Biochar influences nitrogen and phosphorus dynamics in two texturally different soils

Nitrogen (N) and phosphorus (P) are vital for crop growth. However, most agricultural systems have limited inherent ability to supply N and P to crops. Biochars (BCs) are strongly advocated in agrosystems and are known to improve the availability of N and P in crops through different chemical transformations. Herein, a soil-biochar incubation experiment was carried out to investigate the transformations of N and P in two different textured soils, namely clay loam and loamy sand, on mixing with rice straw biochar (RSB) and acacia wood biochar (ACB) at each level (0, 0.5, and 1.0% w/w). Ammonium N (NH4-N) decreased continuously with the increasing incubation period. The ammonium N content disappeared rapidly in both the soils incubated with biochars compared to the unamended soil. RSB increased the nitrate N (NO3-N) content significantly compared to ACB for the entire study period in both texturally divergent soils. The nitrate N content increased with the enhanced biochar addition rate in clay loam soil until 15 days after incubation; however, it was reduced for the biochar addition rate of 1% compared to 0.5% at 30 and 60 days after incubation in loamy sand soil. With ACB, the net increase in nitrate N content with the biochar addition rate of 1% remained higher than the 0.5% rate for 60 days in clay loam and 30 days in loamy sand soil. The phosphorus content remained consistently higher in both the soils amended with two types of biochars till the completion of the experiment.

An efficient and simple approach to remove Cd(II) in aqueous solution by using rice straw biochar: performance and mechanisms

In recent years, cadmium pollution in water environment has become an environmental problem that could not be ignored. As a porous carbon rich solid material, biochar is an environment-friendly new material because of its ultra-high adsorption capacity and strong chemical stability. In this study, rice straw biochar (RS-Biochar) was successfully prepared at different temperatures for removal of Cd(II) from aqueous solution. Through a series of characterization and adsorption experiments, the adsorption principle of Cd(II) by RS-Biochar was deeply studied. The results showed that RS-Biochar prepared at 600 °C (BioC600) has high specific surface area (232.6 m2/g) and shows high Cd(II) removal rate of 91.23% with the maximum Cd(II) adsorption capacity of 8.62 mg/g. The Langmuir model fit well to describe the adsorption process of Cd(II) on the BioC600. The mechanism analysis showed that hydroxyl and carboxyl groups on the biochar surface were concerned in the removal of Cd(II). The formation of CdCO3 in the adsorption process was also be proven. Importantly, RS-Biochar could be conveniently produced with needed scale, displaying a promising approach for remediating Cd(II)-contaminated water environment and a huge application potential.

Effects of biochar on the manganese enrichment and oxidation by a microalga Scenedesmus quadricauda in the aquatic environment

Microalgae play a significant impact in the biogeochemical cycle of Mn(II) in the aquatic ecosystem. Meanwhile, the inflow of biochar into the water bodies is bound to impact the aquatic organisms. However, the influence of biochar on the manganese transformation in algae-rich water has not drawn much attention. Thus, we studied the effects of rice straw biochar on manganese enrichment and oxidation by a common type of algae in freshwater (Scenedesmus quadricauda). The results showed that Mn(II) was absorbed intracellularly and adsorbed extracellularly by active algal cells. A significant portion of enriched Mn(II) was oxidized to amorphous precipitates MnO2, MnOOH, and Mn2O3. Moreover, the extracellular bound Mn(II) content in the coexistent system of algae and biochar increased compared with the pure Scenedesmus quadricauda system. Nevertheless, the intracellular Mn content was continually lowered as the biochar dose rose from an initial 0.2 to 2.0 g·L-1, suggesting that Mn assimilation of the cell was suppressed. It was calculated that the total enrichment ability of Scenedesmus quadricauda in the algae-biochar coexistent system was 0.31- 15.32 mg Mn/g biomass, more than that in the pure algae system. More importantly, with biochar in the algae system, the amount of generated MnOx increased, and more Mn(II) was oxidized into highly-charged Mn(IV). This was probably because the biochar could relieve the stress of massive Mn(II) on algae and support the MnOx precipitates. In brief, moderate biochar promoted the Mn(II) accumulation by algal cells and its oxidation activity. This study offers deeper insight into the bioconversion of Mn(II) by algae and the potential impact of biochar application to the aquatic system.

Enhancing lead immobilization by biochar: Creation of "surface barrier" via bio-treatment

The long-term effectiveness of heavy metal immobilization is always a concern. This study proposes a completely novel approach to enhance the stability of heavy metals by combined biochar and microbial induced carbonate precipitation (MICP) technology, to create a "surface barrier" of CaCO₃ layer on biochar after lead (Pb²⁺) immobilization. Aqueous sorption studies and chemical and micro-structure tests were used to verify the feasibility. Rice straw biochar (RSB700) was produced at 700 °C, which shows high immobilization capacity of Pb²⁺ (maximum of 118 mg g^-1). But the stable fraction only accounts for 4.8% of the total immobilized Pb²⁺ on biochar. After MICP treatment, the stable fraction of Pb²⁺ significantly increased to a maximum of 92.5%. Microstructural tests confirm the formation of CaCO₃ layer on biochar. The CaCO₃ species are predominantly calcite and vaterite. Higher Ca²⁺ and urea concentrations in cementation solution resulted in higher CaCO₃ yield but lower Ca²⁺ utilization efficiency. The main mechanism of the "surface barrier" to enhance Pb²⁺ stability on biochar was likely the encapsulation effect: it physically blocked the contact between acids and Pb²⁺ on biochar, and chemically buffer the acidic attack from the environment. The performance of the "surface barrier" depends on both the yield of CaCO₃ and their distribution uniformity on biochar's surface. This study shed lights on the potential application of the "surface barrier" strategy combining biochar and MICP technologies for enhanced heavy metal immobilization.

The Mechanism of Cu2+ Sorption by Rice Straw Biochar and Its Sorption-Desorption Capacity to Cu2+ in Soil

Copper (Cu) pollution in soils has received considerable research attention globally, and biochar has been widely used as an adsorbent for soil pollution of Cu. However, most of the studies focused on the adsorption capacity of biochar, the bioavailability of Cu absorbed by biochar remains unclear. In this work, rice straw biomass was pyrolyzed under oxygen-limited conditions at 400°C (BC400) and 600°C (BC600), their apparent structure, group characteristics, and basic physical and chemical properties were determined. The isothermal and kinetics adsorption of Cu by BC400 and BC600 were analyzed. A pot experiment was used to evaluate the passivation of Cu in the soil by biochar and the bioavailability of Cu adsorbed by biochar in the soil. The smooth surfaces of BC400 evolved into more rough surfaces for BC600, and both types of surfaces may give active sorption sites for Cu, according to SEM pictures. FTIR analysis suggested that BC600 is endowed with more condensed aromatic carbon structures and more available polar functional groups. The adsorption processes of Cu²⁺ by biochar were better fitted Langmuir equation and pseudo-second-order kinetic model. The adsorption isotherms showed monolayer adsorption of Cu²⁺ on biochar. The maximum adsorption capacities of BC600 and BC400 on Cu²⁺ were 43.75 and 30.70 mg g^-1, respectively. Moreover, the pot experiment showed that BC400 and BC600 not only have a strong "passivation" effect on Cu in soil but also prevent the release of adsorbed Cu. Overall, more aromatic carbon structure, more polar functional groups, and higher pH are associated with BC600's increased Cu immobilization ability in soil.

Alleviation of microcystin-LR-induced hepatic lipidosis and apoptosis in zebrafish by use of rice straw-derived biochar

Microcystin-LR (MC-LR), mainly released by Microcystis aeruginosa, is posing a tremendous risk to aquatic animals and human health. Meanwhile, biochar (BC) is gradually be used as a sustainable adsorbent to immobilize and remove water pollutants. In our study, we for the first time conducted a full-scale investigation on lipid metabolism and its regulation mechanism of female zebrafish (Danio rerio) exposed to 0, 10 μg/L MC-LR, 100 μg/L BC, and 10 μg/L MC-LR+ 100 μg/L BC. The results indicated that sub-chronic MC-LR exposure induced hepatic lipidosis and apoptosis, including the formation of lipid droplets, significantly elevation of hepatic triglyceride (TG) level as well as significant upregulated expression of lipogenesis-related genes (foxo1a, elovl5, pparγ) and pro-apoptotic genes (bax, casp3). Nevertheless, no significant alteration was observed in the single BC group and the combined exposure group, which indicated that BC may solely functioned as an absorbent agent to lower MC-LR bioaccumulation in zebrafish liver and alleviate MC-LR-induced hepatotoxicity. Our findings revealed that the utilization of rice straw-derived BC can adsorb and immobile MC-LR in the water, subsequently alleviated the MC-LR-induced hepatic lipidosis and apoptosis in female zebrafish. On the basis of fish health, it is urgent to explore the feasibility of using environmentally friendly materials like BC to adsorb pollutants in water.

Accumulation of organic compounds in paddy soils after biochar application is controlled by iron hydroxides

Soil acidity is one of the vital factors that influence organic matter transformation and accumulation. Long-term studies on the mechanisms of biochar's effects on soil organic matter (SOM) accumulation dependent on pH values are lacking. A four-year column experiment was conducted without and with biochar application (11.3 Mg ha^-1 crop^-1) in acid (pH = 5.24) and alkaline (pH = 8.22) soils under paddy rice/wheat annual rotation. To explore organic matter accumulation mechanisms, SOM pools were extracted (physical-chemical fractionation) and their chemical structures were analyzed using advanced solid-state ¹³C nuclear magnetic resonance (¹³C NMR) techniques. Biochar increased the proportion of aromatic carbon (C) in all SOM pools, which led to an increased C content in two soils. The elevated pH after biochar application (∆pH = 1.03) increased Fe (III) oxidation and precipitation, and therefore, stimulated amorphous Fe content in 53-μm pool in the acid soil. This change increased the interaction between organic compounds and Fe (hydr)oxide, which impeded bacteria access to substrates, and in turn, promoted SOM accumulation in the acid soil. Conversely, low Fe (hydr)oxide availability resulted in the decomposition of the labile substrates (di-O-alkyl C, NCH, and OCH) in mobile humic acids via microbial respiration, thereby lowering the effect of SOM sequestration in the alkaline soil. Our study revealed that organic matter accumulation after biochar amendment is not solely dependent on the chemical recalcitrance of biochar, but also is controlled by the transformation of Fe (hydr)oxide in SOM pools.

Efficacy of agricultural waste derived biochar for arsenic removal: Tackling water quality in the Indo-Gangetic plain

Arsenic (As), a geogenic and extremely toxic metalloid can jeopardize terrestrial and aquatic ecosystems through environmental partitioning in natural soil-water compartment, geothermal and marine environments. Although, many researchers have investigated the decontamination potential of different mesoporous engineered bio sorbents for a suite of contaminants, still the removal efficiency of various pyrolyzed agricultural residues needs special attention. In the present study, rice straw derived biochar (RSBC) produced from slow pyrolysis process at 600 °C was used to remove As (V) from aqueous medium. Batch experiments were conducted at room temperature (25 ± 2 °C) under different initial concentrations (10, 30, 50, 100 μg L^-1), adsorbent dosages (0.5-5 μg L^-1), pH (4.0-10.0) and contact times (0-180 min). The adsorption equilibrium was established in 120 min. Adsorption process mainly followed pseudo-second order kinetics (R² ≥ 0.96) and Langmuir isotherm models (R² ≥ 0.99), and the monolayer sorption capacity of 25.6 μg g^-1 for As (V) on RSBC was achieved. Among the different adsorbent dosages and initial concentrations used in the present study, 0.2 g L^-1 (14.8 μg g^-1) and 100 μg L^-1 (13.1 μg g^-1) were selected as an optimum parameters. A comparative analysis of RSBC with other pyrolyzed waste materials revealed that RSBC had comparable adsorption ability (per unit area). These acidic groups are responsible for the electron exchange (electrostatic attraction, ion-exchange, π-π/n-πinteractions) with the anionic arsenate, which facilitates optimum removal (>60%) at 7 < pH < pH_PZC. The future areas of research will focus on decontamination of real wastewater samples containing mixtures of different emerging contaminants and installation of biofilter beds that contains different spent adsorbents/organic substrates (including biochar) for biopurification study in real case scenario.

Application of laccase immobilized rice straw biochar for anthracene degradation

The present study explores the immobilization of ligninolytic enzyme-laccase on the surface of rice straw biochar and evaluates its application for anthracene biodegradation. The rice straw biochar was acid-treated to generate carboxyl functionality on its surface, followed by detailed morphological and chemical characterization. The surface area of functionalized biochar displayed a two-fold increase compared to the untreated biochar. Laccase was immobilized on functionalized biochar, and an immobilization yield of 66% was obtained. The immobilized enzyme demonstrated operational stability up to six cycles while retaining 40% of the initial activity. Laccase immobilization was further investigated by performing adsorption and kinetic studies, which revealed the highest immobilization concentration of 500 U g^-1 at 25 °C. The adsorption followed the Langmuir isotherm model at equilibrium, and the kinetic study confirmed pseudo-second-order kinetics. The equilibrium rate constant (K₂) at 25 °C and 4 °C were 3.6 × 10^-3 g U^-1 min^-1 and 4 × 10^-3 g U^-1 min^-1 respectively for 100 U g^-1 of enzyme loading. This immobilized system was applied for anthracene degradation in the aqueous batch mode, which resulted in complete degradation of 50 mg L^-1 anthracene within 24 h of interaction exposure.

The effects of biochar and AM fungi (Funneliformis mosseae) on bioavailability Cd in a highly contaminated acid soil with different soil phosphorus supplies

Due to the increase of cadmium (Cd)-contaminated land area worldwide, effective measures should be taken to minimize the Cd bioavailability in crops. A study was performed to explore the effectiveness of biochar pyrolyzed from rice straw at 400 °C alone or combined with AM fungi (Funneliformis mosseae) on the corn growth and Cd uptake in corn in Cd-contaminated soil with different levels of phosphorus supplies. The results showed that biochar significantly reduced 66% and 38% of Cd uptake in shoot and root respectively (P < 0.001) attributed to the increase of soil pH and dissolved organic matter. In contrast, AM fungi inoculation of corn plants had little effect on Cd bioavailability due to the AM was suppressed by the highly contaminated acid soil (31.76 mg/kg), and had neither synergistic effect with biochar on decreasing the Cd bioavailability with high or low phosphorus supplies. This study demonstrated that biochar application could be a promising method to immobilize Cd in the contaminated soil to ensure the safety of agro-product while high Cd-contaminated soil would suppress the growth of mycorrhizae, so this remains an open question to be further studied.

Structural and microbial evidence for different soil carbon sequestration after four-year successive biochar application in two different paddy soils

Application of biochar (BC) derived from rice straw has generated increasing interest in long-term storage of soil organic carbon (SOC), however its carbon (C) sequestration potential vary widely among agricultural soils despite the same BC dose used. These discrepancies in the ability of soils to sequester C after BC application are poorly understood. Metabolic quotient (qCO₂) is a reflection of "microbial efficiency" and linked to SOC turnover across ecosystems. Therefore, we investigated the SOC sequestration and qCO₂ in a Yellow River alluvium paddy soil (YP) and a quaternary red clay paddy soil (QP) under rice-wheat annual rotation following 4-year of BC application rate of 11.3 Mg ha^-1 per cropping season. BC application consistently brought 65.3 Mg C ha^-1 into the soils over 4-year experimental period but increased SOC by 57.6 Mg C ha^-1 in YP and 64.5 Mg C ha^-1 in QP. Calculating SOC mass balance showed 11.7% of BC-C losses from YP and only 1.16% from QP. BC application stimulated the G⁺ bacterial, fungi, and actinomycetes by increasing O-alkyl C content in YP, while decreased the same microorganisms by decreasing anomeric C-H content in QP. Importantly, higher clay and amorphous Fe (Fe_o) contents in QP after BC application protected SOC from further decomposition, which in turn decreased microorganisms and resulted in higher SOC sequestration than YP. Our results indicated that soil properties controlled the extent of SOC sequestration after BC application and site-specific soil properties must be carefully considered to maximize long-term SOC sequestration after BC application.

Potential of rice straw biochar, sulfur and ryegrass (Lolium perenne L.) in remediating soil contaminated with nickel through irrigation with untreated wastewater

Background

Untreated wastewater carries substantial amount of heavy metals and causes potential ecological risks to the environment, food quality, soil health and sustainable agriculture.

Methodology

In order to reduce the incidence of nickel (Ni²⁺) contamination in soils, two separate experiments (incubation and greenhouse) were conducted to investigate the potentials of rice straw biochar and elemental sulfur in remediating Ni²⁺ polluted soil due to the irrigation with wastewater. Five incubation periods (1, 7, 14, 28 and 56 days), three biochar doses (0, 10 and 20 g kg⁻¹ of soil) and two doses of sulfur (0 and 5 g kg⁻¹ of soil) were used in the incubation experiment then the Ni²⁺ was extracted from the soil and analyzed, while ryegrass seeds Lolium perenne L. (Poales: Poaceae) and the same doses of biochar and sulfur were used in the greenhouse experiment then the plants Ni²⁺-uptake was determined.

Results

The results of the incubation experiment revealed a dose-dependent reduction of DTPA-extractable Ni²⁺ in soils treated with biochar. Increasing the biochar dose from 0 g kg⁻¹ (control) to 10 or 20 g kg⁻¹ (treatments) decreased the DTPA-extractable Ni²⁺ from the soil by 24.6% and 39.4%, respectively. The application of sulfur increased the Ni²⁺-uptake by ryegrass plant which was used as hyper-accumulator of heavy metals in the green house experiment. However, the biochar decreased the Ni²⁺-uptake by the plant therefore it can be used as animal feed.

Conclusions

These results indicate that the biochar and sulfur could be applied separately to remediate the Ni²⁺-contaminated soils either through adsorbing the Ni²⁺ by biochar or increasing the Ni²⁺ availability by sulfur to be easily uptaken by the hyper-accumulator plant, and hence promote a sustainable agriculture.

Remediation of cadmium and lead polluted soil using thiol-modified biochar

Thiol-modified rice straw biochar (RS) was prepared by an esterification reaction with β-mercaptoethanol and used for the remediation of Cd and Pb polluted soils. Modified biochar was characterized through elemental analysis, BET analysis, FE-SEM, FT-IR and XPS. These analytical results revealed that thiol groups were successfully grafted onto the surface of the biochar and were involved in metal ion complexation. Batch sorption experiments indicated that Cd²⁺ and Pb²⁺ sorption onto RS described well by a pseudo second order kinetic model and a Langmuir isotherm. The maximum adsorption capacities for Cd²⁺ and Pb²⁺, in the single-metal systems, were 45.1 and 61.4 mg g^-1, respectively. In the binary-metal systems, RS selectively adsorbed Cd²⁺ over Pb²⁺. Cd²⁺ and Pb²⁺ were removed mainly through surface complexation. In the soil incubation experiments (28 days), RS reduced the available Cd by 34.8-39.2 %; while, RS reduced the available Pb by 8.6 %-11.1 %. This research demonstrates RS as a potentially effective amendment for the remediation of heavy metal polluted soils.

Potassium-iron rice straw biochar composite for sorption of nitrate, phosphate, and ammonium ions in soil for timely and controlled release

In this study, potassium-iron rice straw biochar composite (KRSB) was produced and compared with rice straw biochar (RSB) for the sorption of NO₃^-, PO₄^3-, and NH₄⁺ in aqueous medium and soil column. RSB was produced by pyrolyzing rice straw at 400 and 600 °C in a slow pyrolysis unit. KRSB was produced through chemical and hydrothermal treatments of rice straw biochar produced at 400 and 600 °C. Batch experiment results indicate that the KRSB showed better sorption capacity for nitrate, phosphate, and ammonium ions compared to pristine RSB. The sorption isotherms of all three nutrients (NO₃^-, PO₄^3-, and NH₄⁺) were better-explained by the Langmuir-Freundlich isotherm model. The column leaching experiment showed that the KRSB loaded soil reached maximum sorption capacity for PO₄^3- and NO₃^- within six and eight days, respectively but, it showed poor sorption capacity for NH₄⁺. The soil fertility index in the 400 and 600 KRSB amended soils were significantly increased by 50.68 and 52.85%, respectively compared to the control. Results indicated that KRSB could be utilized in the soil in two ways: first, to keep the nutrients attached to its surface and second, to release the nutrients in a phased and timely manner to increase their availability for plants.

Rice straw, biochar and calcite incorporation enhance nickel (Ni) immobilization in contaminated soil and Ni removal capacity

Although rice straw (RS), biochar (BI) and calcite (CC) have proved to be effective immobilizing agents in acidic contaminated soil, we lack up-to-date scientific data regarding nickel (Ni) fractionation in soil and removal capacity in water. Therefore, an incubation study was undertaken to investigate the efficacy of RS, BI and CC with three application rates (0, 1 and 2%) of RS, BI and CC on the immobilization of Ni in polluted soil. Various extraction techniques were carried out: sequential extraction procedure, the European Community Bureau of Reference (BCR), extraction with CaCl_2, and the toxicity characteristics leaching procedure (TCLP) techniques. Additionally, Ni sorption behavior was determined using the Langmuir and Freundlich isotherms. Results showed that adding all amendments into Ni contaminated acidic soil, enhanced soil pH, reduced the exchangeable fraction of Ni by 48%-55%, 59%-71% and 58%-66.3%, when RS, BI and CC were applied at 1% and 2% rates, respectively. According to the Langmuir adsorption isotherm results, the maximum sorption capacity was recorded using 2747 mg kg^-1 in 2% CC amended soil. However, biochar exhibited the maximum Ni sorption capacity (13348 mg kg^-1), due to its porous structure, larger surface area, and having more functional groups. Furthermore, the results of FTIR, SEM and zeta potential techniques confirmed that the immobilization and biochar's capacity to remove Ni were more effective when compared to other immobilizing agents.

Effect of amendment of biochar supplemented with Si on Cd mobility and rice uptake over three rice growing seasons in an acidic Cd-tainted paddy from central South China

To examine the effect of rice straw biochar and the synergism with silicon on Cd immobilization, a Cd-contaminated acidic sandy loam paddy, polluted from emissions from industrial activity, was chosen in central South China. A field trial was conducted over three rice growing seasons during 2016-2017. Rice straw biochar (BR), produced by the pyrolysis of rice straw pellets at 450 °C, was amended at 10 t/ha (BR1), 20 t/ha (BR2), and supplemented with 0.75 t/ha sodium silicate (SS) at 10 t/ha, (BR1 + SS) and 20 t/ha (BR2 + SS), compared to the control without biochar and sodium silicate (BR0). BR supplemented with Si enhanced Cd soil immobilization and decreased Cd accumulation in rice plant within three rice seasons. Compared to BR0, BR + SS reduced Cd concentrations in grains by 19.5-73.7%, higher than that of 8.6-50.2% following BR. Cd bio-concentration factor of the root was reduced by an average of 54.6% from BR + SS and by 19.0% from BR, compared to BR0 in last two rice seasons. BR + SS significantly increased soil pH and available Si, and soil CaCl₂-Cd was negatively related to soil available Si (p < 0.05). The synergistic effect of BR and Si induced liming effect and co-precipitation of Cd with Si compounds during the aging process of biochar. Thus, we suggest that an alkaline silicon supplementation is used as an amendment to BR, which could be used as a strategic approach for tackling Cd contamination in South China rice paddies.

Biochar mitigates the N2O emissions from acidic soil by increasing the nosZ and nirK gene abundance and soil pH

Nitrous oxide (N₂O) is a pervasive greenhouse gas, and soil management practices greatly affect its release into the atmosphere. Soil pH management (particularly increasing the pH) using biochar can seriously affect soil N₂O emissions. The current incubation experiment was conducted to explore the response of N₂O emissions from acidic soils using various doses of biochar. Soil with a pH of 5.48 was treated with rice straw biochar at different doses (0%, 1% and 2%) and incubated with 60% water-filled pore spaces (WFPS). The experiment was conducted in a completely randomized design (CRD) with three replications. The soil N₂O emissions, pH, NH₄⁺-N, NO₃^--N, microbial biomass carbon (MBC), and nosZ and nirK gene abundance were determined at various intervals throughout the study. The biochar application (2%) increased the soil pH (from 5.48 to 6.11), triggered the transformation of nitrogen, and augmented the abundance of nosZ and nirK genes. Higher magnitudes of cumulative soil N₂O emissions (48.60 μg kg^-1) were noted in the control (no biochar) compared to 1% (28.10 μg kg^-1) and 2% (14.50 μg kg^-1) biochar application. The 2% biochar application more effectively decreased the soil N₂O emissions, mainly because of the increased nosZ and nirK gene abundance at higher soil pH levels. The findings suggest that the amelioration of acidic soil with rice straw biochar can considerably control soil N₂O emissions by elevating the soil pH and the abundance of nosZ and nirK genes.

Transformation of heavy metals and dewaterability of waste activated sludge during the conditioning by Fe2+-activated peroxymonosulfate oxidation combined with rice straw biochar as skeleton builder

This work investigated the improvement performances and mechanisms of waste activated sludge (WAS) dewaterability and the transformation behavior of heavy metals (HMs, including Cu, Zn, Pb, Cd and Cr) by jointly conditioning of Fe²⁺-activated peroxymonosulfate (PMS) oxidation and rice straw biochar (RS-BC). Experimental results showed that at original WAS pH of 6.5, the joint conditioning was the most effective when PMS dosage was 0.6 mmol·(g-volatile solids (VS))^-1, Fe²⁺/PMS molar ratio was 0.6 and RS-BC dosage was 120 mg·(g-VS)^-1. Under this condition, the lowest moisture content (MC) was 38.5% and the standardized-capillary suction time (SCST) was as high as 8.74. For the improvement mechanism, Fe²⁺-activated PMS oxidation can significantly disintegrate the extracellular polymeric substances (EPS) composing WAS to release EPS-bound water, and the RS-BC was helpful to form porous structures to improve WAS compressibility, facilitating the subsequent dewatering. In addition, Fe²⁺-activated PMS oxidation can obviously improve the solubilization and reduce the leaching toxicity of Cu, Zn, Pb, Cd and Cr, which was further enhanced by RS-BC. Therefore, the joint application of Fe²⁺-activated PMS oxidation and RS-BC can be a feasible way to improve WAS dewaterability and reduce HMs risk during WAS dewatering.

The effect of two different biochars on remediation of Cd-contaminated soil and Cd uptake by Lolium perenne

Biochar can be widely used to reduce the bioavailability of heavy metals in contaminated soil because of its adsorption capacity. But there are few studies about the effects of biochar on cadmium uptake by plants in soil contaminated with cadmium (Cd). Therefore, an incubation experiment was used to investigate the effects of rice straw biochar (RSBC) and coconut shell biochar (CSBC) on Cd immobilization in contaminated soil and, subsequently, Cd uptake by Lolium perenne. The results showed that the microbial counts and soil enzyme activities were significantly increased by biochar in Cd-contaminated soil, which were consistent with the decrease of the bioavailability of Cd by biochar. HOAc-extractable Cd in soil decreased by 11.3-22.6% in treatments with 5% RSBC and by 7.2-17.1% in treatments with 5% CSBC, respectively, compared to controls. The content of available Cd in biochar treatments was significantly lower than in controls, and these differences were more obvious in treatment groups with 5% biochar. The Cd concentration in L. perenne reduced by 4.47-26.13% with biochar. However, the biomass of L. perenne increased by 1.35-2.38 times after adding biochar amendments. So, Cd uptake by whole L. perenne was augmented by RSBC and CSBC. Accordingly, this work suggests that RSBC and CSBC have the potential to be used as a useful aided phytoremediation technology in Cd-contaminated soil.

Assessing the viability of soil successive straw biochar amendment based on a five-year column trial with six different soils: Views from crop production, carbon sequestration and net ecosystem economic benefits

Converting straw to biochar (BC) followed by successive application to soil has been increasingly suggested as a multi-win approach for soil fertility improvement, carbon (C) sequestration and efficient disposal of straw residues in intensive cropping agroecosystems. However, different soil types response differently in terms of crop growth and non-CO₂ greenhouse gas (GHG) emissions after BC application. Furthermore, few studies have comprehensively evaluated the net global warming potential (GWP) and net ecosystem economic benefits (NEEB) after long-term BC incorporation across representative soil types in China. A five-year outdoor column experiment was conducted using three rice-wheat rotated paddy soils and three millet-wheat rotated upland soils developed from different parent materials. Rice straw BC application rates of 0, 2.25 and 11.3 Mg ha^-1 were used in each crop season with identical doses of NPK fertilizers. Compared with the no BC controls, BC significantly boosted crop growth, enhanced C sequestration, and decreased cumulative N₂O and CH₄ emissions in all six soils over five rotation cycles. The response of the upland soils to BC was better in terms of crop growth and N₂O mitigation, whereas the soil organic carbon (SOC) increment and CH₄ mitigation were less effective compared with the paddy soils. Net GWP decreased 0.6-19 fold after BC application; however, given the low trade price of CO₂ (0.21 × 10³ CNY Mg^-1), only a small contribution was made in terms of C costs to the NEEB. The BC-induced NEEB was mainly dependent on grain yield gains and BC costs. These findings highlight that widespread adoption of successive straw BC application to farmland requires an increase in crop yield and substantial lowering of the BC cost regardless of the soil type. From the standpoints of agronomics, environment and economics, acid upland soil shows most potential in terms of BC application.

Effect of different particle-size biochar on methane emissions during pig manure/wheat straw aerobic composting: Insights into pore characterization and microbial mechanisms

This study explored the effects of different particle sizes of rice straw biochar (RSB) on the methane emissions of pig manure/wheat straw aerobic composting experiments to provide a theoretical suggestion for biochar application. The experiments were conducted with a control group, powder (<1 mm) group, and granular (4 mm-1 cm) group. Methane emissions increased by 56.84% in the powder group but decreased by 22.15% in the granular group during the aerobic composting. Methane was generated by methanogens and methanotrophs in the specific anaerobic micro-environment characterized by X-ray micro-computed tomography (micro-CT). The porosity of initial composting samples increased by 4.02% in the granular group but decreased by 3.88% in the powder group. RSB additives typically reduced the mcrA/pmoA ratio and increased the diversity of Bacteria and Archaea. Conclusively, granular biochar benefits to aerobic composting to alleviate the CH₄ emissions.

Effect of biochar on alleviation of cadmium toxicity in wheat (Triticum aestivum L.) grown on Cd-contaminated saline soil

Soil degradation by salinity and accumulation of trace elements such as cadmium (Cd) in the soils are expected to become one of the most critical issues hindering sustainable production and feeding the increasing population. Biochar (BC) has been known to protect the plants against soil salinity and heavy metal stress. A soil culture study was performed to evaluate the effect of BC on wheat (Triticum aestivum L.) growth, biomass, and reducing Cd and sodium (Na) uptake grown in Cd-contaminated saline soil under ambient conditions. Soil salinity decreased the plant growth, biomass, grain yield, chlorophyll contents, and gas exchange parameters and caused oxidative stress in plants compared with Cd stress alone. Salt stress increased Cd and Na uptake and reduced the potassium (K) and zinc (Zn) uptake by plants. AB-DTPA-extractable Cd and soil electrical conductivity (ECe) increased under salt stress compared to the soil without NaCl stress. Biochar application improved the plant growth and reduced the Cd and Na uptake except in plants treated with higher BC and salt stress (5.0% BC + 50 mM NaCl). Biochar application reduced the oxidative stress in plants and modified the antioxidant enzyme activities, and reduced the bioavailable Cd under salt stress. The positive effects of BC under lower salt stress while the negative effects of BC under higher BC and salt levels indicated that BC doses should be used with great care in higher soil salinity levels simultaneously contaminated with Cd to avoid the negative effects of BC on growth and metal uptake.

Insights into the mechanism of persulfate activated by rice straw biochar for the degradation of aniline

This study investigated the degradation of aniline by persulfate (PS) activated with rice straw biochar (RSBC). The results demonstrate that aniline could be rapidly decomposed by a combination of PS and RSBC. The degradation efficiency of aniline was up to 94.1% within 80 min, and meanwhile 52% of the total organic carbon was removed. In the initial pH range of 3-9, aniline could be efficiently removed. Reactive species resulting in the rapid degradation of aniline were investigated via radical and hole quenching experiments with various scavengers (e.g., methanol, tert-butyl alcohol and EDTA) and electron paramagnetic resonance technique. Based on the analysis and observation made here, it is speculated that the predominant reactive species responsible for the degradation of aniline may be holes instead of SO₄^- and OH radicals. It is concluded that RSBC could be used as an effective catalyst to activate PS for the degradation of aniline.

Biochar application increased the growth and yield and reduced cadmium in drought stressed wheat grown in an aged contaminated soil

Cadmium (Cd) and drought stress in plants is a worldwide problem, whereas little is known about the effect of biochar (BC) under combined Cd and drought stress. The current study was conducted to determine the impact of BC on Cd uptake in wheat sown in Cd-contaminated soil under drought stress. Wheat was grown in a soil after incubating the soil for 15 days with three levels of BC (0%, 3.0% and 5.0% w/w). Three levels of drought stress (well-watered, mild drought and severe drought containing 70%, 50%, and 35% of soil water holding capacity respectively) were applied to 45-d-old wheat plants. Drought stress decreased plant height, spike length, chlorophyll contents, gas exchange parameters, root and shoot dry biomasses and grain yields. Drought stress also caused oxidative stress and decreased the antioxidant enzymes activities whereas increased the Cd concentration in plants. Biochar increased morphological and physiological parameters of wheat under combined drought and Cd stress and reduced the oxidative stress and Cd contents and increased antioxidant enzymes activities. The decrease in Cd concentration with BC application in drought-stressed plant might be attributed to BC-induced increase in crop biomass production and reduction in oxidative stress. These results indicate that BC could be used as an amendment in metal contaminated soil for improving wheat growth and reducing Cd concentrations under semiarid conditions.

Effect of biochar on cadmium bioavailability and uptake in wheat (Triticum aestivum L.) grown in a soil with aged contamination

Cadmium (Cd) is a well-known and widespread toxic heavy metal while the effects of biochar (BC) on Cd bioavailability and toxicity in wheat, especially in soils with aged contamination are largely unknown. In the present study, the effect of rice straw BC on Cd immobilization in soil and uptake by wheat in an agricultural contaminated-soil was investigated. Different levels of rice straw BC (0%, 1.5%, 3.0% and 5% w/w) were incorporated into the soil and incubated for two weeks. After this, wheat plants were grown in the amended soil until maturity. The results show that the BC treatments increased the soil and soil solution pH and silicon contents in the plant tissues and in the soil solution while decreased the bioavailable Cd in soil. The BC application increased the plant-height, spike-length, shoot and root dry mass and grain yield in a dose additive manner when compared with control treatment. As compared to control, BC application increased the photosynthetic pigments and gas exchange parameters in leaves. Biochar treatments decreased the oxidative stress while increased the activities of antioxidant enzymes in shoots compared to the control. The BC treatments decreased the Cd and Ni while increased Zn and Mn concentrations in shoots, roots, and grains of wheat compared to the control. As compared to the control, Cd concentration in wheat grains decreased by 26%, 42%, and 57% after the application of 1.5%, 3.0%, and 5.0% BC respectively. Overall, the application of rice straw BC might be effective in immobilization of metal in the soil and reducing its uptake and translocation to grains.