MODULE 2PUBLIC WATER SUPPLY:SOURCES AND PURIFICATIONPROCESS

What are the General Sources ofPublic Water Supply?

DANILO V. RAVINA, NAMPAP - CEBU

The 2 General Sources of Public Water Supply are:

1. Surface Waters: Streams, Rivers & Lakes

a. Upland Surface Water

b. Lowland Surface Water

2. Ground Water

Upland Surface Waters:

DANILO V. RAVINA, NAMPAP - CEBU

Water Divides & Watersheds:

DANILO V. RAVINA, NAMPAP - CEBU

Metro Cebu Watersheds:

DANILO V. RAVINA, NAMPAP - CEBU

The 3 Watersheds identified asmajor water sources for MetroCebu:

1. Kotkot Watershed

2. Lusaran Watershed

3. Mananga Watershed

Metro Cebu Ground Water Source:

Metro Cebu Water Supply & DemandProjections (2000 – 2015)

MCWD supplies only 40% of Metro Cebu’s population.

What is the Purification Process forSurface Water Supply Source?

Surface water basic treatment process employed bycommercial water provider, including the Metro CebuWater District (MCWD) treats the water using theconventional method comprising of the following:1. Storage2. Aeration3. Coagulation / Flocculation4. Sedimentation5. Filtration

Surface Water Supply and Treatment System

The Buhisan Dam at Kalunasan, Cebu City

Runoff or surfacewater is firststored in theDam.Suspendedmatters tend tosink to thebottom. In thecourse of time,disease-producingorganisms tendto die out. Thusthe storing ofwater improvesits quality.

MCWD Tisa Filtration Plant at Labangon,Cebu City

Aeration:Water issprayed into theair or cascadedin order torelease trappedgases & absorbadditionaloxygen forbetter taste. Italso removesironcompounds.

Sample of a Spray Aerator

Section / Elevation of Spray Aerator for the removal of Iron andManganese

Coagulation and Flocculation:

Coagulation – is thechemical process inwhich the coagulantreacts with thesediment to make itcapable of combininginto larger particles.Alum is the commoncoagulant used.

Flocculation – is thephysical process inwhich the sedimentparticles collide witheach other and sticktogether.

Sedimentation:

This is the processby whichsuspended solidsare removed fromthe water by gravitysettling anddeposition. Theobjective of thisprocess is toremove most of thesuspended solidsand thus reducingthe loads on thefilters.

Contents in the SedimentationTanks

Filtration:

Water is passedthrough a bed offine sand in whichthe suspendedmatters that didnot settle duringsedimentation aretrapped and heldin place by theforce of gravity orby the direction offlow.

What are the types of Filters?

The types of filters are:1. Slow Sand Filter – consists of large tankswith a filter bed of 600mm to 1000mm of finesand over 300mm of gravel, with suitabledrainage pipes to conduct water after passingthrough the filter under its own weight.2. Rapid Sand Filter

a. Rapid Gravity Filterb. Rapid Pressure Filter

Sample Plan of a Slow Sand Filter &Filtered Water Storage Tank

The organic matterwhich accumulateson the surface of thesand forms a jelly-likefilm which does stopsthe passage oforganisms. Cleaningof the filter bed isdone throughscraping off a thinlayer of sand togetherwith the surface film.There must be atleast 2 filters in anyfiltration system.

Sections of a Slow Sand Filter andFiltered Water Storage Tank

Section of a Rapid Gravity Filter

When the filterrequires cleaning, it isemptied down to thelevel of the wastechannel. The sand isagitated from belowby means ofcompressed airdelivered through thesame pipes whichpreviously collectedthe filtered water. Thecleaning is completedin a few minutes andthe filter is ready foruse againimmediately.

Section of a Rapid Pressure Filter

This is generally used forthe purification of waterused in swimming pools.The cleaning processconsists of reversing theflow of water through thefilter and allowing thewashings to flow throughthe washout valve. Whilethe flow of water isreversed, the sand isagitated from below bymechanical stirrers or bycompressed air injectedfrom below the filter bed.

Chlorination:

Chlorination is themethod of introducinga controlled amountof chlorine gas orchlorine salts to thewater in order toattain a desireddegree of disinfection.Chlorine kills anydisease – producingorganisms in thewater.

Groundwater Supply and TreatmentSystem

Equipment used in Chlorination

Pot Chlorinator – Used in disinfecting wells

Floating Bowl Chlorinator

References:

Cebu for Sustainable Water Resource. Metro Cebu Water District. Nebel, B.J. and Wright, R.T.: Environmental Science

4th Edition, Prentice – Hall, New Jersey, 1993 National Water Resources Council. Rural Water Supply

Design Manual, Volume 1, NWRC, Quezon City, 1980 Doyle, K.M.: Plumbing and Gas Fitting, Volume 1,

Government Printing Office, Mulgrave St., Wellington,1990