The wastewater treatment process generates large amounts of sludge. First, it is essential to clearly identify the origin of the sludge, its physical and chemical properties, as well as its composition and solid content. Wastewater from different industries has varying pH levels, resulting in sludges with distinct compositions, particle sizes, charge characteristics, and charge densities. Sludge composition can be broadly categorized into organic and inorganic types. For the disposal of organic sludge, cationic polyacrylamide sludge dewatering agents are commonly used—for example, in municipal wastewater treatment plants, paper mills, and chemical plants. On the other hand, anionic polyacrylamide sludge dewatering agents are typically employed for conditioning inorganic sludge. Cationic polyacrylamide sludge dewatering agents, being positively charged, are not well-suited for treating highly alkaline sludge. Conversely, anionic polyacrylamide sludge dewatering agents, carrying a negative charge, are less effective when used for dewatering acidic sludge. If the sludge has a relatively high solid content, the amount of sludge dewatering agent required will be proportionally greater.

For sludge dewatering, cationic polyacrylamide sludge dewatering agents are most commonly used. The specific model to be selected ultimately depends on the properties of the sludge. So how do we choose the right cationic polyacrylamide sludge dewatering agent? There are two main technical indicators for cationic polyacrylamide sludge dewatering agents:

Molecular weight: The selection of molecular weight involves many considerations. If the molecular weight is too low, flocs may fail to form properly or become excessively small. On the other hand, if the molecular weight is too high, the sludge dewatering agent tends to encapsulate the sludge particles, causing flocs to repel each other and resulting in poor flocculation. Belt filter presses require lower molecular weights, whereas centrifuges have higher molecular weight requirements.

Ionic Degree: The ionic degree of cationic polyacrylamide sludge dewatering agents refers to the charge density carried by the molecular chains of these agents. The selection of the ionic degree of cationic polyacrylamide often plays a decisive role in the effectiveness of sludge dewatering. Since different types of wastewater and sludge vary, the appropriate ionic degree of the cationic sludge dewatering agent used will also differ accordingly. If the ionic degree is too low, the sludge flocs will not be tightly bound; conversely, if the ionic degree is too high, the sludge flocs will carry excessive charges and repel each other. For example, for municipal wastewater—which typically contains high levels of organic matter—sludge dewatering agents with higher ionic degrees, such as 50 or 60, generally yield better results. On the other hand, paper mills can usually achieve satisfactory results using cationic sludge dewatering agents with ionic degrees of 20 or 30. Moreover, the type of sludge-dewatering equipment often imposes specific requirements on the cationic polyacrylamide sludge dewatering agents. Generally speaking, centrifuges tend to have slightly higher molecular weight requirements for sludge dewatering agents compared to belt filter presses.