Effect of thermal pretreatment on chemical composition, physical structure and biogas production kinetics of wheat straw

Effect of hydrothermal pretreatment on leachate fed Scenedesmus sp. biomass solubilization and biogas production

The aim of the present study was to assess the effect of hydrothermal pretreatment on the solubilization and anaerobic digestion (AD) of Scenedesmus sp. biomass. At first, the microalgae was cultivated in 5% fresh leachate (FL) to recover nutrients such as nitrogen and phosphorus. Scenedesmus sp. grown in 5% FL obtained 100%, 77% and 97% removal efficiency of ammonium nitrogen (NH4+ - N), total Kjeldahl nitrogen (TKN) and phosphate phosphorous (PO43- -P), respectively. In the following step, the hydrothermal pretreatment of Scenedesmus sp. biomass was carried out at 120, 150 and 170 °C and retention time of 0, 30 and 60 min to evaluate its solubilization and biogas production through AD in batch test. Soluble chemical oxygen demand (sCOD) increased by 260% compared to untreated microalgae at 170 °C for 60 min. In comparison to untreated microalgae, the highest increase in biogas (70%) and methane yield (100%) was observed for 150 °C and 60 min pretreated microalgae as a consequence of hydrothermal pretreatment. Hydrothermal pretreatment has shown effectiveness in enhancing biomass solubilization and increasing biogas yield. Nevertheless, further research at the pilot scale is necessary to thoroughly evaluate the potential and feasibility of hydrothermal pretreatment for full-scale implementation.

CH4 production potential of autotrophic nitrification bacteria produced in the submerged nitrification bioreactor in the laboratory and kinetic analysis

In this study, CH4 production capacity of nitrification bacteria (NB) obtained from the submerged biofilter in the laboratory was investigated. Biochemical methane potential (BMP) test was carried out with the NB amount of zero (control, CR), 5% (R1), 10% (R2), and 15% (R3) at a temperature of about 37 ± 0.5°C. Compared to the CR, significantly higher cumulative CH4 volume of about 290, 490, and 715 mL were determined in the R1, R2, and R3, respectively. All the applied kinetic models gave good results (R2 ≥0.97), while the Transference Function and First-order models provided the better R2 values. The delay phase (λ) was not observed in the AD process, and CH4 production started immediately on the first day of operation. The predicted k value of 0.133 day-1 was high in CR, while it was approximately between 0.078 and 0.112 day-1 for the higher amount of NB containing BMP units, which indicated that the AD required long reaction time.

Enhanced humification of full-scale apple wood and cow manure by promoting lignocellulose degradation via biomass pretreatments

Agroforestry waste and cow manure pollute the environment, of which, agroforestry waste is difficult to degrade. Compost is an effective way to dispose agroforestry waste; however, the low degradation efficiency of lignocellulose in agroforestry waste affects the process of composting humification. This study investigated lignocellulose degradation and composting humification in full-size apple wood and cow manure composting processes by applying different pretreatments (acidic, alkaline, and high-temperature) to apple wood. Simultaneously, physicochemical characterization and metagenome sequencing were combined to analyze the function of carbohydrate-active enzymes database (CAZy). Therefore, microbial communities and functions were linked during the composting process and the lignocellulose degradation mechanism was elaborated. The results showed that the addition of apple wood increased the compost humus (HS) yield, and pretreatment of apple wood enhanced the lignocellulose degradation during composting processes. In addition, pretreatment improved the physicochemical properties, such as temperature, pH, electric conductivity (EC), ammonium nitrogen (NH4+), and nitrate nitrogen (NO3-) in the compost, of which, acid treated apple wood compost (AcAWC) achieved the highest temperature of 58.4 °C, effectively promoting nitrification with NO3- ultimately reaching 0.127 g/kg. In all composts, microbial networks constructed a high proportion of positively correlated connections, and microorganisms promoted the composting process through cooperation. The proportions of glycosyltransferase (GT) and glycoside hydrolase (GH) promoted the separation and degradation of lignocellulose during composting to form HS. Notably, the adverse effects of the alkali-treated apple wood compost on bacteria were greater. AcAWC showed significant correlations between bacterial and fungal communities and both lignin and hemicellulose, and had more biomarkers associated with lignocellulose degradation and humification. The lignin degradation rate was 24.57 % and the HS yield increased by 27.49 %. Therefore, AcAWC has been confirmed to enhance lignocellulose degradation and promote compost humification by altering the properties of the apple wood and establishing a richer microbial community.

Bio-conversion of whey lactose using enzymatic hydrolysis with β-galactosidase: an experimental and kinetic study

Lactose in cheese whey is increasingly challenging to metabolise under normal conditions. The hydrolysis of whey lactose into glucose and galactose using enzymatic methods has been acclaimed to confer benefits like enhanced substrate availability for better degradation in anaerobic digestion. In the present study, whey lactose was subjected to hydrolysis using the enzyme β-galactosidase derived from Aspergillus oryzae fungus to reduce the difficulty of lipid and fat transformation in anaerobic digestion. The individual and combined effects of hydrolysis parameters, pH, enzyme load, reaction time and temperature were studied using Response Surface Methodology by Central Composite Design. The optimum conditions were determined based on variance analyses and surface plots; pH 4.63, temperature 40.47°C, reaction time 25.96 min and enzyme load 0.49%. Results showed a maximum lactose hydrolysis value of 86.21%, while the predicted value was 87.44%. Indeed, enzyme hydrolysis induced a change of soluble chemical oxygen demand around 24.6% and 75.8% reduction in volatile fatty acid concentration. Upon anaerobic digestion, the pre-hydrolysed whey revealed a 3.6-fold higher bio-methane production than that of raw hey, and a visible decrease in volatile fatty acid concentrations. The resultant data agreed with the Gompertz model, and lag phase times were significantly reduced for hydrolysed whey.

The Influence of Poultry Manure-Derived Biochar and Compost on Soil Properties and Plant Biomass Growth

Promising methods for managing poultry manure (PM) include converting poultry manure through pyrolysis to biochar, which can be used for soil applications. The overall goal of this study was to determine the effects of poultry manure-derived biochar and compost on the soil and growth of cherry tomatoes. The biochar obtained at 475 °C was characterized by a relatively high organic matter content of 39.47% and nitrogen content of 3.73%, while it had the lowest C/N ratio of 8.18. According to the recommendations of the EBC, the biochar obtained at 475 °C demonstrated the most beneficial effects in terms of fertilizing potential. The composting of poultry manure with the straw was successful, and the limit of 60 °C was exceeded, which allowed for the hygienization of the compost. The produced compost and biochar are sanitary safe and do not exceed the limits of heavy metal content. The lowest plant biomass was obtained from growing medium A with 3.6 g wet weight (0.24 g dry weight). The measurements of the height of cherry tomatoes showed that growing media D, E, and F allowed the plants to obtain from 602 to 654 mm in height.

A comparison of ultrasonic, ozone, and enzyme pre-treatments on cheese whey degradation for enhancement of anaerobic digestion

Lactose in cheese whey wastewater (CWW) makes it difficult to degrade under normal conditions. The effect of ultra-sonication (US), ozonation and enzymatic hydrolysis on increasing the bioavailability of organic matter in CWW and biogas production were evaluated. The pre-treatment conditions were: specific energy input varied from 2130 to 8773KJ/KgTS for a sonication time of 4.5-18.5 min, Ozone (O₃) dosages ranging from 0.03 to 0.045gO₃/gTS were applied for 4-16 min, pH (3.8-7.1), temperature (35°C-55°C), enzyme dosage (0.18-0.52%), was operated from 7.75 to 53 min for enzymatic hydrolysis by β-galactosidase. The results of the US reported a maximum sCOD solubilisation of 77.15% after 18.5 min of operation, while the corresponding values for ozonation and enzymatic methods were 64.8% at 16 min and 54.79%, respectively. The organic matter degradation rates evaluated in terms of protein and lactose hydrolysis were 68.78%,46.03%; 47.83%,16.15% and 54.22%,86.2%respectively, for US, ozonation and enzymatic methods. The cumulative methane yield for sonicated, ozonised and enzymatically hydrolysed samples were 412.4 ml/g VS, 361.2 ml/g VS and 432.3mlCH₄/gVS, respectively. Regardless of the lower COD solubilisation rates attained, enzymatic pre-treatment showed maximum methane generation compared to US and ozonation. This could be attributable to the increased activity of β-galactosidase in hydrolysing whey lactose. The energy calculations revealed that the pre-conditioning of organic-rich CWW with enzymatic hydrolysis is more effective and efficient, yielding a net energy gain (gross output energy-input energy) of 9166.7 KJ and an energy factor (ratio of output to input energy) of 6.67. The modified Gompertz model well simulated all experimental values.

Improvement of Asterarcys quadricellulare biomass solubilization and subsequent biogas production via pretreatment approaches: structural changes and kinetic modeling evaluation

This study investigated the effect of enzymatic and hydrothermal pretreatment approaches on the solubilization of organic matter, structure, and biogas yield from microalgal biomass. The soluble chemical oxygen demand (sCOD) concentration increased by 1.21-3.30- and 5.54-6.60-fold compared to control by enzymatic and hydrothermal pretreatments respectively. The hydrothermal pretreatment affected the structural changes in the microalgal biomass markedly; nonetheless, increased enzymatic concentration also had a definite effect on it as determined by qualitative approaches like scanning electron microscopy and Fourier transform infrared spectroscopy. Also, the hydrothermal pretreatment (100 °C for 30 min) resulted in the highest biogas production potential (P) of 765.37 mLg^-1 VS at a maximum biogas production rate (R_m) of 22.66 mLg^-1 day^-1 with a very short lag phase (λ) of 0.07 days. The biogas production of pretreated microalgal biomass particularly at higher enzyme dose (20%, 24 h) and higher hydrothermal pretreatment temperature (120 °C, 30 min) showed a significant but weak correlation (R = 0.53) with sCOD, thus demonstrating that the less organic matter was used up for the biogas production. The modified Gompertz model explained the anaerobic digestion of microalgal biomass more accurately and had a better fit to the experimental data comparatively because of the low root mean square error (3.259-16.728), residual sum of squares (78.887-177.025), and Akaike's Information Criterion (38.605-62.853).

Value addition through biohydrogen production and integrated processes from hydrothermal pretreatment of lignocellulosic biomass

Bioenergy production is the most sought-after topics at the crunch of energy demand, climate change and waste generation. In view of this, lignocellulosic biomass (LCB) rich in complex organic content has the potential to produce bioenergy in several forms following the pretreatment. Hydrothermal pretreatment that employs high temperatures and pressures is gaining momentum for organics recovery from LCB which can attain value-addition. Diverse bioprocesses such as dark fermentation, anaerobic digestion etc. can be utilized following the pretreatment of LCB which can result in biohydrogen and biomethane production. Besides, integration approaches for LCB utilization that enhance process efficiency and additional products such as biohythane production as well as application of solid residue obtained after LCB pretreatment were discussed. Importance of hydrothermal pretreatment as one of the suitable strategies for LCB utilization is emphasized suggesting its future potential in large scale energy recovery.

Optimization of alkali, acid and organic solvent pretreatment on rice husk and its techno economic analysis for efficient sugar production

Excessive use of fossil fuels has accelerated climate change and global warming necessitates the need for renewable energy sources that have a lower environmental impact. In the recent decade, lignocellulosic biomass has become a prominent alternative to renewable energy resources for the production of bioenergy. The pretreatment procedure is considered a pivotal step for transforming biomass into value-added products such as sugars, biofuels, etc. Therefore, the present work aims to study the effect of different pretreatment approaches on rice husk with acids (H₂SO₄ and HCl), alkalis (NaOH and KOH), and organic solvents (ethanol and methanol) utilizing different concentrations like (2, 4 and 6% in case of acids), (2,4 and 6% for alkalis) and (50% and 70% for organic solvents) with different residence time (1, 3, 6, and 24 h). The most effective results obtained from the aforementioned steps were further adopted for enzymatic hydrolysis. Further, the changes in structural properties of biomass were assessed in relation to the pretreatment process employing scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier Transform Infrared (FTIR) analyses. This paper also highlights the techno-economic analysis of alkali pretreatment. Additionally, the operational targets for the process were identified by using a modeling software-SuperPro Designer. Results obtained from the study showed a maximum yield of reducing sugar i.e., 1.906 ± 0.2 mg/ml (4% NaOH with 6 h of incubation). This study demonstrates that 4% NaOH pretreatment effectively disintegrates the biomass and yields high sugar recovery which can be used further for the production of biofuels and value-added products.

Hydrothermal and thermal-alkali pretreatments of wheat straw: Co-digestion, substrate solubilization, biogas yield and kinetic study

Agro-waste having lignocellulosic biomass is considered most effective (heating value 16 MJ/kg) for energy production through anaerobic digestion (AD). However, recalcitrant lignocellulosic fraction in agro-waste obstructs its biotransformation and is a rate-limiting step of the process. This study investigated the effects of hydrothermal and thermal-alkaline pretreatment on anaerobic co-digestion of wheat straw (WS). The hydrothermal pretreatment of WS revealed that 60 min was the best pretreatment time to achieve the highest substrate solubilization. It was employed for thermal-alkali pretreatment at variable temperatures and NaOH doses. Thermal-alkali pretreatment at 125°C-7% NaOH shows the highest (34%) biogas yield of 662 mL/gVS, followed by 646 mL/gVS biogas yield at 150°C-1% NaOH assay (31% higher) over control. Although the 125°C-7% NaOH assay achieved the highest biogas yield, the 150°C-1% NaOH assay was found more feasible considering the cost of a 6% higher chemical used in the earlier assay. The thermal-alkali pretreatment was observed to reduce the formation of recalcitrant compounds (HMF, Furfural) and increase the buffering capacity of the slurry over hydrothermal pretreatment. Principal component analysis (PCA) of the various pretreatment and AD operational parameters was carried out to study their in-depth correlation. Moreover, a kinetic study of the experimental data was performed to observe the biodegradation trend and compare it with the Modified Gompertz (MG) and First Order (FO) models.

Impact of solid content on hydrothermal pretreatment of municipal sludge prior to fermentation and anaerobic digestion

This study investigated the impact of the solid sludge content concentrations (SC) on hydrothermal pretreatment (HTP) before fermentation and anaerobic digestion. Five different SC of 3.5%, 7%, 10%, 12%, and 16% were investigated in two different scenarios. The first scenario entailed using only the pretreated samples as substrates, whereas in scenario two, the substrates included pretreated samples combined with the supernatant. Results revealed that the highest overall pCOD solubilization (considering HTP and fermentation) of 64% was achieved for the sample with 12% SC combined with supernatant. The maximum volatile fatty acids production of 2.8 g COD/L occurred with 10% SC without supernatant. The maximum methane yield of 291 mL CH₄/g VSS added was attained at 7% SC without supernatant. Furthermore, the results indicated that increasing the SC beyond 7% in scenario 1 and 10% in scenario two led to a decrease in methane yield. Additionally, optimizing for all desired endpoints may be difficult, and there are limits on the increase in SC concerning methane production.

Comprehensive Review of Hydrothermal Pretreatment Parameters Affecting Fermentation and Anaerobic Digestion of Municipal Sludge

Municipal solid waste treatment and disposal have become one of the major concerns in waste management due to the excessive production of waste and higher levels of pollution. To address these challenges and protect the environment in sustainable ways, the hydrothermal pretreatment (HTP) technique coupled with anaerobic digestion (AD) becomes a preferred alternative technology that can be used for municipal solid waste stabilization and the production of renewable energy. However, the impact of HTP parameters such as temperature, retention time, pH, and solid content on the fermentation of TWAS is yet to be well studied and analyzed. Hence this study was conducted to review the effect of hydrothermal pretreatment of thickened waste-activated sludge (TWAS) on fermentation and anaerobic digestion processes. Many studies reported that fermentation of TWAS at pretreatment temperature ranges from 160 °C to 180 °C resulted in a 50% increase in volatile fatty acid (VFA) yields compared to no pretreatment. However, for the AD process, HTP in the range of 175 °C to 200 °C with a 30–60 min retention time was considered the optimal condition for higher biogas production, with 30% increase in biodegradability and greater than 55% increase in biogas production. Even though there is a direct relationship between increased HTP temperature and the hydrolysis of TWAS, a pretreatment temperature range beyond 200 °C alters the biogas production. The solid content (SC) of sludge plays a crucial role in HTP, where in practice up to 16% SC has been utilized for HTP. Further, a combined alkaline-HTP enhances the process performance.

Low-Temperature Pretreatment of Biomass for Enhancing Biogas Production: A Review

Low-temperature pretreatment (LTPT, Temp. < 100 °C or 140 °C) has the advantages of low input, simplicity, and energy saving, which makes engineering easy to use for improving biogas production. However, compared with high-temperature pretreatment (>150 °C) that can destroy recalcitrant polymerized matter in biomass, the action mechanism of heat treatment of biomass is unclear. Improving LTPT on biogas yield is often influenced by feedstock type, treatment temperature, exposure time, and fermentation conditions. Such as, even when belonging to the same algal biomass, the response to LTPT varies between species. Therefore, forming a unified method for LTPT to be applied in practice is difficult. This review focuses on the LTPT used in different biomass materials to improve anaerobic digestion performance, including food waste, sludge, animal manure, algae, straw, etc. It also discusses the challenge and cost issues faced during LTPT application according to the energy balance and proposes some proposals for economically promoting the implementation of LTPT.

Prospects of soil microbiome application for lignocellulosic biomass degradation: An overview

Sustainable and practically viable biofuels production technology using lignocellulosic biomass is still seeking its way of implementation owing to some major issues involved therein. Unavailability of efficient microbial sources for the degradation of cellulosic biomass is one of the major roadblocks in biomass to biofuels production technology. In this context, utilization of microbiomes to degrade lignocellulaosic biomass is emerging as a rapid and effective approach that can fulfill the requirements of biomass based biofuels production technology. Therefore, the present review is targeted to explore soil metagenomic approach to improve the lignocellulosic biomass degradation processing for the cost-effective and eco-friendly application. Soil microbiomes consist of rich microbial community along with high probability of cellulolytic microbes, and can be identified by culture independent metagenomics method which can be structurally and functionally explored via genomic library. Therefore, in depth analysis and discussion have also been made via structural & functional metagenomics tools along with their contribution to genomic library. Additionally, the present review highlights currently existing bottlenecks along with their feasible solutions. This review will help to understand the basic research as well as industrial concept for the process improvement based on soil microbiome mediated lignocellulosic biomass degradation, and this may likely to implement for the low-cost commercial biofuels production technology.

Integrated system of anaerobic digestion and pyrolysis for valorization of agricultural and food waste towards circular bioeconomy: Review

Agricultural and food waste have become major issue affecting the environment and climate owing to growing population. However, such wastes have potential to produce renewable fuels which will help to meet energy demands. Numerous valorization pathways like anaerobic digestion, pyrolysis, composting and landfilling have been employed for treating such wastes. However, it requires integrated system that could utilize waste and promote circular bioeconomy. This review explores integration of anaerobic digestion and pyrolysis for treating agricultural and food waste. Proposed system examines the production of biochar and pyro-oil by pyrolysis of digestate. The use of this biochar for stabilizing anaerobic digestion process, biogas purification and soil amendment will promote the circular bioeconomy. Kinetic models and framework of techno-economic analysis of system were discussed and knowledge gaps have been identified for future research. This system will provide sustainable approach and offer carbon capture and storage in form of biochar in soil.

Hydrothermal Pretreatment of Wheat Straw—Evaluating the Effect of Substrate Disintegration on the Digestibility in Anaerobic Digestion

The increasing demand for renewable energy sources and demand-oriented electricity provision makes anaerobic digestion (AD) one of the most promising technologies. In addition to energy crops, the use of lignocellulosic residual and waste materials from agriculture is becoming increasingly important. However, AD of such feedstocks is often associated with difficulties due to the high content of lignocellulose and its microbial persistence. In the present work, the effect of hydrothermal pretreatment (HTP) on the digestibility of wheat straw is investigated and evaluated. Under different HTP temperatures (160–180 °C) and retention times (15–45 min), a significant increase in biomethane potential (BMP) can be observed in all cases. The highest BMP (309.64 mL CH4 g−1 volatile solid (VS) is achieved after pretreatment at 160 °C for 45 min, which corresponds to an increase of 19% of untreated wheat straw. The results of a multiple linear regression model show that the solubilization of organic materials is influenced by temperature and time. Furthermore, using two different first-order kinetic models, an enhancement of AD rate during hydrolysis due to pretreatment is observed. However, the increasing intensity of pretreatment conditions is accompanied by a decreasing trend in the conversion of intermediates to methane.

Anaerobic co-digestion of cheese whey and septage: Effect of substrate and inoculum on biogas production

Cheese whey is an industrial waste generated from the cheese processing unit of the dairy industry and requires treatment before its disposal. The present study investigated the possibilities of improving the digestibility from anaerobic digestion of lipid rich dairy by-product, cheese whey using septage as the co-substrate with different inoculum. Biochemical methane potential assays were conducted under mesophilic temperature conditions and results were validated using Modified Gompertz Model. Two sets of BMP tests were done; to assess the individual and combined digestion abilities of septage in anaerobic co-digestion of whey and to assess the ability of 3 inoculum sources (cattle manure, sewage sludge, and acclimatized anaerobic sludge) in the co-digestion process. The results indicated that septage is an excellent co-substrate that has better adaptability with cheese whey and the optimum mix ratio was found as 40:60 (S_CW: S_SP). BMP tests were also conducted with inoculum at S/I ratio of 1 and statistical analysis was performed to study the synergistic effect of both co-digestion and inoculum. The tests revealed that the cattle manure resulted in the highest biogas production (342.22mL/gVS) at 60% whey fraction. Modified Gompertz model fitted the experimental data well and identified an increase in lag phase times when whey fraction is increased. Comparatively higher lag phase times ranging from 1.98 to 4.35 days were obtained for sewage sludge inoculated samples. The maximum methane production (P_max) was obtained at 60% whey fraction (369.63 ± 4.05mL/gVS) at a very short lag time of 0.76 ± 0.17days for cattle manure inoculated mixture.

A waste to energy technology for Enrichment of biomethane generation: A review on operating parameters, types of biodigesters, solar assisted heating systems, socio economic benefits and challenges

Anaerobic Digestion (AD) is one of the promising wastestoenergy (WtE) technologies that convert organic wastes to useful gaseous fuel (biogas). In this process methane is produced in the presence of methanogens (bacteria). The survival and activities of methanogens are based on several parameters such as pH, temperature, organic loading rate, types of biodigester. Moreover, these parameters influence the production of biogas in terms of yield and composition. Maintaining an appropriate temperaturefor AD is highly critical and energy intensive. This study reviews the various hybrid technologies assistedbio gas production schemes particularly from renewable energy sources. Also discuss the direct and indirect solar assisted bio-digester impacts and recommendation to improve its performance. In addition, the performance analysis Solar Photovoltaic (PV) and thermal collector assisted bio gas plants; besides their impact on the performance of anaerobic digesters. Since opportunities of solar energy are attractive, the effective utilization of the same is selected for the discussion. Besides, the various constraints that affect the yield and composition of biogas are also evaluated along with the current biogas technologies and the biodigesters. The environmental benefits, challenges and socio-economic factors are also discussed for the successful implementation of various technologies.

Effect of low levels of oxytetracycline on anaerobic digestion of cattle manure

Cattle manure is rich in organic matter and nutrients, but it may also contain harmful substances such as residual antibiotics and other toxic compounds. Oxytetracycline (OTC) is a widely used veterinary antibiotic and its presence in manure can affect the subsequent anaerobic digestion process. This study evaluated the effect of OTC concentrations viz. 0.12, 0.3, 0.6, 1.2, 3, 6 and 12 mg L^-1 on batch mesophilic anaerobic digestion of cattle manure. The results showed that cumulative biogas yield decreased by 25, 29 and 55% at 3, 6 and 12 mg OTC L^-1 in contrast to control. Volatile solids removal was 39% for control which reduced to 13% in 12 mg L^-1 OTC spiked reactor. Effect on stability parameters was significant at OTC concentrations from 1.2 to 12 mg L^-1. Two different kinetic models were used for biogas data validation and the modified Gompertz model best fitted to the experimental data.

Enrichment of Anaerobic Microbial Communities from Midgut and Hindgut of Sun Beetle Larvae (Pachnoda marginata) on Wheat Straw: Effect of Inoculum Preparation

The Pachnoda marginata larva have complex gut microbiota capable of the effective conversion of lignocellulosic biomass. Biotechnological utilization of these microorganisms in an engineered system can be achieved by establishing enrichment cultures using a lignocellulosic substrate. We established enrichment cultures from contents of the midgut and hindgut of the beetle larva using wheat straw in an alkaline medium at mesophilic conditions. Two different inoculation preparations were used: procedure 1 (P1) was performed in a sterile bench under oxic conditions using 0.4% inoculum and small gauge needles. Procedure 2 (P2) was carried out under anoxic conditions using more inoculum (4%) and bigger gauge needles. Higher methane production was achieved with P2, while the highest acetic acid concentrations were observed with P1. In the enrichment cultures, the most abundant bacterial families were Dysgonomonadaceae, Heliobacteriaceae, Ruminococcaceae, and Marinilabiliaceae. Further, the most abundant methanogenic genera were Methanobrevibacter, Methanoculleus, and Methanosarcina. Our observations suggest that in samples processed with P1, the volatile fatty acids were not completely converted to methane. This is supported by the finding that enrichment cultures obtained with P2 included acetoclastic methanogens, which might have prevented the accumulation of acetic acid. We conclude that differences in the inoculum preparation may have a major influence on the outcome of enrichment cultures from the P. marginata larvae gut.

A review on biological recycling in agricultural waste-based biohydrogen production: Recent developments

Hydrogen has become a research highlight by virtue of its clean energy production technology and high energy content. The technology of biohydrogen production from biological waste via fermentation has lower costs, provides environment-friendly methods regarding energy balance, and creates a pathway for sustainable utilization of massive agricultural waste. However, biohydrogen production is generally limited by lower productivity. Many studies have been conducted aimed at improving biohydrogen production efficiency. Hence, this review is intended to describe improving routes for biohydrogen production from agricultural waste and highlights recent advances in these approaches. In addition, the critical factors affecting biohydrogen production, including the pretreatment method, substrate resource, fermentation conditions, and bioreactor design, were also comprehensively discussed along with challenges and future prospects.

Current advances and future outlook on pretreatment techniques to enhance biosolids disintegration and anaerobic digestion: A critical review

Waste activated sludge (biosolids) treatment is intensely a major problem around the globe. Anaerobic treatment is indeed a fundamental and most popular approach to convert organic wastes into bioenergy, which could be used as a carbon-neutral renewable and clean energy thus eradicating pathogens and eliminating odor. Due to the sheer intricate biosolid matrix (such as exopolymeric substances) and rigid cell structure, hydrolysis becomes a rate-limiting phase. Numerous different pretreatment strategies were proposed to hasten this rate-limiting hydrolysis and enhance the productivity of anaerobic digestion. This study discusses an overview of previous scientific advances in pretreatment options for enhancing biogas production. In addition, the limitations addressed along with the effects of inhibitors in biosolids towards biogas production and strategies to overcome discussed. This review elaborated the cost analysis of various pretreatment methods towards the scale-up process. This review abridges the existing research on augmenting AD efficacy by recognizing the associated knowledge gaps and suggesting future research.

Influence of cavitation, pelleting, extrusion and torrefaction petreatments on anaerobic biodegradability of barley straw and vine shoots

When dealing with lignocellulosic biomass in anaerobic digestion, a pretreatment stage is always required to open the structure of the material, facilitating its degradation. Numerous methods have been developed to pretreat lignocellulosic biomass. Four of them: cavitation, pelleting, extrusion and torrefaction have been comparatively studied in this paper as ways to improve the production of methane by anaerobic digestion of two different feedstocks: barley straw and vine shoots. Additionally, how the selected pretreatments and the nature of the feedstock influence the formation of individual volatile fatty acids was examined. Cavitation was revealed as the most efficient pretreatment, increasing 240% and 360% the methane production for barley straw and vine shoots, respectively, although in absolute terms, barley straw has higher production rate and yield than vine shoots. Torrefaction carried out at 180 °C increased methane production, 81% for straw and 25% for vine shoots, while the process at higher temperatures (220 °C) negatively affected biogas production from both feedstocks. Finally, volatile fatty acids accumulation seems to neutralize any potential positive effects of densification pretreatments.

Solid-state anaerobic digestion of sugarcane bagasse at different solid concentrations: Impact of bio augmented cellulolytic bacteria on methane yield and insights on microbial diversity

This study investigated the impact of the potential cellulose degrading bacteria that could be bioaugmented in the solid-state anaerobic digestion (SSAD) of bagasse to enhance the methane yield. The prospective anaerobic cellulose degrading bacteria was isolated from the soil. SSAD experiments were organized with & without bioaugmentation with a substrate total solid (TS) of 25%, 30%, 40% and 50% at an optimized feed to microorganism (F/M) ratio of 1:1. The maximum yield of 0.44 L CH₄/ (g VS added) was obtained from bioaugmented bagasse at a TS of 40% whereas it was 0.34 L CH₄/(g VS added) for non-bioaugmented bagasse. The isolated bacterial strain was identified that belongs species Pseudomonas of Gamma Proteobacteria which exhibited good cellulolytic activity. Metagenomic studies found 90% of archaeal microorganisms affiliated to Methanosaeta, a strict acetoclastic methanogen.

A novel thermal pretreatment method called air frying improves the enzymatic saccharification effect of straw

Thermal pretreatment is a shared method to improve the efficiency of straw biochemical conversion. However, the process is often accompanied by problems such as the loss of carbon source. The objective of this study was to develop a novel thermal pretreatment method, called air frying, with less loss of biodegradable organic matter and favorable surface hydrophilicity. After pretreatment of two straws, the sugar yields were improved, and the improvement effect of corn stover was more significant. The total saccharification rate of corn stover increased from 31.31 ± 1.06% to 44.77 ± 1.23%, and the cellulose conversion rate increased from 44.10 ± 1.85% to 67.44 ± 2.37%. Functional groups with lower polarity on the surface were oxidized into the one with stronger polarity, so the hydrophilicity was enhanced. The surface roughness decreased, the surface tended to be flat, the original pores collapsed, and the average pore size increased, which was more conducive to the binding of enzyme and active site. The matching relationship between the optimal conditions and substrate, and the possibility of scaling up need further study.

The inhibiting effects of biochar-derived organic materials on rice production

The effects of PBC and HBC on rice production, NUE and corresponding mechanisms were examined. Six treatments, P05, P30, H05, H30 (P: PBC; H: HBC; 05 and 30 represented the application rate of 0.5 and 3.0% w/w), CKU (urea application without char) and CK (no application of char and urea), were set up. Results showed that P05, P30 and H05 increased grain yield by 1.8-7.3% (P > 0.05), whereas H30 reduced grain yield by 60.4% (P < 0.05), compared to CKU. Meanwhile, HI under P05, P30 and H05 increased by 3.4-3.6%, while H30 decreased by 9.1% (P < 0.05). NUE and NAE showed similar trends with rice yield. By investigation, the excessive introduction of BDOM plays a crucial role in the reduction of rice production and NUE under higher HBC application. GC-MS/MS analysis showed that the soluble BDOM of HBC and PBC was quite different, and compounds such as 2,6-dimethoxyphenol might stress rice growth. ESI-FT-ICR-MS analysis showed that the BDOM of HBC contained a certain quantity of aromatic compounds, which may also stress rice growth. Overall, HBC pretreatment should be conducted, and the application rate should be strictly controlled before its agricultural application.

Genomic driven factors enhance biocatalyst-related cellulolysis potential in anaerobic digestion

Anaerobic digestion (AD) is a promising technology to recover bioenergy from biodegradable biomass, including cellulosic wastes. Through a few fractionation/separation techniques, cellulose has demonstrated its potential in AD, but the performance of the process is rather substrate-specific, as cellulolysis bacteria are sensitive to the enzyme-substrate interactions. Cellulosome is a self-assembled enzyme complex with many functionalized modules in the bacteria which has been gradually studied, however the genomic fingerprints of the culture-specific cellulosome in AD are relatively unclear especially under processing conditions. To clarify the key factors affecting the cellulosome induced cellulolysis, this review summarized the most recent publications of AD regarding the fates of cellulose, sources and functional genes of cellulosome, and omics methods for functional analyses. Different processes for organic treatment including applying food grinds in sewer, biomass valorization, cellulose fractionation, microaeration, and enzymatic hydrolysis enhanced fermentation, were highlighted to support the sustainable development of AD technology.

Optimization of biogas yield from lignocellulosic materials with different pretreatment methods: a review

Population increase and industrialization has resulted in high energy demand and consumptions, and presently, fossil fuels are the major source of staple energy, supplying 80% of the entire consumption. This has contributed immensely to the greenhouse gas emission and leading to global warming, and as a result of this, there is a tremendous urgency to investigate and improve fresh and renewable energy sources worldwide. One of such renewable energy sources is biogas that is generated by anaerobic fermentation that uses different wastes such as agricultural residues, animal manure, and other organic wastes. During anaerobic digestion, hydrolysis of substrates is regarded as the most crucial stage in the process of biogas generation. However, this process is not always efficient because of the domineering stableness of substrates to enzymatic or bacteria assaults, but substrates' pretreatment before biogas production will enhance biogas production. The principal objective of pretreatments is to ease the accessibility of the enzymes to the lignin, cellulose, and hemicellulose which leads to degradation of the substrates. Hence, the use of pretreatment for catalysis of lignocellulose substrates is beneficial for the production of cost-efficient and eco-friendly process. In this review, we discussed different pretreatment technologies of hydrolysis and their restrictions. The review has shown that different pretreatments have varying effects on lignin, cellulose, and hemicellulose degradation and biogas yield of different substrate and the choice of pretreatment technique will devolve on the intending final products of the process.

Influences of size reduction, hydration, and thermal-assisted hydration pretreatment to increase the biogas production from Napier grass and Napier silage

Pretreatment of lignocellulose materials prior to biogas production is required to minimize biomass recalcitrance and increase biomass digestibility. In this study, the effects of particle size reduction, hydration, and thermal-assisted hydration on Napier grass and silage for methane production were evaluated. Compared to the 4.75-mm particle size Napier grass and silage, 0.425-mm Napier grass and silage showed 72% and 46% increases in methane yield, respectively, whereas hydration pretreatment using hydrogenic effluent increased the methane yields from Napier grass and silage by 23% and 56%, respectively. Superior effects were observed when Napier grass and silage were pretreated with thermal-assisted hydration using hydrogenic effluent for 60 and 15 min, respectively, resulting in methane yields of 385 and 331 mL CH₄/g substrate_added. The results indicate that size reduction accompanied by thermal-assisted hydration using hydrogenic effluent as a hydration medium significantly improved the biodegradability of Napier grass and silage.

Statistical optimization of methane production from brewery spent grain: Interaction effects of temperature and substrate concentration

This study evaluated the effects of thermal pretreatment of brewery spent grain (BSG) (by autoclave 121 °C, 1.45 atm for 30 min) on methane production (CH₄). Operation temperature (31-59 °C) and substrate concentration (8.3-19.7 g BSG.L^-1) factors were investigated by Response Surface Methodology (RSM) and Central Composite Design (CCD). Values ranging from 81.1 ± 2.0 to 290.1 ± 3.5 mL CH₄.g^-1 TVS were obtained according to operation temperature and substrate concentration variation. The most adverse condition for methanogenesis (81.1 ± 2.0 mL CH₄.g^-1 TVS) was at 59 °C and 14 g BSG.L^-1, in which there was increase in the organic matter concentration from 173.6 ± 4.94 to 3036 ± 7.78 mg.L^-1) result of a higher final concentration of volatile fatty acids (VFA, 2662.7 mg.L^-1). On the other hand, the optimum condition predicted by the statistical model was at 35 °C and 18 g BSG.L^-1 (289.1 mL CH₄.g^-1 TVS), which showed decrease in the organic matter concentration of 78.6% and a lower final concentration of VFA (533.2 mg.L^-1). Hydrogenospora and Methanosaeta were identified in this optimum CH₄ production condition, where acetoclastic methanogenic pathway prevailed. The CH₄ production enhancement was concomitant to acetic acid concentration decrease (from 578.9 to 135.7 mg.L^-1).

Advances in Pretreatment of Straw Biomass for Sugar Production

Straw biomass is an inexpensive, sustainable, and abundant renewable feedstock for the production of valuable chemicals and biofuels, which can surmount the main drawbacks such as greenhouse gas emission and environmental pollution, aroused from the consumption of fossil fuels. It is rich in organic content but is not sufficient for extensive applications because of its natural recalcitrance. Therefore, suitable pretreatment is a prerequisite for the efficient production of fermentable sugars by enzymatic hydrolysis. Here, we provide an overview of various pretreatment methods to effectively separate the major components such as hemicellulose, cellulose, and lignin and enhance the accessibility and susceptibility of every single component. This review outlines the diverse approaches (e.g., chemical, physical, biological, and combined treatments) for the excellent conversion of straw biomass to fermentable sugars, summarizes the benefits and drawbacks of each pretreatment method, and proposes some investigation prospects for the future pretreatments.

Effect of Liquid Hot Water Pretreatment on Hydrolysates Composition and Methane Yield of Rice Processing Residue

Lignocellulosic rice processing residue was pretreated in liquid hot water (LHW) at three different temperatures (140, 160, and 180 °C) and two pretreatment times (10 and 20 min) in order to assess its effects on hydrolysates composition, matrix structural changes and methane yield. The concentrations of acetic acid, 5-hydroxymethylfurfural and furfural increased with pretreatment severity (log Ro). The maximum methane yield (276 L kg−1 VS) was achieved under pretreatment conditions of 180 °C for 20 min, with a 63% increase compared to untreated biomass. Structural changes resulted in a slight removal of silica on the upper portion of rice husks, visible predominantly at maximum severity. However, the outer epidermis was kept well organized. The results indicate, at severities 2.48 ≤ log Ro ≤ 3.66, a significant potential for the use of LHW to improve methane production from rice processing residue.

Effects of NaOH, thermal, and combined NaOH-thermal pretreatments on the biomethane yields from the anaerobic digestion of walnut shells

Anaerobic digestion (AD) of walnut shells (WS) results in only a limited biomethane yield because of their high fibre content, which ultimately represents an essentially nonbiodegradable lignocellulosic biomass. In the present study, thermal (i.e. 50-250 °C), alkaline (i.e. 1-5% w/w NaOH) and combined alkaline-thermal (i.e. 4% w/w NaOH + 150 °C thermal) pretreatment methods have been applied to increase the anaerobic biodegradation of WS. The highest biomethane yields of 159.9 ± 6.8 mL CH₄.g VS^-1 and 169.8 ± 6.8 mL CH₄.g VS^-1 were achieved after pretreatment at both 250 °C and with 4% NaOH. After combined NaOH-thermal pretreatments, the AD process showed the largest total VFA concentration (i.e. 1280.1 mg Hac L^-1) but a relatively high lag phase (i.e. 3.90 days) compared to thermal and NaOH pretreatments alone, from which the highest biomethane yield (i.e. 192.4 ± 8.2 mL CH₄.g VS^-1 ) was achieved at the end of the AD process. The highest biomethane yield from the combined NaOH-thermal pretreated WS was corroborated by the corresponding highest SCOD/TCOD ratio (i.e. 0.37 ± 0.02) and the highest lignocellulosic fibre removal (i.e. 41.1 ± 2.7% cellulose, 35.6 ± 1.8% hemicellulose, and 58.7 ± 3.2% lignin). The cumulative biomethane yields were further simulated via a modified Gompertz model. This study provides a promising strategy in the sense that the biomethane yield of WS containing large amounts of lignin can be significantly increased via thermal, NaOH, and combined NaOH-thermal pretreatment methods.

Effect of thermo-chemical pretreatment on the saccharification and enzymatic digestibility of olive mill stones and their bioconversion towards alcohols

The present study investigated the effect of thermo-chemical pretreatment on the enhancement of enzymatic digestibility of olive mill stones (OMS), as well as its possible valorisation via bioconversion of the generated free sugars to alcohols. Specifically, the influence of parameters such as reaction time, temperature, type and concentration of dilute acids and/or bases, was assessed during the thermo-chemical pretreatment. The hydrolysates and the solids remaining after pretreatment, as well as the whole pretreated slurries, were further evaluated as potential substrates for the simultaneous production of ethanol and xylitol via fermentation with the yeast Pachysolen tannophilus. The digestibility and overall saccharification of OMS were considerably enhanced in all cases, with the maximum enzymatic digestibility observed for dilute sodium hydroxide (almost 4-fold) which also yielded the highest total saccharification yield (91% of the total OMS carbohydrates). Ethanol and xylitol yields from the untreated OMS were 28 g/kg OMS and 25 g/kg OMS, respectively, and were both significantly enhanced by pretreatment. The highest ethanol yield was 79 g/kg OMS and was achieved by the alkali pretreatment and separate fermentation of hydrolysates and solids, whereas the highest xylitol yield was 49 g/kg OMS and was obtained by pretreatment with sulphuric acid and separate fermentation of hydrolysates and solids.

Pretreatments for enhanced biomethane production from buckwheat hull: Effects on organic matter degradation and process sustainability

Buckwheat manufacturing produce a large amount of lignocellulosic residue (buckwheat hull), which could be used as substrate in anaerobic digestion, even if hard lignocellulosic structure represents the main obstacle for its degradation. This study presents the results of a laboratory experiment conducted to evaluate the effects of different pretreatments on buckwheat hull anaerobic digestion. To achieve the aim, five pretreatments (alkaline, thermo-alkaline, microwave, ultrasonication and low temperature thermal pretreatment) were studied and the results were compared to non treated buckwheat hull. Cumulative biomethane yields significantly increased after alkaline and thermo-alkaline pretreatments (+61% and +122% with respect to non treated hull, respectively). These results were mainly related to organic matter solubilisation (+772% and +859% of soluble reducing sugars, respectively) and lignin, hemicellulose and cellulose degradation. Overall, process parameters behaviour and digestate quality were not affected by the pretreatments. Alkaline and thermo-alkaline pretreatments were evaluated for their energetic and economic affordability, showing that combination of thermal and alkaline pretreatments ensures significant advantages.

Socio-Economic and Environmental Impacts of Biomass Valorisation: A Strategic Drive for Sustainable Bioeconomy

In the late twentieth century, the only cost-effective opportunity for waste removal cost at least several thousand dollars, but nowadays, a lot of improvement has occurred. The biomass and waste generation problems attracted concerned authorities to identify and provide environmentally friendly sustainable solutions that possess environmental and economic benefits. The present study emphasises the valorisation of biomass and waste produced by domestic and industrial sectors. Therefore, substantial research is ongoing to replace the traditional treatment methods that potentially acquire less detrimental effects. Synthetic biology can be a unique platform that invites all the relevant characters for designing and assembling an efficient program that could be useful to handle the increasing threat for human beings. In the future, these engineered methods will not only revolutionise our lives but practically lead us to get cheaper biofuels, producing bioenergy, pharmaceutics, and various biochemicals. The bioaugmentation approach concomitant with microbial fuel cells (MFC) is an example that is used to produce electricity from municipal waste, which is directly associated with the loading of waste. Beyond the traditional opportunities, herein, we have spotlighted the new advances in pertinent technology closely related to production and reduction approaches. Various integrated modern techniques and aspects related to the industrial sector are also discussed with suitable examples, including green energy and other industrially relevant products. However, many problems persist in present-day technology that requires essential efforts to handle thoroughly because significant valorisation of biomass and waste involves integrated methods for timely detection, classification, and separation. We reviewed and proposed the anticipated dispensation methods to overcome the growing stream of biomass and waste at a distinct and organisational scale.

Towards an ideotype for food-fuel dual-purpose wheat in Argentina with focus on biogas production

BACKGROUND

Wheat straw, one of the most abundant agricultural residues worldwide, can be used to produce biogas, which is considered one of the most efficiently produced renewable energies. Wheat grown with the dual-purpose of producing food and biogas should display simultaneously high grain and straw yields, low lodging susceptibility and high conversion efficiency of straw into biogas. The aims of this study were to determine the best food-fuel dual-purpose wheat candidates among 36 wheat genotypes-including French, CIMMYT and local (Criollo) germplasm-used in breeding programs in Argentina and to gain some insights into the relationships between key traits relevant for dual-purpose wheat genotypes.

RESULTS

High variability in individual key traits for dual-purpose wheat ideotype has been found. Genotypes of French origin displayed the highest grain yield, and those of CIMMYT origin, the lowest straw yield. Genotypes of Criollo origin showed the highest lodging susceptibility, and French ones, the lowest. Straw yield was positively correlated with grain yield in all genotypes, and negatively correlated with plant height in genotypes of Criollo origin. Straw conversion into biogas was measured in terms of the biogas potential production and kinetic parameters B_max (maximum specific biogas production) and k (first-order kinetic constant) were analyzed. All key traits were analyzed together by a principal component analysis. Baguette 31 and SNR Nogal, two genotypes of French origin, showed high grain yield, high-to-very high straw yield, low lodging susceptibility, and moderate-to-high B_max and k. Buck Guapo and Buck Baqueano, two genotypes of Criollo origin, displayed good values for grain yield, straw yield and B_max and k. However, their high lodging susceptibility precludes their production in shallow soils or high-input systems. Lastly, some old genotypes (e.g. Klein Atlas) harbored a good combination of all key traits and could prove valuable to be included in future breeding programs for dual-purpose wheat.

CONCLUSIONS

While none of the genotypes excelled in every key trait, a few candidates showed potential for dual-purpose ideotype, particularly Baguette 31 and SNR Nogal. The challenge lays in gathering all attributes for food and 2G fuel in the same genotype.

Solubilisation of fruits and vegetable dregs through surfactant mediated sonic disintegration: impact on biomethane potential and energy ratio

This study investigates the symbiotic effect of cetyltrimethylammonium bromide (CTAB) coupled with sonication of fruits and vegetable dregs (FVD) on disintegration and subsequent energy efficient methane production. The liquefaction of FVD experiments was conducted by varying dosage of surfactant from 0.001to 0.01 g/g SS for 60 min in mechanical shaker. The optimised dosage of surfactant was combined with sonication. Finally, the combined pretreatment and sole pretreatment were assessed using methane potential assay. The results revealed that at optimised conditions (sonication specific energy of 5400 kJ/kg TS, CTAB dosage of 0.006 g/g SS), the maximum liquefiable organics release rate and solids reduction of CTAB mediated sonic disintegration (CSD) were found respectively to be 27% and 17% more than the ultrasonic disintegration (16% and 10%). CSD was noticed to be superior than ultrasonic disintegration (UD) based on highest volatile fatty acid yield (2000 mg/L vs. 1250 mg/L) and biochemical methane potential (203 mL/g COD vs. 144 mL/g COD). CSD achieved energy ratio of 0.9 which is greater than ultrasonic disintegration energy ratio 0.4.

Enhancing methane production from dewatered waste activated sludge through alkaline and photocatalytic pretreatment

Waste activated sludge generated from wastewater treatment plants makes an abundant source of biomass. Its effective utilization through anaerobic digestion (AD) requires pretreatment to disintegrate the sludge matrix and increase organic matter availability. In this study, dewatered waste activated sludge (DWAS) was subjected to alkaline, photocatalytic, and alkaline-photocatalytic pretreatment for its disintegration and subsequent methane production using different concentrations of sodium hydroxide and titania nanoparticles. Individual pretreatment resulted in maximum disintegration degree (DD_sCOD) of 11.3 and 5.2% at 0.8% NaOH and 0.6 gTiO₂/L, respectively. Alkaline-photocatalytic pretreatment yielded 37% DD_sCOD at 0.8% NaOH-0.4 g/L TiO₂. As compared to control, AD at 0.4% NaOH and 0.5 g/L TiO₂ pretreatments yielded maximum methane, which was 50.4 and 32.6% higher. Similarly, alkaline-photocatalytic pretreatment at 0.4% NaOH-0.5 g/L TiO₂ yielded methane as 462 N mL/g VS, which was 71.1% higher. Modified Gompertz model fitted the methane yield data well.

Pilot Scale Elimination of Phenolic Cellulase Inhibitors From Alkali Pretreated Wheat Straw for Improved Cellulolytic Digestibility to Fermentable Saccharides

Depleting supplies of fossil fuel, regular price hikes of gasoline and environmental deterioration have necessitated the search for economic and eco-benign alternatives of gasoline like lignocellulosic biomass. However, pre-treatment of such biomass results in development of some phenolic compounds which later hinder the depolymerisation of biomass by cellulases and seriously affect the cost effectiveness of the process. Dephenolification of biomass hydrolysate is well cited in literature. However, elimination of phenolic compounds from pretreated solid biomass is not well studied. The present study was aimed to optimize dephenoliphication of wheat straw using various alkalis i.e., Ca(OH)₂ and NH₃; acids i.e., H₂O₂, H₂SO₄, and H₃PO₄; combinations of NH₃+ H₃PO₄ and H₃PO₄+ H₂O₂ at pilot scale to increase enzymatic saccharification yield. Among all the pretreatment strategies used, maximum reduction in phenolic content was observed as 66 mg Gallic Acid Equivalent/gram Dry Weight (GAE/g DW), compared to control having 210 mg GAE/g DW using 5% (v/v) combination of NH₃+H₃PO₄. Upon subsequent saccharification of dephenoliphied substrate, the hydrolysis yield was recorded as 46.88%. Optimized conditions such as using 1%+5% concentration of NH₃+ H₃PO₄, for 30 min at 110°C temperature reduced total phenolic content (TPC) to 48 mg GAE/g DW. This reduction in phenolic content helped cellulases to act more proficiently on the substrate and saccharification yield of 55.06% was obtained. The findings will result in less utilization of cellulases to get increased yield of saccharides by hydrolyzing wheat straw, thus, making the process economical. Furthermore, pilot scale investigations of current study will help in upgrading the novel process to industrial scale.

The degradation of organic matter coupled with the functional characteristics of microbial community during composting with different surfactants

The purpose of this study was to investigate the effects of anionic and cationic surfactants on the physico-chemical properties, organic matter (OM) degradation, bacterial community structure and metabolic function during composting of dairy manure and sugarcane bagasse. The results showed that the surfactant could optimize the composting conditions to promote the degradation of OM. The most OM degradation and humic substances (HS) synthesis were observed in SAS. Firmicutes and Proteobacteria were more abundant in SAS and CTAC, and Actinobacteria in CK. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) showed that SAS and CTAC are more abundant than CK in genes related to metabolism, environmental and genetic information processing. The correlation analysis showed that the dominant bacteria had more significant correlation with environmental factors. In general, the anionic surfactant could better promote the degradation of OM, change the structure of microbial community, and improve the quality of compost.

A comprehensive review of the recent development and challenges of a solar-assisted biodigester system

The extensive use of fossil fuels and the environmental effect of their combustion products have attracted researchers to look into renewable energy sources. In addition, global mass production of waste has motivated communities to recycle and reuse the waste in a sustainable way to lower landfill waste and associated problems. The development of waste to energy (WtE) technology including the production of bioenergy, e.g. biogas produced from various waste through Anaerobic Digestion (AD), is considered one of the potential measures to achieve the sustainable development goals of the United Nations (UN). Therefore, this study reviews the most recent studies from relevant academic literature on WtE technology (particularly AD technology) for biogas production and the application of a solar-assisted biodigester (SAB) system aimed at improving performance. In addition, socio-economic factors, challenges, and perspectives have been reported. From the analysis of different technologies, further work on effective low-cost technologies is recommended, especially using SAB system upgrading and leveraging the opportunities of this system. The study found that the performance of the AD system is affected by a variety of factors and that different approaches can be applied to improve performance. It has also been found that solar energy systems efficiently raise the biogas digester temperature and through this, they maximize the biogas yield under optimum conditions. The study revealed that the solar-assisted AD system produces less pollution and improves performance compared to the conventional AD system.

Why can hydrothermally pretreating lignocellulose in low severities improve anaerobic digestion performances?

A lignocellulosic residue, rice straw, was hydrothermally pretreated for the whole slurry anaerobic digestion. In contrast to the unpretreated rice straw, 110-120 °C pretreatment promoted biogas yield by 35%-38%, while only 14% promotion happened on the pretreatment at 180 °C. To understand why this improvement happened at lower severities, the pretreated rice straw at 90 °C, 120 °C, and 180 °C were selected for the further investigation, in which the liquor and solid fraction were separated for digestion, and compared with the whole slurry digestion. Results indicated more methane was released from the derived liquor of 180 °C than that of 90 °C and 120 °C, however, solid fraction did not exhibit significantly different methane yields (187.77-193.91 mL/g TS). These results suggested that the released soluble fraction from pretreatment could facilitate the methanogenesis. Furthermore, the released inherent soluble fraction in rice straw was mainly responsible for higher biogas yield at lower temperatures. Pretreatment at higher temperatures disintegrated the rice straw recalcitrance more, and intensified the release of soluble fraction accordingly. Consequently, the methanogenesis of whole slurry could be promoted at the initial digestion; the hydrolysis/acidification of the solid fraction in whole slurry was weakened greatly, which resulted in a lower biogas yield. This can also be proved by the evolution of dominant bacteria and archaea in the anaerobic digestion of whole slurry, separated solid and liquor fraction.

A systematic evaluation of biomethane production from sugarcane trash pretreated by different methods

Biomethane production was systematically evaluated with sugarcane trash pretreated by liquid hot water (LHW), dilute acid (DA) and KOH solutions. Multiple linear regression analysis identified glucan in pretreated solid residue as well as C5 sugars and acetic acid in pretreatment hydrolysate as the key parameters affecting biomethane potentials. Moreover, biomethane production was best simulated using Chen & Hashimoto model with a predicted highest methane yield of 187 mL/g initial total solids (TS) based on LHW (130 °C for 15 min) and KOH (10% on trash, 150 °C for 60 min) pretreatments. KOH pretreatment led to a biomethane yield of 167 mL/g initial TS at day 25, 82%, 34% and 33% higher than those achieved with untreated and pretreated trash samples with optimal LHW and DA conditions, respectively. This study led to the identification of best kinetic model and pretreatment condition for biomethane production from sugarcane trash through a systematic evaluation.

Optimization of pH as a strategy to improve enzymatic saccharification of wheat straw for enhancing bioethanol production

In this work, wheat straw (WS) was used as a lignocellulosic substrate to investigate the influence of pH on enzymatic saccharification. The optimum enzymatic hydrolysis occurred at pH range 5.8–6.0, instead of 4.8–5.0 as has been widely reported in research. Two enzymes cocktails, Celluclast® 1.5 L with Novozymes 188, Cellic® CTec2 and endo-1,4-β-xylanase, were used for the pH investigation over a pH range of 3.0–7.0. The highest concentration of total reduced sugar was found at pH 6.0 for all the different enzymes used in this study. The total reduced sugar produced from the enzymatic saccharification at pH 6.0 was found to be 7.0, 7.4, and 10.8 (g L−1) for Celluclast® 1.5 L with Novozymes 188, endo-1,4-β-xylanase and Cellic® CTec2, respectively. By increasing the pH from 4.8 to 6.0, the total reduced sugar yield increased by 25% for Celluclast® 1.5 L with Novozymes 188 and endo-1 4-β-xylanase and 21% for Cellic® CTec2. The results from this study indicate that WS hydrolysis can be improved significantly by elevating the pH at which the reaction occurs to the range of 5.8 to 6.0.

Anaerobic co-digestion of sewage sludge with cellulose, protein, and lipids: Role of rheology and digestibility

Rheology is known to have an impact on the performance of digesters, but the effect of additional substrates (co-digestion) is poorly understood. The main objective of this study was to investigate the effects of the addition of cellulose, protein and lipids to substrates on the rheological behaviour and biogas production of the mixture of primary sludge (PS) and waste-activated sludge (WAS) in a batch system. A mixture of PS and WAS to form the main substrate was anaerobically co-digested with different types of organic matter (cellulose, protein and lipids) as co-substrates at different co-substrate to main substrate ratios of 2-8 (wt%) under mesophilic conditions and below ammonia inhibition levels. Yield stress (τ_y) and the flow consistency index (k) of the combined feed in the case of cellulose and protein were significantly dependent on the amount of co-substrate added, while there was an insignificant impact on these properties when lipids were added. Cellulose significantly increased τ_y and k in the feed, which resulted in poor fluidity and the improper homogenisation of the digester content, and consequently decreased the biogas yield. In contrast, the biogas yield was improved through the addition of 2% to 6% protein despite an increase in τ_y and k of the feed, but the methane yield decreased at 7% and 8% levels of protein concentration. This observation indicates that the threshold for τ_y and k of the digester media depends on the organic nature and digestibility of the substrate. There was no significant impact on the flow properties of the initial mixture when lipids were added, and their addition increased the biogas yield. A first-order kinetic reaction model was used for predicting the yield of methane from these digesters. The rate constant values revealed an increasing trend, with the highest for protein then lipids then cellulose.

Effect of alkaline and alkaline-photocatalytic pretreatment on characteristics and biogas production of rice straw

To overcome recalcitrant nature and investigate enhancement of biogas production of rice straw (RS), it was subjected to pretreatment under mild conditions. Alkaline pretreatment using sodium hydroxide (NaOH), photocatalytic pretreatment utilizing titania nanoparticles (TiO₂ NPs) and alkaline-photocatalytic pretreatment was used to disrupt the lignocellulose complex. As compared to raw RS, maximum biogas and methane enhancement due to alkaline pretreatment was observed for 1.5% w/v NaOH pretreated RS which was 50 and 71% respectively. Photocatalytic pretreatment of RS at 0.25 g/L TiO₂ increased biogas and methane yield by 30 and 36% respectively. However, maximum biogas and methane enhancement was observed for alkaline-photocatalytic pretreatment at 1.5% w/v NaOH-0.25 g/L TiO₂ which was 74 and 122% respectively. Comparatively high enhancements were observed during alkaline-photocatalytic combined pretreatment due to increased cellulose and decreased lignin content. Moreover, the experimental data obtained from the experiments were validated using a non-linear kinetic model.

Co-treatment of potassium ferrate and peroxymonosulfate enhances the decomposition of the cotton straw and cow manure mixture

Since there is high lignocellulose content in the cotton straw and cow manure mixture (MCC), the appropriate MCC pretreatment is important to promote the anaerobic digestion (AD) hydrolysis. This study mainly explored the effect of potassium ferrate (PF) and peroxymonosulfate (PMS) pretreatments on MCC decomposition. PMS + PF co-treatment showed a higher reduction of total solid and volatile solid than PF pretreatment and PMS pretreatment. Hydrolysis of treated MCC indicated that the PF pretreatment was more effective to the release of organics than the PMS pretreatment and the PMS + PF co-treatment. However, the PMS + PF co-treatment resulted in a higher lignin removal rate (40.4%-50.5%) than the PMS pretreatment (30.8%) and the PF pretreatment (21.4%). The PMS₁ + PF₂ co-treatment (molar ratio of 1:2) acquired the optimal lignin removal rate and the release of organics among the PMS + PF co-treatment with different dosing ratio. Potential mechanism was that PF reduction products activated PMS to produce free radicals (SO₄^-, OH), which attacked lignocellulosic components and promoted MCC decomposition. The PMS₁ + PF₂ co-treatment was deduced to be the optimal pretreatment method when considering MCC decomposition, biodegradability, and mass transfer in the bioreactor.