| Constituent | Unit Processes |
| Turbidity and particles | Coagulation/ flocculation, sedimentation, granular filtration |
| Major dissolved inorganics | Softening, aeration, membranes |
| Minor dissolved inorganics | Membranes |
| Pathogens | Sedimentation, filtration, disinfection |
| Major dissolved organics | Membranes, adsorption |
Energy Consumption
editFor many cities, drinking water and wastewater treatment plants are typically the largest energy consumers, having a total of 30-40% of the cities' energy consumption[1]. More than 4% of the nation's electricity goes towards moving and treating water and wastewater[2]. ost of these energy is consumed in the flocculation basin for drinking water treatment plants and in the aeration basin for wastewater treatment plants. High amount of energy is needed to mix the large volume of water to allow sedimentations to flocculate together. There are current technologies that may aim to reduce this amount of energy. These include optimizing system processes by modifying and improving pumping and aeration equipments.The effectiveness of such technologies are still under discussion as they take up a lot of energy.
Structure and Building of water treatment plants
editEconomies of scale favor a large water treatment plant that small ones. There are various types of waste water treatment plants including sewage treatment plants, tertiary treatment plants, industrial waste water treatment plant, agriculture waste water treatment plant and leachate treatment plant. The largest feature of drinking water treatment plant is the clarifier and each tank is approximately 20 feet deep and 117 feet square[3] Most water treatment plants also have a row of filtration tanks which are 13 feet deep and 77 feet long, almost the length of an Olympic size pool[4]. These are the major components of any water treatment plants and take up the most space for all water treatment plants.This is a clear example of efficiency as this new technology allows much energy and manpower savings by treating wastewater directly to potable water. With new scientific advancements, we can look forward to newer and improved technology which makes our society run more efficiently. It may be thought to be more equitable to have smaller water treatment plants in every city. However, this is ineffective and a waste of resources as the economies of scale allows for great cost savings.
Notable examples
editA notable example that combines both wastewater treatment and drinking water treatment is NEWater in Singapore[5]. NEWater is a technology practised in Singapore that converts wastewater to potable water. More specifically, it is treated wastewater (sewage) that has been purified using dual-membrane (via microfiltration and reverse osmosis) and ultraviolet technologies, in addition to conventional water treatment processes. The water is potable and is consumed by humans, but is mostly used by industries requiring high purity water. The total capacity of the plants is about 20 million US gallons per day (75,700 m3/day). Some 6% of this is used for indirect potable use, equal to about 1% of Singapore's potable water requirement of 380 million US gallons per day (13 m3/s). The rest is used at wafer fabrication plants and other non-potable applications in industries in Woodlands, Tampines, Pasir Ris, and Ang Mo Kio.
Failures of water treatment plants
editWhen water treatment plants fail, the impact reaches a large group of people. These water treatment plants may fail due to a variety of reasons. They include poor maintenance, power shutdown or the plant may simply not be able to withstand and treat such a high influx of water. This is why engineers often employ safe margin and design for a larger volume than expected. There are a few ways in which citizens can deal with a water treatment plant failure. This includes buying water filtration systems such as those from Brita or water filtration tablets.
Regulation by the US government
editThe United States water treatment is regulated by the Environment Protection Agency. The EPA has a set of surface water treatment rules to ensure that the water that is treated is safe for consumption. The purpose of the Surface Water Treatment Rules (SWTRs) is to reduce illnesses caused by pathogens in drinking water[6]. The disease-causing pathogens include Legionella, Giardia lamblia, and Cryptosporidium. The SWTRs requires water systems to filter and disinfect surface water sources. Some water systems are allowed to use disinfection only for surface water sources that meet criteria for water quality and watershed protection..
EPA sets legal limits on over 90 contaminants in drinking water. The legal limit for a contaminant reflects the level that protects human health and that water systems can achieve using the best available technology. EPA rules also set water-testing schedules and methods that water systems must follow. The Safe Drinking Water Act (SDWA) gives individual states the opportunity to set and enforce their own drinking water standards if the standards are at a minimum as stringent as EPA's national standards. However, there are also some unregulated contaminants. EPA uses the Unregulated Contaminant Monitoring Program to collect data for contaminants suspected to be present in drinking water, but that do not have health-based standards set under the SDWA. Every five years EPA reviews the list of contaminants, largely based on the Contaminant Candidate List[7].
The EPA aims to help the various state in providing a Clean Water State Revolving Fund. The Clean Water State Revolving Fund (CWSRF) program is a federal-state partnership that provides communities a permanent, independent source of low-cost financing for a wide range of water quality infrastructure projects.The CWSRF was established by the 1987 amendments to the Clean Water Act (CWA) as a financial assistance program for a wide range of water infrastructure projects, under 33 U.S. Code §1383. The program is a powerful partnership between EPA and the states that replaced EPA's Construction Grants program. States have the flexibility to fund a range of projects that address their highest priority water quality needs. The program was amended in 2014 by the Water Resources Reform and Development Act[8]
The ease of political acceptability for water treatment is often very high as it is undeniable that potable water is a basic necessity valued by all. Additionally, clean water is also needed for industry and economic growth. Hence, the US government and various other governments are willing to spend large amounts of money in ensuring every household gets the water they need.
- ^ "Water-Energy Connection| Region 9: | US EPA". www3.epa.gov. Retrieved 2017-05-03.
- ^ "Energy Costs of Water in California". large.stanford.edu. Retrieved 2017-05-03.
- ^ https://engineering.dartmouth.edu/~d30345d/courses/engs37/Settling.pdf
- ^ "CIVL 1101 - Introduction to Water Filtration". www.ce.memphis.edu. Retrieved 2017-05-03.
- ^ PUB. "PUB, Singapore's National Water Agency". PUB, Singapore's National Water Agency. Retrieved 2017-05-03.
- ^ EPA,OW,OGWDW, US. "Surface Water Treatment Rules". www.epa.gov. Retrieved 2017-05-03.
{{cite web}}: CS1 maint: multiple names: authors list (link) - ^ EPA,OW,OGWDW, US. "Drinking Water Contaminant Candidate List (CCL) and Regulatory Determination". www.epa.gov. Retrieved 2017-05-03.
{{cite web}}: CS1 maint: multiple names: authors list (link) - ^ EPA,OW, US. "Water Resources Reform and Development Act (WRRDA) Guidance for the Clean Water State Revolving Fund (CWSRF)". www.epa.gov. Retrieved 2017-05-03.