Waves of gleaners sift the sweepings of Hanoi's streets, just as children pick over the rubbish of Maputo's main tip.

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Mr Trousdel said he agreed there were contaminants such as oils in gully sweepings, but that he believed leaves would be "perfectly acceptable".

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"We would like to find some way of testing the street sweepings so that either by directly, or after some treatment, we can take it to composting, " he said.

BBC: Berkshire councils say Environment Agency laws costly