Citigroup has landed its second big French M&A mandate of the week by advising Blackstone, the US private equity house, according to a source close to the deal.

Blackstone has led the buyout of the US water treatment business of Suez, the French water and energy company, having agreed to pay just over $4bn (€3.7bn) along with Goldman Sachs Capital Partners and Apollo Management, another US private equity firm.