Thursday, July 31, 2008

Protecting the earth from ourselves

Conceptualise this: the largest passenger airliner in the world, the Airbus A380, can haul 853 passengers and tonnes of cargo. If one were to fill three of these double-deck superjumbos to the brim, they still would not be able to carry away all the waste that Abu Dhabi residents will generate today.

The Environment Agency – Abu Dhabi (EAD) estimates that residents dump about 1,532 tonnes of household rubbish daily. While some of the junk is recycled, lorries brimming with the city’s refuse unload a vast majority of the medical, chemical, household, industrial, construction and agricultural waste at six “dumpsites” around Abu Dhabi emirate.

“A dumpsite – that’s a technical term for a much softer type of landfill that isn’t engineered,” explained Olabode Esan, the director of public sanitation for Abu Dhabi Municipality.

“There’s no containment, so the waste is just dumped in the site. But again, it’s dumped in a systematic manner, and covered with soil every day.”

At least six of the sites are now being re-evaluated by the EAD as part of efforts to revitalise what the government agency considers inadequate design. In line with it strategic plan to improve solid waste management, Abu Dhabi emirate is building two new modern “properly engineered” landfills that will be running by next year, Mr Esan said.

The six current dumpsites have no means of segregating the municipal waste so that it never comes in direct contact with the earth.

At the base of most modern landfill sites, however, a special impermeable lining above the earth prevents trash from reaching the ground. The durable, tear-proof lining system can be as much as 10 centimetres thick and might also be packed with another thicker clay lining.

The linings are meant to seal off potentially hazardous waste from the soil so that pollutants or liquid contaminants cannot seep into groundwater reservoirs.

“With a landfill, you line it and contain the rubbish and you have a proper drainage system so any leachate that is formed cannot seep out,” Mr Esan said.

The lining protects against potentially hazardous liquid runoff that might otherwise percolate through organic waste and leach into aquifers. This liquid containing dissolved contaminants is often acidic.

“Nobody knows what’s going on 10 metres below ground, as it’s a dumpsite that’s been that way for a very, very long time,” he said. “It’s not best practice, so we have to take steps to correct that.”

Mr Esan explained that with a new landfill system being built, a series of overlaying levels, as well as drainage systems to collect runoff from rainwater, would help to contain the rubbish. These layered spaces are known as “cells”, and are reburied and then covered with newer cells.

“You deposit the waste in layers and then when the cell is full, you cup it off,” he said.

Every new cell is then flattened by heavy compression machinery such as bulldozers and rollers and covered with several centimetres of soil.

Several cities are now looking towards new technologies that would allow industries to harness methane gas spewing from the heaps of rotting trash as fuel, effectively turning something foul into something much easier to digest – profits.

During the design phase for the new landfill site at Al Dhafra, Abu Dhabi Municipality explored the methane gas recovery option.

“We were monitoring the gas generation for possible use to put electricity back into the grid,” Mr Esan said. “We were looking into it as part of the design for the projects.”

For now, though, the concept may not be feasible in the capital.

“If you have an engineered landfill and if you have a very high organic content, then it’s very likely that you can produce a lot of methane from the landfill,” he said. “But when [the new landfills] were evaluated originally, the estimates of the organic content did not indicate that we were likely to get a lot of methane, so at this point in time we don’t have plans to collect gas because it’s not viable.”

Methane – a potent greenhouse gas – is said by scientists to be 21 times more harmful in its contribution to climate change than carbon dioxide. Decomposing rubbish also accounts for roughly a quarter of all man-made methane.

Landfill gas, or biogas, is a by-product of the anaerobic process that occurs when the compressed trash begins to break down.

The resulting emissions contain 50 per cent methane, which is highly flammable, with special vents in the landfill drawing in the methane gas from the area.

Rather than burn the gas, however, some companies are realising they can tap into the methane as a prime renewable energy source that could replace fossil fuels. Landfill companies in the US, for instance, extract methane and sell it to other industries in order to power boilers.

Mr Esan said the municipality may eventually move towards retrofitting landfills with methane gas collection systems if it proves viable to do so in the future.

As for rehabilitating the current dumpsites, Mr Esan said they can eventually be replaced by the new landfills, which will be in Al Dhafra and Ruwais in the Western Region. Both landfills will be in accordance with international standards and “best practices”, he added.

Green composting facilities and a new recycling sorting station are part of the drive to overhaul and modernise the emirate’s management of solid waste, at a cost of Dh1.2 billion.

“Once we have a recycling facility ready, then we’re going to change the collection systems as well and start a public awareness campaign to try to create an interest in [recycling],” he said. “It’s the next step to a system that’s much more environmentally appropriate than what we have now.”

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