This thesis describes both batch and continuous processes for water treatment by adsorption with electrochemical regeneration of the adsorbent using an airlift reactor. The process is based on the adsorption of dissolved organic pollutants onto a graphite intercalation compound (GIC) adsorbent and subsequent electrochemical regeneration of the adsorbent by anodic oxidation of the adsorbed pollutant. Batch experiments were carried out to determine the adsorption kinetics and equilibrium isotherm for a sample contaminant, the organic dye Acid Violet 17 on the GIC (Nyex®1000) adsorbent. The adsorption capacity was found to be around 1 ± 0.05 mg/g. The rate of adsorption appeared to follow pseudo-second order kinetics. The increase in the rate adsorption with temperature indicated an activation energy of around 4.2 KJ/mole, suggesting that the mechanism of adsorption was physisorption. It was demonstrated that the adsorbent could be regenerated by anodic oxidation of the adsorbed dye in a simple electrochemical cell. The GIC adsorbent recovered its initial adsorption capacity after 40 to 60 min of treatment at a current density of 10 mA/cm2, corresponding to a charge passed of 12 to 15 C/g of adsorbent. The charge passed is consistent with that expected for mineralisation of the dye suggesting that the dye was removed and destroyed with high charge efficiency. Experiments were carried out to investigate the characterisation and performance of the continuous process, where water is treated continuously in a fluidised adsorption zone and the adsorbent is circulated through a moving bed electrochemical regeneration cell. The adsorbent circulation rate, the residence time distribution (RTD) of the reactor, and water treatment performance by continuous adsorption and electrochemical regeneration were studied. The RTD behaviour could be approximated as a continuously stirred tank. It was found that greater than 90% removal at feed concentrations of up to 100 mg/L were achieved using a single pass through a large continuous treatment unit by adsorption and electrochemical regeneration with a flow rate of 0.25 L/min. In a smaller continuous treatment unit 98% removal at feed concentrations of up to 66 mg/L were achieved in a single pass with a flow rate of 0.24 L/min. Steady state and dynamic models have been developed for the continuous process performance, assuming full regeneration of the adsorbent in the moving bed electrochemical cell. Experimental data and modelled predictions (using parameters for the adsorbent circulation rate, adsorption kinetics and isotherm obtained experimentally) of the dye removal achieved were found to be in good agreement. A higher dye removal was found with a co-current PFR model, but a number of tank in series (n CSTRs) was found to give higher contaminant removal for the same total adsorption zone volume. It was also found that the predicted number of stages of batch adsorption / regeneration required to achieve 99.9% AV17 removal was halved when the adsorptive capacity of the adsorbent was doubled. Similarly the predicted number of continuous CSTR adsorption / electrochemical regeneration process units required in series to achieve 99% AV17 removal was reduced by more than two thirds when the adsorptive capacity of the adsorbent was doubled.
|Date of Award||31 Dec 2011|
- The University of Manchester
|Supervisor||Edward Roberts (Supervisor)|
- Modelling, Design, Adsorption, Electrochemcial Regeneration, GIC, Dye