Treatment Of Black Liquor Research Articles

Chemical characterization of heat‐treated kraft lignin after fractionation with organic solvents and pH effect

AbstractLignin, the main source of renewable aromatics, has a complex structure, high polydispersity, and low reactivity, which hinders its large‐scale use. This study aims to improve lignin reactivity through heat treatment combined with fractionation by organic solvents or the pH effect. Heat treatment of commercial hardwood black liquor was performed at 225 °C for 150 min. The samples were then fractionated either by using organic solvents (ethyl acetate, ethanol, methanol, and acetone) or by lowering pH using hydrochloric acid (HCl) (pH values 1, 3, 5, 7, and 9). The fractionation was carried out in one step and in sequential mode. The fractionated samples were characterized chemically by the content of acid‐soluble and acid‐insoluble lignin, carbohydrates, ash, inorganic compounds (metals), elemental analysis, and by pyrolysis‐gas chromatography–mass spectrometry (Py‐GC–MS). The highest mass yields were obtained using the one‐step mode for both fractionations, with yields as high as 53.3% for organic solvents and 47.8% for the pH effect. Solvent fractionation reduced ash content by up to 75.4% and increased calorific value, carbon content, and total lignin content. Fractionation by pH effect showed an ash reduction of up to 55.9% and an increase in calorific value and carbon content of up to 8.7 MJ kg−1 and 49.7%, respectively. The Hansen solubility parameters were also calculated to address lignin's solubility in each of the tested solvents. These findings indicate that combining heat treatment and fractionation techniques improves lignin's chemical properties significantly, making it a more viable raw material for industrial use. This approach supports the circular economy by transforming lignin into a high‐value product, thereby promoting sustainable and efficient resource utilization across industries.

Utilization of papermaking black liquor as liquid phase for hydrothermal carbonization of corn stalks: The unique role of alkali for production of hydrochar

Papermaking black liquor (BL) contains a large amount of organic matter, alkali, and salt, which has high value in industrial and agricultural production. In the present paper, hydrothermal carbonization (HTC) technology has been employed to deal with BL and corn stalk (CS) under various conditions. A variety of analytical technologies, including Fourier Transform Infrared Spectrometer, X-Ray Diffraction, element analyzer, comprehensive thermal analyzer, scanning electron microscope, chromatography/mass spectrometry, TOC analyzer, and density functional theory (DFT), were used to characterize the physicochemical properties of hydrochar and aqueous phase product. The effects of experimental parameters (temperature, solid-liquid ratio, and time) on the HTC of BL and CS were systematically investigated. The higher energy yield and densification of hydrochar prepared by our HTC technology were obtained at 260 ℃ in 30 min with a solid-liquid ratio of 1:3. Mechanism study indicates that NaOH, which comes from the original BL, could effectively facilitate the cleavage of β–O–4 bond in lignin and β–1–4 glycosidic bond in cellulose and hemicellulose molecules. Hemicellulose and cellulose are more susceptible to degradation relevant to the lignin in the presence of NaOH. Elementary analysis shows that the dosage of BL is important for improving energy densification of hydrochar. The combustion characteristics show that hydrochar presents a thermochemical behavior, which is close to bituminous coal. Owing to hydroxyl ion in NaOH ion pair was consumed in the series of dehydrogenation reactions, pH of HTC aqueous phase product significantly decreases from 11 to 13 in original BL to 4.8–5. Such results indicate that a completely change for the components of BL could be obtained by our HTC technology, which provide a novel idea for the treatment of Papermaking BL without concentration.

Supercritical water depolymerization of black liquor, refining and comprehensive analysis of products including biopolyols

Black liquor (BL) has valuable lignin and its derived compounds, which can be used for many purposes, such as polyol synthesis. Herein, we reveal polyols presence in depolymerized black liquor (DBL) and propose a fast and scalable approach to increase the yield of this fraction. Hydrothermal treatment (HTL) of black liquor (385°C, 26 MPa) was performed in a custom designed supercritical water (SCW) pilot-plant with rapid reaction times of around 0.4 s. Ash-free, total ethyl acetate extracted bio-oil yield was found 77% w/w. In addition to the contribution of the detailed fractionation methods, this study highlights continuous operation (>1 hour), and short reaction times (∼0.4 s) of raw black liquor in SCW to produce biopolyols and aromatic bio-oil.

Performance evaluation of gravity-driven bioreactor (GDB) for simultaneous treatment of black liquor and domestic wastewater.

A lab-scale gravity-driven bioreactor (GDB) was designed and constructed to evaluate the simultaneous treatment of black liquor and domestic wastewater. The GDB was operated with a mixture of black liquor and domestic wastewater at a ratio of 1:1 and maintained at an average organic loading rate of 1235mg-COD/L-Day. The wastewater was fed to the primary sedimentation tank at a flow rate of approximately 12mL/min and subsequently passed through serially connected anaerobic and aerobic chambers with the same flow rate. Each wastewater sample was allowed to undergo a hydraulic retention time of approximately 72h, ensuring effective treatment. The GDB was actively operated for nine samples (W1-W9) at a weekly frequency. The entire process was conducted within the workstation's ambient temperature range of 30-35°C to sustain microbial activity and treatment efficiency in an open environment. The performance of the GDB was evaluated in terms of various pollution indicators, including COD, BOD5, lignin removal, TDS, TSS, EC, PO43-, SO42-, microbial load (CFU/mL and MPN index), total nitrogen, and color reduction. The results showed that the GDB achieved promising treatment efficiencies: 84.5% for COD, 71.80% for BOD5, 82.8% for TDS, 100% for TSS, 74.71% for E.C., 67.25% for PO43-, 81% for SO42-, and 69.36% for TN. Additionally, about 80% reduction in lignin content and 57% color reduction were observed after the treatment. The GDB substantially reduced microbial load in CFU/mL (77.98%) and MPN (90%). This study marks the first to report on wastewater treatment from two different sources (black liquor and domestic wastewater) using a simple GDB design. Furthermore, it highlights the GDB's potential as a cost-effective, environmentally friendly, and efficient solution for wastewater treatment, with no need for supplementary chemical or physical agents and zero operational costs.

Extraction of phenolic compounds from hydrothermal processing of black liquor: Effect of reactor type and pH of recovered liquid phase

The goal of this work was to study the effect of pH on the extraction yield of phenolic compounds from liquid phases recovered after the hydrothermal treatment of black liquor in the batch and continuous reactors at 280 and 350 °C. The pH values of the recovered liquid phases under investigation were adjusted to 9, 8, and 7. The liquid-liquid extraction was subsequently performed using ethyl acetate for 4 h at room temperature. The identification and quantification of phenolic products were conducted using GC-Mass analysis. The main monomeric compounds identified in the aqueous phase were phenol, guaiacol, and syringol. The results indicated that reducing the pH slightly improved the phenol and guaiacol extraction from the various recovered liquid phases after hydrothermal treatment. However, reducing the pH of liquid phases greatly increased the extraction yield of syringol. This was very noticeable in the recovered liquid phases after treatment at 280 °C, where the quantity of syringol was initially high. Additionally, a lower pH hindered the ethyl acetate hydrolysis during liquid-liquid extraction. The extraction experiments with various pH also confirmed the superior performance of the continuous reactor over the batch reactor to obtain the phenolic compounds. In addition, the phenolic products degraded as the treatment temperature increased from 280 to 350 °C.

Thermodynamic and environmental assessment of black liquor supercritical water gasification integrated online salt recovery polygeneration system

Conventional black liquor treatment has weaknesses in pollution. Supercritical water gasification (SCWG) technology makes it possible to utilize the energy of black liquor cleanly. In this work, an auto-thermal SCWG black liquor polygeneration system integrated with online salt recovery was proposed. The performance of salt recovery and gasification was evaluated. The results show that the increasing gasification temperature, black liquor concentration, and salt discharge concentration are favorable to hydrogen production and system efficiency. For salt recovery, the sulfur-containing substances in black liquor are all converted into Na2S/NaHS and recovered in this system. Through exergy analysis, the major exergy destructions are caused by the oxidation unit, SCWG unit, and sub-critical heat transfer. Then, the discharge brine heat is utilized to heat oxygen and feed to reduce the exergy destruction of reaction and heat transfer, which improved the energy efficiency from 78.03% to 88.16%, and the exergy efficiency from 60.86% to 64.10%. After adding a discharge salt utilization unit, the system's hydrogen production is 58,438 Nm3/h and the steam supply is 70,455 kW. This work provides theoretical guidance for the design and establishment of a black liquor SCWG industry system.

Treatment of Pulp Black Liquor with an Ionic Liquid: Optimisation by Using Response Surface Methodology.

: In this study, selective extraction towards ionic liquid trihexyltetradecylphosphonium chloride ([P66614]Cl) of lignin residues, polysaccharides and organic acids present in black liquor (BL), the main principal wastewater of pulping industry was studied. With the objective of finding optimized conditions allowing to extract lignin resideus while polysaccharides and organic acids remain in aqueous solution, a design of experiments approach based on a response surface methodology was used. Three continuous factors, namely initial pH varying from 9 to 13.5, dilution of BL varying from 5 to 20 and volumetric ratio of black liquor vs. ionic liquid RV., varying from 1 to 19, were investigated. Concentration of ligni residues, polysaccharides and organic acids were measured using Folin-Ciocalteu method, the anthrone method and HPLC, respectively. Results showed that a multi-response optimization led to the extraction of 84.8 % of lignin residues, 66.0 % of polysaccharides, and no extraction of OA under optimised conditions.

Preparation of metakaolin-based geopolymer membrane and its application in black liquor treatment

In recent years, inorganic membrane filtration technology has become the most promising treatment option for treating papermaking black liquor and recovering lignin from black liquor. However, the preparation of most inorganic membranes requires sintering or high-cost raw materials, which leads to high cost in the application of black liquor treatment and lignin recovery. For this reason, in this study, a no-sintering, low-cost metakaolin-based geopolymer membranes (MGM) was prepared at room temperature using steel mesh with good ductility and processability as the substrate. The effects of slag doping on the mechanical properties, microstructure and separation properties of MGM were investigated. The results concluded that when the mass ratio of slag to metakaolin is 1:10 (MGM-10), the membrane has the best comprehensive performance. The compressive strength and pure water flux of MGM-10 were 23.94 MPa and 286.62 kg m−2 h−1, respectively. In the application of black liquor treatment and lignin separation and recovery from black liquor, MGM-10 showed excellent separation performance by removing 96% of TSS, 91.75% of COD and 98.97% of BL from black liquor after primary filtration. Compared with ceramic membranes prepared by sintering, MGM has cheaper raw materials and lower energy consumption, which is more promising for industrial scale applications.

Synthesis of C-S-H seeds using the waste solution of acid treatment of recycled concrete aggregates and black liquor

• Finer and well-dispersed C-S-H seeds was prepared using the two waste solutions. • Lignin in black liquor kept C-S-H seeds globular rather than traditional foil-like. • C-S-H seeds from the two waste solutions had a more prominent accelerating effect. For preparing finer and well-dispersed calcium-silicate-hydrate (C-S-H) seeds at a lower cost, the waste solution of acid treatment of recycled concrete aggregates (RCAs) and black liquor from pulping were used for the synthesis of C-S-H seeds. The results show that C-S-H seeds can be successfully fabricated by chemical co-precipitation reaction using the two waste solutions. Interestingly, it was globular rather than traditional foil-like. Furthermore, C-S-H seeds synthesized using the two waste solutions had smaller particle size and better dispersibility. More importantly, it had a more prominent accelerating effect to the strength development of mortar, significantly enhancing the early and long-term compressive strength of mortar.

Energy-efficient microbial electrochemical lignin and alkaline hydroxide recovery from DMR black liquor

Black liquor is a complex waste stream generated from the fast-expanding biorefinery industry, and the high management cost has been known as a major development barrier. In this work, we demonstrated a rationally designed 4-chamber microbial electrolysis process that was capable of recovering the value-added lignin, NaOH, and H2 products while removing waste organics from the Deacetylation and Mechanical Refining (DMR) black liquor, which could potentially reduce the disposal cost by up to 40%. The lab-scale MEC achieved 52% organic removal from a highly concentrated feedstock (28,960 ± 212 mg/L COD) and recovered 83.2 mM NaOH under a small voltage application (1.2 V). Lignin recovery was observed to be as high as 13.98 ± 0.28 g/L, and 0.35 L/L/day H2 was produced with a faradaic efficiency of 93.5%. This work provided a good example on how complex liquid waste stream can be valorized via multi-functional microbial electrochemical technology, and how the traditionally unfavored pH gradient in an electrochemical reactor can be manipulated for lignin precipitation and alkaline recovery at the same time. The versatility and good performance in concurrent contaminants removal, lignin precipitation, H2 production and NaOH recovery demonstrate a good potential for microbial electrolysis in black liquor treatment.

Conversion of carbohydrates to carboxylic acids during hydrothermal and oxidative treatment of concentrated kraft black liquor

Black liquor, a side stream of the kraft pulping process, contains valuable low molecular weight carboxylic acids and carbohydrates. Hydrothermal treatment and wet oxidation of black liquor with a dry matter content of 43 % were investigated as an approach to convert these carbohydrates to carboxylic acids to increase their concentration. Wet oxidation with H2O2 or O2 at 115–185 °C led to partial degradation of carbohydrates, but no significant formation of the investigated carboxylic acids, glycolic, lactic, formic and acetic acid, was detected. Treatment under N2 atmosphere at 185 and 220 °C finally led to an increase of the hydroxy acid concentration. After two hours of heat treatment at 220 °C, 90 % of the carbohydrates were degraded, coupled with a high carbon conversion efficiency of 32 % based on the formation of lactic acid and glycolic acid, of which the concentrations increased by 51 and 73 %, respectively.

Potential and mechanism for bioremediation of papermaking black liquor by a psychrotrophic lignin-degrading bacterium, Arthrobacter sp. C2

To meet the challenge of bioremediation of black liquor in pulp and paper mills at low temperatures, a psychrotrophic lignin-degrading bacterium was employed in black liquor treatment for the first time. In this study, Arthrobacter sp. C2 exhibited excellent cold adaptability and lignin degradation ability, with a lignin degradation rate of 65.5% and a mineralization rate of 43.9% for 3 g/L lignin at 15 °C. Bioinformatics analysis and multiple experiments confirmed that cold shock protein 1 (Csp1) was the dominant cold regulator of strain C2, and dye-decolorizing peroxidase (DyP) played a crucial role in lignin degradation. Moreover, structural equation modeling (SEM), mRNA monitoring, and phenotypic variation analysis demonstrated that Csp1 not only mediated cold adaptation but also modulated DyP activity by controlling dyp gene expression, thus driving lignin depolymerization for strain C2 at low temperatures. Furthermore, 96.4% of color, 64.2% of chemical oxygen demand (COD), and 100% of nitrate nitrogen (NO₃--N) were removed from papermaking black liquor by strain C2 within 15 days at 15 °C. This study provides insights into the association between the cold regulator and catalytic enzyme of psychrotrophic bacteria and offers a feasible alternative strategy for the bioremediation of papermaking black liquor in cold regions.

Production of volatile fatty acids concomitant with phosphorus removal and lignin recovery by co-fermentation of waste activated sludge and black liquor

Waste activated sludge (WAS) and black liquor (BL) are the stubborn solid waste and wastewater in the industry that need high investment and operational costs for treatment. In this study, co-fermentation of WAS and BL was performed following a novel process for the production of volatile fatty acids (VFAs) concomitant with phosphorus removal and lignin recovery. BL offers alkaline liquor for WAS pretreatment, and the organic carbon in BL can be used for fermentation. The results showed that the semi-continuous fermentation test at pH 10 and the addition of 800 mg/L of Mg2+ were the optimal conditions for the production of VFAs (approximately 15,000 mg/L) and P removal (≈94%). Additionally, Mg2+ was suited to remove P due to the weak adsorption of Mg2+ by BL under alkaline conditions. Moreover, the composition of VFAs was affected by the pH, for example, high ratios of acetate and propionate were obtained under conditions of high and low pH, respectively. The dominant functional bacteria of Alkalibacterium, Propionibacterium, Proteiniphilum, and Tessaracoccus were found through the analysis of microbial diversity to be responsible for the production of VFAs. The bioconversion of small molecular lignin was also demonstrated through the characterization analyses. Co-fermentation was suggested as an economic and eco-friendly strategy for the treatment and resource utilization of WAS and BL via the overall assessment of the technical process.

Activated carbon induced hydrothermal carbonization for the treatment of cotton pulp black liquor

Powdered activated carbon (PAC) was introduced into hydrothermal carbonization (HTC) as a catalyst for treatment of cotton pulp black liquor (CPBL) in the present work. The influence of main operating parameters on treatment efficiency in hydrothermal carbonization catalyzed by PAC (PAC-HTC) and changes of PAC due to hydrochar formation on PAC surfaces were studied. Experimental results showed that high temperature and sufficient carbonization time were crucial for HTC of CPBL. The presence of PAC in HTC resulted in significant improvement for CPBL decontamination for 6 h of reaction at 300 °C. Removals of chemical oxygen demand (COD), UV254 and lignin reached 89.59%, 99.71% and 99.79%, respectively. PAC can not only adsorb small molecule organics, but also promote the decomposition and carbonation of biomass macromolecules such as lignin. PAC showed outstanding reusability in the PAC-HTC process, as organics adsorbed on the surface of PAC participated in HTC reactions to realize in-situ regeneration. The PAC-HTC process developed in this work may provide a new alternative for CPBL treatment.

Laccase immobilization on nanoporous aluminum oxide for black liquor treatment

Nanoporous aluminum oxide coating has been successfully synthesized using different anodic synthesis conditions and self-assembled nanoporous with variable pore diameter, thickness and porosity were obtained. The Anodic Aluminum Oxide (AAO) coatings exhibited appropriate morphological characteristics which were employed for the Phebia brevispora BAFC 633 Laccase immobilization. Principal component analysis demonstrated that pH, contact time and enzyme concentration were the main variables which explain the total variation among the Laccase immobilization in the samples. The highest enzymatic activity was reported in the sample synthesized to 0.3 M of electrolyte concentration, 40°C of temperature and 30 V of anodization voltage. Laccase specific activity of 4.1 Ucm−2 could be obtained using an enzymatic concentration of 3.209 UL−1, pH 4.39 and contact time of 1.18 h according to the proposed regression model. Laccase/AAO bionanocatalyst can be easily collected and reserved 95.6% of initial activity after four cycles tests and immobilization yield of around 18.1%. Application of the immobilized Laccase for Black Liquor removal was also investigated. The bionanocatalyst showed better pH stability, 40% higher BL removal efficiency compared to free laccase after 40 min of reaction, and the ability to be collected and used up to twice for BL treatment. The novelty of this work contemplates the development of a bionanocatalyst from a nanoporous coating and immobilized Laccases that can be successfully applied for the treatment of effluents contaminated with black liquor.

Ultrafiltration process for lignin-lean black liquor treatment at different acid conditions

ABSTRACT Black liquor treatment by acid precipitation produces two main streams: the high purity precipitated lignin and the lignin-lean black liquor (a diluted lignin solution). Here, we evaluated the ultrafiltration process for lignin recovery from lignin-lean black liquor at different pH values (9.0, 9.5 and 10.0). The ultrafiltration process was able to retain 83 ± 0.5% of lignin from the lignin-lean black liquor at pH 9.0. The permeate flux increased with the decrease in pH value (steady state flux of 5.3 ± 0.0 L h−1m−2 at pH 9.0). Cake formation was the main fouling occurrence during lignin-lean black liquor filtrations. The weight average molecular weight of the lignin-lean black liquor decreased from 1866 to 1208 Da after the ultrafiltration process. The pH value did not significantly influence the molecular weight of permeate stream. Permeate samples presented lower hydroxyl content and higher syringyl(S):guaiacyl(G) ratios than feed samples. Thus, the ultrafiltration process was able to concentrate lignin from the lignin-lean black liquor and to produce a permeate with a narrow molecular weight distribution. The precipitation at more acid conditions is suggested to improve permeate flux lignin retention from lignin-lean black liquor.

Membrane Filtration Opportunities for the Treatment of Black Liquor in the Paper and Pulp Industry

Black liquor is a highly alkaline liquid by-product of the kraft pulping process, rich in organic molecules (hemicelluloses, lignin, and organic acids) and inorganic pulping chemicals such as sodium salts and sulphur-containing compounds. The release of this wastewater without further treatment could have serious environmental and financial implications. Therefore, a costly treatment process is used nowadays. Nanofiltration has been studied in the last few years as a promising alternative to recycle the cooking chemicals required for the separation of lignin and cellulose, but the development of pH-stable membranes with the potential to operate at industrial scales is fundamental in order to make this possible. In this study, the filtration performance of two in-house made membranes is evaluated and compared with a commercial NF membrane to determine the viability of their use for the treatment of black liquor. For this purpose, filtration experiments with simulated black liquor were performed. We identified that Membrane A has the higher potential for this application due to its competitive permeate flux (ca. 24 L m−2 h−1 at a trans-membrane pressure of 21.5 bar), and high rejection of organic components and salts from the cooking liquor (on average, 92.50% for the TOC, 84.10% for the CO32−, 88.70% for the sulphates, 73.21% for the Na+, and 99.99% for the Mg2+).

Assessment of black liquor hydrothermal treatment under sub- and supercritical conditions: Products distribution and economic perspectives

This study reports an alternative method for black liquor treatment with potential for energy and process savings in the paper and pulp industry. Gasification of black liquor was carried out under sub- and supercritical conditions, varying the black liquor feed composition (0.10, 2.55 and 5.00 wb%) and temperature (350, 425 and 500 °C). Liquid products were identified by high resolution mass spectrometry (FT-Orbitrap MS) and compounds belonging to classes O3 and O4 were found to be the most representative in the products of reactions performed at 500 °C. The mass spectra results also revealed the overall selectivity of reactions, where decarboxylation and demethoxylation reactions were favored under subcritical and supercritical conditions, respectively. Among the gaseous products, hydrogen and methane were produced with maximum of 69.04 and 28.75 mol%, respectively, at 2.55 wb% and 425 °C. The proposed thermodynamic modelling of the reaction system satisfactorily predicted the gas phase behavior of the system. In the economic analysis, the simulated conditions indicated that the main energy requirements for a scaled-up black liquor gasification process are related to the necessary heat exchangers and pressurizing of the black liquor solution. Furthermore, the cost of the black liquor gasification is around 0.06 US$ per kg of feed stream. Liquid and gaseous products from gasification could be obtained at a cost of 56.64 US$ and 3.35 US$ per tonne of stream, respectively. Therefore, black liquor gasification is an interesting route for obtaining combustible gases and value-added bioproducts.

Magnetic composite Ca(OH)2/Fe3O4 for highly efficient flocculation in papermaking black liquor without pH neutralization

Industrially, lignin in pulp liquor not only obstructed the realization of value-added products, but also threatened the aquatic ecosystem. A magnetic composite Ca(OH)2/Fe3O4, combining the eco-friendliness of Ca-based flocculants with the convenience of magnetic flocculation, was simply compounded to efficiently flocculate lignin from papermaking black liquor. Morphologic and structural features of the flocculant before and after flocculation were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM) and X-ray photoelectron spectroscopy (XPS). The flocculant Ca(OH)2/Fe3O4 presented mesoporous and core-shell structure, which acted directly in the sodium lignin aqueous solution without pH neutralization, maintaining high lignin removal between 91% and 95%. Ca(OH)2/Fe3O4 showed a wider salts (0–1 mol/L NaCl) and pH (9–12.5) tolerance. In actual pulp black liquor, Ca(OH)2/Fe3O4 exhibited high removal of 90.16% and 85.93% for lignin and chemical oxygen demand (COD), respectively. The flocculation performance of Ca(OH)2/Fe3O4 outdistanced that of the traditional flocculant polyacrylamide (PAM). It displayed magnetically separable with a good reusability. The removal of lignin could attain 90.54% even after 6 cycles. Charge neutralization, micro-bridging, destabilization and sedimentation were involved in the process of lignin flocculation. Consequently, Ca(OH)2/Fe3O4 presented huge potential in papermaking black liquor treatment.

Forward Black Liquor Acid Precipitation: Lignin Fractionation by Ultrafiltration.

Lignin recovery from black liquor is an important task for producing valuable chemical products. Acidification processes are currently applied by pulp and paper industries for black liquor treatment, in which two main streams are produced: the precipitated lignin fraction and a lignin-lean black liquor. Membrane filtration is a suitable alternative for lignin recovery from black liquor, but studies on lignin-lean black liquor filtration are scarce. Here, we evaluated the ultrafiltration process for lignin recovery from the both fractions of black liquor acidification. The lignin-lean black liquor presented 22 wt% of total solids with 4.6 wt% of lignin. Lignin retention from the lignin-lean black liquor by the 5 kDa ultrafiltration membrane was equal to 85%, with reduction in total solid concentration from 219.8 to 68.1 g L-1. Due to the relatively high solid concentration in the lignin-lean black liquor, cake formation was the main fouling mechanism during ultrafiltrations. The precipitated lignin solution presented 4.8 wt% of total solids with equivalent lignin concentration (4.7 wt%). The used membrane was able to retain almost 100% of solids and lignin from the solution prepared from the precipitated lignin. All fouling mechanisms were responsible for flux decay in ultrafiltration of the precipitated lignin solution. Steady state fluxes for lignin-lean black liquor and precipitated lignin solution were 0.9 and 15.9 L h-1 m-2, respectively. According to TGA analyses up to 800 °C, precipitated lignin and lignin-lean black liquor presented total mass losses of 63.5% and 44.3%, respectively. Also, the permeate samples presented lower mass losses than their respective feed samples. The ultrafiltration process reduced the average weight molar mass (Mw) of the precipitated lignin solution and lignin-lean black liquor from 1817 to 486 g mol-1and from 2876 to 1095 g mol-1, respectively. Thus, the 5 kDa ultrafiltration membrane was efficient for lignin recovery from the lignin-lean black liquor, while membranes with lower cut-off should be proposed for lignin purification from the precipitated fraction.