【Weekly Topic】-007-How to Improve the Coagulation Effect in Physical and Chemical Processes

The most commonly used combination is PAC plus PAM for pH adjustment; the effectiveness can be determined visually. The selection of different types of chemicals, as well as their concentrations, are all crucial factors. PAM also comes in positive and negative forms, and a good choice can be made through experience and preliminary experiments

Common combinations include: 1. Aluminum sulfate + lime (or liquid alkali) + PAM； 2. Ferric trichloride + lime (or liquid alkali) + PAM ； 3. Ferrous sulfate + lime (or liquid alkali) + PAM: 4. PAC + lime (or liquid alkali) + PAM (cationic types are generally more effective) ； Effect evaluation: 1. Particle size and shape; larger, feathery particles are preferred ； 2. A clear supernatant is the main indicator; clarity indicates good efficacy.

The most common combination of flocculants and coagulants is PAC and PAM, as they offer good results, are inexpensive, and easy to use. Other flocculants include polyferric sulfate, ferric trichloride, and polyaluminum ferric sulfate; theoretically, they primarily function by compressing the double electric layer and achieving electroneutralization. Coagulants such as sodium polyacrylate play a role in adsorption, bridging, and trapping. Additionally, adjusting the pH to an appropriate level is key to the success of coagulation. As for how to determine the effectiveness of flocculation, it depends on whether an accurate characterization is required. If accuracy is needed, then specific parameters such as SS, COD, and color intensity must be measured. If quantitative measurement is not required, a qualitative assessment can be made of the size of the flocs, the tightness of their aggregation, the settling velocity, and the amount of sludge. If the coagulation effect is poor, it is necessary to adjust the pH and the amounts of flocculants and coagulant aids added.

Water temperature also has a significant impact on the coagulation effect: higher water temperatures require less dosage of chemicals, while lower temperatures necessitate more chemicals; moreover, chemicals hydrolyze more rapidly at higher water temperatures.

1. Coagulation consists of two processes: the first is coagulation, and the second is flocculation. Agglomeration occurs through electroneutralization, which destabilizes the colloid and leads to the formation of flocs; therefore, positively charged coagulants such as polyferric sulfate and polyaluminum chloride must be added. The second process is the growth of these flocs into larger floccules, and the main mechanism involved in this is adsorption and bridging, which is why polymer flocculants like polyacrylamide are used. 2. The purpose of coagulation is to remove colloidal pollutants; visually, the wastewater after coagulation and sedimentation appears clear and transparent, with good separation between sludge and water. In terms of chemical indicators, values such as SS, colority, and COD have decreased to a certain extent. In particular, SS can be reduced to below 10 mg/L.

Question 1: Coagulation consists of two processes; the first is coagulation, and the second is flocculation. Agglomeration occurs through electroneutralization, which destabilizes the colloid and leads to the formation of flocs; therefore, positively charged coagulants such as polyferric sulfate and polyaluminum chloride must be added. The second process is the growth of these flocs into larger floccules, and the main mechanism involved in this is adsorption and bridging, which is why polymer flocculants like polyacrylamide are used. This reply is based on the responses from Huan.Bao’Tong Technology. Question 2: The purpose of coagulation is to remove colloidal pollutants; apparently, the wastewater after coagulation and sedimentation becomes clear and transparent, with good separation between sludge and water. In terms of chemical indicators, values such as SS, colority, and COD have decreased to a certain extent. In particular, SS can be reduced to below 10 mg/L.

One cannot generalize everything; similarly, there is no standard answer to the issue discussed in this question, and it requires analysis on a case-by-case basis. Overall, it can be analyzed into two main parts. The first part relates to coagulants, including the selection and combination of different types of chemicals, the amount and method of adding these chemicals, as well as the structure and processing capacity of the coagulation tanks and sedimentation tanks. The second part consists of the physical parameters of the material to be treated; the main ones, or those that have an impact on the coagulation effect, include five key factors: solid content, flow rate, pH value, water temperature, and chemical oxygen demand. As for turbidity and color, they can be measured quickly on-site; the former mainly reflects the content of inorganic substances (not absolutely), while the latter reflects the content of organic substances, thus providing a basis for quick decision-making. Therefore, to improve the coagulation effect, actions need to be taken in these areas: if the flow rate is too high and exceeds the processing capacity of the coagulation and sedimentation tanks, iron-based agents (such as polyferric salts and ferric chloride) combined with polyacrylamide can be used. If the pH level is already high, there is no need to add liquid alkali or lime water. When the water temperature is high, the amount of flocculant used can be reduced; otherwise, it should be increased. Inorganic salts provide positive charges that destabilize the colloid, leading to the formation of flocs. Polymer compounds adsorb and bridge together these particles, resulting in flocs that settle more rapidly. The dosage of these substances as well as the equipment used in treatment plants are generally fixed, so there isn’t much room for improvement in these aspects. However, there are various ways in which these substances can be applied; using them effectively can help save materials or increase the treatment capacity. Implementing technical improvements is also not difficult, and it can be considered on its own.

Coagulants are primarily used for the purification of potable water and industrial wastewater, as well as for the treatment of special types of water (such as oily wastewater, wastewater from printing and dyeing and papermaking industries, smelting wastewater, wastewater containing radioactive substances, wastewater containing toxic heavy metals such as Pb and Cr, and fluoride-containing wastewater). It also has wide applications in areas such as precision casting, oil drilling, leather processing, metallurgy, and papermaking. Coagulants are substances that can bind and aggregate colloidal particles in water during the water treatment process; they are generally classified into two categories: organic coagulants and inorganic coagulants. The coagulation process involves adding chemicals during water treatment to cause impurities to aggregate and flocculate. Water treatment: When surface water is used as the source, it removes turbidity and bacteria. After coagulation and sedimentation, the turbidity is generally less than 10 NTU. Wastewater treatment: Industrial wastewater – used for treating certain types of special wastewater, such as for decolorization and removal of suspended solids. Textile dyeing wastewater treatment – suitable for dealing with wastewater containing pigments, disperse dyes, and other dyes with high molecular weights that are soluble in water. The choice of coagulant is related to the type of dye, and coagulation tests are required. Inorganic coagulants can be used alone, or in combination with organic polymer flocculants. Using PAC coagulant at a dosage of 140 mg/L, the TOC removal rate was 68%. Treatment of oily wastewater: Emulsified oil particles are small and carry a charge; coagulants are added to compress the double electric layer. The coagulation-flotation process is usually employed. Specific uses of coagulants as water treatment chemicals: 1. No other additives are required; flocs form quickly and are large in size, with high activity and good sedimentability, allowing for rapid precipitation. Therefore, its purification effect on water with high turbidity is particularly significant. 2. It has a wide range of pH tolerance; it can lower the pH value of raw water to a low level, thus causing no corrosion to pipeline equipment. 3. Strong decolorizing and cleaning power. The water purification efficiency is 4-6 times that of AL2(SO4)3, and 3-5 times that of ALCl3. Low dosage, high efficacy; low cost, high efficiency. Selection principles: There are a wide variety of coagulants available, and it is very important to choose the appropriate coagulant based on the process conditions of the water treatment plant, the quality of the raw water, and the desired quality standards for the treated water. The selection of coagulant types should follow the following general principles: (1) Good coagulation effect. Satisfactory coagulation results can be achieved under specific raw water quality conditions, requirements for the treated water quality, and particular treatment process parameters. (2) No toxic effects. When used to treat potable water, the coagulant selected must not contain components harmful to human health ； When used in industrial production, the coagulant agents selected must not contain components that are harmful to the production process. (3) Sufficient supply of goods. It is necessary to conduct research and investigations into the sources and manufacturers of the coagulant chosen, to find out whether the supply is sufficient, whether a stable supply can be ensured over the long term, and what the quality of the product is like. (4) Low cost. When there are multiple types of coagulants available, it is necessary to take into account factors such as the cost of the agents, transportation expenses, and dosage, and conduct economic comparisons in order to minimize usage costs while ensuring the quality of the treated water. (5) Health permit for new pesticides. For new types of medications that have not yet been widely adopted, obtain permission from the local health authorities. (6) Draw on existing experience. Review relevant literature and examine water treatment plants with the same or similar water quality, drawing on their operational experience to provide guidance for selecting coagulants. Coagulation tests are one of the most effective methods for comparing the coagulation effects of various coagulants and optimizing the dosage of these coagulants.

There are anions, cations, and electrically neutral PAM; each type of PAM comes in different variants with varying molecular weights, and experiments are conducted using different PAMs

Many people have talked about the ingredients of the medication, and I think the impact of mixing on them should not be ignored. During the early stage of adding the chemical, rapid stirring is required, while slow stirring is needed in the later stage.