Comparison of adsorption behavior studies of methylene blue by microalga residue and its biochars produced at different pyrolytic temperatures

Microalgae-based biochar production and applications: A comprehensive review

Biochar, a solid carbonaceous substance synthesized from the thermochemical degradation of biomass, holds significant potential in addressing global challenges such as soil degradation, environmental pollution, and climate change. Its potential as a carbon sequestration agent, together with its versatile applications in soil amendments, pollutant adsorption, and biofuel production, has garnered attention. On the other hand, microalgae, with their outstanding photosynthetic efficiency, adaptability, and ability to accumulate carbohydrates and lipids, have demonstrated potential as emerging feedstock for biochar production. However, despite the significant potential of microalgal biochar, our current understanding of its various aspects, such as the influence of parameters, chemical modifications, and applications, remains limited. Therefore, this review aims to provide a comprehensive analysis of microalgae-based biochar, covering topics such as production techniques, pollutant removal, catalytic applications, soil amendments, and synthesis of carbon quantum dots to bridge the existing knowledge gap in this field.

Use of biochar and a post-coagulation effluent as an adsorbent of malachite green, beneficial bacteria carrier, and seedling substrate for plants belonging to the poaceae family

Wastewater treatment plants produce solid and semi-solid sludge, which treatment minimises secondary environmental pollution because of wastewater treatment and obtaining new bioproducts. For this reason, in this paper, the co-pyrolysis of biogenic biomasses recovered from a biological reactor with immobilised fungal and bacterial biomass and a tertiary reactor with Chlorella sp. used for dye-contaminated wastewater treatment was carried out. Biogenic biomasses mixed with pine bark allowed the production and characterisation of two types of biochar. The raw material and biochar were on the "in vitro" germination of Lolium sp. seeds, followed by adsorption studies for malachite green (MG) dye using the raw material and the biochar. Results showed that using 60 mg L-1 of a cationic coagulant at pH 6.5 allowed for the recovery of more than 90% of the microalgae after 50 min of processing. Two biochar resulted: BC300, at pH 5.08 ± 0.08 and BC500, at pH 6.78 ± 0.01. The raw material and both biochars were co-inoculated with growth-promoting bacteria; their viabilities ranged from 1.7 × 106 ± 1.0 × 101 to 7.5 × 108 ± 6.0 × 102 CFU g-1 for total heterotrophic, nitrogen-fixing and phosphate-solubilising bacteria. Re-use tests on Lolium sp. seed germination showed that with the post-coagulation effluent, the germination was 100%, while with the biochar, with and without beneficial bacteria, the germination was 98 and 99%, respectively. Finally, BC500 adsorbed the highest percentage of malachite green at pH 4.0, obtaining qecal values of 0.5249 mg g-1 (R2: 0.9875) with the pseudo-second-order model.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03766-x.

Efficient Removal of Congo Red, Methylene Blue and Pb(II) by Hydrochar-MgAlLDH Nanocomposite: Synthesis, Performance and Mechanism

Organic dyes and heavy metals often coexist in industrial effluents, and their simultaneous removal is a grand challenge. Herein, a hydrochar and MgAl layered double hydroxide (HC-MgAlLDH) nanocomposite was prepared via a facile one-step hydrothermal route, and applied to remove anionic Congo red (CR), cationic Methylene blue (MB) and Pb(II) from aqueous solutions. The nanocomposite was formed by interweaving amorphous HC and crystalline MgAlLDH nanoplates and possessed more functional groups, lower zeta potential and larger specific surface area than uncomposited MgAlLDH. Batch removal experiments showed that the components HC and LDH dominated the CR and MB removals, respectively, whereas Pb(II) removal was conjointly controlled by the two components. The maximum Langmuir removal capacities of the nanocomposite to sole CR, MB, or Pb(II) were 348.78, 256.54 or 33.55 mg/g. In binary and ternary systems, the removal capacities of CR and MB only slightly decreased, while the capacity of Pb(II) increased by 41.13-88.61%. The increase was related to the coordination of Pb(II) with the sulfur-containing groups in dyes and the precipitation of PbSO₄. Therefore, the simultaneous removal of CR, MB and Pb(II) was involved in a synergistic effect, including electrostatic adsorption, π-π interaction, coordination and precipitation. The present work shows that the HC-MgAlLDH nanocomposite has great potential for wastewater integrative treatment.

Bamboo Nanocellulose/Montmorillonite Nanosheets/Polyethyleneimine Gel Adsorbent for Methylene Blue and Cu(II) Removal from Aqueous Solutions

In recent years, the scarcity of pure water resources has received a lot of attention from society because of the increasing amount of pollution from industrial waste. It is very important to use low-cost adsorbents with high-adsorption performance to reduce water pollution. In this work, a gel adsorbent with a high-adsorption performance on methylene blue (MB) and Cu(II) was prepared from bamboo nanocellulose (BCNF) (derived from waste bamboo paper) and montmorillonite nanosheet (MMTNS) cross-linked by polyethyleneimine (PEI). The resulting gel adsorbent was characterized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (SEM), X-ray photoelectron spectroscopic (XPS), etc. The results indicated that the MB and Cu(II) adsorption capacities of the resulting gel adsorbent increased with the solution pH, contact time, initial concentration, and temperature before equilibrium. The adsorption processes of MB and Cu(II) fitted well with the fractal-like pseudo-second-order model. The maximal adsorption capacities on MB and Cu(II) calculated by the Sips model were 361.9 and 254.6 mg/g, respectively. The removal of MB and Cu(II) from aqueous solutions mainly included electrostatic attraction, ion exchange, hydrogen bonding interaction, etc. These results suggest that the resulting gel adsorbent is an ideal material for the removal of MB and Cu(II) from aqueous solutions.

Biochar-based composites for remediation of polluted wastewater and soil environments: Challenges and prospects

Pharmaceuticals, heavy metals, pesticides, and dyes are the main environmental contaminants that have serious effects on both land and aquatic lives and necessitate the development of effective methods to mitigate these issues. Although some conventional methods are in use to tackle soil contamination, but biochar and biochar-based composites represent a reliable and sustainable means to deal with a spectrum of toxic organic and inorganic pollutants from contaminated environments. The capacity of biochars and derived constructs to remediate inorganic dyes, pesticides, insecticides, heavy metals, and pharmaceuticals from environmental matrices is attributed to their extensive surface area, surface functional groups, pore size distribution, and high sorption capability of these pollutants in water and soil environments. Application conditions, biochar feedstock, pyrolysis conditions and precursor materials are the factors that influence the capacity and functionality of biochar to adsorb pollutants from wastewater and soil. These factors, when improved, can benefit biochar in agrochemical and heavy metal remediation from various environments. However, the processes involved in biochar production and their influence in enhancing pollutant sequestration remain unclear. Therefore, this paper throws light on the current strategies, operational conditions, and sequestration performance of biochar and biochar-based composites for agrochemical and heavy metal in soil and water environments. The main challenges associated with biochar preparation and exploitation, toxicity evaluation, research directions and future prospects for biochar in environmental remediation are also outlined.

Influence of pyrolysis temperature on characteristics and Cr(VI) adsorption performance of carbonaceous nanofibers derived from bacterial cellulose

The effects of pyrolysis temperature on properties and adsorption performance of carbonized bacterial cellulose (CBC) produced from bacterial cellulose at 300, 400, 600 and 800 °C were investigated. As pyrolysis temperature increased, the BET surface area, C and ash contents of CBC increased while its mass yield and the contents of H, N and O decreased. Higher pyrolysis temperature resulted in CBC having more aromatic structure and less hydrophilic. The impacts of pyrolysis temperature, solution pH, contact time and initial concentration on the absorption of Cr(VI) onto CBC were systematically studied as well. The results showed that CBC400 prepared at 400 °C exhibited the highest Cr(VI) adsorption capacity for Cr(VI) up to 250.0 mg/g. The equilibrium adsorption and adsorption kinetics fitted the Langmuir isotherm and pseudo-second-order kinetic models well. The mechanisms of adsorption of Cr(VI) on CBC included electrostatic interaction, π-π interaction and functional groups complexation.

Non-domestic wastewater treatment with fungal/bacterial consortium followed by Chlorella sp., and thermal conversion of the generated sludge

Liquid waste from biological stains is considered non-domestic wastewater difficult to treat, generating high environmental impact. Therefore, the objective of this work was to carry out secondary and tertiary treatment of these effluents at a pilot scale, using a fungal/bacterial consortium followed by Chorella sp., for 15 days. In addition, to obtain an adsorbent material for Malachite Green dye removal, sludge generated in the plant and pine bark co-pyrolysis was performed. For microalgae isolation and selection of the Chlorophyceae class, Chlorococcales order, and Chorella sp. genus Winogradsky columns were employed. After 15 days of pilot plant treatment, removal percentages of 91 ± 2%, 90 ± 4% and 17 ± 2% were obtained for Colour Units, Chemical Oxygen Demand and Nitrates, respectively. Two types of class II biochar (BC₅₀₀ and BC₇₀₀) and one of class III (BC₃₀₀) were produced. The highest value for Fixed carbon (FC) was obtained at 300 °C (27.3 ± 3%), decreasing as the temperature increased by 25.9 ± 5% and 24.8 ± 2%, for BC₅₀₀ and BC₇₀₀, respectively. Biochar yield was 62.1 ± 3%, 46.3 ± 4% and 31.6 ± 3% for BC₃₀₀, BC₅₀₀ and BC₇₀₀, respectively. Finally, BC₅₀₀ and BC₇₀₀ biochar efficiently adsorbed Malachite Green obtaining qe values of 0.290 ± 0.032, 0.281 ± 0.015, 0.186 ± 0.009 and 0.191 ± 0.012 mg g^-1 at pH values of 4.0 and 8.0 ± 0.2, respectively. Pseudo-second order model demonstrated a chemical adsorption took place, which was influenced by pH.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02780-1.