Emerging Drinking Water Treatment Technologies

- Overview

Global drivers associated with population growth, demographic shifts, and climate change place increasing stresses on fresh and sustainable water supplies. Maintaining water treatment to ensure a clean supply to meet growing global populations has been an ongoing challenge throughout human history.  

Thanks to significant technological developments in water treatment, including monitoring and assessment, high-quality drinking water can be supplied and enjoyed around the world. Replicating the earth’s hydrological cycle in which water is continuously recycled, treatment enables the same water to be cleansed through several natural processes. 

To ensure they do not present a health risk, nearly all water sources require treatment before they can be consumed. Many treatment systems are designed to remove microbiological contamination and physical constituents, including suspended solids (turbidity). Following this, a final disinfection stage is nearly always included at the end of the treatment process to help deactivate any remaining microorganisms. If a persistent disinfectant, such as chlorine, is added this can also act as a residual to help prevent biological regrowth during water storage or distribution in larger systems. 

- Water Treatment: Mimicking Earth’s Hydrological Cycle

Water treatment consists of several stages. This can include the initial pre-treatment by settling or through using coarse media, filtration followed by chlorination, called the multiple barrier principle. The latter allows effective water treatment and allows each stage to treat and prepare water to a suitable quality for the next downstream process. For example, filtration can prepare water to ensure it is suitable of UV (ultraviolet) disinfection.  

Depending on the quality and type of the water entering a water plant, treatment may vary. For example, groundwater treatment works abstract water from below ground sources such as aquifers and springs. These sources tend to be relatively clean in comparison to surface water, with fewer water treatment steps required.  

Surface water treatment works take water from above ground sources, such as rivers, lakes and reservoirs. This raw water is subject to direct environmental input. As a result, multiple treatment steps are required and individual processes are required that will enable the configuration of different comabinations to clean and finally disinfect the abstracted water.  
Some water supplies may contain disinfection by-products, inorganic chemicals, organic chemicals and radionuclides. As a result, specialised water treatment methods may also be part of water treatment to help control formation and removal.  

Furthermore, under renewed regulations, tighter limits could be placed on endocrine disrupting chemicals as well as lead limits being halved.

- How Does The Water Treatment Process Work?

Coagulation, flocculation and sedimentation are processes used to remove colour, turbidity, algae and other microorganisms from surface waters. 

Chemical coagulants can be added to the water for the formation of a precipitate, or floc to entrap these impurities. After sedimentation and/or filtration, the floc is separated from the treated water
Aluminium sulphate and ferric sulphate are two of the most commonly used coagulants , although others are available. Raw water quality near to the inlet of a mixing tank or flocculator determines the rate in which coagulants are dosed in solution. 

By adding coagulant at a point of high turbulence, it is rapidly and thoroughly dispersed on dosing. The next stage is the sedimentation tank. Here aggregation of the flocs takes, which settle out to form sludge that will need to be removed. 

One of the advantages of coagulation ais that it reduces the time required to settle out suspended solids. Furthermore, it can be very effective in removing fine particles that are otherwise very difficult to remove. 

The cost and the requirement for accurate dosing, thorough mixing and frequent monitoring, are often cited as the principal disadvantages of using coagulants for treatment of small supplies. Bench scale coagulation tests can be used to determine which coagulant to use for a specific raw water.  

As a result, to remove colour and turbidity, coagulation and flocculation are considered the most effective treatment techniques. However, for small water supplies they may not be suitable. This is due to the level of control required and volumes of sludge generated.
 

[More to come ...]