Comparative investigation of characteristics and phosphate removal by engineered biochars with different loadings of magnesium, aluminum, or iron

Vortex-assisted dispersive micro-solid-phase extraction using silica-supported Fe2O3-modified khat (Catha edulis) biochar nanocomposite followed by GC-MS for the determination of organochlorine pesticides in juice samples

In this paper, dispersive micro-solid phase extraction technique was developed for the purpose of extracting and preconcentrating organochlorine pesticide residues in juice samples before their separation and quantitative analysis by gas chromatography-mass spectrometry. A sorbent composed of a silica-supported Fe2O3-modified khat leftover biochar nanocomposite (SiO2-Fe2O3-KLBNC) was implemented in the process. To improve the dispersion of the sorbent in the solution, vortex mixer was employed. Experimental parameters influencing the performance of the method were optimized, and the optimal conditions were established. With these conditions, linear dynamic ranges ranged from 0.003 to 100.0 ng/mL were achieved, with a correlation coefficient (r2) ≥ 0.9981. The limits of detection and quantification, determined by signal-to-noise ratios of 3 and 10, respectively, were found to be in the ranges of 0.001-0.006 ng/mL and 0.003-0.020 ng/mL. Intra- and inter-day precision, values ranging from 0.3-4.8% and 1.7-5.2% were obtained, respectively. The matrix-matched extraction recoveries demonstrated favorable outcomes, falling within the range of 83.4-108.3%. The utilization of khat leftover as an adsorbent in contemporary sample preparation methodologies offers a cost-effective alternative to the currently available, yet expensive, adsorbents. This renders it economically viable, particularly in resource-constrained regions, and is anticipated to witness widespread adoption in the coming future.

MnOx-Coffea arabica Husk and Catha edulis Leftover Biochar Nanocomposites for Removal of Methylene Blue from Wastewater

In this study, we investigated the use of manganese oxide-biochar nanocomposites (MnOx-BNC), synthesized from coffee husk (CH) and khat leftover (KL) for the removal of methylene blue (MB) from wastewater. Pristine biochars of each biomass (CH and KL) as well as their corresponding biochar-based nanocomposites were synthesized by pyrolyzing at 300°C for 1 h. The biochar-based nanocomposites were synthesized by pretreating 25 g of each biomass with 12.5 mmol of KMnO4. To assess the MB removal efficiency, we conducted preliminary tests using 0.2 g of each adsorbent, 20 mL of 20 mg·L-1 MB, pH 7.5, and shaking the mixture at 200 rpm and for 2 h at 25°C. The results showed that the pristine biochar of CH and KL removed 39.08% and 75.26% of MB from aqueous solutions, respectively. However, the MnOx-BNCs removed 99.27% with manganese oxide-coffee husk biochar nanocomposite (MnOx-CHBNC) and 98.20% with manganese oxide-khat leftover biochar nanocomposite (MnOx-KLBNC) of the MB, which are significantly higher than their corresponding pristine biochars. The adsorption process followed the Langmuir isotherm and a pseudo-second-order model, indicating favorable monolayer adsorption. The MnOx-CHBNC and MnOx-KLBNC demonstrated satisfactory removal efficiencies even after three and six cycles of reuse, respectively, indicating their potential effectiveness for alternative use in removing MB from wastewater.

Kinetics of phosphorous sorption to biochar-amended soils

Biochar has been investigated as a potential soil amendment for increasing P sorption to soils. Several studies of shown that coating biochar with Fe oxides can increase the amount of P sorbed to the biochar, yet little is known about the kinetics of P sorption to soils amended with Fe-coated biochar. In this study, the kinetics of P sorption are measured in four soils with contrasting surface properties and textures. In addition, a wood-based biochar, both unmodified (BC) and modified by chemical precipitation of Fe oxides (BCFe), was added to these four soils at a rate of 5% (w/w). P sorption to each soil with and without the unmodified or Fe-coated biochar was measured at incubation times ranging from 1 to 314 h. The data were fit using five different kinetic models to determine if the addition of the BC or BCFe significantly affected the amount of P sorption and the kinetic behavior of P sorption to the biochar-amended soils. Results showed that amending with BC had minimal impact on P sorption to the four soils, whereas the impact of the BCFe on P sorption varied depending on soil. In the low P sorbing soil, the BCFe nearly doubled the amount of P sorbed whereas in the high P sorbing soil, addition of the BCFe resulted in less-than-expected increases in P sorption. For each biochar and soil treatment, the same kinetic model provided the best fit to the observed sorption over time. In two soils, the kinetic model parameters were significantly different following the addition of the BC whereas the model parameters for all four soils were significantly different following addition of BCFe. This study provides new insights into P sorption kinetics to biochar-amended soils.

Enhancing dissolved inorganic phosphorous capture by gypsum-incorporated biochar: Synergic performance and mechanisms

Excess nutrients, such as phosphorus (P), in watersheds jeopardize water quality and trigger harmful algal blooms. Using phosphorus sorption material (PSM) to capture P from wastewater and agricultural runoff can help recover nutrients and prevent their water pollution. In this study, a novel designer biochar was generated by pyrolyzing woody biomass pretreated with a flue gas desulfurization gypsum. The removal of dissolved inorganic phosphorus (DIP) by the gypsum-incorporated designer biochar was more efficient than the gypsum, suggesting the pretreatment of biomass with the gypsum results in a synergic effect on enhancing DIP capture. The maximum P adsorption capacity of the designer biochar was more than 200 mg g-1 , which is one order of magnitude greater than that of the gypsum. This result clearly showed that the designer biochar is a better PSM to capture DIP from nutrient-contaminated water compared to the gypsum. Post-sorption characterization indicated that the sorption of DIP by the gypsum-incorporated biochar involves multiple mechanisms. The precipitation reactions of calcium (Ca) cations and P anions to form CaHPO4 and Ca3 (PO4 )2 precipitates on the highly alkaline surface of the designer biochar were identified as a main mechanism. By contrast, CaHPO4 ·2H2 O is the only precipitated product for DIP sorption by the gypsum. In addition, the initial solution pH and the coexisting bicarbonate had less effects on the DIP removal by the designer biochar in comparison with the gypsum, which further confirms that the former is an excellent PSM to capture DIP from a variety of aquatic media.

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.

Removal of Pb(II) and phosphorus in water by γ-Al2O3/biochar

In this work, we synthesized activated alumina biochar composites (γ-Al₂O₃/BC) by sol-gel method, which improved the problem that the surface charge of γ-Al₂O₃ was not conducive to the removal of heavy metal cation in a neutral solution, and then explored the feasibility of removing Pb(II) by γ-Al₂O₃/BC as well as reusing Pb-laden waste sludge to remove phosphorus (P) and its micro-adsorption mechanisms. The results show that the maximum adsorption capacity of γ-Al₂O₃/BC for Pb(II) is 182.48 mg/g, and the removing capacity of recycled Pb-laden slag for P also reaches 87.13 mg/g. It was found that the presence of Pb in the slag makes P removal more effective. In addition, in the process of P removal, the Pb in the slag will not be released, which will not cause secondary pollution to the water. The micro-adsorption mechanism of Pb(II) and P on the composites was investigated by XPS, XRD, and FTIR. It demonstrates that special functional groups such as hydroxy-aluminum, hydroxyl, and carboxyl groups can remove Pb(II) through strong surface complexation and electrostatic attraction. Furthermore, the removal mechanism of P from Pb-laden sludge includes chemisorption and complexation, and the precipitation of P and Pb on the adsorbent surface is the main reason for the removal of P. Therefore, it is feasible to further effectively remove P by using the waste biochar containing Pb. The idea of this paper provides a potential method for the reuse of waste adsorbent.

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.

A critical review on the development of lanthanum-engineered biochar for environmental applications

Biochar and lanthanum (La) have been widely used in environment. However, there is a lack of knowledge and perspective on the development of La-engineered biochar (LEB) for environmental applications. This review shows that LEBs with a variety of La species via pre-/post-doping routes are developed for environmental applications. Specifically, precipitation, gelation, and calcination are the common sub-processes involved in the pre-/post-doping of La on the resultant LEB. The dominant La species for LEBs is La(OH)₃, which is formed through precipitation of La ions with various bases. Various La carbonates, e.g., LaOHCO₃, La₂(CO₃)₃, La₂CO₅, and NaLa(CO₃)₂, are also involved in the preparation of LEBs. The LEBs are high-efficient in the adsorption of phosphate, arsenic, antimonate and fluoride ions, attributed to the strong affinity of La to oxyanions and Lewis hard base. Lanthanum is also favorable for co-doping with transition metal species to further enhance the performances in adsorption or catalysis. This review also analyzes the prospects and future challenges for the preparation and application of LEBs in environment. Finally, this review is beneficial to inspire new breakthroughs on the preparation and environmental application of LEBs.

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

A large amount of wastewater containing nitrogen, phosphorus, and fluorine produces in the production of phosphate fertilizer. In this study, to simultaneously recover nitrogen and phosphorus from phosphorus-containing wastewater and realize the resource utilization of red mud and rape straw, red mud-modified rape straw biochar (RM/RSBC) was prepared by facile one step, and the physicochemical properties were characterized by Zeta potential, SEM-EDS, BET specific surface area (SSA), FTIR, XRD, and XPS. The adsorption performance and mechanisms of ammonium and phosphate onto RM/RSBC were explored through static, fixed-bed column adsorption, and practical wastewater experiments. The results showed that pH = 3.0 and 8.0 were favorable for the removal of phosphate and ammonium, respectively. The main adsorption mechanisms of ammonium and phosphate were the interaction between ammonium and surface functional groups and surface precipitation, respectively. The removal efficiencies of ammonium and phosphate by fixed-bed column adsorption mainly depended on the addition amount of RM/RSBC, the concentration of ammonium and phosphate, and the flow rate. The results of the germination experiment showed that adding > 0.5 wt% of RM/RSBC loaded with ammonium and phosphate promoted the growth of mung beans. This study shows that RM/RSBC can not only recover ammonium and phosphate in wastewater, but also realize the resource utilization of red mud and rape straw.

Recovery of phosphorus from wastewater: A review based on current phosphorous removal technologies

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

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.

Phosphorous removal and recovery from urban wastewater: Current practices and new directions

Phosphate rocks are an irreplaceable resource to produce fertilizers, but their availability will not be enough to meet the increasing demands of agriculture for food production. At the same time, the accumulation of phosphorous discharged by municipal wastewater treatment plants (WWTPs) is one of the main causes of eutrophication. In a perspective of circular economy, WWTPs play a key role in phosphorous management. Indeed, phosphorus removal and recovery from WWTPs can both reduce the occurrence of eutrophication and contribute to meeting the demand for phosphorus-based fertilizers. Phosphorous removal and recovery are interconnected phases in WWTP with the former generally involved in the mainstream treatment, while the latter on the side streams. Indeed, by reducing phosphorus concentration in the WWTP side streams, a further improvement of the overall phosphorus removal from the WWTP influent can be obtained. Many studies and patents have been recently focused on treatments and processes aimed at the removal and recovery of phosphorous from wastewater and sewage sludge. Notably, new advances on biological and material sciences are constantly put at the service of conventional or unconventional wastewater treatments to increase the phosphorous removal efficiency and/or reduce the treatment costs. Similarly, many studies have been devoted to the development of processes aimed at the recovery of phosphorus from wastewaters and sludge to produce fertilizers, and a wide range of recovery percentages is reported as a function of the different technologies applied (from 10-25% up to 70-90% of the phosphorous in the WWTP influent). In view of forthcoming and inevitable regulations on phosphorous removal and recovery from WWTP streams, this review summarizes the main recent advances in this field to provide the scientific and technical community with an updated and useful tool for choosing the best strategy to adopt during the design or upgrading of WWTPs.

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.

A Review on Bamboo as an Adsorbent for Removal of Pollutants for Wastewater Treatment

Water and wastewater treatment are very important for obtaining clean and sanitary water as well as protecting the environment from toxic pollutants. Not only enriched with cellulose and carbon but the abundant resources of bamboo also make it suitable to be utilized as an adsorbent. With the right processing technologies and improvements, the potential of bamboo is unlimited. This study review provides knowledge on the use of bamboo-based adsorbents for the removal of contaminants and pollutants in wastewater in the form of activated carbon, biochar, and aerogel. This review highlighted bamboo utilization and its relevance as an adsorbent for wastewater treatment. The technologies for the processing and improvement of bamboo as well as the performance of the bamboo-based adsorbents are also discussed in this study. The adsorption capacity of bamboo has shown improvement with modification and good adsorption capacity achieved with some of the adsorbent being able to be recycled and reused.

Hydrothermal carbonization of distillers grains with clay minerals for enhanced adsorption of phosphate and methylene blue

A novel one-pot synthesis method was developed to prepare modified hydrochar by co-hydrothermal carbonization of waste distillers grains using low-cost clay minerals (attapulgite or vermiculite). The loading of the clay minerals onto hydrochar surfaces altered the structure and surface composition of the hydrochar such that the clay-modified hydrochars showed better ability to adsorb methylene blue and phosphate in aqueous solution than the pristine hydrochar. The maximum methylene blue and phosphate adsorption capacities of the modified hydrochar reached 340.3 and 96.9 mg g^-1, respectively, comparable or higher than that of many commercial sorbents. Multiple mechanisms, including electrostatic attraction, ion exchange, complexation, and physical adsorption, controlled the adsorption process. These results highlight excellent potential for distillers grains-derived hydrochar-clay composites as an environmental sorbent, capable of removing a variety of contaminants from aqueous solutions.

Ball milling biochar iron oxide composites for the removal of chromium (Cr(VI)) from water: Performance and mechanisms

As the first of its kind, a novel biochar/iron oxide composite (BM-Fe-HC) was successfully prepared by simply ball milling iron-laden biochar (Fe-HC). The performance and mechanisms of Cr(VI) removal by BM-Fe-HC were investigated. Ball milling effectively reduced particle size, increased specific surface area, more importantly, enhanced the distribution and increased the exposure of iron oxides on biochar surface. As a result, Cr(VI) removal by BM-Fe-HC showed fast kinetics and large adsorption capacity with the Langmuir maximum capacity of 48.1 mg/g, higher than that of other biochar/iron composites reported in the literature. Acidic pH promoted Cr(VI) removal while competition ions (Cl^-, SO₄^2- and PO₄^3-) inhibited Cr(VI) removal by BM-Fe-HC. Comparison of pre- and post-adsorption samples revealed that iron oxides of the BM-Fe-HC played the dominant role in the adsorption and reduction of Cr(VI) during the removal. After adsorption, part of adsorbed Cr(VI) was reduced by Fe(II) and then stabilized by Fe(III) in the form of amorphous Cr_xFe_1-x(OH)₃ on the composite surface. All the results demonstrate that novel ball-milled biochar/iron oxide composites can be used as an effective adsorbent to remove Cr(VI) from water.

The Occurrence of Legacy P Soils and Potential Mitigation Practices Using Activated Biochar

The long-term application of manures in watersheds with dense animal production has increased soil phosphorus (P) concentration, exceeding plant and soil assimilative capacities. The P accumulated in soils that are heavily manured and contain excess extractable soil P concentrations is known as legacy P. Runoff and leaching can transport legacy P to ground water and surface water bodies, contributing to water quality impairment and environmental pollution, such as eutrophication. This review article analyzes and discusses current and innovative management practices for soil legacy P. Specifically, we address the use of biochar as an emerging novel technology that reduces P movement and bioavailability in legacy P soils. We illustrate that properties of biochar can be affected by pyrolysis temperature and by various activating chemical compounds and by-products. Our approach consists of engineering biochars, using an activation process on poultry litter feedstock before pyrolysis to enhance the binding or precipitation of legacy P. Finally, this review article describes previous examples of biochar activation and offers new approaches to the production of biochars with enhanced P sorption capabilities.

Engineered Biochar Production and Its Potential Benefits in a Closed-Loop Water-Reuse Agriculture System

Biochar’s potential to remove various contaminants from aqueous solutions has been widely discussed. The rapid development of engineered biochar produced using different feedstock materials via various methods for wastewater treatment in recent years urges an up-to-date review on this topic. This article centers on summarizing state-of-the-art methods for engineered biochar production and discussing the multidimensional benefits of applying biochar for water reuse and soil amendment in a closed-loop agriculture system. Based on numerous recent articles (<5 years) published in journals indexed in the Web of Science, engineered biochar’s production methods, modification techniques, physicochemical properties, and performance in removing inorganic, organic, and emerging contaminants from wastewater are reviewed in this study. It is concluded that biochar-based technologies have great potential to be used for treating both point-source and diffuse-source wastewater in agricultural systems, thus decreasing water demand while improving crop yields. As biochar can be produced using crop residues and other biomass wastes, its on-farm production and subsequent applications in a closed-loop agriculture system will not only eliminate expensive transportation costs, but also create a circular flow of materials and energy that promotes additional environmental and economic benefits.