Environmental Engineering Reference
In-Depth Information
Table 1
Selected metal concentrations, based on the assessment guidelines for
contaminated groundwater in Sweden
[11]
Conc. 1 mg/L
extremely
contaminated
Conc. 2 mg/L
5× extremely
contaminated
Conc. 3 mg/L
10× extremel
contaminated
Metal ion
Copper, Cu
2+
20/10 = 2.0
b
10
b
20
b
Zinc, Zn
2+a
20/10 = 2.0
b
10
b
20
b
Chromium, Cr
3+
0.50
2.5
5.0
Nickel, Ni
2+
0.50
2.5
5.0
Molybdenum, Mo
4+a
0.50
2.5
5.0
Tin, Sn
2+a
0.50
2.5
5.0
Vanadium, V
2+a
0.50
2.5
5.0
Lead, Pb
2+
0.10
0.50
1.0
Cadmium, Cd
2+
0.050
0.25
0.50
Cesium, Cs
+a
0.050
0.25
0.50
a
Swedish assessment guideline values missing.
b
Due to the high assessment value, a ten time lower concentration was used.
In order to maintain a constant pH value, a 0.2 M acetate buffer was added to
keep pH at 5.6 as well as a 0.02 M phosphate buffer for pH 7.0. In the beakers without
pH adjustment and no buffer, the pH was initially 10.1-10.4, but dropped to 9.2 after
the addition of the acidic multi-metal solution. Three metal concentrations were
used for each pH level (Table
1
). The concentration for each metal was selected
to represent a real and extremely contaminated groundwater, five and ten times
higher respectively, than the Swedish EPA assessment guidelines for contaminated
groundwater
[11]
.
Zero sample tests, with Milli-Q water and sludge being mixed for 24 h, were also
done at the different pH values in order to determine the leaching of metals. Samples
of the water solution were taken for metal analysis at 0 and 24 h.
A sorption test was also carried out on old sludge material and leachate from a
landfill. The goal was to include ions from real lechate water and to test the material
after ageing. The procedure was the same (zero samples included) as described
above, but carried out at pH 9 with leachate taken from the landfill site. Depending
on the low metal concentrations in the real leachate, it was spiked with the multi-
metal solutions. The pH was initially 11.2, but decreased to 8.7 after the addition of
the metal solutions.
All water samples were filtrated through 0.45 mm cellulose acetate filters and the
filtrates acidified to pH < 2 before being sent to a certified commercial laboratory
for metal analysis by means of inductively coupled plasma atomic emission spec-
trometry (ICP-AES). The samples were analyzed for concentrations of Cd, Cr, Cs,
Cu, Mo, Ni, Pb, Sn, V and Zn.
The results of the sorption tests were presented by means of the calculation of
the metal removal efficiency and sorption capacity. The Freundlich adsorption iso-
therms were also calculated and evaluated to identify whether or not the processes
involved sorption.
