Application of flocculant and coagulant aid

2021-03-11

Adding flocculants in wastewater treatment can accelerate the aggregation and sedimentation of solid particles in wastewater, and can also remove part of the dissolved organic matter.

This method has the advantages of low investment, simple operation, flexibility, etc., and is particularly suitable for treating wastewater with a small amount of water and a large amount of suspended impurities. When using inorganic flocculants, because the dosage is large, the amount of sludge produced is also large. Therefore, in practical applications, synthetic organic polymer flocculants OPF or a combination of inorganic flocculants and OPF are mainly used.

According to related reports, in primary sedimentation tanks, anionic hydrolyzed polyacrylamide is often used to remove suspended impurities in wastewater, while non-ionic polyacrylamide (PAM) does not work well. Experience has shown that adding 1mg/L of hydrolyzed polyacrylamide in the primary sedimentation tank can remove more than 50% of the suspended particles and more than 40% of the BOD5 in the incoming wastewater.

In the primary precipitation treatment of wastewater, the mixed use of organic polymer polyelectrolyte and inorganic flocculant is more effective than using them separately. Because the concentration, particle size distribution and types of suspended particles in the incoming wastewater will change at any time, it is sometimes difficult to control the optimal dosage of flocculants.

At this time, if an excessive amount of inorganic flocculant is added, the rolling sweep mechanism is used to precipitate and remove suspended impurities. Although the method is feasible, its shortcomings are also very prominent. First, the action time is relatively long (15-30min), and then the flocs formed Easy to break. If adding a certain amount of organic polymer polyelectrolyte while adding inorganic flocculant, the flocculation time can be reduced to 2 to 5 minutes, and the flocs formed are also relatively strong.

When using the precipitation method to remove colored organic colloidal impurities in water, a dual electrolyte system can be used. First, a cationic polyelectrolyte with a high positive charge is used to destabilize these organic colloids, and then a large molecular weight non-ionic or anionic polyelectrolyte is used to flocculate the destabilized organic colloids into flocs that are easy to precipitate.

Cationic polyelectrolytes are often used as flocculants in secondary sedimentation tanks, such as polydimethylhexadiene ammonium chloride or polyaminomethyl dimethylhexadiene ammonium chloride, etc., but the dosage is higher than in the initial Less in the sedimentation tank. The reason is that part of the anionic polyelectrolyte added in the primary sedimentation tank continues to function after entering the secondary sedimentation tank, and the polyelectrolyte added in the secondary sedimentation tank can be repeatedly used in the sludge return.

In addition, coagulation treatment can also remove phosphate and heavy metal ions in wastewater. For a long time, people have always used the method of adding metal salt inorganic flocculants to remove part of the phosphate in the wastewater.

However, experiments have shown that under the premise of ensuring that the removal rate of phosphate does not decrease, the same phosphorus removal effect can be achieved by using cationic polymers instead of inorganic flocculants, which shows that the polymer participates in the adsorption of anionic phosphate.

For example, a wastewater treatment plant uses 12mg/L ferric sulfate, 3mg/L high charge density cationic polymer, and 0.2mg/L high molecular weight anionic polymer to replace the original 23mg/L sulfuric acid in the coagulation treatment process. Iron, in the case of the same phosphorus removal rate, the effluent BOD5 removal rate increased from 30% to 55%.

At the same time, the use of coagulation treatment can reduce the inorganic components in the sludge produced in the activated sludge stage and improve the biodegradation function of the activated sludge.

In the treatment processes such as filtration and flotation used in wastewater treatment, the quality of the effluent can be improved by using inorganic flocculants and polyelectrolyte flocculants. Combining the characteristics of wastewater quality, the flocculant can be used alone, or a combination of multiple flocculants or a combination of one main and one auxiliary (the auxiliary is used as a coagulant). The choice of flocculant can be preliminarily screened through static beaker test, and then verified and determined on the production device.

Polyacrylamide flocculantpolyaluminium chloride PAC



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