Recovery of nitrogen and phosphorus in wastewater by red mud-modified biochar and its potential application

Sustainable remediation of butyl xanthate-contaminated mine wastewater by combining emergent macrophyte Cyperus alternifolius with a versatile bacterial isolate

Butyl xanthate (BuX) is an emerging pollutant due to wide use as flotation collector, posing a serious threat to ecosystem health in mining areas. Here we develop a combinational plant-microbe remediation strategy for restoration of BuX-contaminated mining areas. A novel bacterial strain that completely degraded up to 1000 mg/L of BuX within 12 h was isolated and identified as Pseudomonas monteilii W50. It was found to harbor good tolerance to extreme environmental conditions and multiple plant growth-promoting traits such as phosphate and potassium solubilization, indole-3-acetic acid and gibberellin production, and cellulose degradation. This strain can colonize in the rhizosphere of an emergent macrophyte Cyperus alternifolius, improving removal of BuX and chemical oxygen demand (COD) from simulated wastewater. Compared to the phytoremediation alone, the removal of BuX and COD increased from 70 % to 98 % and from 21 % to 46 % respectively in the combined remediation The strain W50 protected the macrophyte from the phytotoxicity of BuX and the macrophyte provided it with a suitable habitat for return, benefiting each other. Compared to the individual treatment using C. alternifolius or strain W50, the combinational treatment significantly improved the plant growth and the residence of inoculated bacteria. Overall, C. alternifolius and strain W50 are the perfect combination for efficient and sustainable remediation of BuX-contaminated mine wastewater, overcoming the constraints of individual phytoremediation or bioaugmentation methods.

Phosphorus recovery and reuse: Innovating with biochar in the circular economy

Global challenges of phosphorus pollution and scarcity underscore an urgent need for the efficient recycling of this critical resource. Biochar, a sustainable and economical material, has demonstrated significant potential as an adsorbent for phosphorus, offering a viable solution for its recovery from wastewater. Various techniques have been explored to improve the ability of biochar to adsorb inorganic phosphate. While numerous studies have reviewed methods of biochar modification, the underlying adsorption mechanisms, and the thermodynamics and kinetics involved, a thorough examination that addresses the practical challenges of real-world wastewater treatment is currently lacking. This review aims to fill this gap by quantitatively analyzing the impact of coexisting species in wastewater on the adsorption of phosphate and by exploring the potential for simultaneous removal of other contaminants, such as nutrients, heavy metals, and dissolved organic matter. The review also discusses factors that affect the desorption of phosphate from biochar and presents practical applications for biochars post-adsorption. These applications include their use as slow-release phosphorus fertilizers, additives in concrete, and as novel adsorbents for the removal of heavy metals. This comprehensive analysis serves to synthesize current research on phosphate recovery by biochars and to propose practical uses for the adsorbed phosphorus, thereby guiding the development of biochar adsorption technology towards more effective and practical phosphorus management strategies.

Assessment of cerium adsorption potential of phosphoric acid activated biochar in aqueous system: Modelling and mechanistic insights

Cerium pollution in waterbodies by improper industrial waste disposal is a major concern due to its detrimental impacts on the environment. Therefore, treatment of cerium-contaminated water is inevitable. Hence, this study is focused on the remediation of cerium pollution using phosphoric acid-activated biochar (PPMB) as an adsorbent, synthesized upon pyrolytic activation of palmyra palm male flower-based pristine biochar (PMFB) with H3PO4 at 500 °C. The physico-chemical surface properties of PMFB and PPMB were evaluated through various microscopic and spectroscopic analyses. The key parameters such as biochar dosage, pH, temperature, contact time and initial cerium concentration were optimized as 0.5 g/L, 5.0, 303 K, 180 min and 50 mg/L respectively via batch adsorption. Pseudo-second order kinetic and Toth isotherm are the best-fitted models. The thermodynamic parameters including ΔG◦ (-30.4707 ± 0.7618 kJ/mol at 303 K), ΔH◦ (16.1499 ± 0.78 kJ/mol), and ΔS◦ (153.617 ± 3.8404 J/mol/K) conveying that cerium adsorption onto PPMB was spontaneous, endothermic, and highly disordered at PPMB-bulk adsorption medium interface. Precipitation, electrostatic attraction, and surface complexation are predicted to be the predominant mechanisms for the chosen PPMB-cerium adsorption system. Moreover, cerium phytotoxicity on Vigna radiata explains the real-time applicability and feasibility of cerium adsorption using PPMB. Thus, the key findings of this study specified that the higher adsorption capacity of PPMB (141.3484 ± 6.9856 mg/g) contributed by the incorporated phosphate groups, predominant mesoporosity, SSABET of 230.559 m2/g and anionic surface at a wider pH range (pH>3.08) make PPMB as efficient, economically feasible and environmentally friendly adsorbent for cerium adsorption in aqueous system.

Removal, conversion and utilization technologies of alkali components in bayer red mud

Bayer red mud is a highly alkaline industrial solid waste generated during alumina production, and its massive discharge and stockpiling poses significant environmental risks. The strong alkalinity of red mud is a primary challenge limiting its effective utilization. This study systematically analyzes the composition and characteristics of alkaline components in red mud, emphasizing the roles of soluble free alkali and chemically bound alkali in regulating its alkalinity. A comprehensive review of current dealkalization technologies, including acid neutralization, CO2 neutralization, and salt precipitation/replacement methods is presented, focusing on their chemical mechanisms, applicability, advantages, and limitations. Specially, this study present the concept of in-situ conversion and utilization of alkali and highlight the beneficial role of alkali components in red mud recycling. The latest technologies for the conversion and utilization of alkali components, including the special roles and principles of alkali in the reaction processes of cement clinker calcination, cement hydration, geopolymers were systematically summarized. Additionally, the environmental potential of red mud in acid wastewater neutralization and flue gas desulfurization is discussed. This study identifies the technical barriers that need to be solved urgently in the current research and proposes a key direction for future study on the regulation of alkali components in red mud.

Engineered biochar for in-situ and ex-situ remediation of contaminants from soil and water

Tailoring physical and chemical properties of biochar enhances its selectivity, treatability, and efficiency in contaminant remediation. Thus, engineered biochar has emerged as a promising remedy for both in-situ and ex-situ remediation of polluted soil and water. Several factors influence the effectiveness of engineered biochar, including feedstock sources, pyrolysis conditions, surface functionalization, mode of application, and site characteristics. The advantages and disadvantages of different modification approaches to engineered biochar and their specific treatability for in-situ and ex-situ remediation are obscure and must be adequately addressed. This review critically evaluates the application of engineered biochar for on/off-spot contamination management, taking into account the long-term stability and biocompatibility prospects. The properties of engineered biochar resulting from modification with clay minerals, nanoparticles, polymers, surfactants, and oxidants/reductants were critically reviewed. Recent progress and advances in remediation mechanisms and modes of application were elaborated for the effective removal of organic and inorganic contaminants, including heavy metals, pesticides, dyes, polycyclic aromatic hydrocarbons, per- and poly-fluoroalkyl substances, and agrochemicals. Several crucial parameters influence in-situ remediation, including the distribution of contaminants, background electrolytes, hydraulic conductivity, as well as dispersion and stability of adsorbents. Ex-situ remediation of pollutants relies heavily on adsorption or degradation kinetics, background electrolytes, adsorbent dose, and pollutant concentrations. In addition, factors restricting the application of engineered biochar were highlighted for long-term sustainable contaminant management and maintaining low environmental impact. Finally, the challenges and future perspectives of utilizing engineered biochar for field-scale demonstration of contaminated sites are proposed.

Effects of flotation reagents with aniline aerofloat and ammonium dibutyl dithiophosphate on a constructed rapid infiltration system: Performance and microbial metabolic pathways

Aniline aerofloat (AAF) and ammonium dibutyl dithiophosphate (ADD) are the key flotation reagents in mineral processing. This study investigated the performance of the constructed rapid infiltration systems with coke and red mud as adsorbents for treatment AAF and ADD wastewater. Meanwhile, the effects of AAF and ADD on the microbial metabolic pathways of the systems were unraveled. Results showed that the AAF concentration in influent was 25 mg/L, which promoted chemical oxygen demand (COD) and total phosphorus (TP) removal of the A column (coke) and B column (red mud). While the COD and TP removal of the C column (coke) and D column (red mud) were inhibited with ADD concentration increasing to 50 mg/L and 100 mg/L. The AAF reduced the binding energy of coke C-O bond by 0.9 eV, and down-regulated the C-C bond ratio by 40.72%. The dominant phyla in the columns were Pseudomonadota and Actinomycetota. The pore structure of coke was more conducive to the growth of the Pseudomonadota, while the metal composition of red mud was more conducive to the redox reaction of microorganisms. The presence of phosphofructokinase (2.7.1.11)-related genes was up-regulated in column C compared to other columns. The ADD was beneficial to the expression of norC and nosZ functional genes during nitrogen metabolism process. In contrast, phosphorus metabolism genes were more expressed in the red mud column for treatment AAF wastewater. This study reveals the potential of coke and red mud for the treatment of flotation reagents wastewater, while providing a theoretical basis for the optimal selection of filler types in the constructed rapid infiltration systems.

Treating Waste with Waste: Activated Bauxite Residue (ABR) as a Potential Wastewater Treatment

Bauxite residue (or red mud) is a highly alkaline waste generated during the extraction of alumina. As a result of the substantial accumulation of bauxite residue in tailings facilities, there is a growing interest in exploring the potential for reusing this material for other purposes. The main objective of this study is to evaluate the use of activated bauxite residue (ABR) for remediating oil sands process-affected water (OSPW) and as a supplement to municipal wastewater treatment through bench-scale, proof-of-concept studies. The ABR is produced through a reduction roasting process that alters the physicochemical properties of bauxite residue, resulting in the generation of potentially effective adsorbent media. The treatment performance via chemical and biological activity removals (cytotoxicity, estrogenicity, and mutagenicity) was also assessed. For OSPW, ABR treatment resulted in the effective removal of recalcitrant acid-extractable organics (AEOs), with kinetics following the pseudo-second-order and comparable adsorption capacity to other waste materials (e.g., petroleum coke). ABR also effectively reduced the estrogenicity and mutagenicity of OSPW, albeit cytotoxicity increased at higher dosages, possibly due to some components leaching out of the material (e.g., metals). For municipal wastewater, ABR treatment reduced fecal coliform concentrations (>99%), total phosphorus (up to 98%), total ammonia-nitrogen (63%), estrogenicity (nondetectable), and mutagenicity (nondetectable), especially in the primary effluent. The ultimate end use of ABR is for the recovery of valuable metals (especially iron) and as a construction material, but additional work is needed to optimize the dosage (currently in the g/L range) and maximize the use of ABR as an adsorbent prior to its subsequent uses.

Unlocking the potential of environmentally friendly adsorbent derived from industrial wastes: A review

With increasing urbanization and industrialization, growing amounts of industrial waste, such as red mud (RM), fly ash (FA), blast furnace slag (BFS), steel slag (SS), and sludge, are being produced, exposing substantial threats to the environment and human health. Given that numerous researchers associate with conventional adsorbents, developing and utilizing industrial wastes derived from adsorption technology still has received limited attention. Utilizing this waste contributes to developing alternative materials with superior performance and significantly reduces the volume of solid waste. The excellent physical and chemical characteristics of these wastes are also investigated in this paper. This review attempts to demonstrate a comprehensive overview of the application of industrial waste-based adsorbent in the adsorption process for removing organic pollutants, dyes, metallic ions, non-metallic ions, and radioactive substances. In addition, industrial waste-based adsorbents are among the most promising and applicable techniques for pollutant removal, offering remarkable adsorption efficiency, rich surface chemistries, reasonable cost, simple operation, and low energy consumption. This review summarizes state-of-the-art advancements in engineered adsorbents (including physical and chemical modifications). It provides a holistic view regarding a comprehensive understanding of the mechanism involved in adsorption for water remediation. The challenges and the prospects for future research in applying these adsorbents are also elucidated, contributing to sustainable waste management and environmental sustainability.

Biochar coupled with multiple technologies for the removal of nitrogen and phosphorus from water: A review

Water eutrophication caused by nitrogen (N) and phosphorus (P) has become a global environmental issue. Biochar is a competent adsorbent for removing N and P from wastewater. However, compared with commercial activated carbon, biochar has relatively limited adsorption capacity. To broaden the field scale application of biochar, biochar coupled with multiple technologies (BC-MTs) (such as microorganisms, electrochemistry, biofilm, phytoremediation, etc.) have been extensively developed for environmental remediation. Nevertheless, due to the fluctuations and differences in biochar types, coupling methods, and wastewater types, various techniques show different removal mechanisms and performance, hindering the promotion and application of BC-MTs. A systematic review of the research progress of BC-MTs is highly necessary to gain a better understanding of the current research status and progress, as well as to promote the application of these techniques. In this paper, the application of pristine and modified biochar in adsorbing N and P in wastewater is critically reviewed. Then the removal performance, influencing factors, mechanisms, and the environmental applications of BC-MTs in wastewater are systematically summarized. In addition, the cost analysis and risk assessment of BC-MTs in environmental applications are conducted. Finally, suggestions and prospects for future research and practical application are put forward.

Study on the adsorption of phosphate by composite biochar of phosphogypsum and rape straw

Wastewater containing phosphorus is often added by industrial activities, which is bad for the environment. In this study, composite biochar (PG-RS700) was prepared from phosphogypsum (PG) and rape straw (RS) for the treatment of phosphate in wastewater. SEM, FTIR, XRD and XPS characterization results showed that PG and RS were successfully combined. When PG-RS700 was dosed at 1.5 g/L and the phosphate solution concentration was 50 mg/L and pH = 8, the phosphate removal rate was 100% and the adsorption capacity was three times higher than the corresponding pure PG and RS. The quasi-secondary kinetic model indicated that the adsorption mechanism was chemisorption, and the maximum adsorption capacity for phosphate in the Langmuir isotherm model was 102.25 mg/g. Through pot experiment, the phosphorus adsorbed material obviously promoted the growth of plants. PG-RS700 can be used as a powerful adsorbent to treat phosphate in water and return it to soil as phosphate fertilizer.

Highly efficient removal of aqueous phosphate via iron-manganese fabricated biochar: Performance and mechanism

Biochar (BC) has emerged as a potential solution to phosphate removal from wastewater primarily resulting from global overuse of fertilizers. Further modification by embedment of iron (Fe)-manganese (Mn) oxides on BC can enhance phosphate removal; however, the modification method serves as a vital factor underlying distinctive removal performances and mechanisms, which have yet been systematically examined. Herein, two Fe-Mn modified BC, Fe/MnBC (comprised of Fe3O4 and MnO2) and Fe-MnBC (comprised of MnFe2O4), were comprehensively investigated for gaining insights into the unsolved perspectives. The results indicated that Fe-MnBC exhibited a markedly greater maximum phosphate adsorption capacity of 135.88 mg g-1 than that of Fe/MnBC with 17.93 mg g-1. The comparative results based on microstructure and spectroscopic analyses suggested that different Fe and Mn oxides were successfully loaded, which played a distinctive role in phosphate removal. Further characterizations unveiled that the key mechanisms for phosphate removal by Fe/MnBC are inner-sphere complexation and precipitation, while electrostatic interaction and outer-sphere complexation are the dominant mechanisms underlying the notable performance of Fe-MnBC. The delicately designed Fe-MnBC with special structure and property also enabled a superior regeneration capacity, which presented a promisingly high phosphate removal efficacy of over 81.34% after five cycles. These results enhance comprehension regarding the impact of biochar modification techniques on phosphate removal, offering positive indications for the remediation of excessive phosphate and other pollutant-containing water through feasible design and green chemicals.

Removal of environmental pollutants using biochar: current status and emerging opportunities

In recent times, biochar has emerged as a novel approach for environmental remediation due to its exceptional adsorption capacity, attributed to its porous structure formed by the pyrolysis of biomass at elevated temperatures in oxygen-restricted conditions. This characteristic has driven its widespread use in environmental remediation to remove pollutants. When biochar is introduced into ecosystems, it usually changes the makeup of microbial communities by offering a favorable habitat. Its porous structure creates a protective environment that shields them from external pressures. Consequently, microorganisms adhering to biochar surfaces exhibit increased resilience to environmental conditions, thereby enhancing their capacity to degrade pollutants. During this process, pollutants are broken down into smaller molecules through the collaborative efforts of biochar surface groups and microorganisms. Biochar is also often used in conjunction with composting techniques to enhance compost quality by improving aeration and serving as a carrier for slow-release fertilizers. The utilization of biochar to support sustainable agricultural practices and combat environmental contamination is a prominent area of current research. This study aims to examine the beneficial impacts of biochar application on the absorption and breakdown of contaminants in environmental and agricultural settings, offering insights into its optimization for enhanced efficacy.

Investigation of the effects of biochar amendment on soil under freeze‒thaw cycles and the underlying mechanism

Biochar (BC) is widely utilized as a soil amendment; however, for widely distributed seasonally frozen soils, the effect of BC on soil and the optimal utilization of BC during the freeze‒thaw process are still unclear. In this study, the effects of freeze‒thaw aged biochar (FT-BC) and BC on soil properties and wheat cultivation were systematically investigated, and the underlying interaction mechanism between BC and soil was explored. The results show that FT-BC dramatically reduces the adverse effects of freeze‒thaw cycles on soil, enhances wheat growth, and increases dry matter yield by 17.5 %, which is mainly attributed to the ability of FT-BC to maintain soil structure, reduce water loss rates to below 0.20 g/h, and decrease nitrogen leaching by more than 20 % during freeze‒thaw cycles. Additionally, fresh BC had a greater effect on the fixation of cadmium than FT-BC in the soil, reducing its accumulation in wheat by 22.5 %. Multiple characterizations revealed that the freeze‒thaw process increased the porosity and specific surface area of FT-BC, providing more sites for water and nitrogen adsorption, whereas the dissolved organic matter released from fresh BC had a better ability to trap cadmium. These findings provide insights into the interactions between BC and soil components during the freeze‒thaw process and suggest the optimized utilization of fresh BC and FT-BC for different soil repair purposes.

Bauxite residue (red mud) treatment: Current situation and promising solution

Bauxite residue, an industrial solid waste generated during alumina production, with over 80 % of bauxite residue worldwide being accumulated around alumina plants, which occupying a significant amount of land resources and posing a threat to the natural environment in the surrounding areas. This paper reviews recent advances in extracting valuable resources from bauxite residue, and its applications in building materials, environmental adsorbents, energy storage materials, and soil alkalinization. It also highlighted the main problem existing in these researches, which is the inability of the existing single processes to achieve the comprehensive utilization of various types of bauxite residue or maximize the utilization of bauxite residue components, resulting in a low comprehensive utilization rate and insignificant absorption effects of bauxite residue. To address these issues, we proposed a strategy of classifying and utilizing bauxite residue based on its components and establishing a multi-industry application system, involving sectors such as steel and building materials. This collaborative approach aims to handle various types of bauxite residue more effectively. Additionally, we suggest selecting suitable treatment methods based on the specific characteristics of bauxite residue and implementing measures to promote its comprehensive and large-scale utilization.

Magnesium doped biochar for simultaneous adsorption of phosphate and nitrogen ions from aqueous solution

Phosphorus (P) and Ammonium Nitrogen (N) are essential nutrients for plants and environmental stability. However, their excess in water causes eutrophication, damaging aquatic ecosystems. While adsorption is a promising solution, finding affordable and efficient adsorbents remains a challenge. In this study, magnesium (Mg), iron (Fe), and Mg/Fe doped biochars (BC) adsorbents were synthesized, and evaluated for adsorption of individual P and N and a P + N mixture from a solution and wastewater from a wastewater treatment plant. Compared to other adsorbents, Mg/BC showed excellent performance in adsorbing phosphorus (P) and ammonium nitrogen (N) from aqueous solutions. It demonstrated a large adsorption capacity of 64.65 mg/g and 62.50 mg/g from individual P and N solutions, and 30.3 mg/g and 27.67 mg/g from the P and N mixture solution, respectively. In addition, Mg/BC efficiently removed P and N from real-life wastewater. In the real wastewater, P and N removal efficiencies reached 88.30% and 59.36%, respectively. Kinetics analysis revealed that the pseudo-second-order model accurately described the adsorption of phosphorus (P) and ammonium nitrogen (N) in all solutions. The adsorbent followed the monolayer-Langmuir isotherm for N ions and the multilayer-Freundlich isotherm for P, indicating efficient adsorption processes. Thermodynamic experiments indicated that the adsorption of P and N was not only feasible but also occurred spontaneously in a natural manner. This study revealed that the strategic modification of biochar plays a crucial role in advancing effective wastewater treatment technologies designed for nutrient removal.

Nano La(OH)3 modified lotus seedpod biochar: A novel solution for effective phosphorus removal from wastewater

Effective removal of phosphorus from water is crucial for controlling eutrophication. Meanwhile, the post-disposal of wetland plants is also an urgent problem that needs to be solved. In this study, seedpods of the common wetland plant lotus were used as a new raw material to prepare biochar, which were further modified by loading nano La(OH)3 particles (LBC-La). The adsorption performance of the modified biochar for phosphate was evaluated through batch adsorption and column adsorption experiments. Adsorption performance of lotus seedpod biochar was significantly improved by La(OH)3 modification, with adsorption equilibrium time shortened from 24 to 4 h and a theoretical maximum adsorption capacity increased from 19.43 to 52.23 mg/g. Moreover, LBC-La maintained a removal rate above 99% for phosphate solutions with concentrations below 20 mg/L. The LBC-La exhibited strong anti-interference ability in pH (3-9) and coexisting ion experiments, with the removal ratio remaining above 99%. The characterization analysis indicated that the main mechanism is the formation of monodentate or bidentate lanthanum phosphate complexes through inner sphere complexation. Electrostatic adsorption and ligand exchange are also the mechanisms of LBC-La adsorption of phosphate. In the dynamic adsorption experiment of simulated wastewater treatment plant effluent, the breakthrough point of the adsorption column was 1620 min, reaching exhaustion point at 6480 min, with a theoretical phosphorus saturation adsorption capacity of 6050 mg/kg. The process was well described by the Thomas and Yoon-Nelson models, which indicated that this is a surface adsorption process, without the internal participation of the adsorbent.

Metal element-based adsorbents for phosphorus capture: Chaperone effect, performance and mechanism

Excessive phosphorus (P) enters the water bodies via wastewater discharges or agricultural runoff, triggering serious environmental problems such as eutrophication. In contrast, P as an irreplaceable key resource, presents notable supply-demand contradictions due to ineffective recovery mechanisms. Hence, constructing a system that simultaneously reduce P contaminants and effective recycling has profound theoretical and practical implications. Metal element-based adsorbents, including metal (hydro) oxides, layered double hydroxides (LDHs) and metal-organic frameworks (MOFs), exhibit a significant chaperone effect stemming from strong orbital hybridization between their intrinsic Lewis acid sites and P (Lewis base). This review aims to parse the structure-effect relationship between metal element-based adsorbents and P, and explores how to optimize the P removal properties. Special emphasis is given to the formation of the metal-P chemical bond, which not only depends on the type of metal in the adsorbent but also closely relates to its surface activity and pore structure. Then, we delve into the intrinsic mechanisms behind these adsorbents' remarkable adsorption capacity and precise targeting. Finally, we offer an insightful discussion of the prospects and challenges of metal element-based adsorbents in terms of precise material control, large-scale production, P-directed adsorption and effective utilization.

Efficient Adsorption of Nitrogen and Phosphorus in Wastewater by Biochar

Nitrogen and phosphorus play essential roles in ecosystems and organisms. However, with the development of industry and agriculture in recent years, excessive N and P have flowed into water bodies, leading to eutrophication, algal proliferation, and red tides, which are harmful to aquatic organisms. Biochar has a high specific surface area, abundant functional groups, and porous structure, which can effectively adsorb nitrogen and phosphorus in water, thus reducing environmental pollution, achieving the reusability of elements. This article provides an overview of the preparation of biochar, modification methods of biochar, advancements in the adsorption of nitrogen and phosphorus by biochar, factors influencing the adsorption of nitrogen and phosphorus in water by biochar, as well as reusability and adsorption mechanisms. Furthermore, the difficulties encountered and future research directions regarding the adsorption of nitrogen and phosphorus by biochar were proposed, providing references for the future application of biochar in nitrogen and phosphorus adsorption.

Biochar supported nanoscale zerovalent iron-calcium alginate composite for simultaneous removal of Mn(II) and Cr(VI) from wastewater: Sorption performance and mechanisms

Heavy metal pollution in water caused by industrial activities has become a global environmental issue. Among them, manganese mining and smelting activities have caused the combined pollution of Cr(VI) and Mn(II) in water, posing a serious ecotoxicological risk to ecological environments and human health. To efficiently remove Cr(VI) and Mn(II) from wastewater, a novel biochar supported nanoscale zerovalent iron-calcium alginate composite (CA/nZVI/RSBC) was synthesized by liquid-phase reduction and calcium alginate embedding methods. The adsorption performance and mechanisms of Cr(VI) and Mn(II) by CA/nZVI/RSBC were investigated. The maximum adsorption capacities of Cr(VI) and Mn(II) onto CA/nZVI/RSBC fitted by the Langmuir model were 5.38 and 39.78 mg/g, respectively, which were much higher than the pristine biochar. The iron release from CA/nZVI/RSBC was comparatively lower than that of nZVI/RSBC. Mn(II) presence enhanced the reduction of Cr(VI) by CA/nZVI/RSBC. The results of XRD, XPS, and site energy distribution analysis indicated that redox was the predominant mechanism of Cr(VI) adsorption, while electrostatic attraction dominated Mn(II) adsorption. This study provides a novel alternative way for the simultaneous removal of Cr(VI) and Mn(II) in wastewater.

Green synthesis of CaxLa1-xMnO3 with modulation of mesoporous and vacancies for efficient low concentration phosphate adsorption

Phosphate concentrations in eutrophic surface waters are usually low, and efficient removal of low concentration phosphate remains a challenge. In this study, Ca-doped LaMnO3 synthesized at doping ratios, designated as CaxLa1-xMnO3 (x = 0, 0.2, 0.4, 0.7), were compared. It was found that, the adsorption capacity of Ca0.4La0.6MnO3 material reached 63.01 mg/g at pH = 5, increased by 63.6% over the undoped LaMnO3 perovskite. For long-term adsorption, Ca0.4La0.6MnO3 could constantly adsorb phosphate to avoid phosphate accumulation (<0.05 mg/L). This proves that Ca0.4La0.6MnO3 has the ability to control dynamic water eutrophication. Characterization and density functional theory results confirmed that CaxLa1-xMnO3 can increase the content of mesopores and oxygen vacancies, providing additional active sites. This reduces the adsorption energy of the La site, promotes electron transfer, and increases its affinity. It provides a new method for removing low-concentration phosphates.

Enhanced simultaneous removal of phosphate and ammonium from swine wastewater using magnetic magnesium-loaded Chinese herbal medicine residues: Performance, mechanism, and resource utilization

Magnetic magnesium (Mg)-loaded Chinese herbal medicine residues (MM-TCMRs) were fabricated to simultaneously remove and recover phosphate and ammonium from wastewater. The MM-TCMRs exhibited larger specific surfaces and rougher structures with massive spherical particles than those of original residues. They could be separated by adjusting the magnetic field. The phosphate and ammonium adsorption by MM-TCMRs were matched with the pseudo-second-order model, while the Langmuir model yielded the maximum adsorption capacities of 635.35 and 615.57 mg g-1, respectively. Struvite precipitation on the MM-TCMRs surface was the primary removal mechanism with electrostatic attraction, ligand exchange, intra-particle diffusion, and ion exchange also involved. The recyclability of MM-TCMRs confirmed their good structural stability. More importantly, the nutrient-loaded MM-TCMRs enhanced alfalfa growth and improved soil fertility in planting experiments. Collectively, the MM-TCMRs are promising candidates for nutrient removal and recovery from wastewater.

Adsorption recovery of phosphorus in contaminated water by calcium modified biochar derived from spent coffee grounds

Phosphate recovery from water is essential for reducing water eutrophication and alleviating the phosphorus resource crisis. In this study, spent coffee grounds and CaCl2 were used as raw materials and a modifier, respectively, to create a novel calcium modified biochar (MBC) for removing phosphorus from water. The modified biochar (MBC) was the best at removing phosphorous when the modifier concentration was 1.5 M with theoretically maximum adsorption capacity of 70.26 mg/g. MBC also performed well in the wide pH range of 3-11 under different phosphorus concentration gradients, with phosphorus removal efficiency of more than 50 %. According to kinetic analysis, the adsorption process at low phosphorus concentrations (50-100 mg/L) can be more properly described by the pseudo-first-order model, while the pseudo-second-order model best describes the adsorption process at high concentrations (200-600 mg/L). The thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic. Characterization results revealed that surface precipitation, complexation, and ligand exchange were the dominant mechanisms of phosphorus adsorption. MBC has great potential to recover phosphorus from wastewater.

Efficient rhodamine B dye degradation by red mud-grapefruit peel biochar catalysts activated persulfate in water

The continuous and rapid development of textile industry intensifies rhodamine B dye (RhB) wastewater pollution. Meanwhile, massive red mud (RM) solid waste generated by the industrial alumina production process poses detrimental effects to the environment after leaching. For resource utilization and to reduce the expansion of RhB pollution, RM and peel red mud-biochar composite (RMBC) catalyst were synthesized in activating peroxydisulfate (PDS) for RhB degradation. Firstly, characterization results showed that compared to RM, RMBC had a higher content of catalytically active metals (Fe, Al, Ti) (higher than 0.92-4.18%), smaller pore size, and larger specific surface area (10 times), which verified RMBC had more potential catalytic oxidation activity. Secondly, under optimal dosage (catalyst, PDS), pH 4.6, and 20 mg L-1 RhB, it was found that the RhB degradation ratio of RM was 76.70%, which was reduced to 41% after three cycles, while that of RMBC was 89.98% and 67%, respectively. The results indicated that the performance of RMBC was significantly superior to that of RM. Furthermore, the quenching experiments, electron paramagnetic resonance spectroscopy tests, FTIR, and XPS analysis showed the function of O-H, C=O, C-O, Fe-O, and Fe-OH functional groups, which converted the PDS to the active state and hydrolyzed it to produce free radicals ([Formula: see text], 1O2, [Formula: see text]) for RhB degradation. And, Q Exactive Plus MS test obtained that RhB was degraded to CO2, H2O, and intermediate products. This study aimed to raise a new insight to the resource utilization of RM and the control of dye pollution.

Synthesis of co-pyrolyzed biochar using red mud and peanut shell for removing phosphate from pickling wastewater: Performance and mechanism

Iron (Fe)/iron oxide-modified biochar has practicable adsorption capability for phosphorus (P), but it is expensive. In this study, we synthesized novel low-cost and eco-friendly adsorbents co-pyrolyzed biochars using Fe-rich red mud (RM) and peanut shell (PS) wastes via a one-step pyrolysis process for removing P from pickling wastewater. The preparation conditions (heating rate, pyrolysis temperature, and feedstock ratio) and P adsorption behaviors were systematically investigated. In addition, a series of characterization and approximate site energy distribution (ASED) analyses were conducted to understand the P adsorption mechanisms. The magnetic biochar (BR7P3) with m (RM):m (PS) of 7:3 prepared at 900°C and 10 °C/min had a high surface area (164.43 m2/g) and different abundant ions (including Fe3+, and Al3+). In addition, BR7P3 exhibited the best P removal capability (142.6 mg/g). The Fe2O3 from RM was successfully reduced to Fe0, which was easily oxidized as Fe3+ to precipitate with H2PO4-. The electrostatic effect, Fe-O-P bonding, and surface precipitation were the main mechanisms of P removal. ASED analyses revealed that high distribution frequency and solution temperature led to a high P adsorption rate of the adsorbent. Therefore, this study provides new insight into the waste-to-wealth strategy by transforming PS and RM into mineral-biomass biochar with excellent P adsorption capability and environmental adaptability.

Sewage phosphorus recovery through sachets loaded with water treatment plant sludge

Conventional wastewater treatment plants (WWTPs) present low phosphorus (P) removal capacity. Conversely, water treatment plants (WTPs) produce sludge with great P sorption from wastewater; however, directly adding the sludge into the wastewater treatment system could increase the effluent turbidity. As a novel approach, the present study evaluated the performance of WTP sludge within paper sachets for P removal from treated sewage. Different sludge concentrations (2-30 g L-1) and contact times (1-27 d) were applied to treat sewage from a university WWTP outlet. The sludge was characterized by P, Fe, and Al content. Larger sludge masses showed higher P removal efficiencies due to their high Fe content, especially at longer contact times (up to 100% at the final of the experiment). However, there is a more significant P reduction in the first 10 d (more than 90% in the most efficient treatment - 30 mg L-1). Based on the kinetic and isotherm analyses and the sludge chemical composition, precipitation proved to be a mechanism of great importance in P removal. Therefore, WTP sludge sachets can be a promising way to remove P from sewage, and the formed solid waste might be reused as an alternative fertilizer.

The role of phosphorus speciation of biochar in reducing available Cd and phytoavailability in mining area soil: Effect and mechanism

The effect of phosphorus (P) speciation in biochar on soil available Cd and its mechanism to alleviate plant Cd stress remain largely unknown. Here, ammonium polyphosphate (PABC)-, phosphoric acid (PHBC)-, potassium dihydrogen phosphate (PKBC)-, and ammonium dihydrogen phosphate (PNBC)-modified biochar were used to investigate P speciation. The Cd immobilization mechanism of biochar was analyzed by XPS and ³¹P NMR, and the soil quality and the mechanism for the biochar to alleviate Cd stress were also determined. The results demonstrated that PBC (pristine biochar), PABC, PHBC, PKBC, and PNBC reduced the content of soil DTPA-Cd by 14.96 % - 32.19 %, 40.44 % - 47.26 %, 17.52 % - 41.78 %, and 21.90 % - 36.64 %, respectively. The XPS and ³¹P NMR results demonstrated that the orthophosphate on the surface of PABC, PHBC, PKBC, and PNBC accounted for 82.06 %, 62.77 %, 33.1 %, and 54.46 %, respectively, indicating that PABC has the highest passivation efficiency on soil Cd, which was ascribed to the highest orthophosphate content on the biochar surface. Pot experiments revealed that PABC could reduce the Cd content by 4.18, 4.41, 4.43, 2.94, and 2.57 folds in roots, stems, leaves, pods, and grains, respectively, and at the same time increase the dry and fresh weight of soybean and decrease Cd toxicity to soybean by improving the antioxidant system. In addition, application of the P-modified biochars improved the enzyme activity and physicochemical properties of the soil. This study provides a new perspective for studying the effect of P-modified biochars on soil Cd immobilization.

Functional biochar fabricated from red mud and walnut shell for phosphorus wastewater treatment: Role of minerals

A novel functional biochar (BC) was prepared from industrial waste red mud (RM) and low-cost walnut shell by one facile-step pyrolysis method to adsorb phosphorus (P) in wastewater. The preparation conditions for RM-BC were optimized using Response Surface Methodology. The adsorption characteristics of P were investigated in batch mode experiments, while a variety of techniques were used to characterize RM-BC composites. The impact of key minerals (hematite, quartz, and calcite) in RM on the P removal efficiency of the RM-BC composite was studied. The results showed that RM-BC composite produced at 320 °C for 58 min, with a 1:1 mass ratio of walnut shell and RM, had a maximum P sorption capacity of 15.48 mg g^-1, which was more than double that of the raw BC. The removal of P from water was found to be facilitated significantly by hematite, which forms Fe-O-P bonds, undergoes surface precipitation, and exchanges ligands. This research provides evidence for the effectiveness of RM-BC in treating P in water, laying the foundation for future scaling-up trials.

Detection and removal technologies for ammonium and antibiotics in agricultural wastewater: Recent advances and prospective

With the extensive development of industrial livestock and poultry production, a considerable part of agricultural wastewater containing tremendous ammonium and antibiotics have been indiscriminately released into the aquatic systems, causing serious harms to ecosystem and human health. In this review, ammonium detection technologies, including spectroscopy and fluorescence methods, and sensors were systematically summarized. Antibiotics analysis methodologies were critically reviewed, including chromatographic methods coupled with mass spectrometry, electrochemical sensors, fluorescence sensors, and biosensors. Current progress in remediation methods for ammonium removal were discussed and analyzed, including chemical precipitation, breakpoint chlorination, air stripping, reverse osmosis, adsorption, advanced oxidation processes (AOPs), and biological methods. Antibiotics removal approaches were comprehensively reviewed, including physical, AOPs, and biological processes. Furthermore, the simultaneous removal strategies for ammonium and antibiotics were reviewed and discussed, including physical adsorption processes, AOPs, biological processes. Finally, research gaps and the future perspectives were discussed. Through conducting comprehensive review, future research priorities include: (1) to improve the stabilities and adaptabilities of detection and analysis techniques for ammonium and antibiotics, (2) to develop innovative, efficient, and low cost approaches for simultaneous removal of ammonium and antibiotics, and (3) to explore the underlying mechanisms that governs the simultaneous removal of ammonium and antibiotics. This review could facilitate the evolution of innovative and efficient technologies for ammonium and antibiotics treatment in agricultural wastewater.