Pulp and paper production consumes a large amount of water and steam. In particular, water is used in brown stock washing system (BSWS) to separate spent white liquor from the pulp stream. The wastewater stream generated from BSWS, known as black liquor, is a potential biomass. In the current practice, black liquor is concentrated and burned in a recovery boiler to produce steam and electricity. However, recent development in an integrated biorefinery offers increased marketability in pulp and paper mills through the generation of both bioproducts and bioenergy. It is common practice for steam generated from the combustion of black liquor to be integrated with pulp and paper mill to satisfy its heating demands. Note that the water consumption in BSWS directly affects the quantity and quality of black liquor. This will later affect the potential for steam generation and integration in pulp and paper mill. Thus, in this work, water and heat integration is performed for a pulp and paper mill with biorefinery. An integrated pulp and paper biorefinery (IPPB) is proposed which accounts for different conversion pathways of pulp and paper mill biomass. Apart from combustion, several gasification pathways are considered. A nonlinear program (NLP) is formulated to synthesize an optimum IPPB with maximum resources conservation. Sensitivity analysis is then carried out based on the most significant parameters to analyze the robustness of the proposed IPPB.