Thermochemical Pretreatment Research Articles

Biochemical Conversion of Lignocellulosic Biomass from Date Palm of Phoenix dactylifera L. into Ethanol Production

Cellulosic fibers from date palm are among the most promising lignocellulose feedstock for biorefinery purposes. The world production is between 1.9 and 2.4 million t/year. Initially, a pretreatment with dilute-sulphuric acid of these fibers was performed using a response surface methodology, with temperature and process time as factors. The aim is to produce bioethanol from young and old fibers from date palm, Phoenix dactylifera L. Optimal thermochemical pretreatment conditions for both fibers palms were 220 °C in hydrothermal conditions (without acid); in these conditions pretreated young fibers presented a maximum content in holocelluloses of 45.18% and old fibers 61.97%. Subsequently, during the enzymatic hydrolysis a maximum yield of total reducing sugars (TRS) was reached, 46.32 g/100 g for pretreated dry young fibers and 48.54 g/100 g for pretreated dry old fibers. After enzymatic saccharification, hydrolysates were fermented by Pachysolen tannophilus (ATCC 32691) to ethanol, reaching yields (YE/TRS) of 37.94 g ethanol/100 g of TRS for young fibers and 35.84 g ethanol/100 g of TRS for old fibers. Globally, considering the full process, in the fermentation of the hydrolysates, a yield (YE) of 10.64 g ethanol/100 g of dry young fibers and 10.88 g ethanol/100 g of dry old fibers was reached.

Hydrothermal Carbonization of Lemon Peel Waste: Preliminary Results on the Effects of Temperature during Process Water Recirculation

Hydrothermal carbonization (HTC) is a promising thermochemical pre-treatment to convert waste biomass into solid biofuels. However, the process yields large amounts of organic process water (PW), which must be properly disposed of or reused. In this study, the PW produced from the hydrothermal carbonization of lemon peel waste (LP) was recycled into HTC process of LP with the aim of maximize energy recovery from the aqueous phase while saving water resources and mitigating the overall environmental impact of the process. The effects of HTC temperature on the properties of solid and liquid products were investigated during PW recirculation. Experiments were carried out at three different operating temperatures (180, 220, 250 °C), fixed residence times of 60 min, and solid to liquid load of 20 wt%, on a dry basis. Hydrochars were characterized in terms of proximate analysis and higher heating values while liquid phases were analyzed in terms of pH and total organic carbon content (TOC). PW recirculation led to a solid mass yield increase and the effect was more pronounced at lower HTC temperature. The increase of solid mass yield, after recirculation steps (maximum increase of about 6% at 180 °C), also led to a significant energy yield enhancement. Results showed that PW recirculation is a viable strategy for a reduction of water consumption and further carbon recovery; moreover preliminary results encourage for an in-depth analysis of the effects of the PW recirculation for different biomasses and at various operating conditions.

Upgraded pongamia pod via torrefaction for the production of bioenergy

Torrefaction can be used to reduce the oxygen content of biomass and improve the feedstock properties for thermochemical conversion. Pongamia (Millettia pinnata), a leguminous, oil-seed bearing tree, is a potential resource for sustainable aviation fuel production due to the high oil content of its seeds. The present work investigates thermochemical pretreatment of pongamia processing residues, i.e. pods. Torrefaction tests were performed with both a fixed bed reactor and a macro thermogravimetric analyzer (TGA) under nitrogen atmospheres. The effects of process conditions on feedstock properties relevant to thermochemical conversion technologies, proximate and ultimate composition, heating value, and Hardgrove grindability index (HGI), were measured. The chemical structure, reactivity, and changes in elemental composition of the torrefied materials were also investigated. The mass and energy yields decreased 43% and 25%, respectively, from the mildest (165 °C) to the most severe (281 °C) torrefaction conditions, while the energy densification index increased from 1.15 to 1.68. The HGIs of pods torrefied at temperatures >215 °C were found to equal or exceed the HGI of a reference bituminous coal sample. A LECO model TGA801 macro-TGA with a sample loading capacity of ~95 g was also used to torrefy pongamia pods. Products from the LECO and the fixed bed reactor were comparable, and the macro-TGA was demonstrated to be a useful fast screening tool to study effects of process parameters.

Potassium Hydroxyde Pre-Treatment Enhances Methane Yield from Giant Reed (Arundo donax L.)

The biogas production through the anaerobic digestion (AD) of giant reed (Arundo donax L.) biomass has received increasing attention. However, due to the presence of lignin, a low CH4 yield can be obtained. Aiming to improve the CH4 yield from giant reed biomass, the effectiveness of a thermo-chemical pre-treatment based on KOH was evaluated in this paper. The usefulness of a washing step before the AD was also assessed. The pre-treatment led to a specific CH4 yield up to 232 mL CH4 g−1 VS which was 21% higher than that from untreated biomass; the maximum daily rate of production was improved by 42%, AD duration was reduced by 10%, and CH4 concentration in the biogas was increased by 23%. On the contrary, the washing step did not improve the AD process. Besides, washing away the liquid fraction led to biomass losses, reducing the overall CH4 production. The use of a KOH-based pre-treatment appears as a good option for enhancing the AD of giant reed, also presenting potential environmental and agronomical benefits, like the avoidance of salty wastewater production and the likely improvement of the digestate quality, due to its enriched K content.

Visualizing plant cell wall changes proves the superiority of hydrochloric acid over sulfuric acid catalyzed γ-valerolactone pretreatment

Thermochemical pretreatment is one of the key steps to process lignocellulosic biomass for production of biofuels and biomaterials. γ-valerolactone (GVL) has been used as a green and renewable solvent to efficiently dissolve lignin under acidic conditions and enhance subsequent enzyme digestibility. Further improvement is still required to lower the pretreatment temperature in order to reduce sugar degradation and irreversible lignin condensation, as well as the capital cost. In this study, we compared the use of HCl and H2SO4 as catalysts during GVL pretreatment, and found the performance of GVL-HCl at 100 °C was comparable to that of GVL-H2SO4 at 120 °C in terms of xylan and lignin removal and enzyme digestibility. We further monitored the lignin removal and cellulose accessibility in the cell walls at different pretreatment time points by imaging the changes in lignin auto-fluorescence and in CtCBM3-GFP binding with confocal laser scanning microscopy (CLSM), respectively. We found GVL-HCl pretreatment at a relative low temperature (100 °C) could rapidly remove lignin in the compound middle lamella and cell corner areas, which concurred with the increase of CtCBM3-GFP binding in these areas. Real-time imaging of cell wall degradation by cellulases further revealed that the secondary cell walls could be digested from both cell lumen and CML sides, and eventually fully deconstructed within 24 h. Our results provide new insight into the effects of chloride anions on plant cell wall structure during GVL pretreatment, and offer potential routes to further optimize and enhance the efficiency of GVL-based pretreatment.

Rewired phenolic metabolism and improved saccharification efficiency of a Zea mays cinnamyl alcohol dehydrogenase 2 (zmcad2) mutant.

Lignocellulosic biomass is an abundant byproduct from cereal crops that can potentially be valorized as a feedstock to produce biomaterials. Zea mays CINNAMYL ALCOHOL DEHYDROGENASE 2 (ZmCAD2) is involved in lignification, and is a promising target to improve the cellulose-to-glucose conversion of maize stover. Here, we analyzed a field-grown zmcad2 Mutator transposon insertional mutant. Zmcad2 mutant plants had an 18% lower Klason lignin content, whereas their cellulose content was similar to that of control lines. The lignin in zmcad2 mutants contained increased levels of hydroxycinnamaldehydes, i.e. the substrates of ZmCAD2, ferulic acid and tricin. Ferulates decorating hemicelluloses were not altered. Phenolic profiling further revealed that hydroxycinnamaldehydes are partly converted into (dihydro)ferulic acid and sinapic acid and their derivatives in zmcad2 mutants. Syringyl lactic acid hexoside, a metabolic sink in CAD-deficient dicot trees, appeared not to be a sink in zmcad2 maize. The enzymatic cellulose-to-glucose conversion efficiency was determined after 10 different thermochemical pre-treatments. Zmcad2 yielded significantly higher conversions compared with controls for almost every pre-treatment. However, the relative increase in glucose yields after alkaline pre-treatment was not higher than the relative increase when no pre-treatment was applied, suggesting that the positive effect of the incorporation of hydroxycinnamaldehydes was leveled off by the negative effect of reduced p-coumarate levels in the cell wall. Taken together, our results reveal how phenolic metabolism is affected in CAD-deficient maize, and further support mutating CAD genes in cereal crops as a promising strategy to improve lignocellulosic biomass for sugar-platform biorefineries.

Liberación de azúcares reductores a partir de lirio acuático por hidrólisis termoquímica y enzimática

Water hyacinth (Eichhornia crassipes) is considered a pernicious herb in many parts of the world due to its rapid growth. However, for its high content of cellulose and hemicellulose, it could be considered as raw material to produce fermentable sugars. In this work, the effect of sulfuric acid concentration by thermochemical pretreatment and enzymatic hydrolysis on the release of sugars from water hyacinth was evaluated. Initially, the effect of the sulfuric acid concentration from 1.5 to 9% at 120 ºC was evaluated. With 1.5%, the release of reducing sugars was 160 milligrams of reducing sugars per gram of dry matter (mg red-sug/g dm). After the thermochemical pretreatment, the enzymatic hydrolysis with the cellulase complex (NS22086) allowed obtaining a reducing sugars concentration up to 317 mg red-sug/g dm. These thermochemical and enzymatic approaches to recover reducing sugars from water hyacinth is promising and should be evaluated for bioprocess using reducing sugars as the main source of carbon, such as bioethanol production.

Facile Fabrication and Characterization of Zn Loaded Cellulose Membrane from Cotton Microdust Waste and its Antibacterial Properties—A Waste to Value Approach

Cotton microdust (CMD) is an abundantly generated waste from textile industry with no commercial value. It is composed of cellulose as the predominant component along with other non-cellulosic components like lignin. The conversion of CMD to value-added materials would further improve the economics of the cotton mills. In this study, the CMD was converted into high value cellulose membrane through thermo-chemical pretreatment and spin coating methods. The thermal pretreated CMD was solubilized in 68 wt% zinc chloride solution prior to preparation of membrane and then the solubilized cellulose was spread on a plate and spin coated with 22% (w/v) sodium chloride. During the spin coating process, the cellulose membrane was formed with the simultaneous separation of lignin. The present method is a novel approach since a separate process for lignin removal from cotton wastes is not required to produce cellulose membrane. The XRD and FTIR analyses showed significant changes in the crystallinity and the composition of the cellulose membrane. The SEM picture of the membrane revealed uniform surface morphology. Moreover, the membrane was associated with good mechanical properties as indicated by rheology and tensile studies. The cellulose membrane had antibacterial activity against E. coli and efficient absorption and release of antibiotics. Therefore, the results would be useful for further development of a process for the production of cellulose membrane as a high value byproduct from the CMD in cotton mills. Development of simple and green process for the valorization of cotton microdust waste from spinning mills into Zn loaded cellulose membrane

Quality of pellets produced from agricultural wood residues specific to the Prut river basin

Quality of pellets produced from agricultural wood residues specific to the Prut river basin This paper presents an overview of the prospects for the use of agricultural wood residues, specific to the climatic zone adjacent to the Prut River and the qualitative characteristics of densified solid biofuels in the form of pellets produced from the main types of the agricultural wood biomass, taken from agricultural plantations in the Republic of Moldova and Botosani, Iasi, Vaslui and Galați counties in Romania. The aim of the paper is to establish the energy potential of the main indigenous agricultural wood residues and to analyze the quality of the pellets produced from these residues. The research results showed that the pellets produced from the studied agricultural residues mainly meet ENPlus 3 requirements for most qualitative parameters, except for those produced from blackberry and currant residues. Residues from the prunning of some types of fruit shrubs can be used to produce pellets by creating mixtures of different proportions, and their qualitative characteristics can be significantly improved by thermo-chemical pre-treatment of the raw material. Keywords: plant biomass, densified solid biofuels, pellets, biofuel, energy potential, agricultural wood residues.

Hydrogen production by Enterobacter sp. LBTM 2 using sugarcane bagasse hemicellulose hydrolysate and a synthetic substrate: understanding and controlling toxicity

Abstract Sugars released by thermochemical pretreatment of lignocellulosic biomass are possible substrate for hydrogen production. However, the major drawback for bacterial fermentation is the toxicity of weak acids and furan derivatives normally present in such substrate. This study aimed to investigate the metabolism involved in hydrogen production by the isolate Enterobacter LBTM2 using 10, 20 and 30-fold diluted synthetic (SH) and sugarcane bagasse hemicellulose (SBH) hydrolysates. In addition, the effects of acetic acid, formic acid and furfural on the bacterial metabolism, as well as detoxification of SBH with activated carbon and molecularly imprinted polymers on the hydrogen production were assessed. The results showed the best hydrogen yield was 0.46 mmol H2/mmol sugar for 20-times diluted SH, which was 2.3-times higher than obtained in SBH experiments. Bacterial growth and hydrogen production were negatively affected by 0.8 g/L of acetic acid when added alone, but were totally inhibited when formic acid (0.4 g/L) and furfural (0.3 g/L) were also supplied. However the maximum hydrogen production of SBH20 has duplicated when 3% of powdered activated carbon was added to the SBH experiment. The results presented herein can be helpful in understanding the bottlenecks in biohydrogen production and could contribute towards development of lignocellulosic biorefinery.

Two Nonnegligible Factors Influencing Lignocellulosic Biomass Valorization: Filtration Method after Pretreatment and Solid Loading during Enzymatic Hydrolysis

Valorization of lignocellulosic biomass into biofuels has received considerable attention for decades with tremendous thermochemical pretreatments proposed. However, inconsistencies among studies in lignin removal can often be misleading and even violate the chemical mechanism, which might be attributed to the variation in the filtration method used after pretreatment. A phenomenon, promoting pretreatment strategies based on sugar conversion efficiency or yield only from single and random low-solid enzymatic hydrolysis, was also observed. Herein, the effects of filtration methods using a slow drip metal filter (SDMF) with an aperture of 0.2 mm and Whatman grade 4 filter paper (WGFP) with an aperture of 20–25 μm under vacuum filtration after liquid hot water (LHW), acid, and alkali pretreatments on the chemical composition of the solid and liquid, sugar recoveries, and lignin removal and solid loading (2–15%) on enzymatic hydrolysis of corn stover and poplar wood were investigated. Results showed that SDMF increased the glucan content (1.1–3.0%) in pretreated biomass and induced solid loss (3.8–12.6%) into the filtrates, resulting in lower sugar recoveries and overestimated lignin removal compared to WGFP. 5-Hydroxymethylfurfural (HMF) and furfural derived from sugar degradation triggered pseudolignin formation, inducing a negative lignin removal for both LHW and acid pretreated biomass. In comparison, alkali pretreatment neutralized the weak acids released from sugar decomposition and achieved a robust delignification (67.8–90.8%). Solid loading used for enzymatic hydrolysis of pretreated biomass determined sugar concentration, conversion efficiency, and yield. This result indicates that promoting pretreatment technologies based on sugar conversion efficiency or yield of enzymatic hydrolysis at low solid loading may be misleading. This work demonstrates that the filtration method used for solid and liquid separations after pretreatment and solid loading for enzymatic hydrolysis should be cautiously selected and implemented when valorizing biomass into biofuels.

NaOH pretreatment and enzymatic hydrolysis of Brassica juncea using mixture of cellulases

Now a days lignocellulosic biomass based bioethanol production has been the centre of major research studies due to its varying significances. Bioethanol production by using lignocellulosic biomass as substrate is an economically feasible process. In the current study, very less concentration of sodium hydroxide was used for delignification (pretreatment) and blends of various cellulases was used for enhanced hydrolysis of carbohydrates (cellulose and hemicellulose). It was seen that most noteworthy measure of reducing sugar (40.50 mg/mL) was acquired from Brassica juncea, when it was delignified using 0.5 M sodium hydroxide at 160 °C, 10% solid loading and 30 min duration. The affectivity of above pretreatment (delignification) process was further confirmed by characterization of substrate (control and pretreated) through using SEM, XRD and FTIR. Mixture of cellulases obtained from Fusarium incarnatum KU377454 (isolated by us), Aspergillus niger MTCC284 and Trichoderma harzianum MTCC8230 was utilized for carbohydrate hydrolysis (saccharification) of delignified biomass which demonstrated highest reducing sugar production (62.35 mg/mL) at 15% solid loading, 50 °C temperature and 48 h of time duration. The current process of enzymatic hydrolysis and thermochemical pretreatment by using mixture of cellulases showed efficient reducing sugar production without the use of any costly chemicals and commercial enzymes.

Optimisation of anaerobic digestion of pot ale after thermochemical pre-treatment through Response Surface Methodology

Valorisation of organic wastes in renewable energy production has attracted a global attention in order to achieve a sustainable industrial growth. Anaerobic digestion (AD) is considered to be one of the most environmentally friendly waste management technology and also fulfils the necessity of a sustainable fuel generation. It has much less energy demand than other technologies like gasification or pyrolysis due to its low operation temperature. Whiskey distillery wastewater, pot ale, is classified as a high strength waste due its high organic content hence rendering it a suitable substrate for anaerobic digestion. Despite its waste-to-energy conversion potential, pot ale contains high lignin fraction which makes it resistant to biodegradation. Therefore introducing a pre-treatment step is required to enhance the biogas production and organic matter degradation. In this study anaerobic digestion of pot ale was assessed at lab scale batch mode reactor after implementation of 1 M NaOH and microwave pre-treatments at varying power settings. Response Surface Methodology was adopted for process modelling and optimisation in which inoculum substrate ratio, initial digestion pH and microwave power were investigated at three different levels. In addition, the mineral quality of the pot ale digestate has been analysed for its agricultural use.

Thermochemical pretreatments of maize stem for sugar recovery: Comparative evaluation of microwave and conventional heating

Microwave (MW) heating is attracting great attention in biorefinery processes, because of its special dipole rotation heating mechanism. In the current study, MW and conventional heating methods were employed to assist the thermochemical pretreatments (H2O, H2SO4 or NaOH) of maize stem biomass. Their influences on sugar release and biomass compositions during pretreatments were comparably evaluated. Compared to conventional heating pretreatment, MW thermochemical pretreatments are highly efficient in sugar recovery, contributing to 4.3 times higher amount of sugar release (1.25 vs 0.30 μmol/mg biomass) with reaction time 8 times shorter (5 vs 40 min) and selectively producing glucose as the major constituent (0.75 μmol/mg biomass) using 0.2 M H2SO4 as pretreatment media. MW thermochemical pretreatment also effectively removed lignin (up to 91.6 %) within 5 min, which was significantly higher than conventional heating pretreatment (51.2 %). Conventional heating pretreatment successfully removed hemicellulose and converted the crystalline cellulose into amorphous cellulose, which is probably due to its longer heating time. Rapid MW thermochemical pretreatments efficiently fractionated hemicellulose and removed lignin content while keeping the crystalline cellulose structure. MW and conventional heating pretreatments led to similar digestibility of biomass solid residues. Overall, MW thermochemical pretreatment represents an energy efficient alternative strategy, as it consumed 25–34 folds less energy than conventional heating pretreatment for effective biomass fractionation and value-added chemical production.

Experimental optimization of thermochemical pretreatment of sal (Shorea robusta) sawdust by Central Composite Design study for bioethanol production by co-fermentation using Saccharomyces cerevisiae (MTCC-36) and Pichia stipitis (NCIM-3498)

Production of bioethanol was attempted using sawdust of sal (Shorea robusta), a hardwood tree species known for its excellent quality timber. Sawdust, a lignocellulosic biomass waste is generated in plenty from the furniture industry. To the best of our knowledge, this is the first study that uses design of experiment (DoE) approach for enhancing total reducing sugar (TRS) from thermochemically pretreated sal sawdust (SS) biomass. Statistical optimization of thermochemical pretreatment was performed using Central Composite Design (CCD) tool of Response Surface Methodology (RSM) using three process parameters (biomass loading, chemical concentration and incubation time). It resulted in about 2.05-fold more reducing sugars (7.0 g L-1) at 121 °C, 1 bar pressure and 30 min incubation time as compared to OVAT approach (3.4 g L-1). Enzymatic hydrolysis carried out by commercial cellulase and pectinase (enzyme loading 5U/g biomass) enzymes facilitated liberation of 19.09 g L-1 TRS. The optimum delignification percentage obtained was 27.27 ± 0.20% under optimized thermochemical conditions. Delignification estimation studies were done using Folin-Ciocalteu (F–C) and phloroglucinol-HCl test. Further analysis involved Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM) analysis and Fourier-transform infrared (FTIR) data which clearly confirmed the breakdown of cellulose and hemicellulose, removal of lignin and morphological changes in the pretreated SS biomass. Fermentation using co-culture of Saccharomyces cerevisiae (MTCC-36) and Pichia stipitis (NCIM-3498) at 30 °C, pH 5.0 resulted in 9.43 g L-1 bioethanol concentration after 24 h with a conversion efficiency of 97%. These results indicate that sal sawdust can serve as a promising feedstock for bioethanol production.

Efficacy of chemical factors on production and extraction of biodiesel by microalgae

Environmental concerning factors responsible for carbon dioxide emissions and depletion of petroleum based fuel are the driving factors for the search of alternative fuels like biodiesel. The growth of microalgal cells and their metabolic activity toward lipid production could be controlled by the nutrient factors employed in production media. The lipid accumulation ability of the microalgal strains could be influenced by the deprivation of vital chemicals like carbon, nitrogen, calcium and magnesium. In the part of commercializing microalgal based biodiesel, cost effective measures in oil extraction and downstream processes have to be considered. Huge varieties of microalgal cellular pretreatment methods are employed to enhance cellular disintegration so as to facilitate oil extraction by structural modification of carbohydrates present in cell wall. The diversified methods used for microalgal pretreatment encompass chemical, thermal, biological, mechanical or combinatorial approaches. Among all the pretreatment methods chemical methods are greatly advantageous while concerning the feasibility in energy and time consumption. Combinatorial approaches like thermochemical pretreatment or microwave assisted extraction methods are very successful in terms of feasible energy production under limited time consumption. Above all, genetic engineered microbes which could be able to withstand suitable pretreatment methods were developed. This present review tried to explore the activity of chemical parameters and also delineate the nutrient deprivation factors involving in the cellular metabolism of microalgal biomass for lipid production.

Response surface methodology (RSM) for optimization of thermochemical pretreatment method and enzymatic hydrolysis of deodar sawdust (DS) for bioethanol production using separate hydrolysis and co-fermentation (SHCF)

In the present work, Cedrus deodara (deodar) sawdust abbreviated as DS was subjected to thermochemical pretreatment followed by enzymatic hydrolysis and fermentation for bioethanol production. Response surface methodology (RSM) based on central composite design (CCD) tool was employed to optimize dilute acid pretreatment method (at 121 °C temperature and 1-bar pressure) and enzymatic hydrolysis processes. Factorial design of experiments used chemical concentration, incubation time, and biomass loading to optimize thermochemical pretreatment method using dilute acid concentration. Maximum total reducing sugar (TRS) concentration (13.62 g/L) was obtained using optimized conditions (1.5% HCl concentration, 10% biomass loading and 30-min incubation time). These significant studies were subjected to optimize enzymatic hydrolysis process using the CCD tool of the RSM where cellulase loading, xylanase loading, pH, and temperature were taken into consideration. TRS concentration obtained was 29.20 g/L after 48 h with enzyme loading of 9 U/g biomass, each for cellulase and xylanase enzyme at pH 5.0 and 30 °C temperature. Fermentation conditions for enzymatically hydrolyzed DS revealed that at 10% (v/v) yeast inoculum concentrations (Saccharomyces cerevisiae (MTCC-36) and Pichia stipitis (NCIM-3498)) after 24-h fermentation time and pH 5.0, bioethanol concentration was 14.25 g/L with 95.68% conversion efficiency. Characterization studies for native and pretreated DS by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM) analyses revealed delignification rate of 30.93% of DS biomass under optimized thermochemical pretreatment conditions. Statistical studies for optimization of pretreatment and enzymatic hydrolysis for bioethanol production stated DS sawdust (a furniture industry waste) as a potential substrate for biofuel production.

Potential of anaerobic co-digestion in improving the environmental quality of agro-textile wastewater sludge.

Sludge from textile effluent treatment plants (ETP) remains a challenge for many industries due to inefficient and limited waste management strategies. This study explores the potential of using anaerobic digestion (AD) to improve the environmental quality of textile ETP sludge. The AD of ETP sludge is affected by the low C/N ratio (3.7), heavy metal content, and toxicity. To improve the process, co-digestion of ETP sludge with different substrates (sewage sludge, cow dung, and sawdust) under mesophilic conditions (37 °C), followed by a thermochemical pretreatment was assessed. The results showed that anaerobic co-digestion of the textile sludge with the co-substrates is effective in reducing pollution load. It was found that organic matters degraded during the 30-day AD process. The chemical oxygen demand and biological oxygen demand reduction was in the range of 33.1-88.5% and 48.1-67.1%, respectively. Also, heavy metal (cadmium, lead, iron, and, mercury) concentration was slightly reduced after digestion. Maximal biogas yield was achieved from co-digestion of textile sludge and sewage sludge at a mixing ratio of 3:1, 1:1, and 1:3, and methane content was respectively 87.9%, 68.9%, and 69.5% of the gas composition. The results from this study show that co-digestion will not only reduce the environmental pollution and health risks from the textile industry but also recover useful energy.

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 28g/kg OMS and 25g/kg OMS, respectively, and were both significantly enhanced by pretreatment. The highest ethanol yield was 79g/kg OMS and was achieved by the alkali pretreatment and separate fermentation of hydrolysates and solids, whereas the highest xylitol yield was 49g/kg OMS and was obtained by pretreatment with sulphuric acid and separate fermentation of hydrolysates and solids.

Bioaugmentation of anaerobic fungus Orpinomyces joyonii boosts sustainable biomethanation of rice straw without pretreatment

Rice straw is an abundant, renewable and energy rich agricultural biomass. Energy recovery in the form of biomethane from rice straw can be a sustainable process. However, one of the drawbacks associated with this process is the recalcitrant nature of rice straw which necessitates energy intensive, expensive and polluting thermochemical pretreatment of the substrate. Fiber digesting anaerobic fungi have the ability to degrade the plant biomass. Hence, the present investigation was undertaken to enhance the biodegradation and subsequently the biomethanation of rice straw by supplementing the startup inoculum with anaerobic fiber digesting fungus, Orpinomyces joyonii. The average daily biogas and methane yield increased by 25.04% and 38.41% respectively over control reactor when the startup inoculum was supplemented with O. joyonii in the test reactor. The reduction in volatile solids, cellulose and hemicellulose components of rice straw during biomethanation process was observed to be 68%, 82%, and 97%, respectively. Orpinomyces joyonii supplementation of startup inoculum enhanced the biodegradation of lignocellulosic component and biomethane yield by anaerobic digestion of rice straw without thermochemical pretreatment.