Study on the adaptability of polymeric ferric sulfate in the treatment of low-temperature and low turbidity wastewater

2025-03-03

Low temperature and low turbidity wastewater treatment is one of the technical difficulties in the field of water treatment. Low temperature (usually below 20 ℃) will slow down the chemical reaction rate and reduce the hydrolysis efficiency of coagulants; Low turbidity is due to the small number of suspended particles and high colloidal stability, which makes it difficult to form flocs. Polyferric sulfate (PFS), as an inorganic polymer coagulant, has shown significant advantages in low-temperature and low turbidity wastewater treatment in recent years due to its unique physicochemical properties. This article combines experimental data and application cases to explore its adaptability and mechanism of action.

Purification of drinking water with polymeric ferric sulfate (2)

Challenges in Treating Low Temperature and Low Turbidity Wastewater

1. Low temperature impact:

Under low temperature conditions, the Brownian motion of molecules weakens, the adsorption capacity of colloidal particles decreases, the hydrolysis rate of coagulants slows down, resulting in slow and loose floc formation and reduced settling efficiency.

2. Low turbidity characteristics:

The concentration of suspended solids in low turbidity water is low, and the surface charge of colloidal particles is stable. Traditional coagulants are difficult to effectively destabilize through electrostatic neutralization and require stronger adsorption bridging ability.

Physical and chemical properties and advantages of polymeric ferric sulfate

1. Wide area pH adaptability:

Polymeric ferric sulfate can effectively function within the pH range of 411, especially suitable for low-temperature and low turbidity raw water (pH 69 is the optimal range), with little impact on the alkalinity of the raw water and reducing the risk of equipment corrosion.

2. Efficient coagulation ability:

Its hydrolysis product is a multi-core complex, which rapidly destabilizes colloidal particles through mechanisms such as electrical neutralization and adsorption bridging, forming dense alum flowers with fast settling speed, significantly improving the solid-liquid separation efficiency in low-temperature environments.

3. Low temperature adaptability mechanism:

Dissolution and hydrolysis characteristics: When the temperature drops to 2 ℃, the hydrolysis rate of polymeric ferric sulfate significantly slows down, but compared to other iron or aluminum salt coagulants, its hydrolysis products can still maintain high activity. By adjusting the dosage (usually increasing by 10% or 20%), the low-temperature effect can be partially compensated for.

Stability of floc structure: The generated flocs are dense and have strong shear resistance, and can maintain good settling performance even at low temperatures.

Experimental and Application Effect Analysis

1. Coagulation effect under low temperature conditions:

Experiments have shown that when the water temperature is below 20 ℃, the removal rate of turbidity and COD by polymeric ferric sulfate can still reach over 85%, significantly better than traditional coagulants such as polyaluminum chloride (PAC). For example, in winter (at a water temperature of 25 ℃), a northern sewage treatment plant used polymeric ferric sulfate, which increased the COD removal rate from 70% to 90% and shortened the settling time of flocs by 30%.

2. Advantages of treating low turbidity raw water:

For raw water with turbidity below 10 NTU, polymeric ferric sulfate can reduce turbidity to below 1 NTU by enhancing adsorption bridging effect, especially suitable for the purification of slightly polluted water bodies and algae containing wastewater.

Purification of drinking water with polymeric ferric sulfate (3)

Purification of drinking water with polymeric ferric sulfate (1)

Application limitations and optimization measures

1. Limitations:

Temperature dependence: When the water temperature is below 2 ℃, insulation measures should be taken (such as indoor heating or pipeline heating), otherwise the hydrolysis reaction will almost stagnate.

Equipment corrosion risk: High concentration iron ions may cause corrosion to metal pipelines, requiring the use of corrosion-resistant materials or the addition of corrosion inhibitors.

2. Optimization direction:

Combination of composite agents: When combined with polyacrylamide (PAM), it can enhance floc structure and reduce dosage at low temperatures.

Process parameter adjustment: Determine the optimal dosage (usually 550 mg/L) and stirring intensity through beaker testing to balance cost and effectiveness.

Conclusion and Prospect

Polymeric ferric sulfate has become one of the preferred agents for treating low-temperature and low turbidity wastewater due to its broad-spectrum pH adaptability, efficient flocculation ability, and stability in low-temperature environments. Future research can further explore its composite application with new materials such as modified diatomaceous earth, or improve low-temperature hydrolysis efficiency by optimizing production processes. In practical engineering, it is necessary to scientifically design dosing schemes based on water quality characteristics and climate conditions to achieve efficient, economical, and sustainable water treatment goals.