How to select sludge conditioner?
Conditioner is also known as dehydrating agent, it is used to regulate the residual sludge before sludge dewatering, and its varieties include some of the above flocculants and coagulant aids.
How to select sludge conditioner?
1. Varieties and Characteristics of Conditioner
As far as the commonly used aluminum salt and iron salt inorganic conditioners are concerned, the dosage of aluminum salt is large, the floc density formed is small, the conditioning effect is poor, and the filter cloth will be blocked during dehydration. Therefore, when selecting inorganic conditioner, iron salt shall be used as far as possible; When using iron salt will cause many problems, consider using aluminum salt.
Compared with the organic conditioner, the inorganic conditioner has a larger dosage, forming fine floc particles, but higher floc strength. Therefore, when using vacuum filter and plate and frame filter press machine to dewater sludge, inorganic conditioner can be considered.
Compared with inorganic conditioners, the dosage of organic conditioners is small, and the flocs formed are thick, but the flocs strength is low, which is easier to break than the flocs formed by inorganic conditioners. Moreover, once the flocs are damaged, it is not easy to restore to the original state whether inorganic or organic conditioners are used. Therefore, when using centrifugal dehydrator and belt filter press machine to dewater sludge, organic conditioner can be considered.
When it is difficult to achieve the ideal conditioning effect by using one of inorganic or organic conditioners, it can be considered to use inorganic and organic conditioners together to achieve better conditioning effect. For example, the combined use of lime and ferric chloride can not only adjust the pH value, but also increase the porosity of sludge and promote the separation of sludge and water.
2. Sludge Property
The type and dosage of conditioner used for sludge with different properties are also very different.
For sludge with high organic content, the more effective conditioner is cationic organic polymer conditioner, and the higher the organic content is, the more suitable it is to use cationic organic polymer conditioner with higher polymerization degree.
For sludge mainly composed of inorganic substances, anionic organic macromolecule conditioner can be considered.
The different properties of sludge directly affect the conditioning effect: the sludge in the primary sedimentation tank is easy to be dewatered, while the scum and residual activated sludge are difficult to be dewatered, and the dewatering performance of mixed sludge is between the two.
In order to achieve a certain conditioning effect, there are significant differences in the amount of conditioning agents required. Generally speaking, the more difficult it is to dewater the sludge, the greater the dosage of conditioning agents, and the smaller the sludge particles, which will lead to an increase in the consumption of conditioning agents. The higher the organic content and alkalinity of the sludge, which will also lead to an increase in the dosage of conditioning agents. In addition, the solid content of sludge also affects the dosage of conditioner. Generally, the higher the solid content of sludge, the greater the dosage of conditioner.
3. Temperature
The temperature of sludge directly affects the hydrolysis of inorganic salt conditioner. When the temperature is low, the hydrolysis will slow down. If the temperature is lower than 10℃, the conditioning effect will be significantly worse, and the conditioning effect can be improved by appropriately extending the conditioning time.
When using organic macromolecule conditioner, if the temperature of mother liquor or tap water for preparing liquid medicine is too low or the temperature of sludge is too low, the dynamic viscosity of water and the viscosity of macromolecule conditioner solution itself will become larger, which is not conducive to uniform dilution and mixing, thus affecting the conditioning effect and dehydration effect of sewage sludge.
Therefore, when the temperature is low in winter, attention should be paid to the insulation of the sludge conveying system (the temperature of the sludge discharged from the sewage treatment system is generally not lower than 15 ℃) to minimize the heat loss in the sludge conveying process. If necessary, the organic polymer conditioner dilution tank can be heated or the mixing and dissolution time can be appropriately extended and the stirring intensity can be increased to improve the dissolution conditions.
4. PH Value
The pH value of sludge determines the hydrolysis product form of inorganic salt conditioner, and the conditioning effect of the same conditioner on sludge with different pH values is also different.
The hydrolysis reaction of aluminum salt is greatly affected by pH value, and the optimal pH value range of its condensation reaction is 5~7. When the pH value is greater than 8 or less than 4, it is difficult to form flocs, which means that the conditioning effect is lost.
The ferric salt conditioner is less affected by the pH value. Whether the sludge is acidic or alkaline, it can form the hydrolysate Fe (OH) 3 floc. The optimal pH value range is 6-11. In the sludge with pH value of 8-10, the hydrolysates with higher solubility of ferrous salts can be oxidized into Fe (OH) 3 flocs with lower solubility.
Therefore, when selecting inorganic salt conditioner, the specific pH value of dewatered sludge must be considered first. If the pH value deviates from the optimal range of its coagulation reaction, it is better to use another conditioner. Otherwise, it is necessary to consider adding acid or alkali to adjust the pH value of sludge before sludge conditioning. Generally, such measures are not taken.
5. Preparation Concentration
The preparation concentration of the conditioner not only affects the conditioning effect, but also affects the consumption of the agent and the mud cake yield, especially the organic polymer conditioner.
Generally speaking, the lower the concentration of organic polymer conditioner is, the less the reagent consumption is, and the better the conditioning effect is. This is because the lower the concentration of organic polymer conditioner is, the easier it is to mix evenly, the better the molecular chain stretches, the better the bridging and condensation function plays, and the better the conditioning effect of course. However, if the preparation concentration is too high or too low, the mud cake yield will be reduced.
The conditioning effect of inorganic polymer conditioner is almost not affected by the preparation concentration. Experience and relevant studies have shown that the 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%.
6. Dosing Sequence
When more than one conditioner is used, the order of adding the conditioner will also affect the conditioning effect.
When iron salt and lime are used as conditioners, generally, iron salt is added first, and then lime is added. In this way, the flocs formed are easier to separate from water, and the total consumption of conditioners is less.
When inorganic conditioner and organic polymer conditioner are used for sludge conditioning, inorganic conditioner is added first, and then organic polymer conditioner is added, which can generally achieve good conditioning effect.
7. Mixed Reaction Conditions
In order to achieve the best conditioning effect, it is necessary to fully mix the sludge and conditioner. However, it is worth noting that the flocs formed by the mixing reaction of sludge and conditioner must not be damaged, because once the flocs are damaged, it is difficult to restore to the original state.
Experience shows that only when the intensity and time of mixed reaction are within a certain range, can a good conditioning effect be achieved by using a certain conditioner for a certain sludge, and the conditioning effect will decrease with the increase of retention time.
That is to say, after the time and intensity of conditioning are determined through tests, it must be strictly observed in actual operation. On the one hand, it is not allowed to prolong or shorten the mixing reaction time at will; on the other hand, it is necessary to make the conditioned sludge enter the sludge dewatering dehydrator as soon as possible.
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