Aspects of the water treatment process that impact how coagulants flocculate

1. Water's pH is one.

• The process of coagulation is significantly influenced by the pH value, including
• Aluminum hydroxide's solubility is affected.
• Colloid aluminum hydroxide's impact on electrical characteristics
• Impacts on water's organic matter
• Factors that affect the flocculation rate of colloidal solutions

2. The volume of coagulant

The amount of coagulant injected cannot be calculated since the coagulation process is not a straightforward chemical reaction. To determine the ideal dose, certain situations must be examined carefully.

When utilizing Al2(SO4)3.18H2O, the ideal alum concentration in water is often 0.1–0.5 mg/1, or 10–50 mg/l or 8–10 mg/1 for polymers. In general, more coagulant is needed the more suspended particles there is in the water. Another possibility is that the water has a low level of organic matter but a high level of coagulation.

3. Water temperature

The water's temperature has a significant impact on the coagulation process when aluminum salt is used as a coagulant. Alum cotton is big and porous, and it contains a lot of water that settles extremely slowly when the water temperature is low (less than 50C), thus the impact is weak.

The lowest water temperature of 25–30°C should be used to coagulate natural water while employing alum aluminum sulfate. Temperature has less of an impact on the coagulation process when iron salt is used as the coagulant.

4. Mixing speed of water and coagulant

The relationship of the mixing speed of water and coagulant to the uniform distribution of the coagulant and the chance of collision between the colloidal particles is also an important factor affecting the flocculation process. The best stirring speed is to switch from fast to slow. When the coagulant is first added to the water, it must be stirred quickly, because the hydrolysis of the coagulant in the water and the formation of the coagulant is very rapid. Therefore, it is necessary to stir quickly to be able to form a large amount of colloidal hydroxides with small particles, making them quickly diffuse to places in the water in time with the impurities in the water. After the mixture has formed and grown, it is not advisable to stir quickly as this may break the formed alum flakes.

5. Water contamination

An aqueous solution may coagulate if the presence of opposing ions is increased. As a result, an impurity of this kind that impacts the coagulation process is the opposite ion.

6. Contact medium

If a certain layer of sludge is kept in the water during coagulation or other precipitation treatments, the precipitation process is more complete, increasing the precipitation rate. The sludge layer serves as a contacting medium and has the effects of adsorption, promotion, and crystallization on its surface. As a result, the majority of equipment used for flocculation or other precipitation treatment includes a sludge layer.

7. Some flocculation products

To reduce or remove the drawbacks of conventional iron and aluminum alum coagulants, people have recently started to pay attention to the study and development of novel flocculants:

• Reducing the pH of the water after treatment, which necessitates using it quickly to adjust the pH, driving up treatment costs.
• A high level of free ions that remain after therapy.
• Less effective in sources of water with considerable turbidity and color.
• Use more flocculation, sedimentation aids, etc.

Since the 1980s, novel coagulants that are water-soluble polymers of aluminum and iron with an anion of Cl- or (SO4)2- and have a very low acidity owing to hydrolysis have been created and used by scientists. When these coagulants are introduced to water, they do not need to go through the polymer formation stage because (with H+ production) has been done in the process of polymer forming products, therefore the flocculation rate is high and the result is a highly desirable amorphous hydroxide precipitate. Polyaluminum chloride (PAC) and polyferric chloride (PFC) are the first. The experiments reveal that both PAC and PFC exhibit excellent processing capacity and good treatment efficiency for turbidity, heavy metals, and COD. at low temperatures and during the treatment of wastewater. However, PFC has no advantage over FC (Iron III chloride), while PAC has many advantages over AS (Aluminum II sulfate).

As aluminate is formed from polymer extremely slowly in a high pH environment (9.5), PAC still has significant flocculation capacity but alum alum (AS) does not. Because the suspension and the coagulant are both positively charged, neither PAC nor AS can coagulate in the pH 5 area. In China, France, Germany, Canada, the United States, Japan, and other countries, PAC is frequently used to replace conventional aluminum alum. Experience with PAC has shown that it is particularly good for source water with turbidity, high, low temperature, and hardness. Vietnam, which has steadily used PAC since 1995, can condense equipment and treatment space since PAC causes the pH of water to alter less, uses fewer water pipelines, and has a quick flocculation rate. After then, research projects continued to emerge beginning in the 1990s, leading to the creation of a number of novel products, including polyaluminum sulfate (PAS), polyaluminium silicate sulfate (PASS), polyferric sulfate (PES), and polyalumino ferric acid (PAFS). The materials gathered indicate that although these items have not yet been discovered in Vietnam, they all share the same benefits as PACs in that they may be employed at low concentrations, do not require the pH of the treated water to be adjusted after treatment, and are all active. Excellent at low temperatures, completely eliminate extra coagulant content in water, and small, portable treatment equipment. The cost of the product is substantially more than that of standard coagulants since it is a novel product and the reaction conditions to make these inorganic polymers are highly severe, requiring equipment, pressure, and temperature. However, the dose utilized is also lowered by many times. Therefore, the choice of coagulant for water treatment relies on the economic capability of each location, each unit, and each plant, although the majority of recently built industries pick this new product for water treatment. and the benefits mentioned above. Vietnam and international markets both carry this novel coagulant product. The Al2O composition of items is continually being improved by manufacturers while product costs are also being reduced.