The process of sludge conditioning usually includes sludge pretreatment, conditioner addition and mixing reaction, sludge maturation, etc. Commonly used agents are inorganic conditioners, organic conditioners, coagulation aids, etc. The following is a specific introduction:
I. Process flow
1, sludge pretreatment: thickening of sludge, reduce the water content of sludge, reduce the volume of sludge, to facilitate subsequent treatment. At the same time, through screening, sand removal and other operations to remove large impurities in the sludge, sand, etc., to prevent it from affecting the conditioning effect and damage to equipment.
2, conditioning agent addition and mixing reaction: according to the sludge properties to determine the type of conditioning agent and dosage, the conditioning agent will be formulated into a certain concentration of solution, through the measurement of the equipment and uniformly added to the sludge. Then carry out rapid stirring and mixing, so that the conditioning agent is quickly and evenly dispersed in the sludge, and the sludge particles are fully contacted and reacted, the time is generally tens of seconds to a few minutes. Then the slow mixing is carried out, so that the sludge particles can be further coagulated and flocculated under the action of conditioning agent to form a larger floc structure, the slow mixing time is usually 10 - 30 minutes.
3. Sludge maturation: After the mixing reaction is completed, the sludge is allowed to stand for a period of time to allow the flocs to further settle and compact, this process is also known as sludge maturation. In this process, the water in the sludge is gradually separated, and the settling performance and dewatering performance of the sludge are improved, and the maturing time is usually about 30 - 60 minutes.
Commonly used chemicals
1、Inorganic conditioning agent
(1) Ferric chloride: It can generate positively charged ions through hydrolysis, neutralize the negative charge on the surface of sludge particles and make the particles cohesive. Its advantage is the formation of floc density, settling speed, acidic sludge conditioning effect is better; the disadvantage is corrosive, may increase the salt content of sludge when the dosage is larger.
Aluminum sulfate: it can also produce coagulation after hydrolysis, and is suitable for many types of sludge. It is more effective under alkaline conditions, and can reduce the specific resistance of sludge and improve the dewatering performance. However, the use of aluminum sulfate may raise the pH value of the sludge and produce a relatively large amount of sludge.
(2) Polymerized aluminum chloride: It is a commonly used inorganic polymer flocculant with the advantages of good flocculation effect, low dosage and wide pH range. It can quickly form large and dense flocs, improve the settling speed and dewatering performance of sludge, and is widely used in the conditioning of industrial wastewater and municipal sewage sludge.

2、Organic conditioning agent
(1) Cationic polyacrylamide: with positive charge, it can combine with negatively charged sludge particles through electrostatic attraction, neutralize the charge on the surface of sludge particles, compress the double layer, make the particles cohesive, and form larger flocs through the bridging effect of molecular chain. It is suitable for organic sludge and sludge with high water content, with low dosage and good conditioning effect, which can significantly improve the performance of sludge dewatering.
(2) Anionic polyacrylamide: It is suitable for some sludge which is mainly inorganic, in the case of sludge particles with positive charge on the surface or neutral, the particles will be aggregated by adsorption and bridging effect. Its price is relatively low, but the conditioning effect may not be as significant as cationic polyacrylamide for organic sludge.
(3) Non-ionic polyacrylamide: no charge on the molecular chain, mainly through the molecular chain of adsorption and bridging effect to make sludge particles cohesion. It is more effective when the pH value of sludge is close to neutral, and it may have unique conditioning effect on some sludge of special nature.

Polyacrylamide
3、Auxiliary coagulant
(1) Lime: often used in conjunction with other conditioning agents, it can regulate the pH value of sludge, improve the alkalinity of sludge, which is conducive to the flocculation reaction. At the same time, lime can also react with heavy metal ions in sludge to generate insoluble hydroxide precipitation and reduce the toxicity and solubility of heavy metals. In addition, it can increase the solid content of sludge and improve the dewatering performance of sludge.
(2) Diatomaceous earth: It is a natural mineral with porous structure, large specific surface area and strong adsorption performance. As a coagulant aid added to the sludge, it can adsorb fine particles and organic matter in the sludge, increase the weight and density of the floc, and improve the settling speed and dewatering effect of the sludge.
In practical application, it is necessary to comprehensively select the appropriate conditioning agent and process according to the specific nature of the sludge, treatment objectives and economic costs and other factors. At the same time, the optimal dosage of chemicals and process parameters are determined through experiments to achieve good sludge conditioning effect.