Semi-continuous Feeding Research Articles

High efficiency production of 5-hydroxyectoine using metabolically engineered Escherichia coli

The 5-hydroxyectoine is a natural protective agent with long-lasting moisturising and radiation resistance properties. It can be naturally synthesized by some extremophiles using the “bacterial milking” process, but this can corrode bioreactors and downstream purification may cause environmental pollution. In this study, an engineered Escherichia coli (E. coli) strain was constructed for the 5-hydroxyectoine production. First, three ectoine hydroxylases were characterised and the enzyme from Halomonas elongata was the most effective. The L-2,4-diaminobutyrate transaminase mutant was introduced into the engineered strain, which could accumulate 2.8 g/L 5-hydroxyectoine in shake flasks. By activating the glyoxylate cycle and balancing the α-ketoglutarate distribution, the 5-hydroxyectoine titer was further increased to 3.4 g/L. Finally, the optimized strain synthesized 58 g/L 5-hydroxyectoine via a semi-continuous feeding process in a NaCl-free medium. Overall, this study reported the highest titer of 5-hydroxyectoine synthesized by E. coli and established a low-salt fermentation process through the aforementioned efforts.

Novel Staged Free-Fall Reactor for the (Catalytic) Pyrolysis of Lignocellulosic Biomass and Waste Plastics.

Pyrolysis of lignocellulosic biomass and waste plastics has been intensely studied in the last few decades to obtain renewable fuels and chemicals. Various pyrolysis devices have been developed for use in a laboratory setting, operated either in batch or continuously at scales ranging from milligrams per hour to tenths of g per hour. We report here the design and operation of a novel staged free-fall (catalytic) pyrolysis unit and demonstrate that the concept works very well for the (catalytic) pyrolysis of pinewood sawdust, paper sludge, and polypropylene as representative feeds. The unit consists of a vertical tube with a pretreatment section, a pyrolysis section, a solid residue collection section, a gas-liquid separation/collection section, and a catalytic reaction section to optionally perform ex situ catalytic upgrading of the pyrolysis vapor. The sample is placed in a tube, which is transported by gravity through various sections of the unit. It allows for rapid testing with semicontinuous feeding (e.g., 50 g h-1) and the opportunity to perform reactions under an (inert) gas (e.g., N2) at atmospheric as well as elevated pressure (e.g., 50 bar). Liquid yields for noncatalytic sawdust pyrolysis at optimized conditions (475 °C and atmospheric pressure) were 63 wt % on biomass intake. A lower yield of 51 wt % (on a biomass basis) was obtained for the noncatalytic pyrolysis of paper sludge, likely due to the presence of minerals (e.g., CaCO3) in the feed. The possibility of using the unit for ex situ catalytic pyrolysis (pyrolysis at 475 °C and catalytic upgrading at 550 °C) was also successfully demonstrated using paper sludge as the feed and H-ZSM-5 as the catalyst (21 wt % catalyst on biomass). This resulted in a biphasic liquid product with 25.6 wt % of an aqueous phase and 11 wt % of an oil phase. The yield of benzene, toluene, and xylenes was 1.9 wt % (on a biomass basis). Finally, the concept was also proven for a representative polyolefin (polypropylene), both noncatalytic as well as in situ catalytic pyrolysis using H-ZSM-5 as the catalyst at 500 °C. The liquid yield of thermal, noncatalytic plastic pyrolysis was as high as 77 wt % on plastic intake, while in situ catalytic pyrolysis gave a combined 7.8 wt % yield of benzene, toluene, and xylenes on plastic intake.

Anaerobic digestion of poultry litter: technical aspects to improve process performance and water saving

In order to mitigate the significant electricity consumption in poultry farming the anaerobic digestion (AD) has been adopted. This study aimed to obtain information about the dilution, solid/liquid separation, mass balance, and reuse of the biofertilizer (recycle) to dilute poultry litter and to promote water saving while generating an organic fertilizer richer in nutrients. Five dilutions (1:4, 1:6, 1:8, 1:10, and 1:12) were submitted to mass balance test followed or not by solid/liquid separation on a sieve. The fractions of the dilutions 1:6 to 1:10 (poultry litter:water, w:v) were subjected to a test to determine the biochemical methane potential, according to the VDI-4630 standards. The highest potential biogas production was obtained in the liquid fraction of the dilution 1:6, reaching 179.4 L CH4 kg−1 VSadded. This condition was subjected to a semi-continuous feeding to evaluate the biofertilizer to replace water to dilute poultry litter (recycle). The results showed that the replacement of 40% of the dilution water by the biofertilizer had no inhibitory effect on the anaerobic digestion process, reaching values of 236 and 226 L CH4 kg−1 VSadded without and with the recycle, respectively. The decrease in the use of water and an increase in nutrients contained in the effluent (biofertilizer) is reflected in a 66% larger area for corn production. A detailed study of economic feasibility is essential for decision-making on investment and its recovery (payback).Thus, the liquid fraction of the dilution 1:6 with the recycle allowed a 40% saving in the use of clean water for poultry litter dilution, providing a biofertilizer with higher amounts of nitrogen, one of the nutrients most demanded by most crops.

Hydraulic Retention Time as an Operational Tool for the Production of Short-Chain Carboxylates via Anaerobic Fermentation of Carbohydrate-Rich Waste.

The carboxylate platform is a sustainable and cost-effective way to valorize wastes into biochemicals that replace those of fossil origin. Short-chain fatty acids (SCFAs) are intermediates generated during anaerobic fermentation (AF) and are considered high-value-added biochemicals among carboxylates. This investigation aimed to produce SCFAs through the AF of sugar beet molasses at 25 °C and semi-continuous feeding mode in completely stirred tank reactors. A particular focus was devoted to the role of hydraulic retention time (HRT) variation in SCFAs production and distribution profile. The highest SCFAs concentration (44.1 ± 2.3 gCOD/L) was reached at the HRT of 30 days. Caproic acid accounted for 32.5-35.5% (COD-concentration basis) at the long HRTs of 20 and 30 days due to the carbon chain elongation of shorter carboxylic acids. The findings of this study proved that HRT could be used to steer the anaerobic process toward the targeted SCFAs for specific uses. Furthermore, the successful operation at low-temperature conditions (i.e., 25 °C) makes the process economically promising.

The impact of semi-continuous and alternating microbial feeding patterns on methane yield from UASB reactors

Feeding strategy represents one of the most important bioreactor operation parameters, however, how different feeding patterns impact reactor microbiome development and treatment performance in up-flow anaerobic sludge blanket (UASB) reactors has not been systematically investigated. In the present study, three feeding strategies, including continuous feeding, semi-continuous feeding (with starvation-feast cycles), and alternate feeding (with high loading-low loading cycles) were assessed and compared using three laboratory-scale UASB reactors. It was observed that both long and short starvation-feast cycles provided by a semi-continuous feeding strategy failed to sustain stable anaerobic digestion under the conditions examined in the present study, while alternate feeding with high and low loading cycles supported microbial development. This feeding pattern resulted in an average methane yield of 74 ± 8.5% and an effluent COD removal efficiency of 89 ± 2.8%, which is comparable to the reactor operated under a continuous feeding pattern (Methane yield of 72 ± 2.4% and a COD removal efficiency of 87 ± 7.7%). Interestingly, as compared to continuous operation, reactors experienced starvation/feast stress (i.e., semi-continuous feeding) developed significantly higher methanogenic activities once continuous feeding was presumed, with dominant methanogens shifted from Methanosaeta in continuous feeding UASB to Methanosarcina in reactors undergone semi-continuous feeding. It was concluded that reactor feeding strategies can significantly impact microbiome communities in UASB, and an alternate feeding pattern is preferred, as compared to semi-continuous operation when reactor feeding cannot be continuously supplied.

Evaluation of the effect of the feeding regime on the removal of metals and pathogens in microalgae-bacterial systems.

Microalgae-bacteria systems are used for the treatment of effluents, using a technology that has stood out with excellent results, as reported in the literature. However, investigating these systems in more depth can improve our understanding of the removal mechanisms for a wide range of existing and emerging pollutants and help improve the guidelines for design and operation, in order to improve the treatment efficiency as well as biomass productivity. This work studied the impact of the feeding regime on the removal of metals and pathogens from primary domestic wastewater in high rate algal ponds (HRAPs). For this, one reactor was fed continuously (HRAP1) while two reactors were fed in semi-continuous mode, during 12 h day-1 (HRAP2) and 0.1 h day-1 (HRAP3). Although removal efficiencies of 82 ± 5% for Mn and 90% for E. coli were reached in the semi-continuously fed reactors, there was no significant difference between the conditions studied. On the other hand, for biomass productivity, the semi-continuous feeding regime was more advantageous with a growth of ≈ 22 mg L-1 day-1.

Simultaneous dairy wastewater treatment and bioelectricity production in a new microbial fuel cell using photosynthetic Synechococcus.

Photosynthetic microbial fuel cell (PMFC) is a novel technology, which employs organic pollutants and organisms to produce electrons and biomass and capture CO2 by bio-reactions. In this study, a new PMFC was developed based on Synechococcus sp. as a biocathode, and dairy wastewater was used in the anode chamber. Different experiments including batch feed mode, semi-continuous feed mode, Synechococcus feedstock to the anode chamber, Synechococcus-Chlorella mixed system, the feedstock of treated wastewater to the cathode chamber, and use of extra nutrients in the anodic chamber were performed to investigate the behavior of the PMFC system. The results indicated that the PMFC with a semi-continuous feed mode is more effective than a batch mode for electricity generation and pollutant removal. Herein, maximum power density, chemical oxygen demand removal, and Coulombic efficiency were 6.95 mW/m2 (450 Ω internal resistance), 62.94, and 43.16%, respectively, through mixing Synechococcus sp. and Chlorella algae in the batch-fed mode. The maximum nitrate and orthophosphate removal rates were 98.83 and 68.5%, respectively, wherein treated wastewater in the anode was added to the cathode. No significant difference in Synechococcus growth rate was found between the cathodic chamber of PMFC and the control cultivation cell. The heating value of the biocathode biomass at maximum Synechococcus growth rate (adding glucose into the anode chamber) was 0.2235MJ/Kg, indicating the cell's high ability for carbon dioxide recovery. This study investigated not only simultaneous bioelectricity production and dairy wastewater in a new PMFC using Synechococcus sp. but also studied several operational parameters and presented useful information about their effect on PMFC performance.

Multi-angle evaluation of the anaerobic digestion of Molasses vinasse using two different feeding patterns

Molasses vinasse (MV) is a waste burden in alcohol production due to its high organic matter content. However, it represents a potential source of energy recovery if adequately treated. In this study, two feeding patterns (pulse feeding: 8 ​L/4 ​h and semi-continuous feeding: 8 ​L/23 ​h) were evaluated for their effects on MV anaerobic digestion from multiple perspectives in a laboratory-scale reactor. The results demonstrated that semi-continuous feeding not only achieved a higher soluble chemical oxygen demand (sCOD) removal rate of 78.48% but also increased the production of biogas and methane by 20.04% and 51.48%, respectively. In addition, the chemical composition analysis suggested that the semi-continuous feeding pattern degraded the majority of lignin/CRAM and aromatic substances more effectively than the pulse feeding pattern. Moreover, the microbial analysis revealed that semi-continuous feeding increased the number of dominant bacteria, including Chloroflexi, Synergistetes, and Cloacimonetea, and methanogenic archaea, including Methanosaeta and Methanosarcina. The findings of this study, therefore, confirm that the semi-continuous feeding model is more effective and has good application potential, laying the groundwork for the MV anaerobic industrial processes.

CO2 Addition and Semicontinuous Feed Regime in Shaded HRAP—Pathogen Removal Performance

The influence of CO2 addition and feeding regime (continuous versus semicontinuous) on the removal of Pseudomonas aeruginosa, Clostridium perfringens, Staphylococcus, Enterococcus faecalis, and Escherichia coli (E. coli) from three shaded high-rate algal ponds (HRAPs) treating raw sewage (RS) was studied. The three HRAPs were operated at an analogous hydraulic retention time (HRT) for 5 days and with shading of 50%. The CO2 addition and feeding regime had no statistically significant influence on the removal of Pseudomonas aeruginosa, Clostridium perfringens, Staphylococcus sp., and Enterococcus faecalis, with 2.39–3.01, 2.07–2.31, 3.02–3.38, and 3.14–3.45 log units, respectively. However, the removal of E. coli decreased significantly with the feeding regime of 0.1 h d−1 and 2.23–3.29 log units. The productivity and the total suspended solids (TSS) removal efficiency were significantly improved with the semicontinuous feeding regime and CO2 addition. The highest productivity was obtained in the semicontinuous feeding regime, 5.93 g m2 d−1, while the TSS removal efficiency was similar between the semicontinuous feeding regime and CO2 addition (31–36%). The control of light intensity led to greater variability in the algal community, and was present in the three reactors, in different proportions, in the form of the microalgae Scenedesmus acutus, Scenedesmus obliquus, and Chlorella sp.

The Three-stage High Solid Anaerobic Digestion (TSHS- AD) under Ambient Temperature for Enhanced Biogas Production from Cow Manure

This research aimed to investigate the three-stage high solid anaerobic digestion (TSHS-AD) at ambient temperature. BMP was conducted at the various substrate to inoculum (S: I) ratios of 2:1, 4:1, and 6:1 on a volatile solid (VS) basis, each of which was conducted at different total solid concentrations (15%, 20%, and 30%). The highest methane yield of 343.97 mL-CH4·gVS-1 was achieved at 2:1-S: I ratio and 15 %TS. Meanwhile, TSHS-AD operated at S: I 2:1 and 15 %TS (20g-TS/L-R1) provide a maximum methane yield of 316.09 mL-CH4·gVS-1. The stage separation of TSHS-AD reduces inhibitors in the methanogenesis step. Moreover, it could create a full microbial function in each stage. Accumulation of VFA and semi-continuous feeding have considerable influence in enhancing anaerobic microbes involved in the biogas system. The annual income from biogas has the greatest impact on the investment attractiveness of TSHS-AD, according to the computation of IRR, NPV, and PB. The results obtained in this research could be potentially helpful to scale up the TSHS-AD system.

Synthesis and Characterization if Large Particle Size Self-Matting Core-shell Acrylic Resin

Acrylic resin plays an important role in leather-making, such as finishing agent, filler and tanning agent. Acrylic resin can be easily fabricated via conventional emulsion polymerization, but how to prepare large particle size with self-matting effect has always been a challenge. In this paper, a continuous three-stage polymerization method: seed-polymerization coupled core-polymerization and shell polymerization was employed to prepare large particle size self-matting acrylic resin emulsion. Simultaneously, the effect of feeding methods on particles size and the effects of latex particle size, shell structure and cross-linking degree on the morphology and gloss of coating were investigated. The Z-average size of PBA seed latex particles was 213.4 nm for semi-continuous feeding method but 82.3nm for batch feeding method. After three-time continuous growth, the seed emulsion turned into core emulsion, and the particle size of core latex reached about 700nm. In third stages ofshell polymerization, the core emulsion was changed into core-shell emulsion, and the latex particle size increased further to 804nm. The latex particle size, core-shell structure and cross-linking degree of shell layer were found to influence the gloss of the coating. Large latex particle size imparted the film spherical micro-rough surface, soft-core combined with hard-shell structure led to deformation resistant during film formation and cross-linking of shell layer increased the densification of shell layer, all contributed to the coating rough surface, as a result, increasing the matting effect of the coating. Finally, the leather gloss was reduced from 5.8° to 1.2°.

Photo-fermentative hydrogen production from cheese whey: Engineering of a mixed culture process in a semi-continuous, tubular photo-bioreactor

This work approaches the engineering of photo fermentative hydrogen production from cheese whey, for the scale-up of photo-bioreactors. Firstly, a brief review has been performed to identify the optimal reactor configuration as well as the main literature lacks. Results of the review analysis suggest that tubular photobioreactors are effective for the photo fermentation process. On the other hand, one of the main drawbacks to the scale-up of the proposed systems is the wide use of pure cultures, which requires aseptic environments and carefully controlled conditions. Based on the critical evaluation of the state of the art, a semi-continuous tubular photobioreactor, performing mixed culture hydrogen production from cheese whey, under unsterile conditions, was started up. Due to the lack of studies in this field, the case study was developed to provide a methodology for the reactor start-up, which represents the most critical phase of its operation. Preliminary tests were performed to choose the optimal operating conditions. To assess the effectiveness of cheese whey, results were compared to those obtained from a glucose based synthetic substrate, under steady state conditions. Experimental outcomes showed that the optimal Hydraulic Retention Time was 2 days and the most appropriate recirculation/pumping system consisted of an intermittent peristaltic pump. The semi-continuous feeding of cheese whey resulted in 87 mL/L d of hydrogen, which was similar to the productivity obtained under glucose feeding. The characterization of the residual organic content further indicated the possible accumulation of polyhydroxyalcanohates, which was estimated to constitute about the 40% of the total residual COD. These results further addressed the identification of key points to be better investigated to promote the effective photo fermentation scale-up for cheese whey valorization, such as the enhancement of the illumination conditions as well as the search for strategies to improve the uniform exposure of microbial cells to light.

Feeding controls H2S production in situ in high solid anaerobic digestion

In this study, a high frequency monitoring method was used to assess how semi-continuous feeding affects H2S production in high solid anaerobic digestion. The results showed that H2S characteristics at a monitoring frequency of 1 point/3 h were different to that of 1 point/24 h, its concentration decreased from 3449 ± 227 mg/m3 at 0 h to 298 ± 45 mg/m3 at 3 h. H2S concentration was negatively correlated with volatile fatty acids (VFAs), and oxidation reduction potential (ORP). 72–82% of H2S reduction in the first 3 h resulted from the introduction of O2 during feeding, and 18–28% of that was closely related to the production of a large quantity of soluble acidic matter, such as VFAs. A more accurate H2S release model was established according to the content of VFAs. Totally, this study implies that feed carrying air is a promising method for in situ control of H2S production in anaerobic digestion.Graphical

Resistance of anaerobic activated sludge acclimated by different feeding patterns: response to different stress shocks.

Anaerobic activated sludge plays a key role in the anaerobic digestion (AD) treatment of wastewater. The ability of anaerobic activated sludge to endure stress shock determines the performance of AD. In this study, the resistance of anaerobic activated sludge acclimated by three feeding patterns (continuous, semi-continuous, and pulse) to four stress shocks, including low pH influent, high OLR (organic loading rate), high ammonium and high sulfate, was investigated respectively. The results showed that the anaerobic activated sludge acclimated by semi-continuous feeding had the best resistance to high OLR shock, followed by pulse feeding, and then continuous feeding. There was no significant difference in the resistance of the three activated sludge to the other stress shocks. Under stress shock, the microbial community structure and abundance of specific functional microorganisms in the activated sludge acclimated by different feeding patterns varied, while the relative abundance of Methanosarcinaceae in the anaerobic activated sludge increased. The variation in the relative abundance of specific functional microorganisms was in charge of the differences in the resistance of anaerobic activated sludge. Overall, the results presented herein provide reference for improving the stability and effectiveness of activated sludge under adverse conditions.

Differential Effects of One Meal per Day in the Evening on Metabolic Health and Physical Performance in Lean Individuals.

Background: Generally, food intake occurs in a three-meal per 24 h fashion with in-between meal snacking. As such, most humans spend more than ∼ 12–16 h per day in the postprandial state. It may be reasoned from an evolutionary point of view, that the human body is physiologically habituated to less frequent meals. Metabolic flexibility (i.e., reciprocal changes in carbohydrate and fatty acid oxidation) is a characteristic of metabolic health and is reduced by semi-continuous feeding. The effects of time-restricted feeding (TRF) on metabolic parameters and physical performance in humans are equivocal.Methods: To investigate the effect of TRF on metabolism and physical performance in free-living healthy lean individuals, we compared the effects of eucaloric feeding provided by a single meal (22/2) vs. three meals per day in a randomized crossover study. We included 13 participants of which 11 (5 males/6 females) completed the study: age 31.0 ± 1.7 years, BMI 24.0 ± 0.6 kg/m2 and fat mass (%) 24.0 ± 0.6 (mean ± SEM). Participants consumed all the calories needed for a stable weight in either three meals (breakfast, lunch and dinner) or one meal per day between 17:00 and 19:00 for 11 days per study period.Results: Eucaloric meal reduction to a single meal per day lowered total body mass (3 meals/day –0.5 ± 0.3 vs. 1 meal/day –1.4 ± 0.3 kg, p = 0.03), fat mass (3 meals/day –0.1 ± 0.2 vs. 1 meal/day –0.7 ± 0.2, p = 0.049) and increased exercise fatty acid oxidation (p < 0.001) without impairment of aerobic capacity or strength (p > 0.05). Furthermore, we found lower plasma glucose concentrations during the second half of the day during the one meal per day intervention (p < 0.05).Conclusion: A single meal per day in the evening lowers body weight and adapts metabolic flexibility during exercise via increased fat oxidation whereas physical performance was not affected.

Development of an Escherichia coli whole cell catalyst harboring conjugated polyketone reductase from Candida glabrata for synthesis of d-(−)-pantolactone

d-(+)-pantothenic acid (DPA) has been widely used in feed and food additives and pharmaceutical industries. d-(−)-pantolactone (DPL) is a key intermediate in the production of DPA. The bio-asymmetric synthesis of DPL from ketopantoyl lactone (KPL) by conjugated polyketone reductases is an attractive route. In this study, high expression of a conjugated polyketone reductase from Candida glabrata (CglCPR) in Escherichia coli was achieved after optimization of vectors. The optimum temperature and pH of purified CglCPR were 40 °C and 4.5, respectively. The Michaelis-Menten constant Km and Vmax of purified CglCPR for KPL are 73.09 μM and 2.29 μmol mg−1 s−1, respectively. To circumvent the spontaneous degradation of KPL in biocatalytic reaction of synthesizing DPL, the reaction was performed by a strategy combing fed-batch addition of whole cell catalyst with substrate semi-continuous feeding. At the final KPL loading of 1000 mM, DPL with an isolated yield of 94.24 % was obtained after 13-h reaction and enantiomeric excess (e.e.) achieved > 99 %. The space-time yield of DPL reached to 228 g L−1 d−1.

Two-phase anaerobic digestion of food waste: Effect of semi-continuous feeding on acidogenesis and methane production

In present investigation, effect of diverting acidogenic off-gas from leached bed reactor (LBR) to up-flow anaerobic sludge blanket (UASB) reactor during semi-continuous food waste (FW) anaerobic digestion was evaluated. In test LBR headspace pressure (3.3 psi) was maintained with intermittent headspace gas transfer into UASB. In control, same headspace pressure was maintained without gas transfer. The semi-continuous FW addition affected the characteristics and production of leachate in control and test LBR. The cumulative COD, total soluble products and methane yields were 1.26, 1.37 and 3 times higher in the test LBR than the control. The acetate and methane yields from test LBR were 697.8 g·kgVSadded−1 and 167.55 mL·gCOD−1feeding. Acidogenic gas transfer maintained low partial pressure of hydrogen and the hydrogen to carbon-di-oxide ratio in the headspace of LBR, which were thermodynamically favorable for microbial metabolism and concomitant high-rate production of acetate-rich volatile fatty acid and methane-rich biogas from FW.

An evolved native microalgal consortium-snow system for the bioremediation of biogas and centrate wastewater: Start-up, optimization and stabilization

It is necessary to develop sustainable technologies for centrate wastewater (CW) and biogas treatment from sludge anaerobic digestion (AD) systems in an environmentally friendly and economical manner. The microalgae-based bioremediation approach presents a competitive alternative due to its capacity for nutrient recovery and carbon sequestration. However, process instabilities and operating challenges limit its development and implementation largely due to the complexities in the CW and biogas. In this study, the evolved native microalgal consortium (ENMC) was firstly developed using the gradual stress increase method to enhance their adaptation in high ammonium condition. The supplementation of local snow (with Ca2+ and Mg2+) and biogas into CW significantly enhanced ENMC growth through batch tests. Subsequently, an integrated ENMC-snow (ENMCS) system was proposed consisting of a hydrolysis-acidification reactor (HAR), biogas upgrade reactor, and photobioreactor (PBR). The ENMCS system was systematically investigated under both batch and semi-continuous operations, by adjusting primary process parameters including the fill ratio, feeding time, hydraulic retention time (HRT), wastewater pretreatment, and PBR type. It was eventually optimized as a 24 h, 70% fermented CW diluted with 30% snow water, semi-continuous feeding system with a fill ratio of 50% and HRT of 6 d in an open-PBR. Long-term operation (310 days) showed superior biomass yield (0.3059 ± 0.0039 g/(L•d)) and nutrient removal efficiencies (95.6 ± 0.13% and 90.8 ± 0.44% for NH4+-N and PO43−-P removal). Meanwhile, biogas was upgraded with an 82.2% CO2 reduction. The economic and environmental analysis further demonstrated the ENMCS system as an effective alternative for the bioremediation of AD effluents while simultaneously producing value-added biomass, especially applicable to snowy regions.

Press-extrusion pretreatment of the organic fraction of municipal solid waste for enhanced methane production

Anaerobic digestion (AD) is a well-established process for the treatment of a wide variety of solid organic substrates, including the organic fraction of municipal solid waste (OFMSW). At industrial scale, the mechanical pretreatment is a fundamental step to reduce OFMSW particle size and to promote the hydrolysis within the subsequent AD process. Among the mechanical pretreatment technologies, press-extrusion has recently raised great interest for its possible application to either enhance the organic load to the digester or improve the overall process stability and methane yields. Aim of this study was in assessing the potential of the press-extrusion pretreatment to improve the performance of OFMSW anaerobic degradation. Batch tests were set up according to a full factorial design of experiments to assess the significance of the main operating parameters. The statistical analysis of results addressed further tests, carried out under semi-continuous feeding mode, to better discuss the possible application of press-extrusion for the greatest valorization of OFMSW under anaerobic conditions.

Quantitative study of mixing/segregation behaviors of binary-mixture particles in pilot-scale fluidized bed reactor

In this study, a three-fluid Eulerian model coupled with the kinetic theory of granular flow was developed to investigate the mixing/segregation behaviors of binary-mixture particles in a pilot-scale fluidized bed reactor. The proposed model was validated by comparing predictions with the classical calculated data and the experimental data. A new mixing index was defined by counting the mixing information in each mesh, and then it was applied to evaluate quantitatively the effects of the key model parameters (i.e., restitution coefficient, friction coefficient) and operating conditions (i.e., inlet gas velocity, particle size ratio) on the mixing characteristics of binary-mixture particles. The hydrodynamic characteristics of binary-mixture particles in semi-continuous feed mode were also obtained. Numerical results demonstrate that the size segregation of particles can be easily realized under the conditions of high air velocity and large particle size ratio when the binary-mixture particles differ only in size.