Chemviron Carbon: Drinking Water Treatment

Drinking water treatment

Granular Activated Carbon in Potable Water Production

Granular Activated Carbon can be used in rapid gravity filters, Slow Sand Sandwich filters and mobile and fixed pressure rated adsorbers.

Today, Granular Activated Carbon is the standard for the treatment of surface sourced drinking water and contaminated ground water in Europe. GAC will improve the quality of drinking water by removing:

• Taste and odour forming compounds
• Pesticides including byproducts
• Colour
• Trihalomethanes and other disinfection byproducts
• Algal toxins
• Chlorinated hydrocarbons

GAC for drinking water treatment needs a pore structure to allow the adsorption of a wide range of organic compounds including specific micro-pollutants and natural organic matter. The GAC must also possess a suitable amount of transport pores which allow the molecules to be transported to the adsorption site. The adsorption capacity for drinking water applications is very difficult to quantify by laboratory evaluation. Parameters such as the iodine number indicate the overall porosity of the carbon, but cannot be used to estimate the performance in drinking water applications. This is illustrated by the fact that Filtrasorb® 200 has a higher capacity than Filtrasorb® 400 for the removal of chlorinated compounds from ground water, even though it is less active. The best way to evaluate the performance of GAC is to carry out on-site pilot tests directly modelling the proposed plant. Alternatively, the design should be based on experience and references.

The pore structure of carbon is strongly influenced by the raw material and the activation process. For example, coconut shell-based activated carbons have very few transport pores. This means the high adsorption capacity of these activated carbons is not utilised very well in drinking water. In contrast, the Chemviron Carbon Filtrasorb® range of coal-based GAC have a very good balance of both adsorption and transport pores, making them optimal for the treatment of drinking water.

Filtrasorb® 100, 200 and TL820 have an adsorption capacity suited to the removal of specific organic compounds in the presence of low concentrations of natural organic matter. In addition, these products are suitable for taste and odour removal.

Filtrasorb® 300, 400 and TL830 have a pore structure and greater number of transport pores making the GAC suitable for the adsorption of a wide range of organic compounds, both specific micro-pollutants and natural organic matter.

Filtrasorb® type carbons have a high density, which means a higher capacity per unit volume. This also ensures the granules do not float and therefore minimises the loss of GAC.

GAC in drinking water requires high mechanical strength for:

• backwashing
• air scouring
• reactivation
• handling and transport

If the carbon is not strong enough, it can result in operating losses and the formation of fine carbon particles in the adsorber which can cause high pressure drop. The hard coal base of Filtrasorb® carbons ensures good mechanical strength and, in general, the operating losses from a well designed adsorber are negligible.

FILTRASORB® are a renowned range of Granular Activated Carbons, which are installed in over 1,000 water treatment plants in Europe, the United States and Asia. FILTRASORB®; carbons are produced by steam activation of selected grades of bituminous coal that have first been pulverised then agglomerated.

Chemviron Carbon has been at the forefront of the development of GAC for drinking water treatment from its first application as a sand replacement for taste and odour removal to more recent developments such as the GAC Sandwich for the installation of GAC in slow sand filters. In addition, Chemviron Carbon has pioneered the use of large scale reactivation centres to provide a complete service for water works. Once granular carbon is saturated or the treatment objective is reached, it can be recycled, by thermal reactivation, for return and reuse in the original water works.

PAC in Potable Water Production

Powder Activated Carbon is used in the potable water production for seasonal or short to medium term problem solving. Chemviron Carbon has developed a range of products, Pulsorb®, which are similar in adsorption characteristics as the Filtrasorb® granular carbon range. These powders are made from bituminous coal and are available in big bags, sacks or in bulk.