Wasterwater treatment polyacrylamide referred to as "PAM’’, commonly known as flocculant, is a linear polymer, molecular weight between 3-26 million, solid product appearance for white or slightly yellow powder, soluble in water, easy to decompose temperature over 120 ℃.Polyacrylamide molecules have positive groups (-CONH2), which can adsorb and bridge suspended particles dispersed in the solution, and have a strong flocculation effect, so they are widely used in water treatment and other fields.
Municipal wasterwater contains high COD and SS and is difficult to treat. Biological and physical methods are commonly used in municipal wastewater treatment. Polyacrylamide flocculants are used in various stages of biological treatment, such as in primary and secondary sedimentation tanks and concentrators. However, the most important application area of polyacrylamide flocculant is to help and promote sludge dewatering. During sludge dewatering, the polyacrylamide causes the sludge to form large and dense flocculation, which can be used in centrifuges, belt machines, or plate and frame filter press to separate from the cleaning liquid.
How to choose the best PAM
polyacrylamide selection should be based on the characteristics of wasterwater, acidity of wasterwater, wasterwater temperature, according to these points to choose polyacrylamide. Fresh wastewater test in the lab is necessary. After selecting the suitable polyacrylamide flocculant in the laboratory, the sludge dewatering device should be tested on the machine. Different sludge dewatering equipment (centrifuge, belt filter press, plate and frame filter press) will have different requirements on polyacrylamide in operation. Therefore, field engineers should timely check and adjust the variety, concentration, dosage and input point of polyacrylamide according to the dewatering equipment.
The municipal sludge treatment is dehydrated by belt filter press, which can dehydrate the sludge to water content 80% to 85%.With plate and frame filter press and wing filter press, it can dehydrate to 75%-83% water content.With membrane filter press, can dehydrate to moisture content 70%-78%;
Different sludges and equipment have different requirements for polyacrylamide to be used as sludge decolorizer, among which belt filter press requires polyacrylamide with medium molecular weight and medium and high cationic degree, and centrifuge requires cationic polyacrylamide with high molecular weight, medium and low cationic degree and moderate cross-linking.
Solid polyacrylamide's absolute dry mud consumption per ton is generally 3-6 kg. Specific dry mud consumption shall be determined according to the beaker experiment, on-machine medium experiment or periodic operation test. The mud quality of each factory is different.
1. Understand the source, nature, composition (such as organic matter/inorganic matter ratio /PH value, etc.) and solid content of the sludge from users.In general, cationic polyacrylamide flocculant is used to treat organic sludge, while anionic polyacrylamide flocculant is used to treat inorganic sludge, cationic polyacrylamide flocculant should not be used when alkalinity is strong, and anionic polyacrylamide flocculant should not be used when acidity is strong.Sludge with high solid content usually has a large amount of polyacrylamide flocculant.
2. Flocculation size: if the flocculation is too small, it will affect the drainage speed.The molecular weight of polyacrylamide flocculant is usually selected to adjust the flocculation size.
3. Cationic polyacrylamide ion degree: for sludge to be dehydrated, different cationic polyacrylamide flocculants are used to screen in the laboratory to select the most suitable
one.In this way, the best flocculation effect can be achieved and the least dosage can be selected.
4. Flocculation strength: flocculation should be stable and not broken under shear.Increasing the molecular weight of polyacrylamide or choosing suitable molecular structure can help to improve the stability of flocculant.
5. Mixing of polyacrylamide flocculating agent and sludge: flocculating agent must be fully reacted with the sludge at a certain position in the dewatering equipment, resulting in flocculation.For this reason, the solution of polyacrylamide flocculant must have proper viscosity and can be evenly mixed with sludge under the condition of existing equipment.Whether the mixture is even or not is the key to success.The viscosity of flocculant solution is directly proportional to its molecular weight and preparation concentration.
6. Dissolution of polyacrylamide flocculant: good dissolution can give full play to flocculation.Sometimes it is necessary to speed up the dissolution, at this time you can consider appropriately raising the water temperature.