Almond and walnut shell-derived biochars affect sorption-desorption, fractionation, and release of phosphorus in two different soils

Efficacy of Agricultural Residue-Derived Biochar for Tackling Cadmium Contamination in an Aqueous Solution

This study aimed to investigate the efficacy of biochar, produced from different agricultural residues varying in lignin and cellulose content and subjected to different pyrolysis temperatures, in removing cadmium ions (Cd (II)) from an aqueous solution. This removal process is crucial for protecting human health and the environment. Specifically, the study focused on the adsorption behaviors of Cd (II) by the biochars made from rice husk biochar (RHB), maize straw biochar (MSB), peanut shell biochar (PSB), cottonseed shell biochar (CHB), and mulberry leaf biochar (MLB), which were prepared at 300 °C and 600 °C. The results indicated that the type of agricultural residue used to produce biochar significantly influenced the adsorption of Cd (II). Notably, mulberry leaf biochar prepared at 300 °C (MLB-300) demonstrated the highest adsorption efficiency, achieving a maximum adsorption capacity of 42.2 mg g-1. Batch adsorption experiments assessed the impact of various factors, including system pH, NO3- concentration, and adsorption duration. The adsorption kinetics were better described by the pseudo-second-order model than the pseudo-first-order model. Moreover, the study found that the lignin content of the biochar plays a major role in determining the adsorption capacity. The surface characteristics of biochar, influenced by the types of agricultural residues and preparation temperature, directly impact its adsorption mechanism and capacity. While biochar produced at 300 °C showed optimal Cd(II) adsorption, those processed at 600 °C were less effective, likely due to the loss of functional groups at higher temperatures.

Simultaneous immobilization of lead and arsenic and improved phosphorus availability in contaminated soil using biochar composite modified with hydroxyapatite and oxidation: Findings from a pot experiment

Multi-metals/metalloids contaminated soil has received extensive attention because of their adverse health effects on the safety of the food chain and environmental health. In order to provide additional insight and aid in mitigating environmental risks, a pot experiment was directed to assess the impacts of biochars derived from rice straw (BC), and modified biochars i-e., hydroxyapatite modified (HAP-BC) and oxidized biochars (Ox-BC) on the redistribution, phytoavailability and bioavailability of phosphorus (P), lead (Pb), and Arsenic (As), as well as their effects on the growth of maize (Zea mays L.) in a Lead (Pb)/Arsenic (As) contaminated soil. The results showed that HAP-BC increased the soil total and available P, compared with raw biochar and control treatment. HAP-BC improved soil properties by elevating soil pH and electric conductivity (EC). The Hedley fractionation scheme revealed that HAP-BC enhanced the labile and moderately labile P species in soil. Both HAP-BC and Ox-BC assisted in the P build-up in plant roots and shoots. The BCR (European Community Bureau of Reference) sequential extraction data for Pb and As in soil showed the pronounced effects of HAP-BC towards the transformation of labile Pb and As forms into more stable species. Compared with control, HAP-BC significantly (P ≤ 0.05) decreased the DTPA-extractable Pb and As by 55% and 28%, respectively, subsequently, resulting in reduced Pb and As plant uptakes. HAP-BC application increased the plant fresh and dry root/shoot biomass by 239%, 72%, 222% and 190%, respectively. The Pb/As immobilization by HAP-BC was mainly driven by precipitation, ion exchange and surface complexation mechanisms in soil. In general, HAP-BC application indicated a great capability to be employed as an effective alternative soil amendment for improving P acquisition in soil, simultaneously immobilizing Pb and As in the soil-plant systems.

Biochar addition regulates soil phosphorus fractions and improves release of available phosphorus under freezing-thawing cycles

Currently, the shortage of phosphorus resources is becoming more and more serious. In general, phosphorus fertilizer is poorly utilized in soil and tends to gradually accumulate. Freezing-thawing cycles (FT) are seasonal phenomenon occurring in high latitudes and altitudes regions, which have obvious influence on the form of phosphorus in soil. This study investigates the effect of biochar on soil physicochemical properties, phosphorus form and availability under FT and thermostatic incubation (TH) condition. Compared with treatment without biochar, 4 % biochar addition increased the soil pH value, electrical conductivity, organic matter and Olsen-P of soil by a maximum of 0.76, 285.55 μS/cm, 28.60 g/kg and 139.27 mg/kg, respectively. Moreover, according to Hedley-P classification results, under FT condition, the content of labile phosphorus pool is always higher than those under TH. FT may promote the conversion of phosphorus from other fractions to labile phosphorus pool. Redundancy analysis results show that biochar addition and FT can not only directly change the soil phosphorus pool, but also alter the soil physicochemical properties and microbial community, which further affect the adsorption and mineralization of phosphorus in soil. The results of this study will be devoted to understanding the changes in soil phosphorus fractions under the effects of biochar addition and FT, providing references for agricultural production in areas where FT occur.

Identifying biotic and abiotic processes of reversing biochar-induced soil phosphorus leaching through biochar modification with MgAl layered (hydr)oxides

Biochar (BC) as a increasing widely adopted soil amendments showed potential threat to soil P leaching, but the relevant mechanisms were not clear enough and relevant strategy should be proposed to address the P leaching induced by BC application. In this study, effects of ordinary corn straw BC, and a fabricated Mg/Al-LDHs modified biochar (LBC) on soil P availability, adsorption, fraction and mobility were compared and investigated by conducting the column and incubation experiments at biochar to soil rate of 1 %, 2 % and 4 % (w/w). Chemical sequential extraction methods and various solid-state method (i.e., three-dimensional excitation emission matrix (EEM), x-ray diffraction (XRD), scanning electron micrograph (SEM) and P K-edge X-ray absorption near edge structure (XANES)) were utilized to give deep insights into the P mobilization and immobilization mechanisms by respectively applying the BC and LBC. Results of incubation experiments showed that applying the LBC reduced the labile P with significant CaP transformation to Al-retained P, while ordinary BC promoted the Fe/Al-P transformation to labile dibasic calcium phosphate and monobasic calcium phosphate evidenced by the EEM analysis, in-situ XANES investigation and chemical sequential extraction methods. Results of phosphatase and microbial analyses indicated that the decreased labile P after 30 days' incubation and the mitigated P leaching in LBC treatment were dominantly ascribed to abiotic processes of inorganic P transformation and (de)sorption. This research gave deep insights into abiotic and biotic processes of ordinary biochar promoting soil P leaching, and important implications for applying engineered biochar in reducing P leaching and improving soil productivity.

Lead removal from aqueous solutions by olive mill wastes derived biochar: Batch experiments and geochemical modelling

In this study, lead removal from aqueous solutions using biochar derived from olive mill solid and liquid wastes has been investigated by applying batch experiments and geochemical modelling. The batch adsorption experiments included the assessment of several key parameters such as the contact time (kinetic), initial concentration (isotherm), pH, adsorbent dose, and the presence of competitive cations, whilst the geochemical modelling focused on the involved adsorption mechanisms using the PHREEQC code. The kinetic studies showed that lead adsorption is a relatively fast process, where intraparticle diffusion is the rate-limiting step. Biochar dose, solution pH and the presence of competitive ions significantly affected the Pb adsorption effectiveness by the biochar. Especially the higher Pb removal percentages were observed in mono-elemental solutions with high biochar dose at mildly acidic solution pH values. The maximum Pb adsorption capacity of biochar was estimated as 40.8 mg g^-1 which is higher than various biochars derived from sludge, lignocellulosic and animal biomasses. On the other hand, the geochemical modelling employing the PHREEQC code showed that ion exchange and Pb precipitation are the main reactions controlling its removal from aqueous solutions, whilst surface complexation is insignificant, mainly due to the low surface functional groups on the used biochar.

Behaviors of Organic Ligands and Phosphate during Biochar-Driven Nitrate Adsorption in the Presence of Low-Molecular-Weight Organic Acids

A batch experiment was conducted to examine the behavior of nitrate, organic ligands, and phosphate in the co-presence of biochar and three common low-molecular-weight organic acids (LMWOAs). The results show that citrate, oxalate, and malate ions competed with nitrate ion for the available adsorption sites on the biochar surfaces. The removal rate of LMWOA ligands by the biochar via adsorption grew with increasing solution pH. The adsorbed divalent organic ligands created negatively charged sites to allow binding of cationic metal nitrate complexes. A higher degree of biochar surface protonation does not necessarily enhance nitrate adsorption. More acidic conditions formed under a higher dose of LMWOAs tended to make organic ligands predominantly in monovalent forms and failed to create negatively charged sites to bind cationic metal nitrate complexes. This could adversely affect nitrate removal efficiency in the investigated systems. LMWOAs caused significant release of phosphate from the biochar. The phosphate in the malic acid treatment tended to decrease over time, while the opposite was observed in the citric- and oxalic-acid treatments. This was caused by re-immobilization of phosphate in the former due to the marked increase in solution pH over time.

Assessing simultaneous immobilization of lead and improvement of phosphorus availability through application of phosphorus-rich biochar in a contaminated soil: A pot experiment

Soil lead (Pb) contamination is often caused by anthropogenic activities. In this study, a pot experiment was conducted to assess the effect of biochars derived from pig-carcass (PCBC) and branches of oriental-plane tree (OPBC) on the bioavailability, redistribution, and phytoavailability of Pb and P, as well as the growth of Ipomoea aquatica Forsk in a Pb-contaminated soil. Application of PCBC increased the total and available P concentrations in the soil as compared to the control, and enhanced the concentrations of labile P and sparingly labile P via direct exogenous P input and improvement of soil pH. Both biochars facilitated P accumulation in plant shoots and roots. Sequential extraction of soil Pb confirmed that biochar application facilitated the transformation of mobile Pb into stable fractions, with greater effects from PCBC than OPBC. Hence, biochar application significantly decreased the soil DTPA-extractable Pb by 90.2% (PCBC) and 64.0% (OPBC) compared to the control, consequently reducing Pb uptake by plants. The Pb immobilization by biochar was driven by the biochar-induced increase of soil pH, Pb-phosphate/carbonate precipitation, ion exchange between Pb²⁺ and biochar-derived cations (e.g., Ca²⁺ and K⁺), and surface complexation with functional groups (e.g., carboxyl, hydroxyl, CO). Application of PCBC simultaneously increased the biomass of plant roots and shoots, by 1.8- and 0.6- folds, respectively. Overall, PCBC showed a potential to function as an effective amendment in the immobilization of Pb and alternative P fertilizer to improve degraded soils.

Modified biochar improves the storage capacity and adsorption affinity of organic phosphorus in soil

The loss of soil organic phosphorus can easily cause water eutrophication. In order to effectively reduce the loss of soil organic phosphorus, this manuscript investigated the adsorption of soil organic phosphorus by lanthanum modified biochar (BC), traditional adsorbent gypsum (GY) and zeolite (ZE) by taking phytic acid as the representative. The adsorption isotherm model and kinetic models were used to fit the phosphorus absorption characteristics of the adsorbents. The effects of initial pH and temperature on the adsorption capacity were discussed, and the adsorption mechanism of each adsorbent was explained by means of FTIR and XRD. The results showed that the adsorption capacity of phytate phosphorus followed the trend of BCTS > GYTS > ZETS > TS (soil), and the maximum phosphorus adsorption capacity obtained from Langmuir isotherm for treatment with BCTS was 2.836 mg g^-1, and the treatment had the strongest affinity for phytate phosphorus and also the ability to store phosphorus. The adsorption process fits well with Langmuir isotherm equation and pseudo-second-order kinetic equation, and the adsorption behavior of phytate phosphorus was mainly controlled by the chemisorption of monolayer. When the concentration of phytate phosphorus was 100 mg L^-1, percentage of modified biochar added to the soil was 3% and the pH was 6, the adsorption capacity reached the maximum, and the maximum adsorption capacity was 2.000 mg g^-1. The results of FTIR and XRD characterization showed that complexation was the main adsorption mechanism. In this study, the combination of modified biochar and soil phytate phosphorus can provide a good theoretical basis for reducing the loss of soil organic phosphorus.

Effects of biochar on transport and retention of phosphorus in porous media: Laboratory test and modeling

Given the complexity of soil components, a detailed understanding of the effects of single factors on phosphorus transport and retention will play a key role in understanding the environmental effects of phosphorus. In this work, quartz sand columns (considering five factors: doping rate, pH, particle size, ionic strength and cation type), combined with a two-site nonequilibrium transport model (TSM), were used to investigate phosphate (P) transport behavior. The results show that changes in doping ratio (0.4%-1.6%) and pH (5-9) have a notable effect on the transport of P, while, particle size of quartz sand hardly impacts the transport. When biochar was added at 1.6%, the surface of biochar increased the P fixation rate by about 37% through direct interaction with phosphate and bridging action with metal ions. As the morphology of P changed under different pH conditions, a part of P was immobilized in the form of precipitation. The immobilization of P was further enhanced with the increase of ionic strength. Compared with the direct interaction of P with biochar in Na⁺ solution, Ca²⁺ and Mg²⁺ solutions are more likely to adsorb P. Meanwhile, the TSM model also fits the transport behavior well. This study provides a perspective for evaluating the environmental behavior of P in the porous media interaction with biochar.

Comparative efficacy of raw and HNO3-modified biochar derived from rice straw on vanadium transformation and its uptake by rice (Oryza sativa L.): Insights from photosynthesis, antioxidative response, and gene-expression profile

Low concentrations of vanadium (V) are essential for various plant species but it becomes toxic to plants, animals, and humans at high levels. A significant amount of V is currently being emitted into the atmosphere due to intensified industrial processing. Therefore, this study aimed at evaluating the effect of raw (BC) and HNO₃-modified biochar (OBC) derived from rice straw on growth, photosynthetic assimilation, relative chlorophyll content, SPAD index, ion leakage, enzyme activities, hydrogen peroxide (H₂O₂), bioavailability and V uptake by rice in a laboratory-scale experiment. Characterization of OBC and BC by FTIR (Fourier transform infrared spectroscopy), SEM (scan electron microscopy), BET (Brunauer-Emmett-Teller), elemental analysis, and z-potential revealed a substantial difference between both of them. The V-stress significantly reduced the rice plant growth, biomass yield, chlorophyll parameters, root length and surface area. Under V-stress conditions, root accumulated more V than shoots and OBC significantly improved the above-mentioned parameters, while, decreasing hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) levels in plants. The antioxidant function and gene expression levels induced by V-stress and OBC application further increased the expression profile of three genes (SOD, POD, and CAT) encoding antioxidant enzymes and one metal-tolerant conferring gene (OsFSD1). In summary, these results demonstrated the critical role of OBC in mitigating the detrimental effects of high V-stress on rice growth and enhancing plant defence against V-stress.

Effects of biochar addition on the abundance, speciation, availability, and leaching loss of soil phosphorus

As a promising soil amendment, biochar has demonstrated its potential for influencing soil nutrient transformations. The effects of biochar on soil phosphorus (P) transformations have received much less attention than its effects on carbon cycling. A review of the literature reveals that biochar applications to soils may have notable effects on the abundance, speciation, availability, and leaching loss of soil P. However, a comprehensive and systematic understanding of the biochar-induced environmental behavior of soil P has not been obtained so far. Therefore, in this review, we analyzed and identified the known and potential mechanisms through which biochar affects P behavior in soils: (1) biochar as a source of P provides soluble and exchangeable P to soil; (2) biochar enhances the availability of endogenic soil P by influencing P-related complexation and metabolism effects; and (3) biochar affects P leaching losses directly or indirectly by adsorbing P, improving P retention by soil, and facilitating P assimilation by plants. By presenting a broad and detailed illustration of P behaviors in biochar-amended soils, this paper suggests that the application of biochar to soils will help enlarge soil P pools, increase soil P availability, and decrease P leaching losses from soil. Additional studies are needed to further elucidate the long-term effects of biochar addition on soil P transformations, explore how biochar-derived dissolved organic matter (BDOM) affects the mobility and availability of soil mineral-associated P, and examine the transport of particulate P in biochar-amended soils.

Effect of organic and inorganic phosphorus fertilizers on phosphorus availability and its leaching over incubation time

The use of organic and inorganic phosphorus (P) fertilizers in agricultural soils is very common, and few studies have been conducted to study the effect of different P sources on relative P extractability (RPE) and leaching using different P extractants and degree of P saturation (DPS), over a long period of time. Thus, this study was conducted to investigate the effect of incubation time and different P sources on RPE, DPS, and to predict the concentration of P leached from soil using different P extractants. In order to achieve these goals, nine sewage sludges (SSs), two biochars, animal manure (AM), poultry manure (PM), wheat residue (WR), diammonium phosphate (DAP), and triple superphosphate (TSP) were added to the soil as much as 100 mg P kg^-1 in a 163 days incubation experiment. On average across all amendments and incubation periods, Mehlich-3 extractable P (M3EP) gave the highest mean RPE (42.9%, SE = 7.1%), with water-extractable P (WEP) the lowest (4.6%, SE = 0.93%), and Olsen-extractable P (OEP) (38.3%, SE = 6.3%) in between. Among SSs and based on average across of all incubation periods, soils treated with Shiraz and Takestan SSs were the least soluble source of P, while the highest soluble source of P were soils treated with Kermanshah and Tehran SSs. The results indicated that soil samples taken 16 days following the addition of amendments should reflect agronomic and environmental purposes aiming to assess available and the potential P loss from agricultural soils. The split line model perfectly fitted to the relation between OEP and M3EP (r = 0.93). The DPSs were calculated and the P leaching rate was estimated. Based on OEP, the soils treated with TSP and DAP were at high risk, the medium risk was for soils treated with Kermanshah, Saveh, Tehran, Rasht, Sanandaj, and Isfahan SSs, and PM. Control soil, and soils treated with WR were at no risk, and the soils treated with Arak, Shiraz, and Takestan SSs, ABC, WBC, and AM were classified as low risk.

Engineered biochar with anisotropic layered double hydroxide nanosheets to simultaneously and efficiently capture Pb2+ and CrO42- from electroplating wastewater

Cationic and anionic heavy metal contaminants generally co-exist in practical industrial effluent, and simultaneously removal of these species is a bottleneck for most of the bio-adsorbents because of their contrary charge. In this work, pinewood sawdust derived engineered biochar (BC) was fabricated with MgAl layered double hydroxide (MgAl-LDH) nanosheets, which could efficiently and simultaneously capture heavy metal cations and oxyanions from wastewater. The synergetic effect between loaded MgAl-LDH and BC substantially improves its adsorption performance towards both cationic and anionic contaminants, i.e., Pb2+ and CrO42-. The adsorption capacity of MgAl-LDH/BC for Pb2+ reached 591.2 mg/g, which is 263% higher than that of BC, and in the case of CrO42-, the adsorption capacity is 330.8 mg/g, 416% higher than that of BC. The elimination of Pb2+ was mainly attributed to forming complexations with surface functional groups. While for oxyanions removal, CrO42- can be reduced to Cr3+ by functional groups, and then generated Cr3+ could replace Al3+ via morphic substitution, consequently formed an MgCr-LDH structure. Further, in the continuous fixed-bed column study, 225 bed volume of simulating electroplating wastewater co-existed with Pb2+ and CrO42- can be efficiently treated. Hence, this study sheds light on the engineered biochar design to efficiently and simultaneously capture heavy metal cations and oxyanions and its feasibility on real wastewater purification.

Critical study of crop-derived biochars for soil amendment and pharmaceutical ecotoxicity reduction

In this study, biochars (BCs) produced from crops (straw and seeds) were tested for the applicability as additive to soils. The effect on pH, water capacity and cation exchange capacity of soil were tested. The ability for the sorption of pharmaceuticals (beta-blockers, anti-inflammatory drugs, sulfonamides, 17α-ethinylestradiol, carbamazepine, caffeine) using the batch sorption test was performed, and the effect of water pH was investigated. In addition, the metals removed from the biochar was analyzed as a potential toxicity factor. The mechanism of adsorption (Langmuir, Freundlich) was tested for sulfadimetoxine. The effect of the rye-derived biochar on water cress germination and the reduction of the sulfonamides toxicity to this plant was tested. The advantages of crop-derived biochar application to different soils (sand soil, clay soil and reference soil) was presented. It was found that tested BCs effectively increase the water capacity of soils, especially sand type soil, but in the same time it had increase the pH of pure-buffering soils. The driving force of pharmaceutical sorption was its ionization form - the highest sorption occurs for cations, medium for neutral forms, while the lowest sorption for anions. The opposite situation have been noted for desorption from biochar. The washing of biochars increases sorption for the neutral and anionic species, but not for the cations. The application of biochars into the soils can from one site protect the plants from toxic impact of sulfonamides, but from the other hamper the root prolongation by the pH increase.