Coagulation, flocculation and sedimentation
#> Warning: Use of .data in tidyselect expressions was deprecated in tidyselect 1.2.0.
#> ℹ Please use `"TreatmentName"` instead of `.data$TreatmentName`
#> This warning is displayed once every 8 hours.
#> Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
#> generated.
Conventional clarification
Consists of coagulant and/or flocculant aid (e.g. polymer) dosing,
rapid mixing, slow mixing and sedimentation. Log removal depends on
process optimisation. Rapid changes in source water quality such as
turbidity increase due to monsoon rainfall or algeal blooms may decrease
treatment effect and require adjustment of process settings.
Dissolved air flotation
Compressed air is injected in the water such that air bubbles bring
suspended solids to the water surface where they are skimmed off.
Coagulant may be dosed. Log removal depends on process optimisation.
Rapid changes in source water quality such as turbidity increase due to
monsoon rainfall or algeal blooms may decrease treatment effect and
require adjustment of process settings.
High-rate clarification
Consists of coagulant and/or flocculant aid (e.g. polymer) dosing,
mixing and enhanced sedimentation by flock blankets, lamellae- or tube
settlers. Log removal depends on process optimisation. Rapid changes in
source water quality such as turbidity increase due to monsoon rainfall
or algeal blooms may decrease treatment effect and require adjustment of
process settings.
Lime softening
Lime is dosed to the water to reduce hardness. When flocks are
formed, they can entrap pathogens. Note that the technical design of the
softening process affects the log reduction. e.g. pellet-softening has
no effect on pathogens.
Filtration
Granular high-rate filtration
Water is filtered through a fixed bed of granular media (e.g. sand)
generally operatied down flow with rates of 5 to 20 m/h and contact
times of 4 to 15 minutes. They are regularly backwashed to remove built
up solids in the filter. Log removal depends on filter media and
coagulation pretreatment;consistent low filtered water turbidity of ?
0.3 NTU (none to exceed 1 NTU) are associated higher log removal of
pathogens
Precoat filtration
Consist of a fine filter (e.g. candle filter or drum filter) that is
precoated by dosing fine granular material (often diatomaceous earth).
This material forms a fine filter cake that removes solids from the
water. The log removal can only be achieved if the filter cake is
present and depends on precoat media grade and filtratin rate.
Slow sand filtration
Water is filtered through a fixed bed sand operatied down flow with
rates of 0.1 to 1 m/h and contact times of 3 to 6 hours. The filter is
not backwashed. In weeks to months a ‘schmutzdecke’ will develop on the
filter which enhances log removal. Grain size, flow rate and temperature
also affect log removal. Consistent low filtered water turbidity of ?
0.3 NTU (none to exceed 1 NTU) are associated higher log removal of
pathogens associated with 1 - 2 log reduction of viruses and 2.5 - 3 log
reduction of Cryptosporidiuma
Membrane filtration
A membrane is a thin sheet with small openings that removes solids
and depending on membrane type, solutes from the water when this is led
through the membrane.
Reverse osmosis
A reverse osmosis membrane is a thin sheet with small openings that
removes solids and most soluble molecules, including salts (< 0,004
µm depending on selected membrane) from the water when this is led
through the membrane. It can take the form of spiral wound membranes,
hollow fibers or sheets. Actual log reduction depends on the selected
membrane and is determined by challenge testing.
Microfiltration
A microfiltration membrane is a thin sheet with small openings that
removes solids (0.1-10 µm depending on selected membrane) from the water
when this is led through the membrane. It can take the form of capilary
tubes, hollow fibers or sheet membranes. Actual log reduction depends on
the selected membrane and is determined by challenge testing.
Ultrafiltration
An ultrafiltration membrane is a thin sheet with small openings that
removes solids (0.005-0,2 µm depending on selected membrane) from the
water when this is led through the membrane. It can take the form of
capilary tubes, hollow fibers, spiral wound or sheet membranes. Actual
log reduction depends on the selected membrane and is determined by
challenge testing.
Nanofiltration
An nanofiltration membrane is a thin sheet with small openings that
removes solids and larger soluble molecules (0.001-0,03 µm depending on
selected membrane) from the water when this is led through the membrane.
It can take the form of spiral wound or hollow fiber membranes. Actual
log reduction depends on the selected membrane and is determined by
challenge testing.
Pretreatment
Bank filtration
Water is abstracted through wells located close to surface water,
thus the bank serves as a natural filter. Log removal depends on travel
distance and time, soil type (grain size), and geochemicl conditions
(oxygen level, pH)
Roughing filters
Water is filtered through a fixed bed of coarse granular media
(e.g. rocks 5-20 mm) operated at high rates. They are not backwashed.
Log removal depends on filter media and coagulation pretreatment.
Storage reservoirs
Water is protected from human recontamination in reservoirs, however
wildlife and waterfoul may introduce pathogens. Log reduction occurs due
to sedimentation, UV radiation from sunlight and die-off in time,
depending on construction (mixing) and temperature. Reporded reduction
based on residence time > 40 days (bacteria), 160 days (protozoa)
Primary treatment
Primary treatment consists of temporarily holding the sewage in a
quiescent basin where heavy solids can settle to the bottom while oil,
grease and lighter solids float to the surface. The settled and floating
materials are removed and the remaining liquid may be discharged or
subjected to secondary treatment
Secondary treatment
Secondary treatment consists of an activated sludge process to break
down organics in the wastewater and a settling stage to separate the
biologiscal sludge from the water.
Primary disinfection
Chlorination, wastewater
Log inactivation depends on free chlorine concentration and contact
time (CT); not effective against Cryptosporidium oocysts, reported
protozoan log reduction is mostly for Giardia. Turbidity and
chlorine-demanding solutes inhibit this process; hence, effect in
wastewater is limited since free chlorine will rapidly decay. Effective
disinfection. Where this is not practical, turbidities should be kept
below 5 NTU with higher chlorine doses or contact times. In addition to
initial disinfection, the benefits of maintaining free chlorine
residuals throughout distribution systems at or above 0.2 mg/l should be
considered
Chlorine dioxide
Log inactivation depends on chlorine dioxide concentration and
contact time (CT); Turbidity and organics inhibit this process; hence,
turbidity should be kept below 1 NTU to support effective disinfection
Chlorine dioxide degrades rapidly and doesn’t leave a disinfectand
residual for distribution.
Ozonation, drinking water
Log inactivation depends on dissolved ozone concentration and contact
time (CT); Turbidity and organics inhibit this process; hence, turbidity
should be kept below 1 NTU to support effective disinfection. Ozone
degrades rapidly and doesn’t leave a disinfectand residual for
distribution. Effective mixing and consistent contact time are crucial
for disinfection due to the rapid degradation of ozone. Cryptosporidium
varies widely
UV disinfection 20 mJ/cm2, drinking
UV-light is mostly effective at 254 nm where it affects DNA or RNA
thus preventing reproduction of the organism (inactivation). Log
reduction for drinking water UV is based on closed UV-reactors wich have
been validated according to appropriate standards (e.g. USEPA or DVGW).
Effectiveness of disinfection depends on delivered fluence (dose in
mJ/cm2), which varies with lamp intensity, exposure time (flow rate) and
UV-absorption by the water (organics). Excessive turbidity and certain
dissolved species inhibit this process; hence, turbidity should be kept
below 1 NTU to support effective disinfection.
Chlorination, drinking water
Log inactivation depends on free chlorine concentration and contact
time (CT); not effective against Cryptosporidium oocysts, reported log
reduction is mostly for Giardia. Turbidity and chlorine-demanding
solutes inhibit this process; hence, turbidity should be kept below 1
NTU to support effective disinfection. Where this is not practical,
turbidities should be kept below 5 NTU with higher chlorine doses or
contact times. In addition to initial disinfection, the benefits of
maintaining free chlorine residuals throughout distribution systems at
or above 0.2 mg/l should be considered
Ozonation, wastewater
Log inactivation depends on dissolved ozone concentration and contact
time (CT); Turbidity and organics inhibit this process; Since wastewater
is often turbidity and contains high organics that consume ozone, the
actual CT cannot be determined accurately and therefore inactivation
cannot be determined accurately. Still, effective mixing and consistent
contact time are crucial for disinfection due to the rapid degradation
of ozone.
UV disinfection, wastewater
UV-light is mostly effective at 254 nm where it affects DNA or RNA
thus preventing reproduction of the organism (inactivation).
Effectiveness of disinfection depends on delivered fluence (dose in
mJ/cm2), which varies with lamp intensity, exposure time (flow rate) and
UV-absorption by the water (organics). Wastewater UV-reactors are
generally open-channel reactors in which UV lamps are placed. Excessive
turbidity and certain dissolved species inhibit this process; hence the
effect in wastewater highly depends on the water quality an is generally
lower than in drinking water at the same dose.
UV disinfection 40 mJ/cm2, drinking
UV-light is mostly effective at 254 nm where it affects DNA or RNA
thus preventing reproduction of the organism (inactivation). Log
reduction for drinking water UV is based on closed UV-reactors wich have
been validated according to appropriate standards (e.g. USEPA or DVGW).
Effectiveness of disinfection depends on delivered fluence (dose in
mJ/cm2), which varies with lamp intensity, exposure time (flow rate) and
UV-absorption by the water (organics). Excessive turbidity and certain
dissolved species inhibit this process; hence, turbidity should be kept
below 1 NTU to support effective disinfection.