Defatted algal biomass as a non-conventional low-cost adsorbent: surface characterization and methylene blue adsorption characteristics

A Holistic Approach to Circular Bioeconomy Through the Sustainable Utilization of Microalgal Biomass for Biofuel and Other Value-Added Products

Emissions from transportation and industry primarily cause global warming, leading to floods, glacier melt, and rising seas. Widespread greenhouse gas emissions and resulting global warming pose significant risks to the environment, economy, and society. The need for alternative fuels drives the development of third-generation feedstocks: microalgae, seaweed, and cyanobacteria. These microalgae offer traits like rapid growth, high lipid content, non-competition with human food, and growth on non-arable land using brackish or waste water, making them promising for biofuel. These unique phototrophic organisms use sunlight, water, and carbon dioxide (CO2) to produce biofuels, biochemicals, and more. This review delves into the realm of microalgal biofuels, exploring contemporary methodologies employed for lipid extraction, significant value-added products, and the challenges inherent in their commercial-scale production. While the cost of microalgae bioproducts remains high, utilizing wastewater nutrients for cultivation could substantially cut production costs. Furthermore, this review summarizes the significance of biocircular economy approaches, which encompass the utilization of microalgal biomass as a feed supplement and biofertilizer, and biosorption of heavy metals and dyes. Besides, the discussion extends to the in-depth analysis and future prospects on the commercial potential of biofuel within the context of sustainable development. An economically efficient microalgae biorefinery should prioritize affordable nutrient inputs, efficient harvesting techniques, and the generation of valuable by-products.

pH-Driven Selective Adsorption of Multi-Dyes Solutions by Loofah Sponge and Polyaniline-Modified Loofah Sponge

In the last decades, sorbent materials characterized by low selectivity have been developed for the removal of pollutants (in particular dyes) from wastewater. However, following the circular economy perspective, the possibility to selectively adsorb and desorb dyes molecules today represents an unavoidable challenge deserving to be faced. Herein, we propose a sequential treatment based on the use of PANI-modified loofah (P-LS) and loofah sponge (LS) to selectively adsorb cationic (rhodamine, RHB, and methylene blue, MB) and anionic (methyl orange, MO) dyes mixed in aqueous solution by tuning the adsorption pH (100% MO removal by P-LS and 100% and 70% abatement of MB and RHB, respectively, by LS). The system maintained high sorption activity for five consecutive cycles. A simple and effective regeneration procedure for the spent adsorbents permits the recovery of the initial sorption capability of the materials (81% for MO, ca. 85% for both RHB and MB, respectively) and, at the same time, the selective release of most of the adsorbed cationic dyes (50% of the adsorbed MB and 50% of the adsorbed RHB), although the procedure failed regarding the release of the anionic component. This approach paved the way to overcome the traditional procedure based on an indiscriminate removal/degradation of pollutants, making the industrial wastewater a potential source of useful chemicals.

Evaluation of diazepam adsorption in aqueous media using low-cost and natural zeolite: equilibrium and kinetics

Diazepam has been detected in water sources around the world affecting the quality of drinking water. Even in small quantities, recent studies have proven the negative effects of the drug on human body. Since traditional water and sewage treatment do not remove this type of contaminant, it became interesting to evaluate forms to remove them from water sources. A cheap and eco-friendly alternative to remove this drug from the water is through adsorption using the natural clinoptilolite zeolite as an adsorbent. This work goal was to study the characterizations of clinoptilolite, such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffractometer (XRD), and Fourier transform infrared spectroscopy (FTIR) and analyze the potential of this material as an adsorbent. Kinetic studies and isotherm analysis were performed in batch. The results showed the potential of the natural zeolite to remove the pollutant in an aqueous medium reaching a maximum adsorption capacity of 8.25 mg g^-1. The adsorption process followed a pseudo-second-order kinetics indicating that the adsorption was based on a chemisorption process. The isotherms curves shown favorable adsorption and the Langmuir isotherm model fit the experimental data better.

Improved Adsorption Capacity of Nannochloropsis sp. through Modification with Cetyltrimethylammonium Bromide on the Removal of Methyl Orange in Solution

In this research, biomass modification of Nannochloropsis sp. with surfactant cetyltrimethylammonium bromide (CTAB) through a cation exchange reaction to produce adsorbent Nannochloropsis sp.-cetyltrimethylammonium bromide (AlgN-CTAB) has been carried out. Biomass modification of Nannochloropsis sp. by CTAB has been successfully carried out through confirmation from the analysis data produced by Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDX). AlgN-CTAB adsorbent has been tested for its adsorption ability against anionic dye of methyl orange (MO) in solution by way of a sequence of experiments by the batch method. The optimum conditions for MO removal from the solution occurred at an adsorbent quantity of 0.1 g, pH of 5, and an interaction time of 60 min. MO adsorption kinetic data by AlgN and AlgN-CTAB tended to take the kinetic model of pseudo-second-order (PSO) with PSO rate constant ( $k_2$ ) values of 0.56 and 2.17 g mg-1 min-1, serially. The MO adsorption isotherm pattern by AlgN tends to take the Freundlich adsorption isotherm, whereas in AlgN-CTAB it follows the Langmuir and Dubinin-Radushkevich adsorption isotherms. The results of the adsorption-desorption of MO by AlgN-CTAB with 4 repetition cycles resulted in % removal of $\text{MO}>80\%$ . The AlgN-CTAB adsorbent can be used repeatedly and is very effective in absorbing MO in water.

Ipomoea carnea: a novel biosorbent for the removal of methylene blue (MB) from aqueous dye solution: kinetic, equilibrium and statistical approach

The biosorption potential of cost-effective and agricultural residue, Ipomoea carnea wood (ICW) was examined by the removal of cationic dye, methylene blue (MB) from aqueous solution. The surface morphology, structural and thermal properties of untreated ICW were analyzed using Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Thermo-gravimetric Analysis (TGA), respectively. The effects of different parameters namely concentration of biosorbent, initial pH, initial MB composition and temperature on biosorption capacity and biosorption (%) were studied. The kinetic and equilibrium models were developed to fit the experimental data on MB biosorption. The maximum biosorption capacity of 39.38 mg g^-1 was obtained at 40 °C using Langmuir model. The removal of MB was found to be significantly varying with temperature. Box-Behnken design was applied to optimize the biosorption parameters. The optimized condition for MB biosorption was evaluated as dosage of 3.1 g L^-1, pH of 7.04, Temperature of 49.1 °C, MB concentration of 30.48 mg L^-1 and maximum biosorption (%) of 83.87. The regeneration of ICW was investigated by five cycles using a suitable eluting agent. Hence, ICW without any pretreatment and chemical modification is a potential candidate for the removal of MB in terms of availability and economy of the process.Novelty statementIpomoea carnea wood (ICW) without any pretreatment explored a potential biosorbent for the removal of methylene blue (MB) in terms of availability and economy of the process.The physico-chemical properties of ICW characterized using Scanning Electron Microscopy, Fourier transform infrared spectroscopy and Thermo-gravimetric Analysis showed ICW as a promising biosorbent for MB removal.Presence of heterogeneous with rugged morphological structure, cavities, irregular shape and size of large pores provide the better biosorption capability for MB molecules using ICW without any pretreatment or chemical modification.Analysis of kinetic and isotherm models was performed to examine the better fitness of experimental data with model. Thermodynamic parameters indicating feasible and endothermic MB biosorption.Statistical design of experiments is used to optimize the condition and corresponding maximum MB removal using Derringer's desired function methodology.Untreated ICW is a potential reusable biosorbents, effectively employed in successive biosorption and desorption process for the removal of MB from aqueous solutions.

Use of algal biorefinery waste and waste office paper in the development of xerogels: A low cost and eco-friendly biosorbent for the effective removal of congo red and Fe (II) from aqueous solutions

The present study investigated the use of algae biorefinery waste and wastepaper in the preparation of cost-effective and eco-friendly xerogels for the removal of congo red (CR) and Fe²⁺. The xerogel properties such as density, swelling degree and porosity were modified by incorporating alginate extracted from the brown seaweed Cystoseira trinodis. The developed biosorbents exhibited a light and porous network structure and were characterized by a fast uptake of CR and Fe²⁺ and adsorption efficiency was increased at pH 6-8. The equilibrium adsorption capacity was found to be 6.20-7.28 mg CR g^-1 biosorbent and 8.08-8.39 mg Fe²⁺ g^-1 biosorbent using different xerogels. The adsorption of CR obeyed first-order kinetics, while, Fe²⁺ followed second-order kinetics. Intraparticle diffusion model suggested a boundary layer effect. The adsorption capacity was maximally obtained as 41.15 mg g^-1 and 169.49 mg g^-1 for CR and Fe²⁺ using wastepaper/Spirulina and wastepaper/alginate/Spirulina xerogel, respectively. Temkin isotherm fitted better to the equilibrium data of CR adsorption than Langmuir and Freundlich models. While, equilibrium data of Fe²⁺ exhibited a best fit to both Langmuir and Freundlich models. Additionally, the Dubinin-Radushkevich isotherm suggested that adsorption mechanism of CR or Fe²⁺ is predominately physisorption. Investigation of thermodynamic parameters such as ΔH° and ΔS° and ΔG° confirmed the feasibility, spontaneity, randomness and endothermic nature of the adsorption process. Electrostatic attraction, H-bonding and n-π interactions were mainly involved in the biosorption process of CR. The results of this study showed that the developed xerogels could be effectively applied for dye and heavy metal removal at low concentrations.

Synthesis and cationic dye biosorption properties of a novel low-cost adsorbent: coconut waste modified with acrylic and polyacrylic acids

Coconut waste (CW), a novel, low cost adsorbent, has been utilized for the removal of methylene blue (MB) dye from an aqueous solution. CW was chemically modified with acrylic (AcA) and polyacrylic acids (PAcA) using different modification methods, such as esterification with AcA, chemically grafting of PAcA, and plasma-enhanced chemical vapor deposition (PECVD) coating with PAcA. CW-based adsorbents were used in the experiments to study MB adsorption probability, and their activities were compared. The adsorption behavior of MB onto the adsorbents was investigated with respect to parameters such as sorbent dosage (0.5-4 g/L), pH (2-10), initial dye concentration (50-250 mg/L), and temperature (22-65 °C). The time taken of AcA modified CW (CW-AcA), PAcA-grafted CW (CW-PAcA_grafted), and PAcA-coated CW (CW-PAcA_coated) for the removal of 94.6%, 97.7%, and 91.0% of MB from 50 mg/L of dye solution is 180 min. Characterization of CW-based adsorbents was achieved using SEM, XRD, BET, XPS, and FT-IR analysis. The adsorption fitted the Langmuir model, and the adsorption kinetics were consistent with a pseudosecond-order kinetics model. The results obtained from the maximum adsorption capacity (q_max) for AcA-, PAcA_coated-, and PAcA_grafted-CWs were 138.88, 136.98, and 98.03 mg/g at adsorbent dose of 0.1 g/50 mL for initial dye concentration of 200 mg/L, 22 ± 1 °C, and pH 10:10:8.

Chlorella vulgaris cultivation in airlift photobioreactor with transparent draft tube: effect of hydrodynamics, light and carbon dioxide on biochemical profile particularly ω-6/ω-3 fatty acid ratio

Chlorella vulgaris is used for food and feed applications due to its nutraceutical, antioxidant and anticancer properties. An airlift photobioreactor comprising transparent draft tube was used for C. vulgaris cultivation. The effect of reactor parameters like hydrodynamics (0.3-1.5 vvm), light intensity (85-400 μmol m^-2 s^-1), photoperiod (12-24 h) and gas-phase carbon dioxide (CO₂) concentration (5-15% v/v) were evaluated on microalgae and associated bacterial growth, biochemical profile; with special emphasis on ω-3, ω-6 fatty acids, and vitamin B₁₂. The optimal growth of C. vulgaris without CO₂ supplementation was observed at 1.2 vvm, which was associated with higher algal productivity, chlorophyll, vitamin B₁₂ content, and bacterial load along with 72% of nitrate removal. The higher light intensity (400 μmol m^-2 s^-1) and photoperiod (24:0) increased biomass productivity and ω-3 fatty acid content (in lipid) up to 2-3 fold. The elevated levels of gas-phase CO₂ concentration (15% v/v) enhanced EPA content up to 7% and biomass productivity up to 171 mg L^-1 day^-1. However, the increase in CO₂ concentration lowered vitamin B₁₂ content (up to 30%) and bacterial load (2-3 log). Also, all the cultivation conditions favoured desirable ω-6/ω-3 ratio(in the range of 1-2).

Hydrothermal liquefaction of Scenedesmus abundans biomass spent for sorption of petroleum residues from wastewater and studies on recycling of post hydrothermal liquefaction wastewater

In this study Scenedesmus abundans was used as a biosorbent material for removing hydrocarbons from simulated petroleum wastewater. Batch experiments resulted in the removal of 92.16% of hydrocarbons from simulated wastewater within 60 min. The spent biosorbent was converted to bio-oil through hydrothermal liquefaction process (HTL) at temperature range from 220 to 320 °C with 1 h holding time. Liquid hydrocarbons (bio-oil) yield was 43.4 wt% at 300 °C with 15 g of spent sorbent loading and possessed HHV of 39.10 MJ/Kg. Additionally the HTL wastewater (aqueous phase) was recycled as reaction medium and studied for its effects on bio-oil yield which increased till second cycle (47.91 wt%). HTL bio-char was employed as adsorbent to remove heavy metals from wastewater. It showed greater removal efficiency of 86.5% to Ni(II) ions. From the results it was concluded that the petroleum residues can be effectively recycled back into liquid hydrocarbons with simple waste management pathway.

Optimization and Evaluation of Alkali-Pretreated Paeonia Ostii Seed Coats as Adsorbent for the Removal of Mb From Aqueous Solution

A novel effi cient adsorbent, alkali-pretreated Paeonia ostii seed coats (AP-PSC), was investigated for the removal of methylene blue (MB) dye from solution. Orthogonal array design was applied to optimize the process parameters viz. alkali concentration, liquid-solid ratio (LSR) and pretreatment time. The results revealed that the optimal pretreatment conditions were at 0.8% (w/w) NaOH with LSR of 0.35 L g-1 treating for 50 min. Equilibrium and kinetic studies indicated that Langmuir isotherm and Pseudo-second-order models described the experimental data well. The maximum adsorption capability was of 368.2 mg g-1 for MB at 25oC. Thermodynamic parameters suggested that the AP-PSC adsorption process was physical, endothermic and spontaneous. Furthermore, the adsorption process was infl uenced by several interactive mechanisms, including ion-exchange, as well as Van der Waals forces and hydrogen bonds that occur concomitantly. It was concluded that AP-PSC may be potential as an effi cient adsorbent to remove MB from solution.

Adsorption characteristics of methylene blue by biochar prepared using sheep, rabbit and pig manure

Sheep manure biochar (SMB₅₀₀), rabbit faeces biochar (RFB₅₀₀) and pig manure biochar (PMB₅₀₀) prepared by controlled thermal decomposition at 500 °C were used to adsorb methylene blue (MB) in water. Elemental analysis, BET and SEM results showed that the specific surface area, total pore volume and average pore diameter of SMB₅₀₀ were 7.59, 4.20 and 1.16 times greater than those of RFB₅₀₀, which were also 12.02, 6.88 and 1.37 times greater than those of PMB_500, respectively. SMB₅₀₀ had stronger stability and aromaticity. When the initial concentration of MB was 50 mg L^-1 and pH was 11, adsorption achieved equilibrium at approximately 210 min. The adsorption followed pseudo-second-order kinetics (R² > 0.96), indicating that liquid film diffusion, surface adsorption and intraparticle diffusion all contributed to the adsorption rate. The results of isothermal adsorption showed that the adsorption performance of SMB₅₀₀ was more consistent with a Freundlich model, whereas the performance of RFB₅₀₀ and PMB₅₀₀ was more consistent with a Langmuir model with a maximum adsorption capacity of 53.68 to 238.31 mg g^-1. Thermodynamic and FTIR studies showed that the adsorption of MB on SMB₅₀₀, RFB₅₀₀ and PMB₅₀₀ was spontaneous and endothermic, and hydrogen bonds and π-π bonds were closely related to the adsorption process. The results of regeneration show that the optimal number of cycles for SMB₅₀₀, RFB₅₀₀ and PMB₅₀₀ are 8, 5 and 3, respectively.

Facile synthesis of highly porous "carbon sponge" with adsorption and co-adsorption behavior of lead ions and atrazine

The rapid industrialization and modern agriculture, increasing emission of heavy metals, and abusing application of pesticide have changed biochemical features of the soil system and water system. Additionally, heavy metals and pesticide compounds may occur together in environments, giving rise to more serious damage to the environment because of their combined toxicity and carcinogenic properties. Therefore, there is a growing need for the development of low-cost adsorbents for their removal. Porous carbon materials have been considered as highly effective materials for pollutant ion control. In this thesis, a novel porous "carbon sponge" is produced using sucrose (S-PCS) with gas-producing molten salt KHCO₃ as the activator at different pyrolysis temperatures under a limited-oxygen condition. Results from these characterizations have indicated that the as-prepared carbon sponges share high surface area (up to 457.6434 m² g^-1) and abundant oxygen-containing functional groups existed on the surface. The essential factors of contact time, initial concentrations, and cyclic availability on adsorption of lead ions and atrazine onto the as-prepared porous samples are also discussed. The typical kinetic and thermodynamic models are carried out to interpret the adsorption behaviors of lead ions and atrazine. The interactive effects and mechanism of lead ions and atrazine adsorption onto S-PCS samples are examined by simultaneous adsorption and preloading adsorption procedures. Combined with the economic and environmental merits of the raw materials, the porous carbon sponges of sucrose by KHCO₃ activated are promising materials for potential practical applications. Graphical abstract The schematic diagram on the preparation of porous carbon sponse from sucrose.

antarctica

Currently, there is a great pollution of water by the dyes; due to this, several studies have been carried out to remove these compounds. However, the total elimination of these pollutants from the aquatic effluents has represented a great challenge for the scientific community, for which it is necessary to carry out investigations that allow the purification of water. In this work, we studied the bioadsorption of methylene blue on the surface of the biomass obtained from the algae D. antarctica. This material was characterized by SEM and FTIR. To the data obtained in the biosorption experiments, different models of biosorption and kinetics were applied, finding that the best fit to the obtained data is given by applying the pseudo-second-order models and the Toth model, respectively. It was also determined that the maximum adsorption capacity of MB on the surface of the biomass is 702.9 mg/g, which shows that this material has great properties as a bioadsorbent.

Magnetically Modified Agricultural and Food Waste: Preparation and Application

The annual food and agricultural waste production reaches enormous numbers. Therefore, an increasing need to valorize produced wastes arises. Waste materials originating from the food and agricultural industry can be considered as functional materials with interesting properties and broad application potential. Moreover, using an appropriate magnetic modification, smart materials exhibiting a rapid response to an external magnetic field can be obtained. Such materials can be easily and selectively separated from desired environments. Magnetically responsive waste derivatives of biological origins have already been prepared and used as efficient biosorbents for the isolation and removal of both biologically active compounds and organic and inorganic pollutants and radionuclides, as biocompatible carriers for the immobilization of diverse types of (bio)molecules, cells, nano- and microparticles, or (bio)catalysts. Potential bactericidal, algicidal, or anti-biofilm properties of magnetic waste composites have also been tested. Furthermore, low cost and availability of waste biomaterials in larger amounts predetermine their utilization in large-scale processes.

An ecofriendly approach for bioremediation of contaminated water environment: Potential contribution of a coastal seaweed community to environmental improvement

High levels of heavy metals like copper ions in many industrial based effluents lead to serious environmental and health problems. Biosorption is a potential environmental biotechnology approach for biotreatment of aquatic sites polluted with heavy metal ions. Seaweeds have received great attention for their high bioremediation potential in recent years. However, the co-application of marine macroalgae for removal of heavy metals from wastewater is very limited. Thus, for the first time in literature, a coastal seaweed community composed of Chaetomorpha sp., Polysiphonia sp., Ulva sp. and Cystoseira sp. species was applied to remove copper ions from synthetic aqueous medium in this study. The biosorption experiments in batch mode were conducted to examine the effects of operating variables including pH, biosorbent amount, metal ion concentration and contact time on the biosorption process. The biosorption behavior of biosorbent was described by various equilibrium, kinetic and thermodynamic models. The biosorption of copper ions was strongly influenced by the operating parameters. The results indicated that the equilibrium data of biosorption were best modeled by Sips isotherm model. The values of mean free energy of biosorption computed from Dubinin-Radushkevich isotherm model and the standard Gibbs free energy change indicated a feasible, spontaneous and physical biotreatment system. The pseudo-second-order rate equation successfully defined the kinetic behavior of copper biosorption. The pore diffusion also played role in the control of biosorption process. The maximum copper uptake capacity of biosorbent was found to be greater than those of many other biosorbents. The obtained results revealed that this novel biosorbent could be a promising material for copper ion bioremediation implementations.

Lotus seedpod as a low-cost biomass for potential methylene blue adsorption

The adsorption of methylene blue (MB) by low cost biomass lotus seedpod (LSP) was optimized by a central composite design combined with response surface methodology in aqueous solution. Solution pH, initial dye concentration and adsorbent dosage were studied as independent variables at five levels each, respectively. Analysis of variance suggested the validity of the regression model. LSP was characterized by Fourier transform infrared spectra and energy dispersive spectroscopy. The kinetics revealed that the adsorption behavior followed the pseudo-second-order model. Langmuir and Freundlich isotherm models were used to evaluate the adsorption, and the experimental data were better fitted by the Langmuir isotherm than the Freundlich isotherm. The maximum monolayer adsorption capacity of the LSP was 157.98 mg g^-1 at 30 °C for MB adsorption. In addition, 0.2 M HCl solution could be used for reusability of LSP via desorption tests. LSP was proven to be an available and effective biosorbent for MB removal from aqueous solution.

Applications of de-oiled microalgal biomass towards development of sustainable biorefinery

In view of commercialization of microalgal biofuel, the de-oiled microalgal biomass (DMB) is a surplus by-product in the biorefinery process that needs to be exploited to make the process economically attractive and feasible. This DMB, rich in carbohydrates, proteins, and minerals, can be used as feed, fertilizer, and substrate for the production of bioethanol/bio-methane. Further, thermo-chemical conversion of DMB results into fuels and industrially important chemicals. Future prospects of DMB also lie with its conversion into novel biomaterials like nanoparticles and carbon-dot which have biomedical importance. The lowest valued application of DMB is to use it for adsorption of dyes and heavy metals from industrial effluents. This study reviews how DMB can be utilized for different applications and in the generation of valuable co-products. The value addition of DMB would thereby improve the overall cost economics of the microalgal bio-refinery.

Banana Fibers as Sorbent for Removal of Acid Green Dye from Water

In this study, banana fibers extracted from banana leaves, stem, and stalk were used to remove acid green dye from aqueous solution. Three initial concentrations (750, 1000, and 1500 ppm) were chosen to determine the kinetic characteristics of the banana fiber sorbents at 25°C, agitation speed of 200 rpm, and total contact time of 3 hours. The pseudo-first-order, pseudo-second-order, and Dunwald-Wagner kinetic models were applied to the experimental kinetic data. For isotherm study, the batch experiments were performed at 25°C, initial pH 2, agitation speed of 200 rpm, and initial concentrations between 100 and 2000 ppm. The experimental data was fitted to the Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherms. The equilibrium was achieved in less than 90 minutes. The removal of the acid green dye was found to be following closely the pseudo-second-order kinetic model. For equilibrium study, the Freundlich isotherm was found to fit well with adsorption of acid green dye on the banana leaves, stem, and stalk sorbents. The calculated mean free energy of 4–11 J/mol indicated that the sorption process was mostly physical in nature. Experimental results also showed the adsorption performance is greatly affected by the initial solution pH.