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Solution

Problem 1

Question 1.1:

The main degradation products are TCE, cis-DCE (for the biological pathway, low

concentrations of the DCE isomers will be formed as well), VC, ethylene, ethane, carbon

dioxide, chloride and water.

A right answer should include at least 5 of the 8 compounds mentioned!

Please note that carbon dioxide is only produced if ethane/ethane is degraded by oxidation.

Question 1.2:

The reaction schemes for the consumption of ethanol are used.

Example:

Molecular weight of ethanol is 46 g/mol

Molecular weight of oxygen is 32 g/mol

1 mol of ethanol reacts with 3 mol of oxygen

46 mg of ethanol reacts with 96 mg of oxygen

The conversion factor will be 0.472 mg ethanol/mg oxygen. All factors are listed in Table 1.3

Table 1.3. Quantification of the needed amount of ethanol to reduce the electron acceptors listed in Table 1.1.

The conversion factor is calculated from the stoichoimetri in Table 1.2.

Depletion of

electron acceptors

Conversion factor Amount pr. l of

groundwater

O2 1.7 0.48 mg ethanol/mg O2 0.816 mg ethanol

NO3

31 0.31 mg ethanol/mg NO3- 9.61 mg ethanol

SO42

59 0.32 mg ethanol/mg SO4-- 18.88 mg/ethanol

Sum 29..31 mg/ethanol

There is 350 l of groundwater pr. m3of aquifer. The total mass of ethanol pr. m3will be:

350 l * Sum = 350 * 29.31 mg ethanol/l = 10.257 mg = 10.3 g pr. m3

Question 1.3:

The conversion factor for oxidised iron is 0.0697g ethanol/g Fe3+.

The amount of oxidised Fe3+is 0.8 g/kg.

The total amount of oxidised iron equals:

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0.8 g/kg * 1740 kg pr. m3 = 1392g pr. m3

The total amount of ethanol for reduction of iron is:

1392 g Fe3+pr. m3 * 0.07 g ethanol/g Fe3+ = 97.4 g ethanol pr. m3

Total mass of ethanol pr. m3= 10.3 + 97.4 = 107.7 g

The needed mass of ethanol for reducing iron is larger than the amount needed for reduction the

dissolved electron acceptors. This makes it critical to incorporate solid iron in the evaluation of

the need for substrate. However, it is uncertain how large a fraction of the extractable Fe3+that

will be available for microbial iron reduction.

Question 1.4:

There is no difference in groundwater quality between inside and outside the plume. Chlorinatedsolvents are not consuming electron acceptors. The redox conditions are aerobic. There is a quite

low content of oxygen, but no signs of nitrate-, manganese-, iron- or sulfate-reduction anywhere.

All reduced species are only present in insignificant concentrations. Anaerobic dechlorination is

not taking place under aerobic conditions so the absence of anaerobic dechlorination is expected.