What is the effect of chloride ions on sewage treatment bacteria?
Mechanism of the effect of chloride ions
The toxic effect of high-concentration chloride ions on wastewater biological treatment is mainly to destroy the cell membrane of microorganisms and enzymes in bacteria through elevated environmental osmotic pressure, thereby destroying the physiological activities of microorganisms.
Microorganisms grow well under isotonic pressure, such as microorganisms in NaCl solution with a mass of 5-8.5g/L; under low osmotic pressure (p(NaCl)=0.1g/L), a large number of solution water molecules infiltrate into microorganisms , make the microbial cells swell, and in severe cases rupture, leading to the death of the microorganism; under high osmotic pressure, (p(NaC1)=200g/L), a large number of water molecules in the microbial body infiltrate into the body (ie: dehydration), causing the cells to undergo mass production. wall separation.
The unit structure of microorganisms is a cell, and the cell wall is equivalent to a semi-permeable membrane. When the chloride ion concentration is less than or equal to 2000 mg/L, the osmotic pressure that the cell wall can withstand is 0.5-1.0 atmospheres, even if the cell wall and cytoplasmic membrane are added. Elastic, the osmotic pressure that the cell wall can withstand will not be greater than 5-6 atmospheres.
However, when the chloride ion concentration in the aqueous solution is above 5000mg/L, the osmotic pressure will increase to about 10-30 atmospheres. Under such a large osmotic pressure, a large number of water molecules in the microorganisms will penetrate into the in vitro solution, causing cells Plasma separation occurs due to water loss, and in severe cases, the microorganisms die. Engineering experience data show that: when the chloride ion concentration in wastewater is greater than 2000mg/L, the activity of microorganisms will be inhibited, and the COD removal rate will be significantly reduced; when the chloride ion concentration in wastewater is greater than 8000mg/L, it will cause sludge volume Swelling, a lot of foam on the water surface, and microorganisms will die one after another.
Inhibits the performance of sludge activity
When the chloride ion concentration in the biochemical system changes greatly, the carbonization performance and nitrification performance of the sludge will quickly weaken or even disappear, resulting in a significant decrease in the COD removal rate and the accumulation of nitrite during the nitrification process. Even if the dissolved oxygen in the sewage is increased, the effect is not effective obvious. That is to say, activated sludge has a certain tolerance for chloride ion concentration. When the chloride ion concentration exceeds a certain value, the degradation capacity of the system decreases until the system loses its processing capacity.
A sudden change in chloride ion is more disturbing to the system than a gradual change in chloride ion. With the increase of chloride ion, the degradation rate of organic matter decreases, so low F/M (the ratio of nutrient to activated sludge in mass) is more suitable for the treatment of chloride ion-containing wastewater.
Chloride ion changes the composition of microorganisms in the sludge, changes the precipitation of the sludge and the effluent SS, resulting in serious sludge loss, a decrease in the concentration of activated sludge, an increase in the sludge index, and a decrease in the 30-minute sedimentation rate.
According to the microscopic examination results of activated sludge, the low salinity shows that the biological phase is relatively abundant, with a wide variety of filamentous bacteria, bacterial micelles, and protozoa, the activated sludge particles are large, the bacterial micelles are closed, and the flocs have a certain tightness. With the increase of the chloride ion concentration in the incoming water, when the chloride ion mutation increased from the original 150mg/L to 1000mg/L, the filamentous bacteria and protozoa basically did not exist, and the bacterial micelle became more dense. The flocs became small and extremely compact. The degradation of organic matter in sewage is mainly completed by the joint action of a large number of microorganisms in sewage. The increase of chloride ions leads to a decrease in the number of microorganisms in activated sludge, thereby reducing the degradation rate of organic matter.
