Substrate Loading Rate Research Articles

Perturbations to common gardens of anaerobic co-digesters reveal relationships between functional resilience and microbial community composition.

We report the relationship between enrichment of adapted populations and enhancement of community functional resilience in methanogenic bioreactors. Although previous studies have shown the positive effects of acclimation, this work directly investigated the relationships between microbiome dynamics and performance of anaerobic co-digesting reactors in response to different levels of an environmental perturbation (loading of grease interceptor waste [GIW]). Using the methanogenic microbiome from a full-scale digester, we developed eight sets of microbial communities in triplicate using different feed sources. These substrate-specific microbiomes were then exposed to three independent disturbance events of low-, mid- and high-GIW loading rates. This approach allowed us to directly attribute differences in community responses to differences in community composition. Despite identical inocula, environment (digester operation, substrate loading rate, and feeding patterns) and general whole-community function (methane production and effluent quality) during the cultivation period, different substrates led to different microbial community assemblies. Lipid pre-acclimation led to enrichment of a pool of specialized populations, along with thriving of sub-dominant communities. The enrichment of these populations improved functional resilience and process performance when exposed to a low level of lipid-rich perturbation compared with less-acclimated communities. At higher levels of perturbation, the communities were not able to recover methanogenesis, indicating a loading limit to the resilience response. This study extends our current understanding of environmental perturbations, feed-specific adaptation, and functional resilience in methanogenic bioreactors.IMPORTANCEThis study demonstrates, for the first time for GIW co-digestion, how applying similar perturbations to different microbial communities was used to directly identify the causal relationships between microbial community, function, and environment in triplicate anaerobic microbiomes. We evaluated the impact of feed-specific adaptation on methanogenic microbiomes and demonstrated how microbiomes can be influenced to improve their functional (methanogenic) resilience to GIW inhibition. These findings demonstrate how an ecological framework can help improve a biological engineering application, and more specifically, increase the potential of anaerobic co-digestion for converting wastes to energy.

Characteristics and performance of algal–bacterial granular sludge in photo-sequencing batch reactors under various substrate loading rates

The algae–bacterial granular sludge (ABGS) technology has garnered significant attention due to its remarkable attributes of low carbon emissions. To investigate the performance of the ABGS system under various substrate loading rates, the parallel photo-sequencing batch reactors (P1 and P2) were set up. The results indicated that chlorophyll-a content and extracellular polymeric substance content were measured at 10.7 ± 0.3 mg/L and 61.4 ± 0.7 mg/g SS in P1 under relatively low substrate loading rate (0.9 kg COD/m3/d and 0.09 kg N/m3/d). Moreover, kinetic study revealed that the maximal specific P uptake rate for P1 reached 0.21 mg P/g SS/h under light conditions, and it achieved 0.078 mg P/g SS/h under dark conditions, highlighting the significant role on phosphorus removal played by algae in the ABGS system. The microbial analysis and scanning electron microscopy confirmed that filamentous algae predominantly colonize the surface in P1, whereas spherical bacteria dominate the surface of granular sludge in P2. Additionally, a diverse array of microorganisms including bacteria, algae, and metazoa such as Rotifers and Nematodes were observed in both systems, providing evidence for the establishment of a symbiotic system. This study not only confirmed the ability of ABGS for efficient N and P removal under different substrate loading conditions but also highlighted its potential to enhance the ecological diversity of the reaction system.

Genome and secretome insights: unravelling the lignocellulolytic potential of Myceliophthora verrucosa for enhanced hydrolysis of lignocellulosic biomass.

Lignocellulolytic enzymes from a novel Myceliophthora verrucosa (5DR) strain was found to potentiate the efficacy of benchmark cellulase during saccharification of acid/alkali treated bagasse by ~ 2.24 fold, indicating it to be an important source of auxiliary enzymes. The De-novo sequencing and analysis of M. verrucosa genome (31.7Mb) revealed to encode for 7989 putative genes, representing a wide array of CAZymes (366) with a high proportions of auxiliary activity (AA) genes (76). The LC/MS QTOF based secretome analysis of M. verrucosa showed high abundance of glycosyl hydrolases and AA proteins with cellobiose dehydrogenase (CDH) (AA8), being the most prominent auxiliary protein. A gene coding for lytic polysaccharide monooxygenase (LPMO) was expressed in Pichia pastoris and CDH produced by M. verrucosa culture on rice straw based solidified medium were purified and characterized. The mass spectrometry of LPMO catalyzed hydrolytic products of avicel showed the release of both C1/C4 oxidized products, indicating it to be type-3. The lignocellulolytic cocktail comprising of in-house cellulase produced by Aspergillus allahabadii strain spiked with LPMO & CDH exhibited enhanced and better hydrolysis of mild alkali deacetylated (MAD) and unwashed acid pretreated rice straw slurry (UWAP), when compared to Cellic CTec3 at high substrate loading rate.

Efficient sulfide and methane removal in anaerobic secondary effluent using a pilot-scale membrane-aerated biofilm reactor

Anaerobic secondary treatment can enable energy-efficient removal of organic matter but may produce effluent containing dissolved methane and sulfide that must be managed before discharge or reuse. In this study, we operated a Membrane-aerated Biofilm Reactor (MABR) to achieve reliable removal of dissolved sulfide and methane from anaerobic secondary effluent at pilot-scale. The pilot-scale MABR was equipped with gas permeable polymethyl pentene (PMP) membranes, promoting surface growth of aerobic biofilm via diffusion-based aeration (lumen-to-surface diffusion). The system treated anaerobic secondary effluent from a demonstration-scale anaerobic membrane bioreactor (AnMBR) processing 90 m3/d primary effluent. MABR influent flow rate was increased from 8.2 to 32.7 m3/d to elevate substrate loading rates to the biofilm. The MABR consistently achieved >99 % removal of sulfide and dissolved methane, even at the maximum substrate loading rate: 2.3 g-S/m2/d for sulfide and 2.5 g-CH4/m2/d for dissolved methane. Despite effective sulfide and methane removal, incomplete nitrification (<25 % ammonia removal) occurred, with a portion of ammonia converted into nitrous oxide (N2O), a greenhouse gas 298 times more potent than CO2. Operating the MABR incurred low energy costs: 0.01 to 0.05 kWh/m3 for the compressor supplying air to the membrane lumen and 0.01 kWh/m3 for the influent pump. An in-depth mass balance of N2O emissions from the MABR revealed that N2O was subject to counter-diffusion (surface-to-lumen diffusion) in which >99 % of the N2O produced within the biofilm was recovered in off-gas from the gas permeable membranes (hollow fibers).

CRISPR/Cas9 mediated gene editing of transcription factor ACE1 for enhanced cellulase production in thermophilic fungus Rasamsonia emersonii

BackgroundThe filamentous fungus Rasamsonia emersonii has immense potential to produce biorefinery relevant thermostable cellulase and hemicellulase enzymes using lignocellulosic biomass. Previously in our lab, a hyper-cellulase producing strain of R. emersonii was developed through classical breeding and system biology approaches. ACE1, a pivotal transcription factor in fungi, plays a crucial role in negatively regulating the expression of cellulase genes. In order to identify the role of ACE1 in cellulase production and to further improve the lignocellulolytic enzyme production in R. emersonii, CRISPR/Cas9 mediated disruption of ACE1 gene was employed.ResultsA gene-edited ∆ACE1 strain (GN11) was created, that showed 21.97, 20.70 and 24.63, 9.42, 18.12%, improved endoglucanase, cellobiohydrolase (CBHI), β-glucosidase, FPase, and xylanase, activities, respectively, as compared to parental strain M36. The transcriptional profiling showed that the expression of global regulator (XlnR) and different CAZymes genes including endoglucanases, cellobiohydrolase, β-xylosidase, xylanase, β-glucosidase and lytic polysaccharide mono-oxygenases (LPMOs) were significantly enhanced, suggesting critical roles of ACE1 in negatively regulating the expression of various key genes associated with cellulase production in R. emersonii. Whereas, the disruption of ACE1 significantly down-regulated the expression of CreA repressor gene as also evidenced by 2-deoxyglucose (2-DG) resistance phenotype exhibited by edited strain GN11 as well as appreciably higher constitutive production of cellulases in the presence of glucose and mixture of glucose and disaccharide (MGDs) both in batch and flask fed batch mode of culturing. Furthermore, ∆ACE1 strains were evaluated for the hydrolysis of biorefinery relevant steam/acid pretreated unwashed rice straw slurry (Praj Industries Ltd; 15% substrate loading rate) and were found to be significantly superior when compared to the benchmark enzymes produced by parent strain M36 and Cellic Ctec3.ConclusionsCurrent work uncovers the crucial role of ACE1 in regulating the expression of the various cellulase genes and carbon catabolite repression mechanism in R. emersonii. This study represents the first successful report of utilizing CRISPR/Cas9 genome editing technology to disrupt the ACE1 gene in the thermophlic fungus R. emersonii. The improved methodologies presented in this work might be applied to other commercially important fungal strains for which genetic manipulation tools are limited.

Critical evaluation of biochar effects on methane production and process stability in anaerobic digestion

Biochar is an emerging biomaterial for managing residual biomass while simultaneously sequestering carbon. To extend the biochar value chain, applying biochar to enhance anaerobic digestion (AD) processes is gaining attention in the context of a circular economy and cascading use of biomass. However, the comparative effects of various biochar dosages under normal and severe AD conditions are still unclear. To further our understanding of its potential application, this work investigated the impact of adding various biochar dosages on AD processes under normal and high substrate loadings. Three inoculum-to-substrate ratios (ISRs): one representing normal substrate loading (ISR 2) and two representing substrate overloading (ISR 1 and 0.5) were investigated. Each substrate loading rate was tested with a biochar dosage of 0% (control), 10%, and 25% based on substrate volatile solids. The results revealed that under the severe condition of high substrate overload (ISR 0.5), a high biochar dosage of 25% significantly increased cumulative methane production by 5.6% (p = 0.06) when compared to the control. Under the same condition (ISR 0.5, 25%), the time required to achieve a particular extent of ultimate methane potential was significantly reduced (p = 0.04), indicating that the methane production rate was increased. At ISR 0.5, the increase of process stability was also significant with 25% biochar addition, while the control (0%) and 10% biochar addition exhibited high variance among replicates. However, biochar did not affect AD processes under normal substrate loading (ISR 2) and mild substrate overload (ISR 1). Thus, a positive effect of biochar on the AD process was only observed under severe conditions with the highest biochar dosage. Future works should consider optimising substrate loadings and biochar dosages under real conditions when testing the practical application of biochar addition in AD processes.

Use of regression models for development of a simple and effective biogas decision-support tool

Anaerobic digestion (AD) is an alternative way to treat manure while producing biogas as a renewable fuel. To increase the efficiency of AD performance, accurate prediction of biogas yield in different working conditions is necessary. In this study, regression models were developed to estimate biogas production from co-digesting swine manure (SM) and waste kitchen oil (WKO) at mesophilic temperatures. A dataset was collected from the semi-continuous AD studies across nine treatments of SM and WKO, evaluated at 30, 35 and 40 °C. Application of polynomial regression models and variable interactions with the selected data resulted in an adjusted R2 value of 0.9656, much higher than the simple linear regression model (R2 = 0.7167). The significance of the model was observed with the mean absolute percentage error score of 4.16%. Biogas estimation using the final model resulted in a difference between predicted and actual values from 0.2 to 6.7%, except for one treatment which was 9.8% different than observed. A spreadsheet was created to estimate biogas production and other operational factors using substrate loading rates and temperature settings. This user-friendly program could be used as a decision-support tool to provide recommendations for some working conditions and estimation of the biogas yield under different scenarios.

Dark fermentative hydrogen gas production from waste peach pulp by intermittent feeding: Effects of hydraulic residence time and substrate loading rate

Peach has a big share of the world fruit market, with significant annual waste production. This study reports dark fermentative hydrogen gas production from waste peach pulp using intermittent feeding. In this context, the effects of hydraulic residence time (HRT) and substrate loading rate (SLR) on hydrogen production were determined in two sets of experiments. All experiments were performed in 310 mL serum bottles. During the first set of experiments, HRT was varied between 1 and 6 days and hydrogen production was more favorable at short HRTs. In the second set of experiments, SLR was varied between 9 and 90 gTOC/L.d, and more efficient hydrogen formation was observed by increasing the SLR. The most convenient HRT and SLR resulting in maximum hydrogen formation rate (931.8 mLH2/L.d) was obtained at 1 day and 90 gTOC/L.d, respectively.

Enhancing methane recovery by intermittent substrate feeding and microbial community response in anaerobic digestion of glycerol

Accumulation of intermediate volatile fatty acids, especially propionic acid, is a limiting factor in anaerobic digestion of glycerol. To mitigate this problem, intermittent substrate feeding was investigated and evaluated. The results showed that intermittent substrate feeding could decrease the effects of high concentrations of propionic acid and improve the performance of CH4 production at high substrate loading rates. CH4 production rate with intermittent substrate feeding (1.60 NL/L/day) was higher than single substrate feeding (1.47 NL/L/day) at 5.0 g COD/L/day of glycerol loading rate. NGS and PICRUSt were applied to monitor the changes in the microbial community. The proportion of dominant bacteria changed with alterations in glycerol loading rate and substrate feeding technique. NGS results elucidated three main bacterial groups that degraded and competed for glycerol, namely: Delftia, Trichococcus, and Desulfuromonas. Trichococcus and Desulfuromonas tended to withstand a higher rate of glycerol loading than Delftia. PICRUSt results demonstrated that Trichococcus is paramount in the glycerol degradation. Delftia and Desulfuromonas might compete with methanogens by utilizing acetate and/or H2. This study suggested the role of microbial communities in CH4 production from glycerol. The intermittent feeding, which balanced organic acid production and its consumption, was clarified to improve methane production from glycerol.

Mechanical response of metallic glass thin films with different components during nanoindentation and nanoscratch

<p indent="0mm">In this paper, the nanoscale mechanical response of metallic glass thin films with different components is studied via the nanoindentation and nanoscratch tests. The serrated flow behaviors of Cu₅₀Zr₅₀, Ni₆₂Nb₃₈, Fe₇₀Nb₁₀B₂₀, and Co₅₆Ta₃₅B₉ metallic glass thin films with different fragilities under various nanoindentation loading rates were systematically studied. The nanoindentation creep behaviors of metallic glass films under different loading conditions were analyzed; the volume of the shear transition zone in each material was calculated. The wear resistance of metallic glass thin films with different components was studied via the nanoscratch experiment. The results show that the serrated mode of a metallic glass film depends on the change in the loading rate. The volume of the internal shear transition zone in a metallic glass film depends on the fragility and the joint effect of the substrate temperature and loading rate. Generally, the larger the degree of material heterogeneity, the more easily the volume of the shear transition zone is affected by the loading rate. Combined with the nanoscratch experiment, the wear resistance of metallic glass film was primarily dependent on its hardness.

Exploring organic micropollutant biodegradation under dynamic substrate loading in rapid sand filters

Microbial removal of trace organic micropollutants (OMPs) from drinking water sources remains challenging. Nitrifying and heterotrophic bacteria in rapid sand filters (RSFs) are capable of biodegrading OMPs while growing on ammonia and dissolved organic matter (DOM). The loading patterns of ammonia and DOM may therefore affect microbial activities as well as OMP biodegradation. So far, there is very limited information on the effect of substrate loading on OMP biodegradation at environmentally relevant concentrations (∼ 1 µg/L) in RSFs. We investigated the biodegradation rates of 16 OMPs at various substrate loading rates and/or empty bed contact times (EBCT). The presence of DOM improved the biodegradation of paracetamol (41.8%) by functioning as supplementary carbon source for the heterotrophic degrader, while hindering the biodegradation of 2,4-D, mecoprop and benzotriazole due to substrate competition. Lower loading ratios of DOM/benzotriazole benefited benzotriazole biodegradation by reducing substrate competition. Higher ammonia loading rates enhanced benzotriazole removal by stimulating nitrification-based co-metabolism. However, stimulating nitrification inhibited heterotrophic activity, which in turn inhibited the biodegradation of paracetamol, 2,4-D and mecoprop. A longer EBCT promoted metformin biodegradation as it is a slowly biodegradable compound, but suppressed the biodegradation of paracetamol and benzotriazole due to limited substrate supply. Therefore, the optimal substrate loading pattern is contingent on the type of OMP, which can be chosen based on the priority compounds in practice. The overall results contribute to understanding OMP biodegradation mechanisms at trace concentrations and offer a step towards enhancing microbial removal of OMPs from drinking water by optimally using RSFs.

Customized design of horizontal flow constructed wetlands employing secondary datasets

Values of areal removal rate constant (k, m/day) were derived by employing a dataset of 74 horizontal flow constructed wetlands (HFCWs) using P-k-C* approach, which showed large variation (0.006–0.40 m/day) as these systems were largely under-loaded. This dataset was classified based on substrate loading rates, temperature, and depth to reduce the SDs of k values among the subsets. Further, the k values for organics removal were optimized by eliminating data of 10%, 20% and 30% of the most underloaded HFCWs, which led to a sharp reduction in observed SDs from 84.74% to 4.85%; 116.48% to 3.42%; and 114.70% to 6.89% respectively for the aforementioned scenarios for organics removal. These stable k values can be adopted for area calculations for optimizing the design of HFCWs and the computations made here will help identify the limiting nutrient that would govern the design under specific requirements.

Designing the vertical flow constructed wetland based on targeted limiting pollutant

The requirement of large land area limits the adoption of constructed wetlands (CWs) in urban settings with limited land availability. The area calculations for CW design are commonly carried out following Kikuth approach where the removal rate constant (K) is derived from literature. Investigation of secondary data of 82 vertical flow CWs, performed in this study, yielded wide variations (0.0003 – 0.822 md−1) in the calculated K values for different pollutants under different environmental and operational conditions indicating that it is important to incorporate the desired levels of pollutant removal to arrive at customized design of CWs. The results indicated that the relative standard deviation of K values could be narrowed by classifying the datasets based on design parameters like depth, hydraulic loading rates and substrate loading rates. These calculations can help arrive at more scientific design of CW to achieve the prevailing standards for the discharge or reuse of sewage.

Combination of system biology and classical approaches for developing biorefinery relevant lignocellulolytic Rasamsonia emersonii strain

The objective of this study was to develop thermophilic fungus Rasamsonia emersonii using integrated system biology tools (genomics, proteomics and transcriptional analysis) in combination with classical strain breeding approaches. Developed hyper cellulolytic mutant strain M36 showed endoglucanase (476.35 U/ml), β-glucosidase (70.54 U/ml), cellobiohydrolase (15.17 U/ml), FPase (4.89 U/ml) and xylanase (485.21 U/ml) on cellulose/gram flour based production medium. Comparison of the expression profile at proteome and transcriptional level of the developed strain and wild type parent gave detailed insight into the up-regulation of different CAZymes including glycosyl hydrolases (GH5, GH6, GH7, GH3, GH10) and auxiliary enzymes (lytic polysaccharide monooxygenase, swollenin) at system level. Furthermore, the potential of lignocellulolytic enzyme produced by the developed strain and custom designed cocktail spiked with heterologously expressed lytic polysaccharide monooxygenase from Mycothermus thermophiloides were analyzed for the hydrolysis of biorefinery relevant unwashed pretreated rice straw slurry (PRAJ and IOCL) @17% substrate loading rate.

Substrate loading rates conducive to nitritation in entrapped cell reactors: performance and microbial community structure.

This study aimed to elucidate the boundaries of ammonia and organic loading rates that allow for nitritation in continuous flow phosphorylated-polyvinyl alcohol entrapped cell reactors and to clarify the community structure of microorganisms involving nitrogen transformation in the gel bead matrices. At operating bulk dissolved oxygen concentration of 2mg/L, nitritation was accomplished when the total ammonia nitrogen (TAN) loading rate was ≥ 0.3 kgN/m3/d. At TAN loading rates of ≤ 0.2 kgN/m3 /d, complete oxidation of ammonia to nitrate took place. Nitritation performance dropped with increased chemical oxygen demand (COD) loading rates indicating limitation of nitritation reactor operation at some COD loading conditions. 16S rRNA gene amplicon sequencing revealed that the uncultured Cytophagaceae bacterium, Arenimonas, Truepera, Nitrosomonas, Comamonas, unclassified Soil Crenarchaeotic Group, and uncultured Chitinophagaceae bacterium were highly abundant taxa in the reactors' gel bead matrices. qPCR with specific primers targeting amoA genes demonstrated the coexistence of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea, and Comammox in the gel bead matrices. AOB was likely the main functioning ammonia-oxidizing microorganisms due to the amoA gene being of highest abundance in most of the studied conditions. Nitrite-oxidizing microorganisms presented in less relative abundance than ammonia-oxidizing microorganisms, with Nitrobacter rather than Nitrospira dominating in the group. Results obtained from this study are expected to further the application of nitritation entrapped cell reactors to real wastewater treatment processes.

Novel β-glucanases along with xylanase identified in Thermomyces lanuginosus secretome for enhanced saccharification of different lignocellulosics

The LC/MS-based exo-proteome analysis of thermophilic fungus Thermomyces lanuginosus showed 22.59% (40 proteins) of the total identified proteins (177) as CAZymes (carbohydrate-active enzymes). The CAZymes were primarily represented by glycosyl hydrolases (72.5%) belonging to 21 different GH families. Xylanase (GH11) was found to be the major protein (24.3%) in addition to the β-glucanase and another complex polysaccharide-degrading (carbohydrate-active enzymes) CAZymes in the secretome. FPLC-based fractionation of secretome was employed to identify proteins responsible for enhancing the catalytic efficacy of Cellic Ctec2 during hydrolysis of acid pre-treated lignocellulosics and eventually xylanase (GH11) and β-glucanases (GH64 and GH81) were identified and purified. The purified xylanase when supplemented with Cellic Ctec2 resulted in 2.05-, 1.79-, and 1.60-fold increase in the release of glucose from acid-treated bagasse at 10, 15, and 20% substrate loading rate, respectively when compared with the control. Similarly, enhanced hydrolysis of acid pre-treated corn residue and rice straw was observed upon supplementation with xylanase. Spiking benchmark cellulase with purified GH64 and GH81 also resulted in 1.18- and 1.23-fold enhanced hydrolysis of acid pre-treated sugarcane bagasse. The supplementation of xylanase (1000 units/g substrate) was found to reduce the Cellic Ctec2 loading rate from 36 mg/g substrate by 2.70-, 2.88-, and 2.57-fold required for hydrolysis of acid treated bagasse, corn residue, and rice straw, respectively, at high substrate loading rate (20%) and thus, it is an important candidate for economizing the 2G ethanol process.

Influence of Inoculum and Substrate Concentration on Anaerobic Digestion of Ocimum Sanctum (Holy Basil)

“Anaerobic digestion is the constrained degradation of usual organic waste in the oxygen deficient environment and the existence of anaerobic microorganisms. Anaerobic digestion is accomplished by microbial diversity. “Substrate loading rate is a measure of biological conversion capacity of anaerobic system and has significant influence on the process performance. Henceforth in the current work, the outcome of different concentrations of substrate to inoculum (0.3, 0.6 and 0.9) on anaerobic digestion of Holy Basil (Ocimum sanctum) used as substrate was explored in batch reactors for 45 days along with heterogenous cowdung as Inoculum. Temperature and biogas were noted daily. “The Volatile Solids (VS), Chemical Oxygen Demand (COD), Total Kjeldhal Nitrogen (TKN) and Phosphorous were analyzed at an interval of 5 days. Though the degradation rates of various parameters showed a higher efficiency at 0.3 inoculum to “substrate concentration, the biogas generation was impending to be maximum at 0.6 among the various digesters.

An industrial scale testing and analysis of waste-to-energy production from various substrates by employing a modern anaerobic digestion plant

This industrial scale study has tested, monitored and analyzed the waste-to-energy yield for different ratios of mixed livestock manure and mixed vegetable waste substrates using a modern industrial scale pilot anaerobic digestion (AD) plant, which consists of four interlinked digesters, having a volume of 272.5 m³. Five substrate treatment ratios between mixed livestock manure (L) and mixed vegetable waste (V) have been tested and they are denoted with L1V0, L0.8V0.2, L0.6V0.4, L0.4V0.6 and L0.2V0.8. The pilot AD plant runs in a semi-continuous mode having a retention time of 30 days for each treatment and a substrate loading rate of 4000 kg d−1 (avg.). The subsequent energy yield in terms of biogas/biomethane in m3.10−3 kg−1 VS (volatile solids), have been recorded as 89/46, 146/98, 133/82, 124/75 and 96/55 for five treatment ratios, respectively. The yield of biogas and methane from the largest to smallest are in the order of L0.8V0.2 > L0.6V0.4 > L0.4V0.6 > L0.2V0.8 > L1V0. For the purpose of biogas yield prediction, a statistical analysis is deliberated to further testify the measured biogas yield data in order to determine a correlation between the yield and its influenced variables. The least significant difference (LSD) and regression coefficient (R2) values are discussed. As such the values of LSD05, LSD01 and R2 have been found as 18, 32 and 0.93 for L1V0 and as 29, 51 and 0.99 for L0.8V0.2, respectively, but they are significantly different for other substrate treatment ratios.

Bio-hydrogen production from tequila vinasses: Effect of detoxification with activated charcoal on dark fermentation performance

Hydrogen production from dark fermentation is a potential source of sustainable fuel when it is generated from waste. This study compared hydrogen production resulting from fermentation using raw and detoxified tequila vinasse. Vinasse was detoxified with granular activated charcoal, which was used to adsorb compounds that could inhibit the production of hydrogen by dark fermentation. In batch cultures detoxification of vinasse led to up to 20% higher maximum velocities of hydrogen production, a 5.4 h reduction in the lag phase and an 11% higher molar yield, compared to results obtained with raw vinasse. Losses of sugars after detoxification provoked that the specific hydrogen volumetric yields obtained with detoxified vinasse were 30–40% lower with 5 g COD/L and 15 g COD/L initial concentrations, compared to the ones obtained with raw vinasse. For an initial 30 g COD/L no differences in specific hydrogen yields were observed between raw or detoxified vinasse in batch fermentation. Continuous culture fermentation of vinasse showed hydrogen production rates between 1.32 ± 0.07 to 1.39 ± 0.14 NL H2/L-d when extra nutrients were added, while a stable production of hydrogen through fermentation of detoxified vinasse could not be maintained despite nutrient addition. Production of hydrogen from vinasse diluted with water with no additional nutrients was assessed and rates close to 0.42 ± 0.02 NL H2/L-d and hydrogen content close to 37% were obtained. Accumulation of lactic acid and a predominant production of butyric acid over acetic acid suggested that the fermentation dynamics of vinasse with no supplementary nutrients were especially susceptible to high substrate loading rates and prolonged hydraulic retention times.

Evaluating novel fungal secretomes for efficient saccharification and fermentation of composite sugars derived from hydrolysate and molasses into ethanol

This paper evaluates the ability of secretome from two thermotolerant fungal strains (Aspergillus terreus 9DR and Achaetomium strumarium 10DR) for boosting the hydrolytic efficiency of benchmark cellulolytic preparation (Cellic CTec2). Further we report enhanced saccharification of different agro-residues under semi-aerobic when compared to aerobic conditions. The mass spectroscopic analysis of the hydrolysates indicates the role of auxiliary oxidative enzymes present in A. terreus and A. strumarium secretomes for enhancing the capability of the cellulolytic cocktails. The paper further demonstrate positive effect of using the cocktails for enhanced saccharification and subsequent fermentation to ethanol of acid pre-treated rice straw, corn residues and sugarcane bagasse at higher substrate loading rates (20% w/v). The paper also reports co-utilization of composite sugars derived from molasses and enzymatic hydrolysate obtained from agnostic lignocellulosics for efficient bioconversion to ethanol applicable for developing BOLT-ON technology.