Private equity firm Kohlberg Kravis Roberts & Co. (NYSE: KKR) has made a $40 million investment in United Envirotech Ltd.

United Envirotech provides engineering services for municipal and industrial waste-water treatment projects, as well as operates a portfolio of waste-water treatment plants across China. The company plans to use the investment to grow its business in China.

The investment follows KKR’s agreement with the company in July 2011 to provide a $113.8 million convertible bond investment.

New York-based KKR has $66.3 billion in assets under management. Its portfolio companies include Dollar General Corp., Del Monte Foods Co. and the Nielsen Co. BV.