Italian police on Thursday placed under house arrest the owner of Europe's biggest landfill outside Rome and six others including a former regional governor as part of an investigation into illegal waste management.

Manlio Cerroni -- dubbed the "King of Waste" by the local press -- manages Malagrotta, a 250-hectare (618-acre) landfill on the outskirts of the Italian capital that has flouted environmental laws for years.

Malagrotta was supposed to have shut in 2007 in line with European rules banning open landfills but local officials had granted successive reprieves for Cerroni.

The landfill was definitively closed in October 2013.

Cerroni owns a number of waste disposal businesses and Italian press reports said he has an annual turnover of 1.0 billion euros.