Environmental Engineering Reference
In-Depth Information
stopped, an event that could explain the plateau in PAH removal and the
lower degradation rate once the process resumed.
In summary, none of the PLFAs within the Gram-positive classification
differed significantly between the LTUs. The Gram-positive input to the
functioning of the LTUs would appear to be negligible. However, the
Gram-negative input was found to be highly significant. The consistent
tilling of LTU 2 appears to have stimulated not just growth but also devel-
opment of a physiologically and taxonomically distinct microbial commu-
nity. Both LTU 1 and LTU 2 demonstrated unique and different biological
populations apparently capable of degrading PAHs. The population shift
could be due to the different management strategies or to production of the
surfactant itself (Colores et al., 2000).
7.4.2.4 Soil respiration
The respiration patterns observed in LTUs 1 and 2 during the initial 6 months
have been discussed in detail in Hansen et al. (1999, 2000). In summary,
peaks of carbon dioxide production in the LTUs corresponded to valleys of
oxygen consumption (Figure 7.28). LTU 2 showed a trend, during the final
2 months of phase 1, toward an increase in carbon dioxide production and
a corresponding decrease in the soil oxygen concentration. These data cor-
respond to microbial biomass estimates, which showed greater cell numbers
(per gram) in LTU 2 from 4 months on. Cultivation and nitrogen addition
both appear to have a positive effect on microbial respiration.
7.4.3 Trough pilot project
7.4.3.1 Chemical characterization
The initial characterization of the trough study soil included total organic
carbon, total phosphate, and Kjeldahl nitrogen, as well as nitrate, nitrite, and
ammonia. Chemical and physical properties examined included pH, soil
buffer capacity, cation exchange capacity, and field moisture capacity. The
results are presented in Table 7.16.
7.4.3.2 PAH removal
The initial concentrations of PAH homologues in each trough are shown in
Table 7.17 along with total PAH and total BaP TEF values. The initial total
soil PAH concentration was 10,500 mg/kg for trough 1 (control), 7300 mg/
kg for trough 2, and 7200 mg/kg for trough 3. Trough 1 (control) had no
amendments. Trough 2 (biostimulation) received bulking agent and fertilizer,
whereas trough 3 (bioaugmentation) received the bulking agent, fertilizer,
and bacteria on a vermiculite carrier.
The final total soil PAH concentrations (16 months) in troughs 1, 2, and
3 were 9000, 900, and 900 mg/kg, respectively (Figure 7.29). The final con-
centrations were not significantly different between troughs 2 and 3, but the
difference was significant between trough 1 and the other troughs (
p
= 0.05).
