NUI Galway – UL Alliance First Annual ENGINEERING AND - ARAN ...

Novel Agri-engineering solutions for amelioration of ground water at
critical source areas
A. Serrenho (1) , O. Fenton (2) , T. G. Ibrahim( 2) , M.G. Healy (1)
(1) Civil Engineering, National University of Ireland, Galway, Galway, Ireland
(2) Teagasc, Johnstown Castle, Environmental Research Centre, Wexford, Ireland
Abstract
This project examines the potential of
carbon-amended remediation trenches to
intercept and remediate nitrate (NO3) in
subsurface waters. Laboratory-scale columns
were constructed to examine the performance
of the following materials in NO3 removal:
lodgepole pine woodchips (LPW), cardboard
(CCB), lodgepole pine needles (LPN) and
barley straw (BBS). Our results suggest that
PRBs are a relatively inexpensive method to
control NO3 plumes.
Introduction
Point-source nitrate (NO3) contamination of
shallow groundwater can result in NO3 plumes
of high concentration. The best way to control
reactive N is by managing denitrification. In
situ permeable reactive barriers (PRBs)
containing carbon (C)-rich materials may be
used. In these systems, nitrogen (N)-rich
wastewater flows through a C-rich mixture to
reduce NO3 concentrations to acceptable
levels. The aim of this study was to investigate
the best filter media to use in a PRB. In
addition, the production of greenhouse gases
(GHGs) as a by-product of the treatment
process was also considered. This is
commonly known as ‘pollution swopping’.
Nitrate removal was defined as the % of NO3
converted to di-nitrogen (N2) gas. Pollution
swapping by N therefore refers to the sum of
all forms of N not resulting from complete
denitrification to N2
Results and Discussion
The results from the study are presented in
Table 1. Table 2 presents the results for the
LPW and CCB columns, considering the
removal rates with and without pollution
swopping. Considering the removal of NO3-N
on the basis of the removal of that parameter
only, approximately 99% denitrification
occurred. However, if we consider NH4-N, the
NO3-N removal decreases. This allows for a
more accurate comparison of the effectiveness
of the media. We also measured the average
hydraulic retention time for the media. It was
lower for the CCB columns because of the
media characteristics and the higher
compaction inside the column.
103
Table 1. pH and final nutrient and organic
concentrations from the experimental columns.
NH4- NO3-N
pH COD
N outlet
mg/L
mg/L mg/L
LPW 7.98 447.33 6.44 0.06
(stdev) 0.23 300.06 4.23 0.13
CCB 7.88 616.51 4.99 0.08
(stdev) 0.54 374.78 4.12 0.29
CSO 8.17 43.84 2.84 26.16
(stdev) 0.15 34.66 2.42 14.98
LPN 5.84 6705.21 5.53 0.16
(stdev) 0.39 6430.76 5.54 0.42
BBS 7.75 1212.74 8.21 0.03
(stdev) 0.35 898.60 8.24 0.09
Table 2 Nitrate removal (%) with and
without pollution swapping.
NO3-N removal
Retention
(steady state)
time
Without
Considering
NH4-N
d % %
LPW 1 17.49 84.89
2 13.03 84.59
CCB
3
1
14.80
10.1
< 99
82.80
89.71
2 8.46 92.33
3 10.9
89.91
Conclusion
Taking pollution swopping into account,
cardboard had the best nitrate removal and the
columns containing barley straw had the worst.
It is important to take pollution swopping into
account to distinguish between media. We
observed negligible nitrite-N (NO2-N) and
nitrous oxide (N2O) concentrations in the
effluent and that is the reason only NH4-N is
considered in Table 2.