Engineered/designer biochar for the removal of phosphate in water and wastewater

Adsorption of phosphate in aqueous solution by ash from the fruit peel of Caryocar coriaceum Wittm: adsorption characteristics and behavior

High phosphate concentrations in natural waters are associated with eutrophication problems that negatively affect the fauna and flora of ecosystems. As an alternative solution to this problem, we evaluated the adsorptive capacity of the fruit peel ash (PPA) of Caryocar coriaceum Wittm and its efficiency in removing phosphate (PO43-) from aqueous solutions. PPA was produced under an oxidative atmosphere and calcinated at 500 °C. The XRF and EDS analyses of PPA after contact with an aqueous PO43- solution showed an increase in its PO43- content, thus confirming the adsorption of PO43-. The Elovich and Langmuir models are the ones fitting the kinetics and the equilibrium state of the process, respectively. The highest PO43- adsorption capacity was approximately 79.50 mg g-1 at 10 °C. PO43- adsorption by PPA is a spontaneous, favorable, and endothermic process involving structural changes. The highest removal efficiency was 97.08% using a 100 mg.L-1 PO43- solution. In sight of this, PPA has shown potential as an excellent natural bioadsorbent.

Remarkably Enhanced Phosphate Sequestration from Waters by Biochar with High-Density Quaternary Ammonium Groups

A new biochar (N-BC) was fabricated by incorporating high-density positively charged quaternary ammonium groups into the pristine biochar without any adsorption for phosphate. N-BC can highly efficiently remove phosphate with an optimal pH of 5.0, a maximum experimental adsorption capacity of 30 mg of P/g, and an adsorption equilibrium time of 180 min. The predicted pore diffusion coefficient D (the diffused surface area of the adsorbate for unit time) for phosphate adsorption by N-BC was 5.3 × 10-9 cm2/s. N-BC can still capture phosphate in the copresence of anion Cl- with a molar concentration 50 times that of phosphate. The exhausted N-BC was completely regenerated using a 10 wt % NaOH solution and further reused without any observable loss in adsorption capacity. Moreover, N-BC yielded ∼324 bed volumes (BV) of wastewater containing 1 mg P/L phosphate and 50 mg/L Cl- before breakthrough occurring (<0.1 mg P/L in effluent) in a fixed-bed column operation system. The introduced quaternary ammonium groups covalently bound to biochar played a dominant role in phosphate sequestration by N-BC through forming the out-sphere complexation with phosphate. All results imply that it is of promising prospect for N-BC practical application for phosphate purification from waters. The present study provided a new strategy to expand the application of biochar, usually serving as an adsorbent for cationic pollutants, to the purification of anionic pollutants such as phosphate from waters.

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.

Adsorption of phosphate onto agricultural waste biochars with ferrite/manganese modified-ball-milled treatment and its reuse in saline soil

Agricultural waste biochar was widely used to absorb phosphorus (P) from eutrophicated water and soil remediation. However, the research on the reuse of the sorbed P on biochar in infertile saline soil is insufficient. Biochars derived from four kinds of agricultural wastes (cotton straws from two origins, maize stalk, and rice husk) were modified and applied to adsorb phosphate in waste water and then be reused in saline soil in this study. The co-modified method combining ball milling and metal coated treatment obtained the higher specific surface area (SSA) of ferrite/manganese modified-ball-milled biochars (Fe/Mn-BMBCs) (226.5-331.5 m2 g-1) than that of pristine biochars (14.02-30.35 m2 g-1) and ferrite/manganese modified biochar (Fe/Mn-BC) (223.7 m2 g-1), which could improve the pore structure of metal modified biochar. The phosphate adsorption capacity (qmax) of Fe/Mn-BMBCs with rich functional groups and high SSA were 44.0-53.8 mg g-1, which was 4.47-5.82 times higher than that of pristine biochars. Fe/Mn-BMBCs showed efficiently adsorption performance at low pH and high temperature. The application of BC to saline soil could promote the availability of P in saline soil. P-loaded biochars could afford P as a nutrient to promote the growth of lettuce (Lactuca sativa L.) in saline soil. The lettuce fresh weight in Fe/Mn-BMBC-P2 treated soil was 8.21 times higher than that grew in control check (CK) treatment. As a P element provider, P-loaded biochars not only improve saline soil fertility and crop productivity, but also convert the agricultural wastes and P in eutrophicated waters to the sustainable resource.

Adsorption of Metal Ions from Single and Binary Aqueous Systems on Bio-Nanocomposite, Alginate-Clay

The aim of this work is to characterize and evaluate the retention of Cu2+ and Ni2+ from single and binary systems by alginate-Moroccan clay bio-composite with the utilization of calcium chloride as a cross-linking agent, using the ionotropic gelation method. The bio-nanocomposite was characterized by using a variety of techniques (SEM, EDX, XRD, and pHPZC). The efficiency of the adsorbent was investigated under different experimental conditions by varying parameters such as pH, initial concentration, and contact time. To demonstrate the adsorption kinetics, various kinetic models were tried and assessed, including pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models. The research results show that the adsorption process of Cu2+ and Ni2+ metal ions follows a pseudo-second-order kinetic model, and the corresponding rate constants were identified. To evaluate the parameters related to the adsorption process in both single and binary systems, different mathematical models of isotherms, such as Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich, were investigated. The correlation coefficients obtained showed that the most suitable isotherm for describing this adsorption process is the Langmuir model. The process is considered to be physical and endothermic, as suggested by the positive values of ΔH° and ΔS°, indicating increased randomness at the solid/liquid interface during Cu2+ and Ni2+ adsorption. Furthermore, the spontaneity of the process is confirmed by the negative values of ∆G°. The bio-nanocomposite beads demonstrated a maximum adsorption capacity of 370.37 mg/g for Ni2+ and 454.54 mg/g for Cu2+ in the single system. In the binary system, the maximum adsorption capacities were observed to be 357.14 mg/g for Ni2+ and 370.37 mg/g for Cu2+. There is significant evidence for the use of alginate-Moroccan clay bio-nanocomposite as a cost-effective alternative adsorbent for the efficient removal of metal ions in single and binary systems.

Simultaneous decontamination of phosphorus and bisphenol A from livestock wastewater with boehmite-modified carbon composite

In this work, a novel boehmite-modified carbon adsorbent (BMCC) derived from moldy corn was used for simultaneous removal of P and bisphenol A (BPA) from livestock wastewater. The results showed that BMCC had a high specific surface area (308.82 m2/g) with boehmite nanoparticles anchored on its surface. BMCC showed high P and BPA decontamination capabilities (40.98 mg/g for P and 54.65 mg/g for BPA by Langmuir model). The adsorbed amount of P declined as pH increased from 4 to 10, while the adsorbed amount of BPA remained steady until pH increased to 10. After 6 cycles of BMCC use, the P and BPA adsorption efficiencies reduced by 21.75 % and 19.41 %, respectively. The adsorption of P was dominated by electrostatic attraction and complexation, while the adsorption of BPA was controlled by hydrogen bonding, electrostatic interaction, and π-π association. In conclusion, BMCC is an effective treatment for decontaminating P- and BPA-contaminated livestock wastewater.

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

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

Alginate-Moroccan Clay, New Bio-Nanocomposite for Removal of H2PO4-, HPO42-, and NO3- Ions from Aqueous Solutions

The aim of this work is to synthesize and characterize alginate-Moroccan clay bio-composite in order to improve our understanding of the adsorption of inorganic pollutants found in textile effluents. Characterization of the bio-composite used was carried out using a variety of techniques (IR-TF, SEM, DRX, and pHZPC). The influence of the medium's physico-chemical parameters (temperature, pH, initial concentration, etc.) on the retention of inorganic pollutants was also studied. Studies of adsorption and inorganic pollutants such as orthophosphate (H2PO4- and HPO42-) and nitrate (NO3-) ions were carried out, using simple solutions from the laboratory, in a batch system. This study explored the impact of adsorbent dose, contact time, solution pH, and temperature on the adsorption process. Various kinetic models, including pseudo-first-order, pseudo-second-order, intra-particle diffusion, and Elovich models, were tested and evaluated, to illustrate the adsorption kinetics. This study's findings demonstrated that the adsorption process follows second-order kinetics, with associated rate constants successfully determined. The correlation coefficient for the pseudo-second-order kinetic model is nearly equal to 1 (>0.98), and the value of theoretical adsorption capacity (qe,the) is comparable to the experimental one (qe,the = 58.14 mg/g for H2PO4-, qe,the = 54.64 mg/g for HPO42-, and qe,the = 52.63 mg/g for NO3-). Additionally, the adsorption equilibrium was investigated through the application of various mathematical models, including the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models, to assess the mechanistic parameters associated with the adsorption process. Among these models, the Langmuir isotherm emerged as the most suitable one for characterizing the adsorption of H2PO4-, HPO42-, and NO3- ions using bio-nanocomposite beads. The maximum adsorbed amounts of metal ions by the bio-nanocomposite used were 625 mg/g for H2PO4-, 909.09 mg/g for HPO42-, and 588.23 mg/g for NO3- from the batch system. The endothermic and physical nature of the adsorption is suggested by the positive values of ΔH°, which is consistent with experimental findings. The adsorption process is spontaneous, as evidenced by the negative ΔG° values. Positive ΔS° values indicate increased randomness at the solid/liquid interface during adsorption of ion-organic ions onto the engineered bio-nanocomposite. The obtained results demonstrated that, from a scientific perspective, alginate-Moroccan clay bio-nanocomposites exhibit a highly significant adsorption capability for the removal of oxyanions in aqueous environments.

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.

Phosphorus Removal from Dirty Farmyard Water by Activated Anaerobic-Digestion-Derived Biochar

The management of anaerobic digestate is important to realize the value of the waste and enhance the whole system sustainability of anaerobic digestion. In this study, the phosphorus treatment of dirty irrigation water by biochar samples derived from digestate of anaerobic digestion were investigated. The biochars were further activated by steam activation with different duration time and KOH activation with different introducing ratios; the textural properties of biochars were optimized after activation from the aspect of biochar characterization. Notably, AD-N2 demonstrates a remarkable adsorption effect of phosphorus, with an adsorption efficiency of 8.99 mg g-1. Besides the effect of biochar dosage on phosphorus removal, adsorption kinetics and thermodynamic isotherms are studied. According to the adsorption kinetics, the adsorption of phosphorus from dirty water fits the Elovich equation (R2 = 0.95). Furthermore, the thermodynamic isotherm results illustrate the process of phosphorus removal by biochar is endothermic (ΔH0 = 17.93 kJ mol-1) and spontaneous (ΔS = 96.24 J mol-1 K-1). Therefore, this work suggests a promising solution to phosphorus-related environmental challenges in industry and agriculture.

Emerging electro-driven technologies for phosphorus enrichment and recovery from wastewater: A review

The recovery of phosphorus from wastewater is a critical step in addressing the scarcity of phosphorus resources. Electro-driven technologies for phosphorus enrichment have gathered significant attention due to their inherent advantages, such as mild operating conditions, absence of secondary pollution, and potential integration with other technologies. This study presents a comprehensive review of recent advancements in the field of phosphorus enrichment, with a specific focus on capacitive deionization and electrodialysis technologies. It highlights the underlying principles and effectiveness of electro-driven techniques for phosphorus enrichment while systematically comparing energy consumption, enrichment rate, and concentration factor among different technologies. Furthermore, the study provides a thorough analysis of the capacity of various technologies to selectively enrich phosphorus and proposes several methods and strategies to enhance selectivity. These insights offer valuable guidance for advancing the future development of electrochemical techniques with enhanced efficiency and effectiveness in phosphorus enrichment from wastewater.

Sustainable utilization of Sedum plumbizincicola as superior hydrochar for efficient nutrients recovery

To realize sound disposal of hyperaccumulator harvested from phytoremediation, hydrothermal carbonization (HTC) has been employed to obtain superior hydrochar adsorbents for removal of phosphate and ammonium from water body. A series of hydrochars have been prepared under tuned HTC conditions to tailor hydrochar with desired properties. Generally, increased temperature and prolonged reaction time facilitated acidic oxygen functional groups on hydrochars, thereby improving adsorption capacity of hydrochar. In single solute system, a superior hydrochar, derived from HTC under 260 °C for 2 h, achieved a maximum phosphate and ammonium adsorption capacity of 52.46 mg/g and 27.56 mg/g at 45 °C, respectively. In binary system, synergistic adsorption was observed only in lower solute concentration, whereas competitive adsorption occurred under higher solute concentration. Characterization and adsorption kinetics suggested chemisorption may dominate the adsorption process, thus the adsorption capacity could be improved by tuning pHpzc of hydrochar. This study firstly demonstrates the sustainable utilization of hyperaccumulators into nutrients-enriched hydrochar as fertilizer for in-situ phytoremediation of contaminated sites with minimized environmental risks towards circular economy.

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.

Optimization of pig manure-derived biochar for ammonium and phosphate simultaneous recovery from livestock wastewater

Livestock wastewater has led to serious eco-environmental issues. To effectively treat livestock wastewater and realize the resource utilization of livestock solid waste, manure waste has been widely used to prepare biochar for the recovery of nitrogen and phosphorus. However, fresh biochar has a poor ability to adsorb phosphate due to its negative charge. To overcome the defect, the proportion of biochar samples prepared at 400 °C and 700 °C was optimized under a mass ratio of 2:3 to obtain mixed biochar PM 4-7, achieving the purpose of enhanced ammonium and phosphate recovery in livestock wastewater simultaneously without any modification. The effects of pyrolysis temperature, dosage, and pH were studied, different adsorption models were used to explore the adsorption mechanism, and the effect of biochar loaded with nutrient elements on seed was verified through a seed germination experiment. It was revealed that the maximum removal rates of phosphate and ammonium were 33.88 % and 41.50 %, respectively, endorsing that mixed biochar PM 4-7 can recover nutrients from livestock wastewater, and could be used as a slow-release fertilizer to promote seed germination and growth. This method provides a new potential way for the efficient resource utilization of pig manure and the recovery of nutrients from breeding wastewater.

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.

Compounds based on iron mining tailing dams and activated carbon from macauba palm for removal of emerging contaminants and phosphate from aqueous systems

In this work, an iron-rich residue, which is widely obtained as a by-product in the iron mining industry, and macauba endocarp, waste from the extraction of vegetable oil for the production of biofuels, were used in the preparation of different composites based on iron and carbon. The composites were obtained by manual grinding of the calcined iron residue and activated carbon prepared by the macauba endocarp followed by thermal treatment under nitrogen atmosphere. The effect of the thermal treatment was analyzed by Mössbauer spectroscopy and X-ray diffraction and showed that the increase in the treatment temperature promoted the formation of different reduced iron phases in the final composite, such as Fe₃O₄, FeO, and Fe⁰. These composites were used in a combined adsorption/oxidation process through photocatalysis to remove up to 93% of amoxicillin from aqueous phase. The formation of possible reaction intermediates was monitored by electrospray ionization mass spectrometry (ESI-MS) and a mechanism of amoxicillin degradation was proposed. Afterward, the Fe/C composites were conducted to evaluate the impact of several parameters on phosphate adsorption processes and showed a maximum adsorption capacity of 40.3 mg g^-1. The adsorption capacity obtained for all the materials were greater than those found in the literature.

Engineered Biomaterials for Reducing Phosphorus and Nitrogen Levels from Downstream Water of Aquaculture Facilities

The United States (U.S.) has a nearly USD 17 billion seafood trade deficit annually. However, the U.S. aquaculture industry faces strict micronutrient (e.g., phosphorus and nitrogen) level mandates that negatively impact fish production, especially for the state of Idaho, which produces 70–75% of the nation’s rainbow trout. This study investigates the sustainability benefits of producing engineered biomaterials from lignocellulosic-based feedstocks near collection sites via portable biorefineries for use by fish farms to reduce eutrophication (oversupply of micronutrients) impacts. In this study, sustainability assessments are performed on a case study in southern Idaho, the largest U.S. commercial producer of rainbow trout. The results show that 20 and 60 min of water treatment, using small particle size biomaterial from lodgepole pine, has the highest total phosphorus removal rate, at 150–180 g of phosphorus per 1 metric ton of engineered biomaterials. The results of techno-economic and environmental impacts studies indicate that pinewood-based biomaterials production cost ranges from USD 213 USD 242 per ton and reduces the eutrophication potential by 5–17 kg PO4eq/ton. Additionally, the environmental impact results show that the total greenhouse gas emission for biomaterial production is 47–54 kg CO2eq/ton; however, the used biomaterials after water treatment can be sold for around USD 850 per ton as nutrient-rich soil conditioners. This study concluded that engineered biomaterials from lignocellulosic-based feedstocks could be a sustainable solution to the challenge that aquaculture faces, particularly capturing micronutrients from eutrophic water and reusing them as fertilizers.

Recyclable Magnesium-Modified Biochar Beads for Efficient Removal of Phosphate from Wastewater

Although ball milling is effective for biochar modification with metal oxides for efficient phosphate removal, the recyclability of the adsorbent as well as the precursors for modification, still need to be optimized. Herein, a magnesium-modified biochar was first prepared with the precursor of MgCl₂·6H₂O through the solvent-free ball milling method. After that, recyclable biochar beads were fabricated with the introduction of sodium alginate and Fe₃O_4. The beads were proved to have excellent adsorption performance for phosphate with a saturated capacity of 53.2 mg g^-1, which is over 12 times higher than that of pristine biochar beads. Although the particle size reduction, surface area, and O-containing group increments after milling are beneficial for adsorption, the remarkable promotion in performance should mainly result from the appropriate formation of magniferous crystals on biochar, which greatly accelerates the electrostatic interactions as well as precipitation for adsorption. The beads also exhibited excellent magnetism-driven recyclability, which greatly avoids secondary contamination and broadens the application field of the adsorbent.

A comparative life-cycle assessment and cost analysis of biofilters amended with sludge-based activated carbon and commercial activated carbon for stormwater treatment

Environmental and economic issues resulting from the unsustainable management of sewage sludge from wastewater have necessitated the development of eco-friendly sewage sludge disposal methods, whereas stormwater effluent contains tremendous amounts of pollutants. This study compares the feasibility and environmental impacts associated with incorporating biofilters with sludge-based activated carbon (SBAC) versus commercial activated carbon (CAC) for stormwater treatment. The results demonstrate that the construction and disposal life-cycle stages are the dominant contributors to several environmental impact categories, including resource scarcity, carcinogenic toxicity, terrestrial ecotoxicity, and ozone formation indicators. Across multiple impact categories, the incorporation of biofilters with SBAC can reduce the negative environmental impacts associated with biofilter construction and disposal by 40% over a 50-year analysis period. In contrast, the most significant improvement is on construction-dominant indicators, where the decreased need for biofilter reconstruction results in a higher reduction in environmental impacts. Economically, amending the biofilter with SBAC can increase profits by up to 66% due to extending its lifespan. This study shows that SBAC has similar performance as CAC for lowering the negative environmental impacts resulting from biofilter construction, while increasing the overall net profits of the system. However, converting sewage sludge to an effective sorbent (SBAC) and incorporating SBAC into a biofilter to capture pollutants from stormwater is an economically and environmentally sustainable solution available to practitioners to manage sewage sludge and stormwater effluent. This solution protects the environment in a cost efficient, sustainable manner.

Preparation of phosphorus-modified biochar for the immobilization of heavy metals in typical lead-zinc contaminated mining soil: Performance, mechanism and microbial community

The use of modified biochar for the remediation of heavy metal (HM) has received much attention. However, the immobilization mechanism of biochar to multiple HMs and the interaction of different forms of HMs with microorganisms are still unclear. K₂HPO₄-modified biochar (PBC) was produced and used in a 90-days immobilization experiment with soil collected from a typic lead-zinc (Pb-Zn) mining soil. Incubation experiments showed that PBC enhanced the transformation of Cd, Pb, Zn and Cu from exchangeable (Ex-) and/or carbonate-bound forms (Car-) to organic matter-bound (Or-) and/or residual forms (Re-). After scanning electron microscopy-energy dispersive X-ray spectrometer (SEM-EDS), X-ray diffractometry (XRD), fourier transform infrared (FTIR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) analysis, the mechanisms of HM immobilization by PBC were proposed as precipitation (PO₄^3-, HPO₄^2-, OH^- and CO₃^2-), electrostatic attraction, complexation (-COOH, -OH and R-O-H) and the indirect roles of soil parameter variations (pH, moisture and microbial community). Microbial community analysis through high-throughput sequencing showed that PBC reduced bacterial and fungal abundance. However, addition of PBC increased the relative proportions of Proteobacteria by 15.04%-42.99%, Actinobacteria by 4.74%-22.04%, Firmicutes by 0.76%-23.35%, Bacteroidota by 0.16%-12.34%, Mortierellomycota by 4.00%-9.66% and Chytridiomycota by 0.10%-13.7%. Ex-Cd/Pb/Zn, Car-Cd/Zn and Re-Cd/Pb/As were significantly positively (0.001<P≤0.05) correlated with bacterial phyla of Crenarchaeota and Methylomirabilota, and Re-Cu and Ex-/Car-/Fe-Mn oxide-bound (Fe-Mn-)/Or-As were significantly positively correlated (0.001<P≤0.05) with the bacterial phyla of Proteobacteria and Bacteroidota. While Car-Cd/Zn and Re-Pb/As were positively correlated (0.01<P≤0.05) with fungal phyla of Ascomycota, Glomeromycota, Kickxellomycota, Basidiomycota and Mucoromycota. The bacterial network contained more complex interactions than the fungal network, suggesting that bacteria play a larger role in HMs transformation processes. The results indicate that PBC is an effective agent for the remediation of HMs polluted soil in Pb-Zn mining areas.

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

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

Synthesis of biochar-CoFe2O4 nanocomposite for adsorption of methylparaben from wastewater under full factorial experimental design

The presence of endocrine-disrupting chemicals in municipal wastewater has emerged as a threat to human health and the environment. Therefore, this study aimed to develop biochar-cobalt ferrite (BCF) nanocomposite for the removal of methylparaben from water under the full factorial experimental design of 4 factors with 3 levels (3⁴). The biochar-CoFe₂O₄ nanocomposite was developed by co-precipitation method from cobalt ferrite and biochar of Eucalyptus tree bark. Adsorbent surface morphology and functional and elemental composition were carried out by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and energy-dispersive X-ray spectroscopy (EDS) techniques which showed the presence of cracks with a rough surface, reasonable surface chemical composition, and many chemical functional groups, respectively. The experimental and predicted adsorption efficiencies ranged from 25.3 to 85.6% and 21.8 to 80.3%, respectively. The maximum adsorption performance (85.6%) reduced the methylparaben concentration from 27.5 to 4.0 mg/L at the optimum condition of adsorbent dose of 55 mg/100 mL, pH 6, contact time 90 min, and the initial methylparaben concentration of 27.5 mg/L. However, the adsorbent dose was the most influential main factor whereas the least influential was the interaction between solution pH and contact time under the regression model. The model also showed that 69% methylparaben removal was described by the regression model. The experimental data best fitted with the Freundlich model indicate multilayer adsorption which is the implication of physisorption. The sorption mechanism is attributed to Vander Waals forces, H-bonding, and dipole interaction. This BCF nanocomposite adsorbent appears to be promising for the removal of methylparaben from wastewater, but a further optimization process is essential to boost the treatment performance.

Efficient removal of levofloxacin by a magnetic NiFe-LDH/N-MWCNTs nanocomposite: Characterization, response surface methodology, and mechanism

Antibiotic pollutants in water bodies, was studied to remove using an oxidized, nitrogen-doped, and Fe₃O₄ and NiFe-LDH decorated MWCNT (magnetic NiFe-LDH/N-MWCNTs) nanocomposite (NC). The novel, engineered NC was characterized by different techniques of SEM, XRD, TEM, EDX, and XPS and then examined under different main effective parameters of NC dose, levofloxacin (LVX) concentration, pH, time, and temprature. The experimentally obtained data then evaluated using the modeling approaches of RSM, GRNN, and ANFIS. The as prepared adsorbent showed an excellent adsorption performance (removal efficiency = 95.28% and adsorption capacity = 344.83-454.55 mg/g) under the respective values of the mentioned parameters of 0.152 g, 23.01 mg/L, 12.00 min, and 37.5 °C, respectively. The comparison of the models showed that although all of them accurately predicted the removal efficiency, ANFIS presented the best capability with R², RMSE, MSE, MAE, as well as AAD of 0.9998, 0.0082, -0.0004, 0.0069, 0.1322, respectively. The adsorption by the NC followed Freundlich isotherm (R² = 0.9993) and PSO kinetic (>0.998) models, confirming a heterogenous chemisorption process. The thermodynamic parameters showed an endothermic and spontaneous nature for LVX removal by magnetic NiFe-LDH/N-MWCNTs NC. A high-performance efficiency, appropriate reusability (five times without loss of efficiency), as well as easy separation due to magnetic properties, makes the NC to a promising option in removing LVX from water.

Performance of lignin impregnated biochar on tetracycline hydrochloride adsorption: Governing factors and mechanisms

Corn stalk-based and wheat straw-based biochar were modified by lignin impregnation and applied to adsorb tetracycline hydrochloride (TCH) in wastewater. Porous properties of lignin impregnated biochar were improved and showed better adsorption performance for TCH. Lignin impregnated wheat straw biochar (WS-L) had the maximum adsorption capacity of 31.48 mg/g, which was 1.89 times compared to corresponding pristine biochar, because excellent pore structure developed via the lignin impregnation and carbonization. The adsorption behavior of TCH molecules on biochar could be interpreted well by two-step process, and it postulated to be a physical adsorption process based on pore filling, hydrogen bonding, π-π interaction, and electrostatic interactions. And cations including Na⁺, K⁺, Mg²⁺ and Al³⁺ could compete with TCH for adsorption, while Ca²⁺ could promote TCH adsorption by forming tetracycline-Ca²⁺ complexes. Maximum TCH adsorption occurred at pH of 7. The best performing lignin impregnated biochar was WS-L that demonstrated the biochar modulated by lignin had the potential to remove antibiotics from aqueous solutions.

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.

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.

Modified and pristine biochars for remediation of chromium contamination in soil and aquatic systems

Chromium (Cr) contamination in soil and water poses high toxicity risks to organisms and threatens food and water security worldwide. Biochar has emerged as a promising material for cleaning up Cr contamination owing to biochar's strong capacity to immobilize Cr. This paper synthesizes information on biochar modification for the efficient remediation of Cr contamination in soil and water, and critically reviews mechanisms of Cr adsorption on pristine and modified biochars. Biochar modification methods include physical activation via ball milling or ultraviolet irradiation, chemical activation via magnetization, alkali/acid treatment, nano-fabrication or loading of reductive agents, and biological activation via integrating biochars with microorganisms and their metabolites. Modified biochars often have multi-fold enhancement in Cr adsorption/reduction capacity than pristine biochars. Iron (Fe)-supported magnetic biochars have the most promising Cr removal abilities with high reusability of the biochars. Pre-pyrolysis modification with Fe could load Fe₃O₄ micro-/nanoparticles on biochars, and increase the surface area and electrostatic attraction between chromate anions and biochar surfaces, and reduce Cr(VI) to Cr(III). Post-pyrolysis modification could enrich oxygen-containing functional groups such as CO and -OH on biochar surfaces and promote Cr reduction and adsorption. Future research directions for Cr mitigation using advanced biochar products are discussed in this review.

Biochar-Mediated Zirconium Ferrite Nanocomposites for Tartrazine Dye Removal from Textile Wastewater

To meet the current challenges concerning the removal of dyes from wastewater, an environmentally friendly and efficient treatment technology is urgently needed. The recalcitrant, noxious, carcinogenic and mutagenic compound dyes are a threat to ecology and its removal from textile wastewater is challenge in the current world. Herein, biochar-mediated zirconium ferrite nanocomposites (BC-ZrFe₂O₅ NCs) were fabricated with wheat straw-derived biochar and applied for the adsorptive elimination of Tartrazine dye from textile wastewater. The optical and structural properties of synthesized BC-ZrFe₂O₅ NCs were characterized via UV/Vis spectroscopy, Fourier transform Infra-red (FTIR), X-Ray diffraction (XRD), Energy dispersive R-Ray (EDX) and Scanning electron microscopy (SEM). The batch modes experiments were executed to explore sorption capacity of BC-ZrFe₂O₅ NCs at varying operative conditions, i.e., pH, temperature, contact time, initial dye concentrations and adsorbent dose. BC-ZrFe₂O₅ NCs exhibited the highest sorption efficiency among all adsorbents (wheat straw biomass (WSBM), wheat straw biochar (WSBC) and BC-ZrFe₂O₅ NCs), having an adsorption capacity of (mg g^-1) 53.64 ± 0.23, 79.49 ± 0.21 and 89.22 ± 0.31, respectively, for Tartrazine dye at optimum conditions of environmental variables: pH 2, dose rate 0.05 g, temperature 303 K, time of contact 360 min and concentration 100 mg L^-1. For the optimization of process variables, response surface methodology (RSM) was employed. In order to study the kinetics and the mechanism of the adsorption process, kinetic and equilibrium mathematical models were used, and results revealed 2nd order kinetics and a multilayer chemisorption mechanism due to complexation of hydroxyl, Fe and Zr with dyes functional groups. The nanocomposites were also recovered in five cycles without significant loss (89 to 63%) in adsorption efficacy. This research work provides insight into the fabrication of nanoadsorbents for the efficient adsorption of Tartrazine dye, which can also be employed for practical engineering applications on an industrial scale as efficient and cost effective materials.

Shielding Effectiveness Measurements of Drywall Panel Coated with Biochar Layers

Shielding against electromagnetic interference (EMI) is a critical issue in civil applications generally solved with metal screens. In recent years, the properties of many composite materials filled with carbon nanotubes or graphene or materials with a carbon-based coating have been analysed with the aim of using them for electromagnetic shielding applications. Among other carbon materials, biochar, derived from biomass and characterized by high carbon content, emerges as a sustainable, renewable, environmentally friendly, and inexpensive material. In this paper, commercial biochar thermally treated at 750 °C is used to coat with several layers common building components such as drywall panel. Shielding effectiveness is measured in the frequency band 1–18 GHz for normal incidence and skew angles 10, 20 and 30 deg in a full anechoic chamber with double ridged, vertically and horizontally polarized broadband horn antennas. The results show that the proposed biochar-coated drywall panels provide a good shielding effectiveness compared to similar solutions, with the advantage of a less expensive and easier to realize building material.

The potential of biochar-photocatalytic nanocomposites for removal of organic micropollutants from wastewater

Biochar (BC)-photocatalyst nanocomposites have emerged as appealing water and wastewater treatment technology. Such nanocomposite materials benefit from the synergistic effect of adsorption and photocatalysis to attain improved removal of pollutants from water and wastewater. Under this review, three BC-based nanocomposite photocatalysts such as BC-TiO₂, BC-ZnO, and BC-spinel ferrites were considered. These nanocomposites acquire intrinsic properties to improve the practical limitations of the pristine BC and photocatalysts. The BC-based nanocomposites attained high photocatalytic activity, mechanical hardness, thermal stability, chemically non-reactive, magnetically permeable, reduced energy band gaps, improved reusability, and simplified recovery. Moreover, BC-based photocatalytic nanocomposites showed reduced recombination rates of the electron-hole pairs which are desirable for photocatalytic applications. However, the surface areas of the composites are usually smaller than that of the BC but higher than those of the pristine photocatalysts. Practically, the performances of the nanocomposites are much superior to those of the corresponding pristine components. This hybrid treatment technology is an emerging field and its industrial application is still at an early stage of the investigation. Therefore, exploring the full potential and practical applications of this technology is highly encouraging. Hence, this review focused on the critical evaluation of the most recent research on the synthesis, characterization, and photocatalytic treatment efficiency of the BC photocatalyst nanocomposites towards emerging pollutants in the aqueous medium. Moreover, the influence of various sources of BC feedstocks and their limitations on adsorption and photodegradation activities are discussed in detail. Finally, concluding remarks and future research directions are given to assist and shape the exploration of BC-based nanocomposite photocatalysts in water treatment.

Unintentional release of antibiotics associated with nutrients recovery from source-separated human urine by biochar

The use of biochar to recover nitrogen and phosphorus from wastewater especially source-separated human urine is attractive from both economic and environmental standpoints. The widespread use of pharmaceuticals has raised concerns as they are not fully metabolized and ended up in human urine. The objective of this study is to examine adsorption of antibiotics (azithromycin, ciprofloxacin, sulfamethoxazole, trimethoprim, and tetracycline) and nutrients (ammonium and phosphate) in source-separated human urine by biochar and subsequent desorption. Batch adsorption experiments were conducted using biochar prepared from oak wood (OW) and paper mill sludge (PMS) to elucidate the effects of adsorption time, pH, and adsorbent dose. The desorption of adsorbed nutrients and antibiotics was also investigated. While the nutrient adsorption was more favorable by the PMS biochar, antibiotic adsorption was more prolific by the OW biochar. Hydrogen bonding and π-π interaction were identified as potential adsorption mechanisms. Experimental results agree with the Freundlich isotherm and pseudo-second order models (except the OW biochar for the kinetics). The findings suggest that biochar can adsorb both nutrients (43.30-266.67 mg g^-1) and antibiotics (246.70-389.0 μg g^-1) simultaneously. Lower solution pH (<5) was better for antibiotic adsorption, while higher solution pH (≥5) favored nutrient recovery. Also, desorption of the antibiotics (maximum of 92.6% for trimethoprim) was observed and might arise in the environment with the applications of biochar for nutrient recovery from human urine and subsequently for soil quality improvement. The findings serve as a foundation for future research on adsorption-based methods for separating nutrients and antibiotics in aqueous solutions, particularly urine.

Microwave biochars produced with activated carbon catalyst: Characterization and sorption of volatile organic compounds (VOCs)

A series of microwave biochars derived from wheat straw in the presence of a granulated activated carbon (GAC) catalyst, using a range of microwave conditions, were produced, characterized and tested as sorbents of three benzene series volatile organic compounds (VOCs). The microwave biochar with the greatest specific surface area (SSA), total pore volume (TPV), and micropore volume (312.62 m² g^-1, 0.2218 cm³ g^-1, and 0.1380 cm³ g^-1, respectively), were produced with 1:3 biomass:GAC catalyst mass ratio, 10 min microwave irradiation time, and at 500 W power level (WB500). Maximum adsorption capacities of WB500 to benzene, toluene and o-xylene were 53.9 mg g^-1, 75.8 mg g^-1 and 63.0 mg g^-1, respectively, and were directly correlated to microwave biochar properties such as SSA, TPV or micropore volume, but were also influenced by VOC properties such as molecular polarity and boiling point. Kinetic modeling suggested that adsorption was governed by both physical partitioning and chemisorption mechanisms. In addition, microwave biochars maintained 79% to 92% of their initial adsorption capacity after ten adsorption/desorption cycles. These results suggest that microwave biochars produced with an GAC catalyst have excellent potential for efficient use in the removal of VOCs from waste gas.

Recent advances in developing innovative sorbents for phosphorus removal-perspective and opportunities

Phosphorus is an essential mineral for the growth of plants which is supplied in the form of fertilizers. Phosphorus remains an inseparable part of developing agrarian economics. Phosphorus enters waterways through three different sources: domestic, agricultural, and industrial sources. Rainfall is the main cause for washing away a large amount of phosphates from farm soils into nearby waterways. The surplus of phosphorus in the water sources cause eutrophication and degradation of the habitat with an adverse effect on aquatic life and plants. Phosphate elimination is necessary to control eutrophication in water sources. Among the different methods reported for the removal and recovery of phosphorus: ion exchange, precipitation, crystallization, and others, adsorption standout as a sustainable solution. The current review offers a comparative assessment of the literature on novel materials and techniques for the removal of phosphorus. Herein, different adsorbents, their behaviors, mechanisms, and capacity of materials are discussed in detail. The adsorbents are categorized under different heads: iron-based, silica-alumina-based, calcium-based, biochar-based wherein the metal and metal oxides are employed in phosphorus removal. The ideal attribute of adsorbent will be the utilization of spent adsorbents as a phosphate plant food and a soil conditioner in agriculture. The review provides the perspective on the current research with potential challenges and directives for possible research in the field.

The use of recycled materials in a biofilter to polish anammox wastewater treatment plant effluent

Anammox is gaining popularity for treating wastewater containing high-strength ammonia due to lower energy demand compared to conventional nitrification-denitrification processes; however, anammox is reported to increase nitrate loads in the effluent. The objective of this study was to assess the applicability of recycled materials [recycled concrete aggregate (RCA) and rice husks (RH)] as a polishing step to improve anammox reactor effluent quality. Anammox effluents were separately passed through two single-stage columns containing RCA and RH, and one two-stage column (50% RCA, 50% RH) to quantify total N, ammonia, nitrate, nitrite, and phosphate removal efficiencies. Langmuir isotherm experiments were conducted to quantify nitrate, nitrite, and phosphate sorption capacities in the columns. The RCA column exhibited the highest phosphate sorption capacity (0.074 mg/g), while the RH column exhibited higher nitrite and nitrate adsorption (0.063 mg/g and 0.023 mg/g respectively). We created a Hydrus-1D model to estimate pseudo-first-order reaction rates in the columns. Because RCA media can form metal-phosphate precipitates, the fastest phosphate reaction rate (1.58 min-1) occurred in the RCA column. The two-stage column demonstrated the greatest overall removals for all nutrients, and removal rates were consistent throughout the experimental period. The two-stage column achieved 15% total N, 94% ammonia-N, 38% nitrate-N, 75% nitrite-N, and 27% phosphate removal. The maximum nitrite, nitrate, and phosphate adsorption capacities in the two-stage column were 0.030 mg/g, 0.017 mg/g, and 0.014 mg/g respectively. This is the first study to demonstrate that recycled materials can successfully be integrated into a biofilter as an effluent polishing step to remove nutrients from anammox wastewater.

Removal of Phosphate from Aqueous Solution by Zeolite-Biochar Composite: Adsorption Performance and Regulation Mechanism

Recently, rampant eutrophication induced by phosphorus enrichment in water has been attracting attention worldwide. However, the mechanisms by which phosphate can be eliminated from the aqueous environment remain unclear. This study was aimed at investigating the adsorption performance and regulation mechanisms of the zeolite-biochar composite for removing phosphate from an aqueous environment. To do this, physicochemical properties of the zeolite-biochar composite were assessed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) specific surface area (SSA) analyzer, and transmission electron microscopy (TEM). Adsorption tests were performed to evaluate the adsorption ability of the composite material for mitigating excess phosphorus in the aqueous environment. The findings evinced that the phosphorus removed by PZC 7:3 (pyrolyzed zeolite and corn straw at a mass ratio of 7:3) can reach 90% of that removed by biochar. The maximum adsorption capacities of zeolite, biochar, and PZC 7:3 were 0.69, 3.60, and 2.41 mg/g, respectively. The main mechanism of phosphate removal by PZC 7:3 was the formation of thin-film amorphous calcium-magnesium phosphate compounds through ligand exchange. This study suggests that PZC 7:3 is a viable adsorbent for the removal of phosphate from aquatic systems.

The effects of aqueous extract from watermelon (Citrullus lanatus) peel on the growth and physiological characteristics of Dolichospermum flos-aquae

Nowadays, the increasing Dolichospermum (Anabaena) blooms pose a major threat to the aquatic environment and public health worldwide. The use of naturally derived chemicals from plants to control cyanobacteria blooms has recently received a tremendous amount of attention. This study investigates the possibility of transforming watermelon peel (WMP) into a biological resource to allelopathically inhibit Dolichospermum flos-aquae blooms. The results demonstrated that the growth of D. flos-aquae was efficiently restricted by the aqueous extract of watermelon peel (WMPAE) in a concentration-dependent manner. Cell viability decreased quickly, intracellular structural damage occurred, chlorophyll a in algal cells degraded, and photosynthesis was clearly inhibited. At the same time, the levels of reactive oxygen species in viable cells increased significantly, as did malondialdehyde levels, indicating that WMPAE elucidated strong oxidative stress and corresponding damage to D. flos-aquae. Capsular polysaccharide (CPS) levels increased in all treatment groups, which represents an adaptive response indicative of the development of resistance to WMPAE stress and oxidative damage. Despite this, WMPAE had clear inhibitory effects on D. flos-aquae. These findings provide fundamental information on an allelopathic system that could be a novel and attractive approach for suppressing D. flos-aquae blooms in small aquatic environments, especially aquaculture ponds.

Characterization of molecular dissolved organic matter removed by modified eucalyptus-based biochar and disinfection by-product formation potential using Orbitrap mass spectrometric analysis

Biochar is an alternative adsorbent, with similar characteristics to activated carbon, that can be applied to water treatment to remove dissolved organic matter (DOM) as disinfection by-product (DBP) precursors with comparable efficiency and better cost-effectiveness and sustainability relative to commercial alternatives. We applied non-targeted analysis with Orbitrap mass spectrometry to investigate changes in molecular DOM and DBP formation after treating DOM-containing water with biochar. Two surface water sources, Phong River (PR) in Khon Kaen, Thailand and Suwannee river (SR), USA, were tested using three types of eucalyptus-derived biochar (i.e., KOH-modified, calcined, and both) were selected as adsorbents and compared to commercial coconut-based activated carbon (ccAC). The results showed that calcination increased the surface area, pore volume, and functional groups of biochar responsible for adsorption. The calcined biochar achieved higher DOC removal efficiencies for both rivers than other adsorbents. PR contains more adsorbable DOM as over 800 molecules with carbon, hydrogen, and oxygen (CHO) features that were decreased or totally removed by all adsorbents. In contrast, for SR treatment, KOH-modified and calcined biochar was found to decrease over 800 CHO features, compared to around 500 and 400 CHO features for calcined biochar and ccAC, respectively. However, numerous background CHO features with reduced character (i.e., low degree of oxidation) were found after water treatment by calcined biochar, resulting in higher DBP formation after chlorination compared to the other adsorbents. The results of this study have important implications for future preparation of biochar for water treatment.

Ball-milled magnetite for efficient arsenic decontamination: Insights into oxidation-adsorption mechanism

Conventional adsorbents for decontaminating arsenic exhibit low efficacy for the removal of arsenite (As(III)). This study aims to develop a robust As adsorbent from natural magnetite (M₀) via a facile ball milling process, and evaluate their performance for decontaminating As(III) and As(V) in water and soil systems. The ball milling process decreased the particle size and crystallinity of M₀, resulting in pronounced As removal by the ball-milled magnetite (M_m). Ball milling under air facilitated the formation of Fe-OH and Fe-COOH functional groups on M_m interface, contributing to effective elimination of As(III) and As(V) via hydrogen bonding and complexation mechanisms. Synergistic oxidation effects of hydroxyl and carboxyl groups, and reactive oxygen species (O₂^·-, and ·OH) on the transformation of As(III) to As(V) during the adsorption were proposed to explain the enhanced As(III) removal by M_m. A short-term soil incubation experiment indicated that the addition of M_m (10 wt%) induced a decrease in the concentration of exchangeable As by 30.25%, and facilitated the transformation of water-soluble As into residual fraction. Ball milling thus is considered as an eco-friendly (chemical-free) and inexpensive (scalable, one-stage process) method for upgrading the performance of natural magnetite towards remediating As, particularly for tackling the highly mobile As(III).

Biochar-based slow-release of fertilizers for sustainable agriculture: A mini review

Increasing global population and decreasing arable land pose tremendous pressures to agricultural production. The application of conventional chemical fertilizers improves agricultural production, but causes serious environmental problems and significant economic burdens. Biochar gains increasing interest as a soil amendment. Recently, more and more attentions have been paid to biochar-based slow-release of fertilizers (SRFs) due to the unique properties of biochar. This review summarizes recent advances in the development, synthesis, application, and tentative mechanism of biochar-based SRFs. The development mainly undergoes three stages: (i) soil amendment using biochar, (ii) interactions between nutrients and biochar, and (iii) biochar-based SRFs. Various methods are proposed to improve the fertilizer efficiency of biochar, majorly including in-situ pyrolysis, co-pyrolysis, impregnation, encapsulation, and granulation. Considering the distinct features of different methods, the integrated methods are promising for fabricating effective biochar-based SRFs. The in-depth understanding of the mechanism of nutrient loading and slow release is discussed based on current knowledge. Additionally, the perspectives and challenges of the potential application of biochar-based SRFs are described. Knowledge surveyed from this review indicates that applying biochar-based SRFs is a viable way of promoting sustainable agriculture.

Enhanced phosphate removal and potential recovery from wastewater by thermo-chemically calcinated shell adsorbents

Shell from the seafood processing industry is an under-utilised waste resource worldwide. Calcite, the major component of shell is commonly used in wastewater treatment for the removal of phosphorus (P). Here, mussel and oyster shell-based adsorbents (MSB and OSB) were used for removal of P as phosphate (PO₄^3-) from aqueous solution and secondary wastewater, following preparation through chemical calcination at 700 °C. Batch adsorption experiments were carried out to identify the effects of various operating parameters (e.g., pH, dosage, contact time, initial concentration of P ions, co-existing ions), while a desorption study helped to understand the availability of the bonded P. The optimal contact time for PO₄^3- removal was 120 min using both adsorbents with the dose at 200 mg. Characterisation of the adsorbent was performed using SEM-EDX, pH_pzc, BET, FTIR and XRD. The XRD analysis showed that both calcite and lime were present on the surface of the shell particles. P was adsorbed effectively through inner-sphere complexation and surface microprecipitation mechanisms, while an enhanced maximum P adsorption capacity of 12.44 mg/g for MSB and 8.25 mg/g for OSB was reached. The Redlich-Peterson isotherm model fitted well with the equilibrium isotherm data (R² ≥ 0.97) which also suggested a heterogenic surface. The desorption study (on the saturated adsorbent) found that ~97% of bonded P could be plant available in soil. These results suggest that a shell-based adsorbent can serve as a promising material for P removal from real wastewater effluent and subsequently could be used as a soil conditioner.

A novel Ca/Mn-modified biochar recycles P from solution: mechanisms and phosphate efficiency

The excessive use of phosphate leads to severe environmental issues, such as a shortage of phosphorus resources and water eutrophication. In this study, a novel Ca-Mn-impregnated biochar (CMBC) composite was synthesized by co-pyrolysis at 600 °C for P recovery from solution. The efficiency of P-sorbed CMBC as a fertilizer was assessed via pot experiments. Kinetic experiments exhibited a higher phosphate sorption efficiency for the CM₁BC and CM₂BC composites. Pot experiments revealed that P-sorbed CMBC treatment significantly improved plant growth and yield. Compared with those of the control, the dry weight, fresh weight, and P content of rape leaf (root) P₅₀-CMBC_1.0% treatment increased by 108.6% (350%), 88.7% (396%), and 132.8% (109.3%), respectively. This may be due to the porous surface structures that develop during the treatment and Ca-P precipitation on P-sorbed biochar partly dissolved in the slightly acidic soil (pH: 6.25). The maximum P adsorption values fitted by the Langmuir isotherm model were up to 9.15, 3.19, 15.58, and 20.84 mg g^-1 for CBC, MBC, CM₁BC, and CM₂BC, respectively. The mechanism of phosphate recovery mainly includes electrostatic attraction, surface precipitation, and the formation of inner-sphere complexes with hydroxyl groups that were assessed using BET, zeta potential, SEM-EDS, FTIR, and XPS analyses. These mechanisms suggest that phosphate may be desorbed from the P-laden sorbent, which was consistent with the results of the pot experiments and desorption experiments in aqueous media. These results imply that P-sorbed modified biochar has the potential to be a promising P fertilizer in soil.

Sorption, separation and recycling of ammonium in agricultural soils: A viable application for magnetic biochar?

Recent research on the magnetisation of biochar, a carbon-based material that can be used as a sorbent, has opened novel opportunities in the field of environmental remediation, as incorporating magnetic particles into biochar can simplify subsequent separation. This could offer a sustainable circular economy-based solution in two areas of waste management; firstly, pyrolysis of agricultural waste for magnetic biochar synthesis could reduce greenhouse gas emissions derived from traditional agricultural waste processing, such as landfill and incineration, while secondly, application of magnetic biochar to remove excess nitrogen from soils (made possible through magnetic separation) could provide opportunities for this pollutant to be used as a recycled fertiliser. While sorption of pollutants by magnetic biochar has been researched in wastewater, few studies have investigated magnetic biochar use in polluted soils. Nitrogen pollution (e.g. NH₄⁺), stemming from agricultural fertiliser management, is a major environmental and economic issue that could be significantly reduced before losses from soils occur. This review demonstrates that the use of magnetic biochar tailored to NH₄⁺ adsorption has potential to remove (and recycle for reuse) excess nitrogen from soils. Analysis of research into recovery of NH₄⁺ by sorption/desorption, biochar magnetisation and biochar-soil interactions, suggests that this is a promising application, but a more cohesive, interdisciplinary approach is called for to elucidate its feasibility. Furthermore, research shows variable impacts of biochar upon soil chemistry and biology, such as pH and microbial diversity. Considering wide concerns surrounding global biodiversity depletion, a more comprehensive understanding of biochar-soil dynamics is required to protect and support soil ecosystems. Finally, addressing research gaps, such as optimisation and scaling-up of magnetic biochar synthesis, would benefit from systems thinking approaches, ensuring the many complex considerations across science, industry, policy and economics are connected by circular-economy principles.

Removal effects of a biomass bottom ash composite on tailwater phosphate and its application in a rural sewage treatment plant

Tailwater phosphate from sewage treatment plants and biomass bottom ash (BA) from power plants has become a global concern for the sustainable environmental development and resource management. However, there are large gaps in the understanding of the removal mechanisms and application conditions of BA on tailwater phosphate. In this study, the removal effect and mechanism of BA and its composites were fully discussed using a series of experiments, including adsorption, desorption, characterization, and incubation experiments. It was found that the combination of BA and red soil at a rate of 4:1 (C_BA) could remove 92.44% of phosphate from tailwater in 3-10 h. Its adsorption process was well fitted by the pseudo-second-order kinetic and Freundlich isotherm adsorption models. The mechanism of phosphate adsorption primarily included ligand exchange, physical adsorption, chemical precipitation, electrostatic attraction, and ion exchange. The C_BA could be used as a better substrate for constructed wetlands because it was effective under wide application conditions, which varying pH values (4.0-8.0), initial concentrations of tailwater phosphate (0.5-5.0 mg L^-1), and even extreme temperatures (heat and cold). Moreover, Hippuris vulgaris L. was optimized and combined with the C_BA to deeply remove 57.45-76.06% of phosphate from a rural sewage treatment plant. The phosphate concentration after treatment could reach below the limit values of the Grade III or IV standard (GB 3838-2002), though the C_BA contained and released phosphate. This study can help provide a recycling route for both BA and tailwater phosphate resources, extend the industrial chain of biomass power plants, and improve the surrounding water environment.

Sustainable approaches for nickel removal from wastewater using bacterial biomass and nanocomposite adsorbents: A review

In this article, the nickel (Ni²⁺) ions removal from the wastewater is reviewed. Adsorption is widely used to remove Ni²⁺ ions from waters and wastewaters. The usage of biomass is becoming more common for Ni²⁺ ions removal, while the commercial activated carbon from different agriculture wastes is preferred as an adsorbent for Ni²⁺ ion removal. The present review aimed to organise the available information regarding sustainable approaches for Ni²⁺ ions removal from water and wastewaters. These include adsorption by nanoparticles, bacterial biomass, and activated carbon from agriculture wastes, since they are the most common used for the Ni²⁺ ions removal. The bacterial and agricultural waste adsorbents exhibited high efficiency with a renewable source of biomass for Ni²⁺ ion removal. The biosorption capacity of the Ni²⁺ ions by the bacterial biomass range from 5.7 to 556 mg/g, while ranging from 5.8 to 150 mg/g by the activated carbon from different organic materials. The biosorption capacity of the nanocomposite adsorbents might reach to 400 mg/g. It appeared that the elimination of nickel ions need a selective biomass adsorbent such as the tolerant bacterial cells biomass which acts as a store for Ni²⁺ ion accumulations as a results for the active and passive transportation of the Ni²⁺ ions through the bacterial cell membrane.

Biochar application in biofiltration systems to remove nutrients, pathogens, and pharmaceutical and personal care products from wastewater

Although conventional on-site wastewater treatment systems (OWTSs) provide only primary treatment of domestic wastewater, removal of a limited level of nutrients (N, P), pathogens, and pharmaceuticals and personal care products (PPCPs) could be achieved by such a treatment process. Biochar has the capacity to remove various contaminants and has been widely used as an ideal soil amendment in agriculture due to its persistence, superior nutrient-retention properties, low cost, and ready availability. However, few applications on the use of biochar in onsite wastewater treatment have been explored. In this review, we systematically reviewed the applications of biochar in filtration-based OWTSs for nutrient (N, P) removal and recovery as well as pathogen and PPCP removal. Although adsorption was the main mechanism for P, pathogen, and PPCP removal, biochar can also serve as the growth media for enhanced biological degradation, improves available alkalinity, and increases water holding capacity in the OWTSs. The biochar source, surface modification methods, and preparation procedures (e.g., pyrolysis temperature change) have significant effects on contaminant removal performance in biochar-amended OWTSs. Specifically, contradictory results have been reported on the effect of pyrolysis temperature change on biochar removal performance (i.e., increased, decreased, or no change) of N, P, and PPCPs. Wastewater composition and environmental pH also play important roles in the removal of nutrients, pathogens, and PPCPs. Overall, biochar holds great potential to serve as an alternative filtration material or to be amended to the current OWTS to improve system performance in removing a variety of contaminants at low cost.

Characterization of dissolved organic carbon and disinfection by-products in biochar filter leachate using orbitrap mass spectrometry

Biochar is a low-cost adsorbent with considerable potential for utilization as a water filtration medium; however, organic matter leaching from biochar can lead to the formation of disinfection by-products (DBPs). This study investigated the leaching of dissolved organic carbon (DOC) from eucalyptus-derived biochar and the formation of DBPs generated by chlorination and chloramination. Column experiments with empty bed contact times (EBCTs) of 10 and 30 min were conducted for 200 bed volumes (BVs). The highest DOC concentration (3.5 µg-C/g-biochar) was detected with an EBCT of 30 min. Chloroform (49 µg/L) and dichloroacetonitrile (7 µg/L) because of chlorination were found during the first five BVs, but were reduced thereafter. During the first 10 BVs, unknown chlorinated DBPs generated (CHOCl) by chlorination and chloramination (193 and 152 formulae, respectively) were tentatively identified via an unknown screening analysis. The release of DBP precursors from biochar tentatively identified in this study will impact water filtration applications.

Dynamic Adsorption Characteristics of Phosphorus Using MBCQ

Biochar is a new type of adsorption material with excellent performance, but it has some problems, such as light texture, poor sedimentation, and difficult recovery, which limits its practical application. In this study, biochar microspheres (MBCQ) were prepared by the sol–gel method using powdery biochar from Hydrocotyle vulgaris as raw material and sodium alginate as a granular carrier. Experiments were performed to investigate the dynamic adsorption characteristics of phosphorus by MBCQ in the adsorption column and the influences of particle size, initial phosphorus concentration, flow rate, and column height on the breakthrough curve. The results showed that the static adsorption properties of different particles varied and that 3-millimeter particles were optimal. The breakthrough time positively correlated with column height and negatively correlated with initial phosphorus concentration, flow rate, and particle size. Flow velocity significantly impacted breakthrough time and length of mass transfer. The bed depth/service time model accurately predicted the relationship between breakthrough times and column heights. When ct/c0 = 0.6, the average relative deviation between predicted and measured values was the lowest. The Thomas model described the MBCQ adsorption process of Ph (R2 > 0.95), which indicated that diffusion in MBCQ adsorption was not a rate-limiting step.

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.