1. School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, China; Department of Bioproducts and Biosystems Engineering, University of Minnesota, St. Paul, MN 55108 e-mail:
2. School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
3. School of Marine Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China e-mail: