In the use of anionic polyacrylamide flocculants, the biggest problem encountered is the dissolution time of the product. Due to the poor solubility of the product, it directly affects the use effect, and it is easy to block the dosing equipment. Therefore, the indicator specified in the second item of the national standard is the dissolution time. Generally, the hydrolyzate product is easy to dissolve, and the dissolution time is 60min-80min, and the non-ionic product is 60min-80min. In addition, the dissolution time varies with the molecular weight of the product, so it is better to control the molecular weight of the anionic polyacrylamide flocculant in water treatment between 3 million and 18 million.
The preparation of anionic polyacrylamide solution generally adopts mechanical stirring. The mechanical stirring speed has a great influence on the solution preparation time, but excessive stirring speed will cause the degradation of the anionic polyacrylamide solution, break the long chain of part of the anionic polyacrylamide, and affect the sedimentation effect, so it is necessary to strictly control the mechanical stirring speed. In some cases, the rotational speed in a 1m-diameter mixing barrel shall not exceed 800rpm, and the rotational speed in a 1.5m-2m diameter mixing barrel shall not exceed 600rpm. Increasing the temperature of the stirred solution can reduce the dissolution time, but the maximum water temperature should not exceed 55 °C, otherwise it will also cause degradation and affect the use effect.
The preparation of anionic polyacrylamide solution must use special equipment, strictly prevent the co-use with other coagulants, or co-dosing in a dosing tank, otherwise the two drugs will cause copolymerization and precipitation, which will not only affect its effect, but also easy to block dosing equipment.
Since the anionic polyacrylamide flocculant solution is a drag reducing agent, there is a large gap between the calibration value of clean water. Therefore, the anionic polyacrylamide solution metering equipment must be calibrated with solution, not with clean water. Otherwise, the dosage of anionic polyacrylamide will be increased, which will not only increase the processing cost, but also cause unnecessary consequences.
The thinner the solution concentration of anionic polyacrylamide dosage, the better the effect. The thinner dosage concentration can make the solution rapidly expand and fully mix in water, preventing the phenomenon of colloid protection with too high concentration and affecting the use effect. Generally, the dosage concentration is 0.5%-1%, and the preparation concentration is 2%.
The flocculation effect of anionic polyacrylamide flocculant in the treatment of high-turbidity water is better than that of one-time administration. If the sedimentation velocity of the muddy liquid surface is used as a comparative value, the former is more than three times that of the latter. The so-called batch dosing is to divide the dosage into two parts and add them to the water respectively. First add a part of the flocculant and mix it with water quickly. After an interval of 1-2min, add another part of the flocculant, and then mix quickly with water. Since the batch administration can avoid the combination of excessive flocculant concentration and sediment, resulting in the result that the active group is blocked, it can achieve better results.
When anionic polyacrylamide is used as a coagulation aid, the general order of dosing is after the coagulant is added. If it is used as a flocculant for treating high turbidity water alone, anionic polyacrylamide flocculant should be added first, otherwise it will affect the use effect. In the design of the dosing room, the measures for changing the dosing sequence should be considered.