ChemicalRegeneration of Activated Carbon: A Feasibility Study

ReportNo WSAA 61

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.

 

Theareas covered and the key findings are summarised below:

 

i)                   Further Studieson Used Carbon from a Water Treatment Plant

 

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

 

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

 

ii)                 TemperatureOptimisation

 

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

 

        50-60C 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 thesurface by regeneration under the most favourable conditions was found to bedependent on the initial surface loading. At 53C the percentage removalvaried from 80%, at low surface loading, to a plateau of around 50% at a highsurface concentration.

 

iv)               Long Term ColumnTests

 

Three types of carbon were investigated: Filtrasorb 400, GAC2 andHydrodarco. Dissolved organic carbon concentrations in the influent and effluentof 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 witha decrease in pH of the effluent. After the pH increased to the backgroundvalue the adsorption properties were consistent with the surface loadings ofthe carbon. The final regeneration increased the surface areas of the carbons,but to different extents. The percentage increases were from 43% to 26%.

 

v)                 ThermalRe-activation

 

The three carbons were re-activated after the lastadsorption/regeneration cycle and the surface areas before and afterre-activation were compared. As with the chemical regeneration procedure, theincrease in surface area varied between the carbons, in this case from 63% to12%.

 

vi)               Removal ofMethylisoborneol

 

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

 

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