* India pushing to improve sanitation infrastructure (Adds details of the deal): HONG KONG (Reuters) - Private equity firm KKR & Co (KKR.N) said it will acquire a 60 percent stake in India’s Ramky Enviro Engineers Ltd (REEL) for $530 million, adding it was one of India’s largest buyouts. KKR will buy the stake via a combination of primary and secondary investments, in a deal that gives the waste management company an enterprise value of $925 million.