Thermo-alkaline Pretreatment Research Articles

Optimization of thermo-alkaline pretreatment on municipal sludge and enhanced subsequent anaerobic digestion

Optimization of thermo-alkaline pretreatment on municipal sludge and enhanced subsequent anaerobic digestion

Anaerobic conversion of Chromolaena odorata (Siam weed) to biogas

This study evaluated the anaerobic mono-digestion of two different samples of Chromolaena odorata. Combinations of mechanical and thermo-alkaline pretreatments were applied to one of the two samples and labeled as “X” while the second had no thermo-alkaline treatment and was labeled as “Y”. The Central Composite Design was used to design the pretreatments. The physicochemical characteristics of the substrates were carried out using standard methods after appropriate pretreatments. From the experimental set-ups, the most probable actual biogas yields in experiments “X” and ”Y” were 0.3554 m3/kg Total Solid (TS)fed and 0.1803 m3/kg TSfed with the desirability of 99 and 100%, respectively. Further shown in the result is a 49.2% higher experimental (actual) biogas yield in experiment “X” over “Y”. Gas chromatographic analysis revealed the CH4 and CO2 content of both experiments to be 65 ± 1.5%; 21 ± 3% and 53.5 ± 2.5%; 26 ± 3%, respectively. Combination of different pretreatment methods enhanced enormous biogas yield from the digested substrates. Optimization of the generated biogas data was carried out using the Response Surface Methodology (RSM) and the Artificial Neural Networks (ANNs). The coefficient of determination (R2) for RSM was lower compared to that of ANN. This shows that ANNs model gives higher accuracy than RSM model. Further utilization of this weed for biogas production is encouraged by the results from this study.

Biochemical conversion of fruit rind of Telfairia occidentalis (fluted pumpkin) and poultry manure

ABSTRACTEnvironmental pollution by solid wastes and inadequate energy supply are some of the major challenges facing the developing world. This study evaluated the potentials of Fluted pumpkin fruit rind and poultry manure for biogas generation. Mechanical and thermo-alkaline pre-treatments were applied to two samples labeled ‘O’ and ‘P’ while the third sample (Q) had no thermo-alkaline treatment. The physicochemical characteristics of the substrates revealed richness in nutrients and mineral elements. The results showed that use of a combination of pre-treatment methods enhanced the biogas yield in the pre-treated substrates. Analysis of the gas composition showed 66.5 ± 2.5% Methane, 25 ± 1% Carbon dioxide; 58.5 ± 2.5% Methane, 26 ± 1% Carbon dioxide; 54.5 ± 1.5% Methane, 28 ± 2% Carbon dioxide for the three experiments, respectively. All the obtained values show the models had a high predictive ability. The substrates should be further used for energy generation.

Effect of Mild-Temperature Thermo-Alkaline Pretreatment on the Solubilization and Anaerobic Digestion of Spent Coffee Grounds

Mild-temperature thermo-alkaline pretreatment of spent coffee grounds (SCG) was studied to improve its solubilization and methanation. The simultaneous effects of NaOH concentration (0–0.2 M) and temperature (60–90 °C) were investigated. Significant solubilization of SCG was achieved by the pretreatment, particularly under high-NaOH-concentration and high-temperature conditions. However, adding NaOH above a certain concentration adversely affected the methane production. Therefore, the degree of solubilization (SD) correlated poorly with methane yield (Ym). Response surface models of SD and Ym were successfully generated. The maximum response of SD (36.4%) was obtained at 0.18 M NaOH and 90.0 °C, while that of Ym (263.31 mL CH4/g COD added) was obtained at 0.13 M NaOH and 70.5 °C. Hydrogenotrophic Methanospirillum species were the dominant methanogens in all the SCG digestion tests. It is likely that NaOH concentration had a more significant influence on the development of microbial community structure, particularly of methanogens than temperature.

Thermo-carbide slag pretreatment of turfgrass pruning: Physical-chemical structure changes, reducing sugar production, and enzymatic hydrolysis kinetics

Alkaline pretreatment shows a good effect on delignification of lignocellulosic biomass, and carbide slag, an alkaline industrial waste, was first applied to pretreat turfgrass pruning. Three thermo-alkaline pretreatment methods were compared to evaluate their ability to destroy the biomass structure and to enhance the enzymatic hydrolysis efficiency of turfgrass pruning, namely thermo-NaOH pretreatment, thermo-lime pretreatment, and thermo-carbide slag pretreatment. Results showed that the maximum net reducing sugar yield of 269.55 mg/g raw biomass was achieved by thermo-carbide slag pretreatment. Compared with raw biomass, the lignin and hemicellulose content of turfgrass pruning after thermo-carbide slag pretreatment reduced by 35.57% and 62.40%, respectively. SEM and FTIR analyses showed that the surface structure and chemical groups of turfgrass pruning were obviously destroyed by thermo-carbide slag pretreatment. There was a high positive correlation between the enzymatic hydrolysis efficiency and cellulose content of substrate. However, a high negative correlation was observed between the enzymatic hydrolysis efficiency and lignin content of substrate. The enzymatic hydrolysis kinetics with different pretreatments were well described by the fractal-like kinetics model, and the rate constant of enzymatic hydrolysis of thermo-alkali pretreated turfgrass pruning was about three times of that of the unpretreated turfgrass pruning. Overall, carbide slag is an ideal pretreatment material for enzymatic hydrolysis of turfgrass pruning in terms of hydrolysis efficiency and waste reuse.

Anaerobic mono-digestion of Tithonia diversifolia (Wild Mexican sunflower)

Anaerobic digestion was carried out in this study using the shoot of Tithonia diversifolia using a consortium of microorganisms. Combinations of mechanical and thermo-alkaline (Sodium hydroxide and Potassium hydroxide) pretreatments were applied to two samples (X and Y) of the mixture while the third sample (Z) had no thermo-alkaline treatment. Prior to pretreatment, the Central Composite Design was used for optimizing the pretreatment temperature and time. The physicochemical characteristics of T. diversifolia shoot were carried out using standard methods. Modeling of the generated biogas data was done using the Response Surface Methodology. The optimal conditions for this process were statistically predicted as Temperature (S1) of 30.00°C, pH (S2) of 7.5, Retention time (S3) of 30day, Total solids (S4) of 12.00g/kg and Volatile solids (S5) of 4.00g/kg. The most desired predicted biogas yields under these conditions were 2249.24, 1519.15 and 1043.50·10−3m3/kg TSfed with the desirability values of 1.000 (100%) in all cases. Analyses revealed the average gas composition to be within the range of 65±1% methane and 26±2% carbon dioxide for digestion ‘X’; 59±1.5% Methane and 22.5±2%% Carbon dioxide for digestion ‘Y’ while it was 53±2% Methane and 20.5±2% Carbon dioxide for digestions ‘Z’. The roots mean squared error, coefficient of determination, and the predicted value were used to determine the fitness of the model. All the obtained values show that the model had a high predictive ability for the study. The energy assessment showed positive energy balances from the thermo-alkaline pretreated experiment and this can be increased via the use of higher substrate loading in order to increase the economic feasibility of the applied pretreatment. In locations where T. diversifolia is abundant, its usage for biofuel could be a lead to solving the prevailing energy crisis.

Simultaneous production of hydrogen and volatile fatty acids from anaerobic digestion of Macrocystis pyrifera biomass residues

The Macrocystis pyrifera biomass residues (MPBRs) after extraction of algin could be applied in anaerobic fermentation. The effects of different pretreatment conditions, substrate concentrations and initial pH values on hydrogen and volatile fatty acid (VFA) production during the anaerobic fermentation of MPBRs were evaluated. The optimal pretreatment conditions, substrate concentration, initial pH values were determined as thermo-alkaline pretreatment at 100 °C with 0.1 mol/L NaOH, 40 g/L and 7.0, respectively. Under these conditions, the maximum hydrogen production was 11.38 mL/g (volatile solids, VS), which was approximately 23 times higher than that of untreated MPBRs. Furthermore, the maximum total volatile fatty acid (TVFA) yield was found to be 0.055 g/g (VS) and the VFA mainly consisted of acetic and butyric acids. The results indicate that the yield of TVFA is positively correlated with hydrogen production, and the MPBRs could produce hydrogen and TVFA simultaneously. In addition, thermo-alkaline pretreatment is proven to be the best method for hydrogen and VFA production.

Pretreatment optimization, process control, mass and energy balances and economics of anaerobic co-digestion of Arachis hypogaea (Peanut) hull and poultry manure

The study explored biogas production from the co-digestion of Arachis hypogaea hull and poultry droppings. Mechanical and thermo-alkaline pretreatments were applied to a sample of the mixture. Another sample was treated mechanically but without thermo-alkaline methods. Optimization was done using the Response Surface Methodology (RSM) and the Artificial Neural Networks (ANNs). The optimal values for each of the five major parameters optimized are Temperature of 32.00°C, pH of 7.62, Retention time of 30.00 day, Total solids of 12.00g/kg and Volatile solids of 10.00g/kg and the predicted biogas yield for RSM was 3903.1510−3m3/kg TSfed and 3338.310−3m3/kg TSfed for ANNs in the thermo-alkaline pretreated experiment. Gas chromatography show the CH4 and CO2 content of biogas generated to be 65.5±1.5%; 26±1% and 53±1%; 26±2% respectively. The co-digestion of peanut hull with poultry droppings and other energy-yielding substrates is further encouraged.

Cleaner energy for cleaner production: Modeling and optimization of biogas generation from Carica papayas (Pawpaw) fruit peels

In this study, the potentials of pretreated and untreated Carica papayas fruit peels for biogas generation was evaluated alongside its process optimization after employing the combination of mechanical and thermo-alkaline pretreatment methods. The peel was anaerobically digested using a consortium of microorganisms from cattle rumen content as inoculum. A batch system designed by the Central Composite Design (CCD) was employed. The physicochemical and microbial characteristics of the substrates and inoculum as well as the constituent of the generated biogas were evaluated using standard methods and results showed elevated levels of most elements after anaerobic digestion. The most feasible experimental biogas yields were 0.1839 m3/kg VS and 0.1361 m3/kg VS for the pretreated and untreated experiments respectively. Microbiologically, members of the genus Clostridium dominated the microbial flora and their succession patterns were affected by temperature and pH. The methane and carbon dioxide content of biogas from both experiments were 61.5± 2.5%; 24± 1% and 52 ± 2%; 25± 1.5% respectively. The Response Surface Methodology (RSM) and the Artificial Neural Networks (ANNs) were employed in data optimization. Based on the optimized values, the predicted biogas yield for RSM was 0.1895 m3/kg VS and 0.1839 m3/kg VS for ANNs in the pretreated experiment. For the experiment without pretreatment, the RSM predicted yield was 0.1361 m3/kg VS while that of ANNs was 0.1392 m3/kg VS. In all, there was a 26.5% increase in predicted biogas yield in the pretreated experiment over the untreated. Further usage of pawpaw peels for biofuels generation is advocated.

Enhancement of microalgae anaerobic digestion by thermo-alkaline pretreatment with lime (CaO)

The aim of this study was to evaluate for the first time the effect of a thermo-alkaline pretreatment with lime (CaO) on microalgae anaerobic digestion. The pretreatment was carried out by adding different CaO doses (4 and 10%) at different temperatures (room temperature (25°C), 55 and 72°C). The exposure time was 4days for pretreatments at 25°C, and 24h for pretreatments at 55 and 72°C. Following, a biochemical methane potential test was conducted with pretreated and untreated microalgae. According to the results, the pretreatment enhanced proteins solubilisation by 32.4% and carbohydrates solubilisation by 31.4% with the highest lime dose and temperature (10% CaO and 72°C). Furthermore, anaerobic digestion kinetics were improved in all cases (from 0.08 to 0.14day−1 for untreated and pretreated microalgae, respectively). The maximum biochemical methane potential increase (25%) was achieved with 10% CaO at 72°C, in accordance with the highest biomass solubilisation. Thus, lime pretreatment appears as a potential strategy to improve microalgae anaerobic digestion.

Anaerobic co-digestion of microalgal biomass and wheat straw with and without thermo-alkaline pretreatment

This study aimed at analyzing the anaerobic co-digestion of microalgal biomass grown in wastewater and wheat straw. To this end, Biochemical Methane Potential (BMP) tests were carried out testing different substrate proportions (20–80, 50–50 and 80–20%, on a volatile solid basis). In order to improve their biodegradability, the co-digestion of both substrates was also evaluated after applying a thermo-alkaline pretreatment (10% CaO at 75°C for 24h). The highest synergies in degradation rates were observed by adding at least 50% of wheat straw. Therefore, the co-digestion of 50% microalgae – 50% wheat straw was investigated in mesophilic lab-scale reactors. The results showed that the methane yield was increased by 77% with the co-digestion as compared to microalgae mono-digestion, while the pretreatment only increased the methane yield by 15% compared to the untreated mixture. Thus, the anaerobic co-digestion of microalgae and wheat straw was successful even without applying a thermo-alkaline pretreatment.

Impact of Thermo-alkaline Pretreatment on the Thermophilic Anaerobic Digestion of Wheat Plant Residues

Background: Wheat plant (WP) residues could be efficiently used as substrate for biogas production via anaerobic digestion (AD). It is a mixture of starchy and lignocellulosic materials. The hydrolysis of wheat plant is the ratelimiting step of its AD. An efficient pretreatment can facilitate the wheat plant hydrolysis and accordingly enhance the AD’s efficiency. The aim of this study was to investigate the effects of thermo-alkaline pretreatment on the WP structure as well as the yield of thermophilic anaerobic digestion of WP. Methods: Anaerobic sludge was used as inoculum. Wheat plant (WP) including its straw and grains was used as substrate. The impact of sodium hydroxide pretreatment (8% w/w) on the thermophilic anaerobic digestion (55 °C) of wheat plant using anaerobic sludge in batch reactors was investigated. Pretreatments were performed at different temperatures of 0, 25, 50, 75, and 100 °C for 60 min. Results: The methane and biogas yields of the untreated WP were 182.1 and 287.3 mL/g VS, respectively. The pretreatments at 50 °C and 75 °C led to the highest methane yields of 232.9 and 358.6 mL/g VS, respectively, while the other pretreatments had no positive effects on the methane yield. The results of scanning electron microscopy showed that the surface of the WP was effectively destructed after pretreatment at 75 °C when compared with the untreated WP. Conclusion: Thermo-alkaline pretreatment (specially at 75 °C for 60 min) could efficiently enhance the yield of anaerobic digestion of wheat plant. Keywords: Anaerobic digestion, biomethane, NaOH, thermo-alkaline pretreatment, wheat plant.

Thermo-chemical pretreatment and enzymatic hydrolysis for enhancing saccharification of catalpa sawdust

To improve the reducing sugar production from catalpa sawdust, thermo-chemical pretreatments were examined and the chemicals used including NaOH, Ca(OH)2, H2SO4, and HCl. The hemicellulose solubilization and cellulose crystallinity index (CrI) were significantly increased after thermo-alkaline pretreatments, and the thermo-Ca(OH)2 pretreatment showed the best improvement for reducing sugar production comparing to other three pretreatments. The conditions of thermo-Ca(OH)2 pretreatment and enzymatic hydrolysis were systematically optimized. Under the optimal conditions, the reducing sugar yield increased by 1185.7% comparing to the control. This study indicates that the thermo-Ca(OH)2 pretreatment is ideal for the saccharification of catalpa sawdust and that catalpa sawdust is a promising raw material for biofuel.

Improvement of anaerobic digestion of waste-activated sludge by using H₂O₂ oxidation, electrolysis, electro-oxidation and thermo-alkaline pretreatments.

Disintegration of municipal waste-activated sludge (WAS) is regarded as a prerequisite of the anaerobic digestion process to reduce sludge volume and improve biogas yield. Pretreatment of WAS using thermo-alkaline (TA), H2O2 oxidation, electrolysis and electro-oxidation (EO) processes were investigated and compared in term of COD solubilization and biogas production. For each pretreatment, the influences of different operational variables were studied in detail. At optimum conditions, EO gave the maximum COD solubilization (28 %). The effects of pretreatments under the optimum conditions on anaerobic digestion were experienced with biochemical methane potential assay. Significant increases in biogas yield up to 78 and 40 % were observed respectively in the EO and TA pretreated samples compared to raw sludge. Results clearly revealed that the application of EO is a significant alternative method for the improvement of WAS anaerobic digestion.

Autohydrolysis and alkaline pretreatment effect on Chlorella vulgaris and Scenedesmus sp. methane production

Among biofuel production processes using microalgae biomass, biogas generation seems to be the least complex. Nevertheless, its efficiency is hampered due to the hard cell wall. In order to enhance its anaerobic biodegradability, the present investigation evaluated the effect of two pretreatments (low temperature autohydrolysis at 50 °C for 24 and 48 h incubation and alkaline (0.5, 2 and 5% w/w NaOH dosages)) on Chlorella vulgaris and Scenedesmus sp. The autohydrolysis resulted in 16 and 6% chemical oxygen demand (COD) solubilisation for Chlorella and Scenedesmus, respectively. During thermoalkaline pretreatment, COD in soluble phase (CODsol) was increased up to 19% for Chlorella and 17% for Scenedesmus sp. The highest carbohydrates solubilisation corresponded to 2 and 5% w/w NaOH dosage for 48 h at 50 °C for Chlorella (20%) and Scenedesmus (40–43%). When compared to Chlorella, Scenedesmus biomass exhibited higher carbohydrates solubilisation, although methane yield enhancement was low for both substrates. Best case scenario for Scenedesmus sp. (20% increase) was attained with 5% NaOH at 50 °C for 24 h. Despite the lower carbohydrates solubilisation observed for Chlorella, similar methane yields were similar to Scenedesmus sp. The low methane production enhancement was ascribed to the fact that the organic matter solubilised were exopolymers released during pretreatments rather than intracellular material.

Two-Stage Alkaline–Enzymatic Pretreatments To Enhance Biohydrogen Production from Sunflower Stalks

Because of their rich composition in carbohydrates, lignocellulosic residues represent an interesting source of biomass to produce biohydrogen by dark fermentation. Nevertheless, pretreatments should be applied to enhance the solubilization of holocelluloses and increase their further conversion into biohydrogen. The aim of this study was to investigate the effect of thermo-alkaline pretreatment alone and combined with enzymatic hydrolysis to enhance biohydrogen production from sunflower stalks. A low increase of hydrogen potentials from 2.3 ± 0.9 to 4.4 ± 2.6 and 20.6 ± 5.6 mL of H2 g(-1) of volatile solids (VS) was observed with raw sunflower stalks and after thermo-alkaline pretreatment at 55 °C, 24 h, and 4% NaOH and 170 °C, 1 h, and 4% NaOH, respectively. Enzymatic pretreatment alone showed an enhancement of the biohydrogen yields to 30.4 mL of H2 g(-1) of initial VS, whereas it led to 49 and 59.5 mL of H2 g(-1) of initial VS when combined with alkaline pretreatment at 55 and 170 °C, respectively. Interestingly, a diauxic effect was observed with sequential consumption of sugars by the mixed cultures during dark fermentation. Glucose was first consumed, and once glucose was completely exhausted, xylose was used by the microorganisms, mainly related to Clostridium species.

Thermo-alkaline pretreatment of waste activated sludge at low-temperatures: Effects on sludge disintegration, methane production, and methanogen community structure

Low-temperature thermo-alkaline pretreatment of waste activated sludge (WAS) was studied, within the region of 0-0.2 M NaOH and 60-90°C, for the effects of NaOH concentration and temperature on sludge degradability in anaerobic digestion (AD). Significant disintegration of sludge solids (up to 75.6%) and an increase in methane production (up to 70.6%) were observed in the pretreatment trials. Two quadratic models were successfully generated by response surface analysis (R(2)>0.9, p<0.05) to approximate how the degree of sludge disintegration (SD) and methane production (MP) respond to changes in the pretreatment conditions. The maximum responses of SD (77.8%) and MP (73.9% increase over the control) were shown at [0.16 M NaOH, 90°C] and [0.10 M NaOH, 73.7°C], respectively. NaOH addition showed a significant influence on the evolution of methanogen community structure during AD, whereas temperature did not. Aceticlastic Methanosaeta and Methanosarcina speceies were likely the major methanogens.

Thermo-chemical pre-treatment to solubilize and improve anaerobic biodegradability of press mud

Different pre-treatment severities by thermo-alkaline conditions (100°C, Ca(OH)2) on press mud were evaluated for different pre-treatment time and lime loading. COD solubilization and the methane yield enhancement were assessed. The biochemical methane potential was determined in batch assays under mesophilic conditions (37±1°C). The best pre-treatment resulted in a surplus of 72% of methane yield, adding 10g Ca(OH)2 100g−1TS−1 for 1h. Pre-treatment also increased the COD solubilization, but the optimal severity for COD solubilization as determined by response surface methodology did not ensure the highest methane production. Inhibitory effects on anaerobic digestion were noticed when the severity was increased. These results demonstrate the relevance of thermo-alkaline pre-treatment severity in terms of both lime loading and pre-treatment time to obtain optimal anaerobic biodegradability of lignocellulosic biomass from press mud.

A comparison of different pre-treatments to increase methane production from two agricultural substrates

To enhance the methane production from ensiled sorghum forage and wheat straw, thermal, alkaline and thermo-alkaline pre-treatments were performed in batch mode. Alkaline pretreatment was conducted at 40°C for 24h with the addition of 1% and 10% gNaOH/gTS; thermal and thermo-alkaline pre-treatments at 100°C, and 160°C for 30min, with and without the addition of NaOH solutions at the above dosages. All the pre-treatments tested led to a solubilization of the organic matter, with a maximum concentration (around 30–40% for both substrates) obtained at 40 and 100°C with 10% NaOH. Furthermore, a reduction in the fibrous fractions was observed for both substrates. The highest lignin reduction, compared to untreated samples, was found at 100°C with 10% NaOH dosage (53% and 72% for wheat straw and sorghum, respectively). Under this pre-treatment condition a high hemicelluloses reduction yield was also found (63% for both substrates). The highest increase in methane yield (up to 32%), compared to the untreated substrate was observed at 40°C with 10% NaOH for sorghum. As for wheat straw, significant increases in methane yield were observed at 40°C with 10% NaOH (43%) and at 100°C with 1–10% NaOH (48% and 67%, respectively). According to the results of the preliminary economic analysis, the pre-treatments seemed to be sustainable for both substrates, especially for wheat straw, due to a higher methane yield increase than that of sorghum.

Improving methane production during the codigestion of waste-activated sludge and fatty wastewater: Impact of thermo-alkaline pretreatment on batch and semi-continuous processes

With the objective of maximising methane production from waste-activated sludge (WAS), codigestion with fatty wastewater (FW) collected from restaurants was studied and the application of both a 170°C thermal pretreatment and thermo-alkaline/saponification to mixed WAS/FW waste was evaluated. Batch anaerobic digestion tests showed that recalcitrant compounds were formed during the 170°C pretreatment of fatty wastewater and thermo-alkaline pretreatments (80°C or 120°C, pH 8, 9 or 10) led to an increased initial methane production rate and to a very slight impact on the methane potential of the mixed waste (+4–7%). Semi-continuous anaerobic digesters were fed over 4months with WAS, two mixed substrates WAS/FW 90/10 and WAS/FW 60/40, and with WAS/FW 90/10 pretreated at softer conditions (80°C and pH=8, 0.14gKOHgVS-1). This pretreatment led to a significant increase in the methane production of semi-continuous reactors (+58%). Finally, this study showed the feasibility of the codigestion of waste activated sludge with highly concentrated fatty wastewater (40% in volume, 49% in VS and 73% in COD, equivalent to 7gL−1 of lipids). It resulted in specific methane production of 362mLCH4g−1 VS whereas WAS alone produced only 116mLCH4g−1 VS.