The Ngau Tam Mei water treatment works combines two advanced technologies—ozonation and dual-stage biological filtration—to deliver high-quality water to a rapidly growing region in Hong Kong. The 230-million-liter-per-day plant treats raw water from the Dongjiang River, which is contaminated by industrial wastewater.
The plant is the world's first to use dual-stage biological filtration with granular activated carbon (GAC) to remove ammonia, replacing break-point chlorination. Ozone provides pre-oxidation and primary disinfection.
Pilot Study Confirms Effective Treatment
CDM conducted a 14-month pilot plant study to confirm design criteria and optimize overall processes for the new waterworks. The pilot study demonstrated the treatment process could be operated safely and effectively to produce high-quality potable water under seasonal variations in raw water quality.
Advanced Technologies Produce High-Quality Results
Features of the plant include:
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Dual-stage biological GAC filtration - First-stage filters remove particles and chlorinated byproducts precursors and reduce tastes and odors. Second-stage filters remove ammonia, replacing break-point chlorination and providing safe drinking water.
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Ozonation for primary disinfection - This process inactivates Giardia and Cryptosporidium, reduces chlorine usage, limits formation of chlorinated byproducts, and makes biological filtration possible without the use of conventional filters.
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In-line ozone injector - Developed and patented by CDM, this injector improves ozone dissolution efficiency by 140 percent and reduces operational costs.
Onsite oxygen generating systems - Vacuum pressure swing adsorption technology produces high-quality oxygen while saving liquid oxygen costs.
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Manganese removal - Manganese is removed using ozone as oxidant and GAC as the medium for catalytic oxidation in the first-stage biofilters. The remaining residues are removed by biological activity in the second-stage filters.
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Sludge treatment facilities - Plate and frame filter presses achieve the minimum sludge solids content (30 percent) required by landfills in Hong Kong.