I. Introduction

Polyacrylamide (PAM for short) is a linear high-molecular polymer. Since its industrial production was achieved in the 1950s, it has become one of the most important chemical agents in the field of water treatment. Due to its unique molecular structure and adjustable performance, PAM plays an irreplaceable role in the processes of drinking water purification, sewage treatment, industrial wastewater treatment and sludge dewatering. With the increasingly strict environmental protection regulations and the intensification of water resource shortage problems, the application research of PAM in water treatment has been continuously deepened, and the development of new modified PAM products has also made remarkable progress.

Ii. Basic Characteristics and Classification of PAM

1.Chemical structure and physical properties

PAM is a high-molecular compound formed by the free radical polymerization of acrylamide monomers. Its molecular chain contains a large number of amide groups (-CONH2), and these polar groups endow PAM with good water solubility and chemical activity. The average molecular weight of PAM is usually between 1 million and 20 million. Products with different molecular weights can be obtained by adjusting the degree of polymerization as needed.

2.Main types of PAM

According to the ionic characteristics, PAM can be classified into three major categories:

●Nonionic PAM (NPAM) : The molecular chains are uncharged and mainly act through hydrogen bonds and van der Waals forces. It is suitable for environments with high salinity or high pH values.

●Anionic PAM (APAM) : By introducing anionic groups such as carboxyl groups through hydrolysis or copolymerization, it has an excellent flocculation effect on positively charged colloidal particles and is widely used in the treatment of urban sewage and mineral processing wastewater.

●Cationic PAM (CPAM) : Prepared by introducing cationic groups such as quaternary ammonium salts, it is particularly suitable for negatively charged organic colloids in fields such as sludge dewatering and papermaking wastewater.

In addition, there are special varieties such as amphoteric PAM and modified PAM, which can be molecular designed according to the characteristics of the treated object.

Iii. The Mechanism of PAM in Water Treatment

1.Flocculation mechanism

PAM mainly achieves the aggregation of suspended solids through the following three ways:

●Electro-neutralization: Charged PAM molecules neutralize the surface charge of colloidal particles through electrostatic interaction, reducing the ζ potential and disrupting the stability of the colloid.

●Adsorption bridging effect: Long-chain PAM molecules simultaneously adsorb multiple particles, forming a "particle-polymer-particle" floc structure, which is a unique mode of action of high-molecular flocculants.

●The net capture and sweeping effect: The three-dimensional network structure formed by PAM can mechanically trap tiny particles during the sedimentation process.

2.Key factors affecting flocculation effect

●Molecular weight: Generally, the larger the molecular weight, the stronger the bridging ability, but the solubility will decrease.

●Ion degree: It determines the charge density and affects the ability of electro-neutralization.

●Dosage: There is an optimal value. Excessive dosage may cause the colloid to restabilize.

●Solution pH value: Affects the ionization degree of PAM and the surface charge properties of particles.

●Stirring conditions: Moderate stirring is conducive to the formation of flocs, while excessive stirring will damage the flocs.

Iv. Applications of PAM in Different Water Treatment Fields

1.Drinking water treatment

In waterworks, PAM is mainly used as a coagulant aid in combination with aluminum or iron salt coagulants, which can reduce the dosage of inorganic coagulants by 30-50% and significantly improve the quality of the effluent. Studies show that the optimized use of APAM can reduce the turbidity of the effluent from the sedimentation tank to below 0.5NTU and effectively remove trace organic matter and algae in the water.

2.Urban sewage treatment

In secondary treatment, PAM can accelerate the sedimentation of activated sludge and improve the efficiency of the secondary sedimentation tank. In the tertiary advanced treatment, PAM assisted filtration can further remove phosphorus and suspended solids. After a certain sewage treatment plant adopted CPAM, the sludge volume index (SVI) decreased from 150mL/g to 80mL/g, and the treatment capacity increased by approximately 40%.

3.Industrial wastewater treatment

●Papermaking wastewater: CPAM can effectively treat high-concentration organic wastewater, with a COD removal rate of over 85%.

●Electroplating wastewater: APAM forms flocs with heavy metal ions, and the removal rate of nickel, chromium, etc. exceeds 99%.

●Oilfield wastewater: PAM is used for the treatment of oily wastewater, and the oil content can be reduced from 1000mg/L to below 10mg/L.

4.Sludge dewatering

PAM conditioning can significantly improve the dewatering performance of sludge, reducing the moisture content of sludge from 98% to below 80%, and greatly reducing the volume of sludge. The advanced automatic dosing system can adjust the dosage and ionization degree of CPAM in real time according to the nature of the sludge, achieving the best dewatering effect.

V. Optimization and Innovation of PAM Usage

1.Compounding technology

The combined use of PAM with inorganic coagulants (such as PAC), oxidants (such as persulfate), or other organic flocculants can produce a synergistic effect. For instance, when PAM and PAC are used in combination to treat printing and dyeing wastewater, the color removal rate can be increased by 20-30%.

2.Development of Modified PAM

●High-temperature and salt-resistant PAM: By introducing strong hydrophilic groups such as sulfonic acid groups, its stability in high-temperature and high-salt environments is enhanced.

●Environmentally friendly PAM: Reduces the content of residual monomer (acrylamide) in the product and enhances biodegradability.

●Nano-composite PAM: Nano-sio2, carbon nanotubes, etc. are added to enhance mechanical strength and flocculation performance.

3.Intelligent control technology

The intelligent dosing system based on online monitoring of Zeta potential, floc particle size, etc. can optimize the PAM dosing parameters in real time and reduce the consumption of chemicals by 15-30%. A certain intelligent water plant adopts AI algorithms to control the addition of PAM, saving more than 500,000 yuan in costs annually.

Vi. Precautions for the Use of PAM

1.Dissolution process: PAM should be slowly sprinkled in clean water and moderately stirred to avoid the formation of "fish eye" -shaped insoluble substances. Usually, a 0.1-0.5% solution is prepared and used immediately after preparation.

2.Safety and environmental protection: Acrylamide monomers have neurotoxicity. High-quality and low-residue single products (<0.05%) should be selected. Waste PAM solution should be properly disposed of to avoid being directly discharged into water bodies.

3.Storage conditions: Solid PAM should be stored in a sealed container in a cool and dry place to prevent moisture absorption and caking. The solution should not be stored for more than 48 hours.

Vii. Future Development Trends

1.Green synthesis technology: Develop environmentally friendly production processes such as bio-enzyme catalytic polymerization to reduce energy consumption and waste generation.

2.Functional design: Specific PAM molecule design for emerging pollutants (such as microplastics, drug residues).

3.Digital management: By integrating the Internet of Things and big data analysis, achieve precise and intelligent use of PAM.

4.Resource recovery: Utilize PAM flocculation to enrich valuable substances in wastewater, such as rare earth elements and precious metals.

Viii. Conclusion

As a "versatile player" in the water treatment field, PAM has been continuously playing a key role in global water resource protection and pollution control, thanks to its high efficiency, economy and wide adaptability. With the advancement of materials science and environmental technology, new PAM products with superior performance and greater environmental friendliness will continue to emerge, providing more solutions to address complex water treatment challenges. The future development of PAM technology should pay more attention to the balance between efficiency improvement and environmental friendliness, promoting the water treatment industry to develop in a more efficient and sustainable direction.