Elucidating dominant factors of PO43–, Cd2+ and nitrobenzene removal by biochar: A comparative investigation based on distinguishable biochars

Adsorption of common greywater pollutants and nutrients by various biochars as potential amendments for nature-based systems: Laboratory tests and molecular dynamics

Spruce wood and Typha (wetland plant) derived biochars pyrolyzed at 350 °C and 600 °C were tested for their sorption affinity for organic pollutants (diclofenac, methylparaben, benzotriazole and sodium 1-decanesulfonate) and nutrients (nitrate, ammonium, phosphate and boron) commonly found in greywater. Batch and column studies combined with molecular dynamics modelling determined the sorption capacity, kinetics, and described the underlying mechanisms. The spruce biochar (600 °C) exhibited the highest sorption capacity mainly for the tested organics. The dynamic test performed for spruce biochar (600 °C) showed that the magnitude of desorption was low, and the desorbed amount ranged between 3 and 11 %. Molecular dynamics modelling (a computational tool for elucidating molecular-level interactions) indicated that the increased sorption of nitrate and boron on spruce biochar (600 °C) could be attributed to hydrophobic interactions. The molecular dynamics shows that predominant adsorption of organic pollutants was governed by π-π stacking, with a minor role of hydrogen-bonding on the biochar surface. In summary, higher pyrolysis temperature biochar yielded greater adsorption capacity greywater borne contaminants and the reaction temperature (10-34 °C) and presence of anionic surfactant had a limited effect on the adsorption of organic pollutants, suggesting efficacious application of biochar in general for greywater treatment in nature-based systems.

Adsorption of sulfamethoxazole via biochar: The key role of characteristic components derived from different growth stage of microalgae

Converting microalgal biomass residues into biochar (BC) after microalgal wastewater treatment is a popular approach that can produce an adsorbent to treat refractory organic pollutants. Moreover, the adsorption efficiency via BC is closely associated with the surface morphology, which may be determined by the composition of the microalgal biomass. However, the intrinsic relationship and advanced mechanism between the adsorption efficiency and microalgal composition have not been thoroughly investigated. In this work, four microalgal BCs were prepared from Chlamydomonas sp. QWY37 (CBC) after collection from four different growth stages of microalgal biomass during wastewater treatment. The adsorption performance for sulfamethoxazole indicates that the CBC collected in the mid-log phase (CBC_L-M) possessed the best adsorption capacity (287.89 mg/g) owing to the higher decomposition of the microalgal cellular protein concentration (70%). Meanwhile, a higher protein content contributed to the largest specific surface area (42.16 m²/g), maximum pore volume (0.037 cm³/g) and abundant surface functional groups of the CBC_L-M. Furthermore, based on the theoretical calculation of the structural analysis, the adsorption mechanism was a multilayer adsorption process in accordance with the Freundlich isotherm. Additionally, the strong hydrogen bond, electron donor-acceptor interaction and electrostatic attraction were the main adsorption mechanisms due to the carboxyl/ester functional groups. The results of this research provide a novel perspective on the reasonable harvest of microalgal biomass for BC fabrication and large-scale implementation of microalgal BC in future applications.

Feasible synthesis of a novel and low-cost seawater-modified biochar and its potential application in phosphate removal/recovery from wastewater

In this study, a novel and low-cost seawater-modified biochar (SBC) was fabricated via the pyrolysis of fir wood waste followed by co-precipitation modification using seawater as the Ca/Mg source. The co-precipitation pH was a vital factor during modification, and the optimal pH was 10.50 according to calculations using PHREEQC 2.5 and experiments. The characterizations indicated that Ca and Mg were loaded on the SBC as irregular CaCO₃ and nanoflake-like Mg(OH)₂, respectively, with the latter dominating. The SBC exhibited a high maximum adsorption capacity of 181.07 mg/g for phosphate, calculated using the Langmuir model, excellent adsorption performance under acidic and neutral conditions (pH = 3.00-7.00), and remarkable selectivity against Cl^-, NO₃^-, and SO₄^2-. The presence of HCO₃^- promoted adsorption. The mechanisms behind phosphate adsorption involved electrostatic attraction, ligand exchange, precipitation, and inner-sphere complexation. Mg, rather than Ca, was served as the main adsorptive sites for phosphate. Additionally, the feasibility of treating real-world wastewater was tested in batch (using SBC powders) and fixed-bed column (using SBC granules) experiments. The results indicate that the SBC powders could reduce the phosphate concentration from 1.26 mg P/L to below 0.5 mg P/L at a low dose of 0.50 g/L, and the SBC granules exhibited a high removal efficiency with excellent recyclability; the capacity still remained at 78.92% of the initial capacity after five adsorption-desorption runs. Furthermore, the modification process almost did not increase the production cost of the SBC, which was estimated to be 0.41 $/kg. Our results demonstrate that seawater is a low-cost and efficient modifier for biochar modification, and the resultant SBC demonstrates great potential for treating actual phosphate-containing wastewater.

Identification of a novel heavy metal resistant Ralstonia strain and its growth response to cadmium exposure

A novel Ralstonia Bcul-1 strain was isolated from soil samples that was closest to Ralstonia pickettii. Broad-spectrum resistance was identified to a group of heavy metal ions and tolerance to concentrations of Cd²⁺ up to 400 mg L^-1. Low concentrations of heavy metal ions did not have distinctive impact on heavy metal resistance genes and appeared to induce greater expression. Under exposure to Cd²⁺, cell wall components were significantly enhanced, and some proteins were also simultaneously expressed allowing the bacteria to adapt to the high Cd²⁺ living environment. The maximum removal rate of Cd²⁺ by the Ralstonia Bcul-1 strain was 78.97% in the culture medium supplemented with 100 mg L^-1 Cd²⁺. Ralstonia Bcul-1 was able to survive and grow in a low nutrient and cadmium contaminated (0.42 mg kg^-1) vegetable soil, and the cadmium removal rate was up to 65.76% in 9th growth. Ralstonia Bcul-1 mixed with biochar could maintain sustainable growth of this strain in the soil up to 75 d and the adsorption efficiency of cadmium increased by 16.23-40.80% as compared to biochar application alone. Results from this work suggests that Ralstonia Bcul-1 is an ideal candidate for bioremediation of nutrient deficient heavy metal contaminated soil.

Efficient removal of tetracycline by a hierarchically porous ZIF-8 metal organic framework

Most reported metal organic frameworks (MOFs) have microporous structures and defective active sites, limiting their practical application to macromolecular substances. A hierarchical porous zeolitic imidazolate framework-8 (ZIF-8) was prepared using poly(diallyldimethylammonium chloride) (PDDA) as a structure-directing agent under facile "aqueous room-temperature" conditions to increase the mass transfer and adsorption capacity tetracycline hydrochloride (TCH). The ZIF-8 pore structure and morphology were synchronously tuned by controlling the PDDA molecular weight and dosage. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Bruner-Emmett-Teller (BET), scanning electron microscopy (SEM), NH₃-temperature-programmed desorption (NH₃-TPD) and adsorption results revealed abundant pore structures and open metal sites in the prepared materials, along with excellent TCH adsorption performance compared with ZIF-8, despite decreased BET surface areas. Initial screens revealed large adsorption capacities of hierarchical porous ZIF-8P3(4) (976.8 mg g^-1) due to the presence of more abundant unsaturated metal sites than ZIF-8 and novel hierarchical porous structures. Therefore, TCH adsorption on ZIF-8 and ZIF-8P3(4), including the kinetics, isotherms, thermodynamics and pH effect, was studied. The adsorption process follows pseudo-second-order kinetics and the Freundlich models better, indicating multilayer adsorption of TCH on the surface of the two absorbents. Adsorption behavior test, FTIR, XPS, BET and XRD results show that TCH adsorption on ZIF-8 and ZIF-8P3(4) most likely involves coordination bonds, electrostatic and π-π interactions, hydrogen bonds, and pore-filling effects. This study provides new insights into the template preparation of MOFs with high adsorption performance as potentially economical adsorbents to remove organic matter from contaminated water.