Environmental Engineering Reference
In-Depth Information
Source water: for each pathogen,
fit PDF
Source:
Treatment stages: filtration flocc/
sedimentation/disinfection
Treatment:
Consumer:
Pathogen(s) consumed per
person; fit PDF
Probability of infection
per person per day
Baseline:
Convert to annualized
infection; find DALYs
Worst case (95
th
percentile)
sensitivity
Infection rates from Baseline +
external Hazardous event at
control points
Baseline
Normal
Excessive
Examples
Water must go through
further filtration e.g.
GAC
Action at
control point
Test
NOT OK
Increase disinfection
dosage (e.g. more Chl;
more UV)
OK
NOT
OK
OK
Water Reserve
Test
Fig. 6.5 Flowchart for the implementation of QMRA (Reproduced from Nilsson and Thorw-
aldsdotter
2006
)
(a) Pathogen densities at intake and outlet of the treatment plant.
(b) If surrogate densities are used (in the absence of actual densities), this
could add another layer of uncertainty.
(c) Reliability of plant SCADA systems for data on turbidity, chlorine
residual, etc.
6. In the pipeline network, de
ciencies may lead to (a) ingress or regrowth of
pathogens, and (b) uneven
flow which may dislodge bio
lm pathogens from
the interiors of pipes to enter the water column
flowing through. These two
events are not captured by QMRA.
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