The factors that affect the coagulation effect (agent dosage) in water treatment are relatively complex, including water temperature, pH value and alkalinity, the nature and concentration of impurities in the water, external water conservancy conditions, etc. Just a few of the main factors are outlined below.
1. The influence of water temperature
Water temperature has a significant impact on chemical consumption, especially low water temperature in winter. Generally, flocculant 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 low-temperature water coagulants;
②. The high viscosity of low-temperature water weakens the Brownian motion intensity of impurity particles in the water and reduces the chance of collision, which is not conducive to the destabilization and cohesion of colloids and also affects the growth of flocculant.
③. When the water temperature is low, the hydration of colloidal particles is enhanced, which hinders colloid aggregation and also affects the adhesion strength between colloidal particles.
④. 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 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 water is acidic or alkaline, which is an indicator of the concentration of H+ in the water. The pH value of the raw water directly affects the hydrolysis reaction of the coagulant, that is, the coagulation effect can be guaranteed only when the pH value of the raw water is within a certain range. When coagulant is added to water, the H+ concentration in the water increases due to hydrolysis of the coagulant, which causes the pH value of the water to decrease and hinders the progress of 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 amount of alkalinity (usually HCO3-), which can neutralize the H+ produced during the hydrolysis 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 excessively, 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 chargeability of SS particles in water will affect the coagulation effect. Generally speaking, if the particle size is small and uniform, the coagulation effect is poor, the particle concentration in the water is low, and the probability of particle collision is small, which is detrimental to coagulation; when the turbidity is large, in order to destabilize the colloid in the water, the required chemical consumption is will be greatly increased. When there is a large amount of organic matter in the water, it can be adsorbed by the clay particles, thus changing the surface characteristics of the original colloidal particles and 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 the organic matter. , 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 beneficial 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 rainwater erosion. The generally adopted method of increasing the dosage of chlorine and coagulant beforehand is based on this.
4. Influence of external water conservancy conditions
The basic conditions for the agglomeration of colloidal particles are, first, to destabilize the colloidal particles, and second, to cause the destabilized colloidal particles to collide with each other. The main function of the coagulant is to destabilize the colloidal particles, while external hydraulic agitation ensures that the colloidal particles can fully contact the coagulant, causing the colloidal particles to collide with each other to form flocculant. To fully contact the colloidal particles with the coagulant, the coagulant must be quickly and evenly dispersed into all parts of the water body after it is put into the water. This is commonly known as rapid mixing, which requires within 10 to 30 seconds and no more than 2 minutes at most.
5. Influence of water volume impact load
Water volume shock refers to the periodic or non-periodic water volume shock of raw water that changes suddenly and greatly. For water plants, urban water consumption and upstream water volume adjustments will affect the amount of water entering the plant. Especially during the peak water supply period in summer, the amount of water entering the plant changes greatly, resulting in frequent adjustments to the dosage of chemicals, and the effect of post-sinking water is not very satisfactory. It is worth noting that this change does not rise linearly. Afterwards, attention should be paid to observing the alum flowers in the reaction tank to avoid excessive dosage and destroying the coagulation effect.
6. Flocculant medication saving measures
In addition to the above influencing factors, there are also some drug-saving measures, such as increasing the number of stirring times in the drug liquid pool, reducing the precipitation of drug solid particles, and stabilizing drug properties, which can also achieve the purpose of saving drug consumption.
1. If you want to save costs when using polyacrylamide, you first need to choose the type of polyacrylamide to use. The principle is to choose the polyacrylamide with the best effect in treating wastewater. Expensive ones are not necessarily the best, and don’t try to be cheap. As a result, the wastewater treatment effect is poor, but it will increase the cost. Select chemicals that not only reduce the moisture content of the sludge, but also have a lower unit dosage of chemicals. First, conduct a flocculation experiment on the provided pharmaceutical samples in the laboratory, select two to three pharmaceuticals with good experimental results, and conduct on-machine experiments respectively to observe their final mud-out effect, and determine the final pharmaceutical variety accordingly.
2. Polyacrylamide is generally solid particles. It needs to be prepared into an aqueous solution with a certain solubility. The concentration is usually between 0.1% and 0.3%. Too thick or too thin will affect the effect, waste chemicals, increase costs, and dissolve granular polymerization. The water in the building should be clean (such as tap water) and not sewage. Normal temperature water is enough and generally does not need to be heated. Dissolution is very slow when the water temperature is lower than 5℃. Increasing the water temperature will speed up the dissolution rate, but above 40℃ will accelerate the degradation of the polymer and affect the use effect. Generally, tap water is suitable for preparing polymer solutions. Water with strong acid, strong alkali and high salt content is not suitable for preparation.
3. When preparing the agent, attention must be paid to the aging time, so that the agent is fully dissolved in the water and does not agglomerate. Otherwise, it will cause waste and affect the mud removal effect. At the same time, it will easily cause blockage of the filter cloth and tube, creating repeated waste. Once the solution is prepared, its storage time is very limited. Generally speaking, when the solution concentration is 0.1%, the non- and anionic polymer solution should not be used for more than one week; the cationic polymer solution should be used for no more than one day.
4. After the agent is prepared, during the dosing process, attention should be paid to the changes in the quality of the incoming mud and the effect of the mud out, and adjust the dosage of the agent in a timely manner to achieve a better dosage ratio.
5. The medicine should be stored in a dry warehouse, and the medicine bag should be sealed. During use, use as much as possible, and the unused medicine should be sealed to avoid moisture. When preparing pharmaceuticals, care should be taken not to prepare too much. Pharmaceutical solutions that have been left for a long time are prone to hydrolysis and cannot be used anymore.
The dosing pump is prone to clogging during the polyaluminum chloride process. We have summarized several reasons for you:
6. There is a problem with the dilution ratio of polyaluminum chloride. Before using polyaluminium chloride, the solid should be fully dissolved in a ratio of 1:10. If such a problem still occurs, you can continue to increase the dilution ratio, because the solid particles are not fully dissolved and are mixed with solid insoluble matter, which can easily block the pipeline.
7. Improper dissolution methods. There are many methods for dissolving polyaluminum chloride. You can check the dissolving ability of the equipment to see if it is fully dissolved. Some impellers may be too small. After dosing, the solids will sink directly to the bottom and the solid particles of polyaluminum chloride at the bottom cannot be stirred.
8. Problems with the quality of polyaluminum chloride. If all the previous situations are checked and there are no problems, then consider whether there is a problem with the quality of polyaluminum chloride. Polyaluminium chloride products of poor quality often contain too much water-insoluble matter, large impurities, slow dissolution time, and even agglomeration. In addition, low content is also a problem. When the content is low, in order to achieve the treatment effect, more products must be added, which creates a vicious cycle. You might as well use some good products. Their dosage is small, there are few impurities, they have good flocculation, and they settle quickly. They can also solve the problem of clogging the dosing pump.
