Environmental Engineering Reference
In-Depth Information
9.4 Metrics of Adsorptive Media Arsenic Removal Technologies
The following information is the minimum required to determine the projected cost per
thousand gallons ($/kgal) of an arsenic removal treatment system:
• Arsenic
3+
inluent concentration (dissolved)
• Arsenic
5+
inluent concentration (dissolved)
• Total As, which is both particulate and dissolved
• Efluent As concentration allowable (10 μg/L)
• Empty bed contact time (EBCT) = time the water is in contact with the media or
(
V
/
Q
) × 7.48 gal/ft
3
• Flow rate in gpm
• Estimated loading of As in milligrams per gram of media (supplied by manufac-
turer or laboratory jar testing)
Convert the BV (50 ft
3
), which equals 374 gal/BV, then take the total gallons
treated; let us say 26,928,000 gallons and divide by 374 BVs, which equals 72,000 BV
processed.
The EBCT determines how long of residence time is needed to remove As below the
10 μg/L level, and this number varies depending on whether the adsorptive media
has the ability to remove both forms of arsenic. Recommended EBCT is 2.34-4.16 min
lowing at 4.4-8.3 gal/ft
2
, with a manufacturer's recommendation of 7-10 gal/ft
2
.
To get cost per thousand ($/kgal), take the total treated volume/1000, which
equals
X
, which equals cost per thousand gallons. This number should be between
$0.15/kgal and $1.00/kgal for domestic applications. In Bangladesh, the treatment
cost goal is under 10 paisa where 100 paisa = 1 rupee and 52 rupees = $1.00 (US).
This example above uses the Titania by HydroGlobe material, and note that
this is for two media beds in parallel totaling 50 ft
3
and is capable of removing
As below the MCL of 10 ppb. The ArseneX
np
shows reaching 8 ppb with a lead-
lag media bed primarily removing As
5+
. The above arsenic removal studies and
handbooks clearly show that there are numerous technologies that show eficacy
for removing dissolved arsenic, and there are numerous metrics for determining
which technology best its the application.
Here is a very good “rule of thumb” for getting to the bottom line of cost for
an arsenic removal system. The only components that are controlled are in bold,
which are the inluent and required efluent arsenic concentrations, low rate,
arsenic loading in mg/g:
Arsenic load
Arsenic inluent (total)
0.035 mg/L
Required arsenic efluent
0.01 mg/L
Total As removed
0.025 mg/L
As (+3)%
As (+5)%
Other ions that may load
