Founded in 1997, the Manila Water Company (MWC) serves the potable water needs of more than five million residents of the Philippines capital and cities to the east. The company serves as the private partner in a public-private partnership with the Philippines government in operating the Metropolitan Waterworks and Sewerage System for Metro Manila's East Zone.
MWC's Balara water facility consists of two separate treatment plants in Quezon City: Balara 1, with a design capacity of 470 million litres per day (mld) (124 million mgd); and Balara 2, with a design capacity of 1,130 mld (298 mgd). Both plants had produced adequate quantities of water to acceptable standards of quality. Only during extreme weather conditions, such as typhoons, had water quality fallen below expectations.
Faced with anticipated regional population growth and ever-tightening water quality regulations, MWC underwent an exploratory study and then a pilot project to determine expansionary requirements that would enable the company to optimize operational performance and meet water quality and flow demand requirements at the Balara facility.
As a result of the successful pilot project, MWC embarked on a formal program in 2009 to upgrade the Balara facility. This program would provide treated water at optimal quality and quantities and maximize the ease of maintenance while incurring the lowest possible level of operation and maintenance costs. Refurbishment of the Balara 2 plant is expected to be completed by 2011. Refurbishment of the Balara 1 plant will follow.
Study reveals need for improved operations
In 2006, MWC undertook a study of the capacity and process optimization at the Balara 1 and 2 plants. The study highlighted the need to improve chemical dosing and the operations of flocculation, desludging and filtration. In addition, the administrative functions of managing operating expenditures and record keeping and reporting – as well as chemical and biological analysis – required attention. Many of the shortcomings identified in the study were the result of equipment that needed upgrading – an ongoing process that has been in progress since the mid-1990s.
Although the Balara 1 and 2 plants were designed to operate at 470 mld (124 mgd) and 1,130 mld (298 mgd), respectively, they were operating to meet current demand at 438 mld (116 mgd) and 969 mld (256 mgd), respectively, at the time of the study. Simple hydraulic analysis of both plants confirmed that they were able to handle 600 mld (158 mgd) and 1,200 mld (317 mgd), respectively, without structural modification. At these elevated flows, however, acceptable water quality levels would not be achieved without operational enhancements and refurbishments to treatment equipment.
As a result, it was determined that the following treatment enhancements would enable the Balara 1 and 2 plants to operate at the higher flow rates:
- Replacement of the "Rotodip" alum feeders with new positive displacement chemical metering pumps
- Rationalization of all dosing points and replacement of all dosing lines for the polymer and alum dosing system in the Balara 1 and 2 plants
- Temporary modifications to allow the correct proportion of the proposed increased flow in the Balara 2 plant of 1,250 mld (330 mgd) to pass through the selected single clarifier and single filter for the proving period detailed in the technical specification
- Removal of the sedimentation tank exit baffle wall and launders in the single clarifier; installation of new launders and lamella separators; and installation of chain scraper sludge removal equipment in the single sedimentation tank
- Removal of existing filter laterals and surface wash pipe work within the single filter; installation of underfloor drains with media retention plates; installation of air scour blowers; and replacement of filter media to a single filter
Replacement of underdrains a key to improved filter backwashing efficiency
In 2008, MWC executed a pilot project to prove the viability of the proposed refurbishment and upgrades for the Balara water treatment facility that were recommended in the 2006 study. The pilot project involved the refurbishment of the chemical dosing system, a single clarifier and a single rapid gravity filter at the Balara 2 plant. The six-month pilot was a success, highlighting the ability of the fully proposed refurbishments to optimize operational performance, meet water quality and flow demand requirements.
The detailed study undertaken in 2006 noted that the condition of the existing filters was, at best, poor. Filters were not being operated optimally nor backwashed effectively, and run times were short. There was evidence of both media depletion and media expansion. Media depletion, particularly for anthracite, is to be expected; however, media expansion can only be caused by sludge and mud accumulation resulting from ineffective backwashing. Complete refurbishment of the filter underdrain and media replacement were required.
While media replacement alone could have offered improvement in filter efficiency, this efficiency would not be realized without effective backwashing. In addition, although an upgrade would be possible by removing the existing laterals and installing a new slab floor with nozzles, underdrain filter blocks provide a more effective backwash than nozzles and greater use could be made of the available filter depth by installing a low profile block-type underdrain system.
As a result, MWC selected the TETRA® LP Block™ dual parallel lateral filter underdrain blocks, featuring the "S-Plate" media retention plate and GroutGrip™ design, from Severn Trent Services.
The TETRA LP Block features a proven design to provide superior distribution for both water and air, separately or concurrently. The blocks cover the floor of the gravity filters, supporting the filter media. Air is distributed evenly across the entire filter bottom area to scour the media and to provide an air lift which, with the water, removes the released solids from the media. This dual backwash action provides intense and extremely effective backwashing of the filter media. It was recommended that air scouring be introduced into the backwashing process. An effective backwashing process was especially critical at the Balara facility, where filtration rates were very high and bed depth was limited.
The TETRA LP blocks have become popular with plant owners throughout the world for their low profile, low headloss, lightweight construction and easy installation, either as a retrofit or for new filter underdrain applications. The filter underdrain blocks are easy to assemble and ensure superior distribution of both air and water for effective backwash, exceptional installation strength and maintenance-free life.
The LP Block filter underdrain blocks feature the GroutGrip design, which helps to alleviate the buoyancy inherent in conventional filter underdrain block designs. In fact, the LP Block features a pull-out strength three times that of a conventional filter underdrain block design. Additionally, the wide, low-profile design requires the installation of fewer blocks to cover a filter floor. Therefore, fewer joints are created and less grout is needed.
TETRA LP Blocks will be installed in 10 filters at the Balara 1 plant and 29 filters at the Balara 2 plant. The S-Plate media retention plate eliminates the need for gravel support media and will enable an increase in media depth, thus improving the solids removal capacity of the filters.
Ease of installation ... more effective backwashing ... improved operational efficiencies and longer run times ... lower operating costs: The investment in the TETRA LP Block technology will yield multiple benefits for MWC and its customers.
For more information, e-mail info@severntrentservices.com.
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