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[Water] [Column] All About Water - (2) Pouring out Plain Water; Recycle by Filtering Wastewater!

by Eco Generation | 05-11-2019 16:20 Comments 3 Comments recommendations 0 recommendations

Pouring out Plain Water;

Recycle by Filtering Wastewater!



By Science Columnist Hyung-Ja Kim


Water accounts for 70% of the earth. However, the amount of water we can use without going through the purification process is merely 1%. This is because the amount of wastewater is growing. It is causing a vicious cycle by accelerating the depletion of water resources through secondary pollution. Wouldn’t there be any way to preserve water quality?

The answer from scientists is to reuse sewage and wastewater that has been used once. In other words, they suggest creating “new water (new-born water).” Wastewater has very complex components, as it is a mixture of many kinds of pollutants. In particular, semiconductor wastewater contains many compounds including fluoride that are hard to be biodegraded. Therefore, it is hard to expect conventional purification methods using chemicals or microorganisms to completely purify wastewater. They may create a large amount of sludge and cannot remove suspended solids completely.

To completely regenerate sewage and wastewater, chemical filter technology using nanofiber separation membranes is used. Nano separation membrane is a technology where the size of the holes on the membrane is reduced to the nano-size (1㎚ is one-billionth of a meter) to filter the pollutants or impurities in water. In the general sewage and wastewater treatment process, advanced treatment is added to adjust the quality of water that can be reused.

The principle is as follows: Coagulant is added to the water from a nearby sewage treatment plant, and the water is filtered once with a UF (Ultra Filtration) filter. The UF filter has fine holes in it so that it can filter out particles larger than 30-50 nm in the water. This once-filtered water is filtered again with a RO (reverse osmosis) filter. The RO filter purifies the water based on the principle of reverse osmosis.

When clean water and polluted water are left on both sides of a thin membrane with fine holes, the clean water moves toward the polluted water. This is so-called “osmotic” phenomenon that lower-concentration solution moves toward higher-concentration solution. On the other hand, if high pressure is added from the polluted water, the polluted water moves toward the clean water. This is the “reverse osmosis.” In this process, the pollutants cannot pass through the thin membrane.

First, the UF filter filters larger particles, and then the RO filter filters out smaller particles. The RO filter can filter even ion components smaller than 1 ㎚. Water gone through the RO treatment can be reused as industrial water, or can be sterilized and disinfected to be used for drinking.

In fact, Singapore is using this highly purified sewage as drinking water. The city-state has the largest RO facility in Asia. The reason why Singapore recycles sewage is because it has no river that can provide water resources. Therefore, the country has pulled water from its neighboring country, Malaysia. However, since Malaysia is also a water-scarce country designated by the UN, it is unknown how long Singapore can get water resources stably. Eventually, Singapore chose the technology of purifying sewage and turning it into drinking water, which currently accounts for 15% of the total water supply in the country.

Chemical filter technology with separation membranes is very attractive in terms of volume. Being the most dense wastewater treatment technology, it the most preferred wastewater treatment process in nations with a high population density and small national territory such as Hong Kong and Singapore. Especially, since the volume is small, it is possible to install the treatment facility in a multi-story structure like 2 or 3 stories, which is the optimal process in places with limited space.

The reverse osmosis method of nano-separation membranes is also used for “desalination of seawater,” which turns seawater into fresh water. It is about filtering salt and pollutants in the seawater so that it can be used as drinking water or industrial water. Seawater desalination technology is the “blue gold” in the 21st century. Singapore, the Middle East, the US, Australia, South America, Europe, China, India and African countries are actively introducing this technology.


[Column] All About Water - (2) Pouring out Plain Water; Recycle by Filtering Wastewater!

Singapore has the best desalination company in the world. It has built not only “new water” but also desalination facilities that produce 30% of the total water supply every day. The most water scarce country in the world has become a developed country in the water industry through water reuse and the desalination technology. It is a remarkable development.

Meanwhile, there is a technology where purified sewage and wastewater are not sent to nearby streams, rivers, or sea but sent back to the factory for reuse. This is called Zero Liquid Discharge (ZLD). As ZLD does not discharge effluents, it is environmentally friendly. It is the technology best used in the US. The country has operated this technology at a public sewage treatment facility in Fountain Hill, ​​Arizona since the 1970s with an installed capacity of 11,000 ㎥/day. Some factories in Europe, China, India and South Korea have introduced the technology.

Another unique technology called electron beam is also used for environmental purification. Electron beam is the light generated by electrons in an electron accelerator, and it is made by Korea Atomic Energy Research Institute, etc. Electron beam is useful for removing CO2 absorbent (MEA) that is mainly used in thermal power plants. Since CO2 absorbent is composed of carbon and nitrogen, it becomes a main cause to pollute streams and the sea, when mixed with the wastewater of the power plant and discharged. By applying electron beam to the wastewater containing CO2 absorbent, 95% of the absorbent is removed.

How can this be possible? The answer is that electron beam turns the water molecules of the wastewater into active molecules. Active molecules tend to react violently with other substances. With such a characteristic, it reacts strongly with CO2 absorbent and decomposes it at a rapid rate. Electron beam technology, isn’t it amazing?

The water we use is purified in these many ways. The wastewater treatment technology is also evolving. However, it costs a lot to make polluted water clean again. The more polluted the water, the higher the treatment costs. Please bear in mind that any carelessly thrown away food waste can become a poison to the earth!



Vazira Ikhtiyorova

Asmita Gaire

  • Asmita Gaire says :

    Thank you so much for this report
    Filtration can be one of the method of purification of water.

    Green cheers
    Asmita Gaire
    Posted 21-12-2019 04:45

Yushika Subedi

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