Some years ago, we looked at carbon isotope compositions of sewage
components at a treatment plant here in Calgary.
Firstly, the mean isotope composition is expected to vary with location
because of variations in the diet (C3 vs C4, terrestrial vs marine
Isotopic fractionations occur in the reactor. At this plant, bacteria
generate CH4 and CO2. Methane is used to heat the building and also raise
the temperature of the reactor to realize maximum bacterial conversion.
Isotopic fractionations during the generation of the CH4 and CO2 are very
large. The mean delta 13C value of the unreacted sewage does not change
much.. Presumeably, the source of the variations are those among the
different compound types and chemical structures, only some of which are
involved in the bacterial conversion.
Compound specific analyses should prove more informative.
We placed some of the reactor sludge in a reactor in the laboratory. Over a
time span of weeks, methane production waned and H2S production commenced.
Methane production finally ceased entirely and the only gases were H2S and
CO2. The isotopic composition of this CO2 was not the same as that when CH4
The extent of our laboratory reaction was obviously greater than that at
the treatment plant which is a flow-through system. The raw materials do not
have a sufficiently long residence time to reach the anaerobic bacterial
reduction stage before entering the effluent and more aerobic
conditions.(This is probably a wise practice!).
This is one of our many interesting "pilot" projects which we did not
prepare for a refereed journal, partly because of the observations being
confined to limited conditions.
Data on the sewage plant CH4 and CO2 are plotted in a figure in a review
paper given at a conference;
Krouse, H.R., Pickering,S. and Batts, B.D. (1992), "Potential applications
of stable isotopes to studies of immiscible groungwater contaminants" in
Proc. IAH Conf. on Subsurface Contamination by Immiscible Fluids, Calgary,
April 18-20, 1990.
The same diagram also refers to some work by John Hayes and colleagues.
From: Troy Gaston <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Sunday, November 25, 2001 3:56 PM
Subject: d13C& d15N of sewage
>I'm after the d13C and d15N values of secondary treated sewage effluent.
>Has anyone looked at this, or can they suggest a reference that states that
>they have analysed secondary treated effluent?
>Thanks for your time
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