Lignocellulosic waste is one of the most abundant and potential feedstocks for anaerobic digestion (AD), but the energy efficiency is limited by the lignocellulosic composition which is recalcitrant to biodegradation. Pre- treatment of feedstock and the post-treatment of biogas and digestate play a significant role in enhancing the AD efficiency as well as the product utilisation. This study aims to determine the cost-optimal pre-and post- treatment pathway for an AD of lignocellulosic waste by applying P-graph. The economic balance between the main operating cost, yield and quality of products were considered. The treatment options were overviewed followed by a case study considered a different combination of physical, chemical and biological pre- treatments, biogas post-treatment (combine heat and power, fuel cell, biomethane, biofuel) and digestate treatments. A total of 9 pre-treatments for lignocellulosic waste, 2 digestate post-treatments and 9 post- treatments for biogas were evaluated in this study. Chemical pre-treatment by CaO, post-treatment by H2S removal with membrane separation for biomethane production and without the composting of digestate is suggested as the optimal treatment pathway for lignocellulosic waste.