1. The transformation of trichloroethene was examined using 100 mL batch reactor
ID: 289994 • Letter: 1
Question
1. The transformation of trichloroethene was examined using 100 mL batch reactors inoculated with 10 grams groundwater aquifer sediment from three different contaminated sites. The results are shown below. For each site, describe two different reasons why the specific results might have been observed (hint: incorporate other generalized curves (e.g., biomass or cell numbers) on the graphs to support part of your answers if you wish). State any assumptions 6 Site 1 Site 2 Site 3 2 100- 100 100 C 50 50 5 0 -0 0 0 20 40 60 80 100 0 20 40 60 80 100 9 0 20 40 60 80 100 7 Time (days) Time (days) Time (days)Explanation / Answer
Biodegradation is the main reason why the concentration of Trichloroethene (TEC) decreases in a groundwater system. The presence of bacteria along with the permeability of aquifer sediments are the major factors of TEC variability.
In site 1, the aquifer sediments are impermeable enough to accumulate water and solubilize the TEC. The high solubility of TEC enhances the rate of biological activity and the concentration of TEC decreases rapidly.
In site 2, the concentration of TEC decreases gradually due to sediments of different characteristics in terms of permeability thus delaying the process of biodegradation. The presence of oxygen in sediments was responsible for the slow removal of TEC as under aerobic conditions the biodegradation of TEC is ineffective (as TEC is already in an oxidized state)
In site 3, there is a huge quantity of highly permeable and dry sands (with no water whatsoever) which doesn't allow TEC to solubilize. The low solubility of TEC makes it extremely difficult for bacteria to degrade the TEC even in small quantities.
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