What causes flocculants to be used more and more often

Flocculant dosage changes, mainly internal and external reasons, the internal reason is whether there is a change in the type of chemicals, suppliers, etc., external factors are mainly environmental conditions, the effect of coagulation in water treatment (agent dosage) is more complex factors, including water temperature, pH and alkalinity, the nature of the impurities in the water and the concentration of the external water conditions, and so on.

Factors affecting the dosage of flocculants

1. Internal factors 

1. Change the type of flocculant 

Different types of flocculants will definitely change the dosage, for example, the molecular weight of Pam changes from 10 million to 8 million, iron salt is replaced by aluminum salt, etc.!

2. Change suppliers 

This is a common internal factor. In many cases, the same type of flocculants from different suppliers have different performances. Sometimes suppliers are changed to save costs or for some unspeakable reasons, but low prices do not necessarily guarantee high efficiency, and the dosage may also be different! 

2. External factors

1. The influence of water temperature

Water temperature has a significant impact on drug consumption, especially low water temperature in winter has a greater impact on drug consumption. Usually, floccules form slowly, and the particles are small and loose. The main reasons are: 1. The hydrolysis of inorganic salt coagulants is an endothermic reaction, and it is difficult to hydrolyze coagulants in low-temperature water; 2. The viscosity of low-temperature water is large, which weakens the Brownian motion intensity of impurity particles in the water, reduces the chance of collision, is not conducive to colloid destabilization and coagulation, and also affects the growth of floccules. 3. When the water temperature is low, the hydration of the colloidal particles is enhanced, which hinders the coagulation of the colloids and also affects the adhesion strength between the colloidal particles. 4. The water temperature is related to the pH value of the water. When the water temperature is low, the pH value of the water increases, and the corresponding optimal pH value for coagulation will also increase. Therefore, in winter in cold areas, it is difficult to obtain a good coagulation effect even if a large amount of coagulant is added. 

2. The influence of pH value and alkalinity 

The pH value is an indicator of whether the water is acidic or alkaline, that is, an indicator of the H+ concentration in the water. The pH value of the raw water directly affects the hydrolysis reaction of the coagulant, that is, when the pH value of the raw water is in a certain range, the coagulation effect can be guaranteed. When the coagulant is added to the water, the H+ concentration in the water increases due to the hydrolysis of the coagulant, which causes the pH value of the water to decrease, hindering the hydrolysis. To keep the pH value within the optimal range, there should be enough alkaline substances in the water to neutralize H+. Natural water contains a certain alkalinity (usually HCO3-), which can neutralize the H+ produced by the hydrolysis process of the coagulant and has a buffering effect on the pH value. When the alkalinity of the raw water is insufficient or the coagulant is added in excess, the pH value of the water will drop significantly, destroying the coagulation effect. 

3. The influence of the nature and concentration of impurities in water 

The size and charge of SS particles in water will affect the coagulation effect. Generally speaking, the coagulation effect is poor when the particle size is small and uniform, the particle concentration in the water is low, and the probability of particle collision is small, which is not conducive to coagulation; when the turbidity is very large, the required drug consumption will be greatly increased in order to destabilize the colloid in the water. When there is a large amount of organic matter in the water, it can be adsorbed by clay particles, thereby changing the surface characteristics of the original colloidal particles, making the colloidal particles more stable, which will seriously affect the coagulation effect. At this time, oxidants must be added to the water to destroy the effect of organic matter and improve the coagulation effect. Soluble salts in water can also affect the coagulation effect. For example, when there are a large amount of calcium and magnesium ions in natural water, it is conducive to coagulation, while a large amount of Cl- is not conducive to coagulation. During the flood season, high-turbidity water containing a large amount of humus enters the plant due to the scouring of rainwater. The general practice of increasing the amount of pre-chlorination and coagulant dosage is based on this.

4. Influence of external hydraulic conditions

The basic conditions for the coagulation of colloidal particles are, first, to destabilize the colloidal particles, and second, to make the destabilized colloidal particles collide with each other. The main function of the coagulant is to destabilize the colloidal particles, and the external hydraulic agitation is to ensure that the colloidal particles can fully contact with the coagulant, so that the colloidal particles collide with each other to form flocs. In order to make the colloidal particles fully contact with the coagulant, it is necessary to quickly and evenly disperse them to all parts of the water body after the coagulant is added to the water, commonly known as rapid mixing, which is required within 10 to 30 seconds, and no more than 2 minutes at most. 

5. Influence of water volume shock load

Water volume shock refers to the periodic or non-periodic, sudden and large change of raw water volume shock. For the water plant, the city's hourly water consumption and upstream water volume adjustment will affect the water volume entering the plant, especially in the peak water supply period in summer, the hourly water volume entering the plant changes greatly, resulting in frequent adjustments to the dosage of reagents, and the effect of water after settling is not very ideal. It is worth noting that this change is not a linear increase, and attention should be paid to observing the alum flowers in the reaction tank to avoid excessive dosage and damage to the coagulation effect.

Flocculant drug-saving measures

In addition to the above factors, there are some drug-saving measures, such as increasing the stirring times of the liquid medicine pool, reducing the precipitation of solid particles of the agent, stabilizing the drug properties, and also achieving the purpose of saving drug consumption.

1. If you want to save costs in the use of polyacrylamide, you first need to choose the model of polyacrylamide. The principle is to choose the polyacrylamide with the best wastewater treatment effect. The expensive one is not necessarily the best, and you should not seek cheapness to cause poor wastewater treatment effect, which will increase the cost. Select the agent that reduces the sludge moisture content and has a lower unit agent usage. First, do a flocculation experiment on the provided agent samples in the laboratory, select two to three agents with good experimental effects, and then do machine experiments to observe their final mud discharge effect, and determine the final agent variety based on this.

2. Polyacrylamide is generally a solid particle, and it needs to be configured into a certain solubility aqueous solution when used. The concentration is usually between 0.1% and 0.3%. Too concentrated or too diluted will affect the effect, waste agents, and increase costs. 

The water that dissolves the granular polymer should be clean (such as tap water) and cannot be sewage. Water at room temperature is sufficient, and generally no heating is required. When the water temperature is below 5°C, the dissolution is very slow. The dissolution speed increases with the increase in water temperature, but above 40°C, the polymer will degrade faster, affecting the use effect. Generally, tap water is suitable for preparing polymer solutions. Strong acid, strong alkali, and high-salt water are not suitable for preparation.

3. In the preparation of the agent, attention must be paid to the aging time, so that the agent should be fully dissolved in the water and not agglomerated, otherwise it will cause waste and affect the mud discharge effect. At the same time, it is easy to cause blockage of the filter cloth and pipeline, creating repeated waste. After the solution is prepared, its storage time is very limited. Generally speaking, when the solution concentration is 0.1%, the non-ionic and anionic polymer solutions do not exceed one week; the cationic polymer solution does not exceed one day.

4. After the agent is prepared, during the addition process, attention should be paid to the changes in the mud quality and the mud discharge effect, and the dosage of the agent should be adjusted in time to achieve a better dosage ratio.

5. The medicine should be stored in a dry warehouse, and the medicine bag should be sealed. When using, use as much as possible, and seal the unused medicine to prevent moisture. When preparing the medicine, be careful not to prepare too much. The medicine solution that has been stored for a long time is easy to hydrolyze and can no longer be used.