It is Greenstar's fourth US acquisition since entering that market last March. Earlier this year it acquired Recycle Management Co, Delta Management Group and Todd Heller. Greenstar reportedly spent $50m ( 36m) acquiring Todd Heller and $20m acquiring the two earlier firms.

Former Waste Management executive Steve Ragiel is the CEO of Greenstar North America, headquartered in Houston, Texas. The company now has a network of 15 recycling facilities and will handle more than 1m tons of recyclables per year.

Sources say that gives Greenstar between 5% and 6% of the US market in just six months.

At its recent AGM, NTR chairman Tom Roche said that NTR would build Greenstar in North America by consolidating numerous mid-level players, mirroring its strategy in Ireland.

The acquisition was inked on the same day NTR's wind energy subsidiary, Airtricity, sold its North American business to German utility E.On for $1.4bn.

The deal nets about 800m for Airtricity, giving it a war chest in Europe to build on-shore and expensive off-shore wind farms, and to further explore its most audacious notion, a "Supergrid" that would connect windfarms across a huge swathe of Northern Europe and the North Sea and aggregate their generation capacity onto a single electricity grid.

However, the latter project would require collaboration with other utilities and with governments. And the price tag of one off-shore windfarm is estimated to run to 750m, meaning that Airtricity will need to raise further capital to fund extensive development.

It is understood that the sale of Airtricity North America is not the "liquidity event" promised to NTR shareholders before 2009.

A trade sale or flotation of Airtricity's European business could not be ruled out in "the middle distance", according to one source, but the plan for the moment is further investment.