Research

14 pages, 993 KiB

Open AccessFeature PaperArticle

Methods for the Evaluation of Industrial Mechanical Pretreatments before Anaerobic Digesters

by Helen Coarita Fernandez, Diana Amaya Ramirez, Ruben Teixeira Franco, Pierre Buffière and Rémy Bayard

Molecules 2020, 25(4), 860; https://doi.org/10.3390/molecules25040860 - 15 Feb 2020

Cited by 7 | Viewed by 2665

Abstract

Different methods were tested to evaluate the performance of a pretreatment before anaerobic digestion. Besides conventional biochemical parameters, such as the biochemical methane potential (BMP), the methane production rate, or the extent of solubilization of organic compounds, methods for physical characterization were also [...] Read more.

Different methods were tested to evaluate the performance of a pretreatment before anaerobic digestion. Besides conventional biochemical parameters, such as the biochemical methane potential (BMP), the methane production rate, or the extent of solubilization of organic compounds, methods for physical characterization were also developed in the present work. Criteria, such as the particle size distribution, the water retention capacity, and the rheological properties, were thus measured. These methods were tested on samples taken in two full-scale digesters operating with cattle manure as a substrate and using hammer mills. The comparison of samples taken before and after the pretreatment unit showed no significant improvement in the methane potential. However, the methane production rate increased by 15% and 26% for the two hammer mills, respectively. A relevant improvement of the rheological properties was also observed. This feature is likely correlated with the average reduction in particle size during the pretreatment operation, but these results needs confirmation in a wider range of systems. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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13 pages, 1406 KiB

Open AccessArticle

High-Rate Anaerobic Digestion of Waste Activated Sludge by Integration of Electro-Fenton Process

by Emna Feki, Audrey Battimelli, Sami Sayadi, Abdelhafidh Dhouib and Sonia Khoufi

Molecules 2020, 25(3), 626; https://doi.org/10.3390/molecules25030626 - 31 Jan 2020

Cited by 16 | Viewed by 3178

Abstract

Anaerobic digestion (AD), being the most effective treatment method of waste activated sludge (WAS), allows for safe disposal. The present study deals with the electro-Fenton (EF) pretreatment for enhancing the WAS biogas potential with low-cost iron electrodes. The effect of pretreatment on the [...] Read more.

Anaerobic digestion (AD), being the most effective treatment method of waste activated sludge (WAS), allows for safe disposal. The present study deals with the electro-Fenton (EF) pretreatment for enhancing the WAS biogas potential with low-cost iron electrodes. The effect of pretreatment on the physicochemical characteristics of sludge was assessed. Following EF pretreatment, the pH, conductivity, soluble chemical oxygen demand (SCOD), and volatile fatty acids (VFA) increased to 7.5, 13.72 mS/cm, 4.1 g/L, and 925 mg/L, respectively. Capillary suction time (CST) analysis highlighted the dewaterability effect of EF on WAS, as demonstrated by the decrease in CST from 429 to 180 s following 30 min of pretreatment. Batch digestion assays presented an increase in the biogas yield to 0.135 L/g volatile solids (VS) after 60 min of EF pretreatment in comparison to raw sludge (0.08 L/g VS). Production of biogas was also found to improve during semi-continuous fermentation of EF-pretreated sludge conducted in a lab-scale reactor. In comparison to raw sludge, EF-pretreated sludge produced the highest biogas yield (0.81 L biogas/g VS) with a high COD removal rate, reaching 96.6% at an organic loading rate (OLR) of 2.5 g VS/L. d. Results revealed that the EF process could be an effective WAS disintegration method with maximum recovery of bioenergy during AD. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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21 pages, 3664 KiB

Open AccessArticle

Impacts of Chemical-Assisted Thermal Pretreatments on Methane Production from Fruit and Vegetable Harvesting Wastes: Process Optimization

by Ümmihan Günerhan, Ender Us, Lütfiye Dumlu, Vedat Yılmaz, Hélène Carrère and Altınay N. Perendeci

Molecules 2020, 25(3), 500; https://doi.org/10.3390/molecules25030500 - 23 Jan 2020

Cited by 12 | Viewed by 2377

Abstract

The increasing population creates excess pressure on the plantation and production of fruits and vegetables across the world. Consumption demand during the whole year has made production compulsory in the covered production system (greenhouse). Production, harvesting, processing, transporting, and distribution chains of fruit [...] Read more.

The increasing population creates excess pressure on the plantation and production of fruits and vegetables across the world. Consumption demand during the whole year has made production compulsory in the covered production system (greenhouse). Production, harvesting, processing, transporting, and distribution chains of fruit and vegetables have resulted in a huge amount of wastes as an alternative source to produce biofuels. In this study, optimization of two pretreatment processes (NaOH and HCl assisted thermal) was investigated to enhance methane production from fruit and vegetable harvesting wastes (FVHW) that originate from greenhouses. NaOH concentration (0–6.5%), HCl concentration (0–5%), reaction temperature (60–100 °C), solid content (1–5%), time of reaction (1–5 h), and mixing speed (0–500 rpm) were chosen in a wide range of levels to optimize the process in a broad design boundary and to evaluate the positive and negative impacts of independent variables along with their ranges. Increasing NaOH and HCl concentrations resulted in higher COD solubilization but decreased the concentration of soluble sugars that can be converted directly into methane. Thus, the increasing concentrations of NaOH and HCl in the pretreatments have resulted in low methane production. The most important independent variables impacting COD and sugar solubilization were found to be chemical concentration (as NaOH and HCl), solid content and reaction temperature for the optimization of pretreatment processes. The high amount of methane productions in the range of 222–365 mL CH₄ gVS⁻¹ was obtained by the simple thermal application without using chemical agents as NaOH or HCl. Maximum enhancement of methane production was 47–68% compared to raw FVHW when 5% solid content, 1-hour reaction time and 60–100 °C reaction temperature were applied in pretreatments. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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19 pages, 2973 KiB

Open AccessArticle

Occurrence of the Persistent Antimicrobial Triclosan in Microwave Pretreated and Anaerobically Digested Municipal Sludges under Various Process Conditions

by Gokce Kor-Bicakci, Timothy Abbott, Emine Ubay-Cokgor and Cigdem Eskicioglu

Molecules 2020, 25(2), 310; https://doi.org/10.3390/molecules25020310 - 12 Jan 2020

Cited by 9 | Viewed by 2282

Abstract

Treatment of emerging contaminants, such as antimicrobials, has become a priority topic for environmental protection. As a persistent, toxic, and bioaccumulative antimicrobial, the accumulation of triclosan (TCS) in wastewater sludge is creating a potential risk to human and ecosystem health via the agricultural [...] Read more.

Treatment of emerging contaminants, such as antimicrobials, has become a priority topic for environmental protection. As a persistent, toxic, and bioaccumulative antimicrobial, the accumulation of triclosan (TCS) in wastewater sludge is creating a potential risk to human and ecosystem health via the agricultural use of biosolids. The impact of microwave (MW) pretreatment on TCS levels in municipal sludge is unknown. This study, for the first time, evaluated how MW pretreatment (80 and 160 °C) itself and together with anaerobic digestion (AD) under various sludge retention times (SRTs: 20, 12, and 6 days) and temperatures (35 and 55 °C) can affect the levels of TCS in municipal sludge. TCS and its potential transformation products were analyzed with ultra-high-performance liquid chromatography and tandem mass spectrometry. Significantly higher TCS concentrations were detected in sludge sampled from the plant in colder compared to those in warmer temperatures. MW temperature did not have a discernible impact on TCS reduction from undigested sludge. However, AD studies indicated that compared to controls (no pretreatment), MW irradiation could make TCS more amenable to biodegradation (up to 46%), especially at the elevated pretreatment and digester temperatures. At different SRTs studied, TCS levels in the thermophilic digesters were considerably lower than that of in the mesophilic digesters. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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14 pages, 2259 KiB

Open AccessFeature PaperArticle

Biogas Production from Physicochemically Pretreated Grass Lawn Waste: Comparison of Different Process Schemes

by Georgia Antonopoulou, Dimitrios Vayenas and Gerasimos Lyberatos

Molecules 2020, 25(2), 296; https://doi.org/10.3390/molecules25020296 - 11 Jan 2020

Cited by 21 | Viewed by 2693

Abstract

Various pretreatment methods, such as thermal, alkaline and acid, were applied on grass lawn (GL) waste and the effect of each pretreatment method on the Biochemical Methane Potential was evaluated for two options, namely using the whole slurry resulting from pretreatment or the [...] Read more.

Various pretreatment methods, such as thermal, alkaline and acid, were applied on grass lawn (GL) waste and the effect of each pretreatment method on the Biochemical Methane Potential was evaluated for two options, namely using the whole slurry resulting from pretreatment or the separate solid and liquid fractions obtained. In addition, the effect of each pretreatment on carbohydrate solubilization and lignocellulossic content fractionation (to cellulose, hemicellulose, lignin) was also evaluated. The experimental results showed that the methane yield was enhanced with alkaline pretreatment and, the higher the NaOH concentration (20 g/100 gTotal Solids (TS)), the higher was the methane yield observed (427.07 L CH₄/kg Volatile Solids (VS), which was almost 25.7% higher than the BMP of the untreated GL). Comparing the BMP obtained under the two options, i.e., that of the whole pretreatment slurry with the sum of the BMPs of both fractions, it was found that direct anaerobic digestion without separation of the pretreated biomass was favored, in almost all cases. A preliminary energy balance and economic assessment indicated that the process could be sustainable, leading to a positive net heat energy only when using a more concentrated pretreated slurry (i.e., 20% organic loading), or when applying NaOH pretreatment at a lower chemical loading. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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15 pages, 1626 KiB

Open AccessArticle

Biogas Production from Sunflower Head and Stalk Residues: Effect of Alkaline Pretreatment

by Marinela Zhurka, Apostolos Spyridonidis, Ioanna A. Vasiliadou and Katerina Stamatelatou

Molecules 2020, 25(1), 164; https://doi.org/10.3390/molecules25010164 - 31 Dec 2019

Cited by 28 | Viewed by 3461

Abstract

Sunflower residues are considered a prominent renewable source for biogas production during anaerobic digestion (AD). However; the recalcitrant structure of this lignocellulosic substrate requires a pretreatment step for efficient biomass transformation and increased bioenergy output. The aim of the present study was to [...] Read more.

Sunflower residues are considered a prominent renewable source for biogas production during anaerobic digestion (AD). However; the recalcitrant structure of this lignocellulosic substrate requires a pretreatment step for efficient biomass transformation and increased bioenergy output. The aim of the present study was to assess the effect of alkaline pretreatment of various parts of the sunflower residues (e.g., heads and stalks) on their methane yield. Experimental data showed that pretreatment at mild conditions (55 °C; 24 h; 4 g NaOH 100 g⁻¹ total solids) caused an increase in the biochemical methane potential (BMP) of both heads and stalks of the sunflower residues as determined in batch tests. The highest methane production (268.35 ± 0.11 mL CH₄ g⁻¹ volatile solids) was achieved from the pretreated sunflower head residues. Thereafter; the effect of alkaline pretreatment of sunflower head residues was assessed in continuous mode; using continuous stirred-tank reactors (CSTRs) under two operational phases. During the first phase; the CSTRs were fed with the liquid fraction produced from the pretreatment of sunflower heads. During the second phase; the CSTRs were fed with the whole slurry resulting from the pretreatment of sunflower heads (i.e., both liquid and solid fractions). In both operating phases; it was observed that the alkaline pretreatment of the sunflower head residues had a negligible (phase I) or even a negative effect on biogas production; which was contradictory to the results of the BMP tests. It seems that; during alkaline pretreatment; this part of the sunflower residues (heads) may release inhibitory compounds; which induce a negative effect on biogas production in the long term (e.g., during continuously run digesters such as CSTR) but not in the short-term (e.g., batch tests) where the effect of the inoculum may not permit the inhibition to be established. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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21 pages, 2612 KiB

Open AccessFeature PaperArticle

Soft Microwave Pretreatment to Extract P-Hydroxycinnamic Acids from Grass Stalks

by Aurélie Bichot, Mickaël Lerosty, Laureline Geirnaert, Valérie Méchin, Hélène Carrère, Nicolas Bernet, Jean-Philippe Delgenès and Diana García-Bernet

Molecules 2019, 24(21), 3885; https://doi.org/10.3390/molecules24213885 - 28 Oct 2019

Cited by 9 | Viewed by 2965

Abstract

The aim of this article is to provide an analysis of microwave effects on ferulic and coumaric acids (FA and CA, respectively) extraction from grass biomass (corn stalks and miscanthus). Microwave pretreatment using various solvents was first compared to conventional heating on corn [...] Read more.

The aim of this article is to provide an analysis of microwave effects on ferulic and coumaric acids (FA and CA, respectively) extraction from grass biomass (corn stalks and miscanthus). Microwave pretreatment using various solvents was first compared to conventional heating on corn stalks. Then, microwave operational conditions were extended in terms of incident power and treatment duration. Optimal conditions were chosen to increase p-hydroxycinnamic acids release. Finally, these optimal conditions determined on corn stalks were tested on miscanthus stalks to underlie the substrate incidence on p-hydroxycinnamic acids release yields. The optimal conditions—a treatment duration of 405 s under 1000 W—allowed extracting 1.38% FA and 1.97% CA in corn stalks and 0.58% FA and 3.89% CA in miscanthus stalks. The different bioaccessibility of these two molecules can explain the higher or lower yields between corn and miscanthus stalks. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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15 pages, 1349 KiB

Open AccessArticle

Matrix Discriminant Analysis Evidenced Surface-Lithium as an Important Factor to Increase the Hydrolytic Saccharification of Sugarcane Bagasse

by Ana Sílvia de Almeida Scarcella, Alexandre Favarin Somera, Christiane da Costa Carreira Nunes, Eleni Gomes, Ana Claudia Vici, Marcos Silveira Buckeridge and Maria de Lourdes Teixeira de Moraes Polizeli

Molecules 2019, 24(19), 3614; https://doi.org/10.3390/molecules24193614 - 08 Oct 2019

Cited by 1 | Viewed by 2167

Abstract

Statistical evidence pointing to the very soft change in the ionic composition on the surface of the sugar cane bagasse is crucial to improve yields of sugars by hydrolytic saccharification. Removal of Li⁺ by pretreatments exposing -OH sites was the most important [...] Read more.

Statistical evidence pointing to the very soft change in the ionic composition on the surface of the sugar cane bagasse is crucial to improve yields of sugars by hydrolytic saccharification. Removal of Li⁺ by pretreatments exposing -OH sites was the most important factor related to the increase of saccharification yields using enzyme cocktails. Steam Explosion and Microwave:H₂SO₄ pretreatments produced unrelated structural changes, but similar ionic distribution patterns. Both increased the saccharification yield 1.74-fold. NaOH produced structural changes related to Steam Explosion, but released surface-bounded Li⁺ obtaining 2.04-fold more reducing sugars than the control. In turn, the higher amounts in relative concentration and periodic structures of Li⁺ on the surface observed in the control or after the pretreatment with Ethanol:DMSO:Ammonium Oxalate, blocked -OH and O⁻ available for ionic sputtering. These changes correlated to 1.90-fold decrease in saccharification yields. Li⁺ was an activator in solution, but its presence and distribution pattern on the substrate was prejudicial to the saccharification. Apparently, it acts as a phase-dependent modulator of enzyme activity. Therefore, no correlations were found between structural changes and the efficiency of the enzymatic cocktail used. However, there were correlations between the Li⁺ distribution patterns and the enzymatic activities that should to be shown. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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14 pages, 4773 KiB

Open AccessArticle

Steam Explosion Conditions Highly Influence the Biogas Yield of Rice Straw

by David Steinbach, Dominik Wüst, Simon Zielonka, Johannes Krümpel, Simon Munder, Matthias Pagel and Andrea Kruse

Molecules 2019, 24(19), 3492; https://doi.org/10.3390/molecules24193492 - 26 Sep 2019

Cited by 26 | Viewed by 4888

Abstract

Straws are agricultural residues that can be used to produce biomethane by anaerobic digestion. The methane yield of rice straw is lower than other straws. Steam explosion was investigated as a pretreatment to increase methane production. Pretreatment conditions with varying reaction times (12–30 [...] Read more.

Straws are agricultural residues that can be used to produce biomethane by anaerobic digestion. The methane yield of rice straw is lower than other straws. Steam explosion was investigated as a pretreatment to increase methane production. Pretreatment conditions with varying reaction times (12–30 min) and maximum temperatures (162–240 °C) were applied. The pretreated material was characterized for its composition and thermal and morphological properties. When the steam explosion was performed with a moderate severity parameter of S₀ = 4.1 min, the methane yield was increased by 32% compared to untreated rice straw. This study shows that a harsher pretreatment at S₀ > 4.3 min causes a drastic reduction of methane yield because inert condensation products are formed from hemicelluloses. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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17 pages, 1679 KiB

Open AccessArticle

Enhancement of Volatile Fatty Acids Production from Food Waste by Mature Compost Addition

by Yen-Keong Cheah, Joan Dosta and Joan Mata-Álvarez

Molecules 2019, 24(16), 2986; https://doi.org/10.3390/molecules24162986 - 17 Aug 2019

Cited by 8 | Viewed by 3824

Abstract

Food waste (FW) collected from a university canteen was treated in acidogenic fermenters to produce volatile fatty acids (VFA) under biological pretreatment with mature compost. Batch assays working at pH 6 revealed an increment of 9.0%, 7.9%, and 4.1% (on COD basis) of [...] Read more.

Food waste (FW) collected from a university canteen was treated in acidogenic fermenters to produce volatile fatty acids (VFA) under biological pretreatment with mature compost. Batch assays working at pH 6 revealed an increment of 9.0%, 7.9%, and 4.1% (on COD basis) of VFA concentration when adding 2.5%, 3.5%, and 4.5% w/w of mature compost, respectively, even though the volatile solids (VS) concentration of food waste was lower in the tests with increasing doses of mature compost. For batch tests at pH 7, this VFA generation improvement was lower, even though enhanced COD solubilization was recorded. Operating in semi-continuous conditions at 35 °C, pH of 6, and hydraulic retention time (HRT) of 3.5 days, the addition of 2.5% w/w of mature compost led to a VFA concentration up to 51.2 ± 12.3% more (on VS basis) when compared to a reference reactor without compost addition. Moreover, the percentage of butyric acid on VS basis in the fermentation broth working at a pH of 6 increased from up to 12.2 ± 1.9% (0% compost addition) to up to 23.5 ± 2.7% (2.5% compost addition). The VFA production was not improved when a higher percentage of mature compost was used (3.5% instead of 2.5% w/w), and it slightly decreased when mature compost addition was lowered to 1.5% w/w. When working at a pH of 7 in the semi-continuous fermenters with the addition of 2.5% w/w mature compost at an HRT of 3.5 days, an improvement of 79% and 104% of the VFA concentration (on VS basis) were recorded as compared to fermenters working at a pH of 6 with 2.5% and 0% w/w of mature compost addition, respectively. At a pH of 7, higher production of propionic and valeric acids was found with respect to the reactor working at a pH of 6. The effect of pH on VFA generation was estimated to have greater contribution than that of only biological pretreatment using mature compost. At a pH of 7, the VFA yield was higher for the fermenter working with 2.5% w/w mature compost but at a pH of 7 and HRT of 5 days, the effect of mature compost on VFA production improvement was lower than that obtained at a pH of 6. Moreover, higher solubilization in terms of soluble chemical oxygen demand and total ammonium was detected when biological pretreatment using mature compost was applied at both a pH of 6 and a pH of 7, which indicates enhanced hydrolysis in both conditions. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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11 pages, 1763 KiB

Open AccessArticle

On the Effect of Aqueous Ammonia Soaking Pre-Treatment on Continuous Anaerobic Digestion of Digested Swine Manure Fibers

by Chrysoula Mirtsou-Xanthopoulou, Ioannis V. Skiadas and Hariklia N. Gavala

Molecules 2019, 24(13), 2469; https://doi.org/10.3390/molecules24132469 - 05 Jul 2019

Cited by 8 | Viewed by 2262

Abstract

(1) Background: The continuously increasing demand for renewable energy sources renders anaerobic digestion as one of the most promising technologies for renewable energy production. Due to the animal production intensification, manure is being used as the primary feedstock for most biogas plants. Their [...] Read more.

(1) Background: The continuously increasing demand for renewable energy sources renders anaerobic digestion as one of the most promising technologies for renewable energy production. Due to the animal production intensification, manure is being used as the primary feedstock for most biogas plants. Their economical profitable operation, however, relies on increasing the methane yield from the solid fraction of manure, which is not so easily degradable. The solid fraction after anaerobic digestion, the so-called digested fibers, consists mainly of hardly biodegradable material and comes at a lower mass per unit volume of manure compared to the solid fraction before anaerobic digestion. Therefore, investigation on how to increase the biodegradability of digested fibers is very relevant. So far, Aqueous Ammonia Soaking (AAS), has been successfully applied on digested fibers separated from the effluent of a manure-fed, full-scale anaerobic digester to enhance their methane productivity in batch experiments. (2) Methods: In the present study, continuous experiments at a mesophilic (38 °C) CSTR-type anaerobic digester fed with swine manure first and a mixture of manure with AAS-treated digested fibers in the sequel, were performed. Anaerobic Digestion Model 1 (ADM1) previously fitted on manure fed digester was used in order to assess the effect of the addition of AAS-pre-treated digested manure fibers on the kinetics of anaerobic digestion process. (3) Results and Conclusions: The methane yield of AAS-treated digested fibers under continuous operation was 49–68% higher than that calculated in batch experiments in the past. It was found that AAS treatment had a profound effect mainly on the disintegration/hydrolysis rate of particulate carbohydrates. Comparison of the data obtained in the present study with the data obtained with AAS-pre-treated raw manure fibers in the past revealed that hydrolysis kinetics after AAS pre-treatment were similar for both types of biomasses. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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15 pages, 4019 KiB

Open AccessArticle

A Citrus Peel Waste Biorefinery for Ethanol and Methane Production

by Maria Patsalou, Charis G. Samanides, Eleni Protopapa, Stella Stavrinou, Ioannis Vyrides and Michalis Koutinas

Molecules 2019, 24(13), 2451; https://doi.org/10.3390/molecules24132451 - 04 Jul 2019

Cited by 54 | Viewed by 6337

Abstract

This paper deals with the development of a citrus peel waste (CPW) biorefinery that employs low environmental impact technologies for production of ethanol and methane. Three major yeasts were compared for ethanol production in batch fermentations using CPW pretreated through acid hydrolysis and [...] Read more.

This paper deals with the development of a citrus peel waste (CPW) biorefinery that employs low environmental impact technologies for production of ethanol and methane. Three major yeasts were compared for ethanol production in batch fermentations using CPW pretreated through acid hydrolysis and a combination of acid and enzyme hydrolysis. The most efficient conditions for production of CPW-based hydrolyzates included processing at 116 °C for 10 min. Pichia kudriavzevii KVMP10 achieved the highest ethanol production that reached 30.7 g L⁻¹ in fermentations conducted at elevated temperatures (42 °C). A zero-waste biorefinery was introduced by using solid biorefinery residues in repeated batch anaerobic digestion fermentations achieving methane formation of 342 mL g_VS⁻¹ (volatile solids). Methane production applying untreated and dried CPW reached a similar level (339–356 mL g_VS⁻¹) to the use of the side stream, demonstrating that the developed bioprocess constitutes an advanced alternative to energy intensive methods for biofuel production. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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14 pages, 3293 KiB

Open AccessArticle

Enhanced Enzymatic Hydrolysis of Pennisetum alopecuroides by Dilute Acid, Alkaline and Ferric Chloride Pretreatments

by Shangyuan Tang, Chunming Xu, Linh Tran Khanh Vu, Sicheng Liu, Peng Ye, Lingci Li, Yuxuan Wu, Mengyu Chen, Yao Xiao, Yue Wu, Yining Wang, Qiong Yan and Xiyu Cheng

Molecules 2019, 24(9), 1715; https://doi.org/10.3390/molecules24091715 - 02 May 2019

Cited by 13 | Viewed by 3120

Abstract

In this study, effects of different pretreatment methods on the enzymatic digestibility of Pennisetum alopecuroides, a ubiquitous wild grass in China, were investigated to evaluate its potential as a feedstock for biofuel production. The stalk samples were separately pretreated with H₂ [...] Read more.

In this study, effects of different pretreatment methods on the enzymatic digestibility of Pennisetum alopecuroides, a ubiquitous wild grass in China, were investigated to evaluate its potential as a feedstock for biofuel production. The stalk samples were separately pretreated with H₂SO₄, NaOH and FeCl₃ solutions of different concentrations at 120 °C for 30 min, after which enzymatic hydrolysis was conducted to measure the digestibility of pretreated samples. Results demonstrated that different pretreatments were effective at removing hemicellulose, among which ferric chloride pretreatment (FCP) gave the highest soluble sugar recovery (200.2 mg/g raw stalk) from the pretreatment stage. In comparison with FCP and dilute acid pretreatment (DAP), dilute alkaline pretreatment (DALP) induced much higher delignification and stronger morphological changes of the biomass, making it more accessible to hydrolysis enzymes. As a result, DALP using 1.2% NaOH showed the highest total soluble sugar yield through the whole process from pretreatment to enzymatic hydrolysis (508.5 mg/g raw stalk). The present work indicates that DALP and FCP have the potential to enhance the effective bioconversion of lignocellulosic biomass like P. alopecuroides, hence making this material a valuable and promising energy plant. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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14 pages, 1563 KiB

Open AccessArticle

Comparison of Two Process Schemes Combining Hydrothermal Treatment and Acidogenic Fermentation of Source-Separated Organics

by Long Lin, Ehssan Hosseini Koupaie, Armineh Azizi, Amir Abbas Bazyar Lakeh, Bipro R. Dhar, Hisham Hafez and Elsayed Elbeshbishy

Molecules 2019, 24(8), 1466; https://doi.org/10.3390/molecules24081466 - 13 Apr 2019

Cited by 8 | Viewed by 2952

Abstract

This study compares the effects of pre- and post-hydrothermal treatment of source- separated organics (SSO) on solubilization of particulate organics and acidogenic fermentation for volatile fatty acids (VFAs) production. The overall COD solubilization and solids removal efficiencies from both schemes were comparable. However, [...] Read more.

This study compares the effects of pre- and post-hydrothermal treatment of source- separated organics (SSO) on solubilization of particulate organics and acidogenic fermentation for volatile fatty acids (VFAs) production. The overall COD solubilization and solids removal efficiencies from both schemes were comparable. However, the pre-hydrolysis of SSO followed by acidogenic fermentation resulted in a relatively higher VFA yield of 433 mg/g VSS, which was 18% higher than that of a process scheme with a post-hydrolysis of dewatered solids from the fermentation process. Regarding the composition of VFA, the dominance of acetate and butyrate was comparable in both process schemes, while propionate concentration considerably increased in the process with pre-hydrolysis of SSO. The microbial community results showed that the relative abundance of Firmicutes increased substantially in the fermentation of pretreated SSO, indicating that there might be different metabolic pathways for production of VFAs in fermentation process operated with pre-treated SSO. The possible reason might be that the abundance of soluble organic matters due to pre-hydrolysis might stimulate the growth of more kinetically efficient fermentative bacteria as indicated by the increase in Firmicutes percentage. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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17 pages, 2556 KiB

Open AccessArticle

The Effect of the Chemical Character of Ionic Liquids on Biomass Pre-Treatment and Posterior Enzymatic Hydrolysis

by Joana R. Bernardo, Francisco M. Gírio and Rafał M. Łukasik

Molecules 2019, 24(4), 808; https://doi.org/10.3390/molecules24040808 - 23 Feb 2019

Cited by 44 | Viewed by 3911

Abstract

Ionic liquids have been recognised as interesting solvents applicable in efficient lignocellulosic biomass valorisation, especially in biomass fractionation into individual polymeric components or direct hydrolysis of some biomass fractions. Considering the chemical character of ionic liquids, two different approaches paved the way for [...] Read more.

Ionic liquids have been recognised as interesting solvents applicable in efficient lignocellulosic biomass valorisation, especially in biomass fractionation into individual polymeric components or direct hydrolysis of some biomass fractions. Considering the chemical character of ionic liquids, two different approaches paved the way for the fractionation of biomass. The first strategy integrated a pre-treatment, hydrolysis and conversion of biomass through the employment of hydrogen-bond acidic 1-ethyl-3-methyimidazolim hydrogen sulphate ionic liquid. The second strategy relied on the use of a three-step fractionation process with hydrogen-bond basic 1-ethyl-3-methylimidazolium acetate to produce high purity cellulose, hemicellulose and lignin fractions. The proposed approaches were scrutinised for wheat straw and eucalyptus residues. These different biomasses enabled an understanding that enzymatic hydrolysis yields are dependent on the crystallinity of the pre-treated biomass. The use of acetate based ionic liquid allowed crystalline cellulose I to change to cellulose II and consequently enhanced the glucan to glucose yield to 93.1 ± 4.1 mol% and 82.9 ± 1.2 mol% for wheat straw and eucalyptus, respectively. However, for hydrogen sulphate ionic liquid, the same enzymatic hydrolysis yields were 61.6 ± 0.2 mol% for wheat straw and only 7.9 ± 0.3 mol% for eucalyptus residues. These results demonstrate the importance of both ionic liquid character and biomass type for efficient biomass processing. Full article

(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass II)

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