Bagasse-derived hierarchical structured carbon (BDHSC) with tunable porosity and improved electrochemical performance is prepared via simple and efficient hydrothermal carbonization combined with KOH activation. Experimental results show that sewage sludge acts as a cheap and efficient structure-directing agent to regulate the morphology, adjust the porosity, and thus improve the supercapacitive performance of BDHSC. The as-resulted BDHSC exhibits an interconnected framework with high specific surface area (2296 m(2) g(-1)), high pore volume (1.34 cm(3) g(-1)), and hierarchical porosity, which offer a more favorable pathway for electrolyte penetration and transportation. Compared to the product obtained from bagasse without sewage sludge, the unique interconnected BDHSC exhibits enhanced supercapacitive performances such as higher specific capacitance (320 F g(-1)), and better rate capability (capacitance retention over 70.8% at a high current density of 50 A g(-1)). Moreover, the BDHSC-based symmetric supercapacitor delivers a maximum energy density of over 20 Wh kg(-1) at 182 W kg(-1) and presents an excellent long-term cycling stability. The developed approach in the present work can be useful not only in production of a variety of novel hierarchical structured carbon with promising applications in high-performance energy storage devices, but also in high-value utilization of biomass wastes and high-ash-content sewage sludge. (C) 2015 Elsevier B.V. All rights reserved.