strument calibrated to TCE only, 3) the combined
where A = ppm hydrocarbons as measured by
sampling and analytical error in TCE, PCE and
model 51 analyzer
TPH liquid concentrations, 4) the assumption of
B = volume of 1 mole of TCE gas at stan-
standard temperature and pressure, and 5) the
dard temperature and pressure
measurement of air flow rate. The near 100% mass
C = molecular weight of TCE.
balance of hydrocarbons indicates that hydrocar-
bon removal in the ShallowTray unit was in fact
The 150 ppm or 1100 ppm detection scales were
by mass transfer to the off-gas and not by other
used when the liquid flow to the air stripper was
phenomena (e.g., sorption, biodegradation).
18.9 L/min and 75.7 L/min, respectively. Ana-
lyzer accuracy was 2% of scale.
VOC removal
A graphic summary of all VOC removal data
is shown in Figures 3 and 4. Trial data are plotted
RESULTS AND DISCUSSION
in the same sequence in which trials were con-
ducted, from left to right. The analytical practical
Hydrocarbon mass balance
quantitation limits (PQLs) are exceptionally low,
Comparison of off-gas hydrocarbon loadings
just 0.625 ppb for TCE and 0.543 ppb for PCE.
to liquid hydrocarbon loadings indicates that 100
5% of the hydrocarbons entering the stripper
Despite such low quantitation limits, however,
treatment efficiency was so high that effluent con-
were accounted for in the off-gas or effluent liq-
centrations were routinely below them, particu-
uid. The sources of standard error in the mass
larly for PCE.
balance estimate are 1) the analyzer accuracy of
2% of scale, 2) the error inherent in measuring
Influent TCE and PCE concentrations varied
TCE, PCE and paraffin hydrocarbons with an in-
over 16-ppm and 6-ppm ranges (respectively),
Trial Temp. Flow
(C) (L/min)
No.
1
16
8.9
75.7
2
22.2
18.9
50
3
22.2
18.9
4
8.9
75.7
5
8.9
18.9
6
22.2
75.9
7
15.6
18.9
12
8
15.6
75.7
40
9
22.2
18.9
30
Influent
8
20
Effluent
4
10
0
PQL = 0.625 ppb
0
1
2
3
4
5
6
7
8
9
Experimental Trials
Figure 3. TCE pre-treatment and post-treatment concentrations for all
experimental trials.
7
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