Treating industrial wastewater with polyaluminum chloride

Polyaluminum chloride (PAC) plays an important role in the treatment of industrial wastewater. The following is a detailed introduction to the treatment of industrial wastewater with polyaluminum chloride:

1、 Working principle

Polyaluminum chloride is an efficient inorganic polymer coagulant, and its main principles of action in wastewater treatment include charge neutralization and adsorption bridging.

Charge neutralization: Suspended particles in wastewater usually carry negative charges, while polyaluminum chloride hydrolyzes in water to produce various hydrolysis products with positive charges. These positively charged hydrolysis products will attract negatively charged suspended particles, neutralize the surface charge of the particles, thereby reducing the electrostatic repulsion between particles and making them easier to approach each other.

Adsorption bridging: The polymer formed by the hydrolysis of polyaluminum chloride has a linear structure with a large number of active groups on its molecular chain. These polymers can adsorb onto multiple suspended particle surfaces through active groups, forming a "bridging" structure between particles. Through this bridging effect, numerous suspended particles can be connected together to form larger flocs, which are more easily precipitated under gravity, thereby achieving the removal of suspended solids in wastewater.

2、 Processing effect

Polyaluminum chloride exhibits excellent performance in treating industrial wastewater, with specific effects including:

Removing suspended solids and colloidal substances: Polyaluminum chloride can coagulate suspended solids and colloidal substances in wastewater, forming clear flocs that are effectively removed in subsequent sedimentation, filtration, and other processes.

Reduce Chemical Oxygen Demand (COD): Polyaluminum chloride can precipitate and filter out particulate matter that can be oxidized by oxidants to form COD, thereby reducing COD.

Phosphorus removal effect: Polyaluminum chloride has a phosphorus removal effect and can form sediment with phosphate ions in wastewater, making it suitable for phosphorus removal in sewage plants.

Removing other harmful substances: Polyaluminum chloride also has functions such as sterilization, deodorization, degreasing, removal of heavy metal salts, removal of radioactive pollutants, color removal, fluoride removal, aluminum removal, chromium removal, phenol removal, etc.

3、 Usage conditions and influencing factors

PH value: pH value has a crucial impact on the hydrolysis process of polyaluminum chloride. Under acidic conditions, the hydrolysis of PAC may be inhibited to some extent; When the pH value is around neutral, PAC can be fully hydrolyzed, producing a large amount of hydrolysis products with appropriate polymerization degree and positive charge density. At this time, the removal effect of suspended solids in sewage is better; In environments with strong alkalinity, PAC may generate aluminum hydroxide precipitation.

Temperature: Temperature can affect the rate of chemical reactions and the formation and settling process of flocs. At lower temperatures, the hydrolysis reaction rate of PAC will slow down, requiring longer time to achieve good treatment results; Meanwhile, low temperature will increase the viscosity of sewage and slow down the settling speed of flocs. Under high temperature conditions, although the hydrolysis reaction rate accelerates, it may also lead to loose floc structure and difficulty in settling.

The properties of impurities in sewage include particle size, surface charge density, hydrophilicity, etc. If the suspended particles in the sewage are small and uniform in size, more PAC is needed to achieve effective charge neutralization and adsorption bridging. When the impurity concentration in sewage is high, it is necessary to increase the dosage of PAC accordingly, but excessive dosage may lead to secondary pollution.

4、 Application Cases

In a sewage treatment plant in a certain city, polyaluminum chloride was introduced as a flocculant to improve the efficiency of sewage treatment. The wastewater treated with polyaluminum chloride has greatly improved its water quality. The originally turbid sewage has become much clearer, and indicators such as chemical oxygen demand (COD) and biochemical oxygen demand (BOD) have significantly decreased. Meanwhile, the use of polyaluminum chloride also reduces processing costs and improves processing efficiency.

In summary, polyaluminum chloride has significant effects and broad application prospects in the treatment of industrial wastewater. During use, it is necessary to adjust and optimize according to factors such as water quality, pH value, temperature, etc. to ensure the best treatment effect.