Thesis Archive

A multi-objective multi-period model for multiple contaminant wastewater reuse networks with regeneration units and fuzzy approach (2007)

Jane Heather Dee
Miguel M. Zavalla


-In the field of environmental research, freshwater conservation is presently one of the advancing topics since this is considered as one of the scarce resources at present. Current researchers have only focused on optimal water allocation, as there is no integration of economic aspects in constructing the network and its reliability. Various graphical or conceptual approaches have been limited to applications in single contaminant wastewater streams. Furthermore, there have been no studies considering multiple periods. Thus, this study addresses the need to build a mathematical model for a multiple contaminant wastewater regeneration network under a long-term planning horizon. Fuzzy programming was also used due to uncertainty on the inlet concentration levels of processes and treatment facilities. Multiple objectives are to minimize overall cost, minimize freshwater usage, maximize reliability and maximize aspiration level.

A Mixed Integer Non-Linear Problem was formulated with freshwater sources, process units, treatment facilities and disposal sites as the nodes. Amount of water flow to allocate, piping connections, choice of material and opening or closing a treatment facility are the decisions made by the model. A heuristic was developed to obtain a logical procedure on how to solve the multiple objectives. The model was validated using GAMS DICOPT Solver, and design of experiments was performed to screen to significant factors to each response. Response surface methodology was also done to highlight the behavior of the significant parameters on the different objectives.

Results show that demand is constantly an important factor for all of the objectives. Pipe diameter and treatment costs with its capacity as well as opening cost were found to have a significant effect on overall cost. On the other hand, freshwater supply and pipe reliability affect the reliability of the entire network. Percentage of regeneration and reuse and freshwater cost affect the overall consumption of freshwater for the system.

For the network's structure, the number of pipes used as well as the number of treatment facilities opened is also analyzed. More pipes are installed when demand is high and when pipe diameter is low. On the other hand, even when demand changes its levels, the number of treatment facilities remains the same. However, it decreases when its capacity increases.


Mr. Dennis Cruz