Simplified guide to the stages of water treatment

How many times have I wondered, what are the stages of treating surface water to make it drinkable? Water treatment is a term referring to the processes that are used to make the treated water drinkable; By ridding it of odors, purifying it, softening it, and removing its hardness (hardness of water).

The term water treatment also extends to include the physical, chemical, biological, and mechanical processes that are carried out to make water suitable for a particular use and not necessarily for drinking.

The type of treatment depends on the required use, and on the source of the water to be treated; This is because the methods of treating gray water, which is the water that results from domestic uses such as showering and washing dishes, differ from the methods of treating black water that results from using latrines.

Drinking water treatment stages

Public water networks use different methods to treat drinking water. To rid them of contaminants and make them safer to use. The method of treatment depends on the source of the water. Surface waters such as lakes, rivers, and streams are often more polluted than groundwater. It contains more sediments.

Drinking water is treated by following the following steps

Coagulation and Flocculation

It is the addition of positively charged chemicals to the water. To neutralize dirt and dissolved materials that carry a negative charge. Thus, the dissolved substances are collected in the form of a large mass called the pomace (in English: floc).

Sedimentation

The bagasse mass, after it becomes heavy, is deposited at the bottom of the tank.

Filtration

After the sedimentation of the pomace, the water passes through filters of various compositions and pore sizes, in order to rid the water of coal, sand, and gravel, in addition to dissolved substances, such as chemicals, dust, viruses, bacteria, and parasites.

Disinfection

It means adding substances such as chlorine or monochloramine to kill the viruses, bacteria, and parasites that remain in the water.

Sewage water treatment stages

Wastewater is water that has been used for various purposes, and there are many sources of sewage, there is domestic wastewater, which includes water from toilets, kitchens, bathing water, and washing clothes. and industrial waste resulting from factories and commercial establishments.

Find out more sources of wastewater here.

Wastewater often contains disease-causing organisms, acids, and toxic substances. The aim of sewage treatment is to improve and purify wastewater to make it usable again. Or to be suitable for discharge into surface waters such as rivers and oceans, or into groundwater.

Wastewater treatment history

In ancient times, humans used to dispose of sewage by throwing it into water crossings. They depend on nature’s ability to get rid of it by diluting it or analyzing it with the help of bacteria. With the increase in population density, the amount of water resulting from human daily use increased.

In the United States of America, for example, water treatment until the beginning of the seventies of the last century was limited to filtering it from floating materials, getting rid of degradable materials, and sterilizing water to get rid of disease-causing organisms. With the beginning of the seventies, interest in environmental and aesthetic issues began, and a slightly developed type of water treatment began; By ridding it of nitrogen and phosphorous.

In the 1980s, coinciding with the emergence of health concerns about toxins, governments began to set water quality standards, and sewage treatment processes began to take into account human health standards in addition to the standards of aquatic life.

Sewage water treatment stages

The process of sewage treatment has undergone some gradation. Wastewater treatment was initially limited to primary treatment. Then the secondary treatment was started after a period of time. Advanced treatment is used when needed.

The following are the stages of wastewater treatment:

Primary treatment

It includes the following stages:

• Clearwater from large floating items such as sticks, and pieces of cloth.
• Using filters to get rid of heavy inorganic materials such as sand, and small pebbles.
• Sedimentation of organic and inorganic materials inside sedimentation tanks and the sediments are later used as fertilizer, or disposed of in a landfill, incinerated, or recycled if they are free of toxic substances.
• Disinfection of water from bacteria using chlorine, ozone, or ultraviolet rays, knowing that the effects of toxic chlorine must be eliminated before water is thrown into water bodies.

Secondary treatment

Wastewater treatment involves the biological disposal of organic matter. and converted into lumps deposited at the bottom of sedimentation basins. It can be used later as a fertilizer. 85% or more of the organic matter is removed during secondary processing. While the percentage of organic materials that are disposed of in the initial treatment stage does not exceed 50%, and this is done in several ways, including:

Activated sludge

This method relies on pumping sewage water to aeration tanks where the bacteria in the sewage water are supplied with oxygen to activate them to consume the organic matter in the water.

Trickling filters

This method relies on passing sewage water over a surface of stones, and industrial materials on which living organisms such as bacteria that work to decompose pollutants grow. Bacteria are supplied with the air necessary for their respiration through special filters.

Advanced processing

With the progress of science and the development of technologies, it has become possible to rid sewage of heavy metals and chemical substances.

toxic substances, and other pollutants, in the following ways:

Microfiltration

It means (the use of a microfiltration membrane to rid sewage of bacteria and impurities, and the pore size of this type of filter ranges between 0.1-10 microns).

Carbon Adsorption

It means (the use of carbon to rid sewage of some soluble substances such as mineral oils).

Evaporation / Distillation

It means (separation of impurities from water depending on the difference in its boiling point, the water is heated and converted into free water vapor

impurities, and then re-condensed again.

Chemical Precipitation

It means separating a solid from a solution by changing the nature of the solvent and reducing the solubility of the substance in it, or changing the nature of the solid to become insoluble.