Environmental Engineering Reference
In-Depth Information
Table 13.9
Flow-weighted geometric log mean pathogen indicator
concentrations in title drains at University of Guelph Campus d'Alfred
experimental plots
E. coli
(log CFU/100 ml)
Salmonella
(log CFU/100 ml)
Plot treatments
15 days after land application
(total precipitation = 11 mm)
Raw manure
1.1 ± 0.1
2.2 ± 1.1
Digestate
1.2 ± 0.1
1.6 ± 0.3
Control (no treatment)
1.2 ± 0.1
1.7 ± 0.6
60 days after land application
(total precipitation = 161 mm)
Raw manure
3.4 ± 2.0
3.6 ± 2.1
Digestate
3.0 ± 1.5
3.1 ± 1.5
Control (no treatment)
1.4 ± 0.1
1.7 ± 0.1
Source: Data collected by University of Guelph.
bacterial survival. Chandler and Craven (1980) found E. coli cells were able
to survive dry loam soil conditions but proliferated once moisture was
restored. Bacterial survival is also favoured by cooler temperatures and
neutral pH, with pH of 6 to 7 being optimum (Abu-Ashour et al., 1994;
Jamieson et al., 2002). Goss et al. (2001) reported that E. coli O157:H7 can
survive for up to 100 days under cold soil temperatures (
C). It should be
noted that freezing and thawing of soils reduces bacterial survival.
Nutrient availability is a key factor in bacterial survival in soils, where
organic matter increases the retention of nutrients and provides a C source.
Low N availability can lead to increased bacterial mortality (Abu-Ashour
et al., 1994; Jamieson et al., 2002). Goss et al. (2001) explain that the
concentration of microorganisms in manure at the time of land application
is important to the transport of the organisms and eventual contamination
of water resources. It can be anticipated that the lower bacterial
concentrations in digestate will lead to reduced bacteria migration to
drainage tiles (also see Chapter 12 of this handbook).
In the same University of Guelph field study described in the previous
section, E. coli and Salmonella pathogen indicators were used to monitor
bacterial migration to drainage tiles comparing plots treated with dairy
manure and digestate. Table 13.9 summarizes the flow-weighted geometric
log mean E. coli and Salmonella concentrations in the tile drains.
After the first 15 days following land application of raw manure and
digestate, the mean E. coli and Salmonella counts in the subsurface drains
were similar to those found in the controls plots (no treatment). During this
15-day period there was only 11mm of precipitation. At 60 days after land
application, with 161mm of precipitation, mean bacteria counts were 2-log
5
8
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