Heavy Metal Ions Removal from Aqueous Solutions by Treated Ajwa Date Pits: Kinetic, Isotherm, and Thermodynamic Approach

Propranolol adsorption onto multiwalled carbon nanotubes modified by green synthesis: pH, kinetic, and equilibrium studies

This research investigated the adsorption of propranolol (PROP) by functionalized green carbon nanotubes (MWCNT-B), assessing the influence of pH, in addition to kinetic, equilibrium, and thermodynamic studies and reuse of the material. For this purpose, speciation of PROP and the point of zero charge (pHPZC) of MWCNT-B were performed, indicating a pKa of 9.67 and pHPZC of 3.31. The adsorption tests at different pH values revealed that in the range of pH 3 to 9, there is no significant variation in PROP uptake, despite this, at pH 11, the removal decreases. Regarding PROP adsorption, the equilibrium time ranged from 30 to 90 min, and the PFO model best represented the kinetic data. The Langmuir model was more predictive in representing isotherms (R2 > 0.95), and the adsorption process was spontaneous and favorable (ΔG <  - 20 kJ mol-1) and indicated exothermic behavior (ΔH =  - 33 kJ mol-1) for PROP removal. In addition, the material showed satisfactory thermal regeneration results and can be reused for four cycles. The results suggest that MWCNT-B is an attractive adsorbent and exhibits effective removal of propranolol from aqueous matrices.

Ameliorating and Therapeutic Impact of Curcumin Nanoparticles Against Aluminum Oxide Nanoparticles Induced Kidney Toxicity, DNA Damage, Oxidative Stress, PCNA and TNFα Alteration in Male Rats

Aluminum oxide nanoparticles (Al2O3 NPs) are among the most extensively utilized nanoparticles in nanotechnology and that have negative impacts on the environment. Therefore, the intention of this work is to investigate the protective and therapeutic effects of curcumin in nanoform (Cur NPs) against Al2O3 NPs induced kidney toxicity, oxidative stress, DNA damage, and changes in necrosis factor alpha (TNFα) and proliferating cell nuclear antigen (PCNA) expressions in male rats. Fifty healthy adult male were divided into five groups [G1, control; G2, received 50 mg/kg/day for 4 weeks of Cur NPs orally; G3, received 6 mg/kg BW orally for 4 weeks of Al2O3 NPs; G4, (Cur NPs + Al2O3 NPs) received Cur NPs and Al2O3 NPs at a dose similar to G2 and G3, respectively for 4 weeks; G5, (Al2O3 NPs + Cur NPs) received Al2O3 NPs at a dose similar to G3 for 4 weeks then received Cur NPs at a dose similar to G2 for another 4 weeks]. Current results revealed that Al2O3 NPs induced a significant elevation in serum urea, creatinine, chloride, calcium, kidney malondialdehyde (MDA), DNA damage, injury, TNFα and PCNA expressions and a significant depletion in serum potassium, kidney superoxide dismutase (SOD), glutathione (GSH) as compared to control. On the other hand, treatments of Al2O3 NPs with Cur NPs induced modulation in all altered parameters and improved kidney functions and structure, with best results for the Al2O3 NPs + Cur NPs than Cur NPs + Al2O3 NPs. In conclusion, Cur NPs has the capacity to mitigate the renal toxicity induced by Al2O3 NPs in male albino rats.

Correction: Azam et al. Heavy Metal Ions Removal from Aqueous Solutions by Treated Ajwa Date Pits: Kinetic, Isotherm, and Thermodynamic Approach. Polymers 2022, 14, 914

In the original publication, there was a mistake in Figure 2B as the wrong image was uploaded [...].

Investigation of the Potential of Repurposing Medium-Density Fiberboard Waste as an Adsorbent for Heavy Metal Ion Removal

Medium-density fiberboard (MDF) waste generation has increased steadily over the past decades, and therefore, the investigation of novel methods to recycle this waste is very important. The potential of repurposing MDF waste as an adsorbent for the treatment of Cd(II), Cu(II), Pb(II), and Zn(II) ions in water was investigated using MDF offcuts. The highest adsorption potential in single-metal ion solution systems was observed for Pb(II) ions. The experimental data of Pb(II) ions fit well with the Freundlich isotherm and pseudo-second-order kinetic models. Complexation and electrostatic interactions were identified as the adsorption mechanisms. The adsorption behavior of multi-metal ion adsorption systems was investigated by introducing Cd(II) ions as a competitive metal ion. The presence of the Cd(II) ions reduced the adsorption potential of Pb(II) ions, yet the preference for the Pb(II) ions remained. Regeneration studies were performed by using 0.1 M HCl as a regeneration agent for both systems. Even though a significant amount of adsorbed metal ions were recovered, the adsorption potential of the MDF was reduced in the subsequent adsorption cycles. Based on these results, MDF fines have the potential to be used as an economical adsorbent for remediation of wastewater containing heavy metal ions.

The effect of carbonization temperature on textural properties of sewage sludge-derived biochars as potential adsorbents

This article presents ways of recovering waste in the form of anaerobically digested and dried sewage sludge (average humidity approx. 6 wt%) by carbonization at various temperatures in the range of 400-900 °C. The resulting products, biochars, are investigated in terms of yield, surface properties and Raman spectra analysis. The sorption capacity of biochars differs depending on the carbonization temperature. The experimental amount of adsorbed CO2 slowly increases with the carbonization temperature from 0.212 mmol/g at 400 °C to the highest value of 0.415 mmol/g, which is achieved at 900 °C by slow carbonization at a rate of 10 °C/min. Additionally, there is a strong positive dependence of the adsorption capacity on the micropore volume. Higher carbonization temperatures support the powerful formation of micropores and improve their sorption capacity.

Effective removal of nitrate and phosphate using graphene nanosheets synthesized from waste plastics

In this work, waste plastics have been used with bentonite clay to produce silica-containing graphene nanosheets (GNs) for adsorption of nitrate and phosphate from synthetic water. The GNs were obtained by the two steps process, namely (1) pyrolysis at 750 °C and (2) ball milling. Then, GNs were characterized by Raman spectroscopy, FTIR, XRD, FESEM, HRTEM and EDX spectroscopy, which provided the details of material's morphology, surface properties, and composition. From Raman spectroscopy, D and G bands were found at 1342 cm-1 and 1594 cm-1, respectively, which confirmed the presence of nanosheets on the graphene surface. Furthermore, the layers of nanosheets were confirmed by the HRTEM analysis and XRD peaks. In analytical study, the batch experiment was conducted to investigate the influence of operational parameters such as pH (03-12), contact time (05-120 min), adsorbent dosage (0.01-0.06 g), and initial concentrations of adsorbates (10-50 mg/L for nitrate and 03-15 mg/L for phosphate) on adsorption process. The removal percentage of nitrate and phosphate at optimum dosage = 0.05 g, pH = 6.5, contact time = 60 min, nitrate concentration = 30 mg/L, and phosphate concentration = 09 mg/L were found to be 85 and 91, respectively. The highest adsorption capacity of nitrate and phosphate was found to be 53 mg/g and 16.4 mg/g, respectively. The adsorption behaviour of both nitrate and phosphate showed chemisorption as the experimental data were well fitted by the pseudo-2nd-order kinetic and Langmuir isotherm model. Life cycle cost analysis (LCCA) of the synthesis process was conducted to evaluate the cost-benefit analysis for commercial feasibility. The estimated price for the synthesis of GNs using 1 kg of waste plastics and bentonite clay as precursor was $4.21, suggesting commercialization.

Novel Chitosan-ZnO nanocomposites derived from Nymphaeaceae fronds for highly efficient removal of Reactive Blue 19, Reactive Orange 16, and Congo Red dyes

The primary aim of this investigation was to synthesise novel adsorbent by incorporating greenly synthesized zinc oxide nanoparticles into chitosan matrix (G-ZnO-Cs). The production of ZnO Nanoparticles via a green approach involved the utilization of extracts derived from Nymphaeaceae fronds. This assertion was substantiated by the application of Field Emission Scanning Electron Microscopy (FESEM) and X-ray Diffraction (XRD) analytical techniques. Several Analytical methods such as Fourier Transform Infrared spectroscopy (FT-IR), Energy Dispersive X-ray Analysis (EDAX), FESEM, Thermogravimetric Analysis (TGA), XRD, Brunauer-Emmett-Teller (BET) analysis, and point-of-zero charge determination were used to characterize G-ZnO-Cs. Further study investigates the impact of five key processing parameters, namely pH, interaction duration, G-ZnO-Cs dosage, temperature, and initial concentration of dyes, on the removal of three organic dyes Reactive Blue 19 (RB 19), Reactive Orange 16 (RO 16), and Congo Red (CR) The adsorption process of Reactive Blue 19 (RB 19), Reactive Orange 16 (RO 16), and Congo Red (CR) dyes on G-ZnO-Cs were determined to comply to the pseudo-second-order (PSO) and Langmuir models, as determined through equilibrium and kinetic experiments. The highest adsorption capabilities for RB 19, RO 16 and CR dye were revealed to be 219.6 mg/g, 129.6 mg/g, and 118.8 mg/g, respectively. The elimination success rate of the fixed-bed column approach for treating huge volumes was highlighted in the conducted research. Moreover, the G-ZnO-Cs composite exhibited significant reusability due to its ability to undergo elution and simultaneous regeneration processes.

Super capacity of ligand-engineered biochar for sorption of malachite green dye: key role of functional moieties and mesoporous structure

This study synthesized a new thiomalic acid-modified rice husk biochar (TMA-BC) as a versatile and eco-friendly sorbent. After undergoing chemical treatments, the mercerized rice husk biochar (NaOH-BC) and TMA-BC samples showed higher BET surface area values of 277.1 m2/g and 305.8 m2/g, respectively, compared to the pristine biochar (BC) sample, which had a surface area of 234.2 m2/g. In batch adsorption experiments, it was found that the highest removal efficiency for malachite green (MG) was achieved with TMA-BC, reaching 96.4%, while NaOH-BC and BC exhibited removal efficiencies of 38.6% and 27.9%, respectively, at pH 8. The engineered TMA-BC exhibited a super adsorption capacity of 104.17 mg/g for MG dye at pH 8.0 and 25 °C with a dosage of 2 g/L. The SEM, TEM, XPS, and FTIR spectroscopy analyses were performed to examine mesoporous features and successful TMA-BC carboxylic and thiol functional groups grafting on biochar. Electrostatic forces, such as π - π interactions, hydrogen bonding, and pore intrusion, were identified as key factors in the sorption of MG dye. As compared to single-solution adsorption experiments, the binary solution experiments performed at optimized dosages of undesired ions, such as humic acid, sodium dodecyl sulfate surfactant, NaCl, and NaSCN, reflected an increase in MG dye removal of 2.8%, 8.7%, 5.4%, and 12.7%, respectively, which was attributed to unique mesoporous features and grafted functional groups of TMA-BC. Furthermore, the TMA-BC showed promising reusability up to three cycles. Our study indicates that mediocre biochar modified with TMA can provide an eco-friendly and cost-effective alternative to commercially accessible adsorbents.

Removal of Malachite Green by Poly(acrylamide-co-acrylic acid) Hydrogels: Analysis of Coulombic and Hydrogen Bond Donor-Acceptor Interactions

Water pollution caused by dyes poses a significant threat to life on earth. Poly(acrylamide-co-acrylic acid) hydrogels are widely used to treat wastewater from various pollutants. This study aims to examine the removal of malachite green (MG), a harmful and persistent dye that could cause extensive environmental damage, from an aqueous solution by adjusting the initial concentration of acrylamide (AM) and the degree of copolymer crosslinking. The copolymer hydrogels efficiently eliminate MG in a brief timeframe. The most successful hydrogel accomplished a removal rate exceeding 96%. The copolymer of 4 wt % 1,6-hexanediol diacrylate and a concentration of 100 mg/mL AM was effective. The degree of swelling was affected by crosslinking density as expected, with low crosslinking ratios resulting in significant swelling and high ratios resulting in less swelling. To evaluate the results, a docking approach was used which presented three crosslinked models: low, medium, and high. The copolymer-dye hydrogel system displayed robust hydrogen bonding interactions, as confirmed by the high quantities of both donors and acceptors. It was determined that MG contains six rotatable bonds, enabling it to adapt and interact with the copolymer chains. The dye and copolymer enhance H-bond formation by providing two hydrogen bond donors and 16 hydrogen bond acceptors, respectively. Through capitalizing on cationic and anionic effects, the ionic MG/copolymer hydrogel system improves retention efficiency by enhancing attraction between opposing charges. It is interesting to note that the synthesized copolymer is able to remove 96.4% of MG from aqueous media within one hour of contact time.

Exploring synergistic effects in physical-chemical activation of Acorus calamus for water treatment solutions

The research proposed a novel method of obtaining sorption material from readily available Acorus calamus biomass through a combination of physical and chemical activation processes. The material with the highest specific surface area (1652 m2 g-1) was obtained by physical activation with CO2, followed by chemical activation with KOH. Reversing the order of activation methods resulted in a lower specific surface area (1014 m2 g-1) of the carbon sample. Chemical activation produced activated carbon with a surface area of 1066 m2 g-1-, while physical activation produced 390 m2 g-1. This confirms the synergistic effect of combining the two activation methods for biocarbon. It was observed that physical activation with CO2 generates a diverse range of pores, including meso- and macropores, while chemical activation induces the formation of micropores. In contrast, reversing the order of these processes leads to the degradation of the porous structure. The application of physical-chemical activation with synergistic effects represents a significant advancement in producing high-quality activated biocarbon for various applications, such as wastewater treatment and energy storage. The combination of the two activation methods resulted in a synergistic effect, leading to the production of carbon material of higher quality. Additionally, the diversified pore sizes will enable the sorption of various pollutants in the aquatic environment and air pollutants, where gas particles are much smaller.

Selective separation of metals from wastewater using sulfide precipitation: A critical review in agents, operational factors and particle aggregation

Extensive research has been conducted on the separation and recovery of heavy metals from wastewater through the targeted precipitation of metal sulfides. It is necessary to integrate various factors to establish the internal correlation between sulfide precipitation and selective separation. This study provides a comprehensive review of the selective precipitation of metal sulfides, considering sulfur source types, operating factors, and particle aggregation. The controllable release of H2S from insoluble metal sulfides has garnered research interest due to its potential for development. The pH value and sulfide ion supersaturation are identified as key operational factors influencing selectivity precipitation. Effective adjustment of sulfide concentration and feeding rate can reduce local supersaturation and improve separation accuracy. The particle surface potential and hydrophilic/hydrophobic properties are crucial factors affecting particle aggregation, and methods to enhance particle settling and filtration performance are summarized. The regulation of pH and sulfur ion saturation also controls the zeta potential and hydrophilic/hydrophobic properties on the particles surface, thereby affecting particle aggregation. Insoluble sulfides can decrease sulfur ion supersaturation and improve separation accuracy, but they can also promote particle nucleation and growth by acting as growth platforms and reducing energy barriers. The combined influence of sulfur source and regulation factors is vital for achieving precise separation of metal ions and particle aggregation. Finally, suggestions and prospects are proposed for the development of agents, kinetic optimization, and product utilization to promote the industrial application of selective precipitation of metal sulfides in a better, safer, and more efficient way.

Adsorption of hexavalent chromium, Rhodamine B and Congo red simultaneously in aquatic by zeolitic imidazolate framework coupling carbon nanotubes

Zeolitic imidazolate framework/carbon nanotube (ZIF-67/CNTs) was prepared by precipitation method. ZIF-67/CNTs maintained the characteristics of large specific surface area and high porosity of ZIFs, showing stable cubic structure. The adsorption capacities of ZIF-67/CNTs for Cong red (CR), Rhodamine B (RhB) and Cr(VI) were 36.82 mg/g, 1421.29 mg/g and 716.67 mg/g under the conditions of 2:1, 3:1 and 1:3 masses of ZIF-67 and CNTs, respectively. The optimum adsorption temperature of CR, RhB and Cr(VI) were 30 °C, and the removal rates at the adsorption equilibrium were 81.22%, 72.87% and 48.35%. The adsorption kinetic model of the three adsorbents on ZIF-67/CNTs was consistent with the quasi-second order reaction model, and the adsorption isotherms were more consistent with adsorption law of Langmuir. The adsorption mechanism for Cr(VI) was mainly electrostatic interaction, and the adsorption mechanism for azo dyes was the combination of physical and chemical adsorption. This study would provide theoretical basis for further developing metal organic framework (MOF) materials for environmental applications.

Hydrogen sulfide removal from normal heptane using zinc oxide, silicon dioxide and zeolite 13X: adsorption capacity, kinetics, selectivity, breakthrough and regeneration

This article focuses on the H2S adsorption from normal heptane (nC7) as synthetic natural gas liquids (NGL) using ZnO, SiO2 and zeolite 13X in static mode. Results of the isotherm and kinetics of the investigated adsorbents for H2S adsorption under ambient condition showed that ZnO had the highest H2S adsorption capacity between 260 and 700 mgH2S.g-1 in the initial concentration range of 2500 and 7500 ppmH2S with an equilibrium time of less than 30 minutes. Additionally, the ZnO selectivity was greater than 3.16. In continued, H2S removal from nC7 with ZnO was examined in dynamic mode. The H2S breakthrough time for ZnO reduced from 210 to 25 minutes as weight hourly space velocity (WHSV) was increased from 5 to 20 h-1 at 30 bar. Also, the breakthrough time at 30 bar was about 2.5 times greater than that at atmospheric pressure. Furthermore, H2S/CO2 mixture (i.e., 1000 ppmH2S + 1000 ppmCO2) caused the H2S breakthrough time to increase approximately by 1.11-fold. Alternatively, the ZnO regeneration conditions with hot stagnant air were optimized at different initial H2S concentrations (1000 ~ 3000 ppmH2S) using the Box-Behnken design. For instance, ZnO contaminated with 1000 ppmH2S was regenerated with an efficiency of more than 98 % for 160 minutes at 285 °C.

Photocatalytic degradation of aqueous methylene blue using ca-alginate supported ZnO nanoparticles: point of zero charge role in adsorption and photodegradation

A novel insoluble Ca-Alginate created from soluble Na-Alginate was used as a support substrate for ZnO nanoparticles producing ZnO@Ca-Alginate composite photocatalyst. Fourier Transform Infrared (FT-IR), Ultraviolet-Visible (UV-Vis), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), and X-ray Diffraction (XRD) analysis techniques were used in the characterization of the prepared ZnO@Ca-Alginate. The ZnO@Ca-Alginate was tested for its potential use in the photodegradation of Methylene Blue (MB) from an aqueous solution under solar-simulated light. This composite photocatalyst efficiency in MB removal was compared with naked ZnO potential considering different conditions and parameters (e.g. pH, MB concentration, amount of photocatalyst, and irradiation time). The MB concentrations were identified using UV-vis spectrophotometric methods. While, high-performance liquid chromatography (HPLC), Total organic carbon (TOC) analysis, and other elemental analyses were used to confirm the MB complete mineralization. The MB photodegradation results were performed by using UV-vis analysis., the results showed that up to 95% of MB (40 mL, 40 ppm) was removed within 30 min of irradiation using either ZnO@Ca-Alginate or naked ZnO. The pH and the zero-charge point (Pzc) values play a main role in the adsorption and photodegradation results. The Pzc values for Ca-Alginate, ZnO, and Zn@Ca-Alginate were 6.5, 8.8, and 6.8 respectively. The prepared composite catalyst showed a maximum adsorption and photodegradation in a basic to slightly basic medium, the MB completely removed at pH of 7.7 within an hour of irradiation. The complete miniralzation of MB at the end of the photodegrdation process was confirmed. Here it is proved that the ZnO@Ca-Alginate photocatalyst can be recovered and reused without any significant decrease in its effectiveness.

Valorization of Fibrous Plant-Based Food Waste as Biosorbents for Remediation of Heavy Metals from Wastewater-A Review

Mobilization of heavy metals in the environment has been a matter of concern for several decades due to their toxicity for humans, environments, and other living organisms. In recent years, use of inexpensive and abundantly available biosorbents generated from fibrous plant-based food-waste materials to remove heavy metals has garnered considerable research attention. The aim of this review is to investigate the applicability of using fibrous plant-based food waste, which comprises different components such as pectin, hemicellulose, cellulose, and lignin, to remove heavy metals from wastewater. This contribution confirms that plant-fiber-based food waste has the potential to bind heavy metals from wastewater and aqueous solutions. The binding capacities of these biosorbents vary depending on the source, chemical structure, type of metal, modification technology applied, and process conditions used to improve functionalities. This review concludes with a discussion of arguments and prospects, as well as future research directions, to support valorization of fibrous plant-based food waste as an efficient and promising strategy for water purification.

Adsorption Capacity of Silica SBA-15 and Titanosilicate ETS-10 toward Indium Ions

Indium is an extremely important element for industry that is distributed in the Earth's crust at very low concentrations. The recovery of indium by silica SBA-15 and titanosilicate ETS-10 was investigated at different pH levels, temperatures, times of contact and indium concentrations. A maximum removal of indium by ETS-10 was achieved at pH 3.0, while by SBA-15 it was within the pH range of 5.0-6.0. By studying kinetics, the applicability of the Elovich model for the description of indium adsorption on silica SBA-15 was shown, while its sorption on titanosilicate ETS-10 fitted well with the pseudo-first-order model. Langmuir and Freundlich adsorption isotherms were used to explain the equanimity of the sorption process. The Langmuir model showed its applicability for the explanation of the equilibrium data obtained for both sorbents, the maximum sorption capacity obtained using the model constituted 366 mg/g for titanosilicate ETS-10 at pH 3.0, temperature 22 °C and contact time 60 min, and 2036 mg/g for silica SBA-15 at pH 6.0, temperature 22 °C and contact time 60 min. Indium recovery was not dependent on the temperature and the sorption process was spontaneous in nature. The interactions between the indium sulfate structure and surfaces of adsorbents were investigated theoretically using the ORCA quantum chemistry program package. The spent SBA-15 and ETS-10 could be easily regenerated by using 0.01 M HCl and reused with up to 6 cycles of adsorption/desorption with a decrease in the removal efficiency between 4% and 10% for SBA-15 and 5% and 10% for ETS-10, respectively.

Wastewater-Irrigated Vegetables Are a Significant Source of Heavy Metal Contaminants: Toxicity and Health Risks

Water contaminated with heavy metals constitutes an important threat. This threat is a real problem with a negative impact in some developing countries where untreated industrial effluents are used for irrigation. The present study examines heavy metals in wastewater-irrigated vegetables (apple gourd, spinach, cauliflower, sponge gourd, and coriander) water, and soil from Chenab Nagar, Chiniot, Pakistan. In particular, the metals quantified were cadmium (Cd), chromium (Cr), cobalt (Co), nickel (Ni), lead (Pb), and manganese (Mn). Among them, Cr and Co in crops irrigated -wastewater exceeded the levels recommended by the World Health Organization (WHO). In contrast, Ni, Cu, Pb, and Mn concentrations were in line with WHO standards. Compared with the limits established by the Food and Agriculture Organization of the United Nations (FAO), all the study vegetables presented higher (thus unsafe) concentrations of Cd (0.38 to 1.205 mg/Kg). There were also unsafe concentrations of Cr in coriander, sponge gourd, and cauliflower. Pb was found at an unsafe concentration (0.59 mg/Kg) in cauliflower. Conversely, Ni and Mn concentrations were below the maximum permissible limits by WHO, and FAO in all of the analyzed samples. The contamination load index (CLI) in soil, bioconcentration factor (BCF) in plants, daily intake of metals (DIM), and health risk index (HRI) have also been evaluated to estimate the potential risk to human health in that area. We have found an important risk of transitions of Pb, Cd, Cr, and Co from water/soil to the edible part of the plant. The highest HRI value associated with Cd (6.10-13.85) followed by Cr (1.25-7.67) for all vegetable samples presented them as high health risk metal contaminants. If the issue is not addressed, consumption of wastewater-irrigated vegetables will continue posing a health risk.

Finding the best combination of autochthonous microorganisms with the most effective biosorption ability for heavy metals removal from wastewater

The presence of heavy metals (HMs) in the environment represents a serious environmental problem. In this regard, this work was conceived with the aim of finding, among indigenous microorganisms, the species and their combinations with the best biosorption activity for the following HMs: zinc, lead, cadmium, copper, and nickel. The experiment was carried out in several steps: (1) isolation and identification of microbial strains from the Central Effluent Treatment Plant’s wastewater; (2) studying the interaction of microorganisms and the ability to form biofilms in 96-well plates; (3) testing the resistance of biofilms to HMs; (4) testing the growth of biofilms on AMB media carriers in the presence of HMS; and (5) biosorption assay. The selected strains used in this study were: Enterobacter cloacae, Klebsiella oxytoca, Serratia odorifera, and Saccharomyces cerevisiae. The best biofilm producers in control medium were K. oxytoca/S. odorifera (KS), followed by K. oxytoca/S. odorifera/S. cerevisiae (KSC), and E. cloacae/K. oxytoca/S. odorifera (EKS) after 10 days of incubation. Mixed cultures composed of three species showed the highest resistance to the presence of all tested metals. The best biosorption capacity was shown by KSC for Cu²⁺ (99.18%), followed by EKS for Pb²⁺ (99.14%) and Cd²⁺ (99.03%), K. oxytoca for Ni²⁺ (98.47%), and E. cloacae for Zn²⁺ (98.06%). This research offers a novel approach to using mixed biofilms for heavy metal removal processes as well as its potential application in the bioremediation of wastewater.

Nanoporous Carbon from Oil Palm Leaves via Hydrothermal Carbonization-Combined KOH Activation for Paraquat Removal

In this study, nano-porous carbon was completely obtained from oil palm leaves (OPL) by hydrothermal pretreatment with chemical activation, using potassium hydroxide (KOH) as an activating agent. Potassium hydroxide was varied, with different ratios of 1:0.25, 1:1, and 1:4 (C: KOH; w/w) during activation. The physical morphology of nano-porous carbon has a spongy, sponge-like structure indicating an increase in specific surface area and porosity with the increasing amount of KOH activating agent. The highest specific surface area of OPL nano-porous carbon is approximately 1685 m²·g^-1, with a total pore volume of 0.907 cm³·g^-1. Moreover, the OPL nano-porous carbon significantly showed a mesoporous structure designed specifically to remove water pollutants. The adsorptive behavior of OPL nano-porous carbon was quantified by using paraquat as the target pollutant. The equilibrium analyzes were explained by the Langmuir model isotherm and pseudo-second-order kinetics. The maximum efficiency of paraquat removal in wastewater was 79%, at a paraquat concentration of 400 mg·L^-1, for 10 min in the adsorption experiment. The results of this work demonstrated the practical application of nano-porous carbon derived from oil palm leaves as an alternative adsorbent for removing paraquat and other organic matter in wastewater.