* Lagos 21 million people produce 10,000 tonnes of waste daily
* Project will convert methane from garbage into electricity
* Aims to have 25 megawatt capacity in five years
By Tim Cocks
LAGOS, Oct 11 (Reuters) - One thing Nigeria's megacity of Lagos, one of the world's largest, generates in abundance is trash. Now it plans to turn that rubbish into electricity which the city desperately lacks.
The equation is simple. In one day Africa's sprawling metropolis of up to 21 million people, according to official estimates, produces more than 10,000 tonnes of waste. In the same day it will get barely a few hours of power, forcing many inhabitants to rely on diesel generators.
Yet the methane from all that rotting waste is latent power.
"Energy is in demand, waste is a headache. If Lagos is able to convert its headache to feed that demand, then it's becoming a smart city," Ola Oresanya, managing director of the Lagos Waste Management Authority (LAWMA) told Reuters at the notoriously pungent Olusosun dump site.
Oresanya aims to complete the project in around five years, by which time it will have a 25 megawatt (mw) capacity, he said. That is only 1 percent of the 2,000 - 3,000 mw that he estimates Lagosians demand, but it is a start.
Despite being Africa's top oil and gas producer, Nigeria's power output is a tenth of South Africa's for a population triple the size, a major brake on economic growth.
A pilot project to get power using methane extracted from rotting fruit has helped clean up a local plantain market and enables traders to switch off their generators when it is on, manager Tolu Adeyo said, demonstrating its power by lighting up the gas coming out of a hose connected to the project tank.
The scheme, modelled on similar ones in Norway and Sweden, is part of broader efforts to clean up a city that had become known as the 'garbage capital of the world.'
Governor Babatunde Fashola has won plaudits for sprucing up bits of Lagos that used to look like the set for a post-apocalyptic movie, clearing out rusting scrap metal and planting trees and hedges in its place.
The Olusosun dump site, spread over 100 acres (40 hectares), rising up to 25 metres high, and, in some places, extending 35 metres under the ground, has created its own geography of jagged hills and gorges formed of plastic bags, old clothes and boxes.
Hundreds of scavengers sift through the site in search of recyclables - old tyres, plastics, electronic goods. On one mound, an old woman shaded from the sun by a parasol issued instructions to a group of four workers collecting stuff for her. White herons feasted on unwanted food waste.
"There was a time when Lagos was sinking under its waste. We moved the waste, but it is still just being buried. Now waste is an asset," Oresanya said, before narrowly avoiding plunging his immaculately polished brown shoes into a puddle of filth.
He declined to put a price tag on it, but said the project is solely funded by the Lagos state government.
There are other benefits too: methane is a greenhouse gas 25 times more potent than the carbon dioxide emitted by burning it.
The site is going to be buried in dirt and a green park with grass and trees built over it, Oresanya said. Pipes in the ground will harness the methane bubbling underneath for the power plant.
"By the time we're done, you won't see a single scavenger, because there won't be anything to scavenge," he said, walking along a graded road covering a 25 metre depth of trash. (Editing by James Jukwey)