1. School of Environmental Science and Engineering Shaanxi University of Science & Technology Xi'an 710021 P.R. China
2. Dipartimento di Ingegneria Università degli Studi di Palermo Viale delle Scienze, Ed. 6 Palermo 90128 Italy
3. Department of Chemical Engineering Taiyuan University of Technology Taiyuan 030024 P.R. China