Lime Loading Research Articles

Carbide lime as substrates to boost energy recuperation and dyestuff removal in constructed wetland-microbial fuel cell integrated with copper oxide/carbon cloth cathode.

Methylene blue (MB) was regarded as a highly toxic and hazardous substance owing to its irreparable hazard and deplorable damage on the ecosystem and the human body. The treatment of this colorant wastewater appeared to be one of the towering challenges in wastewater treatment. In this study, a microbial fuel cell coupled with constructed wetland (CW-MFC) with effective MB elimination and its energy recuperation concurrently based on the incorporation of carbide lime as a substrate in a new copper oxide-loaded on carbon cloth (CuO/CC) cathode system was studied. The crucial influencing parameters were also delved, and the MB degradation and chemical oxygen demand (COD) removal efficiencies were correspondingly incremented by 97.3% and 89.1% with maximum power output up to 74.1 mW m-2 at optimal conditions (0.2 g L-1 carbide lime loading and 500 Ω external resistance). The carbide lime with high calcium ion content was greatly conducive for the enrichment of critical microorganism and metabolic activities. The relative abundances of functional bacteria including Proteobacteria and Actinobacteriota were vividly increased. Moreover, the impressive results obtained in printed ink wastewater treatment with a COD removal efficiency of 81.3% and a maximum power density of 58.2 mW m-2, which showcased the potential application of CW-MFC.

Increase in Fermentable Sugars of Olive Tree Pruning Biomass for Bioethanol Production: Application of an Experimental Design for Optimization of Alkaline Pretreatment

Olive Tree Pruning (OTP) biomass can be considered a suitable source of fermentable sugars for the production of second-generation bioethanol. The present study proposes a remarkable alternative for the valorization of olive tree pruning residues. OTP biomass was processed using a sequential calcium hydroxide pretreatment/enzymatic hydrolysis. A 24–1 half fractional factorial design was adopted for the screening of process variables and a central composite design was used for the optimization stage. Temperature and lime loading resulted statistically significant. The following optimal conditions were obtained: 0.01 g of Ca(OH)2/g of dry material, 20 g of H2O/g of dry material at 160 °C for 2 h. The mathematical model that governs this alkaline pretreatment was obtained with a 76% adjusted determination coefficient, which means that it is a good representation of the process. Under optimal operating conditions, 13% of the cellulose and 88% of the hemicellulose was solubilized. Moreover, the fermentable sugar content increased 1800% compared with the initial conditions, obtaining 240 g of glucose per kg of OTP residue. The fermentable sugars obtained after the calcium hydroxide pretreatment and enzymatic hydrolysis of OTP biomass yielded 2.8 g of ethanol/100 g of raw material.

Conditions for efficient alkaline storage of cover crops for biomethane production

An innovative process aiming to combine storage and alkali pretreatment of cover crops was investigated using lime as a low cost and environmental friendly reactant. Different lime loadings and Total Solid concentrations (TS) allowed to highlight the abiotic mechanisms of deacetylation during the early stages of the process. Long-term storage experiments of rye and sunflower cover crops at 100 g.kgTS−1 lime loading allowed to evaluate the fermentation kinetics and to compare performances in dry and wet conditions to classical silage storage. The dry condition allowed an efficient alkaline storage and up to a 15.7% Biochemical Methane Potential (BMP) increase, while the wet condition underwent a succession of fermentations with a high butyric acid accumulation and H2 production, leading to a 13% BMP loss. Silage experiments allowed an efficient preservation of the BMP, with no significant variation over the 6-month storage duration.

Pearl millet (Pennisetum glaucum) as a sustainable feedstock for bioethanol production by catalytic downflow liquid contact reactor

Future transportation liquid fuels are mainly focused on biological sources due to the scope of carbon-neutral nature. The Government has mandated the blending of 10% ethanol in fuel but right now only around 6% ethanol is being added to the fuel, the IOC source said. This was mainly due to low ethanol production in the country. Nearly 4bn litres of ethanol will be required to achieve the 10% ethanol blending ratio. Among the biological sources, lignocellulosic feedstocks are a good candidate for bioethanol production if adequately pre-treated for lignin removal. The main aim of this study to assess the effectiveness of the combined process (oxidative lime pre-treatment) used in a catalytic reactor to pre-treat the pearl millet straw. To optimize the combined pretreatment process parameters, three levels of three independent parameters viz., lime loading (8, 10 and 12%), reaction time (5, 20 and 60 min.) and reactor column height (0.6, 0.9 and 1.2 m) were selected and analysed via central composite design of experiments with response surface methodology approach. Results of the output responses like percentage reduction in lignin, hemicellulose, cellulose increase and total reducing sugars were discussed. X-Ray diffraction (XRD) analysis supports and confirms these results. The highest lignin reduction and total reducing sugars were achieved as 69% and 155 mg/g, respectively via optimal conditions (lime: 12%, reactor column height: 1.2 m and reaction period: 60 min.). Enzymatic saccharification studies show the highest reducing sugar yield was 40.6±0.6 mg/g in 96 h at 40 FPU/g. Determination of specific reducing sugars: arabinose, xylose, fructose, mannose, galactose and glucose were performed by HPLC RI using COL-AMINO 150×4.6mm column. This innovative pre-treatment reactor was more effective for lignin removal.

Alternative Lime Pretreatment of Corn Stover for Second-Generation Bioethanol Production

In this work, a delignification process, using lime (Ca(OH)2) as an alternative alkali, was evaluated to improve enzymatic saccharification of corn stover cellulose, with the final goal of obtaining second-generation bioethanol. For that, an experimental design was conducted in order to assay the effect of temperature, lime loading, and time on the corn stover fractionation and enzymatic susceptibility of cellulose. Under conditions evaluated, lime pretreatment was selective for the recovery of cellulose (average of 91%) and xylan (average of 75.3%) in the solid phase. In addition, operating in mild conditions, a delignification up to 40% was also attained. On the other hand, a maximal cellulose-to-glucose conversion (CGCMAX) of 89.5% was achieved using the solid, resulting from the treatment carried out at 90 °C for 5 h and lime loading of 0.4 g of Ca(OH)2/g of corn stover. Finally, under selected conditions of pretreatment, 28.7 g/L (or 3.6% v/v) of bioethanol was produced (corresponding to 72.4% of ethanol conversion) by simultaneous saccharification and fermentation. Hence, the process, based on an alternative alkali proposed in this work, allowed the successful production of biofuel from the important and abundant agro-industrial residue of corn stover.

Investigation of By-products from Acetylene Manufacturing for Acid Mine Drainage Remediation

We characterized carbide lime, a by-product of acetylene manufacturing, and compared it to commercial calcium oxide (CaO), which is typically used to treat AMD. Chemical and X-ray diffraction data revealed that the carbide lime was a calcium-rich lime. Morphological analysis indicated that it differed from commercial CaO in its morphology, having a layered structure. The presence of functional groups among the samples was confirmed by a Fourier transform infrared spectral study. Physical characterization, including nitrogen adsorption–desorption isotherm and particle size distribution demonstrated that the carbide lime had greater surface area and finer particle size than the commercial CaO. Jar tests were used to evaluate the effect of the carbide lime and CaO loading on actual AMD. The optimum quantity of carbide lime for treating the AMD was 0.4 g/l, which increased the pH and reduced the metal and sulphate concentrations to acceptable levels. The carbide lime showed superior acid-neutralizing and contaminant diminution at all studied loadings. Additionally, an Imhoff cone test confirmed that the sludge produced using carbide lime settled better that that produced using CaO powder.

Two-stage thermophilic bio-hydrogen and methane production from oil palm trunk hydrolysate using Thermoanaerobacterium thermosaccharolyticum KKU19

The two-stage process for thermophilic bio-hydrogen production followed by methane production was examined on a hydrolysate obtained from oil palm trunk (OPT). The optimum conditions for lime pretreatment and enzymatic hydrolysis of OPT was a lime loading of 0.2 g Ca(OH)2/g-OPT, pretreatment time of 60 min, temperature of 121 °C and enzyme loading of 35 filter paper units/g-OPT. A maximum total reducing sugar yield of 473 mg/g-OPT was obtained, which was 2.7-fold higher than that of untreated OPT. The OPT hydrolysate was used as a substrate for bio-hydrogen production by Thermoanaerobacterium thermosaccharolyticum KKU19 in the first stage. The maximum hydrogen production potential of 2179 mL H2/Lsubstrate was obtained under the optimum conditions of 16.5 g/L initial substrate concentration, initial pH of 6.7 and 54.5 °C, respectively. Acidic effluent was used to produce methane in the second stage in which the methane yield of 272.4 mL/g-chemical oxygen demand (COD) was achieved. The two-stage hydrogen and methane production resulted in energy yield of 10.6 kJ/g-CODadded with 83% COD removal.

Effect of lime loading on the performance of simultaneous lime treatment and dry anaerobic digestion of smooth cordgrass

ABSTRACTThe effects of lime loading on simultaneous lime treatment and dry digestion (SLTDD) of smooth cordgrass (SC) were evaluated at 35°C by batch reactors and leaching bed reactors (LBRs). Biogas yields of 1.5%, 3%, and 5% (w/w) lime loadings decreased by 7.1%, 20%, and 75.7%, respectively, compared with no-lime treatment with 198.0 mL/g total solids (TS) by batch reactors. The LBRs with liquid recycling and pH adjustment enhanced biogas production with 148.1–236.1 mL/g TS. The inhibition occurred SLTDD may be ascribed to be high pH and temperature from lime hydration at the initial stage. The activity for methanogenic bacteria was more inhibited than other anaerobic bacteria.

Evaluation of lime and hydrothermal pretreatments for efficient enzymatic hydrolysis of raw sugarcane bagasse.

BackgroundEthanol production from sugarcane bagasse requires a pretreatment step to disrupt the cellulose-hemicellulose-lignin complex and to increase biomass digestibility, thus allowing the obtaining of high yields of fermentable sugars for the subsequent fermentation. Hydrothermal and lime pretreatments have emerged as effective methods in preparing the lignocellulosic biomass for bioconversion. These pretreatments are advantageous because they can be performed under mild temperature and pressure conditions, resulting in less sugar degradation compared with other pretreatments, and also are cost-effective and environmentally sustainable. In this study, we evaluated the effect of these pretreatments on the efficiency of enzymatic hydrolysis of raw sugarcane bagasse obtained directly from mill without prior screening. In addition, we evaluated the structure and composition modifications of this bagasse after lime and hydrothermal pretreatments.ResultsThe highest cellulose hydrolysis rate (70 % digestion) was obtained for raw sugarcane bagasse pretreated with lime [0.1 g Ca(OH)2/g raw] for 60 min at 120 °C compared with hydrothermally pretreated bagasse (21 % digestion) under the same time and temperature conditions. Chemical composition analyses showed that the lime pretreatment of bagasse promoted high solubilization of lignin (30 %) and hemicellulose (5 %) accompanied by a cellulose accumulation (11 %). Analysis of pretreated bagasse structure revealed that lime pretreatment caused considerable damage to the bagasse fibers, including rupture of the cell wall, exposing the cellulose-rich areas to enzymatic action.ConclusionWe showed that lime pretreatment is effective in improving enzymatic digestibility of raw sugarcane bagasse, even at low lime loading and over a short pretreatment period. It was also demonstrated that this pretreatment caused alterations in the structure and composition of raw bagasse, which had a pronounced effect on the enzymes accessibility to the substrate, resulting in an increase of cellulose hydrolysis rate. These results indicate that the use of raw sugarcane bagasse (without prior screening) pretreated with lime (cheaper and environmentally friendly reagent) may represent a cost reduction in the cellulosic ethanol production.

Combination of Sodium Hydroxide and Lime as a Pretreatment for Conversion of Date Palm Leaves into a Promising Ruminant Feed: An Optimization Approach

A three-factor, three-level optimization design was implemented at moderate temperatures (average = 40 °C) to investigate the impact of the three independent variables, namely both sodium hydroxide (NaOH) and lime (Ca(OH)2) loadings, and a residence reaction time, on the response variable, in vitro cumulative gas production at 24 h from date palm (Phoenix dactilifera L.) leaves. Statistical analysis revealed significant influence (p < 0.0001) of the three independent variables as well as an interaction effect (p = 0.0120) of sodium hydroxide loading and lime loading on the response variable. Under the optimal pretreatment conditions (sodium hydroxide loading of 0.06 g NaOH/g dry biomass, lime loading of 0.09 g Ca(OH)2/g dry biomass, and residence time of 71.4 h), the amount of cumulative gas production after 24 h was 101.4 mL gas/g organic matter, versus 104.6 mL gas/g organic matter for the predicted value. Scanning electron microscope studies showed formation of apertures and cracks on the surface of the substrate pretreated under the optimal conditions. Fourier transform infrared spectroscopic analysis confirmed the saponifying and delignifying effect of combined alkaline pretreatment on date palm leaves. The results of present study hold a promise of a low-cost on-farm pretreatment method to reduce the recalcitrance of date palm leaves for ruminant feeding, particularly suitable for tropical climates.

Low temperature calcium hydroxide treatment enhances anaerobic methane production from (extruded) biomass

Ca(OH)2 treatment was applied to enhance methane yield. Different alkali concentration, incubation temperature and duration were evaluated for their effect on methane production and COD conversion efficiency from (non-)extruded biomass during mesophilic anaerobic digestion at lab-scale. An optimum Ca(OH)2 pretreatment for grass is found at 7.5% lime loading at 10°C for 20h (37.3% surplus), while mild (50°C) and high temperatures perform sub-optimal. Ca(OH)2 post-treatment after fast extrusion gives an additional surplus compared to extruded material of 15.2% (grass), 11.2% (maize straw) and 8.2% (sprout stem) regarding methane production. COD conversion improves accordingly, with additional improvements of 10.3% (grass), 9.0% (maize straw) and 6.8% (sprout stem) by Ca(OH)2 post-treatment. Therefore, Ca(OH)2 pretreatment and post-treatment at low temperature generate an additional effect regarding methane production and COD conversion efficiency. Fast extrusion gives a higher energy efficiency ratio compared to slow extrusion.

Effect of Lime Pretreatment on Granulation of Switchgrass

Densification of switchgrass into consistent and high-density solid feedstock will reduce the cost of transport, handling, and storage to produce fuels and chemicals. Development a novel, low-cost densification technology is critical for reducing the delivered cost of feedstock while improving the bulk flow properties of densified products. In this paper, a novel wet granulation technology was proposed to investigate the effect of lime pretreatment on the production of switchgrass granules. Granulation is a process of agglomerating fine powders by wetting powder surfaces with liquid binders and mild application of shear/vibrating forces. Switchgrass was size reduced into fine powders using a knife mill and pretreated with three lime loading rates (0.05, 0.1, 0.2 g/g of biomass) at 121 °C for 30 min and at room temperature (25 °C) for 72 h. The structural modification of pretreated samples was analyzed by scanning electron microscopy and autofluorescence microscopy. Pretreated samples were granulated using a pan granulator with pre-formulated starch binder. Granules made from 20 % (0.2 g/g of biomass) lime loading rate had significantly higher single granule density and angle of repose with lower binder requirement than that of untreated granules. Lime treatment did not significantly increase the bulk density and hardness of granules. Lime-treated granules had significantly higher ash content and lower gross calorific value than that of untreated granules. In overall, lime treatment was not attractive to produce granules for thermochemical conversion platform, but lime-treated granules could be used to produce liquid biofuels and platform chemicals in biochemical conversion platform.

Pretreatment of corn stover for sugar production using dilute hydrochloric acid followed by lime

In this study, a two stage process was evaluated to increase the sugar recovery. Firstly, corn stover was treated with diluted hydrochloric acid to maximize the xylose yield, and then the residue was treated with lime to alter the lignin structure and swell the cellulose surface. The optimal condition was 120 °C and 40 min for diluted hydrochloric acid pretreatment followed by lime pretreatment at 60 °C for 12h with lime loading at 0.1 g/g of substrate. The glucose and xylose yield was 78.0% and 97.0%, respectively, with cellulase dosage at 5 FPU/g of substrate. The total glucose yield increased to 85.9% when the cellulase loading was increased to 10 FPU/g of substrate. This two stage process was effective due to the swelling of the internal surface, an increase in the porosity and a decrease in the degree of polymerization.

Lime Pretreatment and Fermentation of Enzymatically Hydrolyzed Sugarcane Bagasse

Sugarcane bagasse was subjected to lime (calcium hydroxide) pretreatment and enzymatic hydrolysis for second-generation ethanol production. A central composite factorial design was performed to determine the best combination of pretreatment time, temperature, and lime loading, as well as to evaluate the influence of enzymatic loadings on hydrolysis conversion. The influence of increasing solids loading in the pretreatment and enzymatic hydrolysis stages was also determined. The hydrolysate was fermented using Saccharomyces cerevisiae in batch and continuous mode. In the continuous fermentation, the hydrolysates were concentrated with molasses. Lime pretreatment significantly increased the enzymatic digestibility of sugarcane bagasse without the need for prior particle size reduction. In the optimal pretreatment conditions (90 h, 90 °C, 0.47 glime/g bagasse) and industrially realistic conditions of hydrolysis (12.7 FPU/g of cellulase and 7.3 CBU/g of β-glucosidase), 139.6 kglignin/ton raw bagasse and 126.0 kg hemicellulose in the pretreatment liquor per ton raw bagasse were obtained. The hydrolysate from lime pretreated sugarcane bagasse presented low amounts of inhibitors, leading to ethanol yield of 164.1 kgethanol/ton raw bagasse.

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.

Lime pretreatment to improve methane production of smooth cordgrass (Spartina alterniflora)

Anaerobic conversion of smooth cordgrass (SC; Spartina alterniflora) to methane for energy production presents a viable option for effective management. The effect of lime pretreatment of SC on methane production was investigated in this study. The effect of three selected independent variables (lime loading (0.02–0.12g Ca(OH)2/g SC), pretreatment time (7–28days) and temperature (25–55°C)) on material composition and methane production was explored. Lime pretreatment resulted in significant changes in SC composition: 5.7–60.5% hemicellulose and 10.2–36.2% lignin reductions, and 91–98.7% cellulose remaining in the solid residues after lime pretreatment. Lime pretreatment increased methane yield by between 122% and 180% and the methane production rate constant in the range of 56–212%. The highest methane yield was 218.4mL/g total solids from pretreatment conditions of lime loading 0.12g Ca(OH)2/g SC, for 28days at 45°C. These results were based on a 30-day biochemical methane potential assay. Lime loading had the greatest influence on methane yield of the three pretreatment factors. Considering the energy balance, the optimization of pretreatment experiment was carried out under the condition of 0.10g Ca(OH)2/g SC dry mass, at 25°C for 14days. Based on this study, the pretreatment condition of high lime loading, low temperature and short pretreatment time was a preferential consideration for lime pretreatment.

Enhanced cellulosic hydrogen production from lime-treated cornstalk wastes using thermophilic anaerobic microflora

Lignocellulose-to-hydrogen bioconversion is a promising technology to substitute fossil fuel-based energy. Adequate supplement of pretreatment to improve the digestibility of lignocellulose is required for effective fermentative hydrogen production. This study was conducted to evaluate the H2 production from lime pretreated cornstalk and explored the mechanisms of hydrogen yield enhancement. The accumulative hydrogen yield of 155.4 ml/g-TVS was obtained at recommend conditions of lime loading 0.10 g/g biomass, ambient temperature and residence time 96 h, which was 38.1% higher than 115.3 ml/g-TVS for the untreated sample. The enhancement of the hydrogen yield was attributed to the improvement of biodegradability of the cornstalk through lime pretreatment. Chemical composition analysis showed that 23.5% lignin, 27.4% hemicellulose and 10.2% cellulose were removed, while water-soluble substances were increased by 32.3%. Microscopy observation and FTIR and XPS analysis further confirmed that the rigid structure of lignocellulose was disrupted by lime and more cellulose exposed to the surface.

Selectivity and delignification kinetics for oxidative short‐term lime pretreatment of poplar wood, part I: Constant‐pressure

Kinetic models applied to oxygen bleaching of paper pulp focus on the degradation of polymers, either lignin or carbohydrates. Traditionally, they separately model different moieties that degrade at three different rates: rapid, medium, and slow. These models were successfully applied to lignin and carbohydrate degradation of poplar wood submitted to oxidative pretreatment with lime at the following conditions: temperature 110-180°C, total pressure 7.9-21.7 bar, and excess lime loading of 0.5 g Ca(OH)2 per gram dry biomass. These conditions were held constant for 1-6 h. The models properly fit experimental data and were used to determine pretreatment selectivity in two fashions: differential and integral. By assessing selectivity, the detrimental effect of pretreatment on carbohydrates at high temperatures and at low lignin content was determined. The models can be used to identify pretreatment conditions that selectively remove lignin while preserving carbohydrates. Lignin removal≥50% with glucan preservation≥90% was observed for differential glucan selectivities between ∼10 and ∼30 g lignin degraded per gram glucan degraded. Pretreatment conditions complying with these reference values were preferably observed at 140°C, total pressure≥14.7 bars, and for pretreatment times between 2 and 6 h depending on the total pressure (the higher the pressure, the less time). They were also observed at 160°C, total pressure of 14.7 and 21.7 bars, and pretreatment time of 2 h. Generally, at 110°C lignin removal is insufficient and at 180°C carbohydrates do not preserve well.

Oxidative Lime Pretreatment of Alamo Switchgrass

Previous studies have shown that oxidative lime pretreatment is an effective delignification method that improves the enzymatic digestibility of many biomass feedstocks. The purpose of this work is to determine the recommended oxidative lime pretreatment conditions (reaction temperature, time, pressure, and lime loading) for Alamo switchgrass (Panicum virgatum). Enzymatic hydrolysis of glucan and xylan was used to determine the performance of the 52 studied pretreatment conditions. The recommended condition (110°C, 6.89 bar O(2), 240 min, 0.248 g Ca(OH)(2)/g biomass) achieved glucan and xylan overall yields (grams of sugar hydrolyzed/100 g sugar in raw biomass, 15 filter paper units (FPU)/g raw glucan) of 85.9 and 52.2, respectively. In addition, some glucan oligomers (2.6 g glucan recovered/100 g glucan in raw biomass) and significant levels of xylan oligomers (26.0 g xylan recovered/100 g xylan in raw biomass) were recovered from the pretreatment liquor. Combining a decrystallization technique (ball milling) with oxidative lime pretreatment further improved the overall glucan yield to 90.0 (7 FPU/g raw glucan).

Oxidative Lime Pretreatment of Dacotah Switchgrass

Oxidative lime pretreatment increases the enzymatic digestibility of lignocellulosic biomass primarily by removing lignin. In this study, recommended pretreatment conditions (reaction temperature, oxygen pressure, lime loading, and time) were determined for Dacotah switchgrass. Glucan and xylan overall hydrolysis yields (72h, 15FPU/g raw glucan) were measured for 105 different reaction conditions involving three different reactor configurations (very short term, short term, and long term). The short-term reactor was the most productive. At the recommended pretreatment condition (120°C, 6.89bar O(2), 240min), it achieved an overall glucan hydrolysis yield of 85.2g glucan hydrolyzed/100g raw glucan and an overall xylan yield of 50.1g xylan hydrolyzed/100g raw xylan. At this condition, glucan oligomers (1.80g glucan recovered/100g glucan in raw biomass) and xylan oligomers (25.20g xylan recovered/100g xylan in raw biomass) were recovered from the pretreatment liquor, which compensate for low pretreatment yields.