The regeneration of field-spent granular-activated carbons

The thermal regeneration of field-spent granular-activated carbons (GAC) is being increasingly adopted as a cost-effective alternative to disposal. Th e success of this practice requires the adjustment of process conditions to maximise the recovery of the original carbon characteristics while minimis ing carbon loss. This paper describes an investigation into the regeneratio n of several field-spent GAC representative of those typically generated by the drinking water treatment industry. The carbons were initially investig ated for their ash contents and inorganic compositions in order to determin e the accumulation of metallic species that affect the regeneration process . Regeneration was conducted in steam at 800 degreesC over reaction limes b etween 0 and 60 min in order to achieve different degrees of carbon gasific ation. Weight losses were determined for each condition and the resulting c arbons characterised for their apparent density. porosity. surface area and aqueous adsorption characteristics. Results showed that spent carbons reco vered most of their adsorption characteristics when heated to 800 degreesC under inert conditions. Steam gasification in the range of 5 -10 wt% burn-o ff had some positive effects on the characteristics of the spent carbons wh ich were in most cases counteracted by a reduction in the carbon yield. Ste am gasification in excess of 15 wt% burn-off caused a rapid increase in the carbon mesoporosity but a significant deterioration in the carbon micropor osity, BET surface area and adsorption capacity for organic species of smal l molecular size. (C) 2001 Elsevier Science Ltd. All rights reserved.