Recovery of phosphate from aqueous solution by magnesium oxide decorated magnetic biochar and its potential as phosphate-based fertilizer substitute

Enhanced adsorption of phosphate by rice straw-based biochar prepared via metal impregnation and bio-template technology

Phosphate removal from water through green, highly efficient technologies has received much attention. Biochar is an effective adsorbent for phosphate removal. However, adsorption capacity of phosphate on pristine rice straw-based biochar was not optimistic due to low anion exchange capacity. In this study, Fe-modified, Mg-modified and MgFe-modified rice straw-based biochar (Fe-BC, Mg-BC and MgFe-BC) were prepared by combining metal impregnation and biological template methods to improve the adsorption capacity of phosphate. The surface characteristics of biochar and the adsorption behavior of phosphate on biochar were investigated. The modified biochar had the specific surface area of 17.910-39.336 m2/g, and their surfaces were rich in a large number of functional groups and metal oxides. Phosphate release was observed on pristine rice straw-based biochar without metal impregnation. The maximum adsorption capacities of phosphate on MgFe-BC, Mg-BC and Fe-BC at 298 K were 6.93, 5.75 and 0.23 mg/g, respectively. Adsorption was a spontaneous endothermic process, while chemical adsorption dominated and electrostatic attraction and pores filling existed simultaneously. Based on the site energy distribution theory study, the standard deviation of MgFe-BC decreased from 6.96 to 4.64 kJ/mol with temperature increasing, which proved that the higher the temperature would cause the lower heterogeneity. Moreover, the effects of pH, humic acid, co-existing ions and ionic strength on phosphate adsorption of MgFe-BC were also discussed. MgFe-BC with fine pores and efficient adsorption sites is an ideal adsorbent for phosphate removal from water.

Utilization and value-adding of waste: Fabrication of porous material from chitosan for phosphate capture and energy storage

Efficient removal and recycling of phosphorus from complex water matrices using environmentally friendly and sustainable materials is essential yet challenging. To this end, a novel bio-based adsorbent (DX-FcA-CS) was developed by coupling oxidized dextran-crosslinked chitosan with ferrocene carboxylic acid (FcA). Detailed characterization revealed that the incorporation of FcA reduced the total pore area of DX-FcA-CS to 7.21 m2·g-1, one-third of ferrocene-free DX-CS (21.71 m2·g-1), while enhancing thermal stability and PO43- adsorption performance. Adsorption kinetics and isotherm studies demonstrated that the interaction between DX-FcA-CS and PO43- followed a pseudo-second-order kinetic model and Langmuir model, indicating chemical and monolayered adsorption mechanisms, respectively. Moreover, DX-FcA-CS exhibited excellent anti-interference properties against concentrated co-existing inorganic ions and humic acid, along with high recyclability. The maximum adsorption capacity reached 1285.35 mg·g-1 (∼428.45 mg P g-1), three times that of DX-CS and surpassing many other adsorbents. PO43--loaded DX-FcA-CS could be further carbonized into electrode material due to its rich content of phosphorus and nitrogen, transforming waste into a valuable resource. These outstanding characteristics position DX-FcA-CS as a promising alternative for phosphate capture and recycling. Overall, this study presents a viable approach to designing environmentally friendly, recyclable, and cost-effective biomaterial for wastewater phosphate removal and value-added applications.

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.

Algae removal and algal organic matter chemistry modulated by KMnO4-PAC in simulated karst water

In this study, we examined the modulation of algae removal and algal organic matter (AOM) chemistry by potassium permanganate and poly-aluminum chloride (KMnO4-PAC) in simulated karst water. Specifically, we verified the compositional changes of AOM sourcing from Chlorella sp. and Pseudanabaena sp. in response to the presence of divalent ions (Ca2+ and Mg2+). Aromatic protein and soluble microbial products were identified as the primary AOM components. Divalent ions accelerated dissolved organic carbon (DOC) and UV254 removal, particularly with Pseudanabaena sp. greater than Chlorella sp. (P < 0.05). Surface morphology analysis manifested that the removal of filamentous Pseudanabaena sp. was more feasible in comparison to globular Chlorella sp.. Our results highlight the significance of divalent ions in governing chemical behaviors and subsequent removal of both algae and AOM. This study upscales the understanding of the interactions among divalent ions, algae and AOM during preoxidation and coagulation process in algae-laden karst water.

Lanthanum-doped magnetic biochar activating persulfate in the degradation of florfenicol

In this study, lanthanum-doped magnetic biochar (LaMBC) was synthesized from bagasse by co-doping iron salt and lanthanum salt, and it was characterized for its application in the activation of persulfate (PS) in the degradation of Florfenicol (FLO). The results indicated that the LaMBC/PS system consistently achieved a degradation efficiency of over 99.5 %, with a reaction rate constant 4.71 times as that of MBC. The mechanism of FLO degradation suggested that O2•- and •OH played dominant roles, contributing 40.92 % and 36.96 %, respectively, during FLO degradation. Through physicochemical characterization and quenching experiments, it can be concluded that the key reasons for the enhancement of MBC activation performance are as follows: (1) Lanthanum doping in magnetized biochar increased the Fe(II) content in MBC. (2) Lanthanum doping significantly improved the adsorption capacity of LaMBC, increased the concentration of pollutants on the catalyst surface and effectively enhancing the reaction rate. (3) Lanthanum doping effectively increased the surface Fe(II) content during the reaction process in LaMBC, promoted the generation of active oxygen species in PS. This study delves into synthesizing and applying LaMBC for PS activation and FLO removal. The emphasis is on comprehensively characterizing and experimenting to elucidate the mechanism, proposing an innovative approach for efficiently degrading antibiotic wastewater.

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.

Efficient Adsorption of Nitrogen and Phosphorus in Wastewater by Biochar

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

Experimental investigation on sludge conditioning and dewatering using an agricultural biomass coupled with resource recovery

In this study, the effect of modified areca husk fibre biochar (MAFB-AlCl3) on dairy sludge conditioning and dewatering along with raw and modified coconut shell biochar (MCSB-FeCl3) was investigated. Further, MgO impregnated biochars of areca husk fibre and coconut shells was carried out to evaluate the performance on phosphate recovery from the diary sludge. The enhancement in sludge dewatering with MAFB-AlCl3 were evaluated experimentally and significant reduction of capillary suction time (CST) (51.6 %), moisture content (18%), zeta potential (1.3 mV) and increased settleability (32.7%) were observed. The sludge conditioning parameters namely dosage (% of dry solids (DS)), rapid mixing time (RMT), slow mixing time (SMT) were optimized by response surface methodology for the modified biochars. Optimum CST (31.51 s) was obtained at dosage (50 % of DS), RMT (9.89 min) and SMT (17.23 min). Results of batch study for phosphate recovery by MgO impregnated biochars (MgB) was found to be 96.6 % and 100 % by MgB of areca husk fibre (MgAFB) and coconut shells (MgCSB) respectively. The morphological characteristics and elemental distribution using field emission scanning electron microscopy (FE-SEM) & energy dispersive X-ray spectroscopy (EDS) reveals the structural change in the sludge particles for the modified biochars as well as for sludge. Hence MAFB-AlCl3, MgAFB and MgCSB is proved to be suitable and an effective candidate for sludge conditioning and dewatering coupled with phosphate recovery in handling the diary sludge.

Recovery of ammonia nitrogen and phosphate from livestock farm wastewater by iron-magnesium oxide coupled lignite and its potential for resource utilization

A new adsorbent called iron-magnesium oxide coupled lignite (CIMBC) was developed to address the challenges of recovering high concentrations of ammonia nitrogen and phosphate in livestock farm wastewater and improving the inefficient use of lignite (BC) with low calorific value. CIMBC was synthesized using the modified ferromagnesium salt double-coating method. The experiments demonstrated that Fe2O3 and MgO could be effectively loaded onto the surface of BC at a Fe/Mg molar ratio of 1:2 and pyrolysis temperature of 500 °C. The optimal conditions for adsorption were determined to be an N/P concentration ratio of 2:1, adsorbent dosage of 1 g/L, and pH of 7. The presence of coexisting cations (Ca2+ and Mg2+) inhibited the removal of ammonia nitrogen but enhanced the removal of phosphate. Likewise, the presence of coexisting anions (CO32- and SO42-) hindered the removal of both ammonia nitrogen and phosphate. The adsorption behavior followed the pseudo-second-order model and the Langmuir model, with a maximum adsorption capacity of 95.69 mg N/g for ammonia nitrogen and 101.32 mg P/g for phosphate. The adsorption process was a spontaneous endothermic process controlled by multiple levels. The main mechanisms of adsorption involved electrostatic attraction, intra-particle diffusion, ion exchange, chemical precipitation, and coordination exchange. After 5 times of adsorption-desorption, the recovery rate of CIMBC is less than 50%, and the removal rate of phosphate is less than 40%. Although the RCIMBC exhibited low reusability, but also it showed potential in removing heavy metals (Pb) from wastewater and for use as a slow-release fertilizer. CIMBC is a promising new adsorbent, which can realize resource utilization of lignite with low calorific value while removing nitrogen and phosphorus.

Insight into the impacts of pyrolysis time on adsorption behavior of Pb2+ and Cd2+ by Mg modified biochar: Performance and modification mechanism

Co-pyrolysis biomass and alkaline metals can effectively improve the adsorption performance of heavy metals (HM). Nevertheless, the researchers have ignored the relationship between the change of alkaline metal morphology and adsorption during pyrolysis. In this article, according to control the pyrolysis time (30, 60, and 180 min) synthesized Magnesium (Mg) modified biochar (MBCX) by using MgCl2·6H2O and soybean straw under 400 °C. The sorption capacities of MBC60 and MBC180 for Pb2+/Cd2+ increased by 38.65%/213.29%, 44.57%/230.36%, and the selectivity coefficient of Pb2+/Cd2+ increased by 113.28%/209.49%, 213.58%/253.62%, respectively, compared with MBC30. Additionally, the characterization results demonstrated that MgO dominated the surface phases of MBC60 and MBC180, whereas MgCl2 dominated the surface phases of MBC30. Moreover, according to the results of DFT calculation, the adsorption energy (Eads) of MgO for Pb2+ (-0.537 eV) and Cd2+ (-0.347 eV) was lower than that of MgCl2 (Pb2+: 0.37 eV, Cd2+: -0.185 eV), so that, MBC60 and MBC180 had higher sorption capacities for Pb2+ and Cd2+ than MBC30. Therefore, this work provides a new sight to clear the mechanism for modified biochar by alkali metal oxide and practical and theoretical guidance for adsorbent preparation with high adsorption ability for HMs.

Climate factors and host chemical profiles jointly drives the bacterial community assembly in Mussaenda pubescens stems

Endophytic bacteria residing within host plants can significantly impact on the host's growth, health, and overall relationship with its surrounding environment. However, the process that shape the community assembly of stem bacterial endophytes (SBEs) remains poorly understood. This study explored the community structure, co-occurrence patterns, and ecological processes of the SBEs inhabiting the shrub host, Mussaenda pubescens, across seven locations in southeastern China. We found that the absolute abundances, alpha diversity, and community composition of SBE communities exhibited notable differences among various host populations. Stem chemical characteristics were the most important factors influencing SBE community distribution, followed by geographic distance and climatic factors. The beta diversity decomposition analyses indicated that SBE community dissimilarities between sites were nearly equally driven by similarity, replacement diversity, and richness difference. The co-occurrence network analysis revealed that the keystone taxa were mostly observed in rare species, which may be essential for preserving the ecosystem's functions. Conditionally abundant taxa (CAT) showcased the highest closeness centrality, while exhibiting the lowest degree centrality and betweenness centrality as opposed to rare taxa. In addition, stochastic processes also played an important role in structuring SBE communities, with ecological drift being the dominant factor for both abundant and rare taxa. This study would deepen our understanding of the ecological dynamics and microbial interactions within plant endophytic microbiomes.

The collaborative incentive effect in adsorption-photocatalysis: A special perspective on phosphorus recovery and reuse

Achieving efficient recovery and direct utilization of phosphorus as one of the important components of the green economy is a huge challenge. Herein, we innovatively constructed a coupling adsorption-photocatalytic (CAP) process using synthetic dual-functional Mg-modified carbon nitride (CN-MgO). The CAP could utilize the recovered phosphorus from wastewater to promote the in-situ degradation of refractory organic pollutants via CN-MgO, where its phosphorus adsorption capacity and photocatalytic activity were significantly and synergistically increased. It was specifically reflected in the high phosphorus adsorption capacity of CN-MgO (218 mg/g), which was 153.5 times that of carbon nitride (1.42 mg/g), and its theoretical maximum adsorption capacity could reach 332 mg P/g. Subsequently, the phosphorus-enriched sample (CN-MgO-P) was employed as a photocatalyst to remove tetracycline with a reaction rate (k = 0.07177 min-1) 2.33 times higher than that of carbon nitride (k = 0.0327 min-1). Notably, the coordinated incentive mechanism present in this CAP between adsorption and photocatalysis may be attributed to the more adsorption sites of CN-MgO and the facilitation of hydroxyl production through adsorbed phosphorus, which ensured the feasibility of creating environmental value from the phosphorus in wastewater by means of CAP. This study provides a new perspective on the recovery and reuse of phosphorus resources in wastewater and the integration of environmental technologies in multiple fields.

Enhanced phosphate adsorption and desorption characteristics of MgO-modified biochars prepared via direct co-pyrolysis of MgO and raw materials

Biochar modified by metal ions-particularly Mg-is typically used for the effective recovery of phosphorous. In this study, MgO-modified biochars were synthesized via the direct co-pyrolysis of MgO and raw materials such as rice straw, corn straw, Camellia oleifera shells, and branches from garden waste, which were labeled as MRS, MCS, MOT, and MGW, respectively. The resulting phosphate (PO) adsorption capacities and potential adsorption mechanisms were analyzed. The PO adsorption capacities of the biochars were significantly improved after the modification with MgO: MRS (24.71 ± 0.32 mg/g) > MGW (23.55 ± 0.46 mg/g) > MOT (15.23 ± 0.19 mg/g) > MCS (14.12 ± 0.21 mg/g). PO adsorption on the modified biochars was controlled by physical adsorption, precipitation, and surface inner-sphere complexation processes, although no electrostatic attraction was observed. Furthermore, PO adsorbed on modified biochars could be released under acidic, alkaline, and neutral conditions. The desorption efficiency of MRS was modest, indicating its suitability as a slow-release fertilizer.

Potentially migrating and residual components of biochar: Effects on phosphorus adsorption performance and storage capacity of black soil

Biochar has great potential to increase the soil nutrient storage capacity. However, with aging, biochar gradually disintegrates and releases fractions with migration potential, resulting in unknown effects on soil nutrient regulation. Based on this problem, we used ultrasound to separate original biochar (TB) into potentially migrating biochar (DB) and residual biochar (RB). The elemental composition and pore characteristics of TB, DB and RB were analyzed. Different fractions of biochar were applied to black soil, and the kinetic model and isothermal adsorption models were used to explore the adsorption characteristics of different treatments. Then, the effects of initial pH and coexisting ions on adsorption were compared. The adsorption mechanism and potential leaching process of phosphorus in soil were investigated. The results showed that RB had higher O and H contents and was less stable than TB, while RB was more aromatic. The phosphorus adsorption capacity of different treatments was SRB (1.3318 mg g^-1) > STB (1.2873 mg g^-1) > SDB (1.3025 mg g^-1) > SCK (1.1905 mg g^-1). SRB had optimal phosphorus adsorption performance and storage capacity, with a maximum adsorption capacity of 1.6741 mg g^-1 for the Langmuir isotherm, and it also showed excellent applicability in a pH gradient and with coexisting ions. The main adsorption mode of phosphorus by different treatments was monolayer chemisorption, related to electrostatic repulsion and oxygen-containing functional groups. DB was less effective in inhibiting soil phosphorus migration, with the cumulative leaching of SDB reaching 8.99 mg and the percentage of phosphorus in the 0-6 cm soil layer reaching only 15.42%. Overall, the results can help elucidate potential trends in the adsorption performance and migration process of soil phosphorus by biochar, and improve the comprehensive utilization efficiency of biochar.

Comparative assessment of formation pathways and adsorption behavior reveals the role of NaOH of MgO-modified diatomite on phosphate recovery

The phosphate adsorption behavior on MgO-modified diatomite has been routinely investigated. Batch experiments tend to show that the addition of NaOH during preparation largely promoted adsorption performance, but comparative studies of MgO-modified diatomite with and without NaOH (MODH and MOD) based on morphology, composition, functional groups, isoelectric points and adsorption behavior have not been reported. We demonstrated that NaOH can etch the structure of MODH and promote the migration of phosphate to active sites, which allowed MODH to have a faster adsorption rate, superior environmental adaptability, adsorption selectivity and regeneration performance. The phosphate adsorption ability was enhanced from 96.73 (MOD) to 197.4 mg P/g (MODH) under optimum conditions. Furthermore, the partially hydrolyzed Si-OH group reacted with Mg-OH via a hydrolytic condensation reaction to form a new Si-O-Mg bond. Intraparticle diffusion, electrostatic attraction and surface complexation may be the main modes of phosphate adsorption by MOD, while the MODH surface mainly relied on the synergy of chemical precipitation and electrostatic attraction due to the abundant MgO adsorptive sites. Indeed, the present study provides a new understanding of the microscopic analysis of sample differences.

Application of Box-Behnken Design to Optimize Phosphate Adsorption Conditions from Water onto Novel Adsorbent CS-ZL/ZrO/Fe3O4: Characterization, Equilibrium, Isotherm, Kinetic, and Desorption Studies

Phosphate (PO₄^3-) is an essential nutrient in agriculture; however, it is hazardous to the environment if discharged in excess as in wastewater discharge and runoff from agriculture. Moreover, the stability of chitosan under acidic conditions remains a concern. To address these problems, CS-ZL/ZrO/Fe₃O₄ was synthesized using a crosslinking method as a novel adsorbent for the removal of phosphate (PO₄^3-) from water and to increase the stability of chitosan. The response surface methodology (RSM) with a Box-Behnken design (BBD)-based analysis of variance (ANOVA) was implemented. The ANOVA results clearly showed that the adsorption of PO₄^3- onto CS-ZL/ZrO/Fe₃O₄ was significant (p ≤ 0.05), with good mechanical stability. pH, dosage, and time were the three most important factors for the removal of PO₄^3-. Freundlich isotherm and pseudo-second-order kinetic models generated the best equivalents for PO₄^3- adsorption. The presence of coexisting ions for PO₄^3- removal was also studied. The results indicated no significant effect on PO₄^3- removal (p ≤ 0.05). After adsorption, PO₄^3- was easily released by 1 M NaOH, reaching 95.77% and exhibiting a good capability over three cycles. Thus, this concept is effective for increasing the stability of chitosan and is an alternative adsorbent for the removal of PO₄^3- from water.

Directional regulation and mechanism analysis of the surface properties of hydrothermal carbon by circulating liquid in the hydrothermal carbonization procedure

The complexity of the chemistry behind the hydrothermal conversion is enormous. Components interact with their own physical and chemical structure, making it harsh to understand the conversion as a whole. Herein, the six-water recirculation and loading nano SiO₂ experiment in a one-pot hydrothermal carbonization procedure was designed to elucidate the mechanism of regulating the functional groups and microporous structure of the hydrochar surface. The hydrochar prepared by the second circulating liquid and loading nano-SiO₂ (HBC-R2/Si) was equipped most enriched functional groups (carboxyl = 11.48 μmol/g, phenolic hydroxyl = 52.98 μmol/g, lactone groups = 46.52 μmol/g) and suitable pore size (1.90 nm-1.93 nm) as a sorbent riched in hemicellulose. The sorption kinetics (equilibrium reached ≈ 480 min) are approximately evenly fitted by the pseudo-second-order, Weber and Morris, and Elovich models, indicating that membranes and particles diffusion, pore diffusion, and surface sorption coexisted in the sorption of methylene blue (MB) on the hydrochar materials. Simultaneously, all hydrochar materials achieved over 25% MB removal within 90 min (liquid membrane diffusion) and over 40% for HBC-R2 and HBC-R2/Si, suggesting that liquid membrane diffusion is the predominant rate-limiting step. Pearson's correlation analysis and Mantel's analysis announced that the cation exchange capacity (CEC), pore size, and carboxyl groups on the hemicellulose affect the sorption capacity by limiting the pore diffusion procedure. However, the CEC and the phenolic hydroxyl groups on the cellulose and hemicellulose affect the sorption rate by limiting membrane diffusion. Three consecutive sorption/desorption cycles confirmed the high stability and reusability of HBC-R2/Si composites.

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

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

Graphical Abstract

Magnesium-enriched poultry manure enhances phosphorus bioavailability in biochars

Pyrolysis of calcium-rich feedstock (e.g., poultry manure) generates semi-crystalline and crystalline phosphorus (P) species, compromising its short-term availability to plants. However, enriching poultry manure with magnesium (Mg) before pyrolysis may improve the ability of biochar to supply P. This study investigated how increasing the Mg/Ca ratio and pyrolysis temperature of poultry manure affected its P availability and speciation. Mg enrichment by ∼2.1% increased P availability (extracted using 2% citric and formic acid) by 20% in Mg-biochar at pyrolysis temperatures up to 600 °C. Linear combination fitting of P K-edge XANES of biochar, and Mg/Ca stoichiometry, indicate that P species, mainly Ca-P and Mg-P, are altered after pyrolysis. At 300 °C, adding Mg as magnesium hydroxide [Mg(OH)₂] created MgNH₄PO₄ (18%) and Mg₃(PO₄)₂.8H₂O (23%) in the biochar, while without addition of Mg Ca₃(PO₄)₂ (11%) predominated, both differing only for pyrophosphate, 33 and 16%, respectively. Similarly, the P L_2,3 edge XANES data of biochar made with Mg were indicative of either MgHPO₄.3H₂O or Mg₃(PO₄)₂.8H₂O, in comparison to CaHPO₄.2H₂O or Ca₃(PO₄)₂ without Mg. More importantly, hydroxyapatite [Ca₅(PO₄)₃(OH)] was not identified with Mg additions, while it was abundant in biochars produced without Mg both at 600 (12%) and 700 °C (32%). The presence of Mg formed Mg-P minerals that could enhance P mobility in soil more than Ca-P, and may have resulted in greater P availability in Mg-enriched biochars. Thus, a relatively low Mg enrichment can be an approach for designing and optimize biochar as a P fertilizer from P-rich excreta, with the potential to improve P availability and contribute to the sustainable use of organic residues.

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

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

Graphical Abstract

Optimization of phosphorus recovery using electrochemical struvite precipitation and comparison with iron electrocoagulation system

A batch monopolar reactor was developed for total phosphorus (TP) recovery using electrochemical struvite precipitation. This study involves the optimization of factors using response surface methodology to maximize the TP recovery. The optimal parameters for this study were found to be a pH of 8.40, a retention time of 35 min, a current density of 300 A/m² , and an interelectrode distance of 0.5 cm, resulting in 97.3% of TP recovery and energy consumption of 2.35 kWh/m³ . A kinetic study for TP removal revealed that at optimum operating conditions, TP removal follows second-order kinetics (removal rate constant(K) = 0.0117 mg/(m² ·min)). The system performance was compared to the performance of an iron electrocoagulation system. The composition of the precipitate obtained during the optimal runs were analyzed using X-ray diffraction and EDS analysis. X-ray diffraction analysis of the magnesium precipitate revealed the presence of struvite as the only crystalline compound. PRACTITIONER POINTS: Electrochemical struvite precipitation has the potential to recover total phosphorus from anaerobic bioreactor effluent. Optimum conditions for phosphorus recovery was found at a pH of 8.4, retention time of 35 min, current density of 300 A/m2, and interelectrode distance of 0.5 cm. The quadratic model predicted complete (100 %) TP recovery under optimized conditions, whereas 97.3 % recovery was observed under experimental conditions. TP removal under optimum conditions followed second-order rate equation (removal rate constant(K) = 0.0117 mg/(m² ·min)). XRD analysis of the precipitate revealed struvite as the only crystalline compound.

Municipal Sewage Sludge as a Source for Obtaining Efficient Biosorbents: Analysis of Pyrolysis Products and Adsorption Tests

In the 21st century, the development of industry and population growth have significantly increased the amount of sewage sludge produced. It is a by-product of wastewater treatment, which requires appropriate management due to biological and chemical hazards, as well as several legal regulations. The pyrolysis of sewage sludge to biochar can become an effective way to neutralise and use waste. Tests were carried out to determine the effect of pyrolysis conditions, such as time and temperature, on the properties and composition of the products obtained and the sorption capacity of the generated biochar. Fourier transform infrared analysis (FTIR) showed that the main components of the produced gas phase were CO₂, CO, CH₄ and to a lesser extent volatile organic compounds. In tar, compounds of mainly anthropogenic origin were identified using gas chromatography mass spectrometry (GC-MS). The efficiency of obtaining biochars ranged from 44% to 50%. An increase in the pyrolysis temperature resulted in a decreased amount of biochar produced while improving its physicochemical properties. The biochar obtained at high temperatures showed the good adsorption capacity of Cu²⁺ (26 mg·g^-1) and Zn²⁺ (21 mg·g^-1) cations, which indicates that it can compete with similar sorbents. Adsorption of Cu²⁺ and Zn²⁺ proceeded according to the pseudo-second-order kinetic model and the Langmuir isotherm model. The biosorbent obtained from sewage sludge can be successfully used for the separation of metal cations from water and technological wastewater or be the basis for producing modified and mixed carbon sorbents.

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.

Phosphorus recovery and reuse in water bodies with simple ball-milled Ca-loaded biochar

The demand to control eutrophication in water bodies and the risk of phosphorus scarcity have prompted the search for treatment technologies for phosphorus recovery. In this study, ball-milled Ca-loaded biochar (BMCa@BC) composites were prepared with CaO and corn stover biochar as raw materials by a new ball-milling method to recover phosphorus from water bodies. Experimental results demonstrated that BMCa@BC could efficiently adsorb phosphorus in water bodies with an excellent sorption capacity of 329 mg P/g. Hydrogen bonding, electrostatic attraction, complexation, and surface precipitation were involved in adsorption process. In addition, phosphorus recovered by BMCa@BC had high bioavailability (86.7 % of TP) and low loss (3.3 % of TP) and was a potential slow-release fertilizer. P-laden BMCa@BC significantly enhanced seed germination and growth in planting experiments, proving that it could be used as a substitute for P-based fertilizer. After five cycles of regeneration, BMCa@BC still showed good adsorption recovery and the P-enriched desorption solution could be recovered as Ca-P products with the fertilizer value. Overall, BMCa@BC has good cost-effectiveness and practical applicability in phosphorus recovery. This provides a new way to recover and reuse phosphorus effectively.

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.

Simultaneous Recovery of Nitrogen and Phosphorus from Sewage by Magnesium Ammonium Phosphate Method with Magnesium-Loaded Bentonite

Excessive nitrogen (N) and phosphorus (P) result in serious eutrophication of water. In this study, magnesium modified acid bentonite was prepared by the impregnation method, and nitrogen and phosphorus were simultaneously removed by the magnesium ammonium phosphate method (MAP), which solved the problem of the poor adsorption capacity of bentonite. The morphology and structure of MgO-SBt were characterized by XRD, FT-IR, SEM, EDS, XPS, BET, etc. The results show that the acidified bentonite can increase the distance between bentonite layers, the layer spacing is expanded to 1.560 nm, and the specific surface area is expanded to 95.433 m²/g. After Mg modification, the characteristic peaks of MgO appear at 2θ of 42.95°, 62.31°, and 78.72°, indicating that MgO has been successfully loaded and that MgO bonded to the surface and interior pores of the acidified bentonite, boosting adsorption performance. When the dosage of MgO-SBt is 0.25 g/L, pH = 9, and N/P ratio is 5:1, the maximum adsorption capacity of MgO-SBt for N and P can reach 193.448 mg/g and 322.581 mg/g. In addition, the mechanism of the simultaneous adsorption of nitrogen and phosphorus by MgO-SBt was deeply characterized by the kinetic model, isothermal adsorption model, and thermodynamic model. The results showed that the simultaneous adsorption of nitrogen and phosphorus by MgO-SBt was chemisorption and a spontaneous exothermic process.

Phosphate Removal Mechanisms in Aqueous Solutions by Three Different Fe-Modified Biochars

Iron-modified biochar can be used as an environmentally friendly adsorbent to remove the phosphate in wastewater because of its low cost. In this study, Fe-containing materials, such as zero-valent iron (ZVI), goethite, and magnetite, were successfully loaded on biochar. The phosphate adsorption mechanisms of the three Fe-modified biochars were studied and compared. Different characterization methods, including scanning electron microscopy/energy-dispersive spectrometry (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), were used to study the physicochemical properties of the biochars. The dosage, adsorption time, pH, ionic strength, solution concentration of phosphate, and regeneration evaluations were carried out. Among the three Fe-modified biochars, biochar modified by goethite (GBC) is more suitable for phosphate removal in acidic conditions, especially when the pH = 2, while biochar modified by ZVI (ZBC) exhibits the fastest adsorption rate. The maximum phosphate adsorption capacities, calculated by the Langmuir-Freundlich isothermal model, are 19.66 mg g^-1, 12.33 mg g^-1, and 2.88 mg g^-1 for ZBC, GBC, and CSBC (biochar modified by magnetite), respectively. However, ZBC has a poor capacity for reuse. The dominant mechanism for ZBC is surface precipitation, while for GBC and CSBC, the major mechanisms are ligand exchange and electrostatic attraction. The results of our study can enhance the understanding of phosphate removal mechanisms by Fe-modified biochar and can contribute to the application of Fe-modified biochar for phosphate removal in water.

Phosphate removal from aqueous solution using calcium-rich biochar prepared by the pyrolysis of crab shells

Phosphorus is one of the main pollutants that cause water pollution, and phosphorus is a one-way cycle in the environment, and phosphorus resources will face exhaustion in the next 100 years. Therefore, the recovery and reuse of phosphorus resources have become very important. This article presents a study concerning the removal of phosphate from an aqueous solution by using a calcium-rich biochar prepared by pyrolysis of crab shells. The experimental results show that the optimal pyrolysis temperature of crab shells is 500 ℃, named CSB500, which is more conducive to the adsorption of phosphate. The process of phosphate adsorption conforms to the quasi-second-order kinetics and Freundlich model. On the other hand, the Langmuir isotherm model shows that when the reaction conditions are 25 ℃, 30 ℃, and 35 ℃, the maximum adsorption capacity of CSB500 for phosphate is 164.32 mg/g, 170.47 mg/g, and 209.35 mg/g, respectively. The characterization results show that the overall structure of CSB500 is good, the specific surface area is large, and the main component is calcium carbonate. The potential mechanisms of action in the process of phosphate adsorption may be electrostatic attraction, surface chemical precipitation, ligand exchange, and complexation.

Phase transformation-driven persulfate activation by coupled Fe/N-biochar for bisphenol a degradation: Pyrolysis temperature-dependent catalytic mechanisms and effect of water matrix components

Fe-N co-doped biochar is recently an emerging carbocatalyst for persulfate activation in situ chemical oxidation (ISCO). However, the involved catalytic mechanisms remain controversial and distinct effects of coexisting water components are still not very clear. Herein, we reported a novel N-doped biochar-coupled crystallized Fe phases composite (Fe@N-BC₈₀₀) as efficient and low-cost peroxydisulfate (PDS) activators to degrade bisphenol A (BPA), and the underlying influencing mechanism of coexisting inorganic anions (IA) and humic constituent. Due to the formation of graphitized nanosheets with high defects (AI index>0.5, I_D/I_G = 1.02), Fe@N-BC₈₀₀ exhibited 2.039, 5.536, 8.646, and 23.154-fold higher PDS catalytic activity than that of Fe@N-BC₆₀₀, Fe@N-BC₄₀₀, N-BC, BC. Unlike radical pathway driven by carbonyl group and pyrrolic N of low/mid-temperature Fe@N-BCs. The defective graphitized nanosheets and Fe-Nx acted separately as electron transfer and radical pathway active sites of Fe@N-BC₈₀₀, where π-π sorption assisted with pyrrolic N and pore-filling facilitated BPA degradation. The strong inhibitory effects of PO₄^3- and NO₂^- were ascribed to competitive adsorption of phosphate (61.11 mg g^-1) and nitrate (23.99 mg g^-1) on Fe@N-BC₈₀₀ via electrostatic attraction and hydrogen bonding. In contrast, HA competed for the pyrrolic-N site and hindered electron delivery. Moreover, BPA oxidation pathways initiated by secondary free radicals were proposed. The study facilitates a thorough understanding of the intrinsic properties of designed biochar and contributes new insights into the fate of degradation byproducts formed from ISCO treatment of micropollutants.

Removal of phosphate from synthetic wastewater: A comparative study between both activated clays using an experimental design methodology

Phosphate-loaded industrial wastewaters have resulted in numerous environmental issues that have hard hit the Gulf of Gabes-Tunisia, making the environmental protection one of the most compelling priorities. Consequently, this study aimed first to compare the amounts of phosphate adsorbed by two types of Tunisian activated clays. The second goal was to assess and optimize the phosphate removal efficiency of these clays, using Box-Behnken design (BBD) under response surface methodology. Results showed that the highest adsorption amounts of 130.16 mg g^-1 , 125.42 mg g^-1 were yielded for Jebel Haidoudi clay and Douiret clay, respectively. These values demanded an initial phosphate concentration of 300 mg L^-1 , a contact time of 5 h, and a pH of 2). Thus, kinetic and isotherm studies of phosphate elimination from synthetic solutions demonstrated that for both activated clays, the pseudo-second-order and Langmuir equation fitted very well the experimental data, respectively. These results indicate that phosphate adsorption might be mainly a chimisorption phenomenon and a monolayer process. All these findings confirmed that both activated clays could be considered as a competent, cost-effective, efficient and ecological alternative for the elimination of phosphate from industrial wastewaters. PRACTITIONER POINTS: Activated clay could be adopted as an efficient and cost-effective adsorbent. The optimum conditions were nominated as 300 mg L^-1 of initial phosphate concentration, 5 h contact times and pH = 2. The probable uptake mechanism of phosphate followed predominantly the acid-base interaction and hydrogen bond.

Synthesis and Adsorbent Performance of Modified Biochar with Ag/MgO Nanocomposites for Heat Storage Application

Heat storage is a major problem in the world. Many research is going on the heat storage application. This research investigates the novel Ag/MgO/biochar nanocomposites for heat storage. Ag/MgO/biochar nanocomposites were fabricated using solvent-free ball milling techniques. According to several analytical measurements, the Ag/MgO nanoparticles in biochar are uniformly dispersed across the carbon interface. This type of adsorbent material has been characterized by different techniques such as X-ray diffraction pattern analysis (XRD), FTIR analysis, scanning electron microscope (SEM), and transmission electron microscope (TEM) as all indicate the surface morphology and successful ball milling synthesis of Ag/MgO nanocomposites. The UV visible spectroscopy wavelength range of AgNPs and MgONPs is 330 nm and 470 nm, respectively. FTIR analysis revealed that different functional groups of modified biochar nanocomposites such as O-H group are 3728 cm-1 and for C-H bond is 932 cm-1, C-O group is 1420 cm-1, and C=O is 1785 cm-1, respectively. Adsorption tests showed that 1.0 gL-1 dosage with 60% phosphate removal, an ion, and 0.2 gL-1 of dosages that had 85% methylene blue decomposition, a charged synthetic dye, were the lowest absorption levels. This research suggests that ball milling offers the advantages of stabilization and chemical adaptability for customized remediation of different atmospheric contaminants. Ball milling is a facile and feasible process to fabricate carbon-metal-oxide nanomaterials.

Application of biochar as an innovative soil ameliorant in bioretention system for stormwater treatment: A review of performance and its influencing factors

As an emerging environment functional material, biochar has become a research hotspot in environmental fields because of its excellent ecological and environmental benefits. Recently, biochar has been used as an innovative soil ameliorant in bioretention systems (BRS) to effectively enhance pollutant removal efficiency for BRS. This paper summarizes and evaluates the performance and involved mechanisms of biochar amendment in BRS with respect to the removal of nutrients (TN (34-47.55%) and PO₄^3--P (47-99.8%)), heavy metals (25-100%), pathogenic microorganisms (Escherichia coli (30-98%)), and organic contaminants (77.2-100%). For biochar adsorption, the pseudo-second-order and Langmuir models are the most suitable kinetic and isothermal adsorption models, respectively. Furthermore, we analyzed and elucidated some factors that influence the pollutant removal performance of biochar-amended BRS, such as the types of biochar, the preparation process and physicochemical properties of biochar, the aging of biochar, the chemical modification of biochar, and the hydraulic loading, inflow concentration and drying-rewetting alternation of biochar-amended BRS. The high potential for recycling spent biochar in BRS as a soil ameliorant is proposed. Collectively, biochar can be used as an improved medium in BRS. This review provides a foundation for biochar selection in biochar-amended BRS. Future research and practical applications of biochar-amended BRS should focus on the long-term stability of treatment performances under field conditions, chemical modification with co-impregnated nanomaterials in biochar surface, and the durability, aging, and possible negative effects of biochar.

Nutrient Recovery from Digestate of Agricultural Biogas Plants: A Comparative Study of Innovative Biocoal-Based Additives in Laboratory and Full-Scale Experiments

Nutrients can be recovered from the digestate of an agricultural biogas plant in the form of solid fraction and serve as crop fertilizers. Removal of suspended solids with screw press separators is the most commonly used technique for treating digestate from biogas plants. To increase separation efficiency and nutrient transfer to the solid phase during separation, eight biocoal-based additives were investigated, which were based on beech wood and produced by pyrolysis at temperatures of 350 °C and 600 °C. Four of the biocoals were impregnated with CaCl₂ or MgCl₂ before pyrolysis. The reaction time between the additives and the digestate varied from 5 min to 2 weeks. The application of MgCl₂-impregnated biocoal synthesized at 600 °C for 20 h increased the nutrient removal efficiency by 76.33% for ammonium and 47.15% for phosphorus, compared to the control (the untreated digestate).

Phosphorus removal and recovery: state of the science and challenges

Phosphorus is one of the main nutrients required for all life. Phosphorus as phosphate form plays an important role in different cellular processes. Entrance of phosphorus in the environment leads to serious ecological problems including water quality problems and soil pollution. Furthermore, it may cause eutrophication as well as harmful algae blooms (HABs) in aquatic environments. Several physical, chemical, and biological methods have been presented for phosphorus removal and recovery. In this review, there is an overview of phosphorus role in nature provided, available removal processes are discussed, and each of them is explained in detail. Chemical precipitation, ion exchange, membrane separation, and adsorption can be listed as the most used methods. Identifying advantages of these technologies will allow the performance of phosphorus removal systems to be updated, optimized, evaluate the treatment cost and benefits, and support select directions for further action. Two main applications of biochar and nanoscale materials are recommended.

Removal of ammonia nitrogen, nitrate, and phosphate from aqueous solution using biochar derived from Thalia dealbata Fraser: effect of carbonization temperature

Thalia dealbata Fraser-derived biochar was prepared at different carbonization temperatures to remove nutrients in aqueous solution. Thermogravimetry/differential thermogravimetry (TG/DTG) was used to analyze the carbonization and decomposition procedure of Thalia dealbata Fraser. X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), zeta potential, and N₂ adsorption-desorption isotherms were employed to characterize the prepared biochar. The carbonization temperature obviously effected the physical and chemical properties of biochar. The adsorption efficiency of ammonia (NH₄⁺-N), nitrate (NO₃^--N), and phosphate (PO₄^3-) adsorption on biochar was tested. Pseudo-first-order kinetic, pseudo-second-order kinetic, and intra-particle diffusion kinetic models were used to fit adsorption kinetic. Langmuir and Freundlich models were used to fit adsorption isotherms. The theoretical adsorption capacity of NH₄⁺-N, NO₃^--N, and PO₄^3- on biochar was 5.8 mg/g, 3.8 mg/g, and 1.3 mg/g, respectively. This study provides the insights for effect of carbonization temperature on biochar preparation and application.

Environmental application of engineering magnesite slag for phosphate adsorption from wastewater

Herein, magnesite slags (MS), which remain after sulfuric acid extraction from light burnt magnesite in the magnesite industry, were used as phosphate adsorbents in wastewater. The MS were calcined under 700 °C to enhance phosphate adsorption. The calcined magnesite slags (CMS) were characterized by nitrogen adsorption-desorption isotherm, X-ray diffraction, and scanning electron microscopy. A series of batch adsorption experiments were carried out to test the phosphate adsorption capacity of CMS. The results showed that the calcific treatment promoted the conversion from Mg, Ca, Fe, etc. compound to metal oxide of the MS. The generated metal oxide particles resulted in 237.4 mg/g increase in the phosphate adsorption capacity. The phosphate adsorption isotherm of CMS fitted the Langmuir model better, and the maximum adsorption capacity of CMS was 526 mg/g. The adsorption kinetics of phosphate on CMS can be described by the pseudo-second-order model. The phosphate removal efficiency was greater than 98% in 300 mg/L phosphate solution. Mechanism investigation results indicated that phosphate was adsorbed by CMS through MgO protonation, electrostatic attraction, Mg-P complexation, and ligand exchange. The results obtained in this work demonstrate that the CMS is a potential effective adsorbent for removal and reutilization phosphate from P-contaminated water, due to it can be employed as a fertilizer after phosphate adsorption.

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

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

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.

Solvent-Free Synthesis of MgO-Modified Biochars for Phosphorus Removal from Wastewater

Adsorption is an efficient technology for removing phosphorus from wastewater to control eutrophication. In this work, MgO-modified biochars were synthesized by a solvent-free ball milling method and used to remove phosphorus. The MgO-modified biochars had specific surface areas 20.50–212.65 m² g⁻¹ and pore volume 0.024–0.567 cm³ g⁻¹. The as-prepared 2MgO/BC-450-0.5 had phosphorus adsorption capacities of 171.54 mg g⁻¹ at 25 °C and could remove 100% of phosphorus from livestock wastewater containing 39.51 mg L⁻¹ phosphorus. The kinetic and isotherms studied show that the pseudo-second-order model (R² = 0.999) and Langmuir models (R² = 0.982) could describe the adoption process well. The thermodynamic analysis indicated that the adsorption of phosphorus on the MgO-modified biochars adsorbent was spontaneous and endothermic. The effect of pH, FTIR spectra and XPS spectra studies indicated that the phosphorus adsorption includes a protonation process, electrostatic attraction and precipitation process. This study provides a new strategy for biochar modification via a facile mechanochemical method.

Recovery, regeneration and sustainable management of spent adsorbents from wastewater treatment streams: A review

Adsorption is the most widely adopted, effective, and reliable treatment process for the removal of inorganic and organic contaminants from wastewater. One of the major issues with the adsorption-treatment process for the removal of contaminants from wastewater streams is the recovery and sustainable management of spent adsorbents. This review focuses on the effectiveness of emerging adsorbents and how the spent adsorbents could be recovered, regenerated, and further managed through reuse or safe disposal. The critical analysis of both conventional and emerging adsorbents on organic and inorganic contaminants in wastewater systems are evaluated. The various recovery and regeneration techniques of spent adsorbents including magnetic separation, filtration, thermal desorption and decomposition, chemical desorption, supercritical fluid desorption, advanced oxidation process and microbial assisted adsorbent regeneration are discussed in detail. The current challenges for the recovery and regeneration of adsorbents and the methodologies used for solving those problems are covered. The spent adsorbents are managed through regeneration for reuse (such as soil amendment, capacitor, catalyst/catalyst support) or safe disposal involving incineration and landfilling. Sustainable management of spent adsorbents, including processes involved in the recovery and regeneration of adsorbents for reuse, is examined in the context of resource recovery and circular economy. Finally, the review ends with the current drawbacks in the recovery and management of the spent adsorbents and the future directions for the economic and environmental feasibility of the system for industrial-scale application.

Preparation of structured biochar, its adsorption capacity of N and P and its characterization

Structured biochar (SC) was prepared by biochar from cattail-sludge mixture (CS) and high-density polyethylene (HDPE) and treated as an adsorbent, and the KH₂PO₄ and NH₄Cl solution were treated as adsorbates, to explore the adsorption capacity of phosphorus (P) and nitrogen (N) on SC in water. A single factor experimental method was employed to determine the optimal parameters for SC. The results showed that: 60% sizing amount, 5 N (cm²)^-1 molding pressure, 160 °C molding temperature and 95 min molding time were optimal parameters for SC preparation. The adsorption of P and N on SC conforms to the Langmuir model, with the distribution of adsorption sites on the surface tending to be even. The adsorption of P and N on SC is favorable and spontaneous, and the adsorption tends to be monolayer adsorption with a major role for chemical adsorption. The higher the temperature, the higher the adsorption capacity of P and N on SC is, and the affinity of SC with P is higher than that with N. The pseudo-second-order kinetic model for the adsorption of N and P by SC has a high degree of fit. The pH_pzc value of SC was 8.57. The hydrophobicity and stability of SC are rather high, with the surface particles closely bonded and increased roughness and pore diameter. The adsorption mechanism of P and N on SC can be attributed to pore filling, electrostatic attraction and hydrogen bonding. The results can provide a new technology for the resource utilization of cattails and sludge, a new idea for the recycling and reuse of biochar, and a basis for the selection of materials for the treatment of eutrophic water bodies.

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.

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.

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.

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.

Effect of Consecutive Application of Phosphorus-Enriched Biochar with Different Levels of P on Growth Performance of Maize for Two Successive Growing Seasons

Sustainable management of phosphorus (P) is one of the burning issues in agriculture because the reported P losses, when applied in the form of mineral fertilizer, give rise to another issue of water pollution as P is considered one of the limiting nutrients for eutrophication and so results in costly water treatments. In the present study, the enrichment of biochar with mineral P fertilizer was supposed to reduce such losses from the soil. Additionally, P can also be recycled through this technique at the same time as biochar is derived from biomass. Biochar was prepared using wheat straw followed by its enrichment with di-ammonium phosphate (DAP) at the ratio of 1:1 on a w/w basis. The first pot trial for spring maize (cv. Neelam) was conducted using phosphorus-enriched biochar (PEB) at 0% and 1% with different levels of recommended P (0%, 25%, 50%, and 100%). The treatments were arranged factorially under a complete randomized design (CRD) with three replications. After harvesting the spring maize, pots were kept undisturbed, and a second pot trial was conducted for autumn maize in the same pots to assess the residual impact of 1% PEB. In the second pot trial, only inorganic P was applied to respective treatments because the pots contained 1% PEB supplied to spring maize. The results revealed that the application of 1% PEB at P level 50% significantly increased all the recorded plant traits (growth, yield, and physiological and chemical parameters) and some selected properties of post-harvest soil (available P, organic matter, and EC) but not soil pH. In terms of yield, 1% PEB at 50% P significantly increased both the number of grains and 100-grain weight by around 30% and 21% in spring and autumn maize, respectively, as compared to 100% P without PEB. It is therefore recommended that P-enriched biochar should be used to reduce the inorganic P fertilizer inputs; however, its application under field conditions should be assessed in future research.