Environmental Engineering Reference
In-Depth Information
transport modeling of potential failing scenarios of MNA, due to advancing
lignite mining. The mining company supported the planning by providing
data regarding the anticipated water management of the lignite mine pit and
by facilitating access to a PRB reservation area. The costs and safety issues
were also evaluated. The mining and environmental authorities confirmed
the treatment targets and the operation chart, and the gas PRB technology
became part of a long-term operating closure plan for the Profen site.
10.4.3 Reactive Gas Zones as Part of the GFIadags
®
-Technology
Reactive gas zones were integrated in a drain and gate technology for the
sequential plume treatment of deep aquifers. The treatment train technology
was demonstrated at the Schwarze Pumpe site, a former gasification plant. A
plume containing high concentrations of phenols (30 mg/L), DOC (100 mg/L),
and ammonium (150 mg/L) required treatment in a 37 m deep multilayered
aquifer. The thickness of the saturated zone was 20 m, and average ground-
water velocity was approximately 0.12 m/day. The gate treatment (zone B)
consisted of stripping and chemical oxidation of groundwater contaminants
in collector and distributor well reactors (Kassahun et al., 2005). Gas injection
zones were established to perform iron removal (zone A: treatment area of
900 m²) and posttreatment of ammonium and DOC (zone C: treatment area
of 1.800 m²). The treatment train is presented in Figure 10.19. The construction
of the gas injection zones followed the principles discussed in Section 10.3.
Additional details are reported in Uhlig (2010). Due to high contamination,
partial decontamination of the soil matrix was addressed to form in situ buf-
fer zones against breakthrough of fluctuating contaminant streams.
In zone A, in situ iron removal was first induced by oxygen gas injection.
As seen in Figure 10.19, the competitive effects of matrix oxidation limited
the success. Carbonate precipitation of dissolved iron by ammonia gas injec-
tion was shown to be more efficient, as matrix oxidation did not exert an
influence. Ammonia demand depended mainly on the buffering capacity
of the groundwater flow. A conditioning pH of >7.5 was required, and injec-
tion rates were controlled by mixing ammonia gas to a nitrogen carrier gas
flow of 0.5-1.0 m³/h STP. The ammonia injection approach was found to play
a part in contaminated site restoration; however, in situ processes require
further investigation.
An oxygen gas PRB for bio-oxidation was established in zone C, and was
operated over a period of 550 days. Gas lances and observation elements of
the types MDP and MF were installed by CPT (see Chapter 3). A 3D gas-
hydrogeological model was constructed for groundwater flow and reactive
zone balance modeling. Gas injection rates of 0.6-1.2 m³/h STP were applied,
and ROI of single lances were identified using noble trace gas (Ne, He) in the
range of 15 m. A downstream reactor was not monitored.
Due to high contamination and the natural pyrite content of the matrix,
almost all of the 20 tonnes of injected oxygen gas was consumed by matrix
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