A major problem faced by utilities considering arsenic (As) adsorption media is that pilot
testing requires very long runs and therefore is very costly. For example, a 200 mL lab scale
column (5 cm diameter by 10 cm long) operated for 10,000 BVs at a 5 minute empty bed contact
time (EBCT) requires a run length of 35 d and will use 500 L of water. An accelerated testing
protocol is being developed to rapidly determine the adsorption characteristics of new media
using procedures similar to those developed for granular activated carbon (GAC) adsorption
which are referred to as rapid small scale column testing (RSSCT). Adsorption involves a
sequence of steps including mass transfer processes and adsorption kinetics. For GAC, the
intraparticle surface diffusion rate often controls the overall rate of adsorption, hence
experiments conducted with smaller particles than used in a full scale adsorber can accelerate the
testing process. Similitude was used to develop scaling relationships between laboratory
columns and full scale GAC adsorption systems. There are important differences between
adsorption of organics onto GAC and adsorption of As onto metal oxy-hydroxide surfaces.
These include differences in the nature of the bonds and the internal pore structure of the
adsorbents. These scaling relationships developed for GAC are being examined for As adsorption
onto four metal oxide media; activated alumina, two iron oxy-hydroxide media, and a proprietary
metal oxide media. The testing involves determination of the adsorption equilibria in batch
studies, measurement of the intraparticle surface diffusion, and column studies using media of
various sizes. The most important differences are the nature of the bonds and the physical
characteristics of metal oxide adsorbents. In contrast to the hydrophobic bonds between organic
solutes and GAC arsenic adsorption onto metal oxide surfaces is dominated by electrostatic
attraction, at least initially. Also, metal oxide surfaces have much less internal porosity than
GAC which results in less surface area and different types of mass transfer. Includes 16 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 1.4 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 13 |
| Published : | 06/15/2003 |
