Municipal Water Treatment

Clean water is vital to our modern society.  the world relies on clean water from public sources on an hourly basis. Your community most likely relies on municipal water systems for clean water.

the municipal water treatment plant, storage facilities like water tanks, towers, reservoirs, and water pipe network for distribution are part of a public water supply network that is called a municipal water system.

Almost every municipality or community has struggled to deal with water quality fluctuations, disinfection by-products, emerging contaminants, and regulatory requirements. Additionally, the cost of water scarcity and aging infrastructure, and the global impact of climate change make it even tougher for municipal water treatment communities. abrah co provides solutions for municipal water treatment communities to utilize the latest technologies in water treatment and retrofit or replace them with new sustainable solutions to face new challenges.

Public drinking water systems use different water treatment methods to provide safe drinking water for their communities. Public water systems often use a series of water treatment steps that include coagulation, flocculation, sedimentation, filtration, and disinfection.

Water treatment steps

here are three main steps in the treatment of municipal water.

  1. Primary Treatment
  2. Secondary Treatment
  3. Tertiary Treatment

Primary treatment occurs when water is collected, including supplies from streams and rivers. Primary treatment aims to remove physical contaminants from water.

The removal of fine solids and contaminants by coagulation, filtration and other techniques occurs in secondary treatment. The main difference between the primary and secondary treatment of wastewater is that primary relies mostly on physical cleaning, while secondary treatment introduces chemical procedures and microorganisms.

In the final stage or tertiary treatment, at the municipal water plant, pH adjustment, disinfection, and carbon treatments are applied.

Primary Treatment

There are five processes in the primary phase of municipal water treatment.

  1. Pumping of water from its source to the municipal treatment plant needs to be done with the appropriate equipment in a way that does not contaminate the supply.
  2. At the wastewater screening stage, screens and filters are used to remove items such as twigs and trash.
  3. Water can sometimes be stored in reservoirs to allow for drought and natural biological purification.
  4. In hard-water areas, water is treated with sodium carbonate to precipitate calcium carbonate, a process known as pre-conditioning.
  5. Finally, this primary treatment phase ends with pre-chlorination where water coming into the plant is chlorinated as part of the disinfection proces

 

Secondary Treatment

Several techniques can be used to filter and dissolve solids during the secondary treatment phase. The municipal water treatment methods used will depend on whether this is a hard-water area, cost, and any quality requirements that need to be in place

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).

Reverse osmosis is another filtration method that removes additional particles from water. Water treatment plants often use reverse osmosis when treating recycled water  (also called reused water) or salt water for drinking.

TERTIARY TREATMENT

Water treatment disinfection is the last stage in the treatment of municipal water and is vital for the removal of pathogens. Most municipal water systems have a requirement to maintain a level of disinfection in the supply for a certain number of days before it reaches the consumer.

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  or ozone . 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. Adjusting the pH improves taste, reduces corrosion (breakdown) of pipes, and ensures chemical disinfectants continue killing germs as the water travels through pipes. Drinking water with the right amount of fluoride keeps teeth strong and reduces cavities.

Surface water collects on the ground or in a stream, river, lake, reservoir, or ocean.

Groundwater is located below the surface of the earth in spaces between rock and soil.

Each industry has its special needs for water treatment

Water may be treated differently in different communities depending on the quality of the source water that enters the treatment plant. The water that enters the treatment plant is most often either surface water or groundwater. Surface water typically requires more treatment and filtration than ground water because lakes, rivers, and streams contain more sediment (sand, clay, silt, and other soil particles), germs, chemicals, and toxins than groundwater.

Some water supplies may contain radionuclides (small radioactive particles), specific chemicals (such as nitrates), or toxins (such as those made by cyanobacteria). Specialized methods to control or remove these contaminants can also be part of water treatment. To learn more, visit EPA’s Ground Water and Drinking Water site.