Challenges and Solutions of Polyaluminum Chloride in Papermaking Wastewater Treatment

The composition of papermaking wastewater is complex, especially the high concentration of organic matter (such as lignin, cellulose, and dyes), which often significantly reduces the coagulation efficiency of polyaluminum chloride (PAC) due to interference from organic substances, leading to difficulties in meeting effluent quality standards and increased operational costs. So, how can we tackle this challenge? This article will analyze this issue in detail. Let’s explore it together with PAC manufacturers.

Impact of Organic Matter on the Coagulation Efficiency of PAC

In papermaking wastewater treatment, polyaluminum chloride (PAC) is commonly used as a coagulant to remove suspended solids and some organic matter. However, the high concentration of organic matter (such as lignin, cellulose, and dyes) in papermaking wastewater significantly affects the coagulation efficiency of polyaluminum chloride, leading to reduced treatment performance.

1. Mechanisms of Organic Matter Interference with PAC

Organic Matter Coating Effect: Dissolved organic matter (such as lignosulfonate) in papermaking wastewater adsorbs onto the surface of polyaluminum chloride, forming a "protective film" that hinders its effective contact with suspended particles.

Charge Neutralization Failure: Organic matter typically carries a negative charge, which neutralizes the positive charges generated during PAC hydrolysis, reducing its charge neutralization capability and making it less effective in aggregating suspended particles.

Loose Floc Structure: Organic matter interferes with the "adsorption-bridging" effect between PAC and suspended particles, resulting in loose, small-sized flocs with poor settling performance.

2. Practical Operational Issues

Effluent Quality Non-Compliance: Operational data from a paper mill shows that when the wastewater COD (Chemical Oxygen Demand) exceeds 2000 mg/L, the turbidity removal rate of polyaluminum chloride drops from 90% to 60%, making it difficult to meet discharge standards.

Increased Chemical Consumption: To compensate for the reduced coagulation efficiency, the dosage of PAC needs to be increased by 30%~50%, leading to higher operational costs.

Sludge Handling Challenges: The high moisture content of loose flocs increases the load and processing costs of sludge dewatering equipment.

Enhancing the Coagulation Efficiency of PAC in Papermaking Wastewater

To address the issue of high organic matter content in papermaking wastewater, the coagulation performance of PAC can be improved through chemical modification, process optimization, and pretreatment methods.

1. Chemical Modification and Blending

Combination with Polyacrylamide (PAM): Introducing anionic PAM after PAC dosing enhances floc structure through "charge neutralization-bridging" synergy. Experiments show that adding PAM can increase floc size by 2~3 times and improve settling speed by 50%.

Development of Composite Coagulants: Blending polyaluminum chloride with iron salts (such as polymeric ferric sulfate) to form polyaluminum ferric chloride (PAFC), leveraging the strong oxidizing and coagulation capabilities of iron ions to improve organic matter removal.

2. Process Optimization

Staged Dosing: Initially dosing a small amount of polyaluminum chloride(10~20 mg/L) for preliminary coagulation, followed by PAM for flocculation enhancement, can significantly improve coagulation efficiency and reduce chemical consumption.

pH Adjustment: Adjusting the wastewater pH to 6.0~7.5 optimizes the hydrolysis environment of PAC, enhancing its charge neutralization capability.

3. Pretreatment Technologies

Advanced Oxidation Pretreatment: Using ozone oxidation or Fenton reagents to pretreat wastewater, breaking down large organic molecules into smaller ones, thereby reducing their interference with PAC.

Biological Pretreatment: Utilizing anaerobic or aerobic biological treatment processes to degrade some organic matter, reducing the load on subsequent coagulation treatment.

The reduced coagulation efficiency of polyaluminum chloride in papermaking wastewater due to high organic matter content is a complex but solvable problem. Through the comprehensive application of chemical modification, process optimization, and pretreatment technologies, the coagulation performance of PAC can be effectively enhanced, ensuring effluent quality compliance and reducing operational costs. In the future, the development of more efficient composite coagulants and intelligent dosing systems will be key directions. If you encounter any issues during use, feel free to consult PAC manufacturer. We will arrange professional technicians to assist you, providing free testing, selection, and sample services. We sincerely look forward to cooperating with you!