Wastewater flocculants can be categorized by ion type into anionic, cationic, and non-ionic, and by physical form into liquid and solid.Suspended particle bridges can be introduced into solutions, exhibiting excellent flocculation properties. The molecular weight ranges from 6 to 20 million, with good water solubility. Sewage flocculants are substances that can reduce or eliminate the sedimentation stability and aggregation stability of dispersed particles in water, causing them to coalesce and flocculate into aggregates for removal. According to their chemical composition, flocculants can be categorized into three main types: inorganic, organic, and microbial flocculants.
The following primarily introduces commonly used inorganic and organic wastewater flocculants:
Inorganic flocculants include aluminum salts, iron salts, and their polymers.
Organic flocculants can be classified into anionic, cationic, non-ionic, and amphoteric types based on the charge properties of the charged groups in the monomers. Additionally, they can be divided into two major categories according to their source: synthetically produced and naturally occurring high molecular weight flocculants.
The theoretical foundation is the "Aggregation" theory. Flocculants primarily neutralize groups with positive (negative) charges and some particles or particles in water with difficult-to-separate negative (positive) charges, reducing their electrical potential to an unstable state, and utilize their aggregation properties to concentrate these particles, and then separate them through physical or chemical methods.
Flocculants are the chemicals typically used to achieve this purpose. Wastewater flocculants are mainly applied in various water and wastewater treatment fields.
Principle of Flocculation Reaction in Wastewater Flocculants
Flocculation is a two-step particle aggregation process, during which a large number of small particles form a small amount of large flocs.
Fine particle surfaces typically carry a negative charge that hinders aggregation and precipitation. Coagulating chemicals can adsorb onto particles and balance the charge. The introduction of opposite charges causes the particles to adhere, forming stable, well-suspended submicron flocs (1b). Rapid mixing aids in dispersing the coagulating chemicals, thereby promoting particle collisions and the formation of submicron flocs.
Floc formation requires slow mixing and the use of high molecular weight flocculants. The wastewater flocculants can adsorb submicron flocs, promoting inter-floc bridging. The particles tightly aggregate, forming an effective van der Waals attraction, thereby reducing the energy barrier of flocculation and creating loose flocs. The flocs will undergo clumping and bonding until visible large flocs form in suspension. Sedimentation occurs when the weight, size, and strength are appropriate.
