1. Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Jinan 250100, China, Tel. ; Fax:
2. Department of Mathematics and Statistics, Texas Tech University, Broadway and Boston, Lubbock, TX 79409-1042, USA
3. Shandong province environmental engineering Co., Ltd. of SAES, Jinan 250100, China,