Synthesis and evaluation of a novel cross-linked biochar/ferric chloride hybrid material for integrated coagulation and adsorption of turbidity and humic acid from synthetic wastewater: Implications for sludge valorisation

The deep removal of organic pollutants is challenging for coagulation technology in drinking water and wastewater treatment plants to satisfy the rising water standards. Iron (III) chloride (FeCl3) is a popular inorganic coagulant; although it has good performance in removing the turbidity (TB) in water at an alkaline medium, it cannot remove dissolved pollutants and natural organic matter such as humic acid water solution. Additionally, its hygroscopic nature complicates determining the optimal dosage for effective coagulation. Biochar (BC), a popular adsorbent with abundant functional groups, porous structure, and relatively high surface area, can adsorb adsorbates from water matrices. Therefore, combining BC with FeCl3 presents a potential solution to address the challenges associated with iron chloride. Consequently, this study focused on preparing and characterizing a novel biochar/ferric chloride-based coagulant (BC-FeCl3) for efficient removal of turbidity (TB) and natural organic matter, specifically humic acid (HA), from synthetic wastewater. The potential solution for the disposal of produced sludge was achieved by its recovering and recycling, then used in adsorption of HA from aqueous solution. The novel coagulant presented high TB and HA removal within 10 min of settling period at pH solution of 7.5. Furthermore, the recovered sludge presented a good performance in the adsorption of HA from aqueous solution. Adsorption isotherm and kinetics studies revealed that the Pseudo-second-order model best described kinetic adsorption, while the Freundlich model dominated the adsorption isotherm.

Chemical methods to remove microplastics from wastewater: A review

Microplastics (Mps) have emerged as a pervasive environmental concern, with their presence detected not only in freshwater ecosystems but also in drinking and bottled water sources. While extensive research has centered on understanding the origins, migration patterns, detection techniques, and ecotoxicological impacts of these contaminants, there remains a notable research gap about the strategies for Mps removal. This study reviews existing literature on chemical approaches for mitigating microplastic contamination within wastewater systems, focusing on coagulation precipitation, electrocoagulation, and advanced oxidation methods. Each approach is systematically explored, encompassing their respective mechanisms and operational dynamics. Furthermore, the comparative analysis of these three techniques elucidates their strengths and limitations in the context of MPs removal. By shedding light on the intricate mechanisms underlying these removal methods, this review contributes to the theoretical foundation of microplastic elimination from wastewater and identifies future research trajectories and potential challenges.

A hybrid system for Nickel ions removal from synthesized wastewater using adsorption assisted with electrocoagulation

The presence of heavy metal ions in water environments has raised significant concerns, necessitating practical solutions for their complete removal. In this study, a combination of adsorption and electrocoagulation (ADS + EC) techniques was introduced as an efficient approach for removing high concentrations of nickel ions (Ni2+) from aqueous solutions, employing low-cost sunflower seed shell biochar (SSSB). The combined techniques demonstrated superior removal efficiency compared to individual methods. The synthesized SSSB was characterized using SEM, FT-IR, XRD, N2-adsorption-desorption isotherms, XPS, and TEM. Batch processes were optimized by investigating pH, adsorbent dosage, initial nickel concentration, electrode effects, and current density. An aluminum (Al) electrode electrocoagulated particles and removed residual Ni2+ after adsorption. Kinetic and isotherm models examined Ni2+ adsorption and electrocoagulation coupling with SSSB-based adsorbent. The results indicated that the kinetic data fit well with a pseudo-second-order model, while the experimental equilibrium adsorption data conformed to a Langmuir isotherm under optimized conditions. The maximum adsorption capacity of the activated sunflower seed shell was determined to be 44.247 mg.g-1. The highest nickel ion removal efficiency of 99.98% was observed at initial pH values of 6.0 for ADS and 4.0 for ADS/EC; initial Ni2+ concentrations of 30.0 mg/L and 1.5 g/L of SSSB; initial current densities of 0.59 mA/cm2 and 1.32 kWh/m3 were also found to be optimal. The mechanisms involved in the removal of Ni2+ from wastewater were also examined in this research. These findings suggest that the adsorption-assisted electrocoagulation technique has a remarkable capacity for the cost-effective removal of heavy metals from various wastewater sources.

Nanoscale zero-valent iron/silver@activated carbon-reduced graphene oxide: Efficient removal of trihalomethanes from drinking water

AC-supported nanoscale zero-valent iron composites (nZVI/AC) exhibit significant environmental implications for trihalomethanes (THMs)-contaminated water remediation. To improve the adsorption and degradation capability of AC, herein, a composite (nZVI/Ag@AC-RGO) consisting of AC, reduced graphene oxide (RGO), nanoscale zero-valent iron (nZVI), and silver (Ag) was synthesized and characterized using several techniques, such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, N₂ adsorption-desorption isotherms, and X-ray photoelectron spectroscopy (XPS). The analysis of textural and morphological structures showed that a tightly-attached RGO film, amorphous iron, and weak crystal silver nanoparticles with a size of 20-30 nm were evenly immobilized on the support. Specific surface area increased by 19.12% after supporting RGO, while it decreased after supporting nZVI and Ag due to the partial blockage of micropores. The Fe surface was concurrently coated by iron oxides (Fe₂O₃, FeOOH) and Ag. THMs were eliminated through multilayer reaction processes. The values of the adsorption constant (K_F) of chloroform (CHCl₃), dichlorobromoethane (CHBrCl₂), dibromochloroethane (CHBr₂Cl), and tribromomethane (CHBr₃) adsorbed by nZVI/Ag@AC-RGO increased by 34.4, 33.7, 81.6, and 67.3%, respectively, compared to pristine AC. THMs with more Br atoms exhibited better removal efficiency and adsorption capacity, along with a higher oxidation degree of the Fe surface. CHBrCl₂ and CHBr₂Cl mainly decomposed into chloromethane (CH₃Cl) and dichloromethane (CH₂Cl₂), and CHBr₃ and CHCl₃ primarily degraded into dibromomethane (CH₂Br₂) and CH₂Cl₂, respectively, along with generating Cl^- and Br^-. Conclusively, THMs-contaminated water could be remediated by coupling AC pre-enrichment and the reactivity of nZVI/Ag.

Performance of tidal and non-tidal mangrove constructed wetlands in treating maricultural wastewater

This study aims to evaluate the removal efficiency of nitrogen and phosphorus in the tidal and non-tidal constructed wetlands with typical mangrove (Aegiceras corniculatum) as a wetland plant model to treat simulated marine wastewater. The results showed that the average removals of NO₂^--N, NO₃^--N, NH₄⁺-N, TN and TP were 88.4, 80.5, 81.4, 79.7 and 40.8%, respectively, in the non-tidal subsurface flow (HF) mangrove wetland, and 65.3, 61.3, 90.6, 60.1 and 19.2% in the tidal (TF) mangrove wetland, and 11.4, 64.6, 68.7, 56.6 and 16.3% in the non-tidal free water surface (FWS) mangrove wetland, respectively. Moreover, it was observed that the composition of microbial communities in the HF mangrove wetland was beneficial to the nitrogen cycle and has more quantitative associations of N-metabolism genes. The results indicated that non-tidal HF mangrove wetland has a stable and an effective capacity for potential treatment of marine wastewater compared with the non-tidal FWS mangrove wetland and tidal TF mangrove wetland.

Adsorption performance and mechanisms of mercaptans removal from gasoline oil using core-shell AC-based adsorbents

Sulfur compound detection such as mercaptans in liquid fuels is undesirable because sulfur is the main sourcing emission of sulfur oxide (SO_x) into the air. The use of activated carbon (AC) has proven to efficiently remove mercaptans. In the meantime, it is limited by the generation of the second pollution in oil and the difficulties of recovery and regeneration. A core-shell structured AC with high mechanical strength and big intra-particles space was synthesized and demonstrated to efficiently remove organic pollutants from an aqueous solution without the generation of the second pollution in our previous work. However, the performance and behaviors of mercaptans adsorption from gasoline oil by core-shell structured AC were still unclear. In this study, the mercaptans adsorption behaviors using core-shell powdered activated carbon (CSAC) and core-shell granulated activated carbon (CSGAC), along with raw PAC, PAC-core, raw GAC, and GAC-core, were carried out. The results showed that both the CSAC and CSGAC adsorbents effectively removed sulfur-based pollutants and were provided with good recovery and recyclability without second pollution in gasoline oil. The CSGAC exhibited a higher mercaptans removal efficiency compared to those of CSAC as a result of the bigger intra-particles space. PAC-based adsorbents presented the shrinking of removal efficiency after regeneration. The pseudo-second-order kinetic model was dominated for mercaptans adsorption by both CSAC and CSGAC. The adsorption of ethanethiol on CSGAC was better fitted to the Freundlich model, 1-butanethiol adsorption by CSAC and CSGAC, and ethanethiol adsorption on CSAC which was dominated by Langmuir model.

Effective adsorption of Direct Red 23 by sludge biochar-based adsorbent: adsorption kinetics, thermodynamics and mechanisms study

Using solid adsorbents, such as biochar, has been a potential practice to remove the pollutants from water bodies to render the water safer for potential usage. A potential application of sludge biochar-based adsorbent (SBA), obtained by pyrolysis with hydrothermal treatment, was developed to adsorb Direct Red 23 (DR23) from wastewater. The results showed that for the synthesized SBA (0.5 g/L) in the adsorption of DR23 at low concentration (<20 mg/L), the DR23 was totally removed from the aqueous solution. pH had a limited effect on the adsorption, while an increase in temperature was shown to have a large enhancing effect. The adsorption kinetics were best fitted by the pseudo-second-order kinetic model, while the equilibrium data were best fitted by the Langmuir isotherm. A maximum saturation adsorption capacity of SBA of 111.98 mg/g was achieved. SBA could then be regenerated by pyrolysis, and after three cycles, SBA still retained good adsorption ability for DR23, a removal rate exceeding 97% was achieved. Functional groups, pores, π-π bond, and electrostatic interactions are the key to the adsorption mechanisms. The results proved that SBA would be a promising material in the application of removing dyes in printing and dyeing wastewater.

The synthesis strategy to enhance the performance and cyclic utilization of granulated activated carbon-based sorbent for bisphenol A and triclosan removal

For a potential and efficient solution in the mitigation of aquatic pollution, this study reported a well-designed and developed protected granulated activated carbon (GAC) material which ensures high strength property and adsorption performance to meet the industrial application. The prepared GAC material was shaped into a spherical core using natural binders basically assumed to constitute waste solids materials. Then after, the granulated carbon core (GAC core) was protected by a porous ceramic shell which confined the material with strong protection and high mechanical strength to resist against degeneration and pressure drop as a limiting factor for most sorbents employed in solution. The CSGAC characterization results proved that the ceramic shell has a smaller thickness (0.1 cm), good mechanical strength (2.0 MPa), and additionally, it presents larger porous channels which promote the fast and higher adsorption performance making it the desired material for the application in the real liquid environment. The test results showed that the prepared material had higher removal of triclosan (TCS) (30-40 mg/L) than BPA counterpart from the aqueous solutions. Moreover, it showed higher adsorption performance compared to the unprotected carbon materials. Furthermore, the mechanisms of BPA and TCS adsorption by core-shell granulated activated carbon (CSGAC) were discussed.

Optimized synthesis of a core-shell structure activated carbon and its adsorption performance for Bisphenol A

The presence of endocrine disrupting chemicals (EDCs) in the environmental water poses a serious threat which requires strong practical solutions. The existing activated carbon-based adsorbents exhibit a number of limitations hindering for their use in adsorption in an aquatic environment. In this work, a controlled technique was used to make a protected Core-Shell structure Activated Carbon (CSAC) material with a smaller size (0.82 cm), thinner shell thickness (0.083 cm) and high mechanical strength (2.41 MPa). The experimental results demonstrated that the sizes of shell precursors used for preparing the ceramic shell had a pronounced influence on the produced material. The shell was prepared by using a mixture of kaolinite (400 mesh) and coal fly ash (100 mesh). The pellet activated carbon core was synthesized by a pelletizing method using powder activated carbon (92%) mixed with the binder (8%) from cassava splinters. The kinetic study evidenced that the performance of the material fitted better for pseudo-second-order kinetic and the intraparticle diffusion. Furthermore, the maximum amount of Bisphenol A (BPA) adsorption by CSAC fitting to Langmuir model was 28.5 mg g^-1. The BPA adsorption by CSAC was an endothermic process. Therefore, this material could be applied in the remediation of various aquatic EDCs.