Chemical regeneration of granular activated carbon: Development and evaluation of an optimal regenerant solution

Abstract

The regeneration of the saturated GAC then needs to be carried out to lengthen the GAC bed life. The presence of weakly adsorbable pesticides, such as metaldehyde, in raw water continues to challenge granular activated carbon (GAC) performance, by causing an early GAC filter beds exhaustion. The accelerated exhaustion leads to the need for frequent off-site thermal regeneration, which is the most common practiced carbon regeneration technique, representing a significant operational cost and environmental (energy/CO2) burden to water utilities. An alternative approach is to conduct in situ GAC regeneration by alternative chemical means. In this research, a systematic investigation of chemical regeneration in batch and column tests was conducted in order to find and evaluate the most suitable regenerant solution for GAC exhausted by particular target contaminants, namely phenol, nitrobenzene, isoproturon, clopyralid and metaldehyde.

Based on the findings of this research, it is concluded that the sodium hydroxide and ethanol mixture (NaOH/CH3CH2OH) was effective as a regenerant solution with desorption efficiencies in a range of 31.8 – 89.0%, depending the target contaminants. The sequence adsorption and chemical regeneration cycles in column tests showed that the chemical regeneration may be more beneficial to be applied for carbon exhausted by poorly adsorbed pesticide, such as metaldehyde, compared to thermal regeneration. The RSSCTs study also suggested that the regenerant solution can be re-used up to four times, but with a decreasing performance. The results of the carbon characterization tests showed that the NaOH/CH3CH2OH regenerant did not cause any significant changes in the term of carbon physico-chemical properties, indicating the benign nature of the regenerant.

Overall, the findings of this research contribute to future development of chemical regeneration application in water treatment, and at the same time helping water utilities in considering new and improved methods to the current GAC filter bed practice.