Fabrication of porosity-enhanced MgO/biochar for removal of phosphate from aqueous solution: Application of a novel combined electrochemical modification method

Mechanistic and future prospects in rhizospheric engineering for agricultural contaminants removal, soil health restoration, and management of climate change stress

Climate change, food insecurity, and agricultural pollution are all serious challenges in the twenty-first century, impacting plant growth, soil quality, and food security. Innovative techniques are required to mitigate these negative outcomes. Toxic heavy metals (THMs), organic pollutants (OPs), and emerging contaminants (ECs), as well as other biotic and abiotic stressors, can all affect nutrient availability, plant metabolic pathways, agricultural productivity, and soil-fertility. Comprehending the interactions between root exudates, microorganisms, and modified biochar can aid in the fight against environmental problems such as the accumulation of pollutants and the stressful effects of climate change. Microbes can inhibit THMs uptake, degrade organic pollutants, releases biomolecules that regulate crop development under drought, salinity, pathogenic attack and other stresses. However, these microbial abilities are primarily demonstrated in research facilities rather than in contaminated or stressed habitats. Despite not being a perfect solution, biochar can remove THMs, OPs, and ECs from contaminated areas and reduce the impact of climate change on plants. We hypothesized that combining microorganisms with biochar to address the problems of contaminated soil and climate change stress would be effective in the field. Despite the fact that root exudates have the potential to attract selected microorganisms and biochar, there has been little attention paid to these areas, considering that this work addresses a critical knowledge gap of rhizospheric engineering mediated root exudates to foster microbial and biochar adaptation. Reducing the detrimental impacts of THMs, OPs, ECs, as well as abiotic and biotic stress, requires identifying the best root-associated microbes and biochar adaptation mechanisms.

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.

Characterization of Magnetic Biochar Modified Using the One-Step and Electrochemical Methods and Its Impact on Phosphate Adsorption

The properties and phosphate adsorption capability of the one-step method and electrochemical method in modifying peanut shell biochar have been determined. The one-step method deposits MgO and Fe3O4 onto biochar through chemical impregnation and regularly affects the functional groups and magnetic separation of biochar, thereby enhancing its ability to adsorb phosphate. In contrast, the electrochemical method is not favorable for modifying functional groups of biochar but can promote phosphate adsorption because of the formation of MgFe2O4 and Fe3O4 using electrolysis. The adsorption isotherm and kinetics data suggest that adsorption is monolayer onto a homogeneous surface and phosphate adsorption could be controlled by chemical processes. Biochar with the addition of both Fe2+ and Mg2+ shows better phosphate adsorption capability than those with barely any Fe2+ additions. It was concluded that the one-step method is a better modification method than the electrochemical method for enhancing the phosphate adsorption capability of biochars.

Machine learning-based modeling of malachite green adsorption on hydrochar derived from hydrothermal fulvification of wheat straw

This study investigated the efficiency of hydrochar derived from hydrothermal fulvification of wheat straw in adsorbing malachite green (MG) dye. The characterizations of the hydrochar samples were determined using various analytical techniques like SEM, EDX, FTIR, X-ray spectroscopy, BET surface area analysis, ICP-OES for the determination of inorganic elements, elemental analysis through ultimate analysis, and HPLC for the content of sugars, organic acids, and aromatics. Adsorption experiments demonstrated that hydrochar exhibited superior removal efficiency compared to feedstock. The removal efficiency of 91 % was obtained when a hydrochar dosage of 2 g L-1 was used for 20 mg L-1 of dye concentration in a period of 90 min. The results showed that the study data followed the Freundlich isotherms as well as the pseudo-second order kinetic model. Moreover, the determined activation energy of 7.9 kJ mol-1 indicated that the MG adsorption was a physical and endothermic process that increased at elevated temperatures. The study also employed an artificial neural network (ANN), a machine learning approach that achieved remarkable R2 (0.98 and 0.99) for training and validation dataset, indicating high accuracy in simulating MG adsorption by hydrochar. The model's sensitivity analysis demonstrated that the adsorbent dosage exerted the most substantial influence on the adsorption process, with MG concentration, pH, and time following in decreasing order of impact.

Magnesium activation affects the properties and phosphate sorption capacity of poultry litter biochar

Biochars with a high affinity for phosphorus (P) are promising soil amendments for reducing P in agricultural run-off. Poultry litter (PL) is an abundant biochar feedstock. However, PL-derived biochars are typically high in soluble P and therefore require chemical modification to become effective P sorbents. This study investigated the effect of magnesium (Mg) activation on extractable P (EP) and P sorption capacities of PL-derived biochars. Biochar was produced at 500-900 °C from PL activated with 0-1 M Mg. Three differentially aged PL feedstocks were evaluated (1-, 3-5-, and 7-9-year-old). Increased Mg activation level and pyrolysis temperature both resulted in EP reductions from the biochars. Specifically, biochars produced at temperatures ≥ 700 °C from PL activated with ≥ 0.25 M Mg had negligible EP. X-ray diffractograms indicated that increased Mg loading favored the formation of stable Mg3(PO4)2 phases while increasing temperature favored the formation of both Mg3(PO4)2 and Ca5(PO4)3OH. Maximum P sorption capacities (Pmax) of the biochars were estimated by fitting Langmuir isotherms to batch sorption data and ranged from 0.66-10.35 mg g-1. Average Pmax values were not affected by PL age or pyrolysis temperature; however, biochars produced from 1 M Mg-activated PL did have significantly higher average Pmax values (p < 0.05), likely due to a greater abundance of MgO. Overall, the results demonstrated that Mg activation is an effective strategy for producing PL-derived biochars with the potential ability to reduce P loading into environmentally sensitive ecosystems.

Development of Rice Straw-derived Biochar-Bentonite Composite and its Application for in situ Sequestration of Ammonium and Phosphate Ions in the Degraded Mine Soil

Nutrient pollution has a diverse impact on the environment and human health. The presence of nutrients, such as ammonium and phosphate, is ubiquitous in the environment due to their extensive use in agricultural land and leaching through non-point sources. In this context, biochar-based composites could play an essential role in improving the soil's nutrient retention capacity. The present study aims to develop bentonite-biochar composites (BNT@BC 400 and 600) and utilize them as an ameliorating material in the coal mine degraded soil to reduce the leaching of ammonium and phosphate ions. The bentonite-biochar composite (BNT@BC 400 and 600) was synthesized using the pristine rice straw-derived biochar using the solvothermal method. The biochar was produced at two different pyrolytic temperatures, 400 °C and 600 °C, and denoted as BC 400 and 600, respectively. Hence, the bentonite-biochar composite was denoted as BNT@BC 400 and 600. The BNT@BC 400 and 600 were characterized using the elemental, proximate, SEM, XRD, and FTIR analysis. Subsequently, the BNT@BC composites were evaluated for the adsorptive removal of NH₄⁺ and PO₄^3- ions using batch adsorption and column leaching studies. In the soil columns, the BNT@BC 400 and 600 were mixed with the soil at two different application rates, viz. 1 and 2.5% (w/w). The leaching characteristics data were fitted using three different fixed-bed models to predict the maximum adsorption capacity of the amended soil columns and the dominant mechanism of adsorption. Results indicated that the BNT@BC 600 showed the maximum adsorption capacity of 33.77 and 64.23 mg g^-1 for the adsorption of NH₄⁺ and PO₄^3- ions, respectively. The dominant adsorption mechanisms in the aqueous solution were the electrostatic attraction, complexation, ion exchange, and precipitation processes. In the soil columns, the sorption of NH₄⁺ and PO₄^3- ions was governed by diffusive mass transfer and electrostatic interaction. Findings of the study indicated that incorporating the BNT@BC composite in the soil can significantly reduce the leaching of the NH₄⁺ and PO₄^3- ions and increase the overall soil fertility.

Porous MgO-modified biochar adsorbents fabricated by the activation of Mg(NO3)2 for phosphate removal: Synergistic enhancement of porosity and active sites

Engineering magnesium oxide (MgO)-modified biochar (MgO-biochar) with high porosity and active MgO load is a feasible pathway to enhance phosphate adsorption capacity. However, the blockage to pores caused by MgO particles is ubiquitous during the preparation, which seriously impaired the enhancement in adsorption performance. In this research, with the intent to enhance phosphate adsorption, an in-situ activation method based on Mg(NO₃)₂-activated pyrolysis technology was developed to fabricate MgO-biochar adsorbents with abundant fine pores and active sites simultaneously. The SEM image revealed that the tailor-made adsorbent has well-developed porous structure and abundant fluffy MgO active sites. Its maximum phosphate adsorption capacity was coming up to 1809 mg/g. The phosphate adsorption isotherms are in accordance well with the Langmuir model. The kinetic data, which agreed with the pseudo-second-order model, indicated that chemical interaction is existing between phosphate and MgO active sites. This work verified that the phosphate adsorption mechanism on MgO-biochar was composed of protonation, electrostatic attraction, monodentate complexation and bidentate complexation. In general, the facile in-situ activation method using Mg(NO₃)₂ pyrolysis illuminated biochar activation with fine pores and highly efficient adsorption sites for efficient wastewater treatment.

Bio-assembled MgO-coated tea waste biochar efficiently decontaminates phosphate from water and kitchen waste fermentation liquid

Crystal morphology of metal oxides in engineered metal-biochar composites governs the removal of phosphorus (P) from aqueous solutions. Up to our best knowledge, preparation of bio-assembled MgO-coated biochar and its application for the removal of P from solutions and kitchen waste fermentation liquids have not yet been studied. Therefore, in this study, a needle-like MgO particle coated tea waste biochar composite (MTC) was prepared through a novel biological assembly and template elimination process. The produced MTC was used as an adsorbent for removing P from a synthetic solution and real kitchen waste fermentation liquid. The maximum P sorption capacities of the MTC, deduced from the Langmuir model, were 58.80 mg g−1 from the solution at pH 7 and 192.8 mg g−1 from the fermentation liquid at pH 9. The increase of ionic strength (0–0.1 mol L−1 NaNO3) reduced P removal efficiency from 98.53% to 93.01% in the synthetic solution but had no significant impact on P removal from the fermentation liquid. Precipitation of MgHPO4 and Mg(H2PO4)2 (76.5%), ligand exchange (18.0%), and electrostatic attraction (5.5%) were the potential mechanisms for P sorption from the synthetic solution, while struvite formation (57.6%) and ligand exchange (42.2%) governed the sorption of P from the kitchen waste fermentation liquid. Compared to previously reported MgO-biochar composites, MTC had a lower P sorption capacity in phosphate solution but a higher P sorption capacity in fermentation liquid. Therefore, the studied MTC could be used as an effective candidate for the removal of P from aqueous environments, and especially from the fermentation liquids. In the future, it will be necessary to systematically compare the performance of metal-biochar composites with different metal oxide crystal morphology for P removal from different types of wastewater.

Graphical Abstract

Nitrogen retention potentials of magnesium oxide- and sepiolite-modified biochars and their impacts on bacterial distribution under nitrogen fertilization

Mitigating the loss and negative impacts of reactive N from fertilized soils remains a global environmental challenge. To optimize N retention by biochar, bamboo and pig manure biochars were modified as MgO- and sepiolite-biochar composites and characterized. Novel soil application of the modified biochars and their raw forms were comparatively evaluated for N-retention in a fertilized soil leached for 90 days in a column experiment. Changes in N-cycling-related enzyme and bacterial structure were also reported after 90 days. Results revealed low leaching losses of NH₄⁺, which reduced over time across all the treatments. However, while sole fertilizer (F) increased the initial and cumulative NO₃^- leached from the soil, the MgO-bamboo biochar (MgOBF) and sepiolite-bamboo biochar (SBF) treatments reduced leachate NO₃^- by 22.1 % and 10.5 % compared to raw bamboo biochar (BBF) treatment. However, 15.5 % more NO₃^- was leached from the MgO-pig manure biochar-treated soil (MgOPF) compared to its raw biochar treatment (PMBF) after 90 days. Dissolved organic N leached was reduced by 9.2 % and 0.5 % in MgOBF and SBF, as well as 15.4 % and 40.5 % in MgOPF and SPF compared to their respective raw forms. The total N of the biochars, adjustment of surface charges, cation exchange capacity, surface area, pore filling effects, and the formation of potential MgN precipitates on the modified-biochar surfaces regulated N leaching/retention. In addition, the modified biochar treatments reduced the hydrolysis of urea and stimulated some nitrate-reduction-related bacteria crucial for NO₃^- retention. Hence, unlike the raw biochar and MgOPF treatments, MgOBF, SBF, and SPF hold promise in mitigating inorganic-N losses from fertilized soils while improving the soil's chemical properties.

Adsorption of Phosphates onto Mg/Al-Oxide/Hydroxide/Sulfate-Impregnated Douglas Fir Biochar

Nitrates and phosphates, found in fertilizers, are the most common eutrophication-causing agents. Douglas fir biochar (BC), a syngas byproduct, was treated with different Al/Mg ratios of sulfate (5% w/w metal loading) followed by an NaOH treatment. The greatest phosphate uptake at 25 °C and pH 7 was attributed to the composite with a Mg/Al 2:1 ratio prepared at pH 13 (AMBC). Batch AMBC phosphate uptake was optimized for initial pH, equilibrium time, temperature, and initial phosphate concentration. Phosphate removal following pseudo-2nd-order kinetics and increases gradually before reaching a max at pH 11, with 95% phosphate uptake in 15 mins. The Sips isotherm model provided the best sorption data fit resulting in a 42.1 mg/g capacity at 25 °C and pH 11. Endothermic and spontaneous adsorption were determined using van ’t Hoff’s plots. BET, XRD, XPS, SEM, TEM, and EDS were used to characterize the biochar before and after phosphate sorption. Used AMBC has the potential to be exploited as a phosphate fertilizer as a key part of an environmentally friendly agricultural management plan.

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.

Characteristics and Mechanisms of Phosphorous Adsorption by Peanut Shell-Derived Biochar Modified with Magnesium Chloride by Ultrasonic-Assisted Impregnation

Recovery of phosphate (P) from sludge, domestic wastewater, and industrial wastewater is beneficial for overcoming the problem of shortage of P rock resources. In this study, Mg-functionalized peanut shell-derived biochar was prepared by ultrasound-assisted impregnation. The obtained Mg-laden biochar had a higher content of Mg, a larger specific surface area, and more porosity. The prepared Mg-modified biochar exhibited excellent adsorption properties of phosphorus. Modified biochar has a higher amount of adsorbed P than raw biochar. The capacity of P adsorption by modified biochar was 30.48-114.24% higher than that by raw biochar. Moreover, the Mg-laden biochar can be applied in a wide working environment (pH: 2-10; temperature range: 15-40 °C). This study not only develops a new strategy for the preparation of high-capacity P adsorbents but also provides a new green use for agricultural peanut shells.

MgO-modified activated biochar for biojet fuels from pyrolysis of sawdust on a simple tandem micro-pyrolyzer

The aim of this work was to study on MgO-modified KOH activated biochar (AC) catalysts, in the pyrolysis of sawdust for the direct production of bio-jet fuels using a tandem micro-pyrolyzer. AC catalysts with various MgO contents (5 to 20 wt%) were synthesized using an impregnation method. The mesopores generated (4 to 18 nm) in the carbon has a great potential in the conversion of oxygenated to jet fuel. The importance of basic nature in the catalysts is demonstrated with the maximum bio-jet fuel yield of 29 % at 10 % MgO. Further, the temperature of 600 °C and a catalyst/sawdust ratio of 10 are identified as the optimal conditions. The nanosize of MgO and the synergism of acid and base sites seemed to enhance deoxygenation, via decarboxylation and decarbonylation, and oligomerization, which are required for jet fuel formation in high amounts from sawdust pyrolysis.

Integrated electrocoagulation-flotation of microalgae to produce Mg-laden microalgal biochar for seeding struvite crystallization

Developing sustainable materials for recovering and recycling nutrients from wastewater is critically needed for nutrients such as phosphorus that have a diminishing supply. Struvite crystallization is emerging as a promising strategy for phosphorus recovery which can be enhanced with seeding through microalgal biochar. The main bottleneck of using microalgae is its high harvesting cost. In this study, an integrated electrocoagulation-flotation (ECF) process is used to recover and at the same time modify the algal surface with magnesium anode and inert carbon cathode. Harvesting efficiency of 98% was achieved with 40.78 mA cm⁻², 0.5 cm inter-electrode distance and energy consumption of 4.03 kWh kg⁻¹ in 15 min. The harvested microalgae were pyrolyzed to obtain a yield of 52.90% Mg-laden microalgal biochar. Simultaneously, surface impregnation of 28% magnesium was attained as confirmed by Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Phosphorus recovery and struvite yield of 93.70% and 2.66 g L⁻¹, respectively, were obtained from dosing 1.50 g L⁻¹ Mg-laden microalgal biochar. Comparison of physicochemical characteristics of residual supernatant after microalgal harvesting and struvite recovery showed that the combined use of both the residuals can serve as a sustainable growth medium for microalgae. The overall operating cost of the integrated process was found to be 2.48 USD kg⁻¹ with a total energy consumption of 10.76 kWh kg⁻¹, which was found to be lower than conventional harvesting unit processes such as centrifugation and filtration. This novel approach can help attaining a circular bioeconomy by encompassing nutrient recovery and waste management in an integrated process.

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

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

Production of engineered-biochar under different pyrolysis conditions for phosphorus removal from aqueous solution

Phosphorus (P) recovery from wastewater through biochar is an alternative to build a sustainable circular economy and save non-renewable P reservoirs. The efficiency of cations in removing P from wastewater under different pyrolysis conditions is still lacking. We aimed at studying P adsorption and release from biochar enriched with Al³⁺ and Mg²⁺, prepared under air-limited and N₂-flow pyrolysis conditions. Biochar samples were produced from pig manure (PMB) and impregnated, separately, with 20% of AlCl₃ and MgCl₂ solutions on both pyrolysis conditions. The materials were characterized for pH, electrical conductivity (EC), total nutrient content, ash, specific surface area (SSA), pore-volume, FTIR, XRD, and SEM-EDX. Phosphorus adsorption was studied by kinetics and adsorption isotherms, as well as desorption. The biochar impregnated with Mg²⁺ and produced in the muffle furnace achieved the maximum P adsorption (231 mg g^-1), and 100% of the adsorbed P was released in solutions of Mehlich-1 and citric acid 2%. The pyrolysis conditions had a small or no influence on the biochar properties governing P adsorption, such as chemical functional groups, surface area, quantity and size of pores, and formation of synthetic minerals. Therefore, it is possible to produce biochar without using N₂ as a carrier gas when it comes to P adsorption studies. Mechanisms of P removal comprise precipitation with cations, surface complexation, ligand exchange reactions, and electrostatic attraction on the biochar surface. Overall, Mg-impregnated biochar is a suitable matrix to remove P from aqueous media and to add value to organic residues while producing an environmentally friendly material for reuse in soils.

Efficient and sustainable phosphate removal from water by small-sized Al(OH)3 nanocrystals confined in discarded Artemia Cyst-shell: Ultrahigh sorption capacity and rapid sequestration

We reported a new strategy for efficient phosphate removal from wastewaters, it relies on the discarded Artemia Cyst-shell in-situ growth of Al(OH)₃ nanocluster, the charged amino-acids components of skeleton make available for the small size of Al(OH)₃ formation (< 10 nm) with high activity, and the three-dimensional porous structure of discarded matrix provides fast kinetics and efficient Al(OH)₃ nanoparticles utilization. These hybrid adsorbents exhibit ultrahigh capacity (850.5 mg/g) and fast kinetics (~2 min) by recent ten-years (2011-2020) survey, the superior selectivity against various foreign ions, with a distribution coefficient (K_d) as high as 4820 mL/g, the porous structure and fast kinetics also accelerate the phosphate accessibility, yielding a satisfactory capacity of ~3000 L/kg sorbent (Artemia CS-Al) for the application, even varying at high feeding-speeds. The saturated adsorbent can be readily regenerated and reused without decrease in performance, this technology is promising for mitigating the contamination problem of excess phosphate worldwide.

Mitigation of greenhouse gas emissions from a red acidic soil by using magnesium-modified wheat straw biochar

To mitigate greenhouse gas (GHG) emissions, different strategies have been proposed, including application of dolomite, crop straw and biochar, thus contributing to cope with the increasing global warming affecting the planet. In the current study, pristine wheat straw biochar (WBC) and magnesium (MgCl₂.6H₂O) modified wheat straw biochar (MWBC) were used. Treatments included control (CK), two WBC dosages (1% and 2.5%), and two MWBC doses (1% and 2.5%). After 90 days of incubation, WBC and MWBC improved the soil physiochemical properties, being more pronounced with increasing rates of biochar. MWBC_2.5 significantly decreased microbial biomass carbon (MBC), while microbial biomass nitrogen (MBN) increased when both biochar materials (WBC₁ and MWBC₁) were applied at low rate. Compared to control soil, Urease and Alkaline phosphatase activities increased with the increasing rate of WBC and MWBC. The activities of dehydrogenase and β-glucosidase decreased with the WBC and MWBC application, compared to CK. The fluxes of all the three GHGs evaluated (CO₂, CH₄ and N₂O) decreased with time for both biochar amendments, while cumulative emission of CO₂ increased by 58% and 45% for WBC, and by 54% and 41% for MWBC, as compared to CK. The N₂O cumulative emissions decreased by 18 and 34% for WBC, and by 25 and 41% for MWBC, compared to CK, whereas cumulative methane emission showed non-significant differences among all treatments. These findings indicate that Mg-modified wheat straw biochar would be an appropriate management strategy aiding to reduce GHG emissions and improving the physiochemical properties of affected soils, and specifically of the red dry land soil investigated in the current work.

Biomass as source for hydrochar and biochar production to recover phosphates from wastewater: A review on challenges, commercialization, and future perspectives

Excessive phosphate run-off with total phosphorus concentration greater than 20 μg P L^-1 triggers the growth of harmful algal species in waterbodies and potentially leads to eutrophication. This has severe negative implications on aquatic environment and impacts human health. The annual economic impact of harmful algal blooms is reported to be as high as $25 million for public health and commercial fishery sector, $29 million for recreation/tourism sector and $2 million for monitoring and management. Adsorption is widely considered as an effective and economic strategy to achieve extremely low concentration of phosphorus. The char produced by valorizing various waste biomasses have been gaining attention in phosphorus remediation owing to their availability, their ability to regenerate and reuse. This review paper exclusively focuses on utilizing hydrochar and biochar synthesized from waste biomass, respectively, through hydrothermal carbonization and slow pyrolysis to mitigate phosphorus concentration and potential strategies for handling the spent char. The key mechanisms involved in phosphate adsorption are electrostatic interaction, ion exchange and complexation. The maximum adsorption capacity of hydrochar and biochar ranges from 14-386 mg g^-1 and 3-887 mg g^-1, respectively. Hydrochar and biochar are cost-effective alternative to commercial activated carbon and spent char can be used for multiple adsorption cycles. Furthermore, extensive research studies on optimizing the feedstock, reaction and activation conditions coupled with technoeconomic analysis and life cycle assessment could pave way for commercialization of char-based adsorption technology.

Green Hydrogel-Biochar Composite for Enhanced Adsorption of Uranium

Uranium is the backbone of the nuclear fuel used for energy production but is still a hazardous environmental contaminant; thus, its removal and recovery are important for energy security and environmental protection. So far, the development of biocompatible, efficient, economical, and reusable adsorbents for uranium is still a challenge. In this work, a new orange peel biochar-based hydrogel composite was prepared by graft polymerization using guar gum and acrylamide. The composite's structural, morphological, and thermal characteristics were investigated via Fourier transform infrared (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) methods. The composite's water absorption properties were investigated in different media. The performance of the prepared composite in adsorbing uranium (VI) ions from aqueous media was systematically investigated under varying conditions including solution's acidity and temperature, composite dose, contact time, and starting amount of uranium. The adsorption efficiency increased with solution pH from 2 to 5.5 and composite dose from 15 to 50 mg. The adsorption kinetics, isotherms, and thermodynamics parameters were analyzed to get insights into the process's feasibility and viability. The equilibrium data were better described through a pseudo-second-order mechanism and a Langmuir isotherm model, indicating a homogeneous composite surface with the maximum uranium (VI) adsorption capacity of 263.2 mg/g. The calculated thermodynamic parameters suggested that a spontaneous and endothermic process prevailed. Interference studies showed high selectivity toward uranium (VI) against other competing cations. Desorption and recyclability studies indicated the good recycling performance of the prepared composite. The adsorption mechanism was discussed in view of the kinetics and thermodynamics data. Based on the results, the prepared hydrogel composite can be applied as a promising, cost-effective, eco-friendly, and efficient material for uranium (VI) decontamination.

Sustainable remediation of hazardous environmental pollutants using biochar-based nanohybrid materials

Biochar is a well-known carbon material with diversified functionalities and excellent physicochemical characteristics with high wastewater treatment potential. This review aims to summarize recent advancements in the development of biochar and biochar-based nanohybrid materials as a potential tool for the removal of harmful organic compounds such as synthetic dyes/effluents. The formation of biochar using pyrolysis of renewable feedstocks and their applications in various industries are explained hereafter. The characteristics and construction of biochar-based hybrid materials are explained in detail. Diversity of feedstocks, including municipal wastes, industrial byproducts, agricultural, and forestry residues, endows different biochar types with a wide structural variety. The production of cost-effective biochar drives the interest in manipulating biochars and induces desire functionality using nanoscale reinforcements. Various types of biochars, such as magnetic biochar, layered nanomaterial coated biochar, nanometallic oxide composites, chemically and physically functionalized biochar, have been produced. With the aid of nanomaterial, hybrid biochar exhibits a high potential to remove toxic contaminants. Depending upon biochar type, dyes/effluents can be removed via different mechanisms, including the Fenton process, photocatalytic degradation, π-π interaction, electrostatic interaction, and physical adsorption. In conclusion, desired physicochemical features, and tunable surface properties of biochar present high potential material in removing organic dyes and other effluents. The blended biochar with different materials/nanomaterials endows broader development and multi-functional opportunities for treating dyes/effluents.

Enhanced adsorption of phosphorus in soil by lanthanum-modified biochar: improving phosphorus retention and storage capacity

Use of soil adsorbent is an effective method for the promotion of phosphorus adsorption capacity of soil, though most of the soil adsorbents have weak phosphorus retention ability. Herein, we compared the traditional gypsum (GP) and zeolite (ZP) adsorbents to explore the phosphorus retention ability of lanthanum modified walnut shell biochar (La-BC) in soil. The results showed that with the increase of exogenous phosphorus concentration, the adsorption amount of phosphorus by adsorbents in soil increased at first and then tended to be stable. The maximum adsorption capacity of soil to phosphorus is gypsum, lanthanum-modified biochar > zeolite, and the addition of lanthanum-modified biochar can improve the adsorption capacity of soil to phosphorus, enhance the binding strength of soil and phosphorus, improve the ability of soil to store phosphorus, reducing phosphorus adsorption saturation, and is beneficial to control the leaching of soil phosphorus. FTIR and XRD analysis showed that the adsorption of phosphorus by each adsorbent in soil was mainly chemical precipitation. The response surface analysis showed that the adsorption performance of La-BC+S was the best when the concentration of exogenous phosphorus was 50.0 mg/L, pH was 6.47, and the reaction time was 436.98 min. This study provides a reference for soil adsorbents to hold phosphorus and reduce the risk of phosphorus leaching to avoid groundwater pollution.

Phosphate recovery from aqueous solution through adsorption by magnesium modified multi-walled carbon nanotubes

In this study, multi-walled carbon nanotubes modified by magnesium (Mg@CNT) was prepared as a novel adsorbent to recover phosphate from wastewater. Mg@CNT with the mass ratio of 0.48 (Mg versus MWCNTs) was the most efficient for phosphate adsorption and the maximum experimental adsorption capacity was up to 198 mg P/g. The Mg@CNT characterization was done by Field emission scanning electron microscope coupled with energy-dispersive spectroscopy detector (FESEM-EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), surface area analyzer (BET), Transmission electron microscope coupled with energy-dispersive spectroscopy detector (TEM-EDS). The MgO nanoflakes spread on the surface of multi-walled carbon nanotubes and reacted with phosphate to generate Mg₃(PO₄)₂·10H₂O as the end product. Phosphate adsorption on Mg@CNT was chemisorption onto heterogeneous surface according to the kinetic model and isotherm model fitting results. Several common co-existing ions, e.g., Cl^-, NO₃^- and humic acid, had no obvious negative impact on the phosphate adsorption capacity; while SO₄^2- and CO₃^2- expressed stronger negative impacts and led to 13.2% and 39.5% decrease in phosphate adsorption capacity, respectively. After five adsorption-desorption cycles, Mg@CNT still maintained more than 80% adsorption capacity of the initial and high phosphate desorbability. These results implied that Mg@CNT possessed great application potential in phosphate recovery.

Co-adsorption performance and mechanism of nitrogen and phosphorus onto eupatorium adenophorum biochar in water

To reduce the eutrophication caused by nitrogen and phosphorus in water, invasive plant Eupatorium adenophorum was used to prepare biochar under different pyrolysis temperatures for the co-adsorption of nitrogen and phosphorus. The influencing factors of the co-adsorption of ammonium and phosphate onto EBC and its adsorption mechanism were systematically studied. The results show that Eupatorium adenophorum biochar (EBC) has rich functional groups and high specific surface area. Low pyrolysis temperature (300 °C) and alkaline conditions are beneficial for the co-adsorption. The adsorption of ammonium and phosphate by EBC is more in line with the pseudo-second-order kinetics and Langmuir-Freundlich model (Q_max is 2.32 mg P/g and 1.909 mg N/g). Site energy analysis further confirms that electrostatic attraction is the main mechanism. This study shows that EBC could be used as a low-cost and effective adsorbent to simultaneously remove ammonium and phosphate from water, providing a method for resource utilization of invasive plants.

Biochar affects the fate of phosphorus in soil and water: A critical review

Biochar is a promising novel material for managing phosphorus (P), a nutrient often limiting for primary production but can also be a pollutant, in the environment. Reducing P input to the environment and finding cost-effective approaches to remediate P contamination are major challenges in P management. There is currently no review that systematically summarizes biochar effects on soil P availability and its P removal potential from water systems. In this paper, we comprehensively reviewed biochar effects on soil P availability and P removal from water systems and discussed the mechanisms involved. Biochar affects soil P cycling by altering P chemical forms, changing soil P sorption and desorption capacities, and influencing microbial population size, enzyme activities, mycorrhizal associations and microbial production of metal-chelating organic acids. The porous structure, high specific surface area, and metal oxide and surface functional groups make biochars effective materials for removing P from eutrophic water via ligand exchange, cation bridge, and P precipitation. Because soil and biochar properties are widely variable, the effect of biochar on the fate of P in soil and water systems is inconsistent among different studies. Knowledge gaps in the economic practicability of large-scale biochar application, the longevity of biochar benefits, and the potential ecological risks of biochar application should be addressed in future research.

Recent advances and challenges on removal and recycling of phosphate from wastewater using biomass-derived adsorbents

As the severe damage of phosphate enrichment in the water ecosystem and the supply shortage of phosphate rock, developing an efficient method for the removal and recycling of phosphate from wastewater is of great significance. To achieve this goal, adsorption technology has been widely investigated, and various adsorbents were developed. Among them, the biomass-derived adsorbents including biomass-derived carbon-based materials, biomass-based anion exchangers and metal-biomass composites have attracted increasing attention over the past years due to the low cost, abundant renewable raw materials and environmental friendliness. However, different adsorbents usually exhibit variable adsorption performances for phosphate, which highly depends on their design strategies, preparation methods and potential adsorption mechanisms. Thus, this review comprehensively summarizes the recent researches on the removal and recycling of phosphate from wastewater using the biomass-derived adsorbents. Especially, the design strategies, preparation methods, adsorption performances and mechanisms of these reported biomass-derived adsorbents are discussed in detail. Moreover, as the significant strategies to recover and recycling phosphate, the elution and direct use of phosphate-loaded adsorbents as fertilizers are also presented. Although the excellent adsorption performance has been obtained, some challenges are still existing, which should be given more attention in the following researches to facilitate the development and industrial application of biomass-derived adsorbents.

Magnesium-Palm Kernel Shell Biochar Composite for Effective Methylene Blue Removal: Optimization via Response Surface Methodology

This study investigates the properties and potential application of Mg-PKS biochar composite for methylene blue solution (MB) adsorption. The Mg-PKS biochar composite was developed from palm kernel shell biochar via steam activation followed by MgSO4 treatment and carbonization. The effect of process parameters such as solution pH (4-10), contact time (30-90 min) and adsorbent dosage (0.1-0.5 g) were investigated via central composite design, response surface methodology. Results revealed that the Mg-PKS biochar composite has irregular shapes pore structure from SEM analysis, a surface area of 674 m2g-1 and average pore diameters of 7.2195 μm based on BET analysis. RSM results showed that the optimum adsorption of MB onto Mg-biochar composite was at pH 10, 30 min contact time and 0.5 g/100 mL dosage with a removal efficiency of 98.50%. In conclusion, Mg treatment is a potential alternative to other expensive chemical treatment methods for biochar upgrading to the adsorbent.

Engineered biochars for recovering phosphate and ammonium from wastewater: A review

Biochar has gained great scientific attention as a promising agent for agricultural and environmental applications. A variety of biochars with excellent properties such as high porosity, surface area and functional groups have been developed for nutrients recovery from wastewater. Compared to pristine biochar, engineered biochar with enlarged surface area and abundant functional groups has been prepared which shows a new type of carbon-based material with enhanced adsorption potential for nutrients in wastewater. To date, a few reviews have been specifically focused on several important aspects of engineered biochar, such as its application to recover phosphate and ammonium from wastewater and subsequent use as a slow-release fertilizer. In this work, novel modification/treatment methods including activation with acid/alkali, functionalization with amides, thiols and oxidizing agents, metal salt impregnation, loading with various minerals and carbon-based materials are reviewed for preparing engineered biochar with improved adsorption capacity. Various sources of biomass for producing biochars were estimated, and the intrinsic characteristics and potential of biochar products for simultaneous recovery/removal of phosphate and ammonium from wastewater were evaluated. Relevant interaction mechanisms of phosphate and ammonium adsorption on engineered biochars have been discussed in details. Finally, important future prospects as well as industrial/commercial-scale application of engineered biochars for phosphate and ammonium recovery from wastewater have been emphasized. We believe that this review will provide broad scientific opportunities for thorough understanding of applying engineered biochar as a low-cost and environmentally sustainable material for nutrients recovery from wastewater.

Phosphate Elimination and Recovery Lightweight (PEARL) membrane: A sustainable environmental remediation approach

Aqueous phosphate pollution can dramatically impact ecosystems, introducing a variety of environmental, economic, and public health problems. While novel remediation tactics based on nanoparticle binding have shown considerable promise in nutrient recovery from water, they are challenging to deploy at scale. To bridge the gap between the laboratory-scale nature of these nanostructure solutions and the practical benchmarks for deploying an environmental remediation tool, we have developed a nanocomposite material. Here, an economical, readily available, porous substrate is dip coated using scalable, water-based processes with a slurry of nanostructures. These nanomaterials have tailored affinity for specific adsorption of pollutants. Our Phosphate Elimination and Recovery Lightweight (PEARL) membrane can selectively sequester up to 99% of phosphate ions from polluted waters at environmentally relevant concentrations. Moreover, mild tuning of pH promotes at will adsorption and desorption of nutrients. This timed release allows for phosphate recovery and reuse of the PEARL membrane repeatedly for numerous cycles. We combine correlative microscopy and spectroscopy techniques to characterize the complex microstructure of the PEARL membrane and to unravel the mechanism of phosphate sorption. More broadly, through the example of phosphate pollution, this work describes a platform membrane approach based on nanostructures with specific affinity coated on a porous structure. Such a strategy can be tuned to address other environmental remediation challenges through the incorporation of other nanomaterials.

A comparative study on phosphate removal from water using Phragmites australis biochars loaded with different metal oxides

Metal oxide-loaded biochars are a promising material to remove phosphate from polluted water to ultra-low concentrations. To facilitate preparing the metal oxide-loaded biochar with the best phosphate adsorption performance, five biochars loaded with Al, Ca, Fe, La and Mg oxides, respectively (Al-BC, Ca-BC, Fe-BC, La-BC and Mg-BC) were produced using Phragmites australis pretreated with 0.1 mol AlCl3, CaCl2, FeCl3, LaCl3 and MgCl2, respectively, characterized, and phosphate adsorption kinetics and isotherms of the biochars were determined. The maximum phosphate adsorption capacities (Qm ) of the biochars ranked as Al-BC (219.87 mg g-1) > Mg-BC (112.45 mg g-1) > Ca-BC (81.46 mg g-1) > Fe-BC (46.61 mg g-1) > La-BC (38.93 mg g-1). The time to reach the adsorption equilibrium ranked as La-BC (1 h) < Ca-BC (12 h) < Mg-BC (24 h) = Fe-BC (24 h) Collapse

Key Words

• adsorption rate
• biochar
• maximum adsorption capacity
• metal oxides
• phosphate removal and recovery

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MESH Headings Collapse

Grants

• Major Science and Technology Program for Water Pollution Control and Treatment
• Research Initiation Fund for Young Teachers of Beijing Technology and Business University

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Affiliation(s)

Pengfei Wang National Engineering Laboratory for Lake Pollution Control and Ecological Restoration, State Environment Protection Key Laboratory for Lake Pollution Control, Chinese Research Academy of Environmental Sciences, Beijing 100012, People's Republic of China
Mengmeng Zhi School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, People's Republic of China
Guannan Cui School of Ecology and Environment, Beijing Technology and Business University, Beijing 100048, People's Republic of China
Zhaosheng Chu National Engineering Laboratory for Lake Pollution Control and Ecological Restoration, State Environment Protection Key Laboratory for Lake Pollution Control, Chinese Research Academy of Environmental Sciences, Beijing 100012, People's Republic of China
Shuhang Wang National Engineering Laboratory for Lake Pollution Control and Ecological Restoration, State Environment Protection Key Laboratory for Lake Pollution Control, Chinese Research Academy of Environmental Sciences, Beijing 100012, People's Republic of China

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Modification of Hardwood Derived Biochar to Improve Phosphorus Adsorption

The excessive application of phosphorus in agricultural lands leads to serious environmental issues. Efficient application is beneficial from an economic and environmental perspectives. Biochar can be used as a carrier for slow release of phosphate. However, its adsorption capacity is limited. In this work, biochar was prepared at different pyrolysis temperatures (350–550 °C). The biochar prepared at 550 °C had the highest adsorption capacity and was selected for modification by magnesium impregnation. Magnesium modification enhanced the adsorption capacity by 34% to a theoretical max adsorption capacity of 463.5 mg·g−1. The adsorbed phosphate can be desorbed. The desorption was bi-phasic with fast- and slow-release fractions. The distribution of the phosphate fractions was pH dependent with slow release being most prominent in neutral conditions. Mg modified biochar can be used to recover phosphate and then used as a carrier for slow release of phosphate. The bi-phasic desorption behaviour is useful as the fast release fraction can provide the immediate phosphate needed during plant establishment, while the slow-release fraction maintains steady supply over extended periods.

High capacity aqueous phosphate reclamation using Fe/Mg-layered double hydroxide (LDH) dispersed on biochar

Phosphate is a primary plant nutrient, serving integral role in environmental stability. Excessive phosphate in water causes eutrophication; hence, phosphate ions need to be harvested from soil nutrient levels and water and used efficiently. Fe-Mg (1:2) layered double hydroxides (LDH) were chemically co-precipitated and widely dispersed on a cheap, commercial Douglas fir biochar (695 m²/g surface area and 0.26 cm³/g pore volume) byproduct from syn gas production. This hybrid multiphase LDH dispersed on biochar (LDHBC) robustly adsorbed (~5h equilibrium) phosphate from aqueous solutions in exceptional sorption capacities and no pH dependence between pH 1-11. High phosphate Langmuir sorption capacities were found for both LDH (154 to 241 mg/g) and LDH-modified biochar (117 to 1589 mg/g). LDHBC was able to provide excellent sorption performance in the presence of nine competitive anion contaminants (CO₃^2-, AsO₄^3-, SeO₄^2-, NO₃^-, Cr₂O₇^2-, Cl^-, F^-, SO₄^2-, and MoO₄^2-) and also upon remediating natural eutrophic water samples. Regeneration was demonstrated by stripping with aqueous 1 M NaOH. No dramatic performance drop was observed over 3 sorption-stripping cycles for low concentrations (5 ppm). The adsorbents and phosphate-laden adsorbents were characterized using Elemental analysis, BET, PZC, TGA, DSC, XRD, SEM, TEM, and XPS. The primary sorption mechanism is ion-exchange from low to moderate concentrations (10-500 ppm). Chemisorption and stoichiometric phosphate compound formation were also considered at higher phosphate concentrations (>500 ppm) and at 40 °C. This work advances the state of the art for environmentally friendly phosphate reclamation. These phosphate-laden adsorbents also have potential to be used as a slow-release phosphate fertilizer.

Removal of ammonia nitrogen and phosphorus by biochar prepared from sludge residue after rusty scrap iron and reduced iron powder enhanced fermentation

The rusty scrap iron (RSI) or a mixture of rusty scrap iron and reduced iron powder (RSI-RIP) can be used as an exogenous additive to enhance the anaerobic fermentation of sewage sludge. In order to make rational use of the fermentation residue, the sludge after intensified fermentation was pyrolyzed to produce biochar in this study, which was used in the adsorption of ammonia and phosphorus from the anaerobic fermentation broth. The experimental results demonstrated that the pore structure of the sludge biochar was greatly improved after enhanced fermentation with RSI and RIP. Meanwhile, there was an increase in the proportion of metallic elements such as Ca, Fe and Mg. On the other hand, the RSI-RIP co-enhanced fermented biochar (ES600) prepared at 600 °C showed a higher adsorption capacity, which was comparable to the commercially activated carbon. Neutral or weakly alkaline environments were preferred during the adsorption process. At a suitable pH condition, the maximum removal efficiency of ammonia nitrogen (NH₄⁺-N) and total phosphorus (TP) on ES600 reached 91.3% and 98.6%, respectively. In addition, the saturated ES600 was regenerated by simple washing with ammonia-free water. After three cycles, the removal efficiency of NH₄⁺-N and TP remained at 71.3% and 83.2%, respectively. As a result, the biochar prepared from RSI-RIP enhanced fermented sludge can be used as a promising low-cost adsorbent.

Chemico-nanotreatment methods for the removal of persistent organic pollutants and xenobiotics in water - A review

While the technologies available today can generate high-quality water from wastewater, the majority of the wastewater treatment plants are not intended to eliminate emerging xenobiotic pollutants, pharmaceutical and personal care items. Most endocrine disrupting compounds (EDCs) and personal care products (PPCPs) are more arctic than most regulated pollutants, and several of them have acid or critical functional groups. Together with the trace occurrence, EDCs and PPCPs create specific challenges for removal and subsequent improvements of wastewater treatment plants. Various technologies have been investigated extensively because they are highly persistent which leads to bioaccumulation. Researchers are increasingly addressing the human health hazards of xenobiotics and their removal. The emphasis of this review was on the promising methods available, especially nanotechnology, for the treatment of xenobiotic compounds that are accidentally released into the setting. In terms of xenobiotic elimination, nanotechnology provides better treatment than chemical treatments and their degradation mechanisms are addressed.

Phosphorus Removal from Wastewater: The Potential Use of Biochar and the Key Controlling Factors

In recent years, a large volume of literature has been published regarding the removal of phosphorus (P) from wastewater. Various sorbing materials, such as metal oxides and hydroxides, carbonates and hydroxides of calcium (Ca) and magnesium (Mg), hydrotalcite, activated carbon, anion exchange resins, industrial solid wastes and organic solid wastes, have been suggested for P removal. Many of these sorbents are expensive and/or may cause some environmental problems. In contrast, biochar, as an economical and environmentally friendly sorbing material, has received much attention in recent years and has been used as a novel sorbent for the removal of different organic and inorganic pollutants. Biochar is a type of sustainable carbonaceous material that is produced from the thermal treatment of agricultural organic residues and other organic waste streams under oxygen free conditions. This paper reviews the potential use of biochar and the key controlling factors affecting P removal from wastewater. The ability of biochar to remove P from wastewater depends on its physical and chemical properties. Some of the most important physicochemical properties of biochar (structural characteristics, electrical conductivity (EC), mineral composition, pH, zeta potential, cation exchange capacity (CEC) and anion exchange capacity (AEC)) are affected by the feedstock type as well as temperature of pyrolysis and the P sorption capacity is highly dependent on these properties. The P removal is also affected by the water matrix chemistry, such as the presence of competing ions and bulk pH conditions. Finally, several recommendations for future research have been proposed to facilitate and enhance the environmental efficiency of biochar application.

Application of biochar for the remediation of polluted sediments

Polluted sediments pose potential threats to environmental and human health and challenges to water management. Biochar is a carbon-rich material produced through pyrolysis of biomass waste, which performs well in soil amendment, climate improvement, and water treatment. Unlike soil and aqueous solutions, sediments are both the sink and source of water pollutants. Regarding in-situ sediment remediation, biochar also shows unique advantages in removing or immobilizing inorganic and organic pollutants (OPs). This paper provides a comprehensive review of the current methods of in-situ biochar amendments specific to polluted sediments. Physicochemical properties (pore structure, surface functional groups, pH and surface charge, mineral components) were influenced by the pyrolysis conditions, feedstock types, and modification of biochar. Furthermore, the remediation mechanisms and efficiency of pollutants (heavy metals [HMs] and OPs) vary with the biochar properties. Biochar influences microbial compositions and benthic organisms in sediments. Depending on the location or flow rate of polluted sediments, potential utilization methods of biochar alone or coupled with other materials are discussed. Finally, future practical challenges of biochar as a sediment amendment are addressed. This review provides an overview and outlook for sediment remediation using biochar, which will be valuable for further scientific research and engineering applications.

Emerging nano-structured innovative materials as adsorbents in wastewater treatment

Water supply around the globe is struggling to meet the rapidly increasing demand by the population, drastic changes in climate and degrading water quality. Even though, many large-scale methods are employed for wastewater treatment they display several negative impacts owing to the presence of pollutants. Technological innovation is required for integrated water management with different groups of nanomaterials for the removal of toxic metal ions, microbial disease, organic and inorganic solutes. The method of manipulating atoms on a nanoscale is nanotechnology. Nanomembranes are used in nanotechnology to soften water and eliminate physical, chemical and biological pollutants. The present review concentrates on various nanotechnological approaches in wastewater remedy, mechanisms involved to promote implementation, benefits and limitations in comparison with current processes, properties, barriers and commercialization research needs. Also the review identifies opportunities for further exploiting the exclusive features for green water management by following the advances in nanotechnology.

Degradation of sulfamethazine by biochar-supported bimetallic oxide/persulfate system in natural water: Performance and reaction mechanism

The rapid development of aquaculture results in the increased concentrations and kinds of antibiotics in water environment, and the sharply growing antibiotic contamination has caused increasing concerns. Herein, an innovative sulfamethazine (SMT) removal approach was developed by activation of persulfate (PS) using biochar-based materials prepared by co-precipitation and pyrolysis: Fe-Mg oxide/biochar (FeMgO/BC). Experiments on the activation of PS by FeMgO/BC under different factors were carried out. The involved mechanism and degradation pathway were also studied. Notably, the SMT removal rate reached 99 % under the optimum reaction condition, while the TOC removal efficiency reached 77.9 %. PS was activated by FeMgO/BC and the dominated active radical was SO_4•^-. Fe²⁺ from FeMgO and the hydroxyl and carboxyl groups on the surface of biochar contributed to the production of SO_4•^-. The dehydrogenation, bond cracking and unsaturated bond addition process occurred in the degradation of SMT. Furthermore, FeMgO/BC exhibits excellent reusability and stability. Considering the outstanding actual water application performances and the weak biotoxicity, FeMgO/BC shows a promising potential in the removal of antibiotics under actual water conditions.

High adsorption capacity of Mg-Al-modified biochar for phosphate and its potential for phosphate interception in soil

In this study, Mg and/or Al modified biochars (MABC¹, MBC², ABC³) prepared by co-precipitation were to explore their phosphate adsorption capacity from aqueous solution and the potential for soil phosphate interception. The results revealed that MABC composites contained more functional groups than MBC and showed a higher surface area than ABC. The surface of MABC contained dispersed MgAl₂O₄, Mg(OH)₂, AlOOH and Al₂O₃ crystals that were associated with its enhanced maximum phosphate adsorption capacity (153.40 mg g^-1). According to Langmuir model, the maximum adsorption capacity of MABC was 15.91, 1.85, and 93.54 times the capacity of MBC, ABC, and raw biochar (BC⁴), respectively. The addition of MABC in red soil could significantly slow down the release of soil phosphorus, and MABC also had a stronger phosphate interception capacity (59.89%) than other BCs. In summary, MABC exhibits superior phosphate adsorption and interception capacity, making it ideal for treatment and prevention of phosphorus-polluted water.

Preparation of nitrogen doped magnesium oxide modified biochar and its sorption efficiency of lead ions in aqueous solution

A N-doped couping MgO-modified biochar (MgO-N-BC) was synthesized from corncob-to-xylose residue by two-step slow pyrolysis method. The biochar exhibited a remarkable Pb(II) sorption capacity (maximum 1429 mg·g^-1) in aqueous solution. The sorption of Pb(II) onto MgO-N-BC best fitted Freundlich model and pseudo-second-order equation. Further analysis demonstrated the final product of Pb were mainly hexagonal crystal hydrocerussite flakes. The combine of ion-exchange and precipitation process play key role in the sorption of Pb(II), while interactions between Pb(II) and functional groups work, too. The sorption capacity decreased by 63.5% with CO₂ free, however over supply of CO₂ effects little on the sorption capacity while that can shorten equilibrium time from near 360 min to about 30 min. Only few co-existing ions such as Ba²⁺ and Fe³⁺ can decrease the sorption partly, and NH₄⁺ block the sorption obviously, while Mg²⁺ had an enhancement effect.

Preparation, environmental application and prospect of biochar-supported metal nanoparticles: A review

Biochar is a low-cost, porous, and carbon-rich material and it exhibits a great potential as an adsorbent and a supporting matrix due to its high surface activity, high specific surface area, and high ion exchange capacity. Metal nanomaterials are nanometer-sized solid particles which have high reactivity, high surface area, and high surface energy. Owing to their aggregation and passivation, metal nanomaterials will lose excellent physiochemical properties. Carbon-enriched biochar can be applied to overcome these drawbacks of metal nanomaterials. Combining the advantages of biochar and metal nanomaterials, supporting metal nanomaterials on porous and stable biochar creates a new biochar-supported metal nanoparticles (MNPs@BC). Therefore, MNPs@BC can be used to design the properties of metal nanoparticles, stabilize the anchored metal nanoparticles, and facilitate the catalytic/redox reactions at the biochar-metal interfaces, which maximizes the efficiency of biochar and metal nanoparticles in environmental application. This work detailedly reviews the synthesis methods of MNPs@BC and the effects of preparation conditions on the properties of MNPs@BC during the preparation processes. The characterization methods of MNPs@BC, the removal/remediation performance of MNPs@BC for organic contaminants, heavy metals and other inorganic contaminants in water and soil, and the effect of MNPs@BC properties on the remediation efficiency were discussed. In addition, this paper summarizes the effect of various parameters on the removal of contaminants from water, the effect of MNPs@BC remediation on soil properties, and the removal/remediation mechanisms of the contaminants by MNPs@BC in water and soil. Moreover, the potential directions for future research and development of MNPs@BC have also been discussed.

Effects of excessive impregnation, magnesium content, and pyrolysis temperature on MgO-coated watermelon rind biochar and its lead removal capacity

MgO-coated watermelon rind biochar (MWRB) is a potentially highly-effective waste-derived material in environmental applications. This research aims to provide valuable insights into the optimization of the production of MWRB for superior environmental performance. It was found that the Mg content of the MWRB could be easily controlled by adjusting the Mg/feedstock mass ratio during excessive impregnation. The BET surface area was found to first increase and then decrease as the Mg content of the MWRB (produced at 600 °C) increased from 1.52% to 10.1%, with an optimal surface area of 293 m²/g observed at 2.51%. Similarly, an optimum pyrolysis temperature of 600 °C was observed in the range of 400-800 °C for a maximum surface area of the MWRB at a fixed Mg/feedstock ratio of 0.48% (resulting in MWRBs with Mg contents of 1.89-2.51%). The Pb removal capacity of the MWRB (produced at 600 °C) increased with increasing Mg content, with a greatest Pb removal capacity of 558 mg/g found for the MWRB with the highest Mg content (10.1%), an improvement of 208% over the 181 mg/g Pb removal capacity of unmodified WRB produced at 600 °C. The Pb removal capacity of the MWRB (produced with 1.89-2.51% Mg) was also discovered to increase from 81.7 mg/g (at 400 °C) to 742 mg/g (at 700 °C), before dropping to 368 mg/g at 800 °C. These findings suggest that the MWRB can be more efficiently utilized in soil and water remediation by optimizing its synthesis conditions.

Adsorption of sulfate ion from water by zirconium oxide-modified biochar derived from pomelo peel

Zirconium oxide-modified pomelo peel biochar (ZrBC) was synthesized for the adsorption of sulfate ion from aqueous solution. Zirconyl chloride octahydrate (ZCO) was used to modify pomelo peel biochar into ZrBC. The optimal dose of ZCO for modification is 0.5 mol/L, at which ZrBC shows the highest adsorption of sulfate ion. The adsorbents were characterized by the field emission scanning electron microscopy, X-ray photoelectron spectroscopy and surface area measurement. The results confirm that the presence of zirconium oxides and hydroxide groups on the ZrBC surface, and ZrBC has a porous structure and a higher specific surface area in comparison with pomelo peel biochar. ZrBC shows good affinity for sulfate ion with a maximum sulfate adsorption capacity of 35.21 mg/g, which is much higher than that of pomelo peel biochar (1.02 mg/g). The adsorption of sulfate on ZrBC is pH dependent, and acidic conditions favor the adsorption. The adsorption can reach near-equilibrium in approximately 120 min. The adsorption kinetics and isotherm follow the pseudo second-order equation and Langmuir adsorption model, respectively. Furthermore, nitrate and fluoride anions exhibit little influence on the adsorption of sulfate by ZrBC, whereas phosphate inhibits the adsorption under the same concentration conditions. ZrBC has the potential to be used for removal of sulfate from aqueous solution.

Enhanced removal of phosphate and ammonium by MgO-biochar composites with NH3·H2O hydrolysis pretreatment

In this study, a novel MgO-biochar composite was generated for nutrient recovery from biogas slurry using magnesium chloride (MgCl₂) and ammonia hydroxide (NH₃·H₂O). Biochar properties, including pH, CEC, pHpzc, magnesium content, surface area, and total pore volume (V_total), were evaluated. Moreover, the removal of NH₄⁺ and PO₄^3- in both single and bi-solute system were investigated. Results indicated that NH₃·H₂O pretreatment and MgO-coating enhanced biochar pH, CEC, and pHpzc. Additionally, there were generally higher surface area and V_total in MgAWS₅₅₀. The maximum adsorption capacities for NH₄⁺ and PO₄^3-, respectively, increased as WS₅₅₀ (0.555 and 1.57 mg g^-1) < MgWS₅₅₀ (15.4 and 21.8 mg g^-1) < MgAWS₅₅₀ (17.5 and 31.3 mg g^-1). Moreover, higher removal efficiencies were achieved in the bi-solute system, and over 25% and 90% of NH₄⁺ and PO₄^3-, respectively, was removed from biogas slurry by MgASW₅₅₀. Mechanically, NH₄⁺ removal was mainly attributed to ionic exchange, while PO₄^3- adsorption on MgO-coated biochars was due to electrostatic attraction and precipitation. Furthermore, the formation of struvite (MgNH₄PO₄·6H₂O) further enhanced N and P in the bi-solute system.

A Review of Non-Soil Biochar Applications

Biochar is the solid residue that is recovered after the thermal cracking of biomasses in an oxygen-free atmosphere. Biochar has been used for many years as a soil amendment and in general soil applications. Nonetheless, biochar is far more than a mere soil amendment. In this review, we report all the non-soil applications of biochar including environmental remediation, energy storage, composites, and catalyst production. We provide a general overview of the recent uses of biochar in material science, thus presenting this cheap and waste-derived material as a high value-added and carbonaceous source.

Removal of phosphate from aqueous solution using MgO-modified magnetic biochar derived from anaerobic digestion residue

A novel MgO-modified magnetic biochar (MgO@MBC) was made by chemical co-precipitation of Mg²⁺/Fe³⁺ on anaerobic digestion residue (ADR) and subsequently pyrolyzing at different temperatures. MgO@MBC was used for phosphate recovery from aqueous solution. The physicochemical properties of MgO@MBC were comprehensively investigated using TEM-EDS, FT-IR, XRD, VSM, N₂ adsorption-desorption and TGA. Results showed that MgO/γ-Fe₂O₃ nanoparticles were successfully deposited onto the surface of BC. The effects of reaction temperature, initial solution pH, MgO@MBC dosage, coexisting anions and phosphate concentration on the removal of phosphate by MgO@MBC were researched. Additionally, the adsorption process of phosphate onto MgO@MBC was well described by the pseudo second-order and pseudo first-order models, which indicated a chemisorption and physisorption process. Besides, the maximum adsorption capacity of MgO@MBC for phosphate by the Langmuir model were 149.25 mg/g at 25 °C. Moreover, the thermodynamic study suggested that the adsorption of phosphate onto MgO@MBC was a spontaneous and endothermic process. The adsorption mechanisms including physical absorption, surface electrostatic attraction, surface complexation and precipitation were revealed. It could be concluded that MgO@MBC exhibited high removal efficiency of phosphate and excellent magnetic property for the recovery. MgO@MBC could be utilized as a magnetically recoverable adsorbent to realize phosphate recovery and MgO@MBC after the adsorpion of phosphate could be applied in agricultural production as a fertilizer.