Sludge Biochar Research Articles

Enhanced sludge dewatering by PDMDAAC coupled with Fenton-like reaction initiated by Fe-rich sludge biochar with in-situ generation of H2O2: Fe/C structure as an electron shuttle

Fenton-like reaction has been used to enhance sludge dewaterability effectively. However, the unstable characteristic, ignitability, and corrosivity of H2O2 make it difficult for application. To address this challenge, a novel process of in-situ H2O2 generation by Fe-rich sludge biochar under aeration condition combined with poly-diallyldimethylammonium chloride (PDMDAAC) was proposed to enhance sludge dewaterability. Under optimized conditions, the capillary suction time and specific resistance to filterability of the conditioned sludge were reduced significantly compared with raw sludge (54.2 vs. 351 s, 0.249×1013 vs. 2.68×1013 m/kg, respectively). The carbon skeleton in Fe-rich sludge biochar can reduce the charge transfer impedance between Fe and O2, promoting in-situ generation of H2O2. The degradation of hydrophilic organics in extracellular polymeric substances of sludge floc and the PDMDAAC coagulation effect promoted the release of bound water. This study provides a strategy to enhance sludge dewaterability by Fenton-like reaction initiated by Fe-rich biochar with no H2O2 addition.

Using a combination of different conditioners to promote dewatering of digested sludge: Rheological characteristics

The dewatering capacity of sludge is a key factor in sludge disposal and reuse. In this study, the effects of conditioning with three conditioners (polyacrylamide (PAM), poly aluminum sulfate (PAS), and sludge biochar (SAC)) and their combined conditioning effect at different doses on the dewatering performance of digested sludge were systematically investigated. The mechanism of change in dewatering performance was analyzed based on rheological principles. A Box‒Behnken multifactor experiment based on the response surface method (RSM) was also used to establish a quadratic multiple prediction model for the solids content of filter cake to obtain the optimal ratio of coupled treatment. The results showed for individual conditioner use, PAM with a dose of 3‰ had the best effect on sludge dewatering, and the dewatering effect of the combined conditioner sludge treatment was better than that of the sludge treated with individual conditioners, with the solids content of the filter cake exceeding 35%. The Herschel-Bulkley model was used to fit the rheological data, and the results showed that the yield stress decreased with increasing PAM dose and gradually increased with increasing PAS and SAC doses. The thixotropy of sludge after SAC conditioning was evident compared to that after PAM and PAS conditioning. The yield stress of sludge decreased and flowability deteriorated after combined conditioning. There was a linear relationship between the dewatering performance of conditioned sludge and thixotropy and yield stress, which indicated the feasibility of using rheological indices to evaluate changes in sludge dewatering performance.

Synthesis of modified sludge biochar for flue gas denitration: Biochar properties, synergistic efficiency and mechanism

Biochar has been recommended as a carbon material with high porosity, rich functional groups, and low cost for flue gas denitration. In this study, five different biochar materials, including original sludge biochar (SC), the KOH-impregnated biochar (SCK), the biochar of SCK washing by ultra-water (SCK-W), the H2SO4-impregnated biochar (SCS), and the biochar of SCS washing by ultra-water (SCS-W), prepared using a one-step activation method were applied to remove NO from flue gases, acting as both reductants and catalysts. The results indicate that the SCK-700 can lead to the highest NO conversion of 100% at 325 °C, and can suppress the acidic gas generation compared with SCS. The order of reduction capacity at 300–400 °C was SCK-700 > SCK-W-700 > SC-700 > SCS-700 > SCS-W-700. Furthermore, the kinetics indicated that adsorption capacity enhanced with the rise in temperature, and that SCK-700 had the largest adsorption capacity, reaching 337.15 mg/g at 400 °C.

Systematic assessment of the ecotoxicological effects and mechanisms of biochar-derived dissolved organic matter (DOM) on the earthworm Eisenia fetida

Biochar-derived dissolved organic matter (DOM) contains toxic substances that are first released into the soil after biochar application. However, the ecological risks of biochar-derived DOM on soil invertebrate earthworms are unclear. Therefore, this study investigated the ecological risks and toxic mechanisms of sewage sludge biochar (SSB)-derived DOM on the earthworm Eisenia fetida (E. fetida) via microcosm experiments. DOM exposure induced earthworm death, growth inhibition, and cocoon decline. Moreover, DOM, especially the 10% DOM300 (derived from SSB prepared at 300 °C) treatments, disrupted the antioxidant defense response and lysosomal stability in earthworms. Integrated biomarker response v2 (IBRv2) analysis was performed to assess the comprehensive toxicity of DOM in E. fetida, and the results revealed that DOM300 might exert more hazardous effects on earthworms than DOM500 (prepared at 500 °C) and DOM700 (prepared at 700 °C), as revealed by increases in the IBRv2 value of 3.48–18.21. Transcriptome analysis revealed that 10% DOM300 exposure significantly disrupted carbohydrate and protein digestion and absorption and induced endocrine disorder. Interestingly, 10% DOM300 exposure also significantly downregulated the expression of genes involved in signaling pathways, e.g., the P13K-AKT, cGMP-PKG, and ErbB signaling pathways, which are related to cell growth, survival, and metabolism, suggesting that DOM300 might induce neurotoxicity in E. fetida. Altogether, these results may contribute to a better understanding of the toxicity and defense mechanisms of biochar-derived DOM on earthworms, especially during long-term applications, and thus provide guidelines for using biochar as a soil amendment.

Carbon Loss During Preparation and Aging of Sludge Livestock Manure Biochars

Biochar has high carbon stability and is a good carbon sequestration material. Sludge biochar is rich in inorganic minerals, which would provide enrichment in the preparation process of pyrolysis, affecting its carbon sequestration capacity in practice. In this study, municipal sludge biochar (SZB), pharmaceutical sludge biochar (YCB), and chicken manure biochar (JFB) were prepared under the pyrolysis process at 500, 600, and 700℃, respectively, and their aging process in soil for 70-100 years was simulated. The physicochemical properties and the carbon loss calculation of the biochars were determined using elemental analysis, FTIR, XRF, ICP, and XRD. The results demonstrated that the type and mass fraction of endogenous minerals in the biochars determined their carbon loss during pyrolysis. Ca and Mg were the main carbon-protecting minerals, whereas Fe may have reduced the carbon stability of the sludge biochars and therefore increased the carbon loss. For the aging process, the stability of the endogenous carbon in the biochars played a major role in its carbon loss, whereas the endogenous minerals played a supporting role. These findings elucidated the effect of the stability of endogenous carbon and the composition of mineral components on the carbon loss of biochars, which may provide references for soil carbon sequestration using sludge and chicken manure biochar.

Precise preparation of CoOx@KSB catalysts by atomic layer deposition for peroxymonosulfate activation and landfill leachate treatment

The construction of desired active sites is critical for enhanced activity in heterogeneous peroxymonosulfate (PMS) systems. In view of the shortcomings of the current construction methods, such as low precision and harsh conditions, CoOx@KSB catalysts were precisely prepared at the atomic level using atomic layer deposition in this study. Using alkali-modified sludge biochar (KSB) as a feedstock, two different deposition processes were proposed to investigate the preparation pattern on the treatment efficiency of landfill leachate. Results showed that the small-cycle layer-by-layer deposition (B process) not only preserved the original N sites of the catalyst after 150 depositions, but also obtained satisfactory Co2+. Under the optimal experimental conditions, KSB-B150 degraded more than 90% of SMX within 120 ​min. After 8 ​h of continuous operation in the packed column reactor, the COD concentration of the effluent landfill leachate was still below 100 ​mg/L, and the biotoxicity of the effluent was reduced to 0.41 times of the original. The Co2+, OV and graphite N sites could generate SO4•− and •OH, which played dominant roles in SMX degradation. This study provides a new strategy for constructing active sites in heterogeneous PMS system. It is beneficial to promote the application of heterogeneous advanced oxidation technology in landfill leachate treatment.

Applicability of magnetic biochar derived from Fe-enriched sewage sludge for chromate removal from aqueous solution

In this work, inexpensive biochar derived from different feedstock was synthesized, characterized, and tested for Cr(VI) removal from synthetic wastewater. The physical properties of the sludge-based magnetic biochars (SSB) were analyzed using FT-IR, XRD, BET surface area, SEM-EDS, and XPS techniques. The effects of pyrolysis temperature (300–900 ℃), initial Cr(VI) concentration (2–30 mg/L), rotation speed (50–200 rpm), pH (3–11), and co-ions (Na+, Ca2+, Mg2+, K+, Cl−, HCO3− and SO42−) on Cr(VI) removal by the SSB were determined in batch modes. It was found that the SSB had the highest Cr(VI) removal (43.7%), as compared to the other feedstock-derived biochars (p ≤ 0.05; Anova test). The characterization data indicated that with an increasing pyrolysis temperature from 300 to 900℃, the surface area, pore volume, and pore size decreased, while the Fe3O4 on SSB was gradually reduced to α-Fe0. With respect to Cr(VI) removal, under the optimized conditions of 900℃ of pyrolysis temperature, 2 mg/L of Cr(VI) concentration, 200 rpm of agitation speed, and pH 6.8, a complete Cr(VI) removal could be attained by the SSB900. Its treated effluents could comply with the required Cr(VI) discharge limit of <0.01 mg/L (GB3838-2002) mandated by local legislation. Therefore, further treatment was not required, avoiding additional cost. Coexisting ions experiments showed that all of them inhibited the Cr(VI) removal by the adsorbent after 1 h of reaction. The Cr(VI) removal followed the pseudo-second-order kinetics and the Langmuir isotherm model. The removal mechanism was based on the reduction of Cr(VI) by nZVI on the SSB900 and the Fe leakage might have facilitated the Cr(VI) removal. Overall, iron-enriched sewage sludge biochar is promising and cost-effective for treatment of low-level Cr(VI)-contaminated wastewater.

Removal of Cr(VI) ions from wastewater by Fe3O4-loaded porous sludge biochar.

In this work, porous sludge biochar (PSBC) was prepared by molten salt-assisted pyrolysis of municipal sludge, and PSBC loaded with Fe3O4 (Fe3O4@PSBC) was synthesized by chemical precipitation. The effects of pH (2.0-10.0), sorbent dosage (0.1-2 g/L), coexisting ions (Ca2+, Mg2+, Cu2+, Pb2+, Cl-, SiO32-, NO3-, CO32-, SO42-, and PO43-), adsorption temperature (288, 298, and 308 K), initial Cr(VI) ion concentrations (50-150 mg/L), and adsorption time (5-300 min) on the removal of Cr(VI) ions by the sorbent were investigated. The mechanism of the removal of Cr(VI) ions was characterized by scanning electron microscope (SEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The result showed that the removal of Cr(VI) ions on PSBC and Fe3O4@PSBC had a strong dependence on the pH of solution. The maximum adsorption capacity of Cr(VI) ions by PSBC and Fe3O4@PSBC was 162 and 209 mg/g, respectively, at a dosage of 0.4 g/L, pH of 3, and temperature of 298 K. The removal process of Cr(VI) ions could be fitted by the Langmuir isotherm model and pseudo-second-order kinetic model. The breakthrough curves were in good agreement with the theoretical values of the Thomas model. The mechanism of the removal of Cr(VI) ions by Fe3O4@PSBC mainly contain complexation, reduction, and electrostatic interaction. This work proposes a new removal material for Cr(VI)-containing wastewater.

Optimization of Mixed-Based Biochar Preparation Process and Adsorption Performance of Lead and Cadmium

Irreversible pollution by heavy metals such as lead (Pb) and cadmium (Cd) adversely affects the ecological environment and human health. Due to its high adsorption, microporosity, and specific surface area, biochar possesses excellent potential for use in heavy metal pollution remediation. The preparation of mixed-based biochar from sludge and cotton stalk can solve the problems inherent to pure sludge biochar, such as undeveloped pore structure and a small specific surface area, while resourcefully utilizing both waste biomass types. This study investigated the adsorption capacity for Pb2+ and Cd2+ of mixed-based biochar prepared at different pyrolysis temperatures, different pyrolysis residence times, and different cotton stalks percentages. Response surface experiments revealed the optimum process conditions for preparing mixed-based biochar, which included a pyrolysis temperature of 638 °C, a pyrolysis residence time of 86 min, and an addition ratio of 50% for cotton stalks. The isothermal adsorption experiments revealed that the maximum adsorption capacities of mixed-based biochar for Pb2+ and Cd2+ were 111.11 and 86.21 mg/g, respectively. Our findings suggest the co-pyrolysis of sludge and cotton stalk as a green and sustainable method for safely disposing of Pb and Cd.

Effects of biochar on earthworms during remediation of potentially toxic elements contaminated soils

With the widespread use of biochar for soil remediation and improvement, its effects on soil organisms are receiving increased attention. The impacts of biochar on earthworms are still poorly understood. This study aimed to assess the potential ecotoxicity of rice husk biochar (RB) and sludge biochar (SB) on earthworms during potentially toxic elements (PTEs) contaminated soil remediation. The results showed that high rates of RB addition (5% and 10%) caused earthworm mortality, but SB addition did not affect earthworm survival. When added at non-lethal rates (3%), RB and SB addition did not affect survival, weight loss, and PTEs accumulation of earthworms, while resulting in apparent avoidance behavior and oxidative stress response. Among them, RB addition was more likely to cause avoidance behavior, while SB addition had a more pronounced stress effect on earthworms. Additionally, the bacterial communities in the earthworm gut were more sensitive to biochar addition than those in soil. SB addition had a greater impact on earthworm gut bacterial communities than RB addition. The addition of RB and SB increased the abundance of Bacillaceae while decreasing the abundance of Rhizobiaceae in the earthworm gut. This change in the composition of bacterial community may impact the nitrogen cycle and organic matter degradation functions of earthworms. The study suggests that RB and SB may have different effects on earthworms during PTEs-contaminated soil remediation, depending on their properties. It will assist us to understand the potential ecotoxicity of biochar and provide several guidance for its safe application.

Assessing the suitability of municipal sewage sludge and coconut bran as breeding medium for Oryza sativa L. seedlings and developing a standardized substrate

The utilization of organic solid waste (OSW) for preparing standardized seedling substrates is a main challenge due to its temporal and spatial variability. This study aims to form models based on data from the literature and validate them through experiments to explore a standardized seedling substrate. The typical OSW in Hainan Province, including municipal sewage sludge (MSS), coconut bran (CB), seaweed mud (SM), and municipal sewage sludge biochar (MSSB), was used as raw material. A series of six mixing ratios was tested, namely: T1 (0% MSS: 90% CB), T2 (10% MSS: 80% CB), T3 (30% MSS: 60% CB), T4 (50% MSS: 40% CB), T5 (70% MSS: 20% CB), and T6 (90% MSS: 0% CB). SM and MSSB were added as amendment materials at 5% (w/w) for each treatment. The physicochemical properties of substrates, agronomic traits of rice seedlings and microbial diversity were analyzed. The results showed that the four kinds of OSW played an active role in providing rich sources of nutrients. The dry weight of the above-ground part was 2.98 times greater in T3 than that of the commercial substrate. Furthermore, the microbial analysis showed a higher abundance of Actinobacteria in T3, representing the stability of the composted products. Finally, the successful fitting of the results with the linear regression models could establish relationship equations between the physicochemical properties of the substrate and the growth characteristics of seedlings. The relevant parameters suitable for the growth of rice seedlings were as follows: pH (6.46–7.01), EC (less than 2.12 mS cm−1), DD (0.13–0.16 g cm−3), and TPS (65.68–82.73%). This study proposed relevant parameters and models for standardization of seedling substrate, which would contribute to ensuring the quality of seedlings and OSW resource utilization.

Mitigation of Cd(II) contamination in aqueous solution and soil by multifunctional hydroxyapatite/sludge biochar composite.

Biochar with well-developed pore structure is an ideal carrier for easily agglomerated hydroxyapatite (HAP). Hence, a novel multifunctional hydroxyapatite/sludge biochar composite (HAP@BC) was synthesized by chemical precipitation method and used for mitigating Cd(II) contamination form aqueous solution/soil. Compared to sludge biochar (BC), HAP@BC exhibited rougher and more porous surface. Meanwhile, the HAP was dispersed on the sludge biochar surface, which reduced the agglomeration of HAP. The adsorption performance of HAP@BC on Cd(II) was better than that of BC under the influence of different single-factor batch adsorption experiments. Moreover, the Cd(II) adsorption behavior by BC and HAP@BC was uniform monolayer adsorption, and this reaction process was endothermic and spontaneous. The Cd(II) maximum adsorption capacities of BC and HAP@BC were 79.96 and 190.72mg/g at 298K, respectively. Moreover, the Cd(II) adsorption mechanism on BC and HAP@BC included complexation, ion exchange, dissolution-precipitation and Cd(II)-π interaction. According to the semi-quantitative analysis, ion exchange was the main mechanism for Cd(II) removal by HAP@BC. Notably, HAP played a role in the Cd(II) removal by dissolution-precipitation and ion exchange. This result suggested that there was a synergistic effect between HAP and sludge biochar for the Cd(II) removal. HAP@BC reduced the leaching toxicity of Cd(II) in soil better than BC, indicating that the HAP@BC was able to mitigate Cd(II) contamination in soil more effectively. This work demonstrated that sludge biochar was an ideal carrier for dispersed HAP and provided an effective HAP/biochar composite for the mitigation of Cd(II) contamination in aqueous solution/soil.

Production and characterization of graphene oxide-engineered biochars and application for organic micro-pollutant adsorption from aqueous solutions.

In this study, conventional and Graphene Oxide-engineered biochars were produced and thoroughly characterized, in order to investigate their potential as adsorptive materials. Two types of biomass, Rice Husks (RH) and Sewage Sludge (SS), two Graphene Oxide (GO) doses, 0.1% and 1%, and two pyrolysis temperatures, 400°C and 600°C were investigated. The produced biochars were characterized in physicochemical terms and the effect of biomass, GO functionalization and pyrolysis temperature on biochar properties was studied. The produced samples were then applied as adsorbents for the removal of six organic micro-pollutants from water and treated secondary wastewater. Results showed that the main factors affecting biochar structure was biomass type and pyrolysis temperature, while GO functionalization caused significant changes on biochar surface by increasing the available C- and O- based functional groups. Biochars produced at 600°C showed higher C content and Specific Surface Area, presenting more stable graphitic structure, compared to biochars produced at 400°C. Micro-pollutant adsorption rates were in the range of 39.9%-98.3% and 9.4%-97.5% in table water and 28.3%-97.5% and 0.0%-97.5% in treated municipal wastewater, for the Rice Husk and Sewage Sludge biochars respectively. The best biochars, in terms of structural properties and adsorption efficiency were the GO-functionalized biochars, produced from Rice Husks at 600°C, while the most difficult pollutant to remove was 2.4-Dichlorophenol.

Release behavior of fertilizers and heavy metals from iron-loaded sludge biochar in the aqueous environment

In this study, the release behavior of fertilizers (NH4+-N, PO43− and K) and heavy metals (Mn, Zn, Ni, Cu, Pb and Cr) from iron-loaded sludge biochar (ISBC) was investigated to evaluated the feasibility and risks of ISBC as a slow release fertilizer. Their release capacity was significantly enhanced with decreasing initial pH, increasing solid-liquid ratio (RS-L) and rising temperature (p < 0.05). When the initial pH, RS-L and temperature were separately 5 (fertilizers)/1 (heavy metals), 1:5 and 298 K, the final concentrations of NH4+-N, PO43−, K, Mn, Zn and Ni were 6.60, 14.13, 149.4, 53.69, 72.56, and 1.01 mg L−1, while the maximum concentrations of Cu, Pb and Cr were 0.94, 0.77, and 0.22 mg L−1, respectively. Due to the tiny difference between the R2 values, revised pseudo-first-order and pseudo-second-order kinetics models described their release behavior well, suggesting that physical and chemical interactions played an important role. Activation energies greater than 40 kJ mol−1 indicated that the rate-controlling steps of the release of NH4+-N, PO43− and Ni were chemical reactions, while chemical reactions and diffusion together determined the release rates of K, Mn, Zn, Cu, Pb and Cr because their activation energies were in the range of 20–40 kJ mol−1. The increasingly negative ΔG and positive ΔH and ΔS suggested that their release was a spontaneous (except Cr) and endothermic process with an increase of randomness between the solid-liquid interface. The release efficiency of NH4+-N, PO43− and K were in the ranges of 28.21%–53.97%, 2.09%–18.06% and 39.46%–66.14%, respectively. Meanwhile, the pollution index and evaluation index of heavy metals were in the ranges of 33.31–227.4 and 4.64–29.24, respectively. In summary, ISBC could be used as a slow-release fertilizer with low risk when the RS-L was less than 1:40.

A novel magnetic sludge biochar was prepared by making full use of internal iron in sludge combining KMnO4–NaOH modification to enhance the adsorption of Pb (Ⅱ), Cu (Ⅱ) and Cd (Ⅱ)

This study synthesized novel magnetic biochar (PCMN600) by KMnO4–NaOH combined modification using iron-containing pharmaceutical sludge to remove toxic metals from wastewater effectively. Various characterization experiments of engineered biochar showed that the modification process introduced ultrafine MnOx particles on the carbon surface and resulted in higher BET surface area and porosity along with more oxygen-containing surface functional groups. Batch adsorption studies indicated that the maximum adsorption capacities of PCMN600 for Pb2+, Cu2+ and Cd2+ were 181.82 mg/g, 30.03 mg/g and 27.47 mg/g, respectively, at a temperature of 25 °C and pH of 5.0, which were much higher than that of pristine biochar (26.46 mg/g, 6.56 mg/g and 6.40 mg/g). The adsorption datums of three toxic metal ions fitted well to the pseudo-second-order model and Langmuir isotherm, and the sorption mechanisms were identified as electrostatic attraction, ion exchange, surface complexation, cation-π interaction and precipitation. The strong magnetic properties of the engineered biochar endowed the adsorbent with remarkable reusability, and after five cycles of recycling, PCMN600 still retained nearly 80% of its initial adsorption capacities.

Potential removals of tetracycline and sulfamethoxazole by iron-loaded sludge biochar

In this study, the potential of iron-loaded sludge biochar (ISBC) to remove tetracycline (TC) and sulfamethoxazole (SMX) was investigated. Under the optimized conditions (initial pH of 4 and 5, ISBC dose of 1.0 g/L, contact time of 720 min, and temperature of 298 K), the maximum removal capacity of ISBC for TC and SMX was 81.04 mg/g and 80.19 mg/g, respectively. The better simulations of TC and SMX removal by Langmuir model and pseudo-second-order kinetic model indicated that monolayer chemisorption dominated their removal. Their removal rates depended on liquid film diffusion, intraparticle diffusion and chemical reactions. Moreover, their removal was a spontaneous and endothermic process with increasing randomness between the solid-liquid interfaces. Besides, their removal likely included two simultaneous pathways: adsorption/surface degradation and degradation/adsorption/surface degradation. Furthermore, ISBCs could be effectively desorbed and regenerated by ultrapure water and NaOH. In summary, ISBCs had the potential to be practically applicable for TC and SMX removal.

The effectiveness of sewage sludge biochar amendment with Boehmeria nivea L. in improving physicochemical properties and rehabilitating microbial communities in mine tailings

Biochar amendment can be adopted to improve soil substrate, in turn facilitated phytoremediation. However, improvements to the properties of tailings following different feedstocks of biochar amendment in phytoremediation, particularly the impacts on nitrogen cycle and the related nitrogen-fixing microorganisms remain unclear. In this study, a 100-day pot experiment was designed to determine the co-effects of different combinations of woody and non-woody biochar, namely hibiscus cannabinus core biochar (HB), sewage sludge biochar (SB), chicken manure biochar (MB) and two crops (Cassia alata L., Boehmeria nivea L.). It was found that, on the one hand, biochar amendment directly immobilized heavy metal (loid) contamination in the tailings; on the other hand, biochar amendment, particularly non-woody SB, improved soil properties (i.e., the combination of SB with crops increased the total nitrogen content by 4.7–7.5 times). This indirectly improved phytostabilization (i.e., SB increased crop height 1.5–1.8 fold, root length 3.3–3.7 fold, decreased NH4NO3-extractable Pb, Cu, Cd and also increased the relative abundance of nitrogen-fixing bacteria such as Mesorhizobium, Bradyrhizobium, and Rhizobium). Besides this, redundant analysis shown that the carbon, nitrogen sources, and pH provided by the biochar were identified as the key factors associated with the nitrogen-fixing bacteria. Through the comprehensive evaluation of different biochar amendment in phytoremediation, it was found that the non-woody SB got higher comprehensive score (3.1–3.6) in biochar amendment in phytoremediation, especially in Boehmeria nivea L. Thus, the combination of non-woody SB and Boehmeria nivea L. improved microbial function, while the microorganisms in turn promoted crop growth. Our results revealed the prospect of using non-woody SB assisted Boehmeria nivea L. for phytoremediation in multi-metal mine tailings.

Characteristics of a Novel Decomposed Corn Straw-Sludge Biochar and Its Mechanism of Removing Cadmium from Water.

The utilization of high-efficiency adsorption materials to reduce cadmium pollution in aquatic environments is the focus of current environmental remediation research. Straw waste and sludge, which are available in huge amounts, can be best utilized in the preparation of environmental remediation materials. In this study, six types of biochar (SBC, CBC, DBC, SD1BC, SRDBC, and SCDBC) were prepared from straw and sludge by co-pyrolysis, and their cadmium adsorption mechanisms were explored. Cd(II) adsorption isotherms and kinetics on the biochar were determined and fitted to different models. Kinetic modeling was used to characterize the Cd(II) adsorption of biochar, and findings revealed the process of sorption followed pseudo-second-order kinetics (R2 > 0.96). The Langmuir model accurately represented the isotherms of adsorption, indicating that the process was monolayer and controlled by chemical adsorption. SCDBC had the highest capacity for Cd(II) adsorption (72.2 mg g-1), 1.5 times greater than that of sludge biochar, and 3 times greater than that of corn straw biochar. As the pH level rose within the range of pH 5.0 to 7.0 and the ionic strength decreased, the adsorption capacity experienced an increase. SCDBC contained CaCO3 mineral crystals before Cd(II) adsorption, and CdCO3 was found in SCDBC after adsorbing Cd(II) via X-ray diffraction analysis; the peak of Cd could be observed by Fourier transform infrared spectroscopy after the adsorption of Cd(II). The possible adsorption of Cd(II) by SCDBC occurred primarily via surface complexation with active sorption sites, precipitation with inorganic anions, and coordination with π electrons. Collectively, the study suggested that the six types of biochar, particularly SCDBC, could be used as highly efficient adsorbents for Cd(II) removal from aquatic environments.

Effect of iron-loaded sludge biochar amendments on phytoremediation potential of Cr-contaminated soils by Leersia hexandra swartz

In this study, the effect of iron-loaded sludge biochar (ISBC) with different amendment dosages (mass ratio of biochar to soil equal to 0, 0.01, 0.025 and 0.05) on the phytoremediation potential of Leersia hexandra swartz (L. hexandra) to Cr-contaminated soil was investigated. With increasing ISBC dosage from 0 to 0.05, plant height, aerial tissue biomass and root biomass increased from 15.70 cm, 0.152 g pot−1 and 0.058 g pot−1 to 24.33 cm, 0.304 g pot−1 and 0.125 g pot−1, respectively. Simultaneously, the Cr contents in aerial tissues and roots increased from 1039.68 mg kg−1 to 2427.87 mg kg−1 to 1526.57 mg kg−1 and 3242.62 mg kg−1, respectively. Thus, the corresponding bioenrichment factor (BCF), bioaccumulation factor (BAF), total phytoextraction (TPE) and translocation factor (TF) values were also increased from 10.52, 6.20, 0.158 mg pot−1 (aerial tissue)/0.140 mg pot−1 (roots) and 0.428 to 15.15, 9.42, 0.464 mg pot−1 (aerial tissue)/0.405 mg pot−1 (roots) and 0.471, respectively. The significant positive effect of ISBC amendment was primarily attributed to the following three aspects: 1) the root resistance index (RRI), tolerance index (TI) and growth toxicity index (GTI) of L. hexandra to Cr were increased from 100%, 100% and 0%–216.88%, 155.02% and 42.18%, respectively; 2) the bio-available Cr content in the soil was decreased from 1.89 mg L−1 to 1.48 mg L−1, while the corresponding TU (toxicity units) value was declined from 0.303 to 0.217; 3) the activities of urease, sucrase and alkaline phosphatase in soil were increased from 0.186 mg g−1, 1.40 mg g−1 and 0.156 mg g−1 to 0.242 mg g−1, 1.86 mg g−1 and 0.287 mg g−1, respectively. In summary, ISBC amendment was able to significantly improve the phytoremediation of Cr-contaminated soils by L. hexandra.

Response of bacterial communities to the application of sewage sludge biochar and Penicillium aculeatum in rhizosphere and bulk soil of wheat

The application of sewage sludge biochar (SSB) in agriculture is a promising solution for detoxifying and recycling the nutrient-rich sludge. However, knowledge is required on how SSB alone or in combination with biofertilizers influences the soil microbial communities. This work used a wheat pot experiment with a root free soil compartment to study effects of SSB and the phosphate-solubilizing Penicillium aculeatum on bacterial communities in wheat rhizosphere and bulk soil. Treatments were applied only to the root free soil compartment. Analysis by 16S rRNA gene amplicon sequencing showed that SSB increased the alpha diversity and induced taxon-specific shifts. These shifts occurred in both rhizosphere and bulk soil, and they were dominated by increased relative abundance of Gemmatimonadetes and Chloroflexi which were primarily explained by increases in soil P availability and soil pH, respectively. Application of P. aculeatum had smaller effects on bacterial communities and these effects occurred mainly in rhizosphere soil and were probably related to unidentified interactive rhizosphere processes. The combined application of SSB and P. aculeatum did not reveal any additive effects on the bacterial communities as compared to the sole application of SSB. Due to the different treatment effects on rhizosphere and bulk soil communities, the analysis of both soil compartments will provide a better understanding of interactions between biochar, soil, bacteria and plants.