The function of polyacrylamide will not be introduced here. In the following content, we will combine some relevant information on the stirring time, stirring speed, dosage concentration, and dosage order of polyacrylamide to understand several common problems in the use process, and provide a brief introduction. There will be many problems in practical applications, and specific problems will be analyzed. To get straight to the topic, let's start with the stirring time and speed of polyacrylamide solution.
1. Mixing speed
When preparing a solution, mechanical stirring is generally used, and the stirring speed has a significant impact on the preparation time of the solution, so the mechanical stirring speed is strictly controlled. Excessive stirring speed can cause degradation of polyacrylamide solution, resulting in partial breakage of polyacrylamide molecular chains and affecting its flocculation effect. In general, the speed of rotation in a mixing tank with a diameter of 1 meter should not exceed 800 rpm, and in a mixing tank with a diameter of 1.5-2 meters, the speed of rotation should not exceed 600 rpm. If you want to speed up the dissolution time, you can increase the temperature of the stirring solution, but the water temperature should be controlled below 60 ℃, otherwise it will also affect its effectiveness.
2. Mixing time
The stirring time in the mixing tank varies depending on the external temperature and on-site environment, and there are many uncertain factors. Under normal circumstances, it is 40-60 minutes.
3. Addition concentration
The optimal concentration for general addition is 0.5% to 1%, and the optimal concentration for preparation is 2%. Excessive concentration of polyacrylamide solution can cause colloidal protection, affecting its effectiveness. The thinner the concentration, the better the effect. A thinner concentration can quickly expand and fully mix the solution in water, but a concentration that is too dilute can cause a large dosing equipment. So adjust according to the on-site facilities.
4. Order of addition
When designing the dosing room, measures for changing the dosing sequence should be considered. When polyacrylamide is used as a coagulant aid, the general dosing sequence is after adding the coagulant. If used alone as a flocculant for treating high turbidity water, polyacrylamide flocculant should be added first, otherwise it will affect the effectiveness of use.
5. Batch administration of medication
Divide the dosage into two parts and add them separately to the water. First, add a portion of the flocculant and mix it quickly with the water. After 1-2 minutes, add another portion of the flocculant and mix it quickly with the water. Due to the ability to prevent excessive concentration of flocculants from binding with sediment, resulting in the closure of active groups, batch administration can achieve better results. The proportion of batch administration is generally 60% first, followed by 40%. In the design of water supply engineering, if conditions permit, measures such as batch dosing should be adopted as much as possible. The advantage of batch dosing is that it has a better flocculation effect than single dosing when dealing with highly turbid water.
In addition, specialized equipment is used for the preparation of polyacrylamide solution, and it is strictly prohibited to use it together with other coagulants or to add it together in a mixing tank. Otherwise, the two agents will produce co precipitation, which not only affects their effectiveness but also easily clogs the feeding equipment.
