Search

Phosphorus (P) as an essential nutrient for life sustains the productivity of food systems; yet misdirected P often accumulates in wastewater and triggers water eutrophication if not properly treated. Although technologies have been developed to remove P, little attention has been paid to the recovery of P from wastewater. This work provides a comprehensive review of the state-of-the-art P removal technologies in the science of wastewater treatment. Our analyses focus on the mechanisms, removal efficiencies, and recovery potential of four typical water and wastewater treatment processes including precipitation, biological treatment, membrane separation, and adsorption. The design principles, feasibility, operation parameters, and pros & cons of these technologies are analyzed and compared. Perspectives and future research of P removal and recovery are also proposed in the context of paradigm shift to sustainable water treatment technology. P removal efficiencies and P recovery potential of four typical wastewater treatment processes are critically reviewed. Feasibility, transfer routes, operation parameters, and pros & cons of these technologies in P recovery are analyzed and compared P can be recovered from wastewater into value-added fertilizers or soil amendment. Perspectives and future research directions of P removal and recovery are outlined. [ABSTRACT FROM AUTHOR]

[Display omitted] • H 2 O 2 -modified ball-milled biochar were synthesized to adsorb methylene blue (MB). • H 2 O 2 modification increased the oxygen-containing functional groups of biochar. • H 2 O 2 modification improved the adsorption capacity of biochar to MB. In this work, hickory chip biochars developed at distinctive pyrolysis temperatures were ball milled (BMHC) and then post-modified with a 10% hydrogen peroxide (H 2 O 2) solution to obtain a set of novel sorbents (BMHC-H 2 O 2). The specific surface area (SSA) was dramatically increased after ball-milling while the hydroxyl and carboxyl groups on the surface of the biochars were further increased through H 2 O 2 modification. Additionally, thermal stability of the biochar treated with ball-milling was not greatly reduced by H 2 O 2 modification and hydrodynamic radius was decreased. Ball milling enhanced the adsorption efficiency to methylene blue (MB) by the biochar, and this ability was further increased by H 2 O 2 modification, because of the increasing in oxygen-containing functional groups (OCFG) to interact with MB. The rate of MB adsorption to BMHC-H 2 O 2 was faster than that of BMHC, reaching equilibrium after about 6 h. Among adsorbents tested, the 450 °C BMHC-H 2 O 2 had the greatest MB adsorption capacity (310 mg g−1). [ABSTRACT FROM AUTHOR]

Engineered biochars (EBCs) loaded with metal oxides/hydroxides have been used as sorbents to remove and recycle phosphate (P) from wastewater. However, P removal by EBCs made with different types and loading of metals have rarely been compared in a single study. Thus, in this study, EBCs were synthesized through pyrolysis of bamboo or hickory wood chips (25 g) pretreated with four amounts (25, 50, 75, and 100 mmol) of magnesium (Mg), aluminum (Al), or iron (Fe) salt solutions (Mg-EBC, Al-EBC, and Fe-EBC, respectively). The resulting EBCs were loaded with metal oxides/hydroxides that served as P adsorption sites. Al-EBCs showed the highest aqueous stability with little metal dissolution, which can be attributed to the low level of residual (unconverted) metal salt as well as the extremely low solubility of loaded Al metal oxyhydroxide. After the leaching/washing, the metal loading efficiencies of the Al- and Mg-EBCs were similar (50–60%) and stable metal loadings increased with pretreatment salt amounts, indicating that the amount of the two metal oxides/hydroxides in the EBCs can be controlled during pretreatment. However, stable iron oxide on the Fe-EBCs remained almost the same for all the four levels of pretreatment, reflecting saturation of the biochar surface. All the EBCs showed increasing P adsorption with increasing metal loading. At low initial P concentrations of 31 mg/L, Fe- and Al-EBCs removed up to 68% and 94% of P, likely through an electrostatic interaction mechanism. At high P concentrations, Mg-EBC had the largest P adsorption capacity (119.6 mg P/g), mainly through the combination of surface precipitation and electrostatic interaction mechanisms. This study demonstrates that metal oxide/hydroxide-loaded EBCs are promising sorbents that can be designed to meet specific needs for the removal of aqueous P in various applications. Unlabelled Image • Engineered biochars (EBCs) were produced from two feedstock with different loadings of metals. • EBCs presented increasing P adsorption with increasing metal loadings. • Mg-EBC showed the largest P adsorption capacity (119.6 mg P/g). • Al-EBCs showed the highest aqueous stability with little metal dissolution. • Metal-loaded EBCs are promising sorbents for environmental applications. [ABSTRACT FROM AUTHOR]

Sorption is one of the most efficient and low cost strategies for volatile organic compound (VOC) removal, but VOC sorption by biochar has seen limited research. In this work, gas phase sorption experiments were conducted to determine the sorption potential and mechanisms of VOCs onto biochar. A total of 15 biochars produced from 5 common feedstocks at 300, 450, and 600 °C were evaluated as sorbents. Three common VOCs (acetone, cyclohexane, and toluene) were chosen as sorbates. The results showed that all the tested biochars had VOC sorption capacity in the range of 5.58–91.2 mg g −1 . The sorption capacities were mainly influenced by both the surface area of biochar and its noncarbonized organic matter content. The vapor sorption process was exothermic, and the removal of VOCs by the biochars decreased with increasing feedstock temperature. Both the physical adsorption and partition mechanisms played important roles in controlling the VOC removal by the biochars. Biochar maintained its VOC removal ability after five consecutive sorption-desorption cycles, which indicated good reusability. Findings of this work suggest that biochar is a promising alternative sorbent for gaseous VOC removal. [ABSTRACT FROM AUTHOR]

In this study, biochar derived from bamboo pretreated with aluminum salt was synthesized for the removal of two sulfonamide antibiotics, sulfamethoxazole (SMX) and sulfapyridine (SPY), from wastewater. Batch sorption experiments showed that Al-modified bamboo biochar (Al-BB-600) removed both sulfonamides effectively with the maximum sorption capacity of 1200–2200 mg/kg. The sorption mechanism was mainly controlled by hydrophobic, π-π, and electrostatic interactions. Fixed bed column experiments with Al-modified biochar packed in different dosages (250, 500 and 1000 mg) and flow rates (1, 2 and 4 mL/min) showed the dosage of 1000 mg and flow rate of 1 mL/min performed the best for the removal of both SMX and SPY from wastewater. Among the breakthrough (BT) models used to evaluate the fixed bed filtration performance of Al-BB-600, the Yan model best described the BT behavior of the two sulfonamides, suggesting that the adsorption process involved multiple rate-liming factors such as mass transfer at the solid surface and diffusion Additionally, the Bed Depth Service Time (BDST) model results indicated that Al-BB-600 can be efficiently used in fixed bed column for the removal of both SMX and SPY in scaled-up continuous wastewater flow operations. Therefore, Al-modified biochar can be considered a reliable sorbent in real-world application for the removal of SMX and SPY from wastewater. [Display omitted] • Fixed bed column packed with Al-modified biochar effectively removed SMX and SPY from wastewater. • SMX and SPY adsorption on Al-modified biochar was controlled by multiple mechanisms. • Yan model best described the breakthrough behaviors of SMX and SPY. • BDST model showed a strong linear relationship between service time and the amount of Al-modified biochar. [ABSTRACT FROM AUTHOR]

There are challenges in developing multifunctional materials that can not only effectively adsorb but also completely eliminate organic contaminants in water. In this work, novel ZnO/biochar nanocomposites were synthesized using a facile ball-milling method. A series of characterization results showed that the ZnO nanoparticles dispersed uniformly on carbon surface within the biochar matrix. Ball milling increased the mesopores and macropores of the nanocomposites by breaking biochar and squeezing ZnO. The addition of appropriate amount of ZnO into biochar enhanced both the adsorption capacity and photocatalytic ability of the nanocomposites for methylene blue (MB) removal. When the initial concentration of MB was 160 mg/g, the nanocomposites exhibited high MB removal efficiency (up to 95.19%) under visible light through the combination of adsorption and photocatalysis. This work provides a feasible synthesis of metal oxide/biochar nanocomposites with excellent adsorption and photocatalysis properties for the treatment of organic dye wastewater. [Display omitted] • ZnO/biochar nanocomposites were fabricated through simple ball milling. • Varied sized ZnO nanoparticles dispersed uniformly in the biochar matrix. • Ball milling increased the mesopores and macropores of nanocomposites. • Adsorption and photocatalytic activity were enhanced with proper ZnO addition. • BZ-X exhibited efficient MB removal by combining adsorption and photocatalysis. [ABSTRACT FROM AUTHOR]

Pristine and ball milled wheat stalk biochars pyrolysed at 300 °C, 450 °C, 600 °C were studied for tetracycline hydrochloride (TCH) adsorption from aqueous solution. Surface characteristics of ball milled biochar (BM-biochar) were significantly enhanced over their pristine counterparts. TCH adsorption occurred largely on external surface and by filling pores of biochars as evidenced by strong positive correlation between adsorption and external specific surface area (SSA), total pore volume, or mesoporous volume. A two-stage intra-particle diffusion model, limited by the TCH diffusion through the boundary liquid layer, well described TCH adsorption. Maximum TCH adsorption occurred at about pH = 6–8. While solution cations including Na+, K+ and Mg2+ subdued TCH adsorption as they competed for adsorption sites, Ca2+ promoted TCH adsorption due to formation of tetracycline-Ca2+ complexes. The best performing BM-biochar was the one pyrolysed at 600 °C with TCH adsorption amount of 84.54 mg/g. Therefore, this BM-biochar has the potential for TCH removal from aqueous solutions. And the research shed light on the management of organic contaminants in real wastewater by BM-biochar. Image 1 • Ball milling enhanced external specific surface area and mesoporous volume of biochar. • Ball milling increased sorption ability of biochars to TCH. • TCH adsorption by BM-biochars was controlled by surface adsorption and pore filling. • TCH adsorption on BM-biochars was affected by pH and cation in solution. [ABSTRACT FROM AUTHOR]

• Adsorption kinetic rate of dye on g-C 3 N 4 was faster than those of photodegradation processes. • Surface photodegradation kinetic rate of dye adsorbed on g-C 3 N 4 was faster than that in solution. • Synergy between adsorption and photodegradation of dye by g-C 3 N 4 was confirmed and elucidated. • Modified Elovich model was the best to simulate the integrated adsorption and photodegradation kinetics. The synergy between adsorption and photocatalysis has been well recognized in contaminant photodegradation; however, the governing mechanism is still not clear. The main objective of this work is to understand the kinetic processes of synergic adsorption-photocatalysis of graphitic carbon nitrate (g-C 3 N 4), a visible light responsive photocatalyst with a planar graphitic-like structure, in organic contaminant removal. An anionic dye Reactive Red 120 (RR120), which has six sulphonate groups and a complex aromatic molecular structure, was selected as a model contaminant compound. A range of experiments were conducted to determine the kinetics of adsorption, photodegradation, and the integrated process. Various kinetic models were used to simulate and interpret the experimental data and thus to unveil the governing mechanisms. The integrated adsorption and photodegradation of the dye by g-C 3 N 4 was mainly controlled by: 1) adsorption of dye onto g-C 3 N 4 surface, 2) photodegradation of dye in bulk solution, and 3) photodegradation of adsorbed dye on g-C 3 N 4 surface. Both experimental and modeling results showed that the adsorption kinetic rate (3.37 min−1) was faster than the photodegradation kinetic rates. In addition, the surface photodegradation kinetic rate of adsorbed dye (0.149 min−1) was faster than that in solution (0.005 min−1). Adsorption process thus can promote the photodegradation of contaminants by g-C 3 N 4. On the other hand, photodegradation of dye-laden g-C 3 N 4 regenerated its adsorption capacity for multiple times, suggesting photocatalysis process can also promote the adsorption of contaminates on g-C 3 N 4. [ABSTRACT FROM AUTHOR]