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The impact of drying-rewetting (DRW) cycles on soil phosphorus (P) behavior is well-established; however, its impact on the different-sized colloidal P (CP) in agricultural soils is still unclear. To investigate the effect of DRW events on the mobilization of CP in agricultural soils, and to understand how this impact varies with different DRW cycles and drought intensities, the study explored the role of soil type, CP fractions, and compositions. The concentration of CP was measured in paddy soil and vegetable soil after 3, 6, and 9 DRW cycles of varying intensities. The CP was then fractionated into fine-sized colloids (FC-P; 1-220 nm), medium-sized colloids (MC-P; 220-450 nm), and coarse-sized colloids (CC-P; 450-1000 nm) through soil supernatant filtration. CP accounted for 71.1 % and 55.6 % of water-dispersible colloidal P (<1000 nm) in paddy and vegetable soils, with FC-P constituting the greatest proportion at 50 % and 44 % of CP respectively. The colloidal fraction correlated with organic carbon, aluminum, and iron. DRW cycles did not change the overall distribution of the three CP size fractions. However, they affected the concentration and composition of CP. This study concluded that DRW can have significant implications for nutrient release and water quality in agricultural soils and that maintaining soil moisture at 50 % to 70 % of water-holding capacity could alleviate CP accumulation resulting from DRW cycles., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Colloidal phosphorus (CP) has high mobility and great loss risk; their biogeochemical processes are influenced by agricultural management such as redox oscillation and biochar-amendment application. This study monitored CP concentration in pore-water, soil P species and P adsorption capacity, to investigate CP release from paddy soils as affected by the interactive effects of oxygen status (continuous anoxic/oxic for 12 days, CA/CO; intermittent anoxic for 2, 4, 6, 8, 10 days during the 12-day cycle, IA 2 - 10 ) and management (soil only, CK; bulk/micro/nano-sized biochar with various properties: SB Bulk , SB Micro , and SB Nano ). Compared to the control (0.25-0.84 mg L -1 , CK-CA), the single intermittent anoxic treatment (CK-IA) reduced CP concentrations by 45 %, due to the rise of Eh and pH and the decline of the degree of P saturation along with the increased soil Fe/Al-P and organic-P. Longer anoxic duration under the CK-IA reduced CP release, probably donated from massive production of redox-stable amorphous Fe/Al-bound P. The single biochar treatment (SB-CA: SB Bulk -CA > SB Micro -CA > SB Nano -CA) decreased CP release by 37 % as compared to the CK-CA, ascribed to the increased soil pH, Eh, and P adsorption capacity. The combined treatment (SB-IA: SB Bulk -IA 2  > SB Nano -IA 10 ) synergistically reduced CP release by 68 % in comparison with the CK-CA, due to the increase of adsorption through interactions of soil Fe/Al/Ca- and organic-P. Therefore, nano-sized biochar and long intermittent anoxic duration are recommended for reducing CP release from paddy soils., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The manure fertilizer increases the phosphorus (P) saturation of soils and the colloidal P release to water bodies. Manure of different particle-sizes may have different effects on colloidal P release by soil, and to date there is limited knowledge on colloidal P release from soils amended with different size manures. We produced sheep micro- (S Micro ) and nano-manure (S Nano ), and poultry micro- (P Micro ), nano-manure (P Nano ) from bulk samples by wet fractionation method. The fractionation reduced the P contents of micro- and nano-manures, and enriched them in ash and calcium, iron (Fe), magnesium, and aluminum (Al) phosphate minerals compared with the bulk manures. The degree of P saturation (DPS) in Anthorsol and Cambisol was decreased (S Micro , 17.6 and 17.2 %; S Nano , 14.5 and 13.3 % and P Micro , 19.0 and 19.7 mg kg -1 ; P Nano , 17.0 and 14.3 mg kg -1 ) and released less colloidal P (S Micro , 3.12 and 3.78 mg kg -1 ; S Nano , 3.01 and 3.56 mg kg -1 and P Micro , 3.34 and 3.92 mg kg -1 ; P Nano , 3.21 and 3.65 mg kg -1 ) than the soils receiving the bulk manures. The decrease in colloidal P was correlated with less DPS in both soils amended with micro and nano manures. That is, the only measurable effect of manure particle size on colloidal P release from the amended soils was due to chemical fractionation during separation of the size fractions. It was suggested that nano and micro manures were the effective approach to reduce colloidal P release from manure amended soils., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Developing effective modification methods and obtaining a comprehensive understanding of adsorption mechanisms are essential for the practical application of biochars for the removal of heavy metals from solutions. In this study, rice straw was impregnated with sodium phytate and pyrolyzed at 350 °C, 450 °C, and 550 °C to synthesize modified biochars (i.e., MBC350, MBC450, and MBC550). The Cd(II) adsorption capacities and contributions of different mechanisms, including the effects of biochar-derived dissolved organic matter (BDOM), were investigated using batch sorption experiments and characterization analyses. The modification of sodium phytate promoted the pyrolysis of biomass, thereby increasing the BDOM content and aromatic structures at low and high pyrolysis temperatures, respectively. Moreover, the modification also increased the exchangeable Na + and carbonate contents in the modified biochars. Compared with the raw biochars, the Cd(II) adsorption capacities of modified biochars increased by 3.3-4.3 times, and MBC550 had the highest Cd(II) adsorption capacity (126.5 mg/g), of which precipitation with minerals and interaction with π-electrons contributed 41.7% and 45.8%, respectively. However, at a lower pyrolysis temperature, the Cd(II) adsorption attributed to ion exchange and co-deposition with BDOM significantly increased, especially on MBC350 (33.9 and 12.6 mg/g, respectively). These results indicate that modification by sodium phytate effectively enhanced various adsorption mechanisms, thereby increasing the Cd(II) adsorption capacity. In addition, the contribution of co-deposition with BDOM to adsorption was unneglectable for the biochars pyrolyzed at low temperatures., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Blending waste biomass for co-pyrolysis is generally regarded as a promising method for reduced-volume, value-added, and hazard-free treatment of sewage sludge. Hence, a comparison was made of the co-pyrolysis of sewage sludge with rice husk and with bamboo sawdust (1:1, w/w) at 400 and 700 °C and the properties and behaviors of selected metals in the corresponding biochars. Biochar produced by co-pyrolysis with both biomass wastes had larger (5 × 5 rectangle) aromatic clusters than did the sewage sludge biochar (4 × 4 rectangle) using the rectangle-like model on the basis of biochar molar H/C ratio, indicating increased aromaticity of the co-pyrolyzed biochars. Moreover, the molar O/C ratio of the sewage sludge-bamboo biochar was much lower than that of the sewage sludge-husk biochar, especially after pyrolysis at 700 °C (0.02 vs 0.27), suggesting greater recalcitrance to ageing. Co-pyrolysis of sewage sludge with husk invariably resulted in a higher percentage of metals studied in the residual fraction than co-pyrolysis with sawdust at the same temperature, leading to a lower risk index (14.2) because of the maximum metal encapsulation in the sewage sludge-husk biochar at 700 °C. Overall, co-pyrolysis of sewage sludge with husk provided higher metal immobilization but apparently lower biochar stability than co-pyrolysis with sawdust. These results provide an alternatively practical strategy for the safe disposal of sewage sludge and biomass wastes., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Dried raw sludge was pyrolyzed at temperatures ranging from 400 to 600°C at the increase of 50°C intervals to investigate the influence of pyrolysis temperature on properties and environmental safety of heavy metals in biochar derived from municipal sewage sludge. The sludge biochar yield decreased significantly with increasing pyrolysis temperature but the pH, ash content and specific surface area increased. Conversion of sludge to biochar markedly decreased the H/C and N/C ratios. FT-IR analysis confirmed a dramatic depletion of H and N and a higher degree of aromatic condensation in process of biochar formation at higher temperatures. The total concentrations of Cu, Zn, Pb, Cr, Mn, and Ni increased with conversion of sludge to biochar and increasing pyrolysis temperature. However, using BCR sequential extraction and analysis, it was found that most of the heavy metals existed in the oxizable and residual forms after pyrolysis, especially at 600°C, resulting in a significant reduction in their bioavailability, leading to a very low environmental risk of the biochar. The present study indicates pyrolysis is a promising sludge treatment method for heavy metals immobilization in biochar, and highlights the potential to minimize the harmful effects of biochar by controlling pyrolysis temperature., (Copyright © 2016 Elsevier B.V. All rights reserved.)