• How A Water Treatment Plant Works

    Water in nature is not always safe for drinking without proper treatment. Natural water may contain a variety of bacteria, viruses, toxic chemicals, hazardous waste, and many more potentially harmful substances. Learn how a water treatment plant works to remove all of these contaminants and provide you with safe and pleasant drinking water. Water is an essential requirement for life, so it is important that yours is healthy.

    Raw Water Collection:

    There are two main types of raw water collection (sources of water in nature).

    raw-waterOne type of raw water is groundwater, which is water that has been absorbed into the ground into aquifers. Groundwater must be pumped out of the ground via well pumps. The other type of raw water is surface water. Surface water consists of the water collected in above-ground features such as rivers, lakes, streams, and reservoirs.

    Regardless of where the raw water is collected, the water will be routed to a water treatment plant for processing. At the water treatment plant, the water will go through several steps of mechanical, biological, and chemical filtration in order to produce safe and pleasant drinking water for the public.

    Pre-Screen Filtration:

    Pre-screening water intake structures will prevent large objects such as sticks, leaves, and even fish from entering the water transmission pipes and affecting treatment processes down the road. Without this proper screening, large objects may clog transmission lines and cause damage to expensive pumping equipment. This is a very simple, yet important step.

    Coagulation:

    When water enters the water treatment plant it will contain particles in the water which are measured as turbidity. Turbidity may be caused by small particles of sediment such as mud, sand, or clay along with other things such as microscopic bacteria. Water with a high turbidity will appear slightly dirty or murky, and will obviously be objectionable to consumers and carry a higher risk of consuming potentially harmful substances. So how are these particles removed?

    Coagulation is a chemical process in which small atoms and molecules are bonded together to form larger molecules. The bond of these particles is due to natural forces of positive and negative charges. By introducing a coagulant, such as the popular “alum,” you can effectively convert small particles into larger particles in order to increase the probability of those larger molecules being collected in your filtration systems. The bigger they are… the easier they are to catch!

    Flocculation:

    FlocculationProcessFlocculation is a slow mixing process that takes place immediately after coagulation. Coagulation combines small particles into slightly larger molecules, and then flocculation further increases the size of these particle clumps. After 20 – 60 minutes of flocculation, large clumps of “floc” should be formed which will be much easier to remove from the water due to their larger size.

    A visual representation of this concept is displayed in the image above. Once large clumps of floc are formed, it is time to let them settle to the bottom of a tank during the next water treatment plant process known as sedimentation.

    Flocculation:

    Flocculation is a slow mixing process that takes place immediately after coagulation. Coagulation combines small particles into slightly larger molecules, and then flocculation further increases the size of these particle clumps. After 20 – 60 minutes of flocculation, large clumps of “floc” should be formed which will be much easier to remove from the water due to their larger size.

    A visual representation of this concept is displayed in the image above. Once large clumps of floc are formed, it is time to let them settle to the bottom of a tank during the next water treatment plant process known as sedimentation.

    Sedimentation:

    After the previous combined processes of coagulation and flocculation have joined smaller particles together to form larger particles they are allowed time to settle down to the bottom of the tank due to the forces of gravity. This process is known as sedimentation.

    Bayview_sedimentationIn a sedimentaion tank, the water is allowed to remain motionless inside a large tank to allow particles to gradually sink to the bottom of the tank where they are collected and pumped out of the tank for disposal. The process of sedimentation may take up to several hours. Once complete, the “sludge” accumulation on the tank floor is disposed of in a landfill or other form of waste management and the clean water on top is then passed through filtration units to remove the much smaller particles that were not large/heavy enough to settle out during sedimentation.

    Filtration:

    Filtration methods are used to remove the remaining turbidity (particles in the water) that were not large enough to sink and settle out in the sedimentation tank. There are three types of filtration: mechanical, biological, and chemical filtration.

    An example of mechanical filtration is a sand bed in which water passes through the sand. The particles in the water get “stuck” in the sand bed and allow the water to pass through, leaving the junk behind. Another example is reverse osmosis membrane units which only allow water to pass through the semi-permeable membrane.

    An example of biological filtration can be bacteria breaking down substances in the water.

    Chemical filtration can be something such as granular activated carbon (GAC) which adsorbs chemicals onto its surface. Notice the term “adsorb” with a “d” instead of “absorb” with a “b.” Absorb means to soak up, while adsorb means to adhere to a surface.

    After sedimentation and filtration remove nearly all particles in the water it is time to perform one last process to be sure that no harmful substances are still present in the water: disinfection!

    Disinfection

    It is not always possible to remove 100% of particles from the water being treated, and that is why water treatment plants use disinfection as the final step in the process. Disinfection disables harmful bacteria and viruses, and also oxidizes other chemicals in the water that may have passed through previous removal mechanisms.

    The most popular form of disinfection is chlorine which has been used for decades as the primary source of disinfection. Chlorine disinfection unfortunately creates disinfection by-products (DBP’s) such as trihalomethanes which are suspected carcinogens, which is why water treatment plants are currently experimenting with new forms of disinfection. Other forms of disinfection include chloramines, chlorine dioxide, ozone, and UV rays.

    Delivery To Water Distribution System:

    After a water treatment plant works to remove turbidity and produce safe and pleasant drinking water, it is then released into the public water distribution system where it will travel through miles and miles of underground pipes before reaching your household plumbing. A chlorine residual (leftover chlorine) is present in the released water in order to prevent the addition of harmful bacteria or other microbes that may have made their way into the city pipes.

    No matter how clean and safe the water is when it leaves the water treatment plant, it will always be vulnerable to contamination by substances in the water distribution pipes.

    This is why distribution system maintenance is essential to make sure that the clean and safe drinking water remains clean and safe as it comes out of your kitchen sink. Due to this possibility, it is always advisable to purchase a tap water filter system as an extra means for protection.

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