The National Environment Agency (NEA) has won a coveted international award for its outstanding engineering feat in developing the Semakau Landfill.

The 2019 Hassib J. Sabbagh Award for Engineering Construction Excellence was presented to NEA on Saturday evening in Melbourne, Australia, by the World Federation of Engineering Organisations (WFEO).

The award affirms the role of engineering in sustainable development - in this case, in developing the 350ha Semakau Landfill, the first offshore landfill in the world.

But winning an award was far from the minds of the team that first built the landfill.

"I think our main aim was to just solve the problem we were facing at the time... We didn't do it for personal glory," said Mr Eng Tiang Sing, who oversaw the first phase of the landfill's construction from 1995 to 1999.

Mr Eng, who was chief engineer at the then Ministry of the Environment's Engineering Services Department, told The Straits Times on Friday that before the landfill was built, waste was thrown into dumping grounds across Singapore, which were filling up fast in the 1970s.

With an increase in trash linked to a growing population and economy, Singapore had to look for alternative methods of waste disposal.

"We searched the whole of Singapore and couldn't find another super big piece of land to build the next dumping ground. We had a pressing need," said Mr Eng.

So he and a team decided that the waste needed to be dumped on an offshore island. They travelled to different countries to see if any were already disposing of their waste in a similar manner. "But we never found another equivalent landfill for us to follow," Mr Eng said.

Back home, the team was also having a difficult time finding a location for the landfill on one of Singapore's offshore islands - many were already used for other purposes - until it found Pulau Sakeng, next to Pulau Semakau.

Pulau Sakeng was occupied only by a number of fishermen and a Police Coast Guard outpost, so the team decided it was the best option.

As no other country had built an offshore landfill at the time, the team faced a daunting task.

"There was no other example we could follow. We really had to start from scratch," said Mr Eng.

They needed to overcome many challenges, including inventing a method to safely transport the waste across the water while reducing the risk of accidental pollution, preventing seepage out of the landfill into the surrounding waters, and expanding tiny Pulau Sakeng to receive the large volumes of waste.

In addition, much of the construction work had to be done underwater by divers in precise coordination with a floating barge, which would lower marine sand and huge rocks into the deep waters under GPS guidance. All this, while trying to prevent damage to surrounding corals and nearby mangroves.

But under Mr Eng's supervision, the team worked together with engineers and experts and completed the first phase in 1999 with a capacity of 13.6 million cubic m.

Just one decade later, however, it was foreseen that the landfill was at risk of running out of space.

It then fell to Mr Ong Chong Peng, general manager of the landfill at the time, to tackle this new crisis.

Plans had previously been put in place to expand the landfill, but as the price of sand had shot up since the plans were drawn up, the proposal was rejected for being too expensive, said Mr Ong.

So his team proposed the bold idea of dumping waste into a single large cell, rather than building smaller cells as it had in the past.

But this design involved additional risks, including a potential build-up of wastewater and the possibility that dump trucks might fall into the dumping area.

So the team conducted overseas studies and developed a floating platform and a wastewater treatment plant to mitigate these risks.

Extra care also had to be taken to harvest, protect and relocate new corals which had grown in the area.

The second phase was completed in July 2015, adding 14.5 million cubic m to the landfill's capacity.

Thanks to the project's ingenious design and prudent operation, the biological ecosystems on and around it have remained vibrant. More than 80 species of birds, including endangered species, have been spotted around Semakau Landfill, NEA noted.

Said NEA chief executive Tan Meng Dui: "The current generation of NEA engineers stands on the shoulders of the past generation. This award is therefore also a recognition of the industry and pioneering spirit of the engineers and leaders that have come before us."

Mr Eng reflected on the work past teams had done, noting: "It was out of necessity. We turned adversity into an opportunity, something that is now being recognised... We came up with a solution, not because we wanted it so badly, but because we needed it and had no choice.

"Singapore is like this: We always learn from the best, but we always come up with something better than what we learnt from."

Past winners of the award include the London 2012 Olympic Park project, China's Jinping hydroelectric project and the Nacala Corridor railway project in East Africa.

The award includes a cash prize of US$10,000 (S$13,600), which NEA will be donating to a WFEO project on capacity building for climate change education in the Small Island Developing States. The agency said it will fund training and teaching aids for climate change awareness in schools, and underscores the commitment of NEA and the Ministry of the Environment and Water Resources to global and regional cooperation on climate action.