Selection points of flocculant for screw dewatering machine

1. Sludge properties.
For sludge with high organic matter content, cationic flocculants are more effective flocculants. The higher the organic matter content, the more cationic flocculants with higher degree of polymerization should be selected. For sludge dominated by inorganic matter, anion can be considered. The difference in sludge properties directly affects the conditioning effect, while scum and excess activated sludge are more difficult to dewater, and the dewatering performance of mixed sludge is in between. Generally speaking, the more difficult to dehydrate the sludge, the greater the flocculant dose, and the finer sludge particles will lead to an increase in the consumption of flocculants, and the higher the organic content and alkalinity in the sludge will also lead to the increase in the amount of flocculants. In addition, the solid content of sludge also affects the dosage of flocculant. Generally, the higher the solid content of sludge, the greater the dosage of flocculant when using the sludge dehydrator.

2. Sludge pH.
The pH of the sludge determines the form of the hydrolyzed product, and the same flocculant has different treatment effects on sludge with different pH. The hydrolysis reaction of aluminum salt is greatly affected by pH, and the pH range of its coagulation reaction is 5~7. High-iron salt conditioners are less affected by pH, and the pH range is 6-11. In the sludge with a pH of 8-10, the hydrolyzate with higher solubility of ferrous salt can be oxidized into flocs with lower solubility. Therefore, when choosing an inorganic salt flocculant, the specific pH of the dewatered sludge must first be considered. If the pH deviates from the range of its coagulation reaction, another one should be used instead. Otherwise, it is necessary to consider adding acid or alkali to adjust the pH of the sludge before conditioning the sludge.

3. Concentration of flocculant.
The preparation concentration of flocculant not only affects the conditioning effect, but also affects the consumption of chemicals and the output rate of mud cake of sludge dewatering machine, among which the effect of organic polymer flocculant is more significant. Generally speaking, the lower the concentration of the organic polymer flocculant is, the less the agent consumption is, and the better the conditioning effect is. However, if the concentration is too high or too low, the output rate of mud cake will be reduced. However, the conditioning effect of inorganic polymer flocculants is hardly affected by the preparation concentration. The appropriate concentration of organic polymer conditioner is 0.05%~0.1%, the concentration of ferric chloride is 10%, and the concentration of aluminum salt is 4%~5%.

4. The temperature of the mixed treatment liquid.
The temperature of the sludge directly affects the hydrolysis of the flocculant, and when the temperature is low, the hydrolysis will slow down. If the temperature is lower than 10°C, the flocculation effect of the sludge dewatering machine will be significantly worse, and the conditioning effect can be improved by properly extending the flocculation time. When the temperature is low in winter, attention should be paid to the heat preservation of the sludge dewatering machine, not lower than 15°C, to minimize heat loss during sludge transportation.

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