## 1 Introduction  
Energy is a fundamental resource for all human activities, development in modern society, and sustainability. The global increase in the world's population and economic activities ultimately leads to an increase in energy demands in the coming decades, which have adverse effects and implications on the environment and ecosystem of the earth. Excessive utilization of conventional energy resources resulted in environmental pollution and degradation. To overcome these challenges, the scientific community focused on renewable energy resources that are environmentally friendly, reliable, and are vastly available. Developments and utilization of renewable energy have become common several countries in the world are investing in securing huge budgets for research and development, product development, and exploitation of energy [1]. Many developing countries like Pakistan are facing a severe energy crisis and are focusing on the utilization of available indigenous energy resources to meet the growing energy demands of the country. Pakistan's energy sector depends on the conventional methods for energy generation and imports crude oil of 14.5 US billion dollars which makes it 20% of foreign exchange for the import of fossil fuel [2]. Pakistan is enriched with solar, biomass, and wind energy resources. Biomass and bio-based energy can play a central role in the elimination of energy crisis and is an important energy resource due to its agriculture-based economy. Developed countries are utilizing waste in energy systems for energy production, although developing countries like Pakistan lack the appropriate methodology and execution of biomass as an alternative energy resource. The majority of the world's population lives in rural areas of developing countries they have limited access to fossil fuels and therefore use biomass directly for space heating and cooking purposes [3]. Bioenergy generation resources include crop residues, forest residues, municipal solid waste, sewage sludge, food processing waste, and animal waste. Pakistan's total land constitutes 60% of agricultural land, and the main agricultural crops include wheat, sugarcane, cotton, maize, and rice; these crops generate residues that are utilized for bioenergy production. Bioenergy production from crop residues is either through thermal conversion technologies (combustion, pyrolysis, and gasification) or through biochemical conversion technologies (anaerobic digestion or co-digestion, fermentation, and transesterification). The anaerobic digestion process degrades the organic substrate into two products, biogas and digestate, Anaerobic co-digestion from organic waste and other feedstock through digestion of two or more substrates [4]. Anaerobic Co-digestion has several advantages like improved nutrient balance, methane production, and increases organic diversion and system economics [4; 5]. Biogas production through anaerobic digestion is challenging due to the complex structure of lignocellulosic residues. Lignocellulosic crop residues have a complex structure composed of cellulose (23-32%), hemicellulose (38-50%), and lignin (10-25%). Lignin is a major component of such crops, and it endows the structural support impermeability and resists the microbial attack, and is recalcitrant to digest by microbes for renewable biochemical conversion [6]. During anaerobic digestion of lignocellulosic agricultural residues lignin inhibits the methanogenic bacteria to produce methane, whereas cellulose plays a vital role in the production of methane so, to enhance enzyme accessibility to cellulose pretreatment is required, which could reduce the cellulose crystallinity, degrade lignin, and hemicellulose and increase surface area or porosity so more bacteria could adhere to produce maximum biomethane. To overcome this challenge, lignocellulosic residues are pretreated and is co-digested with other feedstock.