What are the three types of sewage treatment agent?

With the accelerating pace of industrialization and urbanization, wastewater discharge volumes continue to rise, making water pollution an increasingly pressing issue. As essential materials for water purification, wastewater treatment chemicals play an irreplaceable role in municipal sewage, industrial effluent, rural wastewater, landscape water bodies, and wastewater reuse. Among the myriad water treatment chemicals, the most fundamental and commonly used agents fall into three primary categories: coagulants, oxidants, and flocculants (polymeric coagulants). These three agents form the foundation of modern wastewater treatment systems, determining the efficiency and effectiveness of the entire treatment process.

1. The Core Significance of Wastewater Treatment Agents

Against the backdrop of increasingly stringent environmental regulations, high-efficiency wastewater treatment agents have become the key guarantee for industries to achieve compliant discharge standards.

Wastewater treatment agents are specialized chemicals that improve water quality through chemical, physical, or combined chemical-physical actions, ensuring compliance with environmental discharge standards. Their primary functions include:

(1) Removing suspended solids and colloids: Facilitating the precipitation of suspended particles and colloidal substances to eliminate impurities.

(2) Destroying bacteria and viruses: Eliminating pathogenic microorganisms through oxidation, disinfection, and other methods.

(3) Removing organic pollutants: Degrading organic matter to reduce chemical oxygen demand (COD) and biological oxygen demand (BOD) in water.

(4) Eliminating odors and color: Removing harmful gases and colored substances to improve water quality.

(5) Reducing turbidity and enhancing settling properties: Improving wastewater settling and dewatering performance to optimize subsequent treatment outcomes.

In modern wastewater treatment processes, treatment agents play a crucial role in enabling industries to achieve efficient, compliant discharges and advancing ecological conservation.

2. Three Major Types of Wastewater Treatment Chemicals

(1) Coagulants

- Definition and Principle:

Coagulants are chemicals that disrupt the stability of colloidal particles in wastewater. Colloidal particles typically carry charges that repel each other, making sedimentation difficult. Upon addition, coagulants rapidly: neutralize charges, aggregate fine suspended solids, and form large, settleable flocs. This constitutes the first critical step in wastewater treatment.

- Primary Types

The most commonly used coagulants include:

Inorganic coagulants: Poly aluminum chloride (PAC), Poly ferric sulfate (PFS), Ferric chloride, Alum.

Characteristics: Lower cost, strong removal effects on turbidity and color.

Organic coagulants: Organic amine-based, Cationic polymeric compounds.

Characteristics: High treatment efficiency, low dosage requirements, minimal sludge production.

- Application Areas: Municipal wastewater treatment plants, food processing, textile dyeing, electroplating, papermaking wastewater, iron/manganese removal from groundwater, river remediation, pretreatment for industrial circulating water systems. Coagulants are the critical first step transforming wastewater from “turbid” to “clear.”

(2) Flocculants

- Definition and Function

Flocculants, typically high-molecular-weight polymers (commonly called “coagulation aids”), further enhance post-coagulation processes by: promoting particle aggregation, increasing floc size, accelerating settling rates, and improving sludge dewatering properties. They act as the “amplifier” of the coagulation process.

- Common Flocculants

The most prevalent is polyacrylamide (PAM), categorized as:

Anionic PAM: Used for river management, municipal wastewater, metallurgical mining, and silt-laden wastewater.

Cationic PAM: Used for dyeing, electroplating, pharmaceuticals, chemicals, organic wastewater, and sludge dewatering.

Nonionic PAM: Used for wastewater with significant pH fluctuations or high salinity.

- Key Advantages: Rapid flocculation, minimal dosage, low sludge production, enhanced sedimentation and filtration efficiency, significantly reduced downstream treatment loads. Flocculants are core chemicals for accelerating and improving wastewater treatment efficiency.

(3) Oxidizing Agents

- Definition and Function

Oxidizing disinfectants can: eliminate bacteria, viruses, and algae; decompose organic matter; remove odors and color; reduce COD and ammonia nitrogen; inhibit sludge bulking. They are essential agents for terminal treatment and reuse disinfection of wastewater.

- Primary Types

Chlorine-based disinfectants: calcium hypochlorite, trichloroisocyanuric acid (TCCA), sodium hypochlorite.

Characteristics: Strong bactericidal effect, low cost, wide applicability.

Oxygen-based oxidants: hydrogen peroxide, sodium percarbonate, ozone (O₃)

Characteristics: No residuals, environmentally friendly.

Advanced Oxidants: Fenton's Reagent, Photocatalytic Oxidation, Advanced Ozone Oxidation Systems.

Characteristics: Capable of decomposing refractory organic compounds, serving as a critical technology for highly polluted industrial wastewater.

- Application Areas: Disinfection of municipal effluent, hospital wastewater, food processing plant effluent, dyeing and printing wastewater, electroplating wastewater, pharmaceutical wastewater, black and odorous water body remediation, and sterilization of reclaimed water. Oxidants serve as the final barrier ensuring water quality meets safety standards.

3. Relationship Among Three Types of Wastewater Treatment Agents

These three agents are typically “used in combination” to form a complete process chain:

(1) Coagulants: Destroy colloidal stability

(2) Flocculants: Rapidly aggregate and settle particles

(3) Oxidizing agents: Disinfect, deodorize, and remove organic matter

They are not substitutes but complementary agents, functioning as: coagulation as “pretreatment,” flocculation as “enhanced treatment,” and oxidation disinfection as “advanced treatment.” Together, they achieve compliant wastewater discharge and resource recovery.

4. Primary Application Industries for Wastewater Treatment Chemicals

(1) Industrial Applications

Various factories and enterprises in industrial sectors generate substantial wastewater containing pollutants like heavy metal ions. Specialized wastewater treatment chemicals like flocculants and oxidants effectively precipitate suspended solids and decompose organic matter to purify water quality.

(2) Municipal Water Treatment

Urban drainage systems frequently require various wastewater treatment chemicals to process mixed sewage from domestic sources, ensuring compliant discharge and preventing environmental harm. Common agents include decolorizing agents, phosphorus removal agents, and disinfectants.

(3) Agricultural Applications

Agricultural irrigation often generates wastewater containing pesticide residues and fertilizer components. Adding specialized chemical agents like bioenzyme preparations helps degrade organic matter, improve soil conditions, and enhance crop yield and quality.

(4) Other Application Areas

Beyond the primary sectors mentioned above, specialized industries such as healthcare and pharmaceuticals also require corresponding wastewater treatment chemicals to ensure production wastewater meets relevant discharge standards, thereby safeguarding ecological safety.

5. Industry Trends for Wastewater Treatment Agents

Driven by the “dual carbon” policy and advancing environmental regulations, wastewater treatment agents will exhibit the following trends:

- Low dosage requirements with high efficiency;

- Non-toxic, biodegradable, and eco-friendly formulations;

- Composite agents replacing single-component solutions;

- Integration of intelligent dosing systems with real-time water quality monitoring;

- Increased adoption of advanced oxidation processes (AOP) for challenging wastewater streams;

- Green and high-efficiency solutions will become mainstream.

Amid escalating environmental demands and intensifying water resource pressures, coagulants, flocculants, and oxidants—the three core agents in wastewater treatment systems—are assuming increasingly critical roles. They not only determine treatment efficiency and stability but also determine whether enterprises can achieve compliant discharge, reduce processing costs, and advance water resource reuse. With the continuous advancement of new materials, technologies, and intelligent dosing systems, wastewater treatment chemicals are evolving toward greater efficiency, environmental friendliness, and safety. As industry technology upgrades and environmental policies advance further, these chemicals will shoulder increasingly vital responsibilities in water environment management, providing robust support for achieving clean production, circular development, and ecological civilization.