I. Overview of Polyaluminium Chloride

Polyaluminium Chloride (PAC for short) is a highly efficient inorganic high-molecular coagulant, which is generated by the bridging effect of hydroxide ions and the polymeric effect of multivalent anions. Compared with traditional coagulants, PAC has significant advantages such as fast flocculation speed, large flocs, low dosage, low cost, low corrosiveness and strong adaptability. It is widely used in drinking water treatment, industrial wastewater treatment, urban sewage treatment and other fields.

Ii. Types and Selection of Polyaluminium Chloride Products

1.Product form classification

Liquid PAC: The content is generally 10%-12%. It has a high transportation cost but is convenient to use

Solid PAC: Content 28%-30%, convenient for transportation and storage, needs to be dissolved before use

2.Classification by production process

Drum drying type: Content 28-30%, high water-insoluble matter

Plate and frame filter type: Content 30%, low water-insoluble matter

Spray-dried type: Content 30-32%, extremely low water-insoluble matter, the best quality

3.Basis for selection

Water quality characteristics (such as pH value, turbidity, organic matter content)

Processing technology requirements

Cost budget

Requirements for subsequent processing procedures

Iii. Usage Method of Polyaluminium Chloride

1.Dissolution preparation

Dissolution method of solid PAC:

Add clear water to the dissolution tank in a ratio of 3:1 (water :PAC) first

Turn on the mixer and slowly add the solid PAC, stirring until it is completely dissolved

Prepare it into a 10%-15% solution for later use

Dilute it again to a working concentration of 1%-3% for use

Notes:

The water used for dissolution should be clear water at normal temperature. Do not use sewage or acidic water

When dissolving, it should be added slowly to avoid caking

The stirring speed should be moderate (60-80 RPM). Stirring too fast will damage the molecular structure

The prepared solution should not be stored for a long time (no more than 24 hours).

2.The dosage is determined

General reference range:

Low turbidity water (below 50NTU) : 5-10mg/L

Medium turbidity water (50-200NTU) : 10-20mg/L

High turbidity water (above 200NTU) : 20-50mg/L

Industrial wastewater: 50-1000mg/L(subject to specific water quality tests)

Method for determining the optimal dosage:

Beaker test method: Take 6 beakers and add the same amount of raw water, then add different amounts of PAC respectively

Stir rapidly (150 RPM) for 1 minute and slowly (30rpm) for 10 minutes

Observe the flocculation effect after standing for 10 minutes

The dosage is best when the flocs are large, the sedimentation is fast and the supernatant is clear

3.Addition method

Common addition methods:

Gravity dosing: Suitable for small and medium-sized water plants, it is dosed by gravity in the high-level solution tank

Pump dosing: Accurate measurement, suitable for treatment plants of all scales

Siphon dosing: The equipment is simple, but the vacuum degree needs to be well controlled

The principle for choosing the betting point:

Where the mixture is thorough (such as the suction pipe of the water pump, the mixing tank)

Where the water flow is turbulent

Avoid locations where short-circuiting is likely to occur

4.Key points of operation control

pH value control: The optimal pH range is 6.5-7.5. If it exceeds this range, adjustment is required

Temperature influence: The effect decreases at low temperatures (<5℃). The dosage can be increased or a dedicated low-temperature PAC can be used instead

Stirring conditions: Rapid mixing (30-60 seconds) followed by slow stirring (10-20 minutes)

Sedimentation time: Generally 30 to 60 minutes, adjusted according to water quality

Iv. Application Methods in Different Fields

1.Drinking water treatment

High-purity (food-grade)PAC is adopted

Strictly control the aluminum residue (<0.2mg/L)

When used in combination with activated carbon, it can remove organic matter

Typical dosage: 2-15mg/L

2.Urban sewage treatment

The addition before the primary sedimentation tank can increase the removal rate of SS

Adding it before the secondary sedimentation tank can enhance phosphorus removal

It is used in advanced treatment to further remove pollutants

Typical dosage: 10-50mg/L

3.Industrial wastewater treatment

Papermaking wastewater

The dosing point is placed before the air flotation or sedimentation unit

The dosage is 50-200mg/L

The best effect is achieved when the pH is adjusted to 7-8

Printing and dyeing wastewater

First adjust the pH to 7-8.5

The dosage is 100-500mg/L

It can be used in combination with PAM to increase the decolorization rate

Electroplating wastewater

Used for heavy metal removal

It needs to be adjusted in conjunction with pH (generally set to 8-9).

The dosage is 200-1000mg/L

V. Common Problems and Solutions

1.The flocs are fine and do not settle

Reason: Insufficient dosage or unsuitable pH

Solution: Adjust the dosage or pH value

2.The supernatant is turbid

Reason: Excessive addition led to the re-stabilization of the colloid

Solution: Reduce the dosage or add in sections

3.The aluminum content in the treated water exceeded the standard

Reason: Excessive dosage or improper pH control

Solution: Optimize the dosage and control the pH between 6.5 and 7.5

4.Equipment corrosion

Reason: PAC is highly acidic or the material is not corrosion-resistant

Solution: Select corrosion-resistant materials and rinse promptly after addition

Vi. Safety Precautions for Use

1.Operators should wear protective gloves and glasses

2.Avoid direct contact with skin. If contact occurs, rinse immediately with plenty of water

3.Store in a cool and dry place, away from direct sunlight and rain

4.Do not store or transport together with alkaline substances

5.Liquid products should be protected from freezing in winter

Vii. The Combined use of PAC with other chemicals

1.In combination with polyacrylamide (PAM) :

Add PAC first and then PAM(with an interval of 30 to 60 seconds)

It can significantly improve the flocculation effect and reduce the dosage of PAC

2.Used in combination with lime:

It is used for water with high turbidity or when pH adjustment is required

Generally, lime is added first to adjust the pH, and then PAC is added

3.In combination with activated carbon:

Used for removing organic matter and odors

It can be added simultaneously or successively

Conclusion

Polyaluminium chloride, as an efficient and economical coagulant, its application effect depends on the correct usage method. Users should determine the optimal dosage and process conditions through experiments based on the actual water quality conditions, and pay attention to adjustments and optimizations during operation. The rational use of PAC can not only improve the treatment effect, but also reduce the operating cost, achieving a win-win situation of economic and environmental benefits.