AWWA ACE58106

A major problem faced by utilities considering arsenic (As) adsorption media is that pilottesting requires very long runs and therefore is very costly. For example, a 200 mL lab scalecolumn (5 cm diameter by 10 cm long) operated for 10,000 BVs at a 5 minute empty bed contacttime (EBCT) requires a run length of 35 d and will use 500 L of water. An accelerated testingprotocol is being developed to rapidly determine the adsorption characteristics of new mediausing procedures similar to those developed for granular activated carbon (GAC) adsorptionwhich are referred to as rapid small scale column testing (RSSCT). Adsorption involves asequence of steps including mass transfer processes and adsorption kinetics. For GAC, theintraparticle surface diffusion rate often controls the overall rate of adsorption, henceexperiments conducted with smaller particles than used in a full scale adsorber can accelerate thetesting process. Similitude was used to develop scaling relationships between laboratorycolumns and full scale GAC adsorption systems. There are important differences betweenadsorption 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 theadsorbents. These scaling relationships developed for GAC are being examined for As adsorptiononto four metal oxide media; activated alumina, two iron oxy-hydroxide media, and a proprietarymetal oxide media. The testing involves determination of the adsorption equilibria in batchstudies, measurement of the intraparticle surface diffusion, and column studies using media ofvarious sizes. The most important differences are the nature of the bonds and the physicalcharacteristics of metal oxide adsorbents. In contrast to the hydrophobic bonds between organicsolutes and GAC arsenic adsorption onto metal oxide surfaces is dominated by electrostaticattraction, at least initially. Also, metal oxide surfaces have much less internal porosity thanGAC which results in less surface area and different types of mass transfer. Includes 16 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

06/15/2003

Number of Pages:

13

File Size:

1 file , 1.4 MB