Damon S. Williams Associates (DSWA) was contracted by the City of Mesa to conduct arsenic
pilot testing on their drinking water system, which has approximately 22 wells impacted by the
new Maximum Contaminant Level (MCL) of 10 parts per billion (ppb). DSWA teamed with
Arizona State University (ASU) to perform arsenic removal bench testing. The project focused
on testing and evaluating seven adsorptive arsenic removal media and one ion exchange resin
system. Several of the media had not yet been tested on complex waters found in Arizona and
throughout the arid Southwest. All tests were conducted with a natural groundwater containing
approximately 33 ppb of arsenic (present as arsenate), an ambient pH of 7.7 and other parameters
(e.g. silica, vanadium, phosphate), which are known to cause treatment difficulties for some
media.
The bench testing consisted of two phases. Jar tests were used in Phase I to screen seven media
for arsenic removal efficiencies at three pH's.
Phase II involved
Rapid Small-Scale Column Testing (RSSCT), which focused on media kinetics and provided
laboratory generated breakthrough curves.
DSWA generated a ranking system to determine which media to pilot test. Ranking system
variables included the following: NSF approval status; results of the bench testing; capital cost
projections; O&M cost projections; and operational issues (e.g., iron release or pH adjustment
requirements). Pilot testing was conducted with the three most favorably ranked media: WRT
Z33, GFH, and Bayoxide E33, utilizing the DSWA-designed arsenic removal pilot system. The
pilot system's contactors operate in parallel and series configurations, as well as in upflow or
downflow modes of operation to accommodate a wide variety of the media on the market today.
These pilot tests were conducted in parallel until breakthrough. DSWA also tested the Basin
Water ion exchange package pilot system as a comparison to adsorptive media.
Competing contaminants (e.g. silica, vanadium, phosphate) were evaluated during piloting to
determine their impact on media life. Each media was also evaluated for potential contaminant
releases (e.g., iron), as well as potential increases in treated water turbidity, as they may create
impacts to the distribution system.
This paper demonstrates the validity of the RSSCT results for this water through comparison
of pilot test results. Pilot testing results will be discussed, with an emphasis on the impacts of
competing and/or released contaminants and the biological impacts on media with intermittent
well use. The findings of this paper will be useful for all water systems that must consider
treatment for arsenic removal to better understand the process that is required for selecting
appropriate adsorptive media. Includes table, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 540 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 16 |
| Published : | 11/02/2003 |
