TRANSFORMING BASE SUBSTANCES INTO GOLD

Potable Water Treatment Technology: A Step-by-Step Overview

 

Introduction

Water is essential for life—without it, there is no civilization. Some of the world’s greatest civilizations, like those along the Euphrates, Volga, Danube, Amazon, and Nile rivers, thrived because of their proximity to abundant water sources. Today, ensuring clean, safe drinking water is a global priority, and the treatment of potable water is vital for public health.

The Potable Water Treatment Process

While there are variations in the methods used, the fundamental goal of potable water treatment is to create multiple barriers against pathogens and remove toxic chemicals from the water. This approach ensures that if one step fails, others can still protect public health. Depending on the source, raw water can be treated using different pathways. For example, if the drinking water source is coming from an ecologically clean area, say from a spring, then it might be ready for consumption without any treatment. However, surface water say from a polluted river like the Thames in London,  would require multiple treatment steps. Also note that countries that drink from the sea need to remove TDS from the water using Desalination technology.

Below are some traditional drinking water treatment steps.

Traditional potable water treatment process steps:

Water Source and Pumping

The process begins with pumping water from either surface water (e.g., rivers, lakes) or well water. In arid regions like Saudi Arabia and Australia, desalinated water is sometimes used as the feed source for potable water. When desalinated water is used, many of the subsequent treatment steps may be unnecessary since it’s already relatively clean. When picking a site for a potable water borehole, it is advisable to pick a location that is far and safe from industrial pollution. There are EU regulations in place that codify this in the Drinking Water Directive.

Water Treatment Steps

1. Aeration

Aeration introduces air into the water to remove undesirable gases such as hydrogen sulfide (H2S) and to oxidize ferrous iron into ferric iron. Aeration is especially necessary for well water, as surface water is naturally aerated by exposure to air.

2. Coagulation, Softening, Flocculation, and Settling

In this stage, suspended solids—both organic and inorganic—are removed using the following techniques:

• Coagulation: A coagulant is added to help tiny suspended particles stick together, forming larger particles called flocs, which can then settle more easily.
• Softening: Lime and/or soda ash are added to reduce water hardness.
• Flocculation: Polymers (flocculants) are used to help flocs bind together more efficiently, speeding up the process.
• Settling or DAF (Dissolved Air Flotation): Flocs settle at the bottom of clarifiers, or suspended particles are removed through flotation.
• Sometimes Powdered Activated Carbon can be added if there hare PFAS or CEC’s/EDC’s in the water.

Alternatively, Ultrafiltration (UF) can be used to remove suspended solids, bacteria, and viruses, eliminating the need for some of the coagulation/flocculation/settling processes.

3. Ozonation/Chlorination – First Level Disinfection

In this step, ozone/chlorine is introduced to disinfect the water by killing bacteria and viruses. It also helps to remove any taste or odor molecules that may have survived the previous treatments. Certain bacteria naturally produce compounds that affect water taste, and ozonation helps eliminate these nuisances.

4. Filtration

Water is passed through slow fine sand filters or activated carbon (AC) filters, which act as biofilters. These filters help to remove smaller particles and assimilate nutrients like nitrogen and phosphorus, making it harder for bacteria to thrive in the water. The principle is similar to how biofilters work in fish aquariums. Sometimes Ultra Filtration is used. Sometimes specialized filters are used to remove heavy metals such as Iron, Managense and Arsenic.

5. Sodium Bisulfite (SBS) Dosing

Sodium bisulfite is added to remove any residual ozone/chlorine left in the water, ensuring that the treated water is safe to store in tanks or basins.

6. Chlorination – Second Level Disinfection

Chlorine is introduced as a secondary disinfectant to kill any remaining pathogens and ensure that the water stays free of harmful organisms.

7. Post Chlorination – UV Disinfection – Third Level Disinfection

UV lamps are used to disinfect the water further by targeting pathogens such as Cryptosporidium and Giardia cysts that may have eluded earlier steps.

8. Additives for Health and Pipe Protection

• Fluoride is added to promote dental health and prevent tooth decay.
• Phosphate is used to prevent corrosion in old pipes, particularly those made from lead or carbon steel.

Storage in Underground/Above Ground Basins/Tanks

The treated water is stored in underground basins, waiting to be distributed to the public. There are important risk assessments and safety/security/quality considerations in designing and managing these basins.

Distribution Network

The treated water is pumped through underground basins and into water towers, from where it’s distributed to homes and businesses. Residual chlorine is maintained in the distribution system to ensure that the water remains safe during transportation, especially if leaks occur in the network.

It’s important to note that some countries, like the Netherlands, distribute safe drinking water without using chlorine. You can explore this approach further in an article on the TU Delft website.

Wastewater /Sludge Management

Sludge from the clarification process and filter backwash is dewatered. The water is recycled, while the solid waste is sent to a landfill.

 Potable Water Treatment for Developing Countries

Sometimes you have no access to electricity or chemicals or pumps or fancy filters. I have been to Africa and met people from a Kenyan Village named Olengaji Nabo who drink from a local creek. Their teeth are stained yellow because of the iron in the creek water. Many kids get GI diseases because local drinking water sources get contaminated by sewage especially during floods. Many African people living in villages have manual wells or manual pumps from small boreholes. Here technologies like SODIS – Solar Disinfection help to minimize the risk of water borne diseases. Some researchers in Tanzania are looking into clay pot filters. One technology that is spreading is GDM – Gravity Driven Membrane treatment – a sort of UF that is driven by gravity.

 

Sea Water Desalination

Note that countries that neighbour oceans or seas that have dry climates and no surface/ground water aquifers resort to sea water desalination using Evaporation or Reverse Osmosis. This process removes TDS or dissolved salts from the sea water to make it potable.

 

Treating Sewage Effluent to Potable Water Quality

Some water stressed countries like Namibia and Singapore cannot afford to waste a single drop of water. Their cities collect sewage and treat it up to potable water quality. The process in Singapore is called Newater.

 

 

Prominent Potable Water Utilities

Some of the most well-known water utilities worldwide include:

• United Utilities (UK) – Serving Greater Manchester
• Anglian Water (UK)
• Southern Water (UK)
• Severn Trent (UK)
• Thames Water (UK)
• Veolia (France)
• Suez (France)
• Gelsenwasser AG (Germany)
• Mainova AG (Germany)

• Berliner Wasserbetriebe (Berlin, Germany)

• Eau De Paris (paris, France)
• Vitens and Dunea in the Netherlands

 

Quality Assurance and Quality Control

Every potable water utility conducts extensive water quality tests and adheres to a strict Quality Assurance program. Some of the water parameters like turbidity are constantly measured online. Other tests like taste, odor and physico-chemical testing are performed in ISO 17025/UKAS certified labs. I have personally been to the Anglian Water drinking water quality lab and it was an eye opening experience. The hero chemists and microbiologists that are checking our drinking water quality behind the scenes are true unsung heroes.

Regulation and Legislation

In the UK, the primary drinking water regulator for England and Wales is the Drinking Water Inspectorate (DWI), while the Drinking Water Quality Regulator (DWQR) oversees Scottish Water in Scotland. 

 

The European Union’s main law on drinking water, the Drinking Water Directive (DWD), sets minimum quality standards for water intended for human consumption, and the European Commission is responsible for ensuring the DWD is implemented by member states. 

 

Globally, many countries follow the WHO’s guidelines on drinking water.

 

 

 

 

This article has been prepared by Chartered Scientist Rami E. Kremesti M.Sc., CSci, CEnv, CWEM

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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