Substrate Conversion Efficiency Research Articles

Lag in pollutant removal efficiency relative to microbial community dynamics in a denitrifying phosphorus removal bioreactor

Determining the system status in advance is critical for implementing timely control strategies, preventing wastewater treatment instability due to overload stress, and enhancing system resilience to impact loads. Unlike traditional instability monitoring methods, identifying temporal relationships between pollutant removal efficiency and microbial community dynamics can offer novel insights into identifying optimal intervention windows. Here, we chose nitrite, a vital intermediate of nitrogen reaction in wastewater treatment, as a stress factor. Then, we investigated the effects of nitrite stress on denitrifying phosphorus removal system performance and microbiome. By monitoring carbon, nitrogen, and phosphorus removal efficiency and analyzing microbiome information, we found that variations in bacterial ecology preceded pollutant removal efficiency. The lag in pollutant removal efficiency relative to microbial community dynamics reflects the complex dynamics of species traits, metabolic functions, and functional redundancy. Species in clusters may drove specific pollutant removal; e.g., Betaproteobacteria are more closely associated with nitrogen removal, while Gammaproteobacteria are more linked to phosphorus removal. The cellular secretion function displayed greater susceptibility to overload stress compared to the substrate conversion function, resulting in decreased stability observed after 30 cycles, preceding the decline in substrate conversion efficiency. The lag in performance relative to community stability can be attributed to functional redundancy. Under overload stress conditions, functional redundancy within the microbiome decreased by 30.77% from 60 cycles to 120 cycles. Our results support a novel strategy for system collapse prediction via changes in the microbiome,enabling proactive regulation and ensuring system stability before irreversible deterioration occurs.

Metabolic performance and feed efficiency of black soldier fly larvae.

The black soldier fly (BSF), Hermetia illucens, is used in entomoremediation processes because its larvae can use a variety of organic residues with high efficiency. However, feed efficiencies are variable and characterized by uncertainties. Recently developed growth and metabolic performance models have predicted across different studies that BSF larvae have used 53%-58% of the feed components they have assimilated, in terms of carbon equivalents, for growth throughout their lifetime when reared on chicken feed. This is termed their average net growth efficiency. The remainder of the carbon has been lost as CO2. However, mass balances made under similar conditions show that the weight gained by BSF larvae corresponds to only 14%-48% of the feed substrates removed, indicating substrate conversion efficiency. Both performance indicators show even greater variability if more feed substrates are considered. Feed assimilation and growth rates, costs of growth, maintenance, and larval lifespan have been shown to affect how efficiently BSF larvae convert feed into growth. The differences between average net growth efficiencies and substrate conversion efficiencies further indicate that feed is often not used optimally in entomoremediation processes and that the overall yield of such processes is not determined by larval performance alone but is the result of processes and interactions between larvae, substrates, microbes, and their physical environment. The purpose of this study is to illustrate how quantification of the metabolic performance of BSF larvae can help improve our understanding of the role of the larvae in entomoremediation processes.

Design and validation of a multiplex PCR method for the simultaneous quantification of Clostridium acetobutylicum, Clostridium carboxidivorans and Clostridium cellulovorans

Co-cultures of clostridia with distinct physiological properties have emerged as an alternative to increase the production of butanol and other added-value compounds from biomass. The optimal performance of mixed tandem cultures may depend on the stability and fitness of each species in the consortium, making the development of specific quantification methods to separate their members crucial. In this study, we developed and tested a multiplex qPCR method targeting the 16S rRNA gene for the simultaneous quantification of Clostridium acetobutylicum, Clostridium carboxidivorans and Clostridium cellulovorans in co-cultures. Designed primer pairs and probes could specifically quantify the three Clostridium species with no cross-reactions thus allowing significant changes in their growth kinetics in the consortia to be detected and correlated with productivity. The method was used to test a suitable medium composition for simultaneous growth of the three species. We show that higher alcohol productions were obtained when combining C. carboxidivorans and C. acetobutylicum compared to individual cultures, and further improved (> 90%) in the triplet consortium. Altogether, the methodology could be applied to fermentation processes targeting butanol productions from lignocellulosic feedstocks with a higher substrate conversion efficiency.

Bioconversion performances of black soldier fly larvae (<em>Hermetia illucens</em> L. Diptera: Stratiomyidae) on selected organic substrates

Black Soldier Fly Larvae (BSFL; Hermetia illucens L.) is a bioconversion agent of organic substrates and its proven ability to degrade and biotransform of waste strengthens organic waste management and waste recycling strategies. BSFL have the advantages of rapid development and very efficient conversion of various organic wastes into body biomass. This process reduces the disposal costs of organic waste as well as the use of energy providing a sustainable solution to the treatment of organic waste. In addition, it provides valuable products and fertilizers for agriculture, potentially reducing crop production costs for farmers. The current study investigated the potential live biomass production of BSFL using different organic substrates available locally while understanding their decomposition ability. Seven treatments were compared (T1- equal proportion of poultry manure and rice bran, T2- equal proportion of goat manure and rice bran, T3- rabbit droppings, T4- soybean meal, T5- coconut scrapings, T6- equal proportion of vegetable and fruit waste and T7- cow dung) and the experiment was set up as completely randomized design with three replicates. The study results examined the ability of BSFL to reduce the weight of the end-substrate and promote the degradation of organic waste materials. The live biomass production of larvae, changes in live biomass production, substrate consumption rate, the weight of the end-substrate and substrate conversion efficiency were significantly different among treatments. The greatest live biomass production of BSFL was recorded in coconut scrapings and vegetables & fruit waste mixture while the lowest value was observed in cow dung. Coconut scrapings reduced most of their weight at the end of the study indicating the highest substrate consumption rate and the total weight of the end-substrate consisted of < 2mm particle in size. However, the highest substrate conversion rate was observed in cow dung. Aqueous solutions prepared from the end-substrates varied widely in pH, electrical conductivity, total dissolved solids, and salinity. In addition, significant differences were found among treatments for the colour and texture of the end-substrate. However, the appearance and odour did not differ significantly. According to the results of the present study, it can be concluded that the most efficient media for BSFL was coconut scraping though; it cannot be used as organic fertilizer as it exceeded the pH value of the SLS recommendation for compost. Overall, BSFL can be recognized as an effective and environmentally friendly tool to use in the biotransformation process of locally available organic waste materials.

Simultaneous optimization of the hydrogen production rate and substrate conversion efficiency using a response surface methodology

ABSTRACT This study investigated the use of the E. coli ATCC8739 strain for bio-hydrogen production in the dark-fermentation process, and the optimization of the bioprocess using a Box-Behnken design (BBD) and response surface methodology (RSM). The effects of substrate concentration (S), pH, and temperature (T) on the biohydrogen production rate (R H2) and substrate conversion efficiency (SCE) were evaluated. The highest R H2 of 55.32 ± 5 ml/l/h was achieved at initial pH (6.58), S (21.08 g/l), and T (36.6°C), with SCE at 90%. Maximum SCE (100%) was obtained at S (11 g/l), pH (7), and T (33°C), while R H2 was around 47 ml/l/h. Simultaneous optimization of SCE and R H2 was obtained at S (15.2 g/l), pH (6.9), and T (33.5°C), with SCE at 100% and R H2 of 52.64 ± 5 ml/l/h. The interactive effects of S, pH, and T on R H2 and SCE were also analyzed. The predicted models of the R H2 and SCE were in good agreement with the experimental data with an absolute error of 3% and 1%, respectively.

Ethanol production by Kluyveromyces marxianus ATCC 36907: Fermentation features and mathematical modeling

The effects of different temperatures (30 °C, 35 °C, 40 °C, and 45 °C) and initial glucose concentrations (50 g/L, 120 g/L, and 190 g/L) on the fermentative metabolism of Kluyveromyces marxianus ATCC 36907 were evaluated to optimize ethanol production. Mathematical models were developed based on experimental data to describe cell growth, substrate consumption, and ethanol production. Various kinetic models integrated with material balances were examined. The Akaike information criterion (AIC) was employed to identify the most accurate model representing the experimental behavior. Interestingly, the ethanol production rate was independent of the growth rate of K. marxianus. The growth kinetics indicated that the growth rate could be controlled by the oxygen concentration, which was influenced by cell concentration rather than glucose consumption. A desirability function was utilized to optimize ethanol productivity, substrate conversion efficiency and temperature, considering the conditions for future applications in simultaneous saccharification and fermentation (SSF) processes. The optimized experimental conditions obtained were validated, resulting in a new model specific to these conditions. This new model analysis confirmed the achievement of the objective to prioritize ethanol production. The optimized conditions for maximum ethanol production were initial glucose concentration of 91 g/L and temperature of 40 °C. Under these conditions, the ethanol concentration reached 12 g/L, with glucose conversion efficiency into ethanol of 0.13 g/g and productivity of 1.09 g/L/h after 11 h. This approach provided valuable insights into the fermentative behavior of K. marxianus, serving as a foundation for the design, optimization, and process control in biorefineries.

Continuous dark-fermentative H2 production using carbon components of lignocellulose hydrolysates: Insight into the difference between mixed and single substrates

Hydrogen produced from lignocellulosic biomass via dark fermentation is a promising alternative to fossil fuels. This study assessed fermentative H2 production from single sugars and sugar mixtures mimicking real lignocellulose hydrolysates during a continuous process. The highest hydrogen production rate (HPR) was obtained with pentose sugars, reaching 8.80 and 8.09 L/L-d for arabinose and xylose, respectively. Glucose showed the lowest HPR (6.19 L/L-d), while in the case of sugar mixtures (glucose, cellobiose, xylose, arabinose), HPR was approximately 7.3 L/L-d and was lower than expected from calculations. Thus, cofermentation reduced the H2 production potential. It was shown that pentose sugars are preferred for hydrogen production, but their utilization is limited by the presence of glucose, which is utilized preferentially in sugar mixtures. Xylose, arabinose and sugar mixtures showed similar H2 yields (approximately 0.29 mol H2/mol C), so the efficiency of substrate conversion into H2 was comparable for these substrates. The microbial community distribution showed that the Clostridium genus was dominant regardless of the substrate, with Clostridium beijerinckii and Clostridium guangxiense being the main bacterial species. Different substrates did not significantly affect the type of microorganisms present in the microbiome and changed only their relative abundance.

An anaerobic dynamic membrane bioreactor (AnDMBR) system enhanced the biogas conversion efficiency and stability of mesophilic codigestion with waste activated sludge and food waste

To enhance the substrate conversion efficiency and further improve the reactor stability of codigestion with waste activated sludge (WAS) and food waste (FW), a new type of anaerobic dynamic membrane bioreactor (AnDMBR) was designed and operated in parallel with a conventional continuous stirred tank reactor (CSTR) for approximately 500 days. The results showed that a higher methane yield (330–350 mL/g COD) was realized in the AnDMBR than in the CSTR (96–326 mL/g COD) under the same organic loading rates (OLRs) in the range of 8.16–22.8 g COD/L/d, which was consistent with the high methane production, specific methanogenic activity, coenzyme F420 concentration, and stable pH in the AnDMBR. Furthermore, the dynamic membrane performance of the AnDMBR was compared with that of the CSTR system; the measured characteristics, including the particle diameter and suspended solid concentration in the permeate or discharge sludge, suggested that the substrate and microorganisms can both be effectively intercepted by the dynamic membrane during long-term periodic operation. 16S rRNA high-throughput sequencing analysis indicated that the microbiological community structures in the AnDMBR and CSTR were similar, but the relative abundances of dominant bacteria (Treponema and Lutispora) and archaea (Methanoculleus) in the AnDMBR were both higher than those in the CSTR. This difference in relative abundance is the main reason why the AnDMBR enhanced the biogas conversion efficiency and stability of mesophilic codigestion with WAS and FW, other than substrate retention by the dynamic membrane. A comparison of the microbial metabolism functions of the AnDMBR and CSTR showed that the proportions of carbohydrate/coenzyme transport and metabolism and signal transduction mechanisms in the AnDMBR with stainless steel mesh were significantly improved after long-term parallel operation.

Quorum quenching enhanced methane production in anaerobic systems – performance and mechanisms

In our previous study, quorum quenching (QQ) bacteria can effectively enhance methane production in an anaerobic membrane bioreactor (AnMBR) while mitigating membrane biofouling. However, the mechanism of such enhancement is unclear. In this study, we analyzed the potential effects from separated hydrolysis, acidogenesis, acetogenesis and methanogenesis steps. The cumulative methane production improved by 26.13%, 22.54%, 48.70% and 44.93% at QQ bacteria dosage of 0.5, 1, 5 and 10 mg strain/g beads, respectively. It was found that the presence of QQ bacteria enhanced acidogenesis step resulting in higher volatile fatty acids (VFA) production, while it had no obvious influence on hydrolysis, acetogenesis and methanogenesis steps. The substrate (glucose) conversion efficiency in acidogenesis step was also accelerated (1.45 folds vs control within first eight hours). The abundance of hydrolytic fermentation gram-positive bacteria and several acidogenic bacteria, such as Hungateiclostridiaceae, was promoted in QQ amended culture, which enhanced VFA production and accumulation. Although the abundance of acetoclastic methanogen Methanosaeta reduced by 54.2% on the 1st day of QQ beads addition, the overall performance of methane production was not affected. This study revealed that QQ had a greater impact on the acidogenesis step in the anaerobic digestion process, though the microbial community in acetogenesis and methanogenesis steps was altered. This work can provide a theoretical basis for using QQ technology to slow down the rate of membrane biofouling in anaerobic membrane bioreactors while increasing methane production and maximizing economic benefits.

Oriented Conversion of a LA/HMF Mixture to GVL and FDCA in a Biphasic Solvent over a Ru Single-Atom/Nanoparticle Dual-Site Catalyst

The industrial use of lignocellulose is limited by the copresence of C5 and C6 carbohydrates in this feedstock and the low selectivity of the corresponding catalytic conversion reaction, which collectively result in suboptimal product yields and necessitate energy-intensive purification/separation processes. Herein, we designed a composite dual-site Ru single-atom (SA)/Ru nanoparticle (NP) catalyst for the hydrogenation of levulinic acid (LA) and the oxidation of 5-hydroxymethyl furfural (HMF) in a biphasic solvent (γ-valerolactone (GVL)-saturated aqueous Na2CO3). Ru-SAs activated LA, while Ru-NPs boosted H2 dissociation to promote the hydrogenation of LA to GVL and ensured the efficient oxidation of HMF to 2,5-furandicarboxylic acid (FDCA). The SA/NP site design increased the oriented conversion efficiency of complex substrates, and the alternate hydrogenation–oxidation process ensured the stability of catalyst activity. The biphasic solvent system not only facilitated the mass transfer process but also allowed the spontaneous and non-energy-intensive separation of the produced GVL and FDCA. The obtained results pave the way for the design of SA/NP dual-site catalysts for the one-pot oriented conversion of complex substrates and the facile separation of products.

Comparison of alkali and ionic liquid pretreatment methods on the biochemical methane potential of date palm waste biomass

Date palm waste biomass is a readily accessible agricultural waste biomass that may be used to produce biogas. Because the complex structure of date palm waste biomass prevents the embedded holo-cellulosic sugars from biodegrading, pretreatment is required to increase methane (CH4) yield. The present investigation aimed to comparatively determine the impact of alkali and ionic liquid pretreatment on the biochemical methane potential (BMP) of different types of date palm waste biomass. The findings revealed that ionic liquid pretreated Palm and Fruit bunch showed the highest BMP (321.67 mL CH4/g-TS) and substrate conversion efficiency (68.01%), respectively, over other biomass samples. In alkali pretreatment, the highest BMP and substrate conversion efficiency were detected with Palm (309.76 mL CH4/g-TS) and Spathe (62.09%). The high BMP and substrate conversion efficiency of date palm waste biomass may be harnessed for bioenergy production when this ionic liquid pretreatment technology is used.

Bacillus velezensis EEAM 10B Strengthens Nutrient Metabolic Process in Black Soldier Fly Larvae (Hermetia illucens) via Changing Gut Microbiome and Metabolic Pathways

Insects are a potential alternative protein source to solve the food shortage crisis. Previous studies have illustrated that probiotics can improve the substrate conversion efficiency of insects and increase insect protein content. However, the effects of probiotics on insect physiology and nutrient metabolism are still not well understood. Here, the black soldier fly larvae (BSFL), Hermetia illucens (Diptera: Stratiomyidae), was used as a study subject to deeply investigate the specific interaction among a novel probiotic, Bacillus velezensis EEAM 10B (10B), intestinal microbiota, and the host. In this study, the effects of 10B on the survival and physiology of BSFL were first analyzed. It shows that 10B significantly elevated the substrate conversion rate, average dry weight, and protein content of BSFL by 5%, 0.13 g/pc, and 8%, respectively. Then, we assessed the effect of 10B on the microbial community composition in the gut and frass of BSFL using Illumina Miseq sequencing. It shows that 10B significantly altered the microbial composition of the gut, but not that of the frass. Pearson’s correlation analysis further showed that the Bacillus, unclassified_of_Caloramatoraceae, and Gracilibacillus were positively correlated with the survival rate, crude protein content, and substrate conversion rate of BSFL. To further investigate the effect of 10B on host metabolism, metabolic analyses on germ-free BSFL, monobacterial intestinal BSFL, and natural BSFL were also performed. The results proved that 10B (i) played a vital role in the survival of BSFL; and (ii) regulated the amino acid synthetic and metabolic process of BSFL, thus leading to the rise of the protein content of BSFL. In addition, vitamin backfill assays verified that the BSFL survival rate was significantly improved by supplying the germ-free BSFL with riboflavin, which further suggests that 10B determines the survival of BSFL via delivering riboflavin. Overall, this study provides a reference for understanding the comprehensive contribution of a specific probiotic to its host.

Surfactants-induced photo-fermentative biohydrogen production from corncob

Surfactants could improve the mass transfer capacity by avoiding agglomeration and sedimentation of substrate. This study evaluated the effects of diverse Tween series surfactants on hydrogen production performance of photo-fermentative biohydrogen production (PFHP) process. Tween 80 was found to be the most suitable surfactant. The maximum cumulative hydrogen yield (CHY) reached 49.38 ± 1.90 mL/g TS under 0.20% (v/v) Tween 80 addition. Highest energy recovery efficiency of 3.41 ± 0.13% and substrate conversion efficiency of 94.93 ± 0.44% were obtained, which was 50.37% and 1.7% higher than that of the control group, respectively. The effect of diverse Tween series surfactants on photosynthetic bacteria (PSB) was further studied. Results showed that Tween 80 significantly improved the growth and activity of PSB. The modified Han-Levenspiel model was adopted to analyze the effects of Tween 80 addition on PFHP. Results indicated that the reaction system was non-competitive inhibition, the predicted critical concentration of Tween 80 was 0.42% (v/v). This study provides a way to increase the CHY of corncob by the PFHP process.

Illustration of the variation in the content of flavanone rutinosides in various citrus germplasms from genetic and enzymatic perspectives.

In citrus, 1,6-rhamnosytransferase (1,6RhaT) and 1,2-rhamnosytransferase (1,2RhaT) catalyze flavanone-7-O-glucosides to form nonbitter flavanone rutinosides (FRs) and bitter flavanone neohesperidosides (FNs), respectively. As revealed in this study of fruit peels from 36 citrus accessions, FRs varied from undetectable levels in pummelo and kumquat to being the dominant flavonoids in sweet orange and loose-skin mandarins. Furthermore, a previously annotated full-length 1,6RhaT-like gene was identified as another 1,6RhaT-encoding gene by in vitro experiments. In total, 28 alleles of full-length 1,6RhaTs were isolated and classified into A, B and C types with only type A alleles encoding a functional protein. Coincidently, only the accessions that contained FRs harbored type A alleles, as was further verified in two F1 hybrid populations. Moreover, the inferior substrate conversion efficiency of 1,6RhaTs in comparison with that of 1,2RhaT in vitro might partly explain the lower proportions of FRs to total flavanone disaccharides in citrus hybrids harboring both functional rhamnosyltransferases. Our findings provide a better understanding of FR content variations among citrus and are meaningful for a mechanistic illustration of citrus flavonoid metabolism and fruit quality improvement practices.

Comparative study on Thermotoga maritima and Rhodobacter meghalophilus for hydrogen gas production using crude glycerol from Biodiesel plants

Hydrogen gas is a clean fuel with high calorific value. The current study is focused on production of hydrogen gas using Rhodobacter meghalophilus and Thermatoga maritima through anaerobic fermentation. Crude glycerol, by-product from biodiesel plant is used as carbon substrate due to its rich organic composition. Batch experiments have been carried out to study the impact of the inoculum size (1, 2 and 4 mL/L) and crude glycerol (5,10 and 15 mL/L) on the bacterial growth and hydrogen production rates by both the organisms. Inoculum size of 2 mL/L and crude glycerol of 15 mL/L of crude glycerol in medium for fermentation by R. meghalophilus, is found to produce 160 mL/L of gas with hydrogen production rate at 1.163×10-8 m3/kg.s and substrate conversion efficiency of 43.28%. Anaerobic fermentation by T. maritima is found to produce 120 mL/L of gas with 2 mL/L of inoculum and 10 mL/L of crude glycerol with hydrogen production rate of 9.4×10-9 m3/kg.s and substrate conversion efficiency of 23.88%. GC analysis of gas produced by T. maritima and R. meghalophilus shows 25% (v/v) and 19% (v/v) of hydrogen respectively. Thus, R. meghalophilus is found to acclimatize faster and exhibit better hydrogen production rate while T.maritima produces higher yield of hydrogen.

Enhancing the biotransformation efficiency of human CYP17A1 in Pichia pastoris by co-expressing CPR and glucose-6-phosphate dehydrogenase simultaneously

Steroids are a widely used class of drugs, and their hydroxylation modification has important pharmacological significance. Cytochrome P450 is the core enzyme for hydroxylation modification of steroid molecules, but its use is significantly restricted because of low activity and poor catalytic efficiency. In the present study, we optimized the codons of the human CYP17A1 (hCYP17A1) gene and performed its functional expression in Pichia pastoris GS115. The GS115-hCYP17A1 cells exhibited activities of dual function, and the following two products were detected: 17α-hydroxyprogesterone (17-HP, titer: 40.12 ± 3.16 mg/L) and androstenedione (AD, titer: 4.70 ± 0.31 mg/L). Subsequently, we compared the activity of hCYP17A1 co-expression with NADPH-cytochrome P450 oxidoreductases (CPRs) from five different strains of P. pastoris. Moreover, to strengthen the NADPH regeneration system, glucose-6-phosphate dehydrogenase (G6PDH) from three different species was introduced into the pathway from progesterone to 17-HP and AD by the GS115-hCYP17A1 cells. After optimizing CPRs and G6PDHs, three foreign proteins were co-expressed in the host cell, namely CYP17A1, CPRYP from Yorkshire pig, and G6PDHc from Candida tropicalis. Finally, the substrate conversion efficiency was found to be increased by 2.21-fold (46.88%) of that of the starting strains. We obtained a heterologous expression system with the highest biotransformation efficiency achieved to date. This work provided an essential reference for the study of the introduction of crucial enzyme systems into heterologous model organisms to construct an efficient steroid biotransformation system.

Relative evaluation of acid, alkali, and hydrothermal pretreatment influence on biochemical methane potential of date biomass

Date biomass is a carbon-rich renewable resource that can be considered a potential carbon-rich substrate for energy generation over anaerobic digestion (AD). However, due to its complex nature, appropriate pretreatment is necessary to achieve a higher methane yield. Hence, the current study was envisioned to evaluate the influence of three different pretreatment strategies, namely acid, alkali, and hydrothermal pretreatment on biochemical methane potential (BMP) of seven diverse sorts of Algerian date biomass, namely Pedicels, Fibrilium, Petiole, Fruit bunch, Spath, Palm, and its mixture. Among all the pretreatment conditions, alkaline pretreatment highly influenced the lignin composition of date biomass and showed higher BMP. Among all sorts of biomass, higher BMP was detected through Palm as 295.9 mL CH4/g-TS, whereas the lowest BMP values were recorded with Petiole as 226.74 mL CH4/g-TS. Among all the experimental variations, ammonium pretreated Palm biomass documented the highest substrate conversion efficiency (63.80%), which correlates well with the observed higher BMP values. Nevertheless, there was a very marginal improvement in BMP detected in the case of other pretreatment strategies compared to alkaline pretreatment. This might be due to the efficacy of the applied pretreatment method on delignification of date biomass.

Photo-fermentative biohydrogen production from corncob treated by microwave irradiation

The complex structure of corncob is the bottleneck that restricts its efficient biohydrogen production. Hence, effective treatment is an important exploration to break this limitation. The effect of microwave irradiation (MI) on photo-fermentative biohydrogen production (PFHP) process was evaluated in this paper. Diverse conditions (irradiation time, microwave power, and surfactant addition) were applied. Comparisons of cumulative hydrogen yield (CHY), microstructure, liquid products, and substrate conversion efficiency (Sconv) were conducted. Results showed that the highest CHY of 27.34 ± 1.13 mL/g TS was achieved when the corncob was treated by MI assisted with surfactant addition. Optimal treatment conditions (5.51 min irradiation time, 772.03 W microwave power, and 0.08 g/L rhamnolipids addition) were obtained. MI assisted with surfactant addition helped with the structure destroys and content degradation, displaying a great improves on PFHP. Lower ethanol content and higher butyric acid content were obtained. An 80.94% increase in CHY and Sconv of 90.44% were obtained than untreated corncob.

Hydrogen production during direct cellulose fermentation by mixed bacterial culture: The relationship between the key process parameters using response surface methodology

Dark fermentation is a promising method to produce hydrogen from lignocellulosic biomass. This study assessed the influence of temperature, phosphate buffer concentration and substrate concentration on direct hydrogen production form cellulose using response surface methodology. Mixed bacterial culture was successfully enriched on cellulose and used as an inoculum for hydrogen production. The model indicated that the highest cumulative hydrogen production (CHP) of 2.14 L H2/Lmedium could be obtained at 13.5 gcellulose/L, 79.5 mM buffer and 32.6 °C. However, hydrogen yield is then only 0.58 mol H2/molhexose due to low substrate conversion efficiency (SCE). Simultaneous optimization of CHP and SCE with desirability function approach resulted in the H2 yield of 2.71 ± 0.1 mol H2/molhexose and 93.8 ± 1.8% SCE at 3.35 gcellulose/L, 69 mM buffer and 32.9 °C. Phosphate concentration above 80 mM decreased H2 production, but had positive effect on cellulose consumption. The bacterial community analysis showed that Ruminiclostridium papyrosolvens was responsible for cellulose hydrolysis. Lachnoclostridium sp. was positively correlated with ethanol production at high phosphate buffer concentration, while Caproiciproducens sp. with caproate production at low buffer concentration. The obtained results opens the possibility of simultaneous hydrogen and caproate production from cellulosic substrates.

Tailor-made novel electrospun polystyrene/poly(d,l-lactide-co-glycolide) for oxidoreductases immobilization: Improvement of catalytic properties under extreme reaction conditions

Immobilized enzymes find applications in many areas such as pharmacy, medicine, food production and environmental protection. However, protecting these biocatalysts against harsh reaction conditions and retaining their enzymatic activity even after several biocatalytic cycles are major challenges. Properly selected supports and type of surface modifier therefore seem to be crucial for achieving high retention of catalytic activity of immobilized biomolecules. Here we propose production of novel composite electrospun fibers from polystyrene/poly(d,l-lactide-co-glycolide) (PS/PDLG) and its application as a support for immobilization of oxidoreductases such as alcohol dehydrogenase (ADH) and laccase (LAC). Two strategies of covalent binding, (i) (3-aminopropyl)triethoxysilane (APTES) with glutaraldehyde (GA) and (ii) polydopamine (PDA), were applied to attach oxidoreductases to PS/PDLG. The average fiber diameter was shown to increase from 1.252 µm to even 3.367 µm after enzyme immobilization. Effective production of PS/PDLG fibers and biomolecule attachment were confirmed by Fourier transform infrared spectroscopy analysis. The highest substrate conversion efficiency was observed at pH 6.5 and 5 for ADH and LAC, respectively, and at 25 °C for enzymes attached using the APTES + GA approach. Improvement of enzyme stabilization at high temperatures was confirmed in that relative activities of enzymes immobilized onto PS/PDLG fibers were over 20% higher than those of the free biomolecules, and enzyme leaching from the support using acetate and MES buffers was below 10 mg/g.