This diploma project is a joint effort between Industrial Energy System Laboratory (LENI) of EPFL and CanmetENERGY-Varennes of Natural Resources Canada on the application of advanced process integration methods for the optimal water and energy integration in the context of Canadian pulping mills. The ultimate goal is bridging the researchers from LENI and CanmetENERGY to rethink the conventional methodologies used in combined water and energy optimization. In the context of finding efficient ways of water and energy consumption, the objective of this project is to improve a mathematical superstructure for simultaneous optimization of water and energy in industrial processes. This methodology, first developed by Renard (2011), is refined on several features in the present work. The superstructure is developed using linear programming techniques and is able to employ non-isothermal mixing options to reduce utility consumption. Multi-contaminant problems are also addressed with linear programming. The first part of this work concerns a literature review of the available methodologies on simultaneous optimization of water and energy. A benchmarking analysis is carried out to evaluate these methodologies with regard to different aspects such as mathematical approach and water and heat exchange network indicators. Secondly, non-isothermal Mixing(NIM) is tailored to be used in a linear programming environment by establishing several temperature levels in which NIM can occur at the inlet of water demands. Furthermore, the methodology is adapted to pulp and paper industry context by adding new concepts to the initial superstructure. These are water tanks and restricted matches. The superstructure is evaluated using different examples from the literature. Finally a case study using data obtained from CanmetENERGY validates the developed methodology and provides useful information on the application of this methodology in pulp and paper industry.