What is the difference between sedimentation and coagulation

Figure 4. Table 2. Figure 5. Scanning electron micrograph SEM : a uncoagulated laterite particles, b coagulated laterite particles, and c coagulated and flocculated laterite particles. Figure 6. Figure 7. Concentrated laterite suspension undergoing sedimentation after adding alum Al , FeCl 3 Fe , and Grewia spp.

Figure 8. Figure 9. Sediment concentration factor vs. References D. Dihang, P. Aimar, J. Kayem, and S. Flamant, A. Cockx, V. Guimet, and Z. Martin, I. Berrios, J. Siles, and A. View at: Google Scholar N. Fedala, H. Lounici, N. Drouiche, N. Mameri, and M. Zhu, H. Zheng, Z. Zhang, T. Tshukudu, P. Zhang, and X.

Teh, P. Budiman, K. Shak, and T. Antov, M. Choy, K. Prasad, T. Wu, and R. Zharim, C. Tizaoui, and N. View at: Google Scholar J. Li, S. Jiao, L. Zhong, J. Pan, and Q. Freitas, V. Oliveira, M. Ghimici, M. Constantin, and G. Jadhav and Y. Veeramalini Sravanakumar and J. View at: Google Scholar M. Pritchard, T. Craven, T. Mkandawire, A. Edmondson, and J.

Li, T. Cai, B. Yuan, R. Li, H. Yang, and A. Shak and T. Ndi, G. Kofa, P. Ngnie, K. Bernard, and G. View at: Google Scholar A. Kaya, A. Kang, X. Zhao, and B. View at: Google Scholar S. Wang, L. Zhang, B. Yan, H. Xu, Q. Liu, and H. Somboonpanyakul, Q. Wang, W. Cui, S. Barbut, and P. Elijah Nep and R. View at: Google Scholar F. Li, Z. Zhu, D. Wang, C. Yao, and H. Niu, W. Zhang, D. Wang, Y. Hence, the characteristics of water to be submitted to the coagulation plant should be properly studied before deciding the details of the plant.

Usual coagulants. Following six are the usual coagulants which are adopted for coagulation. Aluminium sulphate. Chlorinated chopperas. Ferrous sulphate and lime. Magnesium carbonate. Sodium aluminate. Site news. Module 1. Module 2. Module 3. Module 4. Lesson Introduction to water treatment. Lesson Quantity of water. Lesson Water treatment - sedimentation and coag Lesson Water treatment - Filtration. Module 5. Module 6. Module 7. Module 8. Module 9. Environmental Engg.

Sedimentation Having examined the quality of water, a line of treatment is to be recommended for impure water to make it potable or fit for drinking purposes. Theory of sedimentation The particles which are heavier than water are naturally likely to settle down due to force of gravity. The process of settlement of a particle is obstructed or opposed by the following three forces: 1 Velocity of flow : The particle is moved in the horizontal direction by the velocity of flow 2 Size and shape of particle : The force of gravity depends on the weight of particle and tends to move the particle in vertical direction.

Coagulation The source of water supply for the most of public water supply project is surface water. Principle of coagulation The principal of coagulation can be explained from the following two considerations. Floc formation When coagulants are dissolved in water and thoroughly mixed with it, they produce a thick gelatinous precipitate.

Electric charges The ions of the floc are found to possess positive electric charge. Flocculation The floc produced by the action of coagulants with water is heavy and hence, it starts to settle down at the bottom of tank. Dosage of coagulant The dosage or quantity of coagulant should be carefully determined so as to cause visible floc. Feeding The feeding of coagulants may be in powder form or in solution form, the latter being more popular 3.

Mixing The coagulants should be properly mixed with water so as to cause a uniform mass. Velocity The floc should be allowed to move gently after initial quick mixing, The gentle movement of floc results in collision of particles and ultimately, the floc grows in size. Usual coagulants Following six are the usual coagulants which are adopted for coagulation Aluminium sulphate Chlorinated chopperas Ferrous sulphate and lime Magnesium carbonate Polyelectrolytes Sodium aluminate.

Skip Navigation. These suspended materials mostly arise from land erosion, the dissolution of minerals and the decay of vegetation and from several domestic and industrial waste discharges.

This material has to be removed, as it causes deterioration of water quality by reducing the clarity e. To separate the dissolved and suspended particles from the water coagulation and flocculation processes are used. Coagulation and flocculation is relatively simple and cost-effective, provided that chemicals are available and dosage is adapted to the water composition. Regardless of the nature of the treated water and the overall applied treatment scheme, coagulation-flocculation is usually included, either as pre-treatment e.

Most solids suspended in water possess a negative charge; they consequently repel each other. This repulsion prevents the particles from agglomerating, causing them to remain in suspension. Coagulation and flocculation occur in successive steps intended to overcome the forces stabilising the suspended particles, allowing particle collision and growth of flocs, which then can be settled and removed by sedimentation or filtered out of the water.

Coagulation-Flocculation is also a common process to treat industrial and domestic wastewater in order to remove suspended particles from the water. Coagulants with charges opposite to those of the suspended solids are added to the water to neutralise the negative charges on dispersed non-settable solids such as clay and organic substances.

Once the charge is neutralised, the small-suspended particles are capable of sticking together. The slightly larger particles formed through this process are called microflocs and are still too small to be visible to the naked eye. A high-energy, rapid-mix to properly disperse the coagulant and promote particle collisions is needed to achieve good coagulation and formation of the microflocs. Over-mixing does not affect coagulation, but insufficient mixing will leave this step incomplete.

Proper contact time in the rapid-mix chamber is typically 1 to 3 minutes. Following coagulation, flocculation, a gentle mixing stage, increases the particle size from submicroscopic microfloc to visible suspended particles. The microflocs are brought into contact with each other through the process of slow mixing.

Collisions of the microfloc particles cause them to bond to produce larger, visible flocs. The floc size continues to build through additional collisions and interaction with inorganic polymers formed by the coagulant or with organic polymers added.

Macroflocs are formed. High molecular weight polymers, called coagulant aids, may be added during this step to help bridge, bind, and strengthen the floc, add weight, and increase settling rate. Once the floc has reached its optimum size and strength, the water is ready for the separation process sedimentation , floatation or filtration.

Design contact times for flocculation range from 15 or 20 minutes to an hour or more. In water treatment, coagulation and flocculation are practically always applied subsequently before a physical separation. The Coagulation-Flocculation process consists of the following steps:. Certain heavy metal chelating agents can also be added during the coagulation step.

The jar test is used to identify the most adapted mix of chemical compounds and concentrations for coagulation-flocculation. It is a batch test consisting of using several identical jars containing the same volume and concentration of feed, which are charged simultaneously with six different doses of a potentially effective coagulant. The six jars can be stirred simultaneously at known speeds. The treated feed samples are mixed rapidly and then slowly and then allowed to settle.

These three stages are an approximation of the sequences based on the large-scale plants of rapid mix, coagulation flocculation and settling basins. At the end of the settling period, test samples are drawn from the jars and turbidity of supernatant liquid is measured. A plot of turbidity against coagulant dose gives an indication of the optimum dosage i. The criteria thus obtained from a bench jar test are the quality of resultant floc and the clarity of the supernatant liquid after settling.

The design of the full-scale plant process is then done based on the bench-scale selection of chemicals and their concentrations. Unfortunately, the jar test suffers from a number of disadvantages, despite its widespread application. It is a batch test, which can be very time-consuming. And the results obtained from a series of jar tests might not correspond to the results obtained on a full-scale plant.