Semakau Landfill Phase II

2016 International Innovations Awards semi-finalist: National Environment Agency, Singapore

BACKGROUND 

Due to land scarcity, Singapore faced the challenge of finding solutions for its expanding waste disposal needs. Before 1979, all waste was sent to landfills on the main island of Singapore. However, with rising affluence and a growing population, generated waste increased more than six-fold from about 1,260 tonnes per day in 1970 to about 8,402 tonnes per day in 2015. To handle this upsurge and slow landfill use, Singapore’s then Ministry of the Environment (ENV) adopted incineration technology. The volume of waste was reduced by over 90% and the incineration ash was disposed into the landfills. The first waste-to-energy (WTE) incineration plant startedoperation in 1979 and, today, there are four WTE incineration plants with a combined capacity of 7,600 tonnes per day.
 
While incineration extended the lifespan of the landfills, in the late eighties it was projected that existing landfills would be exhausted by the turn of 20th century and land to create additional landfill sites was unavailable. Singapore’s projected land needs for future housing, industry and recreation led to the National Environment Agency (NEA)1 building the world’s first-of-its-kind offshore landfill, Semakau Landfill.
 
Semakau Landfill is located eight kilometres south of the main island of Singapore. Two offshore islands, Pulau Sakeng and Pulau Semakau, were amalgamated to form Semakau Landfill through the construction of a seven- kilometre perimeter bund that encloses 350 hectares of sea space. The endeavour was no ordinary engineering feat given the challenges of constructing a landfill entirely in deep sea. To overcome the obstacles, engineers devised prudent and creative engineering solutions to ensure minimal impact on the surrounding marine ecosystems.
 
Semakau Landfill development was carried out over two phases, with an internal sand bund dividing them. Phase I was further divided into 11 smaller cells with internal sand bunds. The small cells allowed for ease of landfilling using conventional methods. Covering an area of 178 hectares with a landfill capacity of 11.4 million m3, the landfill space of Phase I of Semakau Landfill commenced on 1 April 1999 and was completed by 2016. (Please refer to the following for an overview of Semakau Landfill Phase 1: https://www.youtube.com/watch?v=jF1UCbS3zVY).
 
To address Singapore’s waste disposal needs, NEA embarked on the Phase II development in 2011 to convert the remaining 157-hectare sea space into landfill space. In July 2015, Singapore’s waste disposal needs received a 16.7 million cubic metres boost, with the completion of the Phase II development of Semakau Landfill.
 
The Phase II development was highlighted by an innovative design change from the 11 cells design in Phase I to a single cell design in Phase II. The size of Phase II is equivalent to nearly 6,700 Olympic-sized pools, and Singapore now has the capacity to meet its waste disposal needs to 2035 and beyond.


 
ENGINEERING ACHIEVEMENTS 

Phase II features three engineering feats: (i) a single cell layout, (ii) a 200-metre long floating platform and (iii) a floating wastewater treatment plant.

(i) Single cell layout
To minimise the amount of sand used for the construction of cells and maximise the landfill capacity, a single cell layout is adopted for Phase II. To create the single cell layout, the 160-metre gap at the southern tip of the perimeter bund is closed with the construction of a sand bund. The 160-metre gap was previously open and connected to the open sea to keep the seawater in the cell fresh and clean. The innovative single-cell design resulted in big cost savings in construction and sand costs as there is no longer any need tobuild internal sand bunds. This enabled NEA to eliminate the difficulty of getting the sand needed to construct the bunds and also contributed to the increase of the landfill capacity, thereby extending the landfill lifespan.

The bund was lined with impermeable geomembrane and a layer of marine clay to ensure that the leachate from the landfill waste is contained within thereby keeping the surrounding sea pollution-free.
 
(ii) Floating Platform 
Developing a single cell to maximise landfill capacity presents occupational hazards regarding landfill operations. The large area and uneven seabed limit the efficiency of conventional landfilling and presents a high risk of waste sliding. To mitigate this, a floating platform was constructed for safe landfilling operations. The floating platform is used to deposit incineration ash/waste into the Semakau Landfill Phase II Cell to even out and raise the seabed level, reaching a water depth of about two metres. Once achieved, conventional landfilling can be carried out safely from shore without the risk of circular slip failure and waste sliding. The floating platform can be shifted from one location to another location of the lagoon as landfilling operations progress to fill up the single cell.The successful development, commissioning and construction of the floating platform is an efficient method of landfilling in deep water. The floating platform has contributed to operations since the Phase II cell opening and commencement of landfill operations on 11 July 2015.


 
(iii) Floating Wastewater Treatment Plant
With closure of the 160-metre gap to form a single cell as part of the Phase II development of Semakau Landfill, flooding risks increased due to prolonged heavy rain and incineration ash/waste dumping into the cell. In response, NEA commissioned the development of a floating wastewater treatment plant that treats excess water in the cell to meet effluent discharge standards and release the treated water into the open sea surrounding Semakau Landfill. The impounded wastewater, a mixture of seawater, rainwater and landfill leachates, is treated to meet the Trade Effluent Discharge standards. This approach prevents flooding in Semakau Landfill, which would hinder landfilling operations, and ensures minimal environmental damage and pollution to surrounding waters and precious biodiversity.
 
The wastewater treatment plant is installed on a floating structure two times the size of an Olympic swimming pool and is designed to treat up to 18,000m3 wastewater daily. The operation of the plant is automated and highly reliable. The treatment plant consists of a number of unique systems to sustain discharge water quality and ensure the treatment plant remains reliable, secure and automated for a lifespan of 20 years.




CONSERVATION OF SEMAKAU’S RICH BIODIVERSITY
 
To protect Semakau Island’s vibrant ecosystem and rich biodiversity, measures were taken to minimise the environmental impact on Pulau Semakau’s natural ecosystems. For Phase I development, the design of the Semakau Landfill perimeter bund resulted in the loss of about 13.6 hectares of mangroves. Upon the recommendation by leading local biologists, some 400,000 mangrove saplings were replanted on two new plots on the northern and southern fringes of Pulau Semakau. These mangroves also serve as biological indicators to detect any waste leakage from the landfill. In the Phase II development area, NEA also embarked on a coral transplantation project to preserve the marine inhabitants. Due to the presence of fresh seawater in the Semakau Landfill Phase II lagoon, marine habitats developed in the lagoon. In March 2014, NEA commissioned an independent coral reef survey of the lagoon to mitigate threats to the biodiversity in Semakau Lagoon during the development of Phase II. It was recommended that 27 genera of corals be earmarked for transplant to minimise impact of landfilling operations on the coral reef community. One of these 27 genera is Polyphyllia, which is ranked eighth rarest among the 56 hard coral genera found in Singapore’s reefs.

Table 1: Top 10 coral genera identified from survey and ranked by rarity
 
Genera Colony Count Rarity Rank
Polyphyllia 1 8
Goniopora 62 16
Pavona 2 20
Acanthastrea 2 23
Lobophyllia 1 24
Turbinaria 9 25
Oulophyllia 1 27
Porites 34 28
Astreopora 3 29
Podabacia 1 30
 


The process of harvesting and transplanting corals and related reef species was completed over a period of five months from September 2014 to January 2015. A total of 42 genera of hard corals with a total colony count of 761 amounting to 60 m2 of live coral cover were harvested from the lagoon and transplanted successfully at the Sisters’ Island Marine Park south of the landfill. Prior to the transplantation at Sisters’ island Marine Park, the corals were transferred to a temporary holding area west of Pulau Semakau where conditions were favourable for the growth and survival of the coral colonies. Two rare and threatened reef-associated species were also relocated from the lagoon – Neptune’s Cup Sponge (Cliona patera) and two Fluted Giant Clams (Tridacnasquamosa).


 
A nine-month monitoring programme was established with the objectives of assessing and evaluating the health and survival rate of the relocated corals while assessing ambient environmental conditions pertinent to the wellbeing of the corals, namely water quality and sediment conditions at the recipient sites. No transient or long-term impacts of the transplantation on coral colonies and reef-associated organisms were observed. This NEA biodiversity conservation project was largely successful and represents the agency’s goal of creating a sustainable future for the rich biodiversity present in Singapore.




ENVIRONMENTAL MONITORING AND MANAGEMENT PLAN 

Designed to be filled with incineration ash from Singapore’s incineration plants and non-incinerable waste (NIW), the 350 hectare Semakau Landfill perimeter bund is lined with marine clay and impermeable geo-membrane to ensure leachates are fully contained. Regular water testing is conducted to ensure the integrity of the impermeable liners and that water quality meets the required standards around the landfill.
 
Care is taken to ensure that the high standards regarding preservation of the environment are upheld. Establishment of strong and recommended environmental protection standards are especially crucial to Singapore’sposition.
 
The NEA implemented strategies to enable Singapore to remain environmentally sustainable by increasing recycling rates and minimising waste generation. Eliminating the production of waste is an essential part of meeting Singapore’s future needs. The ultimate goal is to strive towards a zero-waste situation where the need to build new incineration plants and waste treatment facilities is thoroughly reduced. Waste generation at source and recycling will be at the forefront of NEA’s efforts, with public education, industry collaborations and the implementation of viable technologies identified as components of the arsenal employed for waste management.
 
A PLACE FOR ENVIRONMENTAL PARTNERSHIP AND LEARNING
 
In Semakau Island, the coexistence of an active landfill and healthy ecosystems offers an ideal launchpad on which to showcase Singapore’s commitment to sustainable development and nurture partnerships with individuals and groups who share this vision. NEA itself practices this principle and officially opened Semakau Landfill to the public for recreational and nature activities. These activities include educational tours, an inter-tidal walk, bird watching, and sport fishing. NEA also invested in a renewable energy system at the southern tip of the landfill bund. Consisting of solar panels and a wind-powered turbine, the system generates electricity to light up the area for nocturnal activities such as stargazing, camping and barbeques.
 
Semakau Landfill also offers a promising location for the testing of eco-friendly projects, and NEA has welcomed private as well as public proposals that could support or extend its mission to make the facility a showcase and centre for eco-friendly activities and technologies. The sea bass nursery and farm is another example of how Semakau Landfill is giving Singapore a taste of environmental quality through healthy fish reared in the waters by the landfill. The nursery uses water pumped from beneath the nearby pier to raise the young fish. Meanwhile, older fish at the floating cages located just west of the bund grow to marketable sizes in a natural marine environment free from disease and pollution.
 
Singapore’s success in turning two small islands into an offshore landfill has captured the imagination of the world at large. The sheer novelty of turning two small islands into an offshore landfill and the careful protection of the surrounding natural habitats have drawn the attention of scientists, engineers and leaders from other countries.
 
One of the first foreign leaders to visit and learn about the design and operation of Semakau Landfill was Datuk Seri Azmi Khalid, Malaysia’s Natural Resources and Environment Minister. Environment ministers from Brunei, Philippines, New Zealand, Japan and the Independent State of Samoa have also visited the site.
 
The international press corps showcased Semakau Landfill as an example of urban planning and environmental foresight that demonstrates how a small city-state can combine solid waste disposal with nature preservation. The international media such as CNN News, the Discovery Channel, the New York Times, Rod & Line (Malaysia), and Waste Management World have reported on this initiative, and New Scientist Magazine called it the “Garbage of Eden” in a feature article.
 
Semakau Landfill is serving as an incomparable outdoor classroom. School groups, grassroots organisations, tours by international delegations and dignitaries come to learn how Singapore combined solid waste disposal with environmental sustainability. NEA, through Singapore Environment Institute (SEI) also operates a Programme for Environmental and Experiential Learning (PEEL) that allows members of the public and environment industry professionals to go behind the scenes of Singapore’s solid waste management system through tours to the incineration facilities and the Semakau Landfill.
 
NEA is committed to promoting long-term environmental sustainability. Semakau Landfill is an excellent success story that showcases sustainable waste management co-existing with thriving marine life and habitats. Singapore’s only landfill represents a balancing feat between physical development and environmental conservation and it is a testament to Singapore’s engineering capability and the success of its novel approach to waste management.
1NEA was formed under ENV on 1 July 2002 as a statutory board to focus on the implementation of environmental policies. In September 2004, ENV was renamed to the Ministry of the Environment and Water Resources (MEWR).