Life is unimaginable without water, so it is essential to use it efficiently and conserve it wherever possible. In many places wastewater is treated to produce clean water, and one effective way of doing so is with activated carbon for water treatment. It works by adsorption, a process in which molecules and ions attach to the surface of the activated carbon particles.
KEIKEN offers a range of wastewater treatment solutions with activated carbon equipment. Read on to find out more about how carbon is activated and used.
What are the main activation methods?
There are two main methods of activating carbon before use: chemical activation and thermal (steam) activation. The raw material can be anything with a high carbon content, including coconut shells, coal, macadamia nut shells, lignite, wood, bamboo and peat. Depending on the activation method, some raw materials are more suitable than others.
Chemical activation
The chemicals most commonly used in chemical activation are zinc chloride, phosphoric acid and potassium hydroxide. They produce activated carbon with very high porosity, and since the effectiveness of activated carbon increases with porosity, this is an important advantage. It is also the usual method when the raw material is peat or wood.
The chosen material is first crushed to the required particle size and mixed with a concentrated solution of the dehydrating agent. It is then dried and heat-treated in an inert atmosphere at 400–700 °C. Finally, it is washed with water to remove the activating agent, separated, dried and made ready for use.
Steam activation
In steam activation, the raw material is first carbonised into char and then placed in a kiln, where it is heated to 927–980 °C with steam in the absence of oxygen. At this stage all volatile compounds are driven off, and layers of carbon are removed to open up enlarged internal pores in the carbon skeleton. Once cooled, the activated carbon is washed with water or acid to remove ash; if acid is used, it is then rinsed thoroughly with water.
How is activated carbon used in water treatment?
Both industrial and municipal wastewater can be treated to remove impurities and produce clean water for a range of uses. In this process, activated carbon is used in the final stages, after settlement and flocculation.
Once the suspended solids have been removed, the water passes through activated carbon filters. Each filter should be used to its full capacity, and impurities not adsorbed in one filter can be captured in the next.
The treated water can then be used for drinking or as service water, for example in swimming pools and aquariums. The intended use of the water determines which activated carbon filtration system is used.
Chlorine removal
Chlorine is used to disinfect public water supplies because it is a powerful, effective disinfectant. In large quantities, however, it can cause problems and give water an unpleasant taste. Activated carbon removes chlorine from water effectively.
Granular activated carbon is the type most widely used in large water treatment filters. Flow rates of 2–3 US gallons per minute per cubic foot of carbon are typical, because the contact time with the carbon is directly related to the amount of chlorine removed.
Organic matter removal
Activated carbon also removes organic matter from wastewater, including decaying plant material and man-made compounds, which are trapped in the carbon filter by adsorption.
Carbon with very fine pores is the most effective filter, as it prevents contaminants from passing through. Depending on the purpose of the treatment, the activated carbon is selected to interact with the specific organic matter in the water.
Key points
Activated carbon for water treatment is an economical and effective solution. If you are looking for filters and equipment for water treatment, see our activated carbon or contact KEIKEN for advice on the right solution.
