PAC (polyaluminium chloride) is a common chemical used in water and wastewater treatment processes since it highly removes contaminants. PAC is available in liquid and spray-dried (powder) form.
Although both forms share the same fundamental objective and work well, they exhibit strict differences within their respective spheres.
It is important to understand these differences in industries and municipalities so that they can make the right choice on the cost and logistics. This article focuses on what distinguishes spray dried poly aluminium chloride and the advantages and issues with both.
Spray-Dried vs. Liquid PAC: Key Differences in Industrial Water Treatment Applications
Production Process and Physical Form
Liquid PAC is usually synthesised through a reaction of hydrochloric acid with aluminum hydroxide. This produces a clear or slightly yellow aqueous solution. This form is provided in containers or tanks ready to be used in water treatment.
On the other hand, spray-dried PAC is produced by carrying out a drying process in which a liquid form of PAC is converted to fine, yellowish powder. In spray drying, atomized liquid PAC is dried by hot air in a chamber. This quick drying solidifies the droplets into quick, transportable, and storeable powder particles. PAC powder form is lightweight and has a longer shelf life compared to liquid PAC.
Chemical Composition and Purity
Higher levels of aluminum oxide are found in spray-dried PAC. The percentage normally fluctuates between 28–33 percent, depending on the grade. This results in high concentration, leading to reduced water content and increased purity. That is to say, it is presenting increased active coagulant material at a lesser amount of volume.
Liquid PAC typically contains less aluminum (10 percent to 15 percent). It may also contain water and, in some cases, increased levels of water-insoluble contaminants because of the processing procedures.
Storage and Shelf Life
The other major benefit of spray-dried PAC is that it has an extended shelf life and does not require much storage space. As a powder, it can be stored in sealed containers or bags and retains its shelf-life without depreciation since it is a stable form.
Of course, liquid PAC has a shorter shelf life. It can deteriorate over time, particularly in the presence of temperature or light variations. Contamination can also render it unusable. Moreover, the liquid form requires a larger storage space and necessitates special containment to prevent spillage.
Dosage and Dissolution Characteristics
The fine powder form of spray-dried PAC readily and thoroughly mixes in water. This allows the operator to precisely control concentration/dosing. This has proven to be very advantageous in large-scale treatment plants where chemical balancing is of extreme importance.
On the other hand, liquid PAC does not need to be dissolved before being used, as compared to dry PAC. This convenience can make processing in-facility with a direct dosing system simpler.
Performance Differences in Water Treatment
Both the liquid and spray-dried PAC have outstanding coagulation and flocculation ability.
Spray-dried PAC can have a tendency to exhibit a superior capability of forming large, dense flocs owing to its uniform quality and higher active aluminum content. These superior flocs settle quickly, enhancing efficiency and water clarity.
Liquid PAC can also be administered, but will require slightly increased dosages as a result of the dilution and impurities. However, it has continued to be a solid and widely used solution in the case of industrial wastewater.
Economic and Environmental Considerations
Spray-dried PAC has much less mass per volume. Its cost of shipping and storage is also low, but it involves additional preparation, including dissolving before application.
Liquid PAC may be simpler to apply in the short term, but due to the cost of shipping, courtesy of its weight and packaging, it is more costly than solid PAC. There is also a risk of increased costs in storing liquids.
Distinctly environmental, spray-dried PAC will save by way of less chemical addition and minimized sludge stabilization. Smaller packages allow for space savings. This produces less waste and decreases the carbon footprint.
Applications and Industry Preferences
The spray-dried PAC is preferred where standardized, high-purity coagulation chemicals are needed by the municipality's water treatment facilities and industries. Its increased shelf life and its effectiveness will make it suitable for centralised distribution and large-scale operations.
Liquid PAC is Commonly Used In On-Site Industry Wastewater Treatment Plants. They are utilized in those areas where instant dosing is preferred.
Geographical location usually plays into determining the form that is selected. Areas with well-developed distribution channels would tend to go for spray-dried PAC. On the other hand, a batch treatment onsite may be deemed more practical using liquid PAC.
Conclusion
Spray-dried and liquid Poly Aluminium Chloride play a fundamental role in water treatment, with their relevance determined by their applicability in various water treatment processes. PAC in its spray-dried form has advantages that make it suitable for large-scale use in municipal applications.
In liquid form, PAC is convenient to use in direct application and in many industrial applications. The choice of appropriate form is consistent with an organization's operational objectives and costs.