FORUM Reverse Problem Formulation for Integrating Process Discharges with Watersheds and Drainage Systems Managing Phosphorus in Lake Manzala Eva M. Lovelady, Amro A. El-Baz, Diaa El-Monayeri, and Mahmoud M. El-Halwagi Keywords: industrial ecology material flow analysis (MFA) reverse formulation substance flow analysis (SFA) system analysis water quality Address correspondence to: Prof. Mahmoud El-Halwagi Department of Chemical Engineering Texas A&M University College Station, TX 77843-3122 El-Halwagi@tamu.edu http://che.tamu.edu/el-halwagi/ c  2009 by Yale University DOI: 10.1111/j.1530-9290.2009.00179.x Volume 13, Number 6 Summary This work introduces a new approach to integrating the dis- charges of industrial processes with macroscopic watershed systems. The key concept is that environmental quality models (such as material flow analysis) can be inverted and included in an optimization formulation that seeks to determine the maximum allowable target for the process discharges while meeting the overall environmental requirements of the water- shed. Because of its holistic nature, this approach simultane- ously considers the effects of the inputs and outputs to the watershed (e.g., agricultural, residential, wastewater treatment plants, industrial, and so on) and the various physical, chemical, and biological phenomena occurring within the watershed. An optimization formulation is developed to systematically repre- sent the reverse problem formulation. To illustrate the effec- tiveness of this approach, a case study is solved to manage phosphorus in Bahr El-Baqar drainage system leading to Lake Manzala in Egypt. The key environmental and economic as- pects are addressed and used to screen plant location and discharges. 914 Journal of Industrial Ecology www.blackwellpublishing.com/jie