Agriculture Reference
In-Depth Information
Table 12.1 Product distribution of the denitrification process with the three nano-iron materials
after complete removal of NO
3
NO
2
NH
4
+
Initial concentration
of NO
3
(mg/L)
Concentration
(mg/L)
Proportion
(%)
Concentration
(mg/L)
Proportion
(%)
Nano-
Fe
0
46.57
0.01
0.00
24.03
51.59
Nano-
Fe/Ni
45.53
0.00
0.00
31.40
68.97
Nano-
Fe/Cu
49.27
16.73
33.07
19.05
38.66
Unlike Ni, addition of Cu improved the NO
3
removal rate and significantly
increased the selectivity of NO
2
; therefore, the rate of NO
2
production was rapid
in the nano-iron/Cu reaction system. On the other hand, the surface of the nano-
iron/Cu exhibited poor capacity for NO
2
; thus, the conversion of NO
2
to NH
4
+
was relatively slow. In other words, Cu changed the selectivity of the products
during NO
3
reduction, as a result of which the denitrification products remained as
NO
2
, rather than being further converted to NH
4
+
.TheNO
2
residue in the system
with denitrifying bacteria was degraded into gaseous nitrogen, separated from the
aqueous phase, thereby reducing the toxicity of the denitrification products in the
composite system. The product distribution of the denitrification process in the
three systems of nano-iron materials and denitrifying bacteria is shown in
Table
12.1
. After the reaction, the proportion of NH
4
+
in the three systems was as
follows: nano-iron/Ni
>
>
nano-iron/Cu.
The results presented in Table
12.1
demonstrate that the Ni catalyst increased the
proportion of NH
4
+
from 51.59 to 68.97 % and enhanced the toxicity of the products
rather than decreasing it, thus indicating that Ni is not a suitable catalyst in the
composite system. On the other hand, the Cu catalyst decreased the NH
4
+
concen-
tration from 51.59 to 38.66 % with 33.07 % of NO
2
production; the NO
2
produced was removed completely in the next 2 days with no NH
4
+
generation
(Fig.
12.4
). Furthermore, microbial denitrification transformed the residual NO
2
in
the solution to nitrogen gas or nitrogen oxide, which was separated from the
aqueous phase. Therefore, it can be concluded that Cu is a more suitable catalyst
in the composite system for the denitrification process.
nano-iron
