What can be used to replace polyaluminum chloride in sewage treatment？
Release time: 2025-08-27
What can be used to replace polyaluminum chloride in sewage treatment?
In sewage treatment, polyaluminum chloride (PAC) is commonly used, but the following alternatives can be considered in specific scenarios (such as reducing aluminum residue, adapting to low temperature water quality or cost optimization):
I. INHITIFICANT ALTERNATIVES
Polyferric sulfate (PFS)
· Advantages: Stronger adaptability to low temperature environment (still effective at 4℃), fast sedimentation speed, no risk of residual aluminum ion, suitable for drinking water treatment;
· Applicable scenarios: high turbidity wastewater, oily wastewater and areas requiring strict control of aluminum (such as waterworks);
· Cost: 30-50% less than PAC in dosage, and better sludge dewatering performance.
Aluminum iron polychloride (PAFC)
· Features: combined with the advantages of aluminum salt and iron salt, the alum flower is more compact, the sedimentation speed is fast, suitable for high turbidity/low temperature wastewater;
· Scope of application: industrial wastewater (e.g., printing and dyeing, paper making), low temperature and low turbidity water source.
Traditional inorganic agents
· Aluminum sulfate: low cost, but the flocculation effect is weaker than PAC, it should be used with coagulant aid;
· Lime (CaO): used to adjust pH and remove phosphorus, but the sludge production is large, so it needs to be combined with other agents.
II. Organic and Composite Alternatives
Polyacrylamide (PAM)
· Function: It is often used as a coagulant aid in combination with PAC. When used alone, it should be selected according to water quality (cationic/PAM for sludge dewatering);
· Limitations: It can not completely replace the coagulation function of PAC, and it needs to be used with inorganic agents.
Composite flocculant
· PFS+PAM/modified PAM: improve the efficiency of oil-containing wastewater treatment and reduce the total amount of chemicals;
· Chitosan/gelatin based natural flocculant: suitable for food processing wastewater, high safety but high cost.
New patent technology
· Magnetic composite filler +PAC reduction: the adsorption and photocatalytic capacity is enhanced by loading iron oxide, and the amount of PAC is reduced by more than 30%.
III. Special functional alternatives
Dedrophilic agents
· Lime or calcium salt: chemical precipitation method for phosphorus removal, but may increase water hardness;
· Iron salt (e.g., PFS): simultaneous removal of phosphorus and heavy metals, better than aluminum salt.
Decolorization and COD degradation
· Special decolorizer + ferrous sulfate: for dyeing wastewater, replace the decolorization function of PAC.
IV. Recommendations for alternative options
scene | Recommended alternatives | Key strengths |
Low temperature/low turbidity water | Polyferric sulfate (PFS) | Adaptable, no aluminum residue |
High turbidity industrial wastewater | PAFC or PFS+PAM in combination | Alum flowers are dense and settle quickly |
Food/drinking water treatment | Chitosan/gelatin based flocculant | Safe and non-toxic |
Strict control of phosphorus demand | Ferric salt (PFS) or lime | Efficient dephosphorization, low cost |
Reduce PAC usage | Magnetic composite filler technology | Reduce the cost of the agent and improve the catalytic efficiency |
matters need attention ：
- Before replacement, the best dosage and pH range should be determined through pilot test (for example, PFS is suitable for pH 4-11, PAC is 5-8);
- The residue of aluminum-based agents (such as PAC and PAFC) needs to be evaluated, especially in ecologically sensitive water bodies;
- The composite agent may increase the sludge amount, so the dehydration process should be optimized.
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