Biochar Nitrogen Research Articles

A Nature-Inspired Design for Sequestering Polycyclic Aromatic Hydrocarbons in Asphalt-Surfaced Areas

Asphalts for pavement and roofing are known to emit volatile organic compounds (VOCs), contributing to air pollution, including the formation of ozone and secondary organic aerosols, which further worsen air quality. These emissions become more pronounced with higher sun intensity and higher temperature, accelerating the loss of essential components and the aging of bitumen. Consequently, the durability and functionality of bitumen are compromised. In this study, we investigate the efficacy of nitrogen-carrying functional groups in biochar at retaining VOCs in bitumen and prolonging the service life of asphalt surfaces. Biochar derived by hydrothermal liquefaction of red microalgae, rich in N-functional groups, is compared with low-N biochar obtained through acid-washing. Laboratory tests demonstrate that bitumen modified with high-N biochar exhibits greater resistance to aging after 200 h of ultraviolet radiation exposure compared to bitumen modified with low-N biochar. The values of an aging index based on the crossover modulus and an aging index based on the crossover frequency indicate greater susceptibility to aging in neat bitumen compared to biochar-modified bitumen, and bitumen modified with high-N biochar showed the lowest aging index. Compared to neat bitumen, measurements of carbonyl and sulfoxide as aging indicators showed an improvement of 12.9% for high-N biochar in slowing bitumen aging, while low-N biochar provided only a 3.1% improvement. Dynamic vapor sorption analysis showed 35% less mass loss in bitumen with high-N biochar compared to bitumen with low-N biochar. These improvements can be attributed to the increased retention of VOCs in bitumen facilitated by the N-functional groups in high-N biochar. Modeling with density functional theory shows the mechanisms by which biochar rich in N-functional groups exhibits enhanced adsorption of VOCs. This modeling highlights the importance of biochar's nitrogen functional groups in biochar's electronic structure and molecular structure in retaining VOCs in the bitumen matrix. The study outcomes promote sustainability and resource conservation in the construction industry and align with goals of carbon neutrality.

Biochar–Nitrogen Composites: Synthesis, Properties, and Use as Fertilizer for Maize

Biochar–Nitrogen Composites: Synthesis, Properties, and Use as Fertilizer for Maize

Production of bio-oil and biochar by the nitrogen-rich pyrolysis of cellulose with urea: Pathway of nitrile in bio-oil and evolution of nitrogen in biochar

The production of nitrogen-containing chemicals from renewable biomass under nitrogen-rich conditions represents a promising technological pathway. Urea, as a nitrogen carrier, offers advantages over gaseous ammonia due to its easier storage and transportation. In this study, cellulose and two of its model compounds (cellobiose and glucose) were used as raw materials. The effects of different urea concentrations on the types and relative contents of bio-oil components and the properties of nitrogen-doped biochar were analyzed using GC-MS, FT-IR, and elemental analysis. We further clarified the evolution of exogenous nitrogen in nitrogen-rich pyrolyzed bio-oil and biochar with different urea concentrations. Cellobiose was found to be a more suitable feedstock for the production of nitrogen-containing compounds from nitrile than cellulose or glucose. A significant increase in the relative content of nitrile compounds (44.45%) was observed at a ratio of 40% cellulose to nitrogen carrier. Analysis of the bio-oil fraction led to the conclusion that there may be two main pathways for the production of the two nitrile compounds, acetonitrile and propionitrile. This research provides a better understanding of the N transfer pathways during the nitrogen-rich pyrolysis of cellulose and its model compounds (cellobiose and glucose) when using urea as the nitrogen carrier. This will facilitate further improvements in the yield of nitrogen-containing compounds in bio-oil.

Novel maricultural-solid-waste derived biochar for removing eutrophic nutrients and enrofloxacin: Property, mechanism, and application assessment

Land-based seawater aquaculture accompanied by high stocking density usually involves producing excess eutrophic nutrients, residual baits, excrement, and antibiotics. Because of limited technology and salinity, proper and efficient treatment of these wastes is still an unsolved issue. In this study, the feasibility of maricultural fish residual bait and excrement-derived biochar as water pollutant remover and saline–alkaline soil amendment were firstly assessed. The biochar was pyrolyzed at 300, 500, 700, 800, 900 ℃ (marked as BC300, BC500, BC700, BC800, BC900) and modified by zirconium or iron (BC700-Zr or BC700-Fe). BC700-Zr had the highest specific surface area. BC700-Zr and BC700-Fe exhibited higher nitrogen removal efficiency. The biochars exhibited nitrogen and phosphate desorption, while we observed no obvious phosphate desorption in BC700-Zr or BC700-Fe. Adsorption kinetics analysis indicated that adsorption processes of nitrate, nitrite and enrofloxacin were consistent with pseudo-second-order model, while ammonium and phosphate adsorption processes fitted pseudo-first-order model better. The biochar showed nitrogen and phosphate nutrients release effects, indicating potential application in saline–alkaline soil improvement. Multi-linear regression analysis indicated that nitrogen release was closely related to biochar nitrogen content, pH and average pore width. Phosphate release was inversely related to pH and positively related to average pore width.

Study on synchronous immobilization technology of heavy metals and hydrolyzed nitrogen during pyrolysis of sewage sludge

The difficulty to simultaneously passivate heavy metals and enrich nutrients content in sewage sludge limits its application as soil nutrients. This paper concentrated on the synchronous immobilization effect of heavy metals and hydrolyzed nitrogen during pyrolysis of sewage sludge. Results showed that the forms of heavy metals transformed from bioavailable forms (F1 + F2) to stable forms (F3 + F4) and the leaching concentration reduced after low-temperature pyrolysis. However, hydrolyzed nitrogen would inevitably lose during pyrolysis treatment. With the addition of CaO, more hydrolyzed nitrogen could be retained in biochar by forming more stable nitrogen-containing compounds. The preservation efficiency of hydrolyzed nitrogen in biochar was over 50% when pyrolysis at 300 ºC with CaO. In addition, the addition of CaO would further reduce the heavy metals toxicity. In this study, the synchronous immobilization of heavy metals and hydrolyzed nitrogen in biochar was realized by adding CaO during low-temperature pyrolysis, contributing to achieving the resource utilization of sewage sludge as N-fertilizer to land use.

Effect of biomass type and pyrolysis temperature on nitrogen in biochar, and the comparison with hydrochar

In this paper, two different biomasses (soybean straw and Chlorella) were pyrolyzed at temperatures 300–800 °C to obtain biochars. The impacts of biomass type and pyrolysis temperature on the physical and chemical properties of biochar, especially the effects on nitrogen (N) content and composition, were investigated. Furthermore, the hydrochar obtained from hydrothermal carbonization (HTC) of the same biomass was compared with the pyrolysis biochar. Biochar N content was positively correlated with biomass N content and negatively correlated with pyrolysis temperature. For raw biomass, N mainly existed as protein-N and inorganic-N, which converted to more stable structures through the pyrolysis process, including pyridinic-N, pyrrolic-N, graphitic-N (or quaternary-N) and pyridinicN-O. While in hydrochar, N-containing species mainly include protein-N, pyrrolic-N and pyridinic-N. Biochar had more kinds of N-containing species, more aromatic structures, and higher stability compared with hydrochar.

Response of Microbial Biomass Carbon and Nitrogen and Rice Quality in a Yellow Soil Paddy Field to Biochar Combined with Nitrogen Fertilizer

The effects of biochar combined with nitrogen fertilizer on soil microbial carbon, nitrogen (SMBC, SMBN), and rice yield and quality were investigated to provide a scientific basis for soil fertilization and nitrogen fertilizer reduction. Using a field experiment, we set up a nitrogen reduction gradient (T0-T4):0, 10%, 20%, 30%, and 40% reductions. The same amount of biochar nitrogen was used as the substitute and no nitrogen fertilizer was used as the control (CK). The yield was measured and sampled at the mature stage of rice, and the samples were analyzed in the laboratory. The results showed that the range of SMBC and SMBN was 208.42-303.16 mg·kg-1 and 32.28-54.73 mg·kg-1, respectively. SMBC, SMBN, soil microbial entropy (qMB), soil microbial biomass nitrogen to total nitrogen ratio (SMBN/TN), and rice yield increased first and then decreased as the proportion of biochar and nitrogen fertilizer increased. SMBC, SMBN, and rice yield were all the highest in T2, which increased successively by 28.0%, 30.0%, and 13.4% compared with that of the T0 treatment (P<0.05), while those of the T4 treatment decreased slightly (P>0.05). The processing of SMBC, qMB, SMBN, and SMBN/TN showed a significantly positive relationship between the two (P<0.01). Compared with that of the T0 treatment, the T2 treatment significantly increased the Milled rice, gel consistency, and amylose content. In this study, the combination of biochar (5.0 t·hm-2) and nitrogen reduction (20%) effectively improved soil microbial carbon and nitrogen content and increased the yield and quality of rice, which could be a good choice for reducing nitrogen fertilization and increasing the efficiency of rice in a yellow soil paddy field in Guizhou.

Effects of pyrolysis conditions on migration and distribution of biochar nitrogen in the soil-plant-atmosphere system

The use of biochar to amend soil has been gaining increasing attention in recent years. In this study, the 15N tracer technique was used together with elemental analysis-stable isotope ratio analysis and gas isotope mass spectrometry to characterise biochar, soil, plant, and gas samples in order to explore the nitrogen transport mechanisms in the biochar-soil-plant-atmosphere system during the process of returning biochar to the soil (RBS). The results showed that the nitrogen retention rate of biochar was negatively correlated with the pyrolysis temperature during the preparation process, but was less affected by the pyrolysis atmosphere. In the RBS process, the migration of biochar nitrogen to plants was significantly greater than that of straw nitrogen, and it showed an overall decreasing trend with the increase in pyrolysis temperature, but was less influenced by the pyrolysis atmosphere. At temperatures of 300–500 °C, the pyrolysis atmosphere had a slightly smaller effect on the migration of biochar nitrogen to the air, plant, and soil system, and the pyrolysis temperature was much more important. However, the activation with CO2 gas at a higher temperature (600 °C) significantly enhanced the pore structure of biochar, particularly the structure of small pores; therefore, biochar prepared under a CO2 atmosphere at 600 °C reduces gaseous nitrogen emissions better than that under a N2 atmosphere. In the future, more pyrolysis conditions should be examined and their optimal combination should be further explored to reduce gaseous nitrogen emissions.

Transformation and Transport Mechanism of Nitrogenous Compounds in a Biochar “Preparation–Returning to the Field” Process Studied by Employing an Isotope Tracer Method

Due to biochar’s excellent physical and chemical properties, such as rich void ration and large specific surface area, it could improve soil by conserving water and fertilizer and providing breeding grounds for soil microorganisms. Therefore, it has been attracting researchers’ interests for its potential as a soil amendment. In this work, elemental analysis-stable isotope ratio mass spectrometry (EA-IRMS) and X-ray photoelectron spectroscopy (XPS) were conjointly employed to investigate the migration and transformation mechanism of biochar nitrogenous compounds in the “preparation–returning” process. EA-IRMS data indicated that during the preparation process the nitrogen retention rate in biochar first dropped sharply (300–400 °C), then became stable (400–500 °C), and finally decreased slowly (500–800 °C) with increasing pyrolysis temperature. After returning biochar to soil, the measurable total nitrogen in biochar that migrated to soil and plants displayed a nitrogen mass distribution rate in the order of biochar after returning (88.40–90.42%) > soil (8.81–10.07%) > plants (0.77–1.53%). In addition, the pyrolysis temperature was negatively related to the nitrogen mass distribution rate in biochar, soil, and wheat. On the other hand, the pyrolysis atmosphere had little effect on the nitrogen retention rate in biochar before returning and the nitrogen mass distribution rate in biochar after returning to the field. XPS results suggested that alkaloid-N, free amino acid-N, protein-N, and NH4+-N in wheat straw were gradually transformed into pyridine-N, amino-N, pyrrole-N, quaternary-N, NH4+-N, NO2–-N, and NO3–-N in biochar during the biomass pyrolysis process. Biochar produced at 300 °C was in a transition stage that included all nitrogenous compounds present in wheat straw as well as biochar produced at the lower temperatures (≤500 °C). At higher temperatures, inorganic nitrogen species were more abundant and displayed higher contents. For pyrolysis temperatures ≤500 °C, biochars prepared under both N2 and CO2 atmospheres comprised similar nitrogenous compounds and contents. Moreover, the changes in nitrogenous compounds and nitrogen release patterns during the process of returning biochar to the field were not significantly different.

Application of the 15N tracer method to study the effect of pyrolysis temperature and atmosphere on the distribution of biochar nitrogen in the biomass–biochar-plant system

Biochar nitrogen is key to improving soil fertility, but the distribution of biochar nitrogen in the biomass–biochar–plant system is still unclear. To provide clarity, the 15N tracer method was utilised to study the distribution of biochar nitrogen in the biochar both before and after its addition to the soil. The results can be summarised as follows. 1) The retention rate of 15N in biochar decreases from 45.23% to 20.09% with increasing pyrolysis temperature from 400 to 800°C in a CO2 atmosphere. 2) The retention rate of 15N in biochar prepared in a CO2 atmosphere is higher than that prepared in a N2 atmosphere when the pyrolysis temperature is below 600°C. 3) Not only can biochar N slowly facilitate the adsorption of N by plants but the addition of biochar to the soil can also promote the supply of soil nitrogen to the plant; in contrast, the direct return of wheat straw biomass to the soil inhibits the absorption of soil N by plants. 4) In addition, the distribution of nitrogen was clarified; that is, when biochar was prepared by the pyrolysis of wheat straw at 400°C in a CO2 atmosphere, the biochar retained 45.23% N, and after the addition of this biochar to the soil, 39.99% of N was conserved in the biochar residue, 4.55% was released into the soil, and 0.69% was contained in the wheat after growth for 31days. Therefore, this study very clearly shows the distribution of nitrogen in the biomass–biochar-plant system.

Influence of pyrolysis conditions on nitrogen speciation in a biochar ‘preparation-application’ process

To investigate biochar nitrogen conversion in a ‘preparation-application’ system and the response of its transportation in plants, biochar samples were produced from rice straw at different pyrolysis temperatures (400 °C and 800 °C) and atmospheres (N2 and CO2). Subsequently, biochar was synthesized under CO2 atmosphere to explore its nitrogen nutrient characteristics and further improve the chemical and physical properties of soil. Nitrogen speciation of the biochar and plant root samples were evaluated by X-ray photoelectron spectroscopy. Research has shown that organic nitrogen such as protein-N, free amino acid-N, and alkaloid-N in rice straw is converted into organic (nitrile-N, pyridine-N, amino-N, and pyrrole-N) and inorganic (NH4+-N, NO2−-N, and NO3−-N) species in biochar during the biomass pyrolysis process. In turn, biochar nitrogen is transported to plants as protein-N, free amino acid-N, alkaloid-N, NH4+-N, NO2−-N, and NO3−-N. Comprehensive consideration of the biochar quality and preparation cost indicated the lower pyrolysis temperature (400 °C) under CO2 atmosphere as the best conditions for biochar preparation.