Magnetic biochar composite decorated with amino-containing biopolymer for phosphorus recovery from swine wastewater

Divergent responses of phosphorus solubilizing bacteria with P-laden biochar for enhancing nutrient recovery, growth, and yield of canola (Brassica napus L.)

The growing global population has led to a heightened need for food production, and this rise in agricultural activity is closely tied to the application of phosphorus-based fertilizers, which contributes to the depletion of rock phosphate (RP) reserves. Considering the limited P reserves, different approaches were conducted previously for P removal from waste streams, while the adsorption of ions is a novel strategy with more applicability. In this study, a comprehensive method was employed to recover phosphorus from wastewater by utilizing biochar engineered with minerals such as calcium, magnesium, and iron. Elemental analysis of the wastewater following a batch experiment indicated the efficiency of the engineered biochar as an adsorbent. Subsequently, the phosphorus-enriched biochar, hereinafter (PL-BCsb), obtained from the wastewater, underwent further analysis through FTIR, XRD, and nutritional assessments. The results revealed that the PL-BCsb contained four times higher (1.82%) P contents which further reused as a fertilizer supplementation for Brassica napus L growth. PL-BCsb showed citric acid (34.03%), Olsen solution (10.99%), and water soluble (1.74%) P desorption. Additionally, phosphorous solubilizing bacteria (PSB) were incorporated with PL-BCsb along two P fertilizer levels P45 (45 kg ha-1) and P90 (90 kg ha-1) for evaluation of phosphorus reuse efficiency. Integrated application of PL-BCsb with half of the suggested amount of P45 (45 kg ha-1) and PSB increased growth, production, physiological, biochemical, and nutritional qualities of canola by almost two folds when compared to control. Similarly, it also improved soil microbial biomass carbon up to four times, alkaline and acid phosphatases activities both by one and half times respectively as compared to control P (0). Furthermore, this investigation demonstrated that waste-to-fertilizer technology enhanced the phosphorus fertilizer use efficiency by 55-60% while reducing phosphorus losses into water streams by 90%. These results have significant implications for reducing eutrophication, making it a promising approach for mitigating environmental pollution and addressing climate change.

Structural design of La2(CO3)3 loaded magnetic biochar for selective removal of phosphorus from wastewater

High levels of phosphorus released into the environment can cause eutrophication issues in wastewater, therefore discharge concentrations of such element are regulated in many countries. This study addresses the pressing need for effective phosphorus removal methods by developing a novel La2(CO3)3 and MnFe2O4 loaded biochar composite (LMB). A remarkable adsorption capacity towards the three forms of phosphorus from wastewater, including phosphate, phosphite, and etidronic acid monohydrate (as a representative of organic phosphorus), was exhibited by LMB (88.20, 16.35, and 15.95 mg g-1, respectively). The high saturation magnetization value (50.17 emu g-1) highlighted the easy separability and recyclability of the adsorbent. The adsorption process was well described by the Langmuir isotherm model and the pseudo-second-order kinetic model, which mainly involved chemisorption. Characterization results confirm the effective loading of La2(CO3)3 with ligand exchange and electrostatic attraction identified as the primary mechanisms. Importantly, the LMB demonstrated exceptional selectivity for phosphorus in wastewater samples containing various substances, exhibiting minimal interference from competing ions (Cl-, NO3-, SO42-, and CO32-). These findings enhance the understanding of LMB's application in efficient wastewater phosphorus removal. Holding significant promise in wastewater remediation, the LMB acts as an effective adsorbent, contributing substantially to the prevention and control of various types of phosphorus pollutants, thereby mitigating wastewater eutrophication.

An Updated Overview of Magnetic Composites for Water Decontamination

Water contamination by harmful organic and inorganic compounds seriously burdens human health and aquatic life. A series of conventional water purification methods can be employed, yet they come with certain disadvantages, including resulting sludge or solid waste, incomplete treatment process, and high costs. To overcome these limitations, attention has been drawn to nanotechnology for fabricating better-performing adsorbents for contaminant removal. In particular, magnetic nanostructures hold promise for water decontamination applications, benefiting from easy removal from aqueous solutions. In this respect, numerous researchers worldwide have reported incorporating magnetic particles into many composite materials. Therefore, this review aims to present the newest advancements in the field of magnetic composites for water decontamination, describing the appealing properties of a series of base materials and including the results of the most recent studies. In more detail, carbon-, polymer-, hydrogel-, aerogel-, silica-, clay-, biochar-, metal-organic framework-, and covalent organic framework-based magnetic composites are overviewed, which have displayed promising adsorption capacity for industrial pollutants.

Functionalization of Shorea faguetiana biochar using Fe2O3 nanoparticles and MXene for rapid removal of methyl blue and lead from both single and binary systems

The synthesis of polymeric magnetic composites is a promising strategy for the rapid and efficient treatment of wastewater. Lead and methyl blue are extremely hazardous to living organisms. The sorption of Pb2+ and the dye methyl blue (MB) by biochar is an ecologically sustainable method to remediate this type of water pollution. We functionalized Shorea faguetiana biochar with Fe2O3 and MXene, resulting in Fe2O3/BC/MXene composites with an efficient, rapid, and selective adsorption performance. Based on X-ray photoelectron and Fourier transform infrared spectrometry, we found that the Fe2O3/BC/MXene composites had an increased number of surface functional groups (F-, C[double bond, length as m-dash]O, CN, NH, and OH-) compared with the original biochar. The batch sorption findings showed that the maximum sorption capacities for Pb2+ and MB at 293 K were 882.76 and 758.03 mg g-1, respectively. The sorption phenomena obeyed a pseudo-second-order (R2 = 1) model and the Langmuir isotherm. There was no competition between MB and Pb2+ in binary solutions, indicating that MB and Pb2+ did not influence each other as a result of their different adsorption mechanisms (electrostatic interaction for Pb2+ and hydrogen bonding for MB). This illustrates monolayer sorption on the Fe2O3/BC/MXene composite governed by chemical adsorption. Thermodynamic investigations indicated that the sorption process was spontaneous and exothermic at 293-313 K, suggesting that it is feasible for practical applications. Fe2O3/BC/MXene can selectively adsorb Pb2+ ions and MB from wastewater containing multiple interfering metal ions. The sorption capacities were still high after five reusability experiments. This work provides a novel Fe2O3/BC/MXene composite for the rapid and efficient removal of Pb2+ and MB.

Thermal Air Oxidation-Mediated Synchronous Coordination and Carbonation of Lanthanum on Biochar toward Phosphorus Adsorption from Wastewater

Biochar has attracted increasing attention as the sustainable and structure-tunable carrier for lanthanum (La) species for diverse applications. Carbonated La species possesses a higher biocompatibility and a lower leaching potential than other commonly used La species, while less attention is paid on the application of carbonated La in phosphorus (P) adsorption. Herein, thermal air oxidation (TAO) was applied as a novel strategy for synchronously tuning the coordination environment and chemical species of La on biochar surface. The results demonstrated that TAO induced the coordination of La with oxidation-generated oxygenated functional groups (OFGs) and carbonation of La species by the oxidation-generated CO2 on the biochar surface. The batch adsorption results showed that the Qm of resultant biochar remarkably increased from 68.92 to 132.49 mg/g at 1 g/L dosage. It also showed a robust adsorption stability in pH 2-6, a strong resistance to the co-existing Cl-, SO42-, NO3-, CO32-, or HCO3-, a stable adsorption recyclability, and an ultralow La leaching potential. The P adsorption was dominated by ligand exchange-induced inner-sphere complexation. In practical swine wastewater, the resultant biochar composite (1 g/L) removed 99.87% of P from 92.3 to 0.12 mg/L at a practical pH of 7.12. The density functional theory calculation further revealed the significant role of the binding of carbonated La by the biochar surface OFGs in reducing the P adsorption energies, indicating the synergism between the oxygenated biochar carrier and the carbonated La in P adsorption. Finally, this study provided a novel route to synchronously tune the coordination environment and chemical species of La on biochar via a facile TAO process for high-efficient P adsorption from wastewater.

Preparation and Application of Magnetic Composites Using Controllable Assembly for Use in Water Treatment: A Review

The use of magnetic composites in wastewater treatment has become widespread due to their high flocculating characteristics and ferromagnetism. This review provides an analysis and summary of the preparation and application of magnetic composites through controllable assembly for use in wastewater treatment. The applications of magnetic composites include the treatment of dye wastewater, heavy metal wastewater, microalgae suspensions, and oily wastewater. Additionally, the recycling and regeneration of magnetic composites have been investigated. In the future, further research could be focused on improving the assembly and regeneration stability of magnetic composites, such as utilizing polymers with a multibranched structure. Additionally, it would be beneficial to explore the recycling and regeneration properties of these composites.

Recent developments in metallic-nanoparticles-loaded biochars synthesis and use for phosphorus recovery from aqueous solutions. A critical review

Phosphorus (P) represents a major pollutant of water resources and at the same time a vital element for human and plants. P recovery from wastewaters and its reuse is a necessity in order to compensate the current important depletion of P natural reserves. The use of biochars for P recovery from wastewaters and their subsequent valorization in agriculture, instead of synthetic industrial fertilizers, promotes circular economy and sustainability concepts. However, P retention by pristine biochars is usually low and a modification step is always required to improve their P recovery efficiency. The pre- or post-treatment of biochars with metal salts seems to be one of the most efficient approaches. This review aims to summarize and discuss the most recent developments (from 2020- up to now) in: i) the role of the feedstock nature, the metal salt type, the pyrolysis conditions, and the experimental adsorption parameters on metallic-nanoparticles-loaded biochars properties and effectiveness in recovering P from aqueous solutions, as well as the dominant involved mechanisms, ii) the effect of the eluent solutions nature on the regeneration ability of P-loaded biochars, and iii) the practical challenges facing the upscaling of P-loaded biochars production and valorization in agriculture. This review shows that the synthesized biochars through slow pyrolysis at relatively high temperatures (up to 700-800 °C) of mixed biomasses with Ca- Mg-rich materials or impregnated biomasses with specific metals in order to from layered double hydroxides (LDHs) biochars composites exhibit interesting structural, textural and surface chemistry properties allowing high P recovery efficiency. Depending on the pyrolysis's and adsorption's experimental conditions, these modified biochars may recover P through combined mechanisms including mainly electrostatic attraction, ligand exchange, surface complexation, hydrogen bonding, and precipitation. Moreover, the P-loaded biochars can be used directly in agriculture or efficiently regenerated with alkaline solutions. Finally, this review emphasizes the challenges concerning the production and use of P-loaded biochars in a context of circular economy. They concern the optimization of P recovery process from wastewater in real-time scenarios, the reduction of energy-related biochars production costs and the intensification of communication/dissemination campaigns to all the concerned actors (i.e., farmers, consumers, stakeholders, and policymakers) on the benefits of P-loaded biochars reuse. We believe that this review is beneficial for new breakthroughs on the synthesis and green application of metallic-nanoparticles-loaded biochars.

Cyclic desorption based efficacy of polyvinyl alcohol-chitosan variant resins for multi heavy-metal removal

The simultaneous removal of Cu, Pb and Fe from water bodies has been targeted in this work with polyvinyl alcohol (PVA) and chitosan (low, medium, and high molecular weight) derivative and with cyclic desorption efficacy target. For a varied range of adsorbent loading (0.2-2 g L^-1), initial concentration (187.7-563.1 mg L^-1 for Cu, 5.2-15.6 mg L^-1 for Pb, and 61.85-185.55 mg L^-1 for Fe), and resin contact time (5 to 720 min), batch adsorption-desorption studies were conducted. After first adsorption-desorption cycle, the optimum absorption capacity was 6.85 mg g^-1 for Pb, 243.90 mg g^-1 for Cu, and 87.72 mg g^-1 for Fe for the high molecular weight chitosan grafted polyvinyl alcohol resin (HCSPVA). The alternate kinetic and equilibrium models were analyzed along with the interaction mechanism between metal ions and functional groups. The cyclic desorption studies were carried out with simple eluent systems such as HCl, HNO₃, H₂SO₄, KOH, and NaOH. The experiments revealed that the HCSPVA derivative has been an impressive, reusable, and effective sorbent for the mitigation of Pb, Fe, and Cu in complex wastewater systems. This is due to its easy synthesis, excellent adsorption capacity, quick sorption rate, and remarkable regeneration capabilities.

Effect of corn pre-puffing on the efficiency of MgO-engineered biochar for phosphorus recovery from livestock wastewater: mechanistic investigations and cost benefit analyses

To improve the phosphorus (P) recovery efficiency from livestock wastewater, a novel MgO doped mildewed corn biochar with thermal pre-puffing treatment (Mg-PBC) and without pre-puffing (Mg-BC) was synthesized and tested. The thermal-puffing pretreatment improved the effectiveness of metal soaking and MgO dispersion. P recovery time with Mg-PBC (7 h) was significantly shorter than that with Mg-BC (12 h). Moreover, Mg-PBC showed significantly higher P recovery capacity (241 mg g−1) than Mg-BC (96.6 mg g−1). P recovery capacity of the Mg-PBC fitted to the Thomas model was 90.7 mg g−1, which was 4 times higher than that of Mg-BC (22.9 mg g−1) under column test conditions. The mechanisms involved in P recovery included precipitation, surface complexation, and electrostatic interaction. After adsorption, both Mg-BC and Mg-PBC showed relatively low regeneration abilities. The P loaded Mg-BC (Mg-BC-P) and Mg-PBC (Mg-PBC-P), the later particularly, obviously increased the available P content and promoted plant growth. The release of P increased with time in the Mg-PBC-P treated soil, while it decreased with time in the P fertilizer treated soil. A cost–benefit analysis revealed that thermal-puffing pretreatment greatly increased the profit of MgO doped biochar from −0.66 to 5.90 US$ kg−1. These findings highlight that biomass pre-puffing is a feasible treatment to produce MgO modified biochar and to recover P from livestock wastewater, and that the Mg-PBC-P can be used as a slow-release P fertilizer.

Graphical Abstract

Challenges and opportunities for biochar to promote circular economy and carbon neutrality

Biochar, derived from unused biomass, is widely considered for its potential to deal with climate change problems. Global interest in biochar is attributed to its ability to sequester carbon in soil and to remediate aquatic environment from water pollution. As soil conditioner and/or adsorbent, biochar offers opportunity through a circular economy (CE) paradigm. While energy transition continues, progress toward low-emissions materials accelerates their advance towards net-zero emissions. However, none of existing works addresses CE-based biochar management to achieve carbon neutrality. To reflect its novelty, this work provides a critical overview of challenges and opportunities for biochar to promote CE and carbon neutrality. This article also offers seminal perspectives about strengthening biomass management through CE and resource recovery paradigms, while exploring how the unused biomass can promote net zero emissions in its applications. By consolidating scattered knowledge in the body of literature into one place, this work uncovers new research directions to close the loops by implementing the circularity of biomass resources in various fields. It is conclusive from a literature survey of 113 articles (2003-2023) that biomass conversion into biochar can promote net zero emissions and CE in the framework of the UN Sustainable Development Goals (SDGs). Depending on their physico-chemical properties, biochar can become a suitable feedstock for CE. Biochar application as soil enrichment offsets 12% of CO₂ emissions by land use annually. Adding biochar to soil can improve its health and agricultural productivity, while minimizing about 1/8 of CO₂ emissions. Biochar can also sequester CO₂ in the long-term and prevent the release of carbon back into the atmosphere after its decomposition. This practice could sequester 2.5 gigatons (Gt) of CO₂ annually. With the global biochar market reaching USD 368.85 million by 2028, this work facilitates biochar with its versatile characteristics to promote carbon neutrality and CE applications.

Adsorption properties and mechanism research of phosphorus with different molecular structures from aqueous solutions by La-modified biochar

In order to explore the adsorption characteristics of phosphorus from molecules with different molecular structures and varying number of phosphate groups on metal-modified biochar, walnut shell biochar was modified with LaCl₃ to prepare lanthanum-loaded biochar (BC-La). Adsorption of four polar components, namely phytic acid (IHP), adenosine-5'-disodium triphosphate (5-ATP), hydroxyethylidene diphosphonic acid (HEDP), and sodium pyrophosphate (PP), was studied. The adsorption properties and mechanism of phosphorus sorption by BC-La were analyzed by SEM-EDS and FTIR for the different structures. The results showed that the maximum adsorption capacity of BC-La for IHP, 5-ATP, HEDP, and PP was 85.85, 9.04, 15.80, and 14.45 mg/g, respectively. The adsorption capacity was positively correlated with the polarity of organic phosphorus. The adsorption behavior conformed to the quasi second-order kinetic fitting equation, and the increase of temperature was conducive to the removal of all four phosphorus pollutants. BC-La adsorbs IHP and HEDP mainly through electrostatic attraction. The adsorption of 5-ATP and PP is dominated by complexation. The La-modified biochar has broad prospects in water remediation, which can provide a theoretical basis for removal of different forms of phosphorus pollutants and prevention and control of water eutrophication.

Preparation and characterization of MgO hybrid biochar and its mechanism for high efficient recovery of phosphorus from aqueous media

Conversion of organic waste into engineered metal-biochar composite is an effective way of enhancing biochar’s efficiency for adsorptive capture of phosphorus (P) from aqueous media. Thus, various strategies have been created for the production of metal-biochar composites; however, the complex preparation steps, high-cost metal salt reagent application, or extreme process equipment requirements involved in those strategies limited the large-scale production of metal-biochar composites. In this study, a novel biochar composite rich in magnesium oxides (MFBC) was directly produced through co-pyrolysis of magnesite with food waste; the product, MFBC was used to adsorptively capture P from solution and bio-liquid wastewater. The results showed that compared to the pristine food waste biochar, MFBC was a uniformly hybrid MgO biochar composite with a P capture capacity of 523.91 mg/g. The capture of P by MFBC was fitted using the Langmuir and pseudo-first-order kinetic models. The P adsorptive capture was controlled by MgHPO4 formation and electrostatic attraction, which was affected by the coexisting F− and CO32− ions. MFBC could recover more than 98% of P from the solution and bio-liquid wastewater. Although the P-adsorbed MFBC showed very limited reusability but it can be substituted for phosphate fertiliser in agricultural practices. This study provided an innovative technology for preparing MgO-biochar composite against P recovery from aqueous media, and also highlighted high-value-added approaches for resource utilization of bio-liquid wastewater and food waste.

Graphical Abstract

Phosphate capture from biogas slurry with magnesium-doped biochar composite derived from Lycium chinensis branch filings: performance, mechanism, and effect of coexisting ions

The performance, mechanisms, and effects of various coexisting ions on phosphorus (P) adsorptive capture in biogas slurry using MgO-doped biochar (MBC) were investigated. The results revealed that in comparison to the pristine biochar, the introduction of MgO significantly improved the P adsorptive capture feasibility of MBC. In addition, the process of P capture by MBC was not affected by the initial pH of the solution. The process of P capture could reach equilibrium within 120 min and be simulated using both the pseudo-first-order and the pseudo-second-order kinetic models. In addition, the highest P capture capacity calculated from the Langmuir isotherm model was approximately 129.35 mg/g. The coexisting of cations including NH₄⁺, Ca²⁺, Cu²⁺, Cd²⁺, Pb²⁺, Zn²⁺, and Cr³⁺ in higher concentrations of promoted P adsorptive capture through precipitation and ionic atmosphere effects. The presence of coexisting ions including SO₄^2-, HCO₃^-, and fulvic acid (FA) had a certain inhibitory effect on the P adsorptive capture through competitive adsorption with phosphate. The existence of monovalent ions such as K⁺, Na⁺, Cl^-, and NO₃^- had no significant effect on P adsorptive capture. The adsorptive capture of P by MBC was affected by various processes including electrostatic attraction and surface complexation, and the presence of different coexisting substances had different impacts on the P adsorption. Adding to these, the P in the biogas slurry was completely adsorbed by the MBC during the experiment, indicating that MBC is a promising composite in the engineering application for the capture of P from wastewater.

Hydroxyapatite tailored hierarchical porous biochar composite immobilized Cd(II) and Pb(II) and mitigated their hazardous effects in contaminated water and soil

A novel composite of hydroxyapatite tailored hierarchical porous biochar (HA-HPB) was synthesized and used for the adsorptive immobilization of Cd(II) and Pb(II) in water and soil. The hierarchical porous biochar (HPB) was prepared from rice husk through a molten-salt-assisted pyrolysis approach; then, a series of HA-HPB (with 0.5, 1, 2, 3, and 4 g of HPB) was prepared with co-precipitation procedure. All HA-HPBs, particularly HA-3HPB, revealed significantly higher removal efficiency of Cd(II) and Pb(II) (≥99.5%) in water than pristine biochar (5.79 - 24.12%). The immobilization efficiency of HA-3HPB for Cd(II) and Pb(II) was slightly inhibited by the ionic strength and co-existing cations. The Langmuir adsorption capacities of Cd(II) and Pb(II) were 88.1 and 110.2 mg/g, respectively. Ion exchange, complexation, cation-π interaction, and precipitation were the key mechanisms involved in the immobilization of Cd(II) and Pb(II) using HA-3HPB. The HA-3HPB reduced the availability of soil Cd (63.5 - 87.8%) and Pb (64.6 - 92.9%) compared to the unamended soil, and thus reduced their content in the Chinese cabbage shoots by 69.3 -95.4% for Cd and 66.5 -97.2% for Pb. These findings demonstrate the effectiveness of HA-HPB for remediation of Cd(II) and Pb(II) contaminated water and soil and mitigating the potential risks.