Environmental Engineering Reference
In-Depth Information
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S-NZVI
IONP
GNP
AgNP
200
0
0
50
100
150
200
250
Time (h)
FIGURE 37.8
Batch experiment results for BOD while reacting leachate with S-NZVI, IONP, GNP, and AgNP solutions (1 g/l).
a typical curve for carbonaceous matter degradation with a suitable bacterial lora and
adequate amount of nutrients present. In the irst 5 days, it showed an increase in BOD
values, and thereafter, BOD values decreased. This may be due to limiting of the aero-
bic environmental condition and it leads to decreases of aerobic microbes and macroor-
ganisms. Compared with the rate of increase of BOD values, AgNPs showed rapid BOD
increase during the irst 5 days. This can be due to Ag acting as an inhibitor for bacterial
activities; therefore, bacteria can respond by increasing its activity at the beginning [70].
However, S-NZVI showed the slowest BOD increasing rate. This may be due to the inhi-
bition of bacterial activity by S-NZVI [44]. However, S-NZVI showed an increase in BOD
values with time continuously. This may be due to nitrifying bacteria developing by oxida-
tion of reduced nitrogen compounds (ammonia) to nitrate. IONPs showed a typical BOD
curve compared with the other results. In the irst 5 days, a rapid increase of BOD values
was observed. After that, the increase in BOD values became slow, and then equilibrium
was established for S-NZVI. After 5 days, other materials demonstrated a decrease in BOD
values. This may be mainly due to the absence of aerobic conditions in the system.
37.3.6 Metal Ion Removal in Synthetic Leachate
Among the tested materials, S-NZVI and IONP showed considerable metal removal. S-NZVI
and IONP demonstrated very high removal eficiencies of approximately 95% in the irst
hour of reaction time for tested metal ions (Figure 37.9). In addition, GNP showed a slow
removal density compared with the other three absorbents, indicating approximately
5.843 × 10
−8
and 2.784 × 10
−8
mol/m
2
for Pb(II) and Zn(II) removal densities, respectively,
within 72 h. This observation agreed with the previous literature [71]. However, AgNP
showed very low or negligible Zn(II) removal density and for Pb(II), which seemed a grad-
ual removal pattern, but a 2.602 × 10
−8
mol/m
2
Pb(II) removal density after 72 h.
Heavy metal removal may occur through several different mechanisms such as adsorp-
tion, reduction, and precipitation. In the case of S-NZVI, the metals may have been reduced
due to the high oxidation capacity of the NZVI. Also, the pH of the media plays a major
role here. For instance, irst, the medium pH rises when adding S-NZVI and IONP to the
