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Influence of Chloride Ion on Bacteria in Wastewater Treatment

Source:Jiangsu Envset     Time:16 March 2021

With the prosperity of the water treatment industry, technological innovation has brought more diversified sewage filtration and purification solutions. Wastewater biological treatment is one of them, but we must be alert to the negative effects of high concentrations of chloride ions. This article explains in detail the influence of chloride ions on bacteria in sewage treatment and its countermeasures.
chloride ion influence
Chloride ion influence mechanism

The toxic effect of high concentration of chloride ions on wastewater biological treatment is mainly to destroy the cell membrane of microorganisms and the enzymes in the bacteria through the increased environmental osmotic pressure, thereby destroying the physiological activities of microorganisms.

Microorganisms grow well under iso-osmotic pressure, such as microorganisms in a NaC1 solution with a mass of 5—8.5g/L; under low osmotic pressure (p(NaC1)=0.1g/L), a large amount of water molecules in the solution penetrate into the microorganisms. , Causing the microbial cells to swell and rupture in severe cases, leading to the death of the microbes; under high osmotic pressure (p(NaC1)=200g/L), a large amount of water molecules in the microbial body penetrate into the body (ie: dehydration), causing the cells to produce quality The wall is separated.

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 cell plasma membrane have certain toughness and 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 5000 mg/L, the osmotic pressure will increase to 10-30 atmospheres. Under such a large osmotic pressure, the water molecules in the microorganisms will penetrate into the in vitro solution in large quantities, causing cells Plasma wall separation occurs due to loss of water, and the microorganisms die in severe cases. Engineering experience data shows that when the chloride ion concentration 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 chloride ion concentration in the wastewater is greater than 8000mg/L, it will cause sludge volume Expansion, a lot of bubbles appear on the water surface, and the microorganisms will die one after another.

Inhibit the performance of sludge activity

When the chloride ion concentration of the biochemical system changes significantly, the carbonization performance and nitrification performance of the sludge will quickly weaken or even disappear, resulting in a significant decrease in the removal rate of COD and accumulation of nitrite during the nitrification process. Even if the dissolved oxygen in the sewage is increased, the effect will not be effective. obvious. In other words, activated sludge has a certain tolerance to the concentration of chloride ions. When the concentration of chloride ions exceeds a certain value, the degradation capacity of the system will decrease until the system loses its treatment capacity.

Sudden changes in chloride ions interfere more with the system than gradual changes in chloride ions. With the increase of chloride ion, the degradation rate of organic matter decreases, so low F/M (the ratio of nutrients to activated sludge in quality) is more suitable for the treatment of chloride ion-containing wastewater.

Chloride ions change the composition of microorganisms in the sludge, change the sedimentation 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 results of microscopic examination of activated sludge, when the salinity is low, it shows that the biological phase is relatively abundant. There are many kinds of filamentous bacteria, micelles, and protozoa. The activated sludge particles are large, the bacteria micelles are closed, and the flocs have a certain degree of closeness. With the increase of the chloride ion concentration in the incoming water, when the chloride ion mutation increases from the original 150mg/L to 1000mg/L, the filamentous bacteria and protozoa are basically non-existent, and the bacterial micelles become denser. The flocs became small and extremely tight. The degradation of organic matter in sewage is mainly completed by the joint action of a large number of microorganisms in the sewage. The increase of chloride ions leads to a decrease in the number of microorganisms in the activated sludge, thereby reducing the degradation rate of organic matter.

The above is the chloride ion influence mechanism and the performance of inhibiting sludge activity in sewage treatment. For more relevant news, please continue to pay attention to the Jiangsu Envset website.

Tag: chloride ion influence, wastewater biological treatment
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