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1.
Water Sci Technol ; 80(3): 426-436, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31596254

RESUMO

Thermal pre-flocculation to enable dispersed air flotation is an economical and ecofriendly technology for harvesting microalgae from water. However, the underlying mechanism and optimal conditions for this method remain unclear. In this study, Chlorella vulgaris (C. vulgaris) and Scenedesmus obliquus (S. obliquus) were harvested using a thermal flotation process. The surface structure and characteristics (morphology, electricity, and hydrophobicity) of the microalgae were analyzed using FT-IR (Fourier transform infrared spectroscopy), SEM (scanning electron microscopy), zeta potential, and a hydrophobic test. Further, response surface methodology (RSM) was used to optimize the flotation process. The hydrophobicity of S. obliquus exceeded that of C. vulgaris; as such, under the thermal pre-flocculation, S. obliquus (88.16%) was harvested more efficiently than C. vulgaris (47.16%). Thermal pre-flocculation denatured the lipids, carbohydrate, and proteins of microalgal cell surfaces. This resulted in a decrease in the electrostatic repulsion between the cells and air bubbles. The highest harvesting efficiency was 91.96% at 70 °C, 1,412 rpm, and 13.36 min. The results of this study demonstrate the potential for economic and ecofriendly harvesting of microalgae for biofuels and other bioproducts industries.


Assuntos
Chlorella vulgaris , Microalgas , Biocombustíveis , Biomassa , Floculação , Espectroscopia de Infravermelho com Transformada de Fourier
2.
Waste Manag ; 99: 49-59, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31472440

RESUMO

Hydrothermal liquefaction (HTL) of Animal By-Products (ABP) is a promising technology for their recycling and disposal. Different operating parameters have been studied to determine their influence on the process. Higher heating values of biocrudes ranging between 35 and 39 MJ/kg have been obtained showing a maximum yield of 61% at 225 °C. At low HTL temperature, the products are similar to those of rendering process and the biocrude is mainly formed by triglycerides and fatty acids in a 90:10 ratio, approximately. By increasing temperature, the free fatty acid yield increases, as well as amides and heterocyclic compounds as a result of the triglycerides and protein reactions. Between 250 and 290 °C a great difference in the composition of the biocrude obtained is observed. Water content also showed significant effects on the product yields. Large amounts of foams were obtained at low water contents that were minimised when it is increased. This is a very important feature to be considered for scaling up the phase separation process. Glycerine amount in the aqueous phase was remarkable, as a consequence of fat hydrolysis. Increasing pH to 9 increases the extraction of organics into the aqueous phase, whereas operating at pH 5 yields similar amounts of biocrude as compared with neutral pH, with a higher percentage of fatty acids. Reusing of the aqueous phase is necessary for the viability of the process and leads to increasing amounts of dissolved organics in the aqueous phase with the number of cycles, reaching a saturation level after three-four recycling rounds.


Assuntos
Microalgas , Animais , Biocombustíveis , Concentração de Íons de Hidrogênio , Temperatura Ambiente , Água
3.
Bioresour Technol ; 292: 122052, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31473038

RESUMO

This work studied the effects of ammonium carbonate pretreatment on biogas production during sequential anaerobic digestion. The results showed that the addition of ammonium bicarbonate (8%, w/w) obtained the highest biogas production of 14,690 mL with a yield of 222.6 mL g-1, which was 31% higher than that of un-pretreated (control experiment). Interestingly, the COD removal was increased by 100%. Furthermore, it was also helpful in stabilizing the pH of anaerobically digested corn stalk. Based on the results, the modified Gompertz equation fitted the cumulative biogas production curves very well, with high correlation coefficients (>0.994).


Assuntos
Metano , Zea mays , Anaerobiose , Bicarbonatos , Biocombustíveis
4.
Water Sci Technol ; 80(2): 387-396, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31537775

RESUMO

Anaerobic mono-digestion and co-digestion are nowadays widely used in wastewater treatment plants (WWTP). However, the data processing of the conventional biochemical potential test (BMP) carried out to assess potential substrates should be enhanced to reduce the uncertainty of the results. In this study, two methodologies aiming to improve the data processing in anaerobic digestion studies were proposed. The methodologies aimed at the estimation of synergy in anaerobic co-digestion of organic waste and the standardization of the BMP test results by considering the activity of the inoculums under mono-digestion conditions. Both methodologies comprise the application of the Gompertz equation. For the first methodology, four cosubstrates and two types of substrates were used. Regarding synergy estimation, the cosubstrates dairy whey and grease sludge had an impact on the degradation kinetic. In regard to the second methodology, the results indicate that the activity of the inoculums exerts an influence on the BMP analysis, and it should be considered. This can be meaningful when comparing results among studies when different inoculums are used or even for studies where the same inoculum is used but it is taken at different reactor operational moments.


Assuntos
Reatores Biológicos , Eliminação de Resíduos Líquidos , Anaerobiose , Biocombustíveis , Esgotos , Águas Residuárias
5.
Bioresour Technol ; 293: 122043, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31472406

RESUMO

The objective of this study was to investigate the effects of particle size reduction (20, 1, 0.15, and 0.075 mm) on biogas production from rice straw waste through batch anaerobic digestion experiments. To clarify the digestion mechanisms, the microbial community and rice straw properties including fractal dimension, dissolution abilities and the bio-liquefaction degree were determined. Particle size reduction of rice straw improved methane yield from 107 mL g-1 VS to 197 mL g-1 VS. The elevated digestion efficiency was attributed to the cellulose degradation (degradation rate from 27% to 93%) rather than hemicellulose or lignin. The comminution pretreatment improved the basic morphology, dissolution abilities and bio-liquefaction degree, which associated with the shifts in the bacterial community and the decreased bacterial diversity. These results suggested that particle size reduction of the rice straw in conjunction with optimized microbial growth could improve the methane yield in anaerobic digestion processes.


Assuntos
Oryza , Anaerobiose , Biocombustíveis , Metano , Tamanho da Partícula
6.
Bioresour Technol ; 293: 121998, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31473377

RESUMO

In this study, the indigenous native microalgae were isolated from domestic and dairy effluent (DE) and further screened for DE treatment and lipid accumulation. All the isolated microalgae were examined for their growth adaptability in DE. The growth parameters of 15 isolates were determined and the following six isolates further selected for comprehensive analysis and identified as Desmodesmus sp. ASK01, Chlorella sp. ASK14, Scenedesmus sp. ASK16, Scenedesmus sp. ASK22, Chlorella sp. ASK25 and Chlorella sp. ASK27. The nutrient remediation capacity of six isolates as well as its lipid accumulation potential and biomass composition were determined. The Scenedesmus sp. ASK22 showed the best combined results and promising strain for the DE treatment and biofuel production. Biomass composition of Scenedesmus sp. ASK22 showed an oil accumulation of 30.7% (w/w) and biomass yield 1.22 g L-1. The fatty acid methyl ester (FAME) mainly composed of C15:0, C16:0, C18:0, C18:1 and C18:3.


Assuntos
Chlorella , Microalgas , Scenedesmus , Biocombustíveis , Biomassa
7.
Bioresour Technol ; 293: 122076, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31479853

RESUMO

This work comparatively studied the catalytic effect of MgO and MgCO3 on pyrolysis of rice husk (RH). The apparent activation energy (E) was reduced significantly by pyrolysis of RH with MgCO3, thus lowering the decomposition temperature during pyrolysis. MgO could not obviously influence the gas evolution during pyrolysis, while MgCO3 had a better performance on the syngas (H2 and CO) generation at around 600-700 °C. Also, the generation of CO2 was suppressed by the RH pyrolysis with MgCO3. The phenols were the dominant compounds in the bio-oil derived from RH. Furthermore, co-pyrolysis of RH and polyvinyl chloride (PVC) in the presence of MgO or MgCO3 at 600 °C could improve the oils quality by decreasing the acids content and increasing the hydrocarbons content. Particularly, the resulting oils had high hydrocarbons content (>35%) and low acids content (<2%). The decrease of acids, alcohols, and phenols contributed to the increase of hydrocarbons.


Assuntos
Óxido de Magnésio , Pirólise , Biocombustíveis , Biomassa , Plásticos
8.
Bioresour Technol ; 293: 122032, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31491647

RESUMO

Two de-lignified cellulose of loofah sponge and sawdust were applied in two ways to enhance the lipid production from oleaginous yeast using acetic acid. When 30 g/L of acetic acid was used as a carbon source, direct addition of de-lignified loofah sponge or sawdust increased the extracellular lipid content to 33.94% and 53.25%, respectively. The latter reduced the energy input of lipid extraction process from 0.86 to 0.57 GJ per ton of biodiesel production. To relieve the inhibition caused by 40 g/L acetic acid, immobilization of oleaginous yeast on de-lignified sawdust increased the lipid concentration and yield from 3.83 g/L, 0.18 g/g C to 7.15 g/L, 0.20 g/g C, respectively. These improvements occurred due to the cell-immobilized sawdust which play an important role in the loading of cells and adsorption of acetic acid. Immobilized cultivation also increased the fatty acid proportion of C18:1, thereby improving biodiesel performance.


Assuntos
Ácido Acético , Celulose , Biocombustíveis , Ácidos Graxos , Lipídeos
9.
Bioresour Technol ; 293: 122135, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31540787

RESUMO

Microalgae have attracted great attention as a promising sustainable resource for biofuel production. In studies aiming to improve lipid accumulation, many key enzymes involved in lipid biosynthesis were identified and confirmed, but genetic engineering remains a challenge in most species of microalgae. In an alternative approach, various chemical modulators can be used to directly regulate the lipid biosynthesis pathway, with similar effects to gene overexpression and interference approaches, including improving the precursor supply and blocking competing pathways. The produced lipid can be protected from being converted into other metabolites by the chemicals such as lipase inhibitors. In addition, a few chemicals were also demonstrated to greatly influence cell growth and lipid accumulation by indirect regulation of the lipid biosynthesis pathway, such as increasing cell permeability or regulating oxidative stress. Thus, adding chemical modulators can be a useful alternative strategy for improving lipid accumulation in large-scale cultivation of microalgae.


Assuntos
Microalgas , Biocombustíveis , Engenharia Genética , Lipídeos
10.
Bioresour Technol ; 293: 122066, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31557641

RESUMO

This work investigated the effects of different temperatures on methane production, kinetics, and microbial communities during solid-state anaerobic digestion (SS-AD) using rice straw. The results indicated that thermophilic anaerobic digestion led to the faster methane production (13.74 L/kg) and a shorter biogas production cycle (34 days) than mesophilic anaerobic digestion (5.48 L/kg, 58 days). SS-AD under thermophilic conditions resulted in more intense lignocellulose degradation and better fitting results. The species of microorganisms did not differ when the temperature was altered; however, the abundances of various phyla, particularly Firmicutes, differed. Overall, the findings suggested that thermophilic SS-AD had higher methanogenic efficiency and dramatically altered the structure of the microbial community during solid-state anaerobic digestion. Moreover, a potential effective strategy for agricultural waste management by SS-AD was proposed.


Assuntos
Biocombustíveis , Oryza , Anaerobiose , Reatores Biológicos , Metano , Temperatura Ambiente
11.
Bioresour Technol ; 293: 122155, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31561979

RESUMO

Crude glycerol (CG) is a by-product formed during the trans-esterification reaction for biodiesel production. Although crude glycerol is considered a waste stream of the biodiesel industry, it can replace expensive carbon substrates required for lipid production by oleaginous micro-organisms. However, crude glycerol has several impurities, such as methanol, soap, triglycerides, fatty acids, salts and metals, which are created during the trans-esterification process and may affect the cellular metabolism involved in lipid synthesis. This review aims to critically present a variation in crude glycerol composition depending on trans-esterification process and impact of impurities present in the crude glycerol on the cell growth and lipid accumulation by oleaginous microbes. This study also draws comparison between purified and crude glycerol for lipid production. Several techniques for crude glycerol purification (chemical treatment, thermal treatment, membrane technology, ion-exchange chromatography and adsorption) have been presented and discussed with reference to cost and environmental effects.


Assuntos
Carbono , Glicerol , Biocombustíveis , Ácidos Graxos , Lipídeos
12.
Bioresour Technol ; 291: 121892, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31376670

RESUMO

The aim of this study was to investigate the bioenergy potential of red macroalgae GF by evaluating its biofuel physicochemical characteristics, and conducting a kinetic study and thermodynamic analysis of pyrolysis for the first time. The thermal decomposition study was performed at low heating rates (5, 10, 20 and 30 °C min-1) under N2 atmosphere. The thermal behavior of GF pyrolysis indicated the presence of three different decomposition stages, which are associated with different components in its structure and consequently influence the kinetic and thermodynamic parameters. The kinetic triplet obtained for GF provided a suitable description of experimental thermal behavior. The thermodynamic parameters demonstrated that GF is as a new promising feedstock for bioenergy and presented a similar potential to well-known bioenergy feedstock.


Assuntos
Rodófitas/metabolismo , Alga Marinha/metabolismo , Termodinâmica , Biocombustíveis , Cinética , Pirólise
13.
Bioresour Technol ; 291: 121834, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31371157

RESUMO

In present study, lipids were extracted from unbroken microalga Chlorella vulgaris with high water content (50% microalgal solution) through three-phase partitioning (TPP). The method was found to extract around 15.9% of total lipid transformable to methyl esters (LTMEs) from unbroken microalgal cells which is two times of Bligh and Dyer method. We investigated the effects of various parameters on TPP performance and were optimised through response surface methodology. The results indicated that incubation duration, temperature and extraction time were positively correlated with LTME extraction efficiency. The optimum temperature was 60 °C, incubation duration was 120 min, extraction time was 60 min, ratio of solvent to DKP was 1:1. The FAME yield was calculated as 12.05% and major fatty acids together accounted for 71.33% which indicated the great potential of the proposed lipid extraction procedure for microalga-based biodiesel production.


Assuntos
Biocombustíveis , Biomassa , Chlorella vulgaris/metabolismo , Lipídeos/isolamento & purificação , Microalgas/metabolismo , Ácidos Graxos/metabolismo , Lipídeos/biossíntese , Solventes , Temperatura Ambiente , Água
14.
Bioresour Technol ; 291: 121877, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31376672

RESUMO

Bioelectrochemical conversion of CO2 to CH4 is a promising way to increase the calorific value of biogas produced during anaerobic digestion. There are two groups of methanogens enriched in these systems, hydrogenotrophs and acetoclastic methanogens that can also directly accept electrons from an electrode or another microorganism. In this study, a microbial electrolysis cell (MEC) poised at -500 mV (vs. SHE) was operated for biogas upgrading. Methane content in the biogas increased from 71% to >90%, and 8.2% of the CO2 was converted to methane. Methanothrix, an acetoclastic methanogen that can participate in direct electron transfer (DET), and Azonexus, an acetate-oxidizing electrogen, were enriched on the cathode. Transcriptomics revealed that Methanothrix on the cathode were using the CO2 reduction pathway, while Methanothrix in the bulk sludge were using the acetate decarboxylation pathway for production of methane. These results show that stimulation of DET in MEC enhances biogas-upgrading processes.


Assuntos
Biocombustíveis , Methanosarcinaceae , Eletrodos , Eletrólise , Transporte de Elétrons , Elétrons , Metano/metabolismo , Esgotos
15.
Bioresour Technol ; 291: 121872, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31377516

RESUMO

Anaerobic digestion of manure is a common practice; however, the low biogas yield of manure can hamper the profitability of systems in small to medium farms. An increase in biogas yield could be achieved by co-digesting animal manure with co-substrates such as cheese whey. A Techno-economic assessment of anaerobic co-digestion of animal manure and cheese whey (cow, goat and sheep), has been carried out. The results obtained showed that for a farm with 250 adult cattle heads, the revenues generated in an anaerobic mono-digestion process are not able to offset the initial required investment. However, the co-digestion of manure with 30% of cheese whey showed a good economic performance and positive returns (Net Present values >0, Internal Rate of Return >11% and a Return of the investment in <10 years). Electricity selling price and biogas production are the key parameters to determine the profitability of the system.


Assuntos
Queijo , Esterco , Soro do Leite/metabolismo , Anaerobiose , Animais , Biocombustíveis/economia , Bovinos , Fazendas , Feminino , Cabras , Gado , Ovinos
16.
Waste Manag ; 96: 121-127, 2019 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-31376955

RESUMO

Siloxanes present in small concentrations in biogas interfere with the operation of biogas-to-energy facilities. During biogas combustion, siloxanes form white deposits on engine components (engine heads, spark plugs, valves) in crystals or amorphous forms depending on the temperature. The purpose of this study was to evaluate the economic feasibility of biogas-to-energy systems for managing the operational challenges due to siloxanes in biogas. The facility maintenance cost data were compiled by a survey of biogas-to-energy facilities in the United States. Economic analyses were performed to compare the operational costs due to increased maintenance for removing the white deposits forming on the engine components and the installation of a pretreatment system (carbon adsorption) to remove siloxanes prior to combustion. Numerical analyses showed that for the facilities with operating capacities less than 1300 m3/h (750 scfm), the costs for installation and operation of the carbon adsorption system exceeded the maintenance costs for removal of deposits from the engine components. The maintenance costs correlated well with the reported maintenance needs which were between 120 and 800 man hours per year. On the basis of siloxane removal costs alone, it is not economically feasible to install a carbon adsorption system for siloxane removal prior to combustion for small facilities processing less than 1300 m3/h (750 scfm) of biogas. However, using a process for siloxane removal prior to gas engines (e.g., carbon adsorption) would be improve the overall performance of the gas engines and reduce maintenance need at all facilities.


Assuntos
Biocombustíveis , Siloxanas , Adsorção , Carbono , Temperatura Ambiente
17.
Waste Manag ; 98: 1-13, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31421484

RESUMO

Hydrogen (H2) production from sugarcane press-mud, a waste obtained from the non-centrifugal sugarcane agroindustry, was assessed by coupling hydrolysis, fermentation, purification, and ethanol steam reforming (ESR). Two culture media were employed on three different sugarcane press-mud samples to produce bioethanol by fermentation using Saccharomyces cerevisiae at 30 °C. One culture medium was supplemented with nutrients and the other without supplementation. The supplementation did not have a significant effect over ethanol production (∼82.1 g L-1) after 70 h fermentation, but the concentration of the impurities was always lower under supplemented conditions. Among tested impurities, differences in 3-methyl-1-butanol showed the effect of the supplementation on the ESR over RhPt/CeO2-SiO2 catalyst at 700 °C, where the H2 yield decreased significantly in the presence of 3-methyl-1-butanol (p < 0.05). The spearman correlation coefficient showed that the H2 yield was correlated with the 3-methy-1-butanol content (RHO = -0.929) and carbon deposits (RHO = -0.964). Therefore, supplemented bioethanol could deliver 3.0 g H2 kg-1 sugarcane press-mud, which is almost twice that of the non-supplemented samples, likely due to the reduction of harmful impurities in the bioethanol. Additionally, supplemented conditions allowed for energy savings in the process and improved catalyst stability. This study provides insights into the effect of supplementing culture media to produce purer bioethanol samples, which further deliver higher H2 yields by ESR.


Assuntos
Saccharum , Biocombustíveis , Biomassa , Fermentação , Hidrogênio , Hidrólise , Dióxido de Silício , Vapor
18.
Waste Manag ; 97: 115-122, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31447018

RESUMO

The effect of reflux ratio on the anaerobic mono-digestion of pig manure (PM) in leach beds coupled with continuous stirred tank reactors (CSTRs) has been studied in this work, and contents of volatile fatty acids (VFAs) and biogas yields were determined for three groups of leach bed reactor (LBR) - CSTR systems. The obtained results indicated that the reflux of biogas slurry increased both the pH of the acid-producing phase and acetic acid yield and repeatedly degraded the refractory organic matter in the biogas slurry. The larger reflux ratio increased the inoculation volume and substantially enhanced the mass transfer process. The maximum values of the biogas and methane yields equal to 259.49 and 167.44 mL/g volatile solids, respectively, were achieved at a reflux ratio of 100%. Moreover, the weight of the PM leachate residue was reduced by 94.14%, and the total nutrient content (N + P2O5 + K2O) was relatively high (1.48%), which was suitable for vegetable seedling substrates. In conclusion, during the treatment of PM in LBR-CSTRs, the solid phase remains on the leach bed, and the leachate is supplied to a biogas tank, which effectively increases its stability of operation.


Assuntos
Reatores Biológicos , Esterco , Anaerobiose , Animais , Biocombustíveis , Metano , Suínos
19.
Waste Manag ; 97: 38-46, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31447025

RESUMO

Methane losses from biogas plants are problematic, since they contribute to global warming and thus reduce the environmental benefits of biogas production. Total losses of methane from 23 biogas plants were measured by applying a tracer gas dispersion method to assess the magnitude of these emissions. The investigated biogas plants varied in terms of size, substrates used and biogas utilisation. Methane emission rates varied between 2.3 and 33.5 kg CH4 h-1, and losses expressed in percentages of production varied between 0.4 and 14.9%. The average emission rate was 10.4 kg CH4 h-1, and the average loss was 4.6%. Methane losses from the larger biogas plants were generally lower compared to those from the smaller facilities. In general, methane losses were higher from wastewater treatment biogas plants (7.5% in average) in comparison to agricultural biogas plants (2.4% in average). In essence, methane loss may constitute the largest negative environmental impact on the carbon footprint of biogas production.


Assuntos
Biocombustíveis , Metano , Agricultura , Aquecimento Global , Águas Residuárias
20.
Bioresour Technol ; 292: 121286, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31386946

RESUMO

Hydrothermal liquefaction of Ulva prolifera macroalgae (UM), an aquatic biomass, was carried out in an autoclave reactor at different temperature (270, 290 and 310 °C) and reaction holding time (10, 20 and 30 min.). The catalytic reactions of UM were carried out in the presence of three basic catalysts (KOH, NaOH and Na2CO3) with the different catalyst amount. Maximum bio-oil yield for non-catalytic liquefaction was (12.0 wt%) at 290 with 10 min reaction time. In the catalytic reaction the maximum bio-oil yield (26.7 wt%) was observed with KOH (0.1 g) catalyst. The chemical components and functional groups present in the bio-oils are identified by GC-MS, FT-IR, 1H-NMR, TGA and elemental analysis techniques. Majorly nitrogen containing compounds were found with catalytic reaction in bio-oils. The higher heating value (33.6 MJ kg-1) as well as the higher carbon content (64.2%) was observed in the case of catalytic liquefaction bio-oil.


Assuntos
Alga Marinha , Ulva , Biocombustíveis , Biomassa , Espectroscopia de Infravermelho com Transformada de Fourier , Temperatura Ambiente
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