Water & Wastewater Treatment – Page 2

The United States has one of the safest and most reliable drinking water systems in the world. Every year, millions of people living in the United States get their tap water from a public community water system. Before it gets to your tap water is treated at a standard treatment plant. What is a Drinking Water Treatment Plant? Drinking water treatment plants treat raw H2O from ground or surface supplies to be used by their communities using: Chemical processes-oxidation, coagulation Physical processes-flocculation, sedimentation, filtration, adsorption Disinfection with ultraviolet light. Biological activated carbon (BAC) All public water systems in the United States are required to follow the standards and regulations set by the U. S. Environmental Protection Agency (EPA). EPA regulations that protect public water systems do not apply to privately owned wells or other individual water systems. Drinking Water Treatment Plant Drinking water treatment plants are used to remove particles and organisms that lead to diseases and protect the public’s welfare and supply pure drinkable water to the environment, people, and living organisms. In addition, they also provide drinking water that is pleasant to the senses: taste, sight, and smell, and provide safe, reliable drinking water to the communities they serve. Water treatment, as a word originally means the act or process of making water more potable or useful, by purifying, clarifying, softening, or deodorizing it. Providing drinking water to the public is one of the most important jobs of communities and the design of water supply systems has to follow the rules of engineering sciences and also needs technical knowledge and practical experience. Water is treated differently in different communities depending on the quality of the water which enters the plant. For example; groundwater requires less treatment than water from lakes, rivers, and streams. In order to analyze all these technical aspects of the drinking water treatment systems and supplement a training guide on drinking water treatment plants, the PURE-H2O project received a European Grant from the Turkish Agency and formed a competent partnership as follows for the realization of the project and a thorough introduction of a drinking water treatment plant system to the engineers and technicians Raw water sources, for example, an impounding reservoir, lake, or river canal. Intake well. Water pumping system. Cascade aerator. Alum mixer. Clarifier. Filter bed washing system. Sand filters. Water to be supplied for public use must be potable i.e., satisfactory for drinking purposes from the standpoint of its chemical, physical and biological characteristics. Drinking water should, preferably, be obtained from a source free from pollution. The raw water normally available from surface water sources is, however, not directly suitable for drinking purposes. The objective of water treatment is to produce safe and potable drinking water. Some of the common treatment processes used in the past include Plain sedimentation, Slow Sand filtration, and Rapid Sand filtration with Coagulation-flocculation units as essential pretreatment units. Coagulation Coagulation is often the first step in water treatment. During coagulation, chemicals with a positive charge are added to the water. The positive charge neutralizes the negative charge of dirt and other dissolved particles in the water. When this occurs, the particles bind with the chemicals to form slightly larger particles. Common chemicals used in this step include specific types of salts, aluminum, or iron. Flocculation Flocculation follows the coagulation step. Flocculation is the gentle mixing of the water to form larger, heavier particles called flocs. Often, water treatment plants will add additional chemicals during this step to help the flocs form. Sedimentation Sedimentation is one of the steps water treatment plants use to separate out solids from the water. During sedimentation, flocs settle to the bottom of the water because they are heavier than water. Filtration Once the flocs have settled to the bottom of the water, the clear water on top is filtered to separate additional solids from the water. During filtration, the clear water passes through filters that have different pore sizes and are made of different materials (such as sand, gravel, and charcoal). These filters remove dissolved particles and germs, such as dust, chemicals, parasites, bacteria, and viruses. Activated carbon filters also remove any bad odors. Water treatment plants can use a process called ultrafiltration in addition to or instead of traditional filtration. During ultrafiltration, the water goes through a filter membrane with very small pores. This filter only lets through water and other small molecules (such as salts and tiny, charged molecules). Disinfection After the water has been filtered, water treatment plants may add one or more chemical disinfectants (such as chlorine, chloramine, or chlorine dioxide) to kill any remaining parasites, bacteria, or viruses. To help keep water safe as it travels to homes and businesses, water treatment plants will make sure the water has low levels of chemical disinfectant when it leaves the treatment plant. This remaining disinfectant kills germs living in the pipes between the water treatment plant and your tap. In addition to or instead of adding chlorine, chloramine, or chlorine dioxide, water treatment plants can also disinfect water using ultraviolet (UV) light UV light and ozone work well to disinfect water in the treatment plant, but these disinfection methods do not continue killing germs as water travels through the pipes between the treatment plant and your tap. Water treatment plants also commonly adjust water pH and add fluoride after the disinfection step before leaving the plant and entering the Water Distribution System. What is a Water Distribution System? A Water Distribution System is composed of a network of pipes, valves, and pumps through which potable water is moved from a treatment plant to homes, offices, industries, and other consumers it includes storage facilities to store water, meters to measure water use, and hydrants for firefighting .............................................................................. Read more JimGalloway Author/Editor References: CDC- Water Treatment