Lime Pretreatment Research Articles

Revealing the interplay of dissolved organic matters variation with microbial symbiotic network in lime-treated sludge landscaping

Lime pretreatment is commonly used for sludge hygienization. Appropriate lime dosage is crucial for achieving both sludge stabilization (lime dosage >0.2 g/g-TS) and promoting plant and soil health during subsequent landscaping (lime dosage <0.8 g/g-TS). While much research has been conducted on sludge lime treatment, few studies have examined the effects of lime dosing on integrating sludge stabilization and plant growth promotion during landscaping. In this study, we investigated microbial dynamics and dissolved organic matter (DOM) transformation during sludge landscaping with five lime dosage gradients (0, 0.2, 0.4, 0.6, 0.8 g lime/g-TS) over 90 days. Our results showed that a lime dosage of 0.4 g/g-TS is the lower threshold for achieving waste activated sludge (WAS) stabilization during landscaping, leading to maximum humic substance formation and minimal phytotoxicity. Specifically, at 0.4 g/g-TS lime dosage, protein degradation and decarboxylation-induced humification were significantly enhanced. The predominant microbial genera shifted from Aromatoleum to Exiguobacterium and Romboutsia (both affiliated with the phylum Firmicutes). Reactomics analysis further indicated that a 0.4 g/g-TS lime dosage promoted the hydrolysis of proteins (lyase reactions on C-C, C-O, and C-N bonds), amino acid metabolism, and decarboxylation-induced humification (e.g., C1H2O2, C2H4O2, C5H4O2, C6H4O2). The co-occurrence network analysis suggested that the phyla Firmicutes, Proteobacteria, and Bacteroidetes were key players in DOM transformation. This study provides an in-depth understanding of microbe-mediated DOM transformation during sludge landscaping and identifies the optimal lime dosage for improving sludge landscaping efficiency.

Consolidated bioprocessing of lignocellulosic wastes in Northwest China for D-glucaric acid production by an artificial microbial consortium.

D-glucaric acid is a platform chemical of great importance and the consolidated bioprocessing (CBP) of lignocellulose by the microbial consortium of Trichoderma reesei C10 and Saccharomyces cerevisiae LGA-1C3S2 features prospects in biomanufacturing it. Here we compared some representative lignocelluloses in Northwest China including corn stover, wheat straw and switchgrass, and the leading pretreatments including steam explosion, subcritical water pretreatment, sodium hydroxide pretreatment, aqueous ammonia pretreatment, lime pretreatment, and diluted sulfuric acid pretreatment. It was found that sodium hydroxide pretreated switchgrass (SHPSG) was the best substrate for D-glucaric acid production, resulting in the highest D-glucaric acid titers, 11.69 ± 0.73g/L in shake flask and 15.71 ± 0.80g/L in 10L airlift fermenter, respectively. To the best of our knowledge, this is the highest D-glucaric acid production titer from lignocellulosic biomass. This work offers a paradigm of producing low-cost D-glucaric acid for low-carbon polyethylene 2,5-furandicarboxylate (PEF) and a reference on developing biorefinery in Northwest China.

Lime pretreatment of maize stover and solubilization of pretreated solids by enzymatic hydrolysis and Clostridium thermocellum fermentation

Lime pretreatment of maize stover and solubilization of pretreated solids by enzymatic hydrolysis and Clostridium thermocellum fermentation

Pretreatment of digested manure fibers at high temperature (185°C) with lime added enhances methane production

The anaerobic digestion of manure is facing the challenge of limited degradation because of recalcitrant nature of the fibers. In this study different concentrations (1–3%) of lime (CaO) pretreatment for AD of digested manure fibers under thermophilic conditions was evaluated. The results of the study revealed that there was 30.6, 36.4 and 23.5% reduction in cellulose, hemicellulose and lignin fraction of manure fibers during pretreatment when subjected to 3% CaO pretreatment. Degradation of manure fibers also improved because of pretreatment and 40.6% of volatile solids were degraded during AD process. Methane yield was improved by 115.7% in course of this study. Additionally, carbohydrates were main fraction used by anaerobic bacteria to produce methane and 74.9% cellulose and 79.3% hemicellulose was converted to methane in sample which was pretreated using 3% CaO at 185 °C for 30 min.

Lime pretreatment of pelleted corn stover boosts ethanol titers and yields without water washing or detoxifying pretreated biomass

Large-scale industrial cellulosic ethanol production is significantly restricted by the high costs of lignocellulosic biomass handling, transportation and storage. Therefore, biomass densification is thought to be necessary to solve these logistical problems. Nevertheless, because of its high density, densified biomass may have an impact on subsequent biomass processing. In this study, lime pretreatment was investigated on pelleted corn stover (PCS) for ethanol production. The glucan and xylan conversions of lime-PCS exceeded 90% via enzymatic hydrolysis after optimization of pretreatment conditions. Corn stover was characterized using the flourier transform infrared spectrum (FT-IR) and scanning electron microscopy (SEM), which revealed that after lime pretreatment, the acetyl groups in biomass were removed and cell wall decomposition products redeposited on outer cell wall surfaces. Finally, without washing or detoxifying pretreated biomass, enzymatic hydrolysis and fermentation resulted in a high ethanol titer (65.1 g/L). The results indicated that lime pretreatment is efficient in pretreating PCS.

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.

Lactic fermentation of grain sorghum: effect of variety and pretreatment on the production of lactic acid and biomass.

Grain sorghum is a viable feedstock for lactic acid fermentation; however, tannins contained in some varieties affect the efficiency of hydrolysis and fermentation. This work objective was to assess the effect of pre-treatment of grain sorghum on the production of lactic acid and biomass after fermentation. Sorghum varieties with low, medium, and high tannins were pretreated, enzymatically hydrolyzed, and fermented with Lactobacillus casei. The pre-treatments consisted of cooking the grains in lime, cooking in plain water, and no treatment (control). Pretreated sorghum flours were hydrolyzed using thermostable α-amylase from Bacillus licheniformis and amyloglucosidase from Aspergillus niger. Lime pre-treatment showed a significant improvement in protein content, digestibility, and lactic acid production after fermentation, in relation to the non-treated samples. Although differences were not significant for low and medium tannins, lime treatment increase lactic acid production for the cooked-in-lime high-tannin sorghum in relation to the control. For this sorghum/treatment combination, the lactic acid production was 138 g/L, with a volumetric productivity of 1.57 g/L·h and 85/100 g yield based on initial starch, which is equivalent to 69 g of lactic acid per 100 g of sorghum d.b.

Design of hydrothermal and subsequent lime pretreatment for fermentable sugar and bioethanol production from acacia wood

In this study, lime (calcium hydroxide) treatment (LT) was applied as an alkaline pretreatment subsequent to hydrothermal treatment (HT) in terms of fermentable sugar and bioethanol production from acacia wood. To maximize the hydrolysis of cellulose and hemicellulose, the condition of 200 °C for 10 min of HT was selected for subsequent lime treatment. The optimum conditions of LT were established to be a ratio of calcium hydroxide to hydrothermally treated acacia biomass of 12.2%, temperature of 70.9 °C, and reaction time of 23.5 h using a response surface methodology, and the maximum glucose yield by prediction and experiment were determined to be 74.4% and 73.5%, respectively. Further mechanical refining accelerated the access of the enzyme to glucan, resulting in an increase in glucose conversion (80.5%). Although the glucose yield by LT was 21.5% higher than that of HT, the ethanol yield was 33.5% lower due to the negative effect of residual calcium ions on yeast fermentation.

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.

Optimizing lime pretreatment of rice straw for biolipid production using oleaginous microorganisms

This work focuses on the lime pretreatment of rice straw, agricultural waste in northeast Vietnam, for microbial lipid (bio-lipid) production. A response surface methodology approach was performed to optimize parameters for the pretreatment process. These parameters are the concentration of Ca(OH)2, hydrolysis temperature, and maintained time; the effect is considered bio-lipid production yield. The lipid yield was estimated through consolidated bioprocessing of the pretreated rice straw as a substrate and using the fungus strain (Aspergillus oryzae 32) and the yeast strain (Lipomyces starkeyi 22). As a result, the optimal pretreatment conditions for maximum lipid yield were obtained at Ca(OH)2 concentration of 12 g/L and hydrolysis temperature of 110 °C within 60 min. The accumulated lipid in fermentation using these oleaginous microorganisms was 8.5g/100g oven-dry weight of rice straw (10.9g/100g for pretreated rice straw). The biolipid consisted of 42.6% saturated, 21.1% monounsaturated (MUFA), and 35.1% polyunsaturated (PUFA) fatty acids.

Evaluation of Ca(OH)2 disintegration on high-solid sludge floc structures and subsequent anaerobic digestion

Lime pretreatment was tested at different doses on high-solid sludge. Subsequently, the effects of this pretreatment were investigated in terms of the damage of extracellular polymeric substance and cell structures and the subsequent high-solid anaerobic digestion (HSAD). Moreover, the relationship between them was discussed. Results showed that higher lime dose was favorable to COD solubilization, wherein more proteins were released than carbohydrates under the same lime dose. When lime dose was below 0.04 g/g-TS, the COD solubilization was mainly caused by the disintegration of EPS, and when the lime dose was higher than 0.06 g/g-TS, the damages of cell walls and membranes were observed and led to the further COD solubilization. The HSAD process was accelerated by 7–16 days after lime pretreatment, and the biogas production increased by 22.9%–34.8% when lime dose was higher than 0.04 g/g-TS. Thermogravimetric analysis results suggested that Ca2+ could be removed from the liquid phase by precipitating with the CO2 produced during the HSAD process, thereby increasing the methane content.

Oxidative submerged lime pretreatment and high-solids saccharification of corn stover

Economic commercial-scale production of biofuels from lignocellulose depends, in part, on the development of a suitable pretreatment. In pursuit of that goal, this study assesses the repeatability and effectiveness of submerged lime pretreatment (SLP) of two batches of corn stover designated “Field” and “Module.” SLP was performed with 0.15 g Ca(OH)2 g−1 biomass and 10 g H2O g−1 biomass at 50 °C for 4 weeks while purging with air. SLP was repeated 14 times and the results of the mass balances, closures, and compositions of raw and SLP corn stover are presented. The glucan content of corn stover prior to pretreatment was determined to be 36.1 ± 0.7% (Module washed), 37.5 ± 0.4% (Field washed), and 32.6 ± 1.4% (Field unwashed). For washed corn stover (Module and Field), the standard deviation and coefficient of variation were <1%, demonstrating that the measurements were repeatable. For unwashed Field corn stover, because of its higher content of water-soluble components, the variability was slightly higher. The mass closures were above 96% with less than 2% standard deviation. The glucan content of SLP corn stover was 44.3 ± 0.8% (Module washed), 41.5 ± 0.5% (Field washed), and 42.9 ± 2.2% (Field unwashed). This study also presents a reliable analytical method for assessing the enzymatic digestibility of high-solids (15%) lignocellulose. Inositol is used as an internal standard to determine the final reactant volume, which is difficult in high-solids saccharification. After SLP, the overall glucan digestibility was ~80% (standard deviation < 4%, coefficient of variation < 5%), supporting the potential of SLP as a reproducible, cost-effective, and scalable pretreatment.

Sugarcane juice clarification by lanthanum phosphate nanofibril coated ceramic ultrafiltration membrane: PPO removal in absence of lime pre-treatment, fouling and cleaning studies

The present work explores the possibility of employing rare earth phosphates deposited alumina substrates for ceramic membrane applications. Multichannel porous alumina supports are coated with Lanthanum phosphate nanofibrils of thickness 6 µm by sol-gel deposition technique. The performance of lanthanum phosphate coated ultrafiltration (UF) membrane for sugarcane juice clarification was studied by measuring polyphenol oxidase (PPO) enzyme, bacteria removal efficiency and permeate flux decline profile. The PPO enzyme activity was observed to be lower by 70% in permeate along with a less bacterial presence. The analysis of sucrose loss with time is also studied for raw sugarcane juice, clarified and limed sugarcane juice. A hybrid cleaning strategy involving an innovative brushing action on the membrane surface for physical cleaning combined with chemical cleaning was implemented in this study. The fouled membrane was analyzed by FESEM, EDX, and FTIR. Shelf-life study of feed and permeate confirmed that permeate was more stable than the feed. The experimental results conclude that raw sugarcane juice clarification using lanthanum phosphate coated UF membrane was viable with the use of innovative physical cleaning method as proposed in this study.

Mechanical pretreatment of biomass – Part II: Shock treatment

Shock treatment is a novel mechanical pretreatment process that, when combined with oxidative lime pretreatment, greatly increases the digestibility of biomass. This work determined the effectiveness of shock treatment on multiple feedstocks (sugarcane bagasse, corn stover, poplar wood, sorghum, and switchgrass), determined recommended shock treatment conditions for corn stover, and compared cellulose crystallinity and copper number of raw and shock-treated samples. At an enzyme loading of 5 FPU/g raw glucan, the combination of oxidative lime pretreatment (OLP) and shock treatment increased 72-h glucan digestibility (g glucan digested/100 g glucan treated) of corn stover from 15.3 (untreated) to 84.6 (OLP + shock). The other four biomass types showed similar gains in glucan digestibility when compared to the respective untreated biomass: +55.7 (bagasse), +76.3 (poplar wood), +48.2 (sorghum), and +73.1 (switchgrass). Recommended shock treatment conditions show that a single shock at room temperature with never-frozen biomass produces the most digestible corn stover.

Effect of Pretreatments on the Drying Characteristics and Quality of African Star Apple (Chrysophyllum albidum)

Fruits, due to high moisture content, deteriorate quickly when not adequately preserved. Drying, a common preservation method, will affect quality of final product if not properly controlled. Pretreatments prior to drying have been established as a way of retaining product qualities. This study investigated the effect of pretreatments on the qualities of dried African star apple flesh. African star apple fleshes were sliced (2, 4, 6 and 8 mm) and subjected to pretreatments [blanching (80 oC for 3 min), lime juice (100%), ascorbic acid and salt solution (1:25 w/v)]. Untreated samples served as control. Samples were dried in cabinet dryer (50, 55 and 60 oC) at 2 m/s constant air flow-rate, monitored at intervals, until constant weight was obtained. Ascorbic acid and colour measurement of the fresh and dried sample were determined using standard method. The moisture contents of the African star apple flesh were observed to reduce from a mean value of 70.44%, 71.55% and 73.24% to 2.38%, 1.91% and 3.23% at temperatures of 50, 55 and 60 °C, respectively. The total drying time ranged between 7 to 8 h. Colour of the dried African star apple was significantly preserved by the pretreatments used, and low overall color change (?E) was obtained at the lowest drying temperature (50oC). The ascorbic acid and lime pretreatments however had better colour overall. Lime pretreatment for 2 mm thick at 50oC gave the best result in terms of ascorbic acid retention. Hence, lime juice pre-treatment has potentials of retaining quality of dried fruits.

ENHANCEMENT OF BIOGAS PRODUCTION FROM FOOD WASTES IN A HYBRID ANAEROBIC-AEROBIC BIOREACTOR BY MANURE ADDITION AND LIME-PRETREATMENT OF RECYCLED LEACHATE

The production of food wastes is a serious issue in developed and developing countries. The biogas production technology is one of the most sustainable methods for treating food wastes. Currently, there is a great need to implement suitable methods to enhance biodegradation and methane production. This study investigated the effect of manure addition and leachate lime-pretreatment on the biogas and methane production from spoilable municipal solid wastes using a hybrid anaerobic-aerobic bioreactor as a new method. Three laboratory-scale columns were constructed to simulate a hybrid anaerobic-aerobic bioreactor without manure addition and leachate pretreatment as control (R1), two hybrid bioreactors with manure addition and without recycled leachate pretreatment (R2), and manure addition and lime pretreatment of recycled leachate (R3). All simulated bioreactors operated as continuous for about 8 months. Biogas and CH4 production were measured to evaluate the biodegradability of food wastes and efficacy of bioreactors. The results indicated consistently more biogas production under manure addition and leachate pretreatment (R3). The accumulative methane yield was determined to be 17.46, 53.79, and 283.41 mL/gVS for R1, R2, and R3 bioreactors, respectively, after 8 month of operation. The cumulative methane yield in the R3 bioreactor was 16.23 and 5.27 times higher than in R1 and R2 bioreactors, respectively. Therefore, the food waste biodegradation in R3 was greater than in R1 and R2. These results showed that the manure addition and leachate lime-pretreatment were effective in increasing the biogas and methane production of food wastes.

Improved Sugars Release from Chili Post-harvest Residues by Dilute Acid Assisted Lime Pretreatment

Improved Sugars Release from Chili Post-harvest Residues by Dilute Acid Assisted Lime Pretreatment

Lime Pretreatment of Miscanthus: Impact on BMP and Batch Dry Co-Digestion with Cattle Manure.

In Europe, the agricultural biogas sector is currently undergoing fast developments, and cattle manure constitutes an important feedstock. Batch dry digester processes with leachate recirculation prove to be particularly interesting for small-scale plants. However, their startup being relatively slow, the process could be facilitated by co-digestion with energy crops. In this study, Miscanthus x giganteus was chosen for its high biomass yields and low input requirements. The carbohydrate accessibility of this lignocellulosic biomass is limited but may be improved with alkali pretreatment. The efficiency of lime (CaO) pretreatment with low water addition on the biochemical methane potential (BMP) of miscanthus was investigated through two experimental designs (CaO concentrations ranged between 2.5 and 17.5% and pretreatment lasted 1, 3, or 5 days). The pretreated miscanthus was then co-digested with cattle manure in dry leach bed reactors. CaO pretreatments led to a 14–37% improvement of miscanthus BMP, and a 67–227% increase in the first-order kinetics constant; a high contact time was shown to favor methane production. According to these results and to industrial requirements, miscanthus was pretreated with 5 and 10% CaO for 5 days, then co-digested with manure in dry leach bed reactors. Nevertheless, the promising results of the BMP tests were not validated. This could be related to the high water absorption capacity of miscanthus.

Effect of Lime Pretreatment on Microstructure of Cassava Stalk Fibers and Growth of Aspergillus niger

Cassava stalk can be converted into sugar-based product by using microorganism. Unfortunately, lignin act as a barrier of optimal bioconversion. Cassava stalk needs pretreatment process for removing this barrier. The effect of lime pretreatment on microstructure of cassava stalk fibers and the growth of Aspergillus niger FNCC 6114 were observed in this research. The cassava stalks were reduced into 0.147- 0.297 mm size and pretreated with 1 % Ca(OH)2. Lime pretreated and unpretreated cassava stalk was used as solid medium for Aspegillus niger FNCC 6114. The effect of pretreatment method on fibers microstructure of cassava stalk was evaluated through SEM micrograph. The growth and metabolism activities of Aspergillus niger FNCC 6114 were monitored through SEM micrograph of media after fermentation. The other parameters examined were changes in glucosamine, reducing sugar levels, and spores’ quantity. Lime pretreatment altered microstructure of cassava stalk fibers. However, cassava stalk without lime pretreatment gave better growth of Aspergillus niger FNCC 6144 based on metabolism activities parameters. Cassava stalks is suitable as media for Aspergillus niger FNCC 6144 through solid state fermentation. For better growth of Aspergillus niger FNCC 6144 fine-sized cassava stalk should not be lime pretreated. The results of this study provide information about the pretreatment of cassava stems which was effective in supporting the growth of Aspergillus niger. Enhancements the utilization of cassava stems by using fungi, for example Aspergillus niger can overcome the accumulation of organic waste that can interfere with environmental sustainability.

Two-stage thermophilic bio-hydrogen and methane production from lime-pretreated oil palm trunk by simultaneous saccharification and fermentation

A simultaneous saccharification and fermentation (SSF) process was applied for thermophilic bio-hydrogen production from lime-pretreated oil palm trunk (OPT) by Thermoanaerobacterium thermosaccharolyticum KKU19. The SSF hydrogen fermentation conditions were optimized to maximize hydrogen yield (HY). Based on Plackett-Burman design, substrate loading and initial pH had significant effects on HY. The substrate loading and initial pH were further optimized using response surface methodology with a central composite design. The optimum conditions were a substrate loading, enzyme loading, inoculum concentration, initial pH and temperature of 4.6%, 10 filter paper unit (FPU)/g-OPT, 10% (v/v), 6.3 and 50 °C, respectively, which yielded the highest HY of 60.22 mL H2/g-OPT. Structural analysis showed that lime pretreatment and SSF decreased the crystallinity of OPT. Methane production was carried out following the hydrogen production to improve the energy yield from OPT. The results showed that methane production increased total energy yield from 0.65 to 11.79 kJ/g-OPT under the optimal conditions.