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Coagulation in Water Treatment

Updated: May 24, 2021


Water is an essential element of life on our planet. Yet, as much as a greater part of the world is covered by water, not most of it is fit for consumption. Several factors lead to this unfitness, among them being the presence of sediments in the water. Nevertheless, there are several strategies that people have come up with to make such water suitable for consumption. The following sections will look into a test experiment developed to study a technique used in getting sediments off the water. The research question for the experiment is: if the temperature changes in the coagulation process of water treatment will it affect the rate of coagulation?


Coagulation has been used as a means of water treatment for a very long time. Around 2000BC, Egyptians utilized almond seeds as agents for coagulating river water. Romans also relied on alum as a coagulating agent as early as 1757 (Bratby, 2016). In recent times, coagulation has been a crucial part of water treatment as it helps tackle most of the organic impurities in water that other treatment procedures cannot address.


Coagulation is a technique of destabilizing a solution or a suspension and clamping together the destabilized particles for removal (Bratby, 2016). Whichever material is added to the suspension to induce the destabilization is referred to as the coagulant. Coagulants can either be organic or be inorganic (SNF, 2018). The most common natural coagulants are cationic and operate by neutralizing the charge of sediments to clamping together and forming the sludge. There are, however, other organic coagulants such as tannins that work by absorption of organic elements such as oil (SNF, 2018). On the other hand, inorganic coagulants are often used as cost-effective and can be used in most cases. More specifically, inorganic coagulants are applicable for water with low turbidity. Meanwhile, some people blend these coagulants in their water treatments (SNF, 2018). Therefore, coagulation for water treatment has been widely developed and practiced for a long period.


The jar test experiment for coagulation rate at different temperatures is a pilot test I performed to determine the dosage and speed rate for water treatment. The research focuses on temperature as a significant factor in water coagulation. The jar test establishes a base as per the real size of the sediment basin and the flocculation basin and the rate of water flow. The level of the flocculation basin for the experiment is set at 30 550 gallons, the sediment basin at 153,375 gallons, and the rate of water flow at 4500 GPM. Furthermore, the coagulant Aluminium Chloralhydrate 50% (ACH) dosage is set at 9.0 mg/l. Moreover, the experiment uses six jars, each having a capacity of 2 liters. Still, the water used in this experiment should be from the same source and have the same NTU. The water I used was taken 16 feet deep from the Brazos River. The experiment also requires a timer, a thermometer, a lab refrigerator, and a lab oven. The ACH should be available at 12.4% and a specific gravity of 1.33. Again, the test used DI water, a 500 ml beaker, a 12 turbidity test tube, and a turbidity benchtop 2100. All this equipment is necessary for the test procedure.


The test experiment works by comparison of two experiments; the control group test and the sample group test. The control group is a test of coagulation in the raw water at different temperatures without ACH. The lab refrigerator and the lab oven regulate the water temperatures for the different jars at needed levels. The six jars are set with temperatures varying from 8 degrees Celsius. The first jar has water at 40 Celsius, the second at 32 Celsius, and the temperatures drop to the sixth jar at 0 Celsius. After setting the pots, I let the mixer run at full speed for 5 minutes. After that, the mixer is left to run at 80 rpm for 7 minutes. The mixer rate is then lowered to 55 rpm and left to run for another 7 minutes. Finally, the speed of the mixer is lowered to 35 rpm and left to run for 7 minutes. After that, the jars are left to sit for 34 minutes. When the time elapses, water is taken from the jars and filled in different turbidity test tubes. The test tubes are placed on the 2100 benchtop, and respective NTU readings are made and recorded.


After the completion of the control group test, I performed the sample group test. The sample group is prepared by adding 9 ml of ACH to 1000 ml of DI water. This mixture of ACH and DI water gives a 1.5% solution strength. The jars are then prepared the same way as done for the control group, and the steps carried out in the control group are replicated for the sample group. The results from the control group and the sample group are then compared to infer the effect of temperature on coagulation or the lack of it. From the results, I observed that the NTU for the control group remained the same due to no reaction. However, the NTU for the sample group varied with more coagulation in the water with colder temperatures. Such results are in line with the phenomenon of increased coagulation with low temperatures (“Effects of temperature on floc formation process efficiency and subsequent removal in sedimentation process,” 2014). For proper coagulation and formation of sludge, there needs to be gentle movement of water. The low temperatures probably, make the water movements gentler as particles become less mobile than the water of high temperatures.


Water treatment is an important process that allows for easy and safe use of water. Coagulation has been one technique that has been developed and used over a long period to help in water treatment. Coagulation helps remove sediments and organic elements from water through the use of organic and inorganic elements. These elements vary in success and can be used together for better results. Temperature seems to play a significant role in the coagulation process. A jar test experiment developed to study this phenomenon shows that low temperatures increase water coagulation rate. As such, more studies should be done in that perspective for a more valuable practical application.

References

Bratby, J. (2016). Coagulation and flocculation in water and wastewater treatment. IWA Publishing.

Effect of temperature on floc formation process efficiency and subsequent removal in sedimentation process. (2014). Journal of Engineering and Development, 18(4), 176-187. Retrieved from https://www.iasj.net/iasj?func=fulltext&aId=91464

SNF. (2018, April 26). Chemical coagulants used in water treatment. Retrieved from https://www.snf.co.uk/chemical-coagulants-used-water-treatment/



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