Polyacrylamide (PAM) is a linear polymer known for its excellent thermal stability and water solubility. Due to its unique properties, it can also function as a coagulant aid.

When a coagulant is introduced into water, appropriate hydraulic conditions must be created to successfully complete the coagulation process. The coagulation process consists of two stages: mixing and flocculation. Each stage has different requirements for water turbulence. The mixing phase generally lasts less than two minutes, during which the coagulant must be stirred into the water to facilitate rapid hydrolysis and condensation reactions. In contrast, during the flocculation phase, turbulence should be reduced to prevent the flocs from breaking apart under prolonged high-intensity stirring.

When inorganic coagulants are combined with PAM, PAM’s inherent ability to aggregate fine polymer flocs is limited. Inorganic coagulants can easily become neutralized by electrostatic forces. Once aggregates reach a certain size, PAM can effectively perform its bridging function, enhancing the interaction between flocs through electrostatic neutralization, allowing them to come closer together and form larger, denser aggregates.

At this stage, PAM acts as a coagulant aid. It is a high molecular weight polymeric flocculant that stabilizes flocs through bridging adsorption. Fine, uniformly dispersed particles and clay particles in the dispersed phase are adsorbed onto the active groups on the carbon chains of PAM, forming aggregates that interconnect to create larger flocs.

The quality and concentration of wastewater and sludge significantly influence the required amount of flocculant.

Flocculant Dosage of Polyacrylamide: How Much to Add per Ton of Water?

Generally, the quality and concentration of wastewater and sludge, as well as variations in wastewater properties, affect the dosage of flocculants. The turbidity, or concentration, directly impacts the amount added. For wastewater or sludge with low turbidity, a small quantity of flocculant can be effective, whereas highly turbid wastewater requires more substantial amounts.

Dosage Calculation for Polyacrylamide:

1. Anionic PAM:

   – Recommended concentration ratio: 1/1000

   – For 1 ton of water, add 1 kg of PAM.

   – Experimental examples:

     – Add 1 ml of flocculant to 100 ml of wastewater.

     – Add 10 g (L) of flocculant to 1 ton of wastewater.

     – Add 10 g of PAM to 1 ton of wastewater.

2. Cationic PAM:

   – Recommended concentration ratio: 2/1000

   – For 1 ton of water, add 2 kg of PAM.

Flocculant Experimentation:

Solid PAM can dissolve in water at any ratio, resulting in a uniform and transparent solution. The molecular weight has minimal effect on solubility; however, when the solution concentration exceeds 10%, hydrogen bonding between molecules may create a gel-like structure. Prior to use, solid powder products must be dissolved in water to prevent clumping and “fish-eye” phenomena during dissolution. To achieve this:

– Begin by adding half the required amount of warm water (not exceeding 60°C) into the dissolution tank.

– Gradually add the powder while stirring.

– Complete with additional water and stir until fully dissolved.

The typical solution concentration ranges from 0.1% to 0.05%. It is advisable to prepare a concentrated solution (0.1% to 0.2%) and dilute it before use. The solution should not be stored for more than five days; it is best to prepare it fresh as needed. When adding the solution, employ a multi-point continuous addition method to maximize the flocculating effect.

Summary: Approximately 200 g of flocculant is needed for every ton of wastewater. The specific type and dosage of flocculant required for each industry must be determined through preliminary testing, allowing for accurate calculation of the necessary amount per ton of wastewater.