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MTBE-nedbrydning i grundvand vha. alkanoxiderende mikroorganismer
Purpose
The purpose of this project is to investigate whether MTBE contaminated groundwater can
be treated cost-effectively in on-site bioreactors containing alkane-oxidizing
microorganisms. This report summarizes the results from a series of batch tests with the
purpose of revealing the technical potential of the method.
MTBE degrading
enrichment cultures
Three different alkane-oxidizing enrichment cultures with potential for co-metabolic
MTBE degradation were obtained from peat enriched garden soil. Hence, co-metabolic
degradation of MTBE was demonstrated for cultures enriched with propane, iso-butane, and
iso-pentane. Although the culture enriched with iso-pentane exhibited the greatest
degradation potential of the three cultures examined, this culture was excluded from
further study due to substrate handling problems.
Degradation of MTBE
MTBE degradation rates of 10.1 and 15.7 mg MTBE/(g protein·h) were observed for the
propane and iso-butane enriched cultures, respectively. Preliminary results suggests
half-saturation constants, Km, for MTBE degradation of approx. 130 – 150
mg MTBE/L.
Substrate degradation
For the propane-oxidizing culture, a maximum degradation rate, vmax, of 405
mg propane/(g protein·h) and a half-saturation constant, Km, of 9 mg propane/L
were found. For iso-butane, vmax and Km were found at 289 mg
iso-butane/(g protein·h) and 3.5 mg iso-butane/L.
Microbial growth rates
Maximum microbial growth rates of approx. 0.5 to 1.2 d-1 were found. These
growth rates are not sufficient for ensuring the necessary biomass concentration in an
on-site bioreactor, and a unit for biomass retention should be installed.
Preliminary reactor dimensions
Preliminary dimensions can be estimated for an optimized on-site bioreactor designed
for e.g. 90% mass removal and a hydraulic load of 2 m3/hour. Based on the
results for the iso-butane oxidizing microorganisms a necessary volume of approx. 4.6 m3
is calculated.
Potential for on-site treatment
In conclusion, it has been shown that it is relatively easy to produce enrichment
cultures of microorganisms with a potential for MTBE degradation. It has also been shown
that these cultures has a MTBE mass removal potential for groundwater treatment in on-site
bioreactors.
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