2,300 t/d:Capacity of Doha’s integrated solid waste management centre
$522m: Value of the contract to build the plant in Al-Wakrah
At the end of June, a $522m solid waste management centre will begin commercial operations in Qatar, marking a major milestone in the country’s efforts to ensure infrastructure development keeps pace with population growth.
“We are in the final throes of commissioning and handover,” says Geoffrey Piggott, major projects director at Keppel Seghers Engineering, the Singaporean company that won the contract to develop the plant at Al-Wakrah.
Until now, the majority of the 2,264 tonnes of household and commercial waste generated every day in Qatar has been sent to landfill sites at Umm Alafai, Al-Owaina and Rawdat Rashid. But these unlined dump sites leach liquids and constitute an environmental hazard. Complaints about noxious odours are also commonplace.
Integrated strategy for waste management
The need for a new approach to managing household waste was recognised and in 2000, the government began working on an integrated waste strategy. The environmental problems were made worse by rapid population growth, which meant the volumes of domestic waste being sent to landfill were growing by 10-15 per cent a year. Qatar’s population has more than doubled over the past decade.
The utilities must be coordinated in advance … we were constrained as we were waiting for services
Geoffrey Piggott, Keppel Seghers Engineering
The government decided to look for an integrated system that combined the most advanced technology with the most sustainable solutions. It also wanted the flexibility for further expansion to serve Qatar’s waste management needs for the next 25 years.
The answer was a solid waste management centre that sorts waste, separating out anything that can be recycled and removing organic waste to make compost. The remainder is burnt in an incinerator and the energy emitted is used to produce electricity. Only the left over ash needs to go to landfill.
|Qatar domestic waste growth forecast|
|(Tonnes a day)|
|Organic municipal solid waste||1,076|
|e=Estimate; f=Forecast. Source: Keppel Seghers|
The tender was issued in 2005 and the engineering, procurement and construction contract was awarded in October 2006 to Keppel Seghers Engineering. Work began the following month. “We were starting from scratch and had to find the site using GPS,” says Piggott.
Rapid population growth has left landfill sites unable to cope with volumes of waste being generated
The location at Mesaieed had no existing infrastructure or utilities, but under the contract terms the government agreed to provide power and water for the site, which is now served by twin 66kV underground power lines. Piggott says this is one of the key lessons for future projects. “The utilities must be coordinated in advance or well before the contract starts. We were constrained in commissioning as we were waiting for services,” he says. As well as supplying the power, these 66kV lines will also export power to the grid from the centre.
The 2,300 tonne-a-day (t/d) facility is the first integrated domestic solid waste management centre in the Middle East. It comprises a separation area and three main components: a recycling plant, composting plant and the waste-to-energy (WTE) plant. The latter has a capacity of 48.4MW. The waste management centre consumes 15.4MW of power, leaving a maximum export potential of 33MW.
Waste sorting in Qatar
The first step in the process is the waste sorting and separation centre. Four horizontally mounted 3.8-metre diameter steel cylinders with screens separate the waste into three fractions; waste under 45mm; waste measuring 45-300mm; and pieces more than 300mm in size. Each drum can handle 20 tonnes a hour.
The 45-300mm stream then undergoes magnetic separation to remove ferrous metals, eddy current separation to remove the non-ferrous metals and through wind sifters and infra-red radiation, and finally hand removal to take out any plastics. The recyclable metals and plastics are compressed into bales and sent to a storage area from where they are sold to recycling firms.
The waste that is larger than 300mm is sent to the bunker from where the WTE is fed. The waste under 45mm is conveyed to the 750 t/d compost plant where it undergoes anaerobic treatment. The composting process itself has three stages, the first is pre-treatment, which sees the green waste separated from the solid waste. The second is the anaerobic digestion, phase where the waste spends 14 days in a digestor, allowing bacteria present in the waste to break down the organic matter. Methane gas is a by-product of this process. This is recovered and used to power five gas engines that will produce a total of 6.8MW of power.
The third stage is the aerobic composting hall, where the compost is laid out in windrows and turned over regularly. This process takes another 14 days. After that, the compost is matured out in the open, again in wind sifters for another 14 days. Then it is sieved and bagged.
Energy recovery in Qatar
The remaining waste goes to the energy recovery centre, where it is fed into the WTE plant with its three incinerators and associated steam boilers. Each boiler has a capacity of 500 t/d and produces about 67 tonnes an hour of steam.
“Initially, we were just going to have two incineration lines of 500 t/d, with the option to exercise a third line if the volume of waste grew faster, but the government decided to bring that in early,” says Piggott.
This extended the construction period from 37 months to four years.
A new landfill site has been prepared to receive the ash. “This is fully engineered and meets strict design criteria. The ground is so hard that we could only go about 0.5m below ground level so it will end up being a hill,” says Piggott.
A total of 15 hectares has been reserved for the landfill, which has a total capacity of 2.3 million tonnes. To prevent ground contamination, the site is triple lined meeting US Environmental Protection Agency standards.
Once the centre is running at full capacity, it is estimated that less than 5 per cent of the total domestic waste produced in Qatar will be sent to landfill. Keppel Seghers expects that 37 per cent of incoming waste or 857 t/d will be suitable for composting, generating 429 t/d of compost and 255 t/d of liquid fertiliser.
A further 27 per cent of waste, or 637 t/d, will be recycled, while about 40 per cent will be incinerated, with the energy generated used to power the steam turbine to produce electricity. The collection of the waste and the operation of four new waste transfer stations remains the responsibility of the municipal authorities. The waste transfer stations are situated at Doha south, Doha west, Doha Industrial and Dukhan. A fifth is expected to be built at Al-Khor in the future.
Keppel Seghers was also awarded a QR2bn contract to operate and maintain the waste management centre for 20 years. An important feature of the project is the possibility to expand the capacity in line with population growth. Based on current growth forecasts, additional capacity could be required as soon as 2015.
“The plant is designed to be replicated and the current facilities only occupy around one third of the site,” says Piggott. “So there is lots of capacity for the future.” Under a high growth scenario, domestic waste generation is forecast to climb to 3,960 t/d by 2015.
Gulf waste model
For now, the team are working hard to achieve final handover. “The plant has been running since January 2011 and since then we have been testing, getting approvals from the relevant agencies and ensuring that all contract documentation is in place,” says Piggott.
Qatar’s waste management centre offers a model for the rest of the Middle East. GCC governments, in particular are struggling with similar challenges.
Rapid population growth has left landfill sites unable to cope with the amount of waste being generated. Abu Dhabi is currently assessing bids for a 5,000 t/d centre. In 2010, Dubai invited bids for a 6,500 t/d WTE plant, but despite 500 expressions of interest, the project appears to have stalled.
In a region where a culture of recycling has yet to catch on and where per capita waste generation is among the highest in the world, finding a sustainable waste management solution is essential.