How Phase 2 of Semakau Landfill was developed to combine addressing Singapore’s waste disposal needs with protecting a unique habitat for visitors and the island’s wildlife to enjoy.
An island country with a total land area of only 718 square kilometres but a population of around 5.5 million, Singapore has had to be creative about managing its waste.
Nowhere is that innovation more evident than at Semakau Landfill.
This island facility is a remarkable feat of engineering. It demonstrates its developers’ commitment to protect the marine habitat while providing a much- needed solution to the country’s waste disposal needs.
Singapore’s National Environment Agency (NEA) sees Semakau Landfill as unique. It is a popular attraction for educational and nature tours, as the site is scenic, and supports a thriving diverse marine ecosystem and wildlife.
The NEA opened Phase 2 of Semakau Landfill this past July, but getting to that point has been a 20-year journey.
A recent history of waste disposal in Singapore
Semakau Landfill is located eight kilometres south of Singapore. Its construction came after decades of almost primitive management of waste. As recent as the 1960s, municipal employees used to shovel rubbish into handcarts, then dump that into swamps at three regional sites.
When those sites reached capacity in the early 1970s, three more were allocated. However, the Ministry of the Environment started to recognise that tipping untreated solid waste into swamps was inappropriate in the long term, not least because it would run out of suitable land.
At this time, Singapore’s economy and population was booming and generating more solid waste, increasing from 600,000 to 940,000 tonnes a year between 1972 and 1980.
The government turned to incineration plants to address the problem. It opened its first waste to energy plant, and the first outside Japan in Asia, in July 1979. Others were to follow in 1986, 1992 and 2000.
By the mid-1980s, the Ministry was investigating other solutions. Its forecasts had suggested that continued population growth meant its landfills would be full by 2000.
Struggling for suitable sites for a landfill, the Ministry started considering offshore as a possibility. It sent engineers to examine nearshore landfills in Japan and refuse barging systems in the United States to evaluate how these might be adapted for Singapore’s situation.
The Ministry engaged a specialist consultancy to undertake a detailed analysis of the design, construction and operation of an offshore landfill at Semakau, and evaluate its potential impact on its marine environment. It determined that the plan was viable, and made recommendations to protect the mangroves and coral reefs.
Despite the significant investment to construct and run an offshore landfill, the Ministry concluded that this was the best long-term solution to manage Singapore’s growing waste output.
The government approved the Ministry’s proposal for Semakau Landfill in 1994, and development began in 1995.
Phase 1 build
The construction of Semakau Landfill was divided into two phases.
The landfill was created by building a seven-kilometre perimeter rock bund to enclose 350 hectares of sea space off Pulau Semakau and Pulau Sakeng. This was lined with an impermeable membrane and a layer of marine clay to contain leachate from the refuse within the landfill area.
The project’s chief engineer, Eng Tiang Sing, recalls that building the outer bund was the hardest part of the four-year development, as most of this was done underwater.
“Divers had to work in shifts around-the-clock to place the geofabric and geomembrane by hand underwater, while coordinating with the floating barge on the surface,” explains Eng.
“At the same time, huge rocks had to be lowered piece by piece with precision from the barge using GPS, and placed in their correct positions.”
The sea space within the bund was divided into two sections: one half housed 11 wet cells separated by sand bunds; and the other formed a lagoon connected to the sea by a gap in the bund. The inactive landfill cells were flushed daily with seawater from connected concrete pipes. When a cell was needed for tipping, workers sealed the pipes during low tide.
The Tuas Marine Transfer Station was built at the same time as Phase 1. This serves as an intermediate collection point for ash from waste-to-energy plants and non-incinerable waste before transportation to Semakau. It was strategically located next to the Tuas South Incineration Plant.
The Ministry also built ancillary amenities on the island – including a wharf, workshops and a sewage treatment works – to ensure that the operation was self-sustainable.
Semakau Landfill Phase 1 was completed on schedule within four years, and cost $610 million. Formally opened on 1 April 1999, it became Singapore’s only landfill for waste disposal.
The facility successfully fused with the island’s marine ecosystem and habitats, and was landscaped to make it a beauty spot. When the Environment Minister visited in August 2004, he saw the potential for developing it into a leisure and educational destination.
In July 2005, Semakau Landfill was officially opened to the public for bird watching, intertidal walks, astronomy and fishing.
Building Phase 2
The NEA forecasted that Phase 1’s landfill cells would be filled by 2016. Therefore in February 2014, work started on converting the remaining 157-hectare sea space into landfill space. The NEA built it with the aim of balancing development of a much- needed waste disposal facility with conservation of the local habitat, which hosts a vibrant ecosystem and rich biodiversity.
The construction team opted for a one-cell layout with segregation for Phase 2 to avoid flotsam problems that occur when disposing non-incinerable waste into a large area of water. They closed the 160-metre gap at the southern perimeter bund to create the second single cell. This was also designed to maximise the landfill capacity and minimise the amount of sand required, reducing the overall construction cost as a result.
Building Phase 2 required two feats of engineering: a 200-metre long floating platform and a floating wastewater treatment plant.
The floating platform means the dump trucks can discharge incineration ash directly into the cell. As the cell covers a large area on an uneven seabed, a floating platform is needed so ash can be spread to level the seabed to a two-metre depth. Only then can workers use bulldozers and compactors to undertake conventional landfill operations.
After enclosing the cell, the water inside builds up and is displaced by ash and rainfall. To prevent flooding, the excess water within the Phase 2 cell is treated at the Wastewater Treatment Plant to meet Trade Effluent Discharge Standards, before being discharged into the open sea.
Concurrently, NEA embarked on two major projects to preserve the marine life in the Phase 2 development area. Workers harvested over 700 colonies of corals in the lagoon and transplanted them to Sisters’ Islands marine park. From June 2015, NEA also worked with nature groups to catch the fish within the Phase 2 lagoon and transfer them to the open sea. This project alone took four months to complete.
Opening Phase 2
Semakau Landfill Phase 2 officially opened on 11 July.
The guest-of-honour at the opening was Minister of the Environment and Water Resources Dr Vivian Balakrishnan. He officiated the first discharge of ash into the new Phase 2 cell in front of many of those who had worked on the project and site employees.
“The expansion of Semakau Landfill is testament to Singapore’s engineering capability and the success of its novel approach to waste management,” Dr Vivian Balakrishnan said. “While it is necessary to meet the waste disposal needs of Singapore, our priority has always been to ensure that it is done in an environmentally sustainable way.”
The Phase 2 cell provides an additional 17-million cubic metres of landfill capacity, which is expected to meet Singapore’s waste disposal needs until at least 2035.