Activated Carbon (Powdered Activated Carbon and Granular Activated Carbon)
Process Type: Filtration/ Physical Treatment
Powdered Activated Carbon
In theory may be used for tertiary leachate treatment but the author is not aware of any examples.
Granular Activated Carbon
GAC filtration systems generally demand a relatively low level of suspended solids in incoming effluent, which
may require a specific additional treatment stage (e.g. DAF, reed bed, etc), following initial biological treatment
Since biological effluents from treatment of leachates containing high (>1500 mg/l) concentrations of
ammoniacal-N can contain up to or greater than 1000 mg/l of soluble, intractable COD, (e.g. see Robinson et al,
2003), this can make polishing of such effluents relatively expensive.
In general, smaller molecules are adsorbed less well, as are highly water-soluble compounds.
The use of a carbon filter is most commonly adopted after a biological treatment stage when the carbon filter
will be required to further reduce:
- suspended solids
- residual trace organic contaminants (eg mecopop, PCBs etc)
The presence of multiple contaminants can impact overall performance. For example (hypothetical), if the GAC is
required to reduce overall COD in effluent to a specific level, and also to remove a specific contaminant
completely, such as a relatively non-biodegradable pesticide (e.g. isoproturon), then it cannot be presumed that
removal efficiencies for each contaminant will necessarily decline in a similar manner. Bench tests are therefore
essential to estimate carbon usage for mixtures.
Treatment costs can be high if used on effluents with high COD values, following biological treatment, or if
very low final effluent values are required.
Spent carbon, possibly containing some hazardous compounds which, have been concentrated within it (e.g.
chlorinated compounds and pesticides), will require regeneration (and safe destruction of these compounds) at one
of only 2 or 3 locations in the UK. Proximity of the treatment plant to such a location may impact on costs for
carbon, and overall unit costs of treatment.
Where best used:
Where the discharge consent requires a very high standard of effluent but does not include a salinity limit.
Good, however, all activated carbon should be regenerated.
Energy usage comments:
Medium energy usage when compared with other processes.
Chemical usage/by-product production:
The Activated Carbon itself will require disposal or recycling but there are no chemicals used in the process,
other than the activated carbon.