Chemical Regeneration of Activated Carbon: A Feasibility Study

This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.

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Report No UWRAA 146

July 1993

SYNOPSIS

Thisinvestigation was an extension of a preliminary study into the effectiveness ofchemical regeneration of activated carbon (UWRAA Research Report No 20). Theaim of the study was to determine the feasibility of using chemicalregeneration on granular activated carbon in a water treatment plant.

The areas covered and the key findings are summarised below:

i) Further Studies on Used Carbon from a Water Treatment Plant

Surface titrations, electrophoretic mobility measurements and surface area analysis were used to investigate the change in surface properties caused by the adsorption or organic material. The tests were undertaken on virgin carbon (new) and carbon with a high organic loading sampled from the granular activated carbon filters at North Richmond Water Filtration Plant (used).

It was found that the surface charge became much more negative on the adsorption of organic matter, and the surface area of the used carbon was only half that of the new carbon. A small decrease in pH decreased the negative charge on the used carbon significantly but had little effect on the new carbon. It was concluded that this large pH effect was responsible for the very large regeneration efficiencies found in earlier work (UWRAA Research Project No WS-12, Research Report No 20, Chemical Regeneration of Activated Carbon: Preliminary Studies).

ii) Temperature Optimisation

A series of qualitative tests were undertaken to determine if an increase in pressure and/or temperature would facilitate the removal of adsorbed organic material from the carbon surface. it was found that:

· 50-60°C was the optimumtemperature for removal of organic matter

· Boiling or heating the carbon under pressure resulted in the productionof fine particles and no significant improvement in organics removal.

iii) Removal ofAdsorbed Organic Matter

A series of experiments were undertaken to determine the maximumremoval of adsorbed organic matter for a range of surface loadings.

The quantity of adsorbed organic material that can be removed from the surface by regeneration under the most favourable conditions was found to bedependent on the initial surface loading. At 53°C the percentage removal varied from 80%, at low surface loading, to a plateau of around 50% at a high surface concentration.

iv) Long Term Column Tests

Three types of carbon were investigated: Filtrasorb 400, GAC2 and Hydrodarco. Dissolved organic carbon concentrations in the influent and effluent of the columns were monitored over three adsorption/regeneration cycles. Maximum removal of adsorbed matter during regeneration was found to be 40-50%.The three carbons showed initial high regeneration efficiency, coincident with a decrease in pH of the effluent. After the pH increased to the background value the adsorption properties were consistent with the surface loadings of the carbon. The final regeneration increased the surface areas of the carbons, but to different extents. The percentage increases were from 43% to 26%.

v) Thermal Re-activation

The three carbons were re-activated after the last adsorption/regeneration cycle and the surface areas before and after re-activation were compared. As with the chemical regeneration procedure, the increase in surface area varied between the carbons, in this case from 63% to 12%.

vi) Removal of Methylisoborneol

Granular activated carbon from a GAC pilot plant currently running at Anstey Hill Water Filtration Plant was used to investigate the ability of chemical regeneration to improve the adsorption of a taste and odour causing compound, methylisoborneol (MIB), on used carbon. The adsorption of MIB was significantly enhanced by chemical regeneration; the life of the carbon filter (in relation to MIB adsorption) could therefore be expected to be extended by there generation process.

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