Potential use of bamboo resources in energy value‐added conversion technology and energy systems

Bamboo has been identified as a promising solution to the energy crisis and climate change as a source of biomass energy. Due to its rapid growth and high‐value products, bamboo is considered as a potential source of biomass energy. Bamboo contains a significant amount of cellulose and hemicellulose, which can be converted to sugar constituents, making it an ideal raw material for energy production. This article reviews the different processes of producing bioethanol, biogas, biochar, and bio‐oil from bamboo biomass using techniques such as pyrolysis, hydrothermal liquefaction, fermentation, and anaerobic digestion, and discusses the opportunities and challenges of these conversion technologies. It also reviews the main types and morphological characteristics of energy bamboo species and proposes an evaluation system for energy bamboo species, which optimizes the utilization efficiency of bamboo biomass energy and maximizes benefits by adopting appropriate methods for producing bioenergy based on the characteristics of different bamboo species.


| INTRODUCTION
The overconsumption of traditional fossil fuels has led to serious problems of climate change and environmental pollution. Therefore, developing environmentally friendly renewable energy to replace fossil fuels is an effective solution to address clean energy supply. Renewable and clean lignocellulosic biomass from wood can be a substitute for carbon-neutral sustainable energy. Bamboo, due to its fast growth rate, commercial value, and sustainability, has become a promising alternative biomass resource (Sharma et al., 2018). In recent years, the proportion of renewable energy generation globally has increased significantly, from 23.2% in 2018 to 29% in 2020 (Cozzi et al., 2020). Bamboo is widely distributed from north to south within latitude 40° and China, Brazil, and India account for 60% of the world's bamboo forests (Emamverdian et al., 2020). As a potential strategic resource, bamboo is protected and developed in many countries in Southeast Asia, Africa, and South America (Chin et al., 2017;Shah et al., 2021;Tsegaye et al., 2020). China has the most bamboo species, over 500, with Moso bamboo accounting for 72.96% of the total area (Gu et al., 2019).
As one of the most abundant plants growing in tropical and subtropical regions, bamboo provides both aesthetic and intrinsic forest functions (Bhelkar et al., 2019). Bamboo absorbs carbon dioxide and releases 30% more oxygen into the atmosphere than its wood biomass, but increasing bamboo forests entail loss of species diversity and destruction of forest ecosystems (Mulabagal et al., 2017;Yang et al., 2015). Therefore, the adoption of short-term rotation harvesting in bamboo forests offers a dual benefit of maintaining ecosystem stability and facilitating the profitable extraction of significant quantities of bamboo wood Wi et al., 2017).
The lignocellulosic component in bamboo accounts for over 70% of its composition, and this difference is not significant among different bamboo species (Sharma et al., 2011). The lignocellulose content in Moso bamboo can reach up to 78%, making it a natural source of lignocellulosic biomass (Luo, 2013). Bamboo can be converted into energy through various pathways, such as acid-base pretreatment , biodegradation Zhan et al., 2022), and steam explosion (Dai et al., 2022). Through appropriate processing, bamboo lignocellulose can be transformed into alcohol (Huang, Yang, et al., 2020;Huang, Zhan, et al., 2020), biogas , glucose , and bio-oil (Zhuang et al., 2023). In accordance with  and , the pyrolysis parameters demonstrate a significant correlation with the pyrolysis behavior, volatile evolution, and product composition of cellulose, hemicellulose, and lignin within biomass. The pyrolytic process induces alterations in chemical bonding and material structure, giving rise to distinct product parameters obtained from these three distinct biomass fractions. In recent years, bamboo biomass has received increasing attention because it has the potential to become a solid fuel alternative to wood and charcoal in industry (Saha et al., 2022).
To our knowledge, although there is a large amount of literature related to the use of bamboo for biofuel production, there is no dedicated paper summarizing the energy potential of different bamboo species. At the same time, there is a lack of comparison of different technologies and the impact of bamboo species on bioenergy production. Therefore, this review aims to summarize the biochemical composition of some bamboo species, describe the utilization pathways of bamboo, and introduce the potential and advantages of bamboo as a sustainable bioenergy raw material. In addition, different types of bioenergy produced from bamboo through various conversion methods are summarized, and an energy bamboo species assessment system is reviewed.

| Differences in morphological characteristics and biochemical composition among bamboo species
Bamboo is generally classified into two categories: woody and herbaceous, with biomass from woody bamboo being the primary raw material source for processing. Among the energy bamboo species, Bambusa, Dendrocalamus, Phyllostachys, and few genera are commonly utilized. The morphological characteristics indicate their ability of these species to produce a single bamboo biomass (Table 1).
The morphological characteristics, physiological traits, and biochemical composition of bamboo exhibit significant diversity as shown in Table 2. Woody bamboos, in particular, contain over 70% lignocellulose, which has a substantial impact on their processing. Additionally, bamboo species differ greatly in their photosynthetic properties, with Sympodial Bamboo exhibiting the highest rates, followed by Monopodial Bamboo and Mixed Bamboo (Lv et al., 2021).

| Utilization of bamboo as a raw material for bioenergy production
As shown in Figure 1, bamboo can be transformed into four different energy forms through various conversion technologies, namely bioethanol, bio-oil, biogas, and biochar. Due to its high lignocellulose content, bamboo is well suited for bioethanol production, which involves pretreatment followed by hydrolysis and fermentation. Bamboo can also be converted into bio-oil T A B L E 1 Morphological characteristics of energy bamboo species (Zhou et al., 2006).

| Bioethanol
Bamboo is an attractive feedstock for the production of bioethanol, as it is a non-food crop and contains a high lignocellulose content, which makes it a promising source of second-generation biofuels (Sumardiono et al., 2022). However, due to its natural resistance and high lignocellulose content, additional pretreatment steps are required to make the bamboo biomass more digestible, which can reduce the economic feasibility of second-generation bioethanol. The conversion efficiency of lignocellulosic biomass is influenced by lignin content, cellulose, hemicellulose linkages, and crystalline structure, which all affect biomass digestibility. The process of producing bioethanol from lignocellulosic biomass consists of three stages: pretreatment, enzymatic hydrolysis, and fermentation. Pretreatment is essential as it disrupts the crystalline structure of lignocellulose, removes lignin and hemicellulose, and increases the contact area of cellulase on the cellulose surface. Enzymatic hydrolysis converts cellulose into fermentable sugars, such as glucose, using cellulase, followed by the use of various microorganisms to ferment glucose into ethanol (Vélez-mercado et al., 2021). Unlike traditional methods of bioethanol production from starch, bioethanol production from bamboo relies on culms containing high lignocellulose, and pretreatment facilitates the breakdown of the cell wall matrix and lignocellulose. Choosing the right pretreatment method can reduce costs, produce a carbohydrate-rich processing product, and have minimal environmental impact . Table 3 presents recently published literature related to bamboo pretreatment and ethanol production. Currently, bamboo is being used as a raw material for large-scale ethanol production in several countries. For example, the Numaligarh Refinery in Assam, India, reportedly utilizes around 500,000 tons of fresh bamboo annually to produce biomass products, with bioethanol production reaching up to 49,000 tons. The residue waste after production can be burned as a source of electricity (NRL, 2020-21). Figure 2 illustrates the primary process of converting bamboo into bioethanol. The lignocellulose structure is first pretreated to obtain cellulose, which is then hydrolyzed into glucose by enzymes. Microorganisms then degrade glucose as a substrate to convert it into pyruvate, which is decarboxylated to produce acetaldehyde. Finally, acetaldehyde is dehydrogenated to produce ethanol. Cellulose accumulation directly affects ethanol production efficiency; therefore, fast-growing bamboo with high cellulose and hemicellulose content is an effective way for increasing bioethanol production (Kumar et al., 2017).
The pretreatment step is a critical stage in the conversion of bamboo biomass to bioethanol, significantly impacting the subsequent enzymatic hydrolysis. The conversion of lignocellulose to ethanol requires both saccharification and fermentation, with chemical and enzymatic hydrolysis being the conventional methods of hydrolysis. Enzymatic saccharification, which is accelerated by cellulase, has the advantages of high yield and low by-products (Ying et al., 2023). It should be emphasized that in the enzymatic hydrolysis of bamboo biomass, the enzyme activity of xylanase is very important because the bamboo has a high xylan content. For this reason, the advantage of enzymatic hydrolysis process is enhanced by the addition of xylanase (Jin et al., 2019). However, the high cost of the enzyme and difficulties in controlling the enzyme amount can limit its use, and fermentation may be inhibited when the enzyme concentration is too high (Raj et al., 2022).
Chemical hydrolysis is generally more sensitive to temperature and reaction time requirements (Li et al., 2008). Huang et al. (2022) improved the enzymatic yield of dextran and xylan to 59.08% and 88.53%, respectively, after 48 hours of hydrolysis of alkali-pretreated N. affinis using a two-step hydrolysis approach with sulfuric acid and enzymes at 20 FPU/g and 150 U/g of cellulase and xylanase, respectively.
Fermentation is the bioprocess that converts glucose and xylose as the primary substrates into bioalcohols, and it is typically carried out by bacteria and fungi such as Saccharomyces cerevisiae (Yuan et al., 2020), S. clostridia (Kumar et al., 2017), S. klebsiella (Dai et al., 2022), and Bacillus subtilis . The choice of fermentation process is a critical step in connecting hydrolysis and fermentation and involves separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), simultaneous saccharification and co-fermentation (SSCF), and consolidated bioprocessing (CBP) (Singh et al., 2022). In SHF, hydrolysis is carried out separately from fermentation, and the hydrolyzed sugars are fermented in separate units. SSF is more efficient than SHF because hydrolysis and fermentation occur simultaneously, and high concentrations of sugars do not inhibit fermentation. SSCF aims to co-ferment pentoses and hexoses, with cellulose and hemicellulose mixed in with the sugars for fermentation. CBP is a potential low-cost route for industrial bioethanol production, and compared to SHF and SSF, it could minimize the pretreatment step of lignocellulose due to differences in hydrolysis and fermentation temperatures (Raj et al., 2022).
Various hydrolysis and fermentation methods have been investigated for bamboo conversion (Huang, Yang, et al., 2020;Huang, Zhan, et al., 2020;Song et al., 2020Song et al., , 2022. Song et al. (2020) compared the performance of simultaneous saccharification and fermentation (SSF) and separate hydrolysis and fermentation (SHF) for hydrogen peroxide and glacial-acetic acid pretreated bamboo, and reported a slightly higher ethanol yield in SSF (80.3%) than SHF (78.0%). In another study, Song et al. (2022) improved the bioethanol yield by 13% using a sequential fermentation method of S. cerevisiae and Scheffersomyces stipites yeast. Huang, Yang, et al. (2020) and Huang, Zhan, et al. (2020) utilized SSF with alkaline peroxide pretreatment and achieved up to 95.75% xylose metabolism and a maximum ethanol yield of 86.14% using S. cerevisiae and Pichia stipites. Yuan et al. (2020) achieved a 68.9% ethanol recovery after 72 h fermentation of enzymatic products from bamboo using S. cerevisiae Lg8-1 at 35°C.
The high lignocellulose content of bamboo suggests its great potential for bioethanol production. However, in practice, the cost of pretreatment and fermentation processes accounts for the majority of the expenses (Usmani et al., 2021). Commercial pretreatment must meet several criteria, including minimal or no inhibitor formation, minimal water and energy requirements, etc. (Singh et al., 2022). It is difficult for small-scale bamboo bioethanol production processes to meet the requirements of industrial production. Therefore, further research is needed to develop bamboo bioethanol production technology, improve the efficiency of pretreatment and fermentation processes, and optimize the separation methods to fully utilize bamboo biomass (Singh et al., 2022).

| Solid biofuel
The utilization of bamboo biomass for solid biofuel production has received considerable attention in the industry, as summarized in Table 4.
Bamboo solid fuels represent an important alternative to address the challenge of coal shortage. The use of bamboo-based biomass for solid fuel combustion offers more advantages from an environmental perspective compared to other woody plants. This has been confirmed by a life cycle assessment conducted by Partey et al. (2017), based on bamboo, teak, and acacia, who found that the total ecological cost of 1 MJ charcoal production using B. balcooa was 40% and 13% lower than Tectona grandis and Acacia auriculiformis, respectively. Additionally, the activation energy of bamboo solid fuels is low compared to other biomass solid fuels, especially after heat treatment . Notably, the proportion of cellular components in the same bamboo species varies depending on the growth conditions and age of the bamboo, which significantly affects the function and properties of bamboo biofuels (Azeez & Orege, 2018).
Torrefaction, which is a type of pyrolysis process conducted at temperatures between 200 and 300°C, and carbonization are pyrolysis techniques commonly used to convert raw bamboo into high-value biochar. In these processes, the raw bamboo material is heated in the absence of air to produce charcoal, bio-oil, and bio-gas (Adeniyi et al., 2022). The combustion characteristics of bamboo charcoal are significantly influenced by the pyrolysis temperature . Researchers have shown that torrefaction and carbonization are effective ways to increase the calorific value of bamboo biomass. Both Bada et al. (2018) and Makwarela et al. (2017) demonstrated that torrefaction and carbonization can increase the calorific value of B. balcooa from 18-20 MJ/kg to 28-30 MJ/kg. Similarly, Saha et al. (2022) increased the calorific value of Gigantochloa scortechinii from 17.8 MJ/kg to 25.6 MJ/ kg through torrefaction.
Hydrothermal carbonization (HTC) treatment of bamboo residue biofuel has been found to exhibit higher combustion reactivity compared to wet torrefaction and dry torrefaction, while dry torrefaction offers better energy efficiency and yield (Yan et al., 2017;Zhang et al., 2018). Moreover, the physical properties of bamboo solid fuels, such as water absorption, durability, fineness, total calorific value, combustion rate, and exothermic rate, increase with increasing carbonization temperature, and the resulting carbonized pellets meet the minimum requirements of DIN 51731 (>17,500 J/g) for commercial pellets (Liu et al., 2013). However, it is worth noting that the average energy consumption of wood pellets during the pelletizing process is higher than that of straw pellets, necessitating longer pretreatment times or more efficient pretreatment steps. To address this issue, co-pelletizing bamboo and straw have been suggested to reduce energy consumption, and adding wheat straw pellets to bamboo blocks can increase the calorific value (Lu et al., 2014).
The combustion behavior of bamboo can be characterized using thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTA). For B. balcooa, the combustion process can be divided into three stages. The first stage (25-140°C) involves the precipitation of water, oxidation of organic matter, and the first peak, resulting in a weight loss rate of about 5%-10%. The second stage (142-200°C) is the main combustion stage and is where the initiation temperature of volatiles (IT vm) is located, resulting in a weight loss rate of about 90%. The third stage (above 400°C) is the final combustion stage where there is a slight decrease in weight and decomposition of inorganic salts. Compared to coal, which has a peak temperature of 406°C, B. balcooa has a lower peak temperature of 224-250°C and a faster burning rate due to the lower fixed carbon content of raw bamboo (Bada et al., 2015;Makwarela et al., 2017). The temperature ranges for the burning stages of different bamboo species were found to be slightly varied. Biswas et al. (2022) studied seven economically important bamboo species in India and reported three burning stages at 25-150 °C, 250-300 °C, and 300-350 °C, with a maximum decomposition temperature between 320 and 347°C. Zhang, Deng, et al. (2020) and Zhang, Jin, et al. (2020) observed the second burning stage of bamboo at 235°C, when cellulose and hemicellulose decompose, and the maximum decomposition temperature was found to be 360°C. Adeniyi et al. (2022) investigated the pyrolysis of B. vulgaris and found that cellulose pyrolysis occurred between 300 and 450°C and hemicellulose pyrolysis between 200 and 300°C.
The significant increase in the higher calorific value of bamboo after carbonization and torrefaction may have a positive impact on the synergistic effects of bamboo char mixed combustion and co-pyrolysis with other materials, as summarized in Table 5. Co-combustion of bamboo and coal is a common fuel type that reduces CO 2 emissions. However, the interaction between coal and bamboo charcoal during co-combustion is still debated and may depend on material properties and reaction conditions . Moreover, the addition of bamboo charcoal improves the co-combustion properties of coal, resulting in lower burnout and ignition temperatures of both fuels as the bamboo content increases to a certain percentage, as well as shorter peaks and ignition delay durations compared to coal alone (Bada et al., 2015(Bada et al., , 2018Makwarela et al., 2017). Additionally, co-firing bamboo with sludge increases the rate of degradation of sludge residues .
The primary distinction between co-pyrolysis and co-combustion lies in the reaction environment, with pyrolysis usually occurring under anaerobic conditions. Co-pyrolysis of bamboo and plastics has garnered significant interest (Alam et al., 2021;Alam & Peela, 2022;Hou et al., 2022;Yao & Ma, 2018). Alam et al. (2021) investigated the co-pyrolysis capabilities of bamboo sawdust with linear low-density polyethylene and found that the addition of bamboo sawdust accelerated plastic decomposition and enhanced the co-combustion process. Hou et al. (2022) copyrolyzed disposable masks with bamboo residue and observed synergistic effects. They attributed the mechanism underlying this synergy to the reaction between small molecular compounds (propyl, isopropyl, hexyl, isoamyl, and neo-butyl) produced during plastic pyrolysis and bamboo or its pyrolysis volatiles in the high-temperature zone (>400°C). The coke and tar formed during bamboo decomposition likely have a catalytic effect on plastic residue degradation, and the pyrolysis temperature of lignin in the high-temperature zone is higher than that of plastic chemical components, increasing the reaction intensity. Bamboo and plastic biofuels' outstanding performance could be an essential method for current plastic treatment.
Co-pyrolysis of bamboo with various materials for producing solid fuels has shown great potential, with studies demonstrating the value of combining bamboo with pigeon pea stalks (Sahoo et al., 2021), soapstock , and rice husk (Zhang, Deng, et al., 2020;Zhang, Jin, et al., 2020) to produce solid fuels with high calorific and physical properties. The use of bamboo-based solid fuels not only simplifies the co-combustion process with other materials but also improves fuel combustion performance. In comparison to other biomass sources that primarily rely on lipids for energy, such as microalgae (Ye et al., 2020), production of bamboo biomass solid fuels does not contribute to NOx pollution. Therefore, it is reasonable to expect that bamboo-based solid fuels have tremendous potential for development.

| Biogas and bio-oil
Pyrolysis is a process that can produce three-phase products, namely biochar, bio-oil, and bio-gas, which are classified into fast pyrolysis, slow pyrolysis, and flash pyrolysis based on the different heating rates and residence times (Qin & Yuan, 2023). Slow pyrolysis produces higher yields of biochar compared to fast pyrolysis and flash pyrolysis, while high yields of bio-oil and biogas are associated with fast pyrolysis and flash pyrolysis. The properties and yield of the pyrolysis products are influenced by various parameters, including reaction temperature, reaction environment, reaction time, feedstock loading, heating rate, and catalyst. Chen et al. (2014) used moso bamboo as feedstock and produced a three-phase product through slow pyrolysis. Their findings showed that the heating rate had little effect on the pH and viscosity of the bio-oil, but faster heating rate helped to increase the biogas yield and reduce the moisture content in the bio-oil. In addition to the impact of technology, the age of bamboo also significantly affected bio-oil production. By comparing Pseudosasa amabilis and Pleioblastus chino at different ages after pyrolysis, Cheng et al. (2015) found that the viscosity of 3-year-old bamboo was higher than that of 1-and 2-year-old bamboo, and the bio-oil sugar abundance increased with increasing age. However, the ratio of ketone and aldehyde abundance to cellulose content in biomass decreased, suggesting that 1-year-old bamboo possessed good biomass properties for bio-oil production.
Co-pyrolysis of bamboo with other materials, such as microalgae and plastics, has shown potential for bio-oil Co-pyrolysis of bamboo and heavy bio-oil had synergistic effects in the preparation of biochar  Bamboo residues Sewage sludge N 2 Co-pyrolysis of sewage sludge with bamboo sawdust at 700°C produced highly stable biochar Zhang, Jin, et al. (2020) and biogas production. In China, bamboo co-pyrolyzed with brewery waste can yield syngas containing various organic compounds, with a biomass conversion rate of 60% . Similarly, co-pyrolysis with microalgae has been shown to improve the quality of bamboo bio-oil, with an increased yield of long-chain fatty acids and reduced levels of acetic acid, oxygenates, and phenols . Pyrolysis of lignocellulosic materials like bamboo can lead to cross-linking reactions, resulting in a complex bio-oil composition that is rich in acetic acid and nitrogenous compounds, and low in phenolic and polycyclic aromatic hydrocarbons (Dong et al., 2021;Kato et al., 2014). To overcome the limitations of traditional pyrolysis methods, microwave-assisted pyrolysis (MAP) has emerged as a promising heating method due to its ability to provide uniform heating, easy product control, and high penetration. Giorcelli et al. (2021) explained the MAP degradation mechanism of bamboo, which involves direct dehydration of cellulose and formation of dehydrated sugars, as well as the important role of xylan in hemicellulose degradation. Furthermore, during pyrolysis, some lipids and proteins in bamboo undergo a Maillard reaction with carbohydrates, producing a variety of nitrogenous compounds. Hydrothermal liquefaction (HTL) is a straightforward method for producing bio-oil, in which water serves as both solvent and catalyst to depolymerize biomass into bio-oil in a subcritical or supercritical state (Knez et al., 2018). Similar to other thermal treatments, HTL product distribution is mainly influenced by process parameters (Mishra et al., 2022). Typically, HTL parameters are set at 250-400°C and pressure at 10-35 MPa (Castello et al., 2018). Chang et al. (2016) produced bio-oil from waste bamboo chopsticks with K 2 CO 3 as a catalyst and found that the bio-oil yield was only 21.2 wt % at 290°C, which decreased with increasing temperature due to the decomposition of light components into gaseous products. However, few studies have been conducted on the production of bamboo bio-oil via HTL, primarily because of the low solubility of lignin in pure water, which limits its commercial potential. Nevertheless, the solubility of lignin can be improved by appropriate treatments such as acids, bases, organic solvents, and other means . Recently, green solvents such as ionic liquids, deep eutectic solvents, organic carbonates, and water have been reported as feasible options for lignin extraction, contributing to sustainable development goals due to their non-toxic, non-volatile, recyclable, and biodegradable characteristics . Pyrolysis and HTL are the two primary processing options for bio-oil production. However, for bamboo, pyrolysis is currently the more efficient method for converting lignocellulose into bio-oil, although HTL is more economically advantageous and environmentally friendly, but low solubility of lignin in water remains a primary hindrance (Lee et al., 2023).
Biomass gasification has gained increasing attention as a green technology for converting biomass into syngas (H 2 , CH 4 , CO, CO 2 ) using a gasifier (air, oxygen, steam). Among different gasification technologies, steam gasification is more costly than air gasification, but it yields a higher calorific value and reduces tar production (Upadhyay et al., 2020). Zheng et al. (2016) compared the gasification performance of bamboo and polyethylene under steam conditions and found that the highest quality syngas and calorific value of 6.22 MJ/Nm 3 were achieved at 700°C for bamboo, while polyethylene required a higher temperature to yield high-quality syngas. The study also revealed that increasing the steam ratio increased H 2 yield and decreased CO yield for bamboo gasification. Additionally, in a circulating fluidized bed system, a co-mixture of bamboo and rice husk achieved a gas yield of 1.75 Nm 3 /kg and a calorific value of 5.39 MJ/Nm 3 at 800°C (Cao et al., 2022). However, co-gasification of lignocellulose with algae is not yet suitable for large-scale commercialization, as evidenced by the findings of Felix et al. (2022) and Mishra et al. (2023).
Bamboo gasification has become a popular research area for Indian scientists. Kakati et al. (2022) conducted bamboo gasification experiments in a downdraft gasifier under air-steam conditions. Their findings showed that the maximum hydrogen production and lower heating value (LHV) were 37.12% and 5.94 MJ/Nm 3 , respectively, at a steam-to-biomass ratio of 0.35. This is sufficient to generate electricity that can meet 17.37% of the energy consumption in Northeast India. In a separate study, Gopan et al. (2022) used modeling to predict syngas concentration for six bamboo species (B. balcooa, Chimonobambusa callosa Munro, B. vulgaris cv. Wamin, Oxytenanthera albociliata Munro, and Dendrocalamus longispathus Kurz.) under gasification treatment. All bamboo species demonstrated favorable gasification results with slight variations, yielding syngas with good composition at an equivalence ratio of 0.35. For all bamboos, H 2 and CO accounted for over 24% and 25.5% of the syngas, respectively, while CH 4 accounted for the highest concentration of 2.8% in B. vulgaris. Table 6 summarizes the heat treatment of bamboo biomass to produce bio-oil and biogas.
Methane production from bamboo biomass has also been investigated using steam explosion. Kobayashi et al. (2004) demonstrated that steam explosion of bamboo at a pressure of 3.53 MPa and steaming time of 5 min resulted in methane production of 215 mL per gram of biomass. Additionally, bamboo shoot shells have been studied for methane production through biological treatment. Fang et al. (2020) observed a 162.9% increase in methane production after a combined treatment of bamboo shoot T A B L E 6 Review of the heat treatment of bamboo for bio-oil and biogas production. Species  Kakati et al. (2022) shells using microwave radiation and fungal metabolism, which was higher than using microwave or fungal treatment alone.

| Bamboo biomass estimation
The selection of appropriate bamboo species is critical since bamboo production per unit area varies substantially among species (Pathak et al., 2015). Unlike woody trees, bamboo has a unique hollow structure, making wood volume conversion methods inapplicable. Furthermore, there is no generic biomass estimation model that can be universally applied to many bamboo species due to differences in growth behavior, clump characteristics, and culm ages (Petersson et al., 2012;Soares & Tomé, 2004).
The allometric growth model is commonly used to simulate single plant biomass for different bamboo species in various regions. The power function is the most robust equation used to estimate the above-ground biomass of most bamboo species due to its versatility (Liao et al., 2016;Nath et al., 2018;Ouyang et al., 2022). However, for some bamboo species, the power function may not be the best predictor of biomass correlation Singnar et al., 2017). Volume measurements may be a more accurate predictor of biomass than culm diameter or height, which can assist managers in decision-making (Nath et al., 2018;Singnar et al., 2017).

| Energy bamboo species evaluation system
The Energy Bamboo Species Evaluation System (EBSES) is a comprehensive and systematic approach for assessing the feasibility and benefits of using bamboo as a biomass energy source (Table 7). It was first proposed by Wu et al. (2013) and uses the analytic hierarchy process (AHP) to conduct a comprehensive evaluation of nine bamboo species in China. The index system has three levels and 20 specific indicators, including growth characteristics, chemical composition, production costs, energy conversion potential, and environmental benefits of bamboo as a renewable energy source.
The EBSES provides a structured framework for policymakers to evaluate the potential of bamboo as a sustainable energy source, taking into account various factors such as biomass production, feedstock availability, and the overall economic and environmental impacts of bamboo bioenergy systems. The methodology has been utilized in many studies to assess the suitability of bamboo as a renewable energy source and has proven to be an effective tool for guiding policy and investment decisions related to sustainable bioenergy systems development.
The evaluation of energy bamboo species is essential to determine the most suitable bamboo species for energy production. However, the EBSES has its limitations and requires further improvement. One of the main limitations is that the evaluation results heavily rely on expert opinions, which may introduce subjectivity and bias. To address this issue, future studies could incorporate more objective and quantitative data in the evaluation process. Additionally, the indicator system could be refined to better reflect the unique characteristics of different bamboo species and their suitability for specific energy conversion technologies.

PROSPECTS
This paper provides an overview of the potential use of bamboo resources in energy value-added conversion T A B L E 7 Framework and weights of comprehensive evaluation index system of energy bamboo species (Wu et al., 2013).

Bamboo characteristics Indicators Weights
Growth characteristics technology and energy systems. It highlights the rapid growth of bamboo and its potential as a source of biomass energy, particularly due to its high cellulose content. The review of bioenergy products produced using different methods with bamboo suggests that biochar and bioethanol are currently the most promising targets for bamboo biomass production. The paper emphasizes the need to focus on efficient pretreatment and conversion methods, as well as selecting bamboo species with high cellulose content, to optimize the energy, environmental, and economic benefits of bamboo biomass utilization. The paper also presents the energy bamboo species evaluation system, which uses the AHP to comprehensively evaluate the performance of different bamboo species in terms of their potential for energy production. The evaluation system provides a useful tool for selecting the most appropriate bamboo species for different bioenergy production processes, thereby optimizing the overall efficiency of bamboo biomass energy usage. However, it is acknowledged that the evaluation system has some limitations, such as potential bias in the indicator weights determined by consulting with experts. Future research could further refine and validate the evaluation system to enhance its reliability and accuracy.
In conclusion, the paper underscores the significance of bamboo biomass utilization as a promising solution to the growing energy demand and waste disposal problem. The paper suggests that pyrolysis and fermentation methods are the most efficient conversion methods for bamboo biomass, and that future research should focus on developing more efficient and cost-effective pretreatment and conversion methods. The paper also highlights the importance of selecting the most suitable bamboo species for different bioenergy production processes. The energy bamboo species evaluation system provides a valuable tool for achieving this objective, but further research is needed to enhance its reliability and applicability.