Arsenic Technology Overview

Sugden Elements represents the finest treatment approach for arsenic removal. This media is packaged integrated systems for arsenic treatment, which is a proven adsorption process designed specifically for drinking water applications. It was developed in the United Kingdom and has been proven successful in lowering arsenic levels to less than 3 ppb (µg/L) using a unique and proprietary adsorbent media that has a high, selective capacity for arsenic (As) removal from drinking water. Over a half million people around the world are currently using this technology to remove arsenic, and by the end of this year that number will surpass 1 million people and possibly as many as 2 million. The technology is currently installed in approximately a dozen municipal water systems, several hundred POE and POU applications and numerous industrial wastewater clean up sites.

This arsenic removal process for small systems employs a fixed bed adsorption system using the AD-33 granular ferric oxide media (adsorbent) for the adsorption of dissolved arsenic onto the ferric oxide. Groundwater or surface water is simply pumped in a down-flow mode through a single or multiple fixed bed vessel(s) containing the media where the arsenic removal occurs.

With the media, both As (III) and As (V) oxyanions are removed from water via a combination of adsorption, occlusion (adhesion) or solid solution formation by reaction with ferric oxide ions. This is rather unique feature since many conventional processes poorly adsorb As (III) and require pre-oxidation before effective arsenic reduction is achieved. Above pH 7, the primary mechanism is adsorption of the oxyanions to the surface hydroxyl groups of ferric oxide or hydroxide as indicated below:

(HO)2Fe O···H···O4AsHn-(3-n)

Adsorption is a continuous process conducted at a specific flow rate or velocity downward through a fixed bed adsorber. In addition to velocity, the other key process parameter is empty bed contact time (EBCT), which dictates the amount of water residence within the bed required to effect complete arsenic adsorption.

Unlike other adsorbents, AD-33 will adsorb both As (V) and As (III). The arsenite form is nonionic at normal water pHs and, therefore, will not be as quickly adsorbed as an anion. Adsorption kinetics for As (III) are slower than that of As (V).

Once every 3-4 weeks or another frequency dictated by specific applications, the adsorber is taken off-line for a very brief period of time for backwashing to remove media fines that have built up and to “fluff up” or reclassify the compacted bed. This intermittent step will also minimize ?P through the bed. The residual consists of approximately 10 bed volumes of backwash water containing only innocuous iron oxide fines. Based on site specific backwash water data, no soluble arsenic is discharged as a result of this process step. Aside from backwashing, there are no other steps required until the end of the adsorbent’s capacity when it becomes exhausted.

For small system applications, media life typically ranges from 6 months to two years, depending upon:

The influent water’s arsenic concentration

The water’s pH

Concentrations of other ions in the water that could shorten the media’s arsenic adsorption capacity