Sustainable Biotransformation of Food Waste into Biogas Via Microbial Anaerobic Digestion: A Review.

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Learn more: PMC Disclaimer | PMC Copyright Notice Indian J Microbiol . 2025 Mar 11;65(2):697–712. doi: 10.1007/s12088-025-01463-2 Sustainable Biotransformation of Food Waste into Biogas Via Microbial Anaerobic Digestion: A Review Rajeev Singh 1, # , Dan Bahadur Pal 2, # , Basant Lal 3 , Tripti Singh 4 , Irfan Ahamd 5 , Abdullah Mashraqi 6 , Shafiul Haque 7, 8 , Neha Srivastava 9, 10, ✉ Author information Article notes Copyright and License information 1 Department of Environmental Science, Jamia Millia Islamia Central University, New Delhi, 110025 India 2 Department of Chemical Engineering, Harcourt Butler Technical University, Nawabganj Kanpur, Uttar Pradesh 208002 India 3 Department of Chemistry, Institute of Applied Sciences and Humanities, GLA University, Mathura, 281406 India 4 Department of Biosciences, IMS–Ghaziabad (University Courses Campus), Adhyatmik Nagar, NH-09, Ghaziabad, Uttar Pradesh 201015 India 5 Department of Clinical Laboratory Sciences, College of Applied Medical Sciences, King Khalid University, Abha, Saudi Arabia 6 Biology Department, College of Science, Jazan University, 82817 Jazan, Saudi Arabia 7 Department of Nursing, College of Nursing and Health Sciences, Jazan University, 45142 Jazan, Saudi Arabia 8 School of Medicine, Universidad Espíritu Santo, Samborondón, 091952 Ecuador 9 Department of Chemical Engineering & Technology, IIT (BHU), Varanasi, Uttar Pradesh 221005 India 10 Department of Biotechnology, Graphic Era (Deemed to Be University), Dehradun, Uttarakhand 248002 India ✉ Corresponding author. # Contributed equally. Received 2024 Jun 5; Accepted 2025 Feb 17; Issue date 2025 Jun. © Association of Microbiologists of India 2025. Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law. PMC Copyright notice PMCID: PMC12246354  PMID: 40655391 Abstract The continuous rising volume of solid waste and depletion of conventional energy reserves are important global challenges which humanity faces in twenty-first century. Food waste (FW) constitutes major (organic) fraction of solid waste in the developing nations. Therefore, the segregation of food waste and its utilization for the generation of biogas through anaerobic digestion (AD) could provide a viable solution for the global challenges. Therefore, the present review article explores the possibility of sustainable biotransformation of FW into biogas production via AD process. The present article also describes various parameters including operational parameters (pH, temperature), prominent feed stocks, their properties, effective pretreatment impact on the anaerobic digestion of food waste (FW). Additionally, the bioprocess parameters which can improve the possibility of productivity of biogas at pilot scale level has been explored and discussed. Moreover, the most critical and influencing bioprocess parameters which can affect the pilot scale productivity at economical and commercial have been attempted to explored in detail and this is the novelty of this work which impacted adoption of commercial frequency of biogas as potential bioenergy option using FW for sustainable management. Graphical Abstract Sustainable production advantages of biogas production using food waste feedstock and disadvantages of food waste release in the environment. Keywords: Food waste, Biogas, Anaerobic digestion, Fermentation, Feedstock, Bioconversion Introduction Food waste is categorized among significant portion of solid waste which produced in large quantity in day to day life and due to this reason; its management is key target to be addressed for avoiding environmental pollution [ 1 ]. Due to heavy amount production and relatively minimal management approaches, these wastes are the one of the major cause of environmental pollution and their effective settlement based remediation is on urgent settlement agenda to resolve this issue [ 2 ]. Food waste is including ~ 38% contribution of the total energy uses in the chain of food system available globally and it has been estimated that about 13% of the produced food around the globe, faces loss somewhere in between in the process of harvest and retail. Whereas, another 17% food waste occurred during the consumption level and now the FAO have provided largest online worldwide collection of data on food loss and food waste along with the cause of wastage. At global scale, the generated food waste and loss can be categorized as ~ 30% of cereals, followed by about 40–50% occurred from fruits and vegetables, while root crops shared, ~ 20% of oil seeds while meat and dairy products contributed around 35%. Additionally, the possible reason of this wastage could be different stages of harvesting, storage, transportation, processing, packaging, and marketing of food which is generally result of cold chain supply compromise in specifically in low-income countries [ 44 ]. Thus, dumping of these large amount produced wastes in open landfills cause many issues such as leaching, air pollution, and global warming and to avoid this issue certain preferable settlement of these biomasses has been applied as landfill, incineration, compositing and anaerobic digestion (AD). Among these, AD process of FW to produce biogas is most attractive and promising due to compositional background of FW and it is a part of Sustainable Development Goals 2030 of worldwide and in among agendas of many global agencies working in this area. Additionally, due to high moisture content biodegradability is very high relatively other existing organic waste. Moreover, organic matter in FW contains ~ 90% volatile solids (VS) which provides easy medium for microbial growth and biogas production. When compared to other organic waste FW has high biochemical potential (BMP) which varies around ~ 200–670 m 3 Mg −1 s.s.o. In addition to all this, FW has high [ 3 , 45 ]. Amount of carbohydrate, sugar, cellulose and hemicellulose are the potential compositions of the FW which can be effectively converted into biogas production [ 3 ]. Bioenergy generations from biowaste are among most potential and sustainable options in renewable energy sector in order to replace the fossil fuels crises and its massive harmful impact on environment. Severe air pollution, global warming and high cost of petroleum are the major disadvantages associated with fossil fuels consumptions. In contrast, sustainable bioenergy options from renewable resources like biowaste provides advantages like sustainable and clean energy at lower cost with pollution free environment [ 4 ]. Though all existing bioenergy options are preferable and add sustainable advantages in the environment, biogas production of from FW are most potential viable option which is relatively close towards the commercial applications. In addition, biogas production using FW is most frequent and desirable option of AD selected in several research studies [ 36 – 38 ]. Methane, biogas and hydrogen are the major compositional components of biogas [ 5 ]. The digestion and breakdown of these waste as feedstock is a microbial process which is compiled in four major steps as hydrolysis, acidogenesis, acetogenesis as well as methanogenesis and the detail process has been shown in Fig. 1 . Inspite of higher production of sustainable energy options, biogas from FW certainly suffers with strict a challenge which needs immediate attention for smooth flow of biogas for frequent gas production, supply and application [ 6 ]. Lack of suitable and effective pretreatment technology to remove outer layer of lignin and fix the maximum availability of cellulose for hydrolysis, incomplete substrate hydrolysis and product recovery, poor efficiency of extracellular enzymes for breakdown of the substrate and production of inhibitors are the pointed known challenges which hampers the overall process towards higher product recovery and its effective usage. These factors are collectively responsible for poor biogas volume along with the suitable microbial populations, reactors and other process parameters operations [ 7 , 39 ]. To sustainably resolve these concerns several approaches have been tried and applied by researches in which co-digestion, of substrate, their type and composition and processing are important parameters to be address. It has also been discussed in many research studies that compositional part and properties of the substrate are the key factor in biogas production technologies along with the bioprocess parameters which influence overall gas production process. Additionally, temperature, pressure, organic loading and microbial population are type of parameters which influence the biogas production in significant way [ 8 ]. Fig. 1. Open in a new tab Process overview of anaerobic digestion to produce biogas using food waste substrate Therefore, the objective of the present review is to evaluate the process efficiency of biogas production based on current research development prospective using FW feedstock along with the process parameters which have critical impact on the production process are being analyzed in the present review. The availability, process and application of biogas production from food waste has been discussed and explored in detail along with the current challenges and further future scope for lower cost frequent scale up applicability which is the novelty of this review. The Impact of Food Waste Type and Composition on the Biogas Production: Process Overview Based on cultivation preference, need, demand and consumption, FW has been divided into various category options stating from crops waste to vegetable, fruit and animal waste. It has been estimated in the year 2024, around 30% food waste generated annually and post COVID-19 pandemic have affected global food security drastically. Report based on statistical analysis received from the Food and Agriculture Organization of the United Nations (FAO) reflected that ~ 783 million populations were faced hunger issue worldwide in the year 2022. In addition, upto 2050, the global population will be reached around 9.8 billion which forced to raise the global food production around 50–70% for fulfilling the global population feed need. Nevertheless, approximately 1.3 billion tons of food is still wasted annually at global scale which represents one-third of total food production. Moreover as per information of the Global Hunger Index (2021), India ranks 101 among 116 countries in record of the year 2021 as total amount of food waste generated in India is approximately equal to the amount of food consumption in the United Kingdom. Additionally, the household waste including kitchen waste contributed in major amount in Indian system whereas, majority of the research studies were western countries oriented extensively which confirms the major research gap in this area [ 42 ]. Additionally, as per report of UNEP [ 46 ] it has been clearly mentioned that in 2022, the total food waste generation was estimated 1.05 billion tonnes which reflected 132 kg per capita followed by one-fifth of food. Moreover, 60% food waste has been estimated through kitchen based food waste while 28% food services and 12% by retail foods estimated in 2022. These all-time based data simply interpreted the sufficient availability of FW on daily basis and annually which can be efficiently used for feasible value addition. In addition to these all factors, research studies have exposed that food waste adversely affected the ecological and economic sustainability via heading towards, large carbon, water, as well as ecological footprints, developing ~ 8% greenhouse gas emissions annually worldwide which raised the annual economic losses of approximately USD 1 trillion. Thus, there is urgent need to address and balance the food loss and waste to influence the sustainability of environmental, economic and social aspect of this area. The holistic approach of this area lies to minimize the food loss, waste and maximize the value addition of generated waste which can be effectively transformed into sustainable and viable products. The food sector generally categorized into four major foods categorize: fruits, vegetables, dairy, as well as cereals [ 41 ]. General composition of FW indicated total solid (TS) and volatile solid (VS) contents of FW were in the ranges of 18.1–30.9 and 17.1–26.35, respectively reflecting its water retention 70–80% in FW and because of high moisture rate they are biodegradable wherein, their biodegradation rate is very fast [ 9 ]. For AD process and waste reuse, characterization of FW is important factor which includes organic components such as lipids, proteins, and carbohydrates (LPCH) as well as volatile fatty acids (VFA), content of total solids (TS) and volatile solids (VS), nitrogen content (N), carbon content (C), and its C/N ratio. Additionally, these characteristics and composition of FW are mainly based on their origin source and collection of the process which includes non-edible and non-usable materials, followed by agriculture and livestock part which play crucial role in AD process. Moreover, the contamination rate and air pollution chances are quite high due to high moisture content which makes its very sensitive. The other use of FW such as animal feed is at higher risk for animals due to fast spreading of diseases cause by high moisture content. Therefore, critical research studies frequencies are quite high to ensure environmental protection and to ensure food safety. Another way to handle and manage these wastes smoothly is transformation of these wastes into value added products. Due to high nutrient value like macromolecules of carbohydrates and phenols, these wastes are prominent sources of producing fertilizers and bioenergy like biogas [ 7 , 39 ]. These fraction of generated FW generally categorized in ~ 4% used as fertilizer, 12% is applied for energy generation, ~ 56% covers the landfilled while the remained 28% is used for different value addition like animal feed and bio-based material. Moreover, landfilling of FW is environmentally harmful due to methane (CH4) emissions and it was estimated as 16.9% emissions of U.S. only because of landfill and considered as the third largest contributor to methane emissions in the U.S. Additionally, when compared, methane emissions are more dangerous than carbon dioxide (CO 2 ) because of its global warming potential (GWP), which has been estimated ~ 25 times higher CO 2. Thus, the maximum transformation and value addition of FW is the necessity of the time for sustainable environment [ 47 ]. Productions of biogas via AD process of FW are intense area of research due to high organic content (OC) of FW which accelerate the microbial growth over it [ 40 ]. The process FW conversion into biogas has been mediated by following four steps like hydrolysis, acidogenesis, acetogenesis and methanogenesis which generally follow the step braking down macromolecules into smaller one and further converting them into biogas by microbial mode [ 10 ]. The microbial populations involved in this process are generally functioning in syntropy mode under facultative conditions. In the complete digestion process of OC, the complex molecules are firstly converted into soluble simple molecules by microbial enzymes which are generally adsorbed by the solid surface and make this step become rate limiting step in AD process. The small molecule generated via following multistep process to produce biogas as well as inhibitors. Based on microbial growth, type and proliferation on FW, the process of AD may vary with amount of production of biogas which is generally mixture of around 50–75% methane (CH 4 ), approximately 30–40% and around carbon dioxide (CO 2 ) along with production of minor gases such as H 2 S, H 2 and O 2 . The production of gases mainly depend on the functional efficiency of microorganisms involve in the AD process and acid and methane producing microorganisms are the main contributing player of AD process [ 11 ]. Methanogens are strong anaerobic microbial process which transformed OC into methane, carbon dioxide and many short-chain fatty acids, alcohols with CO, CO 2 , and H 2 into methane (CH 4 ). Additionally, the transformation of these compounds occurred through many process like acetoclastic, methanogenesis which also release many complex intermediates products like volatile fatty acids (VFAs). The entire AD process is full of complexity and needs stable environment to switch from one phase to another. Additionally, production of biogas is also depends on the different bioprocess parameters which influence the overall digestion process such as type and content of substrate used and its pretreatment strategies. In addition, composition of substrate and its ratio, along with C/N ratio (carbon to nitrogen ratio). In addition with this, temperature, pH, hydrulitic retention time and reactor shape and design also play important role which need to be explore in detail and in depth understanding is necessary for the process improvement [ 12 ]. Microbial Mechanism and Role of Genetic Engineering in AD Process The four stages carried out systematically in AD process include the chemical reactions of hydrolysis, acidogenesis, acetogenesis, and methanogenesis. From the mechanism and chemical perspective, hydrolysis step of feedstock includes cleavage of chemical bonds by the addition of water followed by. cations and anions reaction with water molecules continuously (Fig. 2 ). This process alters the pH of medium to break H–O bonds with slow reaction rate which limits the rate of entire process specifically in case of solid substrates (Equ 1). C 6 H 10 O 5 n + n H 2 O → n C 6 H 12 O 6 + n H 2 1 Fig. 2. Open in a new tab Microbial process mechanism of AD process using FW The Equation-1 indicated cellulosic (C 6 H 10 O 5 ) hydrolysis via water of to liberate primary product glucose (C 6 H 12 O 6 ) and byproduct H 2 in the reaction while the process is facilitated by either homogeneous or heterogeneous acids catalyst for higher production of primary product. Thereafter this reaction can further proceed in number of successive reactions to produce formic or methanoic acid (CH 2 O 2 ) hydroxymethyl furfural or 5-furfural (C 6 H 6 O 3 ) as well as levulinic or 4-oxopentanoic acid (C 5 H 8 O 3 ). These all formed intermediate compounds have several biotransformation application whereas, Equation-1 also breaks β-1, 4-glycosidic linkages during cellulosic conversion. Relating this hydrolysis stage of AD, insoluble organic compounds are converted into many other intermediate compounds by microorganisms while the soluble compounds are used with in the cells by microorganisms. It is noteworthy to mentioned here that during the hydrolysis process some category of formed small molecules products in reaction like H 2 and CH3COO can be directly used by methanogens, whereas, the large size molecules can be converted into small molecules like and thereafter VFAs. Further, in the acidogenesis step, the formed products in hydrolysis step are converted into CO 2 and H 2 via acidogenic bacteria and the CH 3 COOH is used as substrate by CH 4 -forming microorganisms. The pH of the process is increased over pH 5 by produced VFAs in the production medium whereas, production of ethanol further decreased the pH of the medium below 5 and the reaction has been indicated in Equ 2–4: C 6 H 12 O 6 ↔ 2 CH 3 CH 2 OH + 2 CO 2 2 C 6 H 12 O 6 + 2 H 2 ↔ 2 CH 3 CH 2 COOH + 2 H 2 O 3 C 6 H 12 O 6 → 3 CH 3 COOH 4 The combined and simultaneous utilization of H 2 and CH 3 COO as substrate by methanogenic bacteria. Moreover, facultative and obligate anaerobes are the most diverse microbial group in which acidogenic and acetogenic bacteria are associated. This group of bacteria can survive in both aerobic and anaerobic conditions and specifically characterized by the type of substrate they are utilizing to grow. Further, the step in the step of acetogenesis includes dehydrogenation step because acetogenic bacteria inhibited production H 2 in reaction medium. Additionally, H 2 can also be utilized by methane producing bacteria and the type of reaction has been given in Equations-5,6,7: CH 3 CH 2 COO - + 3 H 2 O ↔ CH 3 COO - + H + HCO 3 - + 3 H 2 5 C 6 H 12 O 6 + 2 H 2 O ↔ 2 CH 3 COOH + 2 CO 2 + 4 H 2 6 CH 3 CH 2 OH + 2 H 2 O ↔ CH 3 COO - + 3 H 2 + H 7 The Equations-5,6,7 show two-way reactions for liberation of H 2 . The first Equation-5 shows acids phase production of acetate and hydrogen which can be consumed by methanogenic bacteria like Methanobacterium suboxydans and Methanobacterium propionicum under symbiosis conditions. The acetogenesis stage is the major driven step to identified the actual of biogas production. In the entire AD process, reduction of CH3COO − gives nearly, 70% CH 4 while around 25% of CH3COO − and 11% H 2 are produced in the acetogenesis stage. Additionally, the VFAs breakdown occurred through obligate hydrogen-producing acetogenic microbes to release CH 3 COOH, CO 2 and H 2 . After this stage, methanogenesis is the final considered fourth stage of the AD process in which conversion of CH 3 COOH and H 2 takes place inCO 2 and CH 4 by methanogens under stricted anaerobic conditions. These methanogenic bacteria are one of the key microbes in the AD processes due to their slow growth and sensitivity towards change in environment and oxygen. One of the main advantage of this group of bacteria is that they can digest simplest substrates and Methanobrevibacter ruminantium , M. bryantic and M. thermoautotrophicum , Methanogenium cariaci and M. marinsnigri are the some potential examples of methanogens. etc. which reduces chemical oxygen demand (COD) or biochemical oxygen demand (BOD) by consuming organic pollutants load potentially. The reaction step is designated by Eq. 8 , 9 , 10 : CH 3 COOH → CH 4 + CO 2 8 CO 2 + 4 H 2 → CH 4 + 2 H 2 O 9 CH 3 CH 2 OH + CO 2 → CH 4 + 2 CH 3 COOH 10 Further, methane producing bacteria categorized into two groups of acetophilic as well as hydrogenophilic. Acetophilic group of methanogens are responsible for decarboxylation conversion of acetate into methane whereas, hydrogenophilic proceeds methane production by reduction of H 2 /CO 2 . Moreover, these groups of bacteria shows six different pathway of methane production in methanogenesis stage in which different substarte can be converted intoCH 4 gas while the major substarte to produce methane is acetic acid and methanoic acid carbon dioxide, dimethyl sulfate methanol and methylamine. Further, the final composition of CH 4 is generally ranges from 50 to 75%, CO 2 from 25 to 50% and H 2 S from ~ 0–3% as well as the concentration of sulfur in the substrate and nitrogen gas which often varies from 0 to10%. In all overall process of AD, the microbial population driven the process and show the braod range of spectrum from mesophilic and thermophilic categories. Additionally, many known strict anaerobic bacterial population and specifically, methanogenic archaea may able to adopt the oxidative conditions of microaerobic environments to generate oxidative enzymes (AOE) to support methane production. by Additionally in the AD process, strictd anaerobic archaea as well as facultative bacteria produce bioflocs with facultative bacteria and covers the outermost layer while archaea covered the inner core layer. Moreover, hydrolytic and fermentative bacteria having higher AOE activity may reduce reactive oxygen species (ROS), in bioflocs layer and therefore, inner-core anaerobes from any oxidative damage [ 49 ]. Further, some examples of methanogens are Methanosarcina mazei , Methanoculleus marisnigri, Methanothermobacter thermautotrophicus, Methanosarcina barkeri . The mainly followed pathway for methane production which covers around two thirds proporation is identified by acetoclastic methanogens which further reduced biogas by increasing ammonium content through hydrogenotrophic pathway. Genetic engineering tools like metagenomics have facilitated the enhancement of the biogas product as this process is culture-independent approach and involved broad range of, microbial phylogenetic and metabolic diversity in all four essential steps [ 50 , 51 ]. Thus unrevealing the microbial capacity, phylogenetic diversity, and deeper understanding of metabolic function for higher substrate utilization and to develop higher product. Metabolic engineering plays important role for enhancing AD process and development under the running capacity system [ 52 , 53 ]. In one of the investigation by Maus et al. [ 54 ], whole genome sequences of 22 bacterial as well as archaeal strains were investigated for their function under AD system in which 15 strain were identified for their function in AD process. Additionally, 7 methanogenic archaea were verified for methane production in the same system. Metagenome-assembled genomes (MAGs) has been confirmed for metagenome assembly and binning approach for identification of microbial species in AD process. Additionally, next-generation sequencing (NGS), facilitated high resolution, rapid and cost effective sequencing of several DNA at single time which improves statistical correlation analysis due to coverage of large scale database. Moreover, 16S rRNA sequencing, name as Roche 454 and Illumina chemistry are mostly used techniques in AD process while for large range sequencing techniquereversible dye terminator (RDT) is used in AD process which categorized into two category name blocked (bRDT) and unblocked (ubRDT). Better second generation sequencing based performance has been identified in bRDT while ubRDTs is more better in the sequence elongation outcomes. The core objective of NGS is to enhance performance and efficiency and make the metagenomics significant tool of microbial assemblages. Application of metagenome, genome, and post-genome tools smoother the microbial identification and classification in AD process via microbial management and engineering [ 55 ]. In gene sequencing method full length16S rRNA amplicon sequencing using the PacBio single molecule, real-time technology (SMRT) are frequently used in biogas production system. Additionally, metagenomics provides the complete microbial investigation about the structure, gene content, as well as function of microbial population in biogas system while the process acclrated further when combined with bioinformatics data [ 56 ]. Further, in various genetic engineering tools, meta-transcriptomics is another potential tool which is apply to analyze the RNA transcripts availability in microbial population and provides information about active gene expression patterns of microbial community in specific environment and thereof validates metagenomic investigations [ 57 ]. In biogas production process, meta-transcriptomics supports optimization process in AD system via assessing and documentation of the microbial process involved in AD system. Moreover this tool also reveals that Clostridium bacterial population is responsible for effective cellulose degradation at 35◦C, while the step of acidogenesis and acetogenesis is completed by Ruminococcus- bacterial population by providing detail of AD pathway. Additionally, tool of meta-transcriptomics can also be applied to determine the microbial health in AD system for smooth reaction, express the stress responses, identification of inhibitors. Therefore, meta-transcriptomics provides all detail of functional aspects of participating community in AD system during biogas production [ 58 , 59 ]. Process Parameters Influencing the AD Performances: Analysis Conversion FW into biogas via AD process is govern by different process parameters which are very sensitive and can vary significantly while slight changing in those parameters. Different process parameters have significant impact on AD process and monitoring of each process factor is important to observe and manage, since it is microbial mediate process [ 13 ]. Among various factors, temperature is important factor which directed the microbial growth, metabolism as well as fermentation process. A suitable functional temperature and its uniform maintenance are crucial to manage the process as many sensitive enzymes are involved in the anaerobic digestion process [ 14 ]. Additionally, based on temperature range the category of the functional microorganisms participating in the AD process is different and varies and mesophilic temperature range which is generally occurred at 37 °C is more preferable range of mesophilic microorganisms in AD process. This temperature range kept the fermentation smooth and productivity high in AD process [ 15 ]. Additionally, it is also possible that microbial growth temperature and fermentation temperature is different which could be due to influence of process parameters on fermentation reaction. Therefore, it is important to keep the temperature stable for the fermentation process [ 16 ]. It has also been noticed that abrupt change in temperature in the AD process, changes the overall reaction due change in microbial growth pattern and their metabolic performance (Fig. 1 ). In one of the study by [ 17 ], methane production has been increased from 60.2 to 71.8% using AD process of organic solid waste under mesophilic temperature range. Similarly, in the research study of Wang et al. [ 18 ], two phase AD has been conducted using co-digestion of substrate cow manure and corn straw and at 25 °C, more than 50% increment in biogas production has been recorded. Further in the study of anaerobic sludge (AS) and cow manure (CM) have been selected for dry AD process for higher methane production and the process has been run for 35 days and 1515 mL of biogas has been noticed at 37 °C. In the research investigation of Ramaraj and Unpaprom [ 19 ], AD process has been performed at 35 °C upto 45 days and has significant impact on biogas production. The above all studies indicated that mesophilic temperature is the most productive for higher biogas production because of higher microbial growth and rapid metabolic activity. Thus for pilot scale biogas production it is the most recommended temperature range. Along with temperature, pH is also a significant factor which influences the production of biogas in AD process. During the course of the process, pH change may cause the blockage in overall process and due to hindrance in buffering capacity in the biogas process which is generally occurred due to dissolved CO 2 , carbonate and ammonia, pH change has not be detectable until significant change will occurred in the system [ 20 ]. However, the careful monitoring of the pH is crucial for AD process because in pH range 6.0–7.0 in which methanogensis process has been occurred while in the pH range 4.5–8.5, the microbial function is smooth. Thus, pH change indicator generally, indicates the imbalance in the overall production process which can be rectify via maintaining the pH balance and generally buffer solutions NaOH, Na 2 CO 3 and Ca(OH) 2 has been recommended for the pH balance. In the study of [ 21 ], impact of pH 5 to 9 has been studied on biogas production using the AD process in which pH 7.0 is found suitable to influence the process. In the study of [ 22 ], impact of low pH has been observed on biogas production of AD process and it has been observed that better methane productivity has been gained in low pH value whereas, relatively higher pH from 4 to 7 were also supported the biogas production. Generally, the neutral pH range is preferable for biogas production and relative safer to avoid any massive change in biogas production process. Moreover, this pH change does not affect the microbial metabolic environment, growth and reaction mechanism. Apart from temperature and pH, nitrogen is another crucial factor which can drastically influence the AD process as well as the productivity of the overall system by influencing microbial growth, metabolism as well as gas production process [ 23 ]. Pig and chicken manure, dairy products are high level source of nitrogen whereas,the general biogas system can tolerate 1500 and 7000 mgNL nitrogen concentration. High concentration of ammonia inhibited the process of methanogensis which generally results from accumulation of volatile fatty acids (VFAs) [ 24 ]. Generally, VFAs like acetic, propionic and butyric acids like VFAs promoted the AD process to produce biogas while, ideal carbon to nitrogen ratio which is C/N ratio is also important for higher production of biogas. In general C/N ratios represent total ammonia nitrogen (TAN) of the digester. Additionally, along with C/N ratio, chemical oxygen demand (COD) also considerable parameter for higher productivity reflection in AD process for biogas production. The COD of the AD system reflected total chemically oxidisable material in a sample and energy content is the material. It also represents quantity of oxygen generally needs to oxidse the sample [ 25 ]. Moreover, addition of macro nutrient and micronutrient also play impactful contribution to enhance the biogas production process. In macronutrient category P, N and S is the major constitutor and used as buffering agent whereas, micronutrients like Fe, Cr, Ni, Mo, Zn, Co, W as well as Se also function as micronutrient while performing in AD process of enzymatic hydrolysis and fermentation process. Along with these all essential parameters, substrate is the main essence of the process and FW is the preferable in existing substrate options and huge bioavailability. However, based on different origin, the overall content is different from cellulose, hemicellulose, carbohydrate and lignin [ 26 ]. Significant removal of lignin is mandatory for effective break down complex carbohydrate into sugars and biogas production. Different types of pretreatment strategies are available for significant removal of lignin and significant availability of the cellulose. The first pretreatment after collecting the biomass is processed as the mechanical pretreatment which includes cutting, washing, squeezing drying and sieving. The concept behind the process is reducing the particle size of the substrate and making the maximum availability of the surface area for reaction [ 27 ]. A suitable mechanical process and pretreatment are required to process the substrate for smooth microbial growth, high product generation and fast reaction in AD digester and methane yield has been reported higher when treated at reduced particle size. Mechanical pretreatment is generally a appropriate pretreatment system and mostly challenge free except the processing of biomass in mills which might sometimes reduce the property of the biomass and this hamper the further results in AD system [ 28 , 48 ]. It has also been confirmed than particle size less than 10 mm supported the microbial growth, digestion, metabolites and biogas production. To further, increase the process the mechanical pretreatment has been combined with thermal pretreatment in which substrate has been heated at fixed temperature and pressure with or without activation of any further chemical treatment. This process is known as thermochemical pretreatment and this process is preferable over the existing thermal and chemical pretreatment process [ 29 ]. In chemical pretreatment process, the substrate can be treated with acid or alkali for removing the lignin process by dissolving it. Due to inclusion of chemicals, it is a very effective process in removal of lignin, though the cost of the high amount consumed chemicals makes it non-suitable for the process [ 30 ]. Additionally, relative high amount of chemicals usage makes the damage to the initial biomass and it can dissolve free cellulose also along with lignin, if not monitored. Generally, alkaline like NaOH and KOH used for the alkaline pretreatment and acids like HCl, H 2 SO 4 and HNO 3 were used for acidic pretreatment process. The biogas production can be enhanced significantly using chemical pretreatment process, the cost of pretreatment makes the overall process cost intensive and technoeconomically unfavorable. Sometimes, these pretreatment processes has been combined with some alternate [ 31 ]. Moreover, the kind of biological system based pretreatment is not suitable when used as sole pretreatment process due to long processing and slow product recovery. Environmental friendly and relatively low process operations are the biggest advantages of biological pretreatment process, slow and time consuming process to breakdown the complex molecules are make them less feasible for adaption for biogas process [ 32 ]. However, combination of biological pretreatment process with other existing pretreatment process is making them suitable for AD process for biogas production. In one of the study by [ 33 ], impact of catalyst has been observed on biogas production in AD process where cobalt (Co) has been identified as the most appropriate catalyst which boosted the biogas production 42% in 28 days of AD using kitchen and vegetable waste. Further, at 20 °C, the AD process ready to start at pH 7.0 while during the whole process, no significant change in pH and nutrients have been observed in this study. Further in the study of two phase AD process of FW has been conducted using microscale zero-valent iron and different salinity rate which is maintained by NaCl and positive results have been recorded which noticed 318.46%, higher methane production at 9 g/L concentration of NaCl. These results concluded that alkaline stress enhanced the biogas production. In the research investigation of [ 34 ], co-digestion based anaerobic digestion has been processed using food waste and algal biomass in 8:2 ratio and significant improvement in biogas production has been recorded in co-digestion mode with stable VFAs production and decrease in pH fall during the co-AD process when compared to mono AD process. In another study by [ 35 ], co-digestion in AD process, by applying cheese whey, grease interceptor wastes as well as pulped food waste have been applied to produce biogas. The results were significant when cheese whey combined with grease interceptor waste while no improvement was observed when cheese whey combined with pulped food waste and by this way authors concluded that co-digestion is not always preferable and it depends on the suitability and compatibility of the selected and participating substrate as well. Co-digestion of the substrate is also promoted organic loading rate (OLR) and reduces the hydraulic retention time (HRT) along with biogas production. Kitchen wastes, FW as well as garden waste were selected as co-digestive substrate in ratio using thermophilic microbial cultures along with dry AD process. Total 24.69% and 44.96% enhanced biogas production has been noticed at highest OLR 3 g VS L −1 d −1 . The study also predicted that combination of co-digestion will also balance VFAs production and pH change and reduces the ammonia imbalance during the AD reaction. Therefore, co-digestion is most recommended process of to improve the AD system. Table 1 provides details on various research studies conducted on different substrate to produce biogas via AD process. As the conclusive remark of the overall AD process for fixed and frequent pilot scale trial, mesophilic temperature and neutral pH range, food waste with low alkaline pretreatment, pig and chicken manure as nitrogen source and to maintain C/N ratio, feedstock under co-digestion mode are the crucial parameters to follow economical and improved biogas production at commercial scale (Fig. 2 ). Additionally, the advantages associated with co-digestion are included buffering balance in the reaction medium, maintaining the C/N ratio and other nutrient balance other than OLR [ 82 ]. Though biorefinary production from food waste is most favorable approach, for saving and addressing environmental safety related issues, in terms of revenue generation and health concern, life-cycle assessment (LCA) has been performed by many research studies. The main agenda of LCA assessment is to evaluate value added product from food waste apart from biogas such volatile fatty acids (VFAs) production and its scale up as well as byproduct of biogas as biofertilizer. Several performed research investigations on LCA provides emphasis on mass scale production of different value added products generated from FW during the process of biogas production [ 43 ]. Table 1. Biogas production using different substrates under AD mode S.No Examples of food waste Source of food waste Production process Key findings(Biogas) References 1 Drinking milk, cheese, yogurt Dairy industry Anaerobic digestion process High amount of biogas production 2 Peels, seeds, tails, kernels, pumpkin marrow, apple waste Fruits and vegetables industry Co- digestion of fruits and vegetables waste at various organic loading ratio in single phase and two phase systems obtained the highest amounts of CH 4 (0.351 –0.455 L (g VS) − 1 d − 1) in the case of a higher level of OLR (≥ 2.0 g (VS) L − 1 d − 1), two-phase digestion 3 Mixed food waste samples Household and restaurants Two-stage anaerobic digestion: pre-treatment followed by mesophilic digestion A 24-h test effectively predicts fermentation capacity; economic feasibility at $0.2944/m 3 [ 61 ] 4 Orange peels, lettuce, cucumber, cooked rice Global food supply chains Various processes reviewed, including thermophilic and mesophilic anaerobic digestion methods Detailed analysis of global practices and conversion techniques for biogas production [ 33 ] 5 Banana peels, bakery waste, vegetable residues Urban food waste collection centres Single-stage anaerobic digestion enhanced with nanoparticles for improved methanogenesis Nanocatalysts enhance the anaerobic digestion process and increase biogas yield 6 Food waste and wastewater – co-digestion of municipal wastewater and food waste under semi-continuous and continuous operation with various hydraulic retention times (HRTs) The highest methane yields of 167.41 ± 66.52, 194.35 ± 85.44, and 214.81 ± 85.44 ml/g-Vs were found in semi-continuous mode and after 10 days, methane yield of 485.58 ± 82.35 ml/g [ 76 ] 7 Municipal solid waste (food waste) Leftovers, fruit and vegetable scraps – Physicochemical analysis, grid electricity prospect of Abuja’s, average net calorific value: 18.1 MJ/kg, 0.53 kg/person/day (Nigeria) Energy, reduced CO 2 emissions, More than 69% of 257,500 tons/y could produce energy, power, and grid power of 2274.42 MWh, 28.43 MW, and 19.19 MW, respectively, and save 67.5 million metric CO 2 t/year [ 66 ] 8 fruit and vegetable waste – Physicochemical analysis, in Bobo-Dioulasso, Burkina Faso (Africa) Enhanced soil, biogas production (90% fecal sludge & 10% of fruits and vegetables waste: 29.4 L/kg of biogas, settled sludge and semi-solid material: 54.4 L/kg of biogas with 51% of CH 4 ) [ 65 ] 9 Yellow oleander, fruit seeds & peels from Kaner – Τhermo-kinetic characterization, Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods Activation energy of fruit peels from KAS and FWO: 184.8 kJ/mol & 182.3 kJ/mol, respectively.Activation energy fruit peels from KAS and FWO: 140.1 kJ/mol & 139.2 kJ/mol, respectively. Kaner fruit peels and seeds have a great deal of promise for pyrolysis-based bioenergy production [ 79 ] 10 Tea waste (TW) – Catalytic pyrolysis with CO 2 Enhanced 28 times more H 2 and CO production [ 71 ] 11 Dried household food waste (FORBI) – AD, bioconversion based on microbiological processes Higher energy recovery was obtained when fermentation and subsequent AD performed [ 62 ] 12 Apple and grape waste from the cider and wine industries Extracting bioactive compounds, pyrolyzing/gasifying Value-added chemical products: biochar, activated carbon, fuel applications, soil reinforcement [ 78 ] 13 grape marc (GM) wine industries Combustion, thermochemical methods, kinetic and thermodynamic analysis, ash analysis, etc GCV: 19.3 MJ/kg, ash: 5.74 wt.%, CaO: 75.5%, MgO:6.8% promising alternative sustainable solid biofuels (enhanced fuel characteristics, low CO x , NO x , SO x emissions per Megajoule) [ 80 ] 13 Food waste – Biochemical methane potential CH 4 , Enhanced TVS of pretreated FDW: 425 NmL CH 4 /g TVS (samples without pre-processing: 375 NmL CH 4 /g TVS [ 75 ] 14 Food waste(Orange peels, banana and other) – 2 anaerobic processes (anaerobic fermentation, AF and then anaerobic digestion, AD) & open mixed cultures Bioproducts (ethanol and Short-chain fatty acids) and bioenergy (CH 4 and H 2 ) [ 68 ] 15 Food and fruits waste( peels,seeds, pulp) With & without different impurities (plastic, chopsticks, eggshell and bones), activated biochar catalysts Eggshell treatment and activated biochar catalysts significantly boost hydrocarbon production, GCV: 36–44.4 MJ/kg, pyrolysis oil’s could be used as a traditional liquid fuel [ 73 ] 16 Seeds(Mango ( Mangifera indica ), lychee ( Litchi chinensis ), avocado ( Persea americana ) – Physical: Chemical method Green energy [ 67 ] 17 Peels(Oranges) ( Citrus sinensis ) – Physical Chemical method Biofuels [ 72 , 77 ] 18 Organic food waste Anaerobic Digestion Reduces GHG emissions by 1000 kg CO 2 equivalent/tonne of waste(Generates biogas for energy production; saves energy costs [ 77 ] 19 Potato peel waste – Co- digestion method Co-digestion improved the biogas yield and CH 4 concentration of 66% [ 63 ] 20 Potato peel waste(Potato) – Fermentation improved yield of biobutanol (96%) [ 70 ] 21 Leftover food – Dark Fermentation Biohydrogen (63.8 mL/ gVS) [ 74 ] 22 Fruits & vegetables(Beetroot, radish, lemon, cucumber, pineapple, and carrot) – Anaerobic digestion biomethane (303.3 m 3 /kg VS) Vian et al. [ 81 ] 23 Vegetable waste(corn waste, green peas, bean waste, carrot peels) – Anaerobic digestion Biomethane (420 L/ kg VS) Borowski et al. [ 64 ] 24 Vegetable(Sweet Potato) – Benthic microbial fuel cells Bioelectricity (154 mV) Ahmad, [ 60 ] 25 Fruit(Avocado) – Microbial Fuel Cell Bioelectricity (3.7326 ± 0.05568 mA) 26 Sludge fermentation liquid and fruit waste extracts(Peel, kernel and residual pulp of banana, apple, pear, tangerine, pine- apple) – Microbial fuel cells Bioelectricity with voltage 0.75 V He et al. [ 69 ] 27 Fruits & Vegetables(Tomato, eggplant, cowpea, snake gourd, green banana, beet, radish, potato, cucumber, onion, and green mango) Anaerobic digestion with three-stage hybrid system Biogas (782 mL/g) [ 40 ] Open in a new tab Existing Challenges and Future Recommendation Biogas production using food waste is significant area which can be frequently practiced for easy and economic commercial application due to higher productively relatively to other existing bioenergy options and abundant availability of FW as feedstock. Easy daily availability, huge production and rich carbohydrate and cellulose content which are very necessary for biogas production can be easily grabbed by food waste based products and at the same time, it’s very smoothly scale up. At the same space and similar line, if this kind of waste cannot valorize, they will become environmental threat for the population across the globe. Thus production of biogas and its sustainable management is important to face and tackle environmental and energy crises. Moreover, their economic and sustainable management for frequent commercial application is the main challenges in this area. Towards improving the productivity of biogas, controlling of feedstock and bioprocess parameters are the important strategies. Carbohydrate and cellulose rich FW with poor lignin content are the primary and increment requirement of the better productivity of biogas production. Suitable and cost efficient pretreatment process is highly recommended for removal of lignin from FW. The cost of the lignin and its removal process, both contributing crucially in AD process and contributed as major factor to raise the overall cost of the AD process and thus, it is very important to careful look after on the pretreatment and its process for effective lignin removal. Where, appropriate nitrogen content and C/N ratio is equally important to initiate and continue maintain the reaction. Therefore, co-digestion mode which can be ideal combination of carbohydrate and cellulose rich substrate with appropriate nitrogen content is preferable for AD process. In various trial approaches pig manure is a potential nitrogen source and ideal for maintenance of C/N ratio. Further, temperature and pH are significant parameters, important to monitor for significant AD process monitoring and mesophilic temperature range with nearly neutral pH is appropriate for rapid AD process and higher product recovery. A careful focus on these factors also improves HRT and OLR of the AD system which are also one of the key factors to improve the pilot scale operations (Fig. 3 ). Additionally, selection, fabrication of suitable reactors and infrastructure are also important to handle and speed up the pilot scale AD process on economic and commercial scale. Fig. 3. Open in a new tab Future recommendation strategies of the process area improvement at pilot scale to improve the process sustainability of the AD method to produce biogas from food waste Conclusions Inspite of being major contributor of solid waste, FW have enormous potential of biogas production due to high organic matter content which can be effectively valorized into biogas production. Due to high content of sugars, this category of waste is most appropriate for AD process. The only barrier in economic pilot scale production and commercial utilization is appropriate processing in combination of bioprocess parameters and suitable digestion as well as pretreatment of FW for effective removal of lignin and smooth hydrolysis of substrate. Additionally, suitable selection of microbial cultures such as mesophilic microbial community and their long term, lower cost cultivation conditions are also important area to be considered for easy processing and high productivity of the process. An appropriate operation which includes addressing all the physicochemical parameters will speed up the process and improves the digestion as well as hydrolysis ability of the FW into biogas through AD process. This will help is sustainable environmental and waste management with potential green energy applications. Acknowledgements All Authors thankfully acknowledge their respective parent institutes. Figures have been designed with the help of avilable free version to use from Biorendar and Canva. The authors are thankful to the Deanship of Research and Graduate Studies, King Khalid University, Abha, Saudi Arabia, for financially supporting this work through the Large Research Group Project under Grant no. R.G.P.2/516/45. Authors Contributions Rajeev Singh: Conceptulization, writing original draft; Dan Bahadur Pal: writing original draft Basant Lal: review and editing; Tripti Singh: data curation, review, editing analysis and supervision; Irfan Ahmad: review, editing analysis and supervision; Abdullah Mashraqi: writing, review, editing; Shafiul Haque: writing, review, editing; Neha Srivastava: review, editing and supervision. Funding Funding support is not available. Declarations Conflict of interest The authors declare that there is no conflict of interest regarding the publication of this article. Footnotes Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Rajeev Singh and Dan Bahadur Pal have contributed equally. References 1. Pilarska AA, Pilarski K, Waliszewska B, Zborowska M, Witaszek K, Waliszewska H (2019) Kolasi nski, M.; Szwarc-Rzepka, K. 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