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

Fuel Characteristics and Phytotoxicity Assay of Biochar Derived from Rose Pruning Waste

The aim of this study was the characterization and evaluation of applicability as a soil amendment of biochar derived from rose pruning waste at different pyrolysis temperatures (200-500 °C) and process durations (20-60 min). The biochar properties were compared to the raw material. The biochars produced at 300 °C for 40 and 60 min demonstrated the best fuel properties. These variants showed high energy gain rates (77.6 ± 1.5% and 74.8 ± 1.5%, respectively), energy densification ratios (1.35 ± 0.00 and 1.37 ± 0.00, respectively), high heating values (24,720 ± 267 J × g-1 and 25,113 ± 731 J × g-1, respectively), and relative low ash contents (5.9 ± 0.5% and 7.1 ± 0.3%, respectively). Regarding fertilizer properties, such as pH value, ash content, heavy metal content, and pollutant elution, the biochars showed better qualities than the raw material. All tested biochar did not exceed the permissible values for heavy metals, including Cr, Cd, Ni, and Pb. The most optimal properties for soil amendments were noted for biochar variants of 400 °C for 40 min, 450 °C for 20 min, and 500 °C for 20 min. Generally, biochars produced at temperatures ≥400 °C did not inhibit root elongation, except for the material produced at 450 °C for 60 min (4.08 ± 23.34%). Biochars obtained at ≥300 °C showed a positive impact on seed germination (86.67 ± 18.48-100 ± 24.14%).

Nutrient retention after crop harvest in a typic hapludults amended with biochar types under no-tillage system

The utilization of biochar's as soil amendments for enhancing nutrient retention in subsoils present potential limitations. To address this issue, we conducted a greenhouse experiment to assess the effects of various biochar's derived from animal manures (swine manure, poultry litter, cattle manure) and plant residues (rice straw, soybean straw, corn straw) when applied to surface of an acidic soil. Our study focused on wheat crops under a no-tillage system, with a subsequent evaluation of the residual impacts on soybeans. The experimental design involved the application of biochar's at different rates i.e. 10 and 20 Mg ha-1, followed by the assessment of their influence on NPK levels, pH, and exchangeable Al in stratified soil layers (0-5, 5-10, 10-15, and 15-25 cm). Furthermore, we investigated the interplay between biochar doses and the application of nitrogen (N) in the top 5 cm of soil, specifically examining NO 3 - , NH 4 + , P and K levels. Our findings revealed that in the top 5 cm of soil, biochar doses and N application significantly affected NO 3 - , NH 4 + , P and K concentrations. However, in deeper soil layers, no significant differences were observed among biochar doses with or without N application. Interestingly, K levels were impacted throughout all soil depths, regardless of the presence or absence of N application. Moreover, biochar application up to a 5 cm depth induced favorable changes in soil pH and reduced exchangeable Al. In contrast, deeper layers experienced a decrease in soil pH and an increase in exchangeable Al following biochar treatment. In conclusion, our study demonstrates that biochar's can effectively retain NPK nutrients, enhance soil pH, and decrease exchangeable Al, independent of the type and dosage of application under a no-tillage system. Nonetheless, the efficacy of biochar amendments may vary with soil depth and type of nutrient, warranting careful consideration for maximizing their benefits in sustainable agricultural practices.

The remediation potential and kinetics of Pb2+ adsorbed by the organic frameworks of Cladophora rupestris

Cladophora rupestris is ubiquitous in many kinds of waterbodies, and C. rupestris biomass can serve as a carrier for adsorbing and transferring heavy metals. Batch experiments and characterization were performed. Results showed that the organic frameworks of C. rupestris (CROF) had a specific surface area of 2.58 m2/g and an external surface area of 2.06 m2/g. Many mesopores were present in CROF, mainly distributed in 2.5-7.5 nm. The zeta potentials were within the range of - 4.46 to - 13.98 mV in the tested pH of 2.0-9.0. CROF could effectively adsorb Pb2+ in large pH range. The maximum adsorption capacity (qmax) of Pb2+ on CROF was 15.02 mg/g, and 97% of Pb2+ was adsorbed onto CROF after 25 min. CROF had a preferential adsorption of Pb2+. The protein secondary structures and carbon skeletons of CROF all worked in adsorption. The main Pb2+ adsorption mechanisms were pore filling, electrostatic attraction, Pb-π interaction, and surface complexation. Therefore, it is valuable as a biosorbent for the removal of Pb2+ from waterbodies.

Acidified manure and nitrogen-enriched biochar showed short-term agronomic benefits on cotton-wheat cropping systems under alkaline arid field conditions

Application of organic residues such as farm manure and biochar in various agricultural environments have shown positive effects on soil carbon sequestration. However, there is a lack of consensus regarding the agronomical benefits of a single and small dose of biochar and farm manure in arid alkaline soils. Therefore, a field experiment with the given treatments (1) control (no amendment), (2) acidified manure (AM) at 300 kg ha-1, (3) nitrogen (N) enriched biochar (NeB) at 3 Mg ha-1, and (4) an equal combination of AM + NeB (150 kg ha-1 AM + 1.5 Mg ha-1 NeB)) was conducted in a typical cotton-wheat cropping system. A parallel laboratory incubation study with the same amendments was carried out to account for soil carbon dioxide emission (CO2). The N enrichment of biochar and its co-application with acidified manure increased soil mineral N (NO3- and NH4+) in the topsoil (0-15 cm), and increased total N uptake (25.92% to 69.91%) in cotton over control, thus reducing N losses and increased uptake over control. Compared to the control, co-application of AM + NeB significantly improved soil N and P bioavailability, leading to increased plant biomass N, P, and K (32%, 40%, 6%, respectively) uptake over control. The plant's physiological and growth improvements [chlorophyll (+ 28.2%), height (+ 47%), leaf area (+ 17%), number of bolls (+ 7%), and average boll weight (+ 8%)] increased the agronomic yield in the first-season crop cotton by 25%. However, no positive response was observed in the second season wheat crop. This field study improved our understanding that co-application of acidified manure and N-enriched biochar in small dose can be a strategy to achieve short-term agronomic benefits and carbon sequestration in the long run.

Biochar derived from hydrolysis of sewage sludge influences soil properties and heavy metals distributed in the soil

Sewage sludge contains a large number of nutrients and dangerous substances, when sludge was processed into sludge hydrochar that was added to the soil, which not only solve the problem of sludge disposal, but also amend the soil and fix pollutants in the soil. However, it was lack of report on the effect of the sludge hydrochar on soil compositions and soil microorganism community structures until now. In the present study, the hydrothermal carbonization method is used to prepare hydrochar from sewage sludge at temperatures of 180 ℃ and 240 ℃ at durations of 6 h and 15 h in this paper. The effects of the prepared sludge hydrochar on soil-derived dissolved organic matter (DOM), the content of total dissolved nitrogen (TDN) and NO₃^--N in soil, and the community structure of soil bacteria and fungi were evaluated. Furthermore, the change rules in heavy metal speciation in soils treated with sludge hydrochar were investigated. With the increase in the preparation temperature and dosage of sludge hydrochar, the main components of DOM changed from soluble microbial byproducts to fulvic acid-like and humic acid-like fractions through UV and fluorescence characterization. The sludge hydrochar prepared at low temperature could significantly increase the contents of TDN and NO₃^--N in the soil. Affected by sludge hydrochar, the dominant phylum of the bacterial community changed from Proteobacteria to Actinobacteria, and the dominant phylum in the fungal community did not change, but its relative abundance increased. Finally, the sludge hydrochar obtained when the carbonization time was 15 h was more beneficial to reduce the total amount and available content of heavy metals in the soil. The study provides a basis for sludge hydrochar application for the soil amendment.

Mulched drip irrigation and biochar application reduce gaseous nitrogen emissions, but increase nitrogen uptake and peanut yield

Nitrous oxide and ammonia emissions from farmland need to be abated as they directly or indirectly affect climate warming and crop yield. We conducted a two-year field experiment to investigate the effect of biochar applied at two rates (no biochar application vs. biochar applied at 10 t ha^-1) on gaseous nitrogen (N) losses (N₂O emissions and NH₃ volatilization), plant N uptake, residual soil mineral N, and peanut (Arachis hypogaea L.) yield under three irrigation regimes: furrow irrigation (FI), drip irrigation (DI), and mulched drip irrigation (MDI). We found that MDI reduced residual (post-harvest) soil mineral N, cumulative N₂O emissions, and yield-scaled N₂O emissions as compared to FI. Biochar application increased residual soil NO₃^--N and decreased yield-scaled N₂O emissions as compared with the control without biochar application. Under the three irrigation regimes, biochar application decreased cumulative NH₃ volatilization and increased plant N uptake and yield compared with the control. Biochar application improved the sustainability of peanut production and could be used to alleviate the environmental damage associated with gaseous N emissions. Where possible, biochar application under MDI in peanut fields is recommended as a management strategy to minimize gaseous N losses.

The Mixed Addition of Biochar and Nitrogen Improves Soil Properties and Microbial Structure of Moderate-Severe Degraded Alpine Grassland in Qinghai-Tibet Plateau

The degradation of the grassland system has severely threatened the safety of the ecological environment and animal husbandry. The supplement of key substances lost due to degradation is widely used to accelerate the restoration of the degraded grassland ecosystem. In this study, we investigated the effects of biochar and nitrogen addition on soil properties and microorganisms of degraded alpine grassland. The experimental treatments consisted of the control without any addition, only nitrogen addition (10 gN/m²), only biochar addition (4.00 kg/m² biochar), and the mixed addition of biochar and nitrogen (4.00 kg/m² biochar and 10 gN/m² nitrogen, respectively). Adding N alone did not significantly change the pH, total organic carbon (TOC), total nitrogen (TN), microbial biomass (MB), and the composition proportion of microbes of the soil, but increased the contents of soil water content (SWC), NH₄ ⁺-N, NO₃ ^--N, available phosphorus (AP), and the biomass of bacteria and fungi. The addition of biochar or the mixture of biochar and nitrogen increased the contents of pH, TOC, TN, MB, SWC, NH₄ ⁺-N, NO₃ ^--N, AP, bacteria, and fungi in the soil and changed the structure of the soil microbial community. The increasing intensity of AP, bacteria, and fungi under the addition of biochar or the mixture of biochar and nitrogen was significantly greater than that under N addition alone. These results indicated that the separated addition of nitrogen and biochar and the mixed addition of biochar and nitrogen all improved the soil condition of the moderate-severe degraded alpine grassland, but the mixed addition of biochar and nitrogen could be a better strategy to remediate the degraded alpine grassland.

The comprehensive measurement method of energy conservation and emission reduction in the whole process of urban sewage treatment based on carbon emission

It is of great significance to establish a carbon emission management system and carbon emission reduction target to put forward emission reduction measures for each subunit of a sewage treatment plant. In this paper, a mathematical model was constructed for calculating carbon emission in the whole sewage treatment system process. Meanwhile, the model calculated the carbon emission changes after upgrading three sewage treatment plants and identified the critical controlling unit. The results showed that the CO₂ produced from electric energy consumption and chemical application was the primary source of carbon emission of wastewater treatment. Raising sewage discharge standards appropriately could effectively reduce the carbon emission generated by each link of the wastewater treatment plant. Further improvement of effluent standards could adversely affect sewage treatment plants in terms of energy, resources, and greenhouse gas emissions. In addition, raising the standard of total phosphorus concentration in the effluent may lead to a corresponding increase in the amount of phosphorus removal agents, as well as an increase in indirect carbon emission, material consumption, and chemical sludge. Therefore, it is necessary to develop sewage treatment technologies that are economical, applicable, energy-saving, and environmental friendly to realize the environmental benefits of carbon emission reduction in sewage treatment and sustainable utilization of energy and resource from wastewater.

Biochar Derived from Domestic Sewage Sludge: Influence of Temperature Pyrolysis on Biochars’ Chemical Properties and Phytotoxicity

The pyrolytic conversion of domestic sewage sludge (SS) into biochar is a promising method to reduce its large volume and recycle its high-value fuel gas as renewable energy and the use of its chemicals as soil fertilizers. Even though the effects of pyrolysis temperature on energy recovery have been extensively studied, little information has been found on nutrient recovery and biochar’s phytotoxicity before its reuse as a soil amendment. This study aims to investigate the ideal pyrolysis temperature that guarantees higher fertility levels as well as meeting quality standards for land disposal. Accordingly, air-dried domestic sewage sludge has been pyrolyzed at 260°C (PSS1), at 420°C (PSS2), and at 610°C (PSS3) with a residence time of 20, 40, and 60 minutes, respectively. The raw sewage sludge and the produced biochars have been analyzed to determine their volatile organic matter (VOM), mineral content (MC), nutrients’ level (total nitrogen TN, available phosphorus P, and potassium K), alkalinity (pH), and salinity (electrical conductivity EC and Na). The toxic effect of biochars derived from SS has been evaluated through the analysis of trace metals (Pb, Cr, Cd, Cu, and Zn) and their toxicity by measuring root elongation inhibition (REI). As expected, pyrolysis temperature has a significant impact on the biochars’ characteristics. This has been justified by higher VOM, TN, and P in the sewage sludge (SS) and the biochar (PSS1) produced at low temperature (260°C). However, higher pH, EC, Na, and K have been found in the biochars (PSS2 and PSS3) produced at higher temperature (420 and 610°C). The effect of pyrolysis temperature on trace metals concentrations has shown different patterns from one element to another, which indicates lower levels in the biochar (PSS2) produced at 420°C. As a result, the lowest REI has been observed in PSS2 compared to that in SS, PSS1, and PSS3, which highlights that 420°C is the ideal pyrolysis temperature for the safe reuse of SS as a soil amendment.

Photosynthesis, Chlorophyll Fluorescence, and Yield of Peanut in Response to Biochar Application

The effect of biochar application on photosynthetic traits and yield in peanut (Arachis hypogaea L.) is not well understood. A 2-year field experiment was conducted in Northwest Liaoning, China to evaluate the effect of biochar application [0, 10, 20, and 40 t ha^-1 (B0, B10, B20, and B40)] on leaf gas exchange parameters, chlorophyll fluorescence parameters, and yield of peanut. B10 improved photochemical quenching at flowering and pod set and reduced non-photochemical quenching at pod set, relative to B0. B10 and B20 increased actual photochemical efficiency and decreased regulated energy dissipated at pod set, relative to B0. B10 significantly increased net photosynthetic rate, transpiration rate, stomatal conductance, and water use efficiency at flowering and pod set, relative to B0. Compared with B0, B10 significantly improved peanut yield (14.6 and 13.7%) and kernel yield (20.2 and 14.4%). Biochar application increased leaf nitrogen content. B10 and B20 significantly increased plant nitrogen accumulation, as compared to B0. The net photosynthetic rate of peanut leaves had a linear correlation with plant nitrogen accumulation and peanut yield. The application of 10 t ha^-1 biochar produced the highest peanut yield by enhancing leaf photosynthetic capacity, and is thus a promising strategy for peanut production in Northwest Liaoning, China.