Combined use of biochar and phosphate rocks on phosphorus and heavy metal availability: A meta-analysis.

Biochar (BC) and phosphate rocks (PR) are alternative nutrient sources with multiple benefits for sustainable agriculture. The combination of these soil amendments serves two main purposes: to increase soil phosphorus (P) availability and to remediate heavy metal (HM) contamination. However, a further demonstration of the benefits and risks associated with the combined use of BC and PR (BC + PR) is needed, considering the specific characteristics of raw materials, soil types, experimental conditions, and climatic contexts. This meta-analysis is based on data from 28 selected studies, including 581 paired combinations evaluating effects on extraction and fractionation of cadmium (Cd) and lead (Pb), and 290 paired combinations for soil labile and non-labile P. The results reveal that BC, PR, and BC + PR significantly increase soil labile and non-labile P, with BC + PR showing a 150% greater increase compared to BC alone. In tropical regions, substantial increases in P levels were observed with BC, PR, and BC + PR exhibiting increments of 317, 798, and 288%, respectively. In contrast, temperate climate conditions showed lower increases, with BC, PR, and BC + PR indicating 54, 123, and 88% rises in soil P levels. Moreover, BC, PR, and BC + PR effectively reduce the bioavailability of Cd and Pb in soil, with BC + PR demonstrating the highest efficacy in immobilizing Cd. The synergistic effect of BC + PR highlights their potential for Cd remediation. BC + PR effectively reduces the exchangeable fraction of Cd and Pb in soil, leading to their immobilization in more stable forms, such as the residual fraction. This study provides valuable insights into the remediation potential and P management benefits of BC and PR, highlighting their importance for sustainable agriculture and soil remediation practices.

The residual effect of sewage sludge biochar on soil availability and bioaccumulation of heavy metals: Evidence from a three-year field experiment.

Conversion of sewage sludge (SS) into biochar through pyrolysis is an alternative to make this residue useful for agricultural purposes. Despite advances in interpreting the functions of SS biochar (SSB) for improving soil quality, it is still necessary to understand its residual effect on the dynamics of heavy metals (HM), especially under field conditions in tropical soils. Therefore, the objective of this study was to evaluate the residual effect of the application of SSB obtained at different pyrolysis temperatures on the accumulation, availability and bioaccumulation of HMs by corn cultivated in a tropical soil. For this purpose, a field experiment was conducted for three years to assess the total and available levels of HMs in the soil and the leaf concentration after suspending the application of 30 t ha-1 of SSB produced at 300 °C (BC300) and 500 °C (BC500). In general, the HM contents were below the maximum allowed by environmental legislation in several countries. SSB, regardless of temperature, was effective in immobilizing non-essential HMs for plants, such as Cd, Co, Cr and Pb, in the soil. On the other hand, SSB was able to supply micronutrients to corn plants after amendment ceased. Thus, the lack of negative long-term effects confirms the feasibility and safety of using SSB in agricultural areas with regards to contamination by HM, and makes it an alternative for the disposal of domestic SS.

Infrared Spectroscopy and Mass Spectrometry of CO2 Clusters during Nucleation and Growth.

CO2 clusters with 2 to 4300 molecules are characterized with mass spectrometry and infrared spectroscopy in the uniform postnozzle flow of Laval expansions at constant temperatures of ∼29 and ∼43 K. The mass spectra provide independent, accurate information on the cluster size distributions and through magic numbers also on cluster structures. The experimental results are complemented with force field, quantum chemical, and vibrational exciton calculations. We find our data to be consistent with predominantly fcc cuboctahedral structures for clusters with more than about 50 molecules. Infrared spectra of cluster size distributions with average sizes above 140-220 molecules are completely dominated by the features from the larger cuboctahedral clusters in the distribution. For very small clusters, exciton simulations predict a pronounced broadening of the infrared band as soon as the average cluster size exceeds about five molecules. The nucleation behavior of CO2 under the present conditions is found to be barrierless in agreement with similar trends previously observed for other compounds at very high supersaturation.

Nitrogen fertilizer is a key factor affecting the soil chemical and microbial communities in a Mollisol.

Microbial communities drive geochemical cycles in soils. Relatively few studies have assessed the long-term impacts of different types of soil amendments under field conditions in long-term experiments. The response of soil microbial organisms in a Mollisol cultivated with maize for 35 years was examined. Treatments involved the use of N, P, and K fertilizers and two doses of straw residue in isolation or combined. Real-time PCR and Illumina MiSeq sequencing methods were used to characterize the microbial community. The results showed that addition of nitrogen fertilizers decreased soil pH, but this was mitigated when a high dose of straw was also incorporated. Long-term application of inorganic fertilizers was able to alter the abundance of functional soil microbial population. Application of inorganic N fertilizer resulted in distinctive changes on N-cycle microorganisms. Phosphate-solubilizing functional genes abundance was lower in plots with no phosphate fertilizer. Sequencing analysis showed that the presence or absence of N in the fertilizer mix is a key factor affecting bacterial community diversity of agricultural soil, and pH, total organic C, and total N show a high correlation with bacterial community composition. Nitrogen addition increased the N concentration in the soil, which could cause changes in the soil pH and change the soil bacterial community. Our findings proved that interaction of N fertilizer with other fertilizers can affect microbial communities.

Water nucleation at extreme supersaturation.

We report water cluster formation in the uniform postnozzle flow of a Laval nozzle at low temperatures of 87.0 and 47.5 K and high supersaturations of lnS ∼ 41 and 104, respectively. Cluster size distributions were measured after soft single-photon ionization at 13.8 eV with mass spectrometry. Critical cluster sizes were determined from cluster size distributions recorded as a function of increasing supersaturation, resulting in critical sizes of 6-15 and 1, respectively. Comparison with previous data for propane and toluene reveals a systematic trend in the nucleation behavior, i.e., a change from a steplike increase to a gradual increase of the maximum cluster size with increasing supersaturation. Experimental nucleation rates of 5 · 1015 cm-3 s-1 and 2 · 1015 cm-3 s-1 for lnS ∼ 41 and 104, respectively, were retrieved from cluster size distributions recorded as a function of nucleation time. These lie 2-3 orders of magnitude below the gas kinetic collision limit assuming unit sticking probability, but they agree very well with a recent prediction by a master equation model based on ab initio transition state theory. The experimental observations are consistent with barrierless growth at 47.5 K, but they hint at a more complex nucleation behavior for the measurement at 87.0 K.

Toluene Cluster Formation in Laval Expansions: Nucleation and Growth.

Toluene cluster formation has been investigated in the postnozzle flows of Laval expansions at flow temperatures between ∼48 and 73 K, toluene number concentrations between ∼1013 and 1015 cm-3, and for growth times of up to ∼170 µs. The clusters were detected by soft ionization mass spectrometry to ensure minimum cluster fragmentation upon ionization. The optimum conditions were achieved with single-photon ionization using vacuum ultraviolet (VUV) photons of 13.3 eV energy and low fluences. The nature of the onset of toluene cluster formation hints at barrierless nucleation, which seems a likely scenario for the high supersaturations (>1019) of the present experiments. This contrasts with the onset behavior observed for propane in earlier studies, which suggested nucleation in the presence of a barrier. Subsequent cluster growth has been studied as a function of the growth time for various toluene partial pressures. Size-resolved growth data have been recorded for all cluster sizes from the dimer to aggregates composed of ∼2400 monomers (∼4.4 nm in size), revealing general trends in the growth behavior. The current experiments provide systematic size- and time-resolved data on cluster formation at high supersaturations as a possible benchmark for the understanding of cluster formation under such conditions.

Observation of propane cluster size distributions during nucleation and growth in a Laval expansion.

We report on molecular-level studies of the condensation of propane gas and propane/ethane gas mixtures in the uniform (constant pressure and temperature) postnozzle flow of Laval expansions using soft single-photon ionization by vacuum ultraviolet light and mass spectrometric detection. The whole process, from the nucleation to the growth to molecular aggregates of sizes of several nanometers (∼5 nm), can be monitored at the molecular level with high time-resolution (∼3 µs) for a broad range of pressures and temperatures. For each time, pressure, and temperature, a whole mass spectrum is recorded, which allows one to determine the critical cluster size range for nucleation as well as the kinetics and mechanisms of cluster-size specific growth. The detailed information about the size, composition, and population of individual molecular clusters upon condensation provides unique experimental data for comparison with future molecular-level simulations.

A pulsed uniform Laval expansion coupled with single photon ionization and mass spectrometric detection for the study of large molecular aggregates.

We report on a new instrument that allows for the investigation of weakly-bound molecular aggregates under equilibrium conditions (constant temperature and pressure). The aggregates are formed in a Laval nozzle and probed with time-of-flight mass spectrometry in the uniform postnozzle flow; i.e. in the equilibrium region of the flow. Aggregates over a very broad size range from the monomer to particle sizes of 10-20 nm can be generated and studied with this setup. Soft ionization of the aggregates is performed with single photons from a homemade vacuum ultraviolet laser. The mass spectrometric detection provides molecular-level information on the size and chemical composition of the aggregates. This new instrument is useful for a broad range of cluster studies that require well-defined conditions.

Spatial distribution and temporal variability of ammonium-nitrogen, phosphorus, and potassium in a rice field in Corrientes, Argentina.

Proper and effective management of soil nutrients requires assessment of their variability at the field scale. We compare the effects of lime amendment rate on the spatial variability of three macronutrient forms (NH4 (+)-N, Olsen P, and Mehlich-1 K) in a paddy soil at three different dates during the growth period of a rice crop. The field work was carried out near Corrientes, Argentina. Lime treatments were 0, 625, and 1250 kg ha(-1) dolomite, and each liming dose was applied to a 1.7 ha field. Ninety-three soil samples per treatment were first collected in aerobic conditions and then two more times after flooding, at bunch formation and flowering. Soil NH4 (+)-N increased along time, whereas P was highest at bunch formation and K steadily decreased along the rice growth period. Dolomite addition increased macronutrient availability at the first and second samplings, but its effects at the third sampling depended on the element. The three soil nutrients analyzed displayed strong patterns of spatial dependence for the three lime treatments and at the three periods studied. The areas with relative high or low macronutrient concentrations within each field were not stable throughout the rice growth period. Seasonality in the spatial distribution of macronutrients may be of agronomic value for site specific management.

Comparative analysis of biochar carbon stability methods and implications for carbon credits.

Biochar is an emerging negative emission technology. Its ability to sequester carbon and subsequent carbon credit valuation hinge on the stability of its carbon structure. The widely used indicators of carbon stability H:Corg and O:Corg provide conservative results as these are based on limited incubation experiments and associated modeling results. The results from these accepted methods and other derived methods have not been compared as indicators of carbon stability in a variety of biochar samples. Furthermore, the influence of contrasting feedstock and production techniques on biochar carbon stability is not well explored. Therefore, to address these challenges, a comprehensive stability analysis of 21 different biochar samples with contrasting feedstocks and pyrolysis techniques was conducted using a combination of instrumental methods and derived indicators of carbon stability. Methods such as biochar carbon half-life, thermo-stable fraction, oxidation resistance (R50), and carbon sequestration potential (CS) were used. Based on the initial carbon content of the biochar, simple pyrolysis techniques have similar potential for carbon credits as biochar produced from advanced pyrolysis techniques. Results indicate that the carbon stability of a biochar product is primarily a factor of feedstock type. We found that biochar carbon stability is not related to volatile matter or fixed carbon content for biochar produced using a simple pyrolysis technique and mixed feedstock. Biochars with H:Corg < 0.4 were deemed to have lower carbon stability when compared using different methods. No correlation was observed between the carbon stability of biochar using H:Corg and other methods, however, correlations were observed between half-life, O:Corg, fixed carbon, number of aromatic peaks in FTIR spectrum, R50, and CS. Therefore, it is recommended that data from additional incubation and modeling studies need to be considered to increase the confidence in carbon stability results having major implications to carbon credits.

Arsenic immobilization in soil affected by mining waste using waste-derived functional hydrochar and iron-encapsulated materials.

Arsenic (As) contamination is a widespread problem. Continued and concerted effort in exploring sustainable remediation strategies is required, with in situ immobilization emerging as a promising option. This work valorized a waste by-product from olive (Olea europaea L.) milling into functional hydrochar (HC). The HC was then transformed into iron oxide-encapsulated carbon with three different iron loading rates (10, 25, and 50% w/w of iron chloride hexahydrate added to the olive mill waste feedstock). The HC and the three iron oxide-encapsulated carbon materials were then tested in a pot trial using a 3% w/w application rate as a means to immobilize As in a mining-contaminated soil (2,580 ± 110 mg kg-1 As). After a 45-d incubation period, the effect of adding the amendments on As mobility and bioaccessibility compared with an untreated control was measured using a sequential extraction procedure and in vitro bioaccessibility, respectively. All four treatments resulted in a decrease in mobility and in vitro bioaccessibility as compared with the control. Specifically, As in the mobile phases was up to 35% less than the in control, whereas bioaccessibility was 21.8% in the control and ranged from 17.5 to 12.3% in the treatments. The efficiency of amendments to immobilize As increased with the iron content of the developed materials. This work positions HCs and iron oxide-encapsulated carbon materials produced from olive mill waste as promising options to immobilize As in situ.

New insights into the production, characterization and potential uses of vineyard pruning waste biochars.

Vineyard pruning waste (VP) can be converted into a useful char using pyrolysis as part of a valorization strategy. This study analyzed the effect of temperature (300 and 600 °C) and residence time (1 and 3 h) on an ample number of properties of VP derived biochars, including potential negative environmental impacts. The results showed a clear influence of temperature on biochar's properties and a weaker effect of residence time. Increasing temperature raised soil pH, electrical conductivity (EC), ash and C contents, aromaticity, specific surface area, solid density, mesoporosity and partial graphitization. However, higher pyrolysis temperature reduced O/C and N/C ratios, total N, P and Mg, and polycyclic aromatic hydrocarbons (PAHs). Particularly, the concentration of water extractable organic carbon (WEOC) decreased dramatically with pyrolysis temperature. Moreover, the WEOC fraction of biochars pyrolyzed at 300 °C exhibited a larger aromaticity than those pyrolyzed at 600 °C. Prolonged residence time increased ash content and fixed carbon (FC) and decreased H/C and O/C ratios; however, most frequently this parameter affected biochar properties following opposite trends for the two pyrolysis temperatures. Hydrophysical properties were adequate to consider VP derived biochars as growing media component. PAH concentration was much lower than thresholds following international standards. The germination index increased with temperature and decreased with residence time, so that phytotoxicity was observed in VP and in biochars pyrolyzed for 3 h. Our research demonstrates that, besides temperature, residence time can be useful to modulate the properties of biochars and that prolonged time effect is temperature-dependent.

Grazing-induced effects on soil properties modify plant competitive interactions in semi-natural mountain grasslands.

Plant-soil feedbacks are widely recognized as playing a significant role in structuring plant communities through their effects on plant-plant interactions. However, the question of whether plant-soil feedbacks can be indirectly driven by other ecological agents, such as large herbivores, which are known to strongly modify plant community structure and soil properties, remains poorly explored. We tested in a glasshouse experiment how changes in soil properties resulting from long-term sheep grazing affect competitive interactions (intra- and inter-specific) of two graminoid species: Nardus stricta, which is typically abundant under high sheep grazing pressure in British mountain grasslands; and Eriophorum vaginatum, whose abundance is typically diminished under grazing. Both species were grown in monocultures and mixtures at different densities in soils taken from adjacent grazed and ungrazed mountain grassland in the Yorkshire Dales, northern England. Nardus stricta performed better (shoot and root biomass) when grown in grazing-conditioned soil, independent of whether or not it grew under inter-specific competition. Eriophorum vaginatum also grew better when planted in soil from the grazed site, but this occurred only when it did not experience inter-specific competition with N. stricta. This indicates that plant-soil feedback for E. vaginatum is dependent on the presence of an inter-specific competitor. A yield density model showed that indirect effects of grazing increased the intensity of intra-specific competition in both species in comparison with ungrazed-conditioned soil. However, indirect effects of grazing on the intensity of inter-specific competition were species-specific favouring N. stricta. We explain these asymmetric grazing-induced effects on competition on the basis of traits of the superior competitor and grazing effects on soil nutrients. Finally, we discuss the relevance of our findings for plant community dynamics in grazed, semi-natural grasslands.

Wet organic waste treatment via hydrothermal processing: A critical review.

There are several recent reviews published in the literature on hydrothermal carbonization, liquefaction and supercritical water gasification of lignocellulosic biomass and algae. The potential of hydrochar, bio-oil or synthesis gas production and applications have also been reviewed individually. The comprehensive review on the hydrothermal treatment of wet wastes (such as municipal solid waste, food waste, sewage sludge, algae) covering carbonization, liquefaction and supercritical water gasification, however, is missing in the literature which formed the basis of the current review paper. The current paper critically reviews the literature around the full spectrum of hydrothermal treatment for wet wastes and establishes a good comparison of the different hydrothermal treatment options for managing wet waste streams. Also, the role of catalysts as well as synthesis of catalysts using hydrothermal treatment of biomass has been critically reviewed. For the first time, efforts have also been made to summarize findings on modelling works as well as techno-economic assessments in the area of hydrothermal treatments of wet wastes. The study concludes with key findings, knowledge gaps and future recommendations to improve the productivity of hydrothermal treatment of wet wastes, helping improve the commercial viability and environmental sustainability.

Long-term effects of sewage sludge-derived biochar on the accumulation and availability of trace elements in a tropical soil.

Thermal treatment by pyrolysis has been proposed as a sustainable alternative to enable the agricultural use of sewage sludge. The solid product obtained via pyrolysis of sewage sludge is called sewage sludge biochar and presents several advantages for its use as a fertilizer or soil conditioner. However, there are concerns about the accumulation and dynamics of trace elements in soil amended with sewage sludge biochar over the years. This study examined the effect of sewage sludge biochar, under field conditions for 5 yr, on the accumulation and availability of trace elements in a tropical soil. For this, 15 t ha-1 of sewage sludge biochar produced at 300 and 500 °C were applied in the first two growing seasons. Application was interrupted from the third to the fifth seasons to assess the residual effect of sewage sludge biochar in the soil. The total and available trace element concentrations were determined. The total contents of trace elements showed the following variation in the soil over the 5 yr (mg kg-1): Cd (16.8-20.0), Co (19.5-21.5), Cr (98.2-125.7), Cu (8.1-17.1), Mn (62.9-85.7), Ni (20.3-35.0), Pb (27.0-52.4), and Zn (20.3-35.8). There was no change in the availability of Cd, Cr, Ni, and Pb over the years. Additionally, a residual effect of the sewage sludge biochar was the increase in availability of trace elements that are considered essential (Cu, Mn, and Zn) and beneficial elements (Co) for plants. Therefore, in relation to contamination by trace elements, the pyrolysis of sewage sludge of domestic origin proved to be an adequate strategy to enable the safe use of this residue in tropical agriculture.

Assessing the potential of sewage sludge-derived biochar as a novel phosphorus fertilizer: Influence of extractant solutions and pyrolysis temperatures.

Sewage sludge-derived biochar (SSB) is a phosphorus (P) source with potential to replace soluble P fertilizers. However, SSB presents a diversity of P compounds, mainly in mineral forms with different degrees of chemical stability. This hinders the prediction of P bioavailability. In the present study we evaluated P solubility and bioavailability using different chemical extractants. Additionally, the relationships between extractable P and physicochemical properties were evaluated for SSB obtained over a wide range of temperatures (200 °C; 300 °C; 500 °C and 600 °C). Available phosphorus content was extracted using 2% citric acid (P-CA), neutral ammonium citrate + water (P-NAC) and Mehlich 1 solution (0.0125 mol L-1 H2SO4 + 0.050 mol L-1 HCl). Physicochemical properties and extractable P were strongly affected by pyrolysis temperature. Higher pyrolysis temperature resulted in increased pH, BET surface area, pore volume, ash, fixed carbon, Ca, Mg and Zn contents, as well as formation of stable Ca minerals (calcite and oxalate). The total P content increased with pyrolysis temperature (≥300 °C). Nevertheless, the solubility of biochar-P in the extractants presented different trends with temperature. The P-NAC content reached a maximum (79% of TP) at 300 °C and then declined at higher temperatures. Only at 600 °C P-CA and available P were affected by the temperature, where the P-CA increased and available P decreased. Therefore, it is recommended that the P solubility in different extractants should be considered when using SSB as an alternative to inorganic P fertilizers.

Sporadic hemiplegic migraine and CREST syndrome.

Hemiplegic migraines are characterised by attacks of migraine with aura accompanied by transient motor weakness. There are both familial and sporadic subtypes, which are now recognised as separate entities by the International Classification of Headache Disorders, edition II (ICHD-II). The sporadic subtype has been associated with other medical conditions, particularly rheumatological diseases. We report the case of a woman with sporadic hemiplegic migraine associated with CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly and telangiectasia). Since there is a close relationship between migraine and Raynaud's phenomenon, it could be speculated that the sporadic hemiplegic migraines in our patient might be secondary to CREST syndrome.

A serial PFASs sorption technique coupled with adapted high volume direct aqueous injection LCMS method.

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous global environmental contaminants, environmentally persistent, mobile, can bioaccumulate and are toxic. Increasing emphasis is placed on the immobilisation and removal of PFAS from contaminated environmental matrices such as: potable water, surface water, groundwater, wastewater, sediments and soils (Dauchy et al., 2017; Cao et al., 2019; Hepburn et al., 2019). To achieve this, development of PFAS sorbents is increasingly undertaken (Du et al., 2014). Sorption studies are used to observe the interaction of sorbent and sorbate, but have two key limitations when undertaking sorption experiments for PFAS (1) the experimental protocol and (2) analytical techniques. The current batch sorption methods approached recommended by OECD Guideline 106 (OECD, 2000) are problematic, firstly, due to large sample numbers and PFAS specific laboratory difficulties, including near ubiquitous background PFAS contamination. Secondly, PFAS analytical techniques currently require solid-phase extraction (SPE) to be employed, which is slow and expensive, prior to instrumental analysis with liquid chromatography-mass spectrometry (LC-MS). A suitable alternative approach is needed to mitigate the drawbacks of current methodologies whilst catering for the high sample throughput required by benchtop trials characterising the sorption behaviour of PFAS - sorbent pairings.•A suitable method for PFAS measurement, overcoming shortcomings of current batch sorption methodologies is presented•The method can be applied to a wide range of sorbents and sorption environment conditions associated with PFAS immobilisation or removal in the environment•The presented method is novel through its high sample throughput, simple approach and minimisation of cross contamination sources.

Evaluation of phytoremediation potential of five Cd (hyper)accumulators in two Cd contaminated soils.

A phytoextraction experiment with five Cd hyperaccumulators (Amaranthus hypochondriacus, Celosia argentea, Solanum nigrum, Phytolacca acinosa and Sedum plumbizincicola) was conducted in two soils with different soil pH (5.93 and 7.43, respectively). Most accumulator plants grew better in the acidic soil, with 19.59-39.63% higher biomass than in the alkaline soil, except for S. plumbizincicola. The potential for a metal-contaminated soil to be cleaned up using phytoremediation is determined by the metal uptake capacity of hyperaccumulator, soil properties, and mutual fitness of plant-soil relationships. In the acidic soil, C. argentea and A. hypochondriacus extracted the highest amount of Cd (1.03 mg pot-1 and 0.92 mg pot-1, respectively). In the alkaline soil, S. plumbizincicola performed best, mainly as a result of high Cd accumulation in plant tissue (541.36 mg kg-1). Most plants achieved leaf Cd bioconcentration factor (BCF) of >10 in the acidic soil, compared to <4 in the alkaline soil. Soil Cd availability was chiefly responsible for such contrasting metal extraction capacity, with 5.02% fraction and 48.50% fraction of total Cd being available in the alkaline and acidic soil, respectively. In the alkaline soil, plants tended to increase rhizosphere soil available Cd mainly through excreting more low molecular weight organic acids, not through changing the soil pH. In the acidic soil, plants slightly decreased soil available Cd. Those species which have high Ca, Zn, Fe uptake capacity extract more Cd from soil, and a positive correlation was found between the concentrations of Cd and Ca, Zn, Fe in leaves. Soil available Ca2+, Mg2+, SO42-, Cl- did not play a key role in Cd uptake by plants. In summary, acidic soil was of higher potential to recover from Cd contamination by phytoextraction, while in the alkaline soil, S. plumbizincicola showed potential for Cd phytoextraction.

Novel Bi2WO6 loaded N-biochar composites with enhanced photocatalytic degradation of rhodamine B and Cr(VI).

In this work we report the production of Bi2WO6 loaded N-biochar composites (BW/N-B) for the removal of rhodamine-B and the reduction of Cr(VI) in water. Biochar was treated with urea to produce a N-modified biochar (N-Biochar), with great conductivity and special 2D sheet platform structure. Materials with different ratios of biochar and urea were produced. These materials were used as platform for supporting Bi2WO6. The characteristics of the as-prepared composites were investigated in detail by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectra (FT-IR), UV-vis diffuse reflectance spectra (UV-DRS), Photoluminescence spectra (PL), Electrochemical Impedance Spectroscopy (EIS) and Mott-Schottky curves. After loading N-Biochar, the band gaps of the as-prepared composites were narrower than those of Bi2WO6, which could improve separation and migration of photogenerated electron-hole pairs of BW/B-N under visible-light excitation, enhancing photocatalytic activity. BW/N1-B (ratio of urea to biochar 2:1 and 1 g/L) exhibited excellent photocatalytic activity for the degradation of 10 mg/L Rhodamine B (RhB) (99.1 %, 45 min) and reduction of Cr(VI) (96.7 %, 30 min) under visible-light irradiation. The results will provide a novel theoretical foundation on the application of biochar for photocatalysis and environmental remediation.