineering experience data shows that when the concentration of chloride ion in the wastewater is greater than 2000mg/L, the activity of microorganisms will be inhibited, and the COD removal rate will be significantly reduced; When the concentration of chloride ion in the wastewater is greater than 8000mg/L, the sludge volume will expand, a lot of foam will appear on the water surface, and microorganisms will die one after another. However, after long-term acclimation, microorganisms will gradually adapt to grow and reproduce in high concentration of salt water. At present, some people have domesticated microorganisms that can adapt to the concentration of chloride ions or sulfate ions above 10000 mg/L. However, the principle of osmotic pressure tells us that microorganisms that have adapted to grow and reproduce in high concentration of salt water, the salt concentration of cell fluid is very high. Once the salt concentration in the wastewater is low or very low, the water molecules in the wastewater will penetrate into the microbial body in a large amount, causing the microbial cells to expand, or even break and die. Therefore, after long-term acclimation and gradually adapting to the growth and reproduction of microorganisms in high concentration of salt water, the salt concentration in the biochemical influent should always be kept at a relatively high level. It should not be high or low, otherwise the microorganisms will die in large numbers.

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