The effect of biochar on the migration theory of nutrient ions

Analysis of the adsorption and fixation process of ammonium nitrogen in arable soil by biochar based on molecular dynamics simulation

The ammonia nitrogen in arable land soil is susceptible to environmental and anthropogenic influences, leading to nutrient loss. This study utilized indoor soil column leaching experiments, combined with adsorption mathematical models, traditional characterization methods, and molecular dynamics simulation methods, to analyze the effects of biochar on changes in ammonium ions in different soil layers and leachate of arable land soil. The study found that applying biochar at a ratio of 10 % to arable land soil could effectively increase the ammonium ion content in the 0-10 cm soil layer by 1.57-2.36 times and reduce loss by 44.83-72.27 %. The adsorption and fixation process of biochar is controlled by electrostatic attraction and ion exchange processes. Interactions between molecules, electrostatic forces, and system internal energy also have certain effects on the process. Near the structure of C6H12O6, there are low-energy adsorption sites for ammonium ions, which can provide the energy required for electrostatic attraction. Structures such as C5H10O5, C-S-H, C-SO3, and C4H7NO4 respectively play roles in physical adsorption or chemical adsorption through displacement reactions, electron exchange, and other forms. The adsorption free energy is -394,590.84 kcal/mol, indicating stable adsorption and a process that tends to interact with the biochar surface. This study addresses issues such as the easy loss of ammonia nitrogen in arable land soil and the unclear adsorption mechanism of biochar on ammonium ions, providing a theoretical basis for the field of environmental science.

Nutrient-rich hydrothermal carbon production by exogenous nutrients combined with seaweed internal water

As a product of hydrothermal carbonization (HTC) technology, hydrothermal carbon has shown excellent application potential in soil improvement, greenhouse gas reduction and pollution remediation. Since a large amount of water and biomass are directly used as reaction media, hydrothermal carbon produced by traditional HTC possesses poor nutrient properties and accompanied by the generation of toxic and hazardous wastewater. Here, a versatile and easily scalable strategy has been demonstrated for the one-step production of industrial nutrient-rich hydrothermal carbon (NRHC) by combining the exogenous nutrients with seaweed internal water. During the reaction process, exogenous nutrients (NH4H2PO3, KNO3, CO(NH2)2) participated in the HTC reaction and were uniformly distributed on the surface of hydrothermal carbon through surface complexation precipitation, ion exchange, and electrostatic interactions. Simulations based on density functional theory revealed that NRHC produced in presence of exogenous nutrients possessed more active sites and surface charges. Moreover, the adsorbent and adsorbate were simultaneously affected by intermolecular forces, electrostatic forces, and internal energy of the system, and the thermodynamics of adsorption process was more stable. Compared with no exogenous nutrient involvement, NRHC produced by exogenous nutrients showed 2.12, 18.56, and 25.69 times increase in the N, P, and K content. The length of the seed germination root system increased by 4.3-5.9 times, which met the standards set for agricultural fertilizer. Due to increased yield per unit volume and reduced wastewater generation, the cost of NRHC production reduced by 47.83-58.23 per cent and profit enhanced by 1.56-1.68 times, as compared to traditional HTC. This low-cost streamlined process provides a new strategy for large-scale production and direct application of hydrothermal carbon.

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.

Biochar-coupled organic fertilizer reduced soil water-dispersible colloidal phosphorus contents in agricultural fields

Soil water-dispersible colloidal phosphorus (WCP) presents high mobility, however, the regulatory effect of biochar-coupled organic fertilizer is rarely known, especially under different cropping patterns. This study investigated the P adsorption, soil aggregate stability, and WCP in three paddy and three vegetable fields. These soils were amended with different fertilizers (chemical fertilizer, CF; substitution of solid-sheep manure or liquid-biogas slurry organic fertilizer, SOF/LOF; substitution of biochar-coupled organic fertilizers, BSOF/BLOF). Results presented that the LOF averagely increased the WCP contents by 50.2% across the sites, but the SOF and BSOF/BLOF averagely decreased their contents by 38.5% and 50.7% in comparison with the CF. The WCP decline in the BSOF/BLOF-amended soils was mainly attributed to the intensive P adsorption capacity and soil aggregate stability. The BSOF/BLOF increased the amorphous Fe and Al contents in the fields in comparison with the CF, which improved the adsorption capacity of soil particles, further improving the maximum absorbed P (Q_max) and reducing the dissolved organic matter (DOC), leading to the improvement of > 2 mm water-stable aggregate (WSA_>2mm) and subsequent WCP decrease. This was proved by the remarkable negative associations between the WCP and Q_max (R² = 0.78, p < 0.01) and WSA_>2mm (R² = 0.74, p < 0.01). This study manifests that biochar-coupled organic fertilizer could effectively reduce soil WCP content via the improvement of P adsorption and aggregate stability.

Combined addition of biochar, lactic acid, and pond sediment improves green waste composting

Composting, as an eco-friendly method to recycle green waste (GW), converts the GW into humus-like compounds. However, conventional GW composting is inefficient and generates poor-quality compost. The objective of this research was to investigate the effects of the combined additions of biochar (BC; 0, 5, and 10 %), lactic acid (LA; 0, 0.5, and 1.0 %), and pond sediment (PS; 0, 20, and 30 %) on GW composting. A treatment without additives served as the control (treatment T1). The results showed that treatment R1 (with 5 % BC, 0.5 % LA, and 20 % PS) was better than the treatments with two additives or no additive and required only 32 days to generate a stable and mature product. Compared with T1, R1 improved water-holding capacity, electrical conductivity, available phosphorus, available potassium, nitrate nitrogen, OM decomposition, and germination index by 51 %, 48 %, 170 %, 93 %, 119 %, 157 %, and 119 %, respectively. R1 also increased the activities of cellulase, lignin peroxidase, and laccase. The results showed that the combined addition of BC, LA, and PS increased the gas exchange, water retention, and the microbial secretion of enzymes, thus accelerating the decomposition of GW. This study demonstrated the effects of BC, LA, and PS addition on GW composting and final compost properties, and analyzed the reasons of the effects. The study therefore increases the understanding of the sustainable disposal of an important solid waste.