Accelerated acidification by inoculation with a microbial consortia in a complex open environment

Taxonomic and enzymatic basis of the cellulolytic microbial consortium KKU-MC1 and its application in enhancing biomethane production

Lignocellulosic biomass is a promising substrate for biogas production. However, its recalcitrant structure limits conversion efficiency. This study aims to design a microbial consortium (MC) capable of producing the cellulolytic enzyme and exploring the taxonomic and genetic aspects of lignocellulose degradation. A diverse range of lignocellulolytic bacteria and degrading enzymes from various habitats were enriched for a known KKU-MC1. The KKU-MC1 was found to be abundant in Bacteroidetes (51%), Proteobacteria (29%), Firmicutes (10%), and other phyla (8% unknown, 0.4% unclassified, 0.6% archaea, and the remaining 1% other bacteria with low predominance). Carbohydrate-active enzyme (CAZyme) annotation revealed that the genera Bacteroides, Ruminiclostridium, Enterococcus, and Parabacteroides encoded a diverse set of cellulose and hemicellulose degradation enzymes. Furthermore, the gene families associated with lignin deconstruction were more abundant in the Pseudomonas genera. Subsequently, the effects of MC on methane production from various biomasses were studied in two ways: bioaugmentation and pre-hydrolysis. Methane yield (MY) of pre-hydrolysis cassava bagasse (CB), Napier grass (NG), and sugarcane bagasse (SB) with KKU-MC1 for 5 days improved by 38-56% compared to non-prehydrolysis substrates, while MY of prehydrolysed filter cake (FC) for 15 days improved by 56% compared to raw FC. The MY of CB, NG, and SB (at 4% initial volatile solid concentration (IVC)) with KKU-MC1 augmentation improved by 29-42% compared to the non-augmentation treatment. FC (1% IVC) had 17% higher MY than the non-augmentation treatment. These findings demonstrated that KKU-MC1 released the cellulolytic enzyme capable of decomposing various lignocellulosic biomasses, resulting in increased biogas production.

Effects of Lactiplantibacillus plantarum and Lactiplantibacillus brevis on fermentation, aerobic stability, and the bacterial community of paper mulberry silage

The present study investigated the dynamic profiles of fermentation quality, aerobic stability, and the bacterial community of paper mulberry silage inoculants without (Control) or with Lactiplantibacillus plantarum (LP), Lactiplantibacillus brevis (LB), or their combination (LPLB), which was screened from naturally fermented paper mulberry. The results showed that the inoculated treatments had significantly reduced neutral detergent fiber, water-soluble carbohydrates, and ammoniacal nitrogen contents compared with the control after 60 days of ensiling (the decreased proportion of LP, LB, and LPLB treatments ranged from 7.33%-11.23%, 9.60%-21.44%, and 21.53%-29.23%, respectively, p < 0.05). The pH value of the LP and LB treatments was significantly lower than that of the control after 60 days of ensiling (4.42 and 4.56 vs. 4.71, p < 0.05). The LP treatment promoted lactic acid accumulation and LAB number compared with the control (66.59% vs. 54.12% and 8.71 log10 CFU/g vs. 8.52 log10 CFU/g, respectively, p < 0.05), and the LB and LPLB treatments inhibited the growth of yeast and mold after 14 days of fermentation. After 5 days of aerobic exposure, both the LB and LPLB treatments increased the aerobic stability time and acetic acid content (from 29 to 75 h and 16.14%-48.72%, respectively, p < 0.05), inhibited the growth of yeast and mold, and did not detect butyric acid. Additionally, the bacteria community of each treatment was dominated by Aerococcus on day 3 of ensilage (accounting for 54.36%-69.31%), while the inoculated treatments reduced the abundance of Aerococcus on day 60 (from 59.73% to 85.16%, p < 0.05), and Lactobacillus became the dominant genus (accounting for 54.57%-70.89%). Inoculation of L. plantarum effectively maintained the acidic environment at the end of the fermentation system by maintaining the abundance of Lactobacillus, maximizing the preservation of dry matter and protein, and reducing protein corruption. Inoculation of L. brevis alone or in combination with L. plantarum significantly inhibited the growth of mold and improved the aerobic stability of paper mulberry silage.

Effect of Pretreatment by Freeze Vacuum Drying on Solid-State Anaerobic Digestion of Corn Straw

As a common agricultural waste, corn straw (CS) has a refractory structure, which is not conducive to anaerobic digestion (AD). Appropriate pretreatment is crucial for addressing this problem. Thus, freeze vacuum drying (FVD) was proposed. In this study, fresh CS (F-CS) pretreated (5 h, −40 °C) by FVD and naturally dried CS (D-CS) were compared. Differences in substrate surface structure and nutrient composition were first investigated. Results show that a loose and porous structure, crystallinity, and broken chemical bonds, as well as higher proportions of VS, C, N, cellulose, hemicellulose, and crude proteins in F-CS show a potential for methane production. Besides, process performance and stability were also examined in both high (4, VS basis) and low (1, VS basis) S/I ratio AD. A higher degradation ratio of hemicellulose as well as richer dissolved microbial metabolites, coenzymes, tyrosine-like proteins, and hydrolysis rate of particulate organic matter in the F-CS system enhanced the efficiency of methane conversion. The cumulative methane yield increased from 169.66 (D-CS) to 209.97 (F-CS) mL/gVS in the high S/I ratio system (p = 0.02 < 0.05), and 156.97 to 171.89 mL/gVS in the low S/I ratio system. Additionally, 16S-rRNA-gene-based analysis was performed. Interestingly, the coordination of key bacteria (Clostridium_sensu_stricto_1, Bacillus, Terrisporobacter. Clostridium_sensu_stricto_7, Thermoclostrium, UCG-012, and HN-HF0106) was more active. Poorer Methanosarcina and Methanomassiliicoccus as well as richer Methanobrevibacter and Methanoculleus stimulated the co-relationship of key archaea with diverse methanogenesis pathways. This study aims to verify the positive effect of FVD pretreatment on AD of CS, so as to provide a reference for applications in waste management.

The combination of aerobic and microaerobic promote hydrolysis and acidification of rice straw and pig manure: Balance of insoluble and soluble substrate

Separated hydrolysis and acidification is an effective pretreatment method for anaerobic digestion of lignocellulose. However, excess consumption of soluble substrates remains a problem. Rice straw and pig manure were used as substrates with biogas slurry as the inoculum, combined with aerobic and microaerobic conditions in the 14-day hydrolysis and acidification. Aeration can significantly accelerate volatile solid degradation (38.25%), especially the lignocellulose. Soluble chemical oxygen demand (29157 mg/L) and volatile fatty acids (13219 mg/L) of the group with 4 days aerobic treatment, reached their peaks on day 5, obtaining a balanced insoluble substrate degradation and soluble substrate consumption. Candida, Lactobacillus, Bifidobacterium, and Acetobacter were enriched at the balanced point for positive contribution to the degradation of the insoluble substrate and the generation of soluble substrate. This study not only reveals the balance between degradation and consumption, but also provides new insight into biogas slurry recycling and anaerobic digestion precursor substrate production.

Structure-function elucidation of a microbial consortium in degrading rice straw and producing acetic and butyric acids via metagenome combining 16S rDNA sequencing

The characterized microbial consortium can efficiently degrade rice straw to produce acetic and butyric acids in high yields. The rice straw lost 86.9% in weight and degradation rates of hemicellulose, cellulose, and lignin attained were 97.1%, 86.4% and 70.3% within 12 days, respectively. During biodegradation via fermentation of rice straw, average concentrations of acetic and butyric acids reached 1570 mg/L and 1270 mg/L, accounting for 47.2% and 35.4% of the total volatile fatty acids, respectively. The consortium mainly composed of Prevotella, Cellulosilyticum, Pseudomonas, Clostridium and Ruminococcaceae, etc. Metagenomic analyses indicated that glycoside hydrolases (GHs) were the largest enzyme group with a relative abundance of 54.5%. Various lignocellulose degrading enzymes were identified in the top 30 abundant GHs, and were primarily distributed in the dominant genera (Prevotella, Cellulosilyticum and Clostridium). These results provide a new route for the commercial recycling of rice straw to produce organic acids.

Enhanced Biogas Production by Ligninolytic Strain Enterobacter hormaechei KA3 for Anaerobic Digestion of Corn Straw

Lignin-feeding insect gut is a natural ligninolytic microbial bank for the sustainable conversion of crop straw to biogas. However, limited studies have been done on highly efficient microbes. Here, an efficient ligninolytic strain Enterobacter hormaechei KA3 was isolated from the gut microbiomes of lignin-feeding Hypomeces squamosus Fabricius, and its effects on lignin degradation and anaerobic digestion were investigated. No research has been reported. Results showed that strain KA3 had better lignin-degrading ability for corn straw with a higher lignin-degrading rate (32.05%) and lignin peroxidase activity (585.2 U/L). Furthermore, the highest cumulative biogas yield (59.19 L/kg-VS) and methane yield (14.76 L/kg-VS) were obtained for KA3 inoculation, which increased by 20% and 31%, respectively, compared to CK. Higher removal rates of COD, TS, and vs. of 41.6%, 43.11%, and 66.59% were also found. Moreover, microbial community diversity increased as digestion time prolonged in TG, and bacteria were more diverse than archaea. The dominant genus taxon, for methanogens, was Methanosate in TG, while in CK was Methanosarcina. For bacteria, dominant taxa were similar for all groups, which were Solibacillus and Clostridium. Therefore, strain KA3 improved the methane conversion of the substrate. This study could provide a new microbial resource and practical application base for lignin degradation.

Integral valorization of orange peel waste through optimized ensiling: Lactic acid and bioethanol production

The management of the huge amount of orange peel waste (OPW) is a complex issue although it has a very high potential in terms of biorefining. One of the main problems in the valorisation of OPW is the seasonality of its production with the ensiling method being largely proposed as a possible solution. During the ensiling process, value added chemicals including lactic acid, acetic acid and ethanol are spontaneously produced together with a significant loss of volatile solids (VS) . In this contribution, the stimulation of lactic acid bacteria by either a biological (inoculation with leachate coming from a previous ensiling process) or chemical (MnCl₂ supplementation) methods has been tested with the aim to increase the chemicals production preventing, at the same time, the VS loss. The inoculation with the leachate improves both the VS recovery (+7%) and the concentration of lactic acid (+113%) with respect to the uninoculated one (control). The overall yields of the process are noticeable, up to about 55 g·kg_TS^-1 of lactic acid, 26 g·kg_TS^-1 of acetic acid and 120 g g·kgTS-1 of ethanol have been produced. On the other hand, the chemical stimulation enhances the production of liquid products together with a significant VS loss. The proposed preservation method, due to its simplicity, can be easily implemented at full-scale allowing the production of added-value chemicals and the concurrent storage of the OPW that can be further valorised (e.g. animal feed, pectin or biomethane production).

Effects of digestate recirculation ratios on biogas production and methane yield of continuous dry anaerobic digestion

This study conducted a small scale, push flow, continuous, dry anaerobic digestion experiment using 50% and 60% digestate recirculation ratios to investigate the effects of digestate recirculation ratio on continuous dry anaerobic digestion and to analyze microbial community succession. The results showed that the volumetric biogas production rate could reach 1.6 L/L·d during the 60% digestate recirculation ratio. A slight, initial accumulation of volatile fatty acids (VFAs) (maximum concentration 1.6 g/L) was subsequently consumed by the Christensenellaceae R-7 group, and VFA concentrations stabilized at around 20 mg/L. The increased digestate recirculation ratio (60%) promoted both VadinBC27 wastewater-sludge group and Methanobacterium proliferation, and the predominance of those microbial strains may be why VFAs decreased and gas production efficiency improved. Those microbial community changes, fostered by the higher digestate recirculation ratio, are important in continuous dry anaerobic digestion. These results aid continued work aimed at improving continuous, dry anaerobic digestion.

Pre-acidification greatly improved granules physicochemical properties and operational stability of Upflow anaerobic sludge Blanket (UASB) reactor treating low-strength starch wastewater

A two-stage process consisting of a pre-acidification unit and an Upflow Anaerobic Sludge Blanket (UASB) reactor (UASB_T-S) was compared with a one-stage UASB reactor (UASB_O-S) to evaluate the treatment stability of starch wastewater (SW). The Two-stage process provided higher treatment stability than UASB_O-S. Sludge floatation occurred in the UASB_O-S when the organic loading rate (OLR) was increased to 4 g-COD/L/d, beyond which a paste-like membrane structure adhered to the granules was observed. Further analysis suggests that the substrate derived polysaccharide components embedded in the loosely-bound extracellular polymeric substances (LB-EPS), triggered significant increase in the protein/polysaccharide ratio in the tightly-bound EPS (TB-EPS), and was suggested to result in the granules floatation and disintegration. During the pre-acidification, the starch was mainly converted to acetic and propionic acids. The pre-acidification was beneficial for reducing the EPS content fluctuations in the UASB_T-S, which greatly improved settling capability and strength of the granular sludge.

Microbial Degradation of Zearalenone by a Novel Microbial Consortium, NZDC-6, and Its Application on Contaminated Corncob by Semisolid Fermentation

A novel microbial consortium (NZDC-6) was screened and characterized to detoxify the estrogenic mycotoxin zearalenone (ZEA), which commonly contaminates maize and is a major threat to food and health security. We found NZDC-6 to be thermophilic and highly effective, with a 90.3% ZEA degradation ratio at an optimum temperature of 60 °C. NZDC-6 was also effective at degrading the more estrogenic ZEA cognates, α-zearalenol (α-ZAL) and β-zearalenol (β-ZAL), with >90% degradation ratios. To evaluate a practical application, ZEA-contaminated corncobs were treated with NZDC-6 via semisolid fermentation. Measurements of physicochemical parameters and 16S microbial diversity and redundancy analysis (RDA) indicated that ZEA removal was most efficient at a low corncob solid content (< 5%), as a high solid content overwhelmed the microbial metabolic load, leading to increased dissolved oxygen and lowered pH. Our results demonstrate that the control of environmental variables is crucial for effective ZEA microbial removal in practical applications.

How methane yield, crucial parameters and microbial communities respond to the stimulating effect of antibiotics during high solid anaerobic digestion

To comprehensively understand how antibiotics affect anaerobic digestion, their stimulating effects on methane production cannot be ignored; however, few studies have evaluated these effects. This study investigated the stimulating effects of three typical antibiotics (oxytetracycline, sulfadimethoxine, and norfloxacin) on high solid anaerobic digestion. The results showed that 100 mg/L antibiotics exhibited a strong stimulating effect on CH₄ yield; while other external carbon sources had no obvious effects. The stimulating effect was more obvious under low inoculation ratios, which could improve the system processing capacity of feed sludge. Lower lag phases were given by the modified Gompertz model when stimulating effects occurred. The variations of physicochemical parameters and microbial Venn maps both showed that day 5 was a critical point for digestion time. The relative abundance of Methanosarcina was enhanced when the stimulating effect occurred, whereas Methanoculleus decreased. Different microbial characteristics were obtained for different samples from the heat maps.

Sequencing batch dry anaerobic digestion of mixed feedstock regulating strategies for methane production: Multi-factor interactions among biotic and abiotic characteristics

This study investigated the synergistic effects and regulation strategy of multiple factors for improving methane production in sequencing batch dry anaerobic digestion (SBD-AD) using corn stalks (CS) and cow dung (CD). The regulation of the spray frequency (SF) and inoculum content (IC) significantly improved methane yield, which increased feedstock ratios (FRs) by 12.4-121.3%. Moreover, the relationship between SF and IC produced distinct interaction modes. An FR of 4:6 increased the SF to 2 h for the CD-rich condition, and an FR of 6:4 decreased the SF during a 6 h interval and increased the IC for the CS-rich condition, resulting in increases in methane yield and the conversion efficiency of volatile fatty acids (VFAs). Methanogenesis (Methanogens) played a key role in SBD-AD. The nutrient substrate (NH₄-N⁺) and key enzyme activities of methanogens were significantly affected such that the synergistic effect of the acetoclastic and hydrogenotrophic methanogenesis pathways was likely strengthened.

Effects of adding EDTA and Fe2+ on the performance of reactor and microbial community structure in two simulated phases of anaerobic digestion

The uptake of trace elements can be impeded by precipitation in the presence of carbonates and sulfates. The objective of this study was to investigate whether ethylenediaminetetraacetic acid (EDTA) enhances the performance of anaerobic digestion by forming dissolved complexes with Fe²⁺. Batch experiments were performed in this study and acidogenic and methanogenic phases were artificially simulated. EDTA was added to both of phases to examine its effects on Fe bioavailability, metabolic parameters and microbial community structure. The results showed that EDTA significantly accelerated the digestion process in both phases because its addition changed the Fe sorption law and increased Fe-bioavailability. The microbial community structure changed following by the change of Fe-fractions which was determined by EDTA. This study demonstrated that EDTA as ligand could increase the Fe-bioavailability and then reduced or replaced the addition of Fe.

Optimization of hydraulic retention time and organic loading rate for volatile fatty acid production from low strength wastewater in an anaerobic membrane bioreactor

This study aims to investigate the production of volatile fatty acids (VFAs) from low strength wastewater at various hydraulic retention time (HRT) and organic loading rate (OLR) in a continuous anaerobic membrane bioreactor (AnMBR) using glucose as carbon source. This experiment was performed without any selective inhibition of methanogens and the reactor pH was maintained at 7.0 ± 0.1. 48, 24, 18, 12, 8 and 6 h-HRTs were applied and the highest VFA concentration was recorded at 8 h with an overall VFA yield of 48.20 ± 1.21 mg VFA/100 mg COD_feed. Three different ORLs were applied (350, 550 and 715 mg COD_feed) at the optimum 8 h-HRT. The acetic and propanoic acid concentration maximums were (1.1845 ± 0.0165 and 0.5160 ± 0.0141 mili-mole/l respectively) at 550 mg COD_feed. The isobutyric acid concentration was highest (0.3580 ± 0.0407 mili-mole/l) at 715 mg COD_feed indicating butyric-type fermentation at higher organic loading rate.

Effects of molybdenum, selenium and manganese supplementation on the performance of anaerobic digestion and the characteristics of bacterial community in acidogenic stage

The addition of trace elements to aid anaerobic digestion has already been widely studied. However, the effects of rare trace elements on anaerobic digestion remain unclear. In this study, the effects of Mo, Se and Mn on anaerobic digestion of rice straw were explored. The results showed the methane yield increased by 59.3%, 47.1% and 48.9% in the first 10 days following addition of Mo (0.01 mg/L), Se (0.1 mg/L) and Mn (1.0 mg/L), respectively. Toxic effects and the accumulation of volatile fatty acids (VFAs) were observed when the Se, Mo and Mn concentrations were greater than 100, 1000 and 1000 mg/L, respectively. The half-maximal inhibitory concentrations (IC₅₀) for Se, Mn and Mo were 79.9 mg/L, 773.9 mg/L and 792.3 mg/L, respectively. The addition of trace elements has changed the bacterial structure of the bacteria, which in turn has affected the digestion performance.

A new perspective of using sequential extraction: To predict the deficiency of trace elements during anaerobic digestion

Trace elements were commonly used as additives to facilitate anaerobic digestion. However, their addition is often blind because of the complexity of reaction conditions, which has impeded their widespread application. Therefore, this study was conducted to evaluate deficiencies in trace elements during anaerobic digestion by establishing relationships between changes in trace element bioavailability (the degree to which elements are available for interaction with biological systems) and digestion performance. To accomplish this, two batch experiments were conducted. In the first, sequential extraction was used to detect changes in trace element fractions and then to evaluate trace element bioavailability in the whole digestion cycle. In the second batch experiment, trace elements (Co, Fe, Cu, Zn, Mn, Mo and Se) were added to the reaction system at three concentrations (low, medium and high) and their effects were monitored. The results showed that sequential extraction was a suitable method for assessment of the bioavailability of trace elements (appropriate coefficient of variation and recovery rate). The results revealed that Se had the highest (44.2%-70.9%) bioavailability, while Fe had the lowest (1.7%-3.0%). A lack of trace elements was not directly related to their absolute bioavailability, but was instead associated with changes in their bioavailability throughout the digestion cycle. Trace elements were insufficient when their bioavailability was steady or increased over the digestion cycle. These results indicate that changes in trace element bioavailability during the digestion cycle can be used to predict their deficiency.

Effect of ensiling and silage additives on biogas production and microbial community dynamics during anaerobic digestion of switchgrass

Silage processing has a crucial positive impact on the methane yield of anaerobic treated substrates. Changes in the characteristics of switchgrass after ensiling with different additives and their effects on methane production and microbial community changes during anaerobic digestion were investigated. After ensiling (CK), methane yield was increased by 33.59% relative to that of fresh switchgrass (FS). In comparison with the CK treatment, methane production was improved by 17.41%, 13.08% and 8.72% in response to ensiling with LBr+X, LBr and X, respectively. A modified Gompertz model predicted that the optimum treatment was LBr+X, with a potential cumulative methane yield of 178.31mL/g total solids (TS) and a maximum biogas production rate of 44.39mL/g TS·d. Firmicutes and Bacteroidetes were the predominant bacteria in FS and silage switchgrass; however, the switchgrass treated with LBr+X was rich in Synergistetes, which was crucial for methane production.

The performance efficiency of bioaugmentation to prevent anaerobic digestion failure from ammonia and propionate inhibition

This study aims to investigate the effect of bioaugmentation with enriched methanogenic propionate degrading microbial consortia on propionate fermentation under ammonia stress from total ammonia nitrogen concentration (TAN) of 3.0gNL^-1. Results demonstrated that bioaugmentation could prevent unstable digestion against further deterioration. After 45days of 1dosage (0.3g dry cell weight L^-1d^-1, DCW L^-1d^-1) of bioaugmentation, the average volumetric methane production (VMP), methane recovery rate and propionic acid (HPr) degradation rate was enhanced by 70mLL^-1d^-1, 21% and 51%, respectively. In contrast, the non-bioaugmentation reactor almost failed. Routine addition of a double dosage (0.6g DCW L^-1d^-1) of bioaugmentation culture was able to effectively recover the failing digester. The results of FISH suggested that the populations of Methanosaetaceae increased significantly, which could be a main contributor for the positive effect on methane production.

Effective degradation of aflatoxin B1 using a novel thermophilic microbial consortium TADC7

We constructed a novel thermophilic microbial consortium, TADC7, with stable and efficient aflatoxin B₁ (AFB₁) degradation activity. The microbial consortium degraded more than 95% of the toxin within 72h when cultured with AFB₁, and the optimum temperature was 55-60°C. TADC7 tolerated high doses of AFB₁, with no inhibitory effects up to 5000μgL^-1 AFB₁; moreover, the degradation kinetics fit well with the Monod model. The proteins or enzymes in the TADC7 cell-free supernatant played a major role in AFB₁ degradation. AFB₁ degradation by the cell-free supernatant was stable up to 90°C, with an optimal pH of 8-10. We performed 16S rRNA sequencing to determine TADC7 community structure dynamics; the results indicated that Geobacillus and Tepidimicrobium played major roles in AFB₁ degradation.

Hydrolysis and acidification of agricultural waste in a non-airtight system: Effect of solid content, temperature, and mixing mode

A two-phase digestion system for treating agricultural waste is beneficial for methane production. This study explored the effect of solid content, temperature, and mixing mode on the process of hydrolysis and acidification using rice straw and cow dung launched in non-airtight acidogenic system. The results showed that the substrate could be hydrolyzed efficiently in the initial stage, the hydrolysis coefficient (k) of maximum cellulose and hemicellulose can be increased by 217.9% and 290.5%, respectively, compared with those of middle and last stages. High solid content played a leading role in promoting hydrolysis, resulted in hydrolysate content (sCOD) that was significantly higher than in treatments with low solid content (P<0.01), and led to organic acids accumulation up to 5.8 and 6.7g/L at mesophilic and thermophilic temperatures. Thermophilic temperature stimulated the hydrolysis and acidification of low solid content (P<0.05), and improved organic acid accumulation of high solid content only during the middle stage (P<0.01). Mixing mode was not a major factor, but increasing the mixing time was necessary for organic acid accumulation during the last stage (P<0.05). In addition, the study comprehensively analyzed a series of corresponding relationships among each operating parameter during the whole treatment process using canonical correspondence analysis.

Optimization of process parameters for production of volatile fatty acid, biohydrogen and methane from anaerobic digestion

The anaerobic digestion process has been primarily utilized for methane containing biogas production over the past few years. However, the digestion process could also be optimized for producing volatile fatty acids (VFAs) and biohydrogen. This is the first review article that combines the optimization approaches for all three possible products from the anaerobic digestion. In this review study, the types and configurations of the bioreactor are discussed for each type of product. This is followed by a review on optimization of common process parameters (e.g. temperature, pH, retention time and organic loading rate) separately for the production of VFA, biohydrogen and methane. This review also includes additional parameters, treatment methods or special additives that wield a significant and positive effect on production rate and these products' yield.

The application of biotechnology on the enhancing of biogas production from lignocellulosic waste

Anaerobic digestion of lignocellulosic waste is considered to be an efficient way to answer present-day energy crisis and environmental challenges. However, the recalcitrance of lignocellulosic material forms a major obstacle for obtaining maximum biogas production. The use of biological pretreatment and bioaugmentation for enhancing the performance of anaerobic digestion is quite recent and still needs to be investigated. This paper reviews the status and perspectives of recent studies on biotechnology concept and investigates its possible use for enhancing biogas production from lignocellulosic waste with main emphases on biological pretreatment and bioaugmentation techniques.