Environmental Engineering Reference
In-Depth Information
has integrated widely used technologies in its design to treat water from both surface and
ground sources.
WaterHealth has to deliberately keep its system installation and operation costs low,
as it has to provide water to communities where people do not have disposable income.
Unbiased by any particular technology, WHI identiies proven, cost-effective technologies
and integrates them into its design in providing water at an affordable price.
Conceptually, WaterHealth design consists of six stages of water treatment. These are
(i) coagulation/sedimentation, (ii) coarse iltration, (iii) organic removal, (iv) ine iltration,
(v) reverse osmosis separation, and (vi) disinfection. These are shown schematically in
Figure 22.4.
The irst treatment stage of coagulation/sedimentation applies more to water drawn
from surface bodies and is to clarify the water by adding coagulants and allowing time for
the colloidal organic and inorganic particles to agglomerate and settle out of the water to
form a bottom sludge layer. For the groundwater, it is just a holding tank that serves as a
quiescent volume that allows larger sand particles drawn from a well to settle out. These
tanks also serve the purpose of buffering the low given that water-processing lows may
not be the same as water drawn from the source. For surface water with a high level of
turbidity, clariication achieved by coagulation/sedimentation can be signiicant with tur-
bidity in the clariied water <5 NTU.
Coarse iltration is achieved by running the water through a bed of graded sand that
removes particulates >10-20 micron in size. This step has the potential to drop the water
turbidity down to <1 NTU. Filtration through a bed of activated carbon reduces levels of
UV disinfection
R.O.
(reverse osmosis)
Purified water
storage tank
Raw water
Anti-
scalant
dosing
Transfer
tank
Dispensing tap bank
Multimedia
filter
Advanced
carbon
filter
Cartridge
filter
FIGURE 22.4
(See color insert.)
Schematic of WHI treatment system.
