The two pilot plants built by Umweltschutz Nord, named Plant 1 and Plant 2, have been filled with soil coming from the polluted sites, in order to obtain results and information specifically devoted to the tuning of the model and to its extension towards the scale of field tests.
The first one, PLANT1, has been filled with soil coming from the US Depot Gemersheim, where an in-situ biodegradation intervention has been realized: the soil in this area is contaminated with heating-oil.
PLANT2, on the other hand, has been filled with the soil coming from the second field test, the NBZ-Deutsche Bahn AG / Frankfurt: this area is contaminated with PAH (Polyciclyc Aromatic Hydrocarbons).
The experiments of both the U.N. pilot plants have several variants, in which the most important difference is the composition of the injected solution. All these variants are composed by three cylinders, each one with a diameter of 10 cm and an overall length of 50 cm, arranged into a pile and connected by pipes where is possible the extraction of water samples. The water flow is from the bottom of the pilot plant to the top, in such a way to maintain saturated conditions.
In the model application we made some assumptions; in particular, we did not explicitly consider some aspects like the loss of pressure due to the connections between the different pairs of cylinders and due to the narrow necks of the pipes which carry the water among the different containers. Therefore, a theoretical schema of a generic variant of the pilot plans could be a unique cylinder 1.5 m height (a one-dimensional simulation of 15 cells), in saturated condition.
U.N. pilot plants scheme and discretization
The experiments on U.N. pilot plats have been performed in four variants each one characterized by a different composition of the water injected. The following table summaries the main characteristics of variants:
Experimental variants / DescriptionVariant I
Variant II
Variant III
Variant IV / Control (water), continuously
Nutrients C:N:P = 100: 20:2
hydrogen peroxide, continuously
Nutrients C:N:P = 100: 20:2
hydrogen peroxide, continuously
Unsaturated conditions
Nutrients C:N:P = 100: 20:2
hydrogen peroxide, co-substrates
continuously
The different variants of U.N. pilot plants
We simulate the biodegradation into the field tests by means of saturated conditions (the most important part of pollutant is very near the water table) and without co-substrate (that is not used in the field tests). Therefore, in the following, we focused our attention on variant 1 and variant 2 of both the U.N. pilot plants.
The figures show the simulation results of Plant 1. An optimization of kinetic and biological parameters is made contemporarily for the first two tubes of variant 1 and 2 (V1 and V2 into the figures - training set); the second tubes of each variant constitute the test set.
Plant 1 training set (degradation rate)
Plant 1 test set (degradation rate)
It is also possible to estimate the contribution of the aerobic and anaerobic bacteria to the bioremediation inside the tube 3 of variant 1. With the terms "anaerobic bacteria" or "anaerobic conditions" we means the following assertion:
It is not possible to simulate all the chemical and biological reactions happening in the soil: particularly, there are biological reactions that don't utilize the oxygen like acceptor of electrons when the oxygen concentration is below a suitable threshold. If any, we could simulate these anaerobic (or not explicitly modeled) situations by means of a first order kinetics, driven by a temporal parameter experimentally determined.
We set the threshold between aerobic and anaerobic (or not modeled) condition at 0.4 ppm of dissolved oxygen. The total amount of the two different contributions in the third vessel is about 13.5% for the aerobic degradation and 86.5% for the anaerobic (or not explicitly modeled) degradation: an estimate of the percentage of contribution of the aerobic and anaerobic conditions for each cell is shown in the following figure.
The percentage contribution of the aerobic and anaerobic (or not explicitly modeled) conditions
In the following figures we can show the final pollutant concentration and the final biodegradation rate for each tube of the variant 1.
Variant 1: the final degradation rate, obtained simulating both
aerobic and anaerobic (or not explicitly modeled) conditions
The statistical indexes of pilot plant 1, computed on the final values of each variant, are:
Variable / BIAS / NMSEVariant 1 (degradation rate) / -0.00378 / 0.04662
Variant 2 (degradation rate) / 0.27 / 0.20
The statistical indexes for the first two variant of pilot plant 1.
On pilot plant 1, we have also made a simple test ofspatialscalability.
In the same way of Plant 1, we can see in the following figures the simulation results of Plant 2. An optimization of the kinetic and biological parameters is made contemporarily for the first two tubes of variant 1 and 2 (V1 and V2 into the figures - training set); the second tubes of each variant constitute the test set.
Plant 2 training set (degradation rate)
Plant 2 test set (degradation rate)
The statistical indexes of pilot plant 2, computed on the final values of each variant, are:
Variable / BIAS / NMSEVariant 1 (degradation rate) / -0.31 / 0.20
Variant 2 (degradation rate) / 0.03 / 0.0017
The statistical indexes of pilot plant 2
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