Why activated carbon plays a critical role in water treatment

Activated carbon is normally utilised to treat process water in two very different processes – powdered activated carbons and granular activated carbons. However, the dosage methods and use cases for each of these forms of activated carbons vary quite considerably. The selection of a specific type of activated carbons for water treatment will depend on the nature of the specific application, the result required and any process restrictions in place.

Powdered Activated Carbons are used by water treatment plants for taste and odour control and to ensure the removal of organic chemicals. PACs are added early in the treatment process to enable a period of sole contact time before other treatment chemicals are added to the water stream.

They should not be coated with any other water treatment chemicals before they have been allowed sufficient contact time with the water stream (typically PACs will require at least 15 minutes sole contact time with the water stream). Most importantly, PACs should never be added concurrently with chlorine or potassium permanganate as such water treatment chemicals will simply be adsorbed by the activated carbon powder.

Typical required dosages can range anywhere between 1 to 100 mg/L depending on the type and level of contaminant, but dosages of 1 to 20 mg/L are most typical where treating water streams for the purpose of taste and odour control.  Higher dosages will be required where PACs are added later in the treatment process, to allow for any adsorption of other treatment chemicals added earlier in the process. PACs are later removed from water streams through a process of sedimentation or by filter beds.

In modern treatment systems, it is often preferred to use granular activated carbon for continuous treatment processes. Despite warranting a higher initial cost investment than PACs, GACs have a much lower operational cost as it can be thermally regenerated to recover the adsorptive properties.

Granular activated carbon offers particularly strong adsorbent properties. Its high surface area to volume ratio facilitates the ability to tackle a large number of contaminants and it can be used in static beds or part of a mobile filter system.

The treated water stream flows counter-currently to the GACs. The GAC can be regularly removed and replaced with new or regenerated GAC at the top of the filter to continue to deliver strong adsorption of contaminants. Reactivation of GAC reduces operational costs, increases ROI and ensure continuous operation of the treatment system.

Existing water treatment rapid sand filters can be continuously modified and reconstructed for filtration-adsorption by replacing all/a portion of the granular media with GACs. This modification can significantly reduce capital costs as no additional filter boxes, underdrains and backwashing systems will be required. However, it is important to note that filter-adsorbers do have shorter filter run times and will need to be backwashed more regularly than post-filter adsorbers.

Activated carbons offer one of the most effective means of removing key contaminants such as THM and DBP as well as removing organic constituents and residual disinfectants in water supplies. This not only improves taste and minimises health hazards but protects other water treatment units such as reverse osmosis membranes and ion exchange resins from possible damage due to oxidation or organic fouling.

Activated carbon continues to remain one of the most favoured water treatment techniques across the U.K. and Ireland because of its extraordinary array of applications and functions.

Enva are leading suppliers of activated carbon. With our partner Jacobi Carbons, we offer the most diverse range of activated carbon powders and activated carbon granules on the market. If you require more information on our range of activated carbons or have a query for our expert team, please feel free to get in touch.