Challenge

More than a decade ago, the largely urban island-nation of Singapore set a goal for water self-sufficiency by the time a long-term water supply agreement with Malaysia expires in 2061, with reclaimed water meeting 50% and desalination 30% of its needs and 20% supplied by internal rainfall catchments – as there are no natural freshwater lakes.

With the idea of capturing all rainfall possible, 19 raw water reservoirs, 9 treatment works, and 17 storage or service reservoirs were built by 2010. Milestones include inauguration of Singapore's first water reclamation plant (WRP) in 2002 and its first desalination plant in 2005.

The WRPs treat water for discharge to deep sea outfalls or as feed for its NEWater factories that further treat the water to levels that exceed USEPA and WHO guidelines for industrial use or indirect potable reuse by mixing with reservoir water. Siemens Water Technologies has played a key role in making that possible.

Solution

The Changi WRP, inaugurated in summer 2009, includes the largest of the NEWater factories. This and the four other WRP/NEWater combinations at Bedok, Kranji, Seletar and Ulu Pandan produce 50 million U.S. gallons per day. The plant also is the cornerstone of the first phase of Singapore's Deep Tunnel Sewerage System (DTSS), a 48-km deep tunnel reclamation network stretching from Kranji to Changi.

Featuring odor control and primary and secondary wastewater treatment equipment, as well as a full-scale membrane bioreactor (MBR) system from Siemens, the Changi WRP reclaims more than 800,000 m3/day of wastewater. Specific equipment from Siemens includes:

• Odor control: Two odor control trains with a LO/PRO® multi-stage chemical scrubber, followed by a dual-bed, horizontal-flow V-bank-style carbon adsorber; and a third with a “Unitary Multi-stage” chemical scrubber system, followed by a V-bank carbon adsorber.
• Aeration: Nearly 50,000 DualAir® fine-bubble and WideBand™ coarse-bubble diffuser systems.
• Solids removal & clarification: Nearly 500 chain and scraper mechanisms for 48 stacked clarifiers. This is the largest chain and scraper stacked clarifier system installation in the world.
• Membrane filtration: Siemens also supplied seven Memcor® CP membrane filtration systems – equipped with 960 membranes each to pretreat feedwater going to the RO system – for the Changi NEWater plant on the Changi WRP's roof. A production capacity of 228,000 m3/day makes the facility the largest of its kind in the region.

With key considerations being the footprint and weight of the membrane filtration and RO systems due to their rooftop location, the Memcor CP membranes weigh only about 20 Kg and deliver more membrane surface area per unit of floor area than many others. They also offer low long-term operating costs for electrical and chemical consumption.

Results

More than half of Singapore's used water is treated at the Changi WRP, which will prove more cost effective over time. And the Changi NEWater factory has more than doubled NEWater production. This has enabled reclaimed water to now meet 30% of the island’s water needs and helped reduce imported water needs to 40% of total consumption.