Dye Wastewater Treatment Research Articles

PVA/AMPS hydrogels: Promising adsorbents for wastewater treatment with high efficiency and reusability

AbstractA PVAMPS hydrogel was synthesized through chemical cross‐linking and semi‐interpenetration of Poly (vinyl Alcohol) (PVA) and 2‐Acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) with glutaraldehyde in distilled water. Various ratios of PVA/AMPS, namely PVAMPS‐1 (2:1), PVAMPS‐2 (1:1), and PVAMPS‐3 (1:2), were examined to understand their individual impacts on gel formation. The synthesis of hydrogels was confirmed using FT‐IR and solid‐state 13C NMR spectroscopy. The PVAMPS hydrogels demonstrated high efficiency as a selective adsorbent for removing cationic dyes, such as Methylene Blue, Safranine‐O, and Thionine, from aqueous solutions, with over 90% removal of cationic dyes observed within 18 hours. Regeneration and reusability studies revealed that even after four cycles, the adsorption capacity of the PVAMPS hydrogels remained exceptionally high, with removal rates exceeding 90% for Methylene Blue. However, for Safranine‐O and Thionine, the removal rates dropped to 20% and 23%, respectively, after four cycles. These findings underscore the promising potential of PVAMPS hydrogels for the removal of cationic dyes in wastewater treatment.

A novel cross-flow Ag/wood composite filter for high-concentration organic dye wastewater treatment

A novel cross-flow Ag/wood composite filter for high-concentration organic dye wastewater treatment

Novel carboxymethyl cellulose-based hydrogel embedded with metal organic framework for efficient cationic dye removal from water

The rGO/CMC/β-CD (RCβ) hydrogel was synthesized from reduced graphene oxide (rGO), β-cyclodextrin (β-CD) and sodium carboxymethyl cellulose (CMC) by radical polymerization. A novel hydrogel adsorbent was created by growing the metal-organic framework (Cu-BTC) in-situ on RCβ hydrogel, which has excellent adsorption capacities for cationic dyes in wastewater. The adsorption parameters such as the amount of adsorbent, pH of solution and adsorption time were optimized through batch adsorption experiments. Under the optimal conditions of pH 6.0, adsorbent dosage of 0.01 g and experimental temperature of 25 °C, Langmuir isothermal model was used to fit the maximum adsorption capacities of methylene blue (MB), crystal violet (CV) and malachite green (MG), which were 892.66, 842.75 and 633.77 mg g−1, respectively. The fitting results of adsorption kinetics revealed that the pseudo-second-order model can describe the adsorption process better. Based on proposed studies, the dye molecules were adsorbed onto RCβ@Cu-BTC hydrogel mainly through electrostatic interaction, hydrogen bonding and π–π interactions. After five cycles, the adsorption efficiency of the RCβ@Cu-BTC hydrogel for MB, CV and MG can still reach 80 %, 77 % and 72 %, which shows that the adsorbent has good adsorption performance. Various adsorption experiments shows that RCβ@Cu-BTC hydrogel has great potential in treating dye wastewater.

Efficient removal of cationic dyes by a bivanadyl capped, highly reduced Keggin polyoxometalate through flocculation

Flocculation is widely applied for dye wastewater treatment, due to its low cost, high efficiency and convenient operation. However, finding novel flocculant with high performance and low cost is still a challenge. Therefore, a fully characterized bivanadyl capped, highly reduced Keggin polyoxometalate (Et3NH)5[PMoV6MoVI6O40(VIVO)2] (PMoV2) was explored as flocculant for the treatment of simulated cationic dye wastewater. The effect of initial pH, PMoV2 dosage, and concentrations of dyes and inorganic salts on the flocculation rate of methylene blue (MB)/ crystal violet (CV)/rhodamine B (RhB) was investigated. Under the optimum conditions, the flocculation rates of MB, CV and RhB were 99.7%, 99.8% and 99.7% in 5min, respectively. In addition, PMoV2 and dyes could be easily recovered from flocs. PMoV2 exhibited high selectivity for CV in the binary systems of CV-MB and CV-MO. Even after five recycling tests, PMoV2 still kept high flocculation rate of MB/CV/RhB. The possible flocculation mechanisms for MB/CV/RhB single system, and MB-CV and MO-CV binary systems were charge neutralization, charge neutralization and π-π interaction, and charge neutralization and electrostatic interaction, respectively. PMoV2 was better than the reported flocculants in the respect of easy availability and operation conditions, reusability and high flocculation rate. The cost effectiveness, eco-friendly nature and excellent flocculation performance in individual and binary dye systems made PMoV2 competitive in the field of water environment remediation and material development. This is the first report about the flocculation activities of bivanadyl capped, highly reduced Keggin polyoxometalate.

High-Performance PBA12F@CS/PVA@ZIF-8 composite membranes for dye wastewater treatment

High-Performance PBA12F@CS/PVA@ZIF-8 composite membranes for dye wastewater treatment

Simultaneous optimization of electric production, azo dye, and yeast wastewater treatment in microbial fuel cell: Selection of the most suitable optimal conditions by PROMETHEE

Microbial fuel cell is a clean technology in which waste treatment and energy production continue simultaneously. Process performance depends on the independent variables and their interaction with each other specific to the waste to be treated. In this study, Microbial Fuel Cell (MFC), in which yeast production process wastewater is oxidized in the anolyte, and azo dye is reduced in the catholyte under abiotic conditions, was optimized using the Response Surface Methodology for maximum waste treatment and energy production. The independent variables were wastewater type, electrode array, and amount of sulfate-reducing inhibitor, while the dependent variables were azo dye removal, maximum power density, chemical oxygen demand (COD) removal, and coulomb efficiency. The effect of variables on all responses was determined using Analysis of Variance (ANOVA) and 3-dimensional (3D) graphs. The suitability of the models was tested by verification experiments under the determined optimum conditions (OPT 1, 2 and 3). Optimum experiments were ranked with the PROMETHEE approach according to azo dye removal (mg/L), maximum power density (mW/m2), COD removal (g/L), coulombic efficiency (%), and electrode cost (€/m2) criteria. The preference order of the optimum experiments was determined as OPT 1>OPT 2>OPT 3. With OPT 1, azo dye removal of 16.8 mg/L, maximum power density of 95.34 mW/m2, COD removal of 5.8 g/L and coulombic efficiency of 0.23 % were achieved. With a 1000 Ω external resistor, the maximum power density and coulombic efficiency increased to 147 mW/m2 and 1.5 %, respectively. In addition, the determined optimum experiments were examined using polarization curve and Electrochemical Impedance Spectroscopy.

Insights into mixed dye pollutant degradation by oxygen and air plasma bubbling array

Abstract Synthetic organic dye pollutants pose a serious threat to the aquatic ecological environment due to their difficulty in complete degradation. This study employed a plasma bubble array reactor to degrade individual and mixed dye pollutant solutions of Sunset Yellow (SY), Methyl Orange (MO), and Methyl Violet (MV). The degradation efficiencies and mechanisms of the plasma were investigated under different working gas atmospheres. It was found that oxygen plasma degraded the target dyes and their mixtures more significantly than air plasma. Specifically, compared with air plasma, the removal of single dyes SY, MO and MV by oxygen plasma was increased by 76.6%, 13.8% and 3%, respectively, after 20 min of treatment. As for mixed dyes, after 25 min treatment, oxygen plasma removed 99.1%, which was 31.6% higher than air plasma. However, the degradation kinetic order in oxygen plasma was SY > MO > MV, while that in air plasma was MV > MO > SY. Combined with the detection of reactive oxygen-nitrogen species (RONS), the results showed that the reactive oxygen species (ROS) played an important role in the degradation of SY, and it was also important for the degradation of MO, whereas both the ROS and reactive nitrogen species (RNS) were important for the degradation of MV. Scavenger experiments revealed that hydroxyl (·OH) and superoxide anion (·O2-) played the most important roles in the degradation process. The three dyes were basically completely degraded within 14-20 minutes of treatment, with corresponding yields of 1.94-2.79 g/kWh. Possible degradation pathways for each dye were deduced based on LC-MS and the toxicities of solutions were evaluated by phytotoxicity tests and ion chromatography. The results showed that the biotoxicity of the intermediates was significantly reduced. This study may provide a feasible option for effective application of plasma technology in organic dye wastewater treatment.

Preparation of Composites Derived from Modified Loess/Chitosan and Its Adsorption Performance for Methyl Orange

A modified loess/chitosan composite (ML@CS) was prepared via solution. The microstructure and physicochemical properties of ML@CS were characterised via scanning electron microscope (SEM), Zeta potential, X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR), and thermogravimetric analysis (TGA). An aqueous solution of methyl orange (MO) was used as simulated wastewater from which the influence of the initial concentration and pH of MO, the dosage amount and regeneration performance of ML@CS, adsorption temperature, and time on the adsorption effect of MO were systematically investigated. The adsorption kinetics, isothermal adsorption, and adsorption mechanism were also analysed. The results indicate that ML@CS had a good adsorption effect on MO. When the initial concentration of MO was 200 mg/L, pH was 5.0, and ML@CS dosage was 1.0 g/L, the adsorption equilibrium could be reached within 180 min at room temperature, and the equilibrium adsorption capacity and removal rate reached 199.52 mg/g and 99.75%, respectively. After five adsorption–desorption cycles, the MO removal rate remained above 82%. The adsorption behaviour of ML@CS for MO conforms to the pseudo–second–order kinetic model and the Langmuir isotherm adsorption model. The spontaneous exothermic process was mainly controlled by monolayer chemical adsorption and the physical adsorption only played an auxiliary role. ML@CS efficiently adsorbed MO in water and can be used as a high-efficiency, low-cost adsorbent for printing and dyeing wastewater treatment.

Comparative treatment of textile dye wastewater with chemical coagulants and bacterial exopolysaccharides

Traces of chemical coagulants, such as alum, commonly used in wastewater treatment, remain in the water effluent and also result in secondary sludge that is difficult to treat. On the other hand, Extracellular Polymeric Substances (EPS) are safer and can be used as alternative bio flocculants. A study was hence done to compare the effectiveness of the treatment of Reactive Black 5 (RB5) textile wastewater with chemical coagulants and bacterial EPS. The jar test method was used to treat the wastewater with Alum and Polyferrous Sulphate (PFS) at varied pH (2–10) and respective dose concentrations. EPS was produced by bacteria isolated from cotton gin trash soil collected from Kitui ginnery in Kenya. EPS treatment was done at 30 °C for 72 h. EPS-producing bacteria isolates were identified by molecular analysis. The chemically and EPS-treated wastewater was analyzed for color, Total Dissolved Solids (TDS), and Chemical Oxygen Demand (COD). Respective color and TDS removal capacity by PFS and alum were (86.1% and 42.18%) and (85.1% and 69%) at their optimal conditions of (pH 7 and 100 mg/L) and (pH 7 and 140 mg/L). Similarly, PFS and alum reduced COD by 27.25% and 26.65%. Respective dye removal by YEAK2 −5 and YEPD K2 −2 EPS was 69.1% and 85.7%. However, YEPD K2 −2 and YEAK2 −5 EPS caused a respective rise of TDS by 40.14% and 67.17%. The respective reduction of COD by YEPD K2 −2 and YEAK2 −5 EPS was 56.25% and 54.24%. The chemically and EPS-treated wastewater met the National Environment Management Authority (NEMA) limits. The YEPD K2 −2 and YEAK2 −5 isolates were both identified as Bacillus sp. GC–MS and FTIR analysis results indicated that the two EPS were heteropolysaccharides composed of different sugar derivatives and hydroxyl as the main functional group. The results for treatment of the dye wastewater by Alum, PFS, and EPS were therefore comparable. The bacterial EPS bio flocculants can therefore serve as effective and cleaner substitutes to the alum and PFS chemical coagulants.

Dye wastewater treatment using nonthermal plasma-treated copper oxide nanoparticles produced through electrolysis technique

Abstract Copper oxide nanoparticles (CuO-NPs) were produced by implementing an electrolysis technique. The prepared CuO-NPs were processed with nonthermal microwave plasma to check the effect of plasma treatment on their morphology and photocatalytic response. The plasma processed and blank CuO-NPs samples were used in dye degradation and water splitting applications under simulated sunlight. The blank sample posed undefined morphology, which turned to spherical particles on plasma processing. The particle size grows slightly with processing time. The blank samples showed a crystallite size of 4.51 nm, which grew to 5.34 nm, 5.40 nm, and 5.49 nm after plasma processing for 10, 20, and 30 min, respectively. The lattice parameter UT sample was measured to be 2.4308, with turned to 3.1091, 3.2112, and 3.3099 after 10, 20, and 30 min of plasma treatment, respectively. Similarly, band gap of CuO-NPs reduced from 2.4 eV to 2.24 eV after plasma processing for 30 min. The porosity of the nanoparticles also showed a similar trend. The plasma processing of CuO-NPs for 30 min produced the best results for photocatalytic water splitting and dye degradation applications. The photocatalytic activity revealed hydrogen evolution of 38.05 mmol.g-1.h-1 and dye removal efficiency of 91%.

Enhanced Salinity Gradient Energy Conversion by Photodegradable MXene/TiO2 Membrane Utilizing Saline Dye Wastewater

AbstractThe utilization of nanochannel membranes for harvesting salinity gradient energy has shown promising potential in addressing the energy crisis and environmental pollution issues. While previous studies have mainly focused on extracting salinity energy from mixing artificial seawater with river water, the research introduces a creative approach involving dye wastewater treatment using MXene/TiO2 membranes to achieve simultaneous photocatalytic degradation and power generation via salinity gradients. The built‐in electric field generated by MXene/TiO2 heterojunctions enhances ionic transport and electron‐hole separation. After photocatalytic treatment of saline dye wastewater, the membrane is defined as a photodegradable membrane. This membrane exhibits increased surface charge and expanded layer spacing to optimize salinity gradient energy conversion efficiency, yielding an impressive power density of up to 11.78 W m−2, which is 20% higher than that of the original MXene/TiO2 membrane. This work offers valuable insights into the development of multifunctional materials for sustainable power generation that comprehensively utilize industrial wastewater and domestic sewage.

A “self-driven” roving membrane with enhanced water-pumping and dye rejection performance

Considering that traditional membrane treatment of dyeing wastewater requires extra driving pressure, this work successfully prepared a roving membrane powered by the siphoning and wicking effects of the roving to separate dyes from dyeing wastewater. In this work, we found that bamboo pulp roving had the optimal siphoning and wicking performance, making it the focus for subsequent research. At the optimized interfacial polymerization parameters, the prepared roving membrane exhibited the optimal water-pumping and dye rejection performance, which reached 9.11 g/h and 99.58 %, respectively. The diameter of the rovings wrapped in polyamide layer became smaller and the wicking performance was improved. In addition, the thickness of polyamide layer with uniformly distributed nanoTiO2 decreased, and the crosslinking degree was enhanced. Ultraviolet light further contributed to the enhanced water-pumping and dye rejection performance of the piperazine/TiO2/trimesoyl chloride roving membrane. During the 120-h continuous filtration, the water-pumping and rejection performance was stable with only small fluctuations. Importantly, high dye retentions and water-pumping rate were achieved. In this study, we successfully prepared a membrane that is easy to use and does not require extra driving pressure, providing a new approach for dye wastewater treatment.

Synthesis, Magnetic, and Photocatalytic Activity of Polypyrrole-Based TiO2–Fe Catalyst for Wastewater Treatment

The primary aim of this study is to investigate the degradation efficacy of the Ppy/TiO2-Fe photocatalyst for MB dye in an aqueous solution. Firstly, the direct addition of TiO2 and Fe was done to prepare Ppy/TiO2-Fe photocatalyst. Fourier transformation infrared spectroscopy, XRD, SEM, BET surface area analysis, and magnetization tests established the formation of the Ppy/TiO2-Fe photocatalyst. The crystallite sizes of TiO2, Fe-TiO2, and Ppy/TiO2-Fe photocatalyst were estimated to be 24.99 nm, 21.94 nm, and 21.84 nm, respectively. For the synthesis confirmation, the FTIR spectrum confirmed the existence of Ti-O, Fe-O, and Ppy-related bonds. While comparing the SEM images, the impact of polypyrrole on the particle shape was observed with less aggregation and increased surface roughness. The VSM analysis revealed that incorporating polypyrrole (Ppy) into Fe-TiO2 significantly enhances its magnetic properties, with Ppy/TiO2-Fe exhibiting superparamagnetic behavior, characterized by a higher saturation magnetization (Ms) of 33.11 emu/g and a lower coercivity (Hc) of 0.160 Oe, compared to Fe-TiO2’s Ms of 1.09 emu/g and Hc of 341.39 Oe. The N2 sorption desorption, with a specific surface area of 2.25 × 102 m2/g, is beneficial for photocatalytic activity. The concentration of dye, amount of catalyst, pH, and temperature were studied to evaluate the photocatalytic efficiency of the synthesized Ppy/TiO2-Fe photocatalyst under different conditions. The findings revealed a degradation efficiency of 91.92%. The degradation rate reached 91.92% under optimal conditions within 120 min and could be fitted well by first-order kinetics. The photocatalytic efficiency was also evaluated for the scavenger, and the concentration of H2O2 and the reusability of the catalyst were demonstrated. Based on the observed results, the Ppy/TiO2-Fe photocatalyst could be applied more effectively and efficiently to photocatalytic degradation of organic dyes in wastewater treatment.

Optimization, purification and characterization of laccase from a new endophytic Trichoderma harzianum AUMC14897 isolated from Opuntia ficus-indica and its applications in dye decolorization and wastewater treatment.

Hazardous synthetic dye wastes have become a growing threat to the environment and public health. Fungal enzymes are eco-friendly, compatible and cost-effective approachfor diversity of applications. Therefore, this study aimed to screen, optimize fermentation conditions, and characterize laccase from fungal endophyte with elucidating its ability to decolorize several wastewater dyes. A new fungal endophyte capable of laccase-producing was firstly isolated from cladodes of Opuntia ficus-indica and identified as T. harzianum AUMC14897 using ITS-rRNA sequencing analysis. Furthermore, the response surface methodology (RSM) was utilized to optimize several fermentation parameters that increase laccase production. The isolated laccase was purified to 13.79-fold. GFC, SDS-PAGE revealed laccase molecular weight at 72kDa and zymogram analysis elucidated a single band without any isozymes. The peak activity of the pure laccase was detected at 50°C, pH 4.5, with thermal stability up to 50°C and half life span for 4h even after 24h retained 30% of its activity. The Km and Vmax values were 0.1mM, 22.22µmol/min and activation energy (Ea) equal to 5.71kcal/mol. Furthermore, the purified laccase effectively decolorized various synthetic and real wastewater dyes. Subsequently, the new endophytic strain produces high laccase activity that possesses a unique characteristic, it could be an appealing candidate for both environmental and industrial applications.

Exploring performance and mechanism of modified metal-organic frameworks in calcium alginate/polyvinyl alcohol double-network hydrogels for effective dye wastewater treatment

To address the growing problem of dye wastewater pollution, a novel MOFs adsorbent calcium alginate/polyvinyl alcohol@UiO-66 was developed using environmentally friendly polymers, sodium alginate and polyvinyl alcohol creating gel spheres with a double-network structure through cross-linking. UiO-66 metal-organic frameworks are then grown onto the gel spheres, resulting in the final CA/PVA@UiO-66 adsorbent. This adsorbent boasts a high surface area (17.4 m2/g) and a mesoporous-nested microporous structure. It effectively removes MB from water, the actual maximum adsorption capacity was measured at 275.8 mg/g, which surpasses most existing adsorbents. Remarkably, the adsorbent retains 93.9 % of its initial capacity even after 10 reuse cycles. The adsorption process adhered to the Redlich-Peterson model and the PFO model. The N2-Sorption isotherm, actual Methylene blue (MB) adsorption experiments, and model analysis further suggest that the adsorption process is a complex heterogeneous diffusion process involving simultaneous chemical and physical adsorption. Additionally, the adsorption process is endothermic, indicating that it can occur spontaneously at 298 K. Increasing the temperature promotes the forward progress of the adsorption reaction, thereby enhancing the adsorption capacity. The gel adsorbent exhibited excellent dye wastewater purification capabilities, coupled with commendable reusability.

Mixed matrix membranes by post-modified UiO-66-NH2 for efficient treatment of dyeing wastewater

The preparation of modified membranes utilizing the UiO-66 framework for wastewater filtration is regarded as one of the most promising approaches to wastewater treatment, owing to its high efficiency and cost-effectiveness. In this study, a post-modified MOF, UiO-66-RSA, was synthesized via the condensation reaction of UiO-66-NH2 and 2,4-dihydroxybenzaldehyde. PVDF mixed matrix membranes (MMMs) were fabricated for the first time by mixing UiO-66-RSA into PVDF using the non-solvent induced phase separation (NIPS) method. Compared to pure PVDF membranes, the newly developed membrane, M4, demonstrated enhanced compatibility and superior mechanical strength. In dyeing wastewater treatment applications, M4 showed excellent separation efficiency for dye and heavy metal mixed wastewater, achieving rejection rates exceeding 90%. Additionally, it maintained a high flux recovery rate (FRR > 90%) and rejection rate (Rejection > 90%) after six filtration cycles of dye-containing wastewater, indicating strong recyclability. These findings suggest that MMMs embedded with UiO-66-RSA hold significant promise for dyeing wastewater treatment.

Micro-nano bubbles in action: AC/TiO2 hybrid photocatalysts for efficient organic pollutant degradation and antibacterial activity

Developing highly active and sustainable photocatalysts is crucial for environmental remediation. This work focuses on the enhanced photocatalytic degradation efficiency of synthetic dyes using TiO2-coated AC hybrid photocatalysts under MNB aeration. The TiO2-coated AC hybrid photocatalyst (HP) was synthesized via a sol-gel method and characterized using XRD, FTIR, SEM, EDS, HR-TEM, and DRS. The study investigated the photocatalytic degradation of three dyes indigo carmine (IC), reactive black 5 (RB5), and methylene blue (MB) in wastewater, with initial dye concentrations ranging from 10 to 100 μM. Under UVA irradiation, the hybrid photocatalyst with MNB aeration (HP + UVA + MNB) achieved the highest degradation efficiencies of 69.09%, 60.06%, and 55.19% for IC, MB, and RB5, respectively. Further analysis showed that the chromophores and complex structures of these dyes were broken into intermediate products. The Langmuir-Hinshelwood kinetic model was used to describe the reaction mechanisms. The HP + UVA + MNB system demonstrated superior photocatalytic degradation activity, making it suitable for operational and environmental applications in dye wastewater treatment. Additionally, the antibacterial properties of AC and HP were tested at 100 μg/mL, showing effectiveness against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli.

Vacancy defect and piezoelectric field assisted photocatalytic performance of BiO(Cl1/3Br1/3I1/3)x for the degradation of organic pollutants

Semiconductor photocatalysts have been widely researched in wastewater treatment of organic dyes, among which bismuth halide semiconductors have shown great application prospects due to their unique layered structure and diverse micromorphology. As for photocatalysis, high concentration of photo-generated carriers and their effective separation are considered to be the key to obtain excellent photocatalytic performance. In view of the common issues of high bandgap energy and low carrier separation rate in bismuth halide, in this paper, the BiO(Cl1/3Br1/3I1/3)x catalysts with different proportions of Bi3+ and (Cl1/3Br1/3I1/3)- were designed and synthesized by hydrothermal method, through constructing hybrid energy levels and thus accomplishing by multi-halogen doping to widen the light absorption range. For another, the efficient separation of electrons and holes was achieved in BiO(Cl1/3Br1/3I1/3)x in virtue of a built-in field stemmed from the intrinsic piezoelectric effect, and band tilting. Meanwhile, more active sites were induced by Vo•• and VBiʹʹʹ due to the directional impact of the built-in field. Ultimately, BiO(Cl1/3Br1/3I1/3)5/7 demonstrated the optimum catalytic performance under the combined light irradiation and ultrasonic vibration, with the degradation efficiency of MB reaching 91.28% in 60 min and the k of 0.0360 min-1, and 97.44% degradation efficiency of Rh B within 18 min and the k of 0.1565 min-1 together with excellent cycling stability. The prepared BiO(Cl1/3Br1/3I1/3)5/7 catalyst has a huge application potential for the degradation of wastewater, taking full advantage of environmental vibration energy and light energy.

Development of the novel advanced electrooxidation process for decolorization of recalcitrant dyes (Methylene Blue, Rhodamine B, Congo Red): Effect of operating factors

The research aims to develop an advanced electrooxidation process for decolorization of recalcitrant dye. To enhance the radical formation, a combination of UV irradiation and electrooxidation (UV/EO) is used. Methylene Blue (MB), Rhodamine B (RB) and Congo Red (CR) dyes were used as model compounds to represent recalcitrant dyes. The performance of UV/EO process was investigated under various operating factors (i.e., current density (CD), voltage, pH, NaCl, anodic material), and compared with chlorination, UV irradiation, and electrooxidation (EO) process. MB was the highest resistant dye to the UV/EO process. The UV/EO process exhibited a synergistic effect on decolorization, and it removed MB 1.35 time faster than the EO process. Based on indirect determination of •OH, the •OH formation in the EO process was 2.4 ×10−13 M, which lower than that in the UV/EO process by 4 times. The second-order rate constant for MB oxidation by HO• (kHO•,MB) was 3.31 × 109 M−1s−1. The pseudo 1st-order decolorization kinetic (k’) was independent with voltages, but directly depended on CD and NaCl concentrations. Lower pH enhanced the k’ value. The specific energy consumption was in a range of 0.408 – 5.303 kWh/m3, depending on the k’ value. The energy consumption decreased with higher the k’ value, except for increasing CD. The Boron Doped Diamond (BDD) was more effective in the decolorization rate than dimensional active anode (DSA) by 1.6 times. Treatment of industrial dye wastewater by the UV/EO process eliminated color intensity (ADMI), COD, and BOD5 by 80 %, 91 %, and 9 %, respectively.

Enhanced biomass densification pretreatment using binary chemicals for efficient lignocellulosic valorization

Many effective pretreatment methods (such as dilute acid, dilute alkali, ionic liquids, etc.) have been developed for lignocellulose upgrading, but several defaults of low working mass, high sugar loss and extra cost of solid-liquid separation and water washing hinder their large-scale application in industry. Besides, the valorization of lignin-rich residue from pretreated biomass after hydrolysis or fermentation greatly contributes to the economy and sustainability of lignocellulosic biorefinery, which is usually underestimated. This study developed a densification pretreatment with binary chemicals (densifying lignocellulosic biomass with sulfuric acid (SA) and metal salt (MS) followed by autoclave treatment ((DLCA(SA-MS)), which was conducted under mild condition (121 °C) with a biomass working mass as high as 400 kg/m3. The DLCA(SA-MS) biomass achieved over 95% sugar retention, 90% enzymatic sugar conversion and a high concentration of fermentable sugar (212.3 g/L) with superior fermentability. Furthermore, bio-adsorbent derived from DLCA(SA-MS) biomass residue was highly adsorptive and suitable for dyeing wastewater treatment, providing a feasible and eco-friendly method for lignin-rich residue valorization. These findings indicated that DLCA(SA-MS) pretreatment enables the full-component utilization of biomass and boosts the economic viability of lignocellulosic biorefinery.