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Analyze the Nature of the Wastewater
Different types of wastewater have distinct characteristics, such as pH, ionic strength, and types of pollutants. For wastewater containing a large number of negatively charged pollutants, cationic polyacrylamide flocculant can be selected. If the wastewater mainly consists of positively charged particles, anionic polyacrylamide flocculant may be more suitable. For some neutral wastewater, nonionic polyacrylamide flocculant might be the better choice. For example, in the treatment of textile dyeing wastewater, which contains a large number of negatively charged dye molecules, cationic polyacrylamide flocculant usually achieves better flocculation results.
Consider Water Quality Changes
The quality of wastewater may change over time and due to factors such as production processes. Therefore, when selecting a polyacrylamide flocculant, potential changes in water quality should be fully considered, and a product with certain adaptability should be chosen. For instance, certain industrial wastewater has varying concentrations and natures of pollutants at different stages of production, in which case a polyacrylamide flocculant product with a wide applicable range might be selected.
Control the Dosage
An insufficient dosage will not fully exert the flocculation effects of the polyacrylamide flocculant, whereas an excessive dosage might result in colloidal protection, causing particles to re-stabilize and disperse, thereby reducing the treatment effect. Determining the optimal dosage through experiments is key. Small-scale tests can be conducted in the laboratory to gradually adjust the dosage, observe the flocculation effect and water quality changes, and find the appropriate dosage range. For example, for a specific domestic wastewater treatment, it was found after several trials that adding 5-10 grams of cationic polyacrylamide flocculant per cubic meter of wastewater achieved the best flocculation effect and significantly improved the quality of the effluent.
Adjust the pH Value
The pH value of the wastewater has a significant impact on the flocculation effect of the polyacrylamide flocculant. Generally, different types of polyacrylamide flocculants perform better within specific pH ranges. By adjusting the pH value of the wastewater, the activity of the polyacrylamide flocculant can be enhanced. For example, anionic polyacrylamide flocculant works better under neutral or alkaline conditions, while cationic polyacrylamide flocculant performs better under acidic to neutral conditions. pH regulators such as hydrochloric acid and sodium hydroxide can be used to adjust the pH value of the wastewater, but care must be taken to control the extent of the adjustment to avoid adverse impacts on the wastewater treatment system.
Control Stirring Speed and Time
After adding the polyacrylamide flocculant, appropriate stirring can promote the thorough mixing of the flocculant with the wastewater, but excessive stirring intensity or prolonged stirring time can destroy the already formed flocs. Generally, after adding the polyacrylamide flocculant, a faster stirring speed can be used initially to disperse the flocculant fully, then the stirring speed can be reduced to allow the flocs to grow gradually. For example, during the initial stirring stage, the stirring speed can be controlled at 100-150 rotations per minute for 1-2 minutes; then reduce the stirring speed to 30-50 rotations per minute, and continue stirring for 3-5 minutes to promote the stable formation of flocs.
Use with Inorganic Flocculants
Polyacrylamide flocculants can be used in conjunction with inorganic flocculants such as polyaluminum chloride and ferric sulfate to exert synergistic effects and improve flocculation efficiency. Inorganic flocculants can quickly neutralize the charges in the wastewater, destabilizing the particles, while polyacrylamide flocculants gather the destabilized particles into larger flocs through bridging action. For example, when treating highly turbid river water, adding an appropriate amount of polyaluminum chloride first can quickly reduce the turbidity, followed by the addition of a polyacrylamide flocculant to further enhance the flocculation effect and produce clearer effluent.
Adopt Pretreatment and Post-treatment Processes
Before using polyacrylamide flocculant, the wastewater can be pretreated through sedimentation, filtration, etc., to remove some larger particulate pollutants and reduce the burden on the polyacrylamide flocculant. Additionally, after flocculation treatment, further treatment processes such as activated carbon adsorption or biological treatment can be used to remove residual pollutants and improve water quality. For instance, for industrial wastewater containing refractory organic compounds, part of the suspended solids can be removed through sedimentation first, then the wastewater treated with polyacrylamide flocculant for flocculation, followed by a biological treatment process using microorganisms to degrade the organic compounds for better treatment effect.
