Every day on the eastern edge of this city of 18 million, hundreds of poor families rake what they can sell to recyclers from household waste dumped at their feet by a legion of freelance dustmen in battered horse-drawn carts.

With little state welfare anywhere in Latin America, trash collection and garbage dumps are sometimes a form of social safety net for the very poor who seek food and household goods others have thrown away.

An ambitious plan to bring waste management into the 21st century is highlighting the human cost of going green.

Hundreds like Santos lost their lunch after Nezahualcoyotl, a trellis of working-class neighbourhoods housing 2 million, began turning its organic waste into compost last year to ease the strain on its overflowing dumps.

Officials say the next step - replacing ugly landfills with parkland and a conveyor-belt separation plant - would reduce the amount of trash buried daily by hundreds of tons, but they also acknowledge it will force pickers off the dumps. They hope the separation plant will be built by the end of the year.

WELFARE AMONG THE WASTE

As dark orange sunlight pierced grey dawn smog in one of Nezahualcoyotl's three sprawling dumps, bundled garbage-pickers warmed their hands over a smouldering sofa before clambering into hills of freshly dumped trash.

Hooded men in makeshift dust masks flicked rope whips as their horses pulled a caravan of overloaded carts toward the stinking hills through an ocean of glinting plastic bottles.

When industrialisation drew rural migrants to Mexico City in the 1950s, Nezahualcoyotl, named after a pre-Hispanic philosopher king, was an unlighted, dirt-track dormitory slum whose residents burned their trash in the street.

Since it evolved into a bustling working-class community of two-storey houses, the 1,600 tons of trash it produces daily have put food on the tables of families the boom left behind.

"There was nothing else to do, so here we came," said 63-year-old Vicente Rodriguez, his lips parched and white under his tattered baseball cap as he raked the trash with his wife, son and daughter-in-law under the blazing afternoon sun.

"People have come to us barefoot," said Manuel Dominguez, a leader in the garbage-picker and collectors' group to which Rodriguez and his family belong. "Somehow we find them work."

The group's headquarters on the dump, complete with tattered plastic and wood-scrap stables for its horses, will be forced out when the new plant is built, authorities say.

A tinny radio chirped through the drone of flies and a dead dog's head protruded from a plastic bag as Rodriguez's 3-year-old grandson played nearby. Rodriguez knew nothing of plans to close the dump where he has worked for 18 years.

"In all honesty, there is nowhere else to work," he said, asked what else he could do. "Businesses aren't giving out jobs, even less so if you're old."

REVOLUTIONISING REFUSE

Waste disposal is a frenzied operation in Nezahualcoyotl.

Aside from trash-pickers in the dump, about 500 unofficial horse-cart drivers from groups linked to different political parties compete with lone trolley-pushers and municipal dumpster trucks for housewives' tips.

Keen to clear the streets of beasts of burden that were essential before paved roads but now clog traffic, officials are giving their owners handcarts and even workshops in environmental science to help them do their jobs.

They say some garbage-pickers will be able to work in the separation plant and are mulling allowing them to develop plant nurseries on old landfills as a source of alternative income.

"Lots of people say that to fix this you have to get rid of all these people," said Gualberto Guerrero, a public hygiene official and sociologist charged with managing the transition. "But you can do this and keep these people employed."

When pressed about the number of people who would be needed to pick through trash under the new system, however, he acknowledged: "They will be reduced by a fair amount."

Near the dump and a nearby sprawling prison, a university is under construction and officials hope the shining complex with a view of parkland will be emblematic of Nezahualcoyotl's future.

Clutching a plastic crate he hoped to sell for a peso (13 US cents) while shuffling in torn shoes and a straw hat, Juan Santos was not sure where he would fit into the dream.