The difference between PAC and PAM

1.PAC

Polyaluminum chloride (PAC), also known as basic aluminum chloride or aluminum hydroxychloride

Through it or its hydrolyzate, colloids in sewage or sludge can quickly form sediments to facilitate the separation of large particle sediments. The molecular formula of PAC is [Al2(OH)nCl6-n]m, where n is any integer from 1 to 5, m is the degree of polymerization, that is, the number of chain links, and the value of m is not greater than 10.

The coagulation effect of PAC is closely related to the ratio of OH and Al (n value), which is usually expressed by the degree of alkalization. The degree of alkalization B=[OH]/(3[Al])X100%. B is required to be 40~60%, and the suitable pH range is 5-9.

The hydrolysis process and mechanism of iron salt coagulant are similar to those of aluminum salt.

The polyaluminum chloride sold on the market is relatively mixed, because each manufacturer's production process and raw materials are different, and the colors produced are also somewhat different. Generally, there are three colors of polyaluminum chloride: white, yellow, and tan.

Polyaluminium chloride with an alumina content between 27 and 30 within the national standard is mostly khaki to yellowish-yellow solid powder.These types of polyaluminium chloride have relatively good water solubility. During the dissolution process, they are accompanied by physical and chemical changes such as electrochemistry, condensation, adsorption and precipitation, and finally form precipitation, thereby achieving the purpose of purification.

Therefore, when using polyaluminum chloride, there is no need to add other additives. The flocs are formed quickly and thickly, with high activity, rapid precipitation, and obvious purification effect on high turbidity water.

(1) White polyaluminum chloride

Because it is called high-purity iron-free white polyaluminum chloride, or food-grade white polyaluminum chloride, it is a product of the highest quality compared with other polyaluminum chlorides. The main raw materials are high-quality aluminum hydroxide powder and hydrochloric acid, using The production process is the most advanced spray drying technology in China.

White polyaluminum chloride is used in many fields such as paper sizing agent, sugar decolorizing and clarifying agent, tanning, medicine, cosmetics, precision casting and water treatment.

(2) Yellow polyaluminum chloride

The raw materials of yellow polyaluminum chloride are calcium aluminate powder, hydrochloric acid, and bauxite. It is mainly used in sewage treatment and drinking water treatment. If it is used for drinking water treatment, the raw materials are aluminum hydroxide powder, hydrochloric acid, and a little calcium aluminate. Powder, the process adopted is plate and frame filter press process or spray drying process. Since countries for drinking water treatment have strict requirements on heavy metals, both raw materials and production processes are better than brown polyaluminum chloride.

Yellow polyaluminium chloride is generally produced by drum drying or spray tower drying. It is available in two solid forms: flakes and powder.

(3) Brown polyaluminum chloride

The raw materials of brown polyaluminum chloride are calcium aluminate powder, hydrochloric acid, bauxite and iron powder.

The production process uses a drum drying method, which is generally used in sewage treatment. Because iron powder is added to it, the color is tan. The more iron powder is added, the darker the color. If the iron powder exceeds a certain amount, the color will be darker at some point. It is called polyaluminum ferric chloride and has excellent results in sewage treatment.

2.PAM

Polyacrylamide (PAM for short), commonly known as flocculant or coagulant, is a coagulant

The average molecular weight of PAM ranges from thousands to tens of millions. It has several functional groups along the bonded molecules and can be mostly ionized in water. It is a polymer electrolyte.

According to the characteristics of its dissociable groups, it is divided into anionic polyacrylamide, cationic polyacrylamide, and nonionic polyacrylamide.

PAM appears as a white powder, easily soluble in water, and almost insoluble in benzene, ether, esters, acetone and other general organic solvents. The polyacrylamide aqueous solution is an almost transparent viscous liquid, which is non-dangerous, non-toxic and non-corrosive. Properties, solid PAM is hygroscopic, and the hygroscopicity increases with the increase in ionicity. PAM has good thermal stability;

It has good stability when heated to 100°C, but it easily decomposes to produce nitrogen when heated above 150°C. It undergoes imidization between molecules and is insoluble in water. Density: 1.302mg/l (23°C). The glass transition temperature is 153°C, and PAM exhibits non-Newtonian fluidity under stress.

Cationic and anionic PAM are suitable for sewage or sludge with negative and positive charges respectively. The activated sludge produced by biochemical methods has a negative charge, so cationic type should be used.

Anionic PAM is effective in treating sewage or sludge with positive charges, such as sewage from steel plants, electroplating plants, metallurgy, coal washing and dust removal. Non-ionic ones have better effects on cations and anions, but the unit price is very expensive, which increases the treatment cost.

Reaction conditions and dosage requirements

1. The function of flocculation tank

The function of the flocculation tank is: after the coagulant is added to the raw water, it is fully mixed with the water body. Most of the colloidal impurities in the water lose their stability. The destabilized colloidal particles collide with each other and agglomerate in the flocculation tank. The final formation can be removed by precipitation. of floc.

2. Reaction conditions

The process of floc growth is the process of contact and collision of tiny particles. The quality of the flocculation effect depends on the following two factors: first, the polymer complex produced after the coagulant is hydrolyzed to form an adsorption bridging connection ability, which is determined by the properties of the coagulant; second, the collision of tiny particles The probabilities and how to control them for reasonable and effective collisions.

The water treatment engineering discipline believes that in order to increase the probability of collision, the velocity gradient must be increased. Increasing the velocity gradient must increase the energy consumption of the water body, that is, increase the flow rate of the flocculation tank. On the one hand, if the particles agglomerate and grow too fast during flocculation, Two problems will arise:

(1) If the floc grows too fast, its strength will weaken. If it encounters strong shear during the flow process, the adsorption bridge will be cut off. The cut adsorption bridge will be difficult to continue, so the flocculation process is also a speed increase. In the restricted process, as the floc grows, the water flow speed should continue to decrease, so that the formed floc is not easily broken.

(2) The excessive growth of some flocs will sharply reduce the specific surface area of the flocs in the water, and some small particles with imperfect reactions will lose their reaction conditions. The probability of collision between these small particles and large particles will be sharply reduced, making it difficult to grow again. These particles are not only unable to be retained by the sedimentation tank, but also difficult to be retained by the filter.

3. Addition requirements

In the early stage of the reaction when coagulant is added, the chance of contact between the agent and sewage should be increased as much as possible, and the stirring or flow rate should be increased.

Relying on the collision between the water flow and the folding plates and the multiple turns of the water flow between the folding plates to increase the speed, the chances of collision of particles in the water are increased and the flocs are agglomerated. In the later stage of the reaction, in order to reduce the velocity gradient, better flocculation and precipitation effects can be obtained.

Instructions

1. PAM and PAC dosing device

The main equipment that constitutes the dosing device is: medicine dissolving tank, medicine storage tank, dosing mixer, dosing pump and metering equipment. .

2. PAC preparation method and dosage

There are no special requirements for preparation. The weight ratio concentration of the prepared solution is generally 10-20%, and the dosage during application is generally around 200-300PPM (200-300 mg of PAC per liter of water).

For the calculation of the set value in the flow meter of the dosing pump, please refer to the method for calculating the PAM dosing amount below.

3. PAM preparation method and dosage

(1) Preparation method:

Powdered products cannot be put directly into sewage. They must be dissolved in water before use and their aqueous solution can be used to treat sewage.

The water used for dissolution should be clean water (tap water), not sewage. It can be at room temperature and generally does not require heating. However, it dissolves slowly when the water temperature is lower than 5 degrees Celsius. If the dissolution temperature is above 60 degrees Celsius, the polymer will accelerate degradation and affect its use effect, and water with strong acid, strong alkali, and high salt content is not suitable for preparation.

For the selection of polymer solution concentration, 0.1~0.3% is recommended.

When dissolving, the agent should be slowly added to the rotating water. Do not add it all at once to avoid affecting the dissolution speed or blocking the pipeline due to insufficient dissolution.

The solution must be prepared immediately before use. If left for a long time, it will degrade and affect the use effect. When the solution concentration is 0.1%, the non-anionic polymer aqueous solution should be stored for no more than one week, and the cationic polymer should be stored for no more than one day.

The stability of the solution is related to the concentration. The more concentrated the solution, the longer it will be stored. However, the highly concentrated solution cannot be used directly for water treatment and needs to be diluted before use.

Iron ions are the catalyst that causes the chemical degradation of all polyacrylamides, so try to avoid the entry of iron ions when preparing, transferring, and storing polyacrylamide solutions. Equipment in contact with solutions is best made of stainless steel, plastic, fiberglass or resin-coated carbon steel.

When adding to wastewater, use low concentration to ensure uniform mixing.

It is necessary to determine the type and optimal dosage of the medicine through experiments when using it. The proportioning concentration of polyacrylamide is 0.2%. The steps are as follows: Use a balance to weigh 0.8g of PAM and set aside; ·Measure 400ml of water and pour it into a 500ml beaker, and place the beaker on the electromagnetic mixer; start the mixer and add 0.8g of PAM in batches Add it into the beaker gradually; stir for about 60 minutes, carefully observe the solution state, and prepare the solution when the granular and thick lumps completely disappear.

(2) Adding amount:

After adding PAM to sewage or sludge, it must be mixed effectively. The mixing time is generally 10-30 seconds and generally no more than 2 minutes.

The specific usage amount of PAM has a great relationship with the concentration and properties of colloids and suspended solids in sewage or sludge, as well as treatment equipment. The dosage when treating sewage is generally within 3-10PPM, that is, 3 per ton of water is added -10 grams, the dosage should be more when treating sludge, and the optimal dosage must be obtained through a large number of experiments.

According to the optimal dosage concentration (the concentration of polyacrylamide to be added in PPM1), the inlet water flow rate (t/h) and the concentration of the configured polyacrylamide solution (the concentration of polyacrylamide prepared in PPM2), the dosing pump can be calculated The value displayed on the flow meter (LPM).

That is: inlet water flow rate (t/h)/60×PPM1 concentration of polyacrylamide to be added/polyacrylamide concentration prepared by PPM2. For example, water inflow = 100 t/h, optimal dosage PPM1 = 10ppm, preparation concentration is 2‰ (3Kg of medicine dissolved in 1.5t of water)

Then: the dosing flow indicator should be adjusted on the 100/60*10/2=8.3LPM scale.

Note: ppm is one part per million; the unit of dosing pump flow count value: on the right, LPM is liters/minute; on the left, GPM is gallons/minute (not used).

Precautions:

When preparing pharmaceutical solutions, strictly follow the operating procedures and instructions for use;

Debris must not be mixed into the liquid medicine to avoid clogging the dosing pump, flow meter, etc.;

According to the amount of water inflow and the chemical dosage notice issued, the dosage should be adjusted in time to achieve the best treatment effect.

Judgment of the effects of PAC and PAM administration