MIXING CHAMBER:

After the waste water has been screened and has passed through the aeration process, the raw water then flows to a flash mixing chamber where a coagulant chemical is added to enhance floc formation for easier removal in the clarification process. In the mixing chamber, the coagulant chemicals are mixed and reacted with raw water. The quick formation of floc depends on the proper mixing of coagulant with the raw water.

Figure 1In the figure 1 above shows that how the coagulant chemicals act after mixed with raw water. In the mixing chamber, coagulant chemicals are added into the raw water and the water is mixed quickly and violently. The purpose of this step is to distribute the chemicals through the raw water evenly. The mixing usually lasts a minute, if the water is mixed for less than thirty seconds, then the chemicals will not be properly mixed with the raw water. There are three components in mixing chamber. Firstly are inlet chamber, the raw water are allowed to enter the mixing chamber through the inlet chamber. In this chamber, the coagulant chemical is added. Secondly are feeding devices, the coagulant chemical is added into the raw water by feeding devices. The devices consist of a conical container which is filled with coagulant. A stop cock is provided at the bottom of the container to control the coagulant dose added. Lastly are mixing devices, the device consists of paddles which are rotated. The paddles rotating continuously and thus the coagulant is mixed thoroughly with raw water.Figure 2 below shows that, where to unstabilized the colloidal by reducing the repulsive force and add attraction force so that the separate particles will stick together.

Figure 2

Figure 3The figure 3 above shows the mixing chamber in Pahang Water Management. After the mixing, the coagulant occurs. During coagulation, the coagulant chemicals neutralize the electrical charges of the fine particles in the raw water and allowing the particles to come closer and stick together then form large clumps. It is observed that, the ions of floc possess positive electric charge and the colloidal particles possess negative electric charge. So, the floc attracts the colloidal particles while it travels towards the bottom of tank.FLOCCULATION TANK:

The goals of flocculation process are to promote growth of flocs to a size that can be removed by sedimentation and filtrations. Now that the particles have a neutral charge and stick together. The raw water from mixing chamber flow into the flocculation tank. Figure 4 below shows that the raw water from mixing chamber flow into the flocculation tank.

Figure 4Flocculation tank is a tank with paddles that provides slow mixing and brings the small particles stick together to form larger particles called flocs.

Figure 5: Flocculation Tank

Figure 6: Baffle PlateThe phenomenon of the formation of flocs is termed as flocculation. The efficiency of flocculation process depends on the following factors. Firstly, the dose of coagulant, the dose of coagulant should be ascertained by laboratory test for the sample water in order to get the optimum value of coagulant dose. Secondly, the mixing, the mixing coagulant should be perfectly done for the quick formation of flocs. Lastly, the pH-value, the pH-value of water should be determined in laboratory to select the type of coagulant. The mixing is done slowly and gently in the flocculation tank and it is allowed to flow at very low velocity so that the flocs may be formed. If the mixing is too fast, the flocs will break apart into smaller particles and it will be difficult to remove by sedimentation or filtration. Usually, flocculation process will last for thirty to forty-five minutes. The flocs goes on settling down, while settling down, the flocs attract more and more suspended impurities and thus the size of flocs goes on increasing and the surface area of flocs becomes sufficiently wide to arrest colloidal matters, organic matters and some amount of bacteria.

SEDIMENTATION TANK:

After the flocculation tank, then raw water flow into the sedimentation tank. Sedimentation tank are where settle able solids settle out of the water due to gravity and are pumped away, while oils float to the top and are skimmed off. The function of sedimentation tank is to remove the heavier suspended particles in the raw water. In this tank, the water is detained for some period or allowed to flow at a very low velocity so that the heavier suspended particles are settling down at the bottom of sedimentation tank. The process of settlement depends on the following factors such as velocity of flow, size and shape of particles and viscosity of water. Settle solids are removed as sludge, and floating solids are removed as scum. The efficiency or performance of the sedimentation process is controlled by detention time, temperature, tank design and condition of the equipment.

Figure 7: Sedimentation Tank

Figure 8: Low Velocity Causing Flocc Deposited at the Bottom of the Tank.

Figure 9: A Good Sedimentation Produce Clear Water