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Drinking water from Laguna LakeBy Juan V. Sarmiento Jr
Philippine Daily InquirerFirst Posted 19:39:00 10/09/2010
Filed Under:Water Supplies
MANILA, PhilippinesResidents of Muntinlupa City now enjoy
potable water from Laguna Lake, the countrys
biggest fresh-water body, thanks to a treatment plant being
built by Maynilad Water Services Inc.
They may continue to enjoy water service even if the water level
in Angat Dam in Bulacan, the main source ofMetro Manilas water,
drops sharply in a severe El Nio event.
Some 19,000 households and establishments in Muntinlupa now have
connections to the treatment plant, a state-
of-the art facility rising on a former National Irrigation
Administration (NIA) station in Barangay Putatan.
The NIA facility went unused because by the time it was
completed the farmlands that it had sought to irrigate
had been converted into subdivisions and industrial estates. The
facility became a pumping station for Ayala
Alabang subdivisions domestic water needs before it was turned
into a Maynilad treatment plant.
Designed by Pall Corp., an American firm, the P1.2-billion
treatment plant, can produce 100 million liters a day
(mld), enough to service 105,000 customers, when completed by
November. With a current capacity of 30 to 40mld, the plant
supplies water to customers in Barangays Putatan, Ayala Alabang,
Alabang, Poblacion and
Tunasan. Installation of pipelines continues in the city.
Maynilad charges households P103.34 for the first 10 cu m;
P174.14 to P340.86 for 11 to 20 cu m; P374.91 toP681.39 for 21 to
30 cu m; and P715.43 to P1,465.15 for 31 to 50 cu mthe same rates
it charges customersgetting water from Angat.
The concessionaire plans to expand the treatment plants capacity
to 300 mld by 2013 to supply water to Caviteand nearby areas.
The facility uses dissolved-air flotation, microfiltration,
reverse osmosis and chlorination to produce water fromthe lake that
Pall Corp. claims exceeds the Philippine National Drinking Water
Standards. (See infographics.)
Despite these processes, water from the plant has a moldy odor
and taste, which consumers can remove with
the use of a carbon filter. (The writer, a resident of
Muntinlupa, has been using water from the treatment plant
since the last week of August. He visited the plant twice and
interviewed Pall Corp. and Maynilad managers,engineers and chemists
for this issue.)
Lake Fast Facts
Surface area 900 sq km
It is the largest inland body of water in the P hilippines
Average volume
2.25 billion cu m
Average depth
2.5 meters
INQUIRER RESEARCH
1. Lake intake
An intake structure 400 meters from the shoreline draws water
from Laguna Lake. The w(2-m x 1.75-m) ducts.
2. Forebay
Water is fed into the forebay by gravity. The water is
continually replenished in the impoon demand.
3. AeratorA twister machine aerates the raw water in the
forebay.
4. Vertical pumpsThree vertical turbines (132 kW, 880 rpm) pump
water from the forebay into dissolved-a
5. Coagulant
Aluminum chlorohydrate, a coagulant, from these tanks is added
before raw water goes i
6. MixersIn the first stage of the DAF process, mixers in four
tanks slowly blend the water with th
to blue-green algae, silt, dust, and metals like iron and
manganese to form flocs (loosely cparticles).
7. Air concentratorIn the second stage of DAF, air from this
tank is injected into two chambers holding the m
coagulant, producing small bubbles that make the flocs
float.
8. Skimmers
Skimmers remove from the surface the flocs that form into
sludge. Scrapers remove solid
bottom. The sludge goes into a trough and into a sludge tank
(lagoon at this time) where i
water. Solids are left for hauling.
9. Feed pumps
Six turbines (215 horsepower at 1,790 rpm) pump water into
strainers and into microfiltrosmosis trains, and finally into the
reservoir.
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10. Strainers
Five stainless strainers remove remaining solids (up to 300
microns) from the water, clear by now, at a maximum
flow of 1,200 cubic meters per hour. A micron is a thousandth of
a millimeter.
11. Microfiltration system
Polyvinylidene-fluoride filters screen out particles up to 0.1
micron, removing most viruses and bacteria. Thisprocess uses 14
racks with 68 modules each.
12. Reverse-osmosis (RO) systemSalt is removed from the water
using six identical RO trains (5.6 mld of permeate flow per train)
when salinity in
the lake reaches 500 parts per million. Last June and July, for
instance, salt water from Manila Bay intruded intothe lake through
the Pasig River. The brine resulting from reverse osmosis is
expelled into the lake.
13. Permeate tankA 30 cubic-meter tank collects water from RO
trains.
14. ChlorineChlorine is added to kill pathogens.
While the chlorine equipment has yet to be installed, granules
of calcium hypochlorite (which have a 70-percent
chlorine content) are used.
15. Reservoir
The reservoir can store 14 million liters a day (mld). It has
two chambersChamber 1 can hold 6.6 mld and
Chamber 2, 7.4 mld.
16. Booster pumps
Three 200-kW booster pumps for Ayala Alabang and three 480-kW
booster pumps for other communitiesdistribute potable water to
May-nilad customers, producing 88 psi (pounds per square inch) of
pressure that
allows water to be sent to multi-story houses and tall
buildings. The pressure drops to 20 psi when water reachesend
users.
Lake-water qualityParameter Average concentration
Chlorides 600 ppm
TDS 1,200 ppm
BOD 10 ppmTurbidity 40 ntu
TSS 50 ppmHardness 450 ppm
Oil and grease 5 ppm
Iron 1 ppm
Manganese 0.5 ppmLead 0.1 ppm
Cadmium 0.03 ppm
Fluorides 1
Phenols 0.03 ppm
Silica 35 ppmColor 40 tcu
Boron 1 ppmTaste objectionable
Odor objectionable
pH 7 to 8.5 units
Ppm = parts per million; tds = total dissolved solids; tss=
total suspended solids; ntu = ne
unit; tcu = true color unit
*Based on some 30 samples taken between 2004 and 2008
Source: Pall Corp. PowerPoint presentation
Drinking-water standard
Parameter* PNSDW**
Chlorides 250 ppmTDS 500 ppm
Turbidity 5 ntuHardness 300 ppm
Iron 1 ppm
Manganese 0.4 ppm
Lead 0.01 ppmCadmium 0.003 ppm
Fluorides 1 ppmPhenols 0.001 ppm
Color 0 tcu
Boron 0.5 ppm
Taste Not objectionableOdor Not objectionable
pH 5 to 7 units
*Selected parameters
**Philippine National Standards for Drinking Water
(Pall Corp., builder of the treatment plant, claims that the
water produced by the facility estandards for drinking water.)
