Biogas Residue Research Articles

Characterization of organic materials in regulating soil carbon sequestration of urban greenspaces: Links to microbial necromass and community composition

Application of organic material is a win-win strategy that effectively boosts soil carbon (C) storage and promotes organic waste recycling in urban ecosystems. However, the divergent responses of C sequestration to organic materials and the underlying mechanisms remain unclear. Using molecular and litterbag methods, this study examined soil organic C (SOC) content, C sequestration efficiency of organic material (CSE-organic material), microbial necromass and community composition in urban greenspaces amended with different types of organic materials. The field experiment had seven treatments: addition of green waste (GreenWaste), green waste compost (GreenWasteCompost), biogas residue (BiogasResidue), biogas residue compost (BiogasResidueCompost), peat (PEAT), biochar (BioChar), and no organic material (Control). Organic materials after 16 months application increased SOC content by 34.1–87.0% compared with the Control and presented CSE-organic material in the order: BioChar > GreenWasteCompost > PEAT > BiogasResidueCompost > GreenWaste > BiogasResidue. Aromaticity index was positively correlated with CSE-organic material, indicating that aromatic C addition had a strong capacity to enhance C sequestration. Microbial necromass increased from 2.7 g C kg−1 in the Control to 3.9–5.0 g C kg−1 under organic materials addition. Bacterial necromass was enriched in the BiogasResidue and BiogasResidueCompost treatments, primarily because of sufficient substrate that facilitated the proliferation and activity of copiotrophic Firmicutes, whereas fungal necromass was 8.8–19.1% higher in the GreenWaste, GreenWasteCompost, and PEAT treatments than that in the BiogasResidue and BiogasResidueCompost treatments, accompanying by an increasing abundance of Ascomycota. However, the contribution of microbial necromass to the increased SOC was negatively correlated with CSE-organic material, suggesting that the input of recalcitrant C weakened the role of microbial necromass in C retention. Overall, this study reveals that the efficiency of organic materials application in promoting soil C accumulation depends largely on recalcitrant C rather than microbial necromass, which highlights the important role of organic waste acting as a C source in achieving urban sustainable development.

Performance response analysis and optimization for integrated renewable energy systems using biomass and heat pumps: a multi-objective approach

The focus of this study is to optimize the exploration of biomass-driven multi-energy systems, which include combined heat, power, and gas generation. The objective is to enhance the thermal, environmental, and economic performance indicators of the system. The optimization objectives encompass the quantities of internal combustion engines and air source heat pumps, as well as the dimensions of tanks utilized for anaerobic fermentation. A mathematical model was developed to optimize multiple objectives for combined heat, power, and gas generation systems by employing multi-objective intelligent optimization algorithms. The validation and analysis were conducted using rural residences in Lanzhou, Gansu Province, China, as a case study. The sensitivity analysis of biomass gasification combined heat and power systems was conducted from both technical and cost perspectives, examining the dynamic impact characteristics on the outcomes of multi-objective optimization. The findings indicate that the annual energy-saving rate of the optimized combined generation system decreased from 3.62% to -6.78%, while the growth in carbon emissions reduction rate increased from 76.05 to 81.38%, and the annual cost-saving rate grew from 0.97 to 14.96%. The power generation efficiency of the cogeneration station and hydraulic retention time were found to have a significant impact on the multi-objective optimization results of the combined generation system among the technical parameters. The unit cost of anaerobic fermentation tanks had a more significant impact on the multi-objective optimization results in terms of cost parameters, compared to the price of biogas residue.

Shift of bacterial and fungal communities upon soil amelioration is driven by carbon degradability of organic amendments

The structural response of bacterial and fungal soil communities to four carbon-rich organic amendments of increasing recalcitrance was investigated. Wheat straw, green compost, a mixed product based on biogas residues, and a fermented biochar were applied to a sandy agricultural soil of low organic carbon content. After laboratory incubation for 6 months, the community structure was investigated via DNA sequencing. All amendments caused changes in the communities of bacteria and fungi, but to different extents, with the communities exposed to more recalcitrant amendments showing the least variation compared to the non-amended soil. Changes in species composition as well as their relative abundances were observed. While the straw had a pronounced effect on bacteria (e.g., the highest number of indicator species), effects of the composted, fermented, or pyrolyzed materials were minor. Hierarchical clustering showed that the fungal communities were more different from each other than the bacterial ones with the straw-soil being most different and the biochar-soil least different from the non-amended soil. While the abundant fungal species in biochar-soil and non-amended soil were very alike, especially rare fungal species shifted upon addition of biochar. An indicator species analysis identified specific taxonomic groups which were triggered by the different organic materials. We conclude that bacterial and fungal communities strongly change upon input of degradable carbon (straw), while fungi in particular respond to the application of processed organic materials. With this study, we report the consequences of applying organic materials for the microbial community in one soil. We provide these data for meta-analyses that are required to unravel all relevant interactions across different soils, organic materials, and time. This will allow to better understand and predict the effects of organic soil amelioration measures on soil microorganisms.

Biogas Residue Carbonization Rather Than Biogas Residue Promoted the Yield of Pakchoi and Reduced the N2O Production Potential in Horticultural Soil

ABSTRACTBiogas residue (BR) and biogas residue‐derived biochar (BRC) are widely used as substitute for inorganic Nitrogen (N) fertilizers in vegetable production. Yet, their comparative research on vegetable production and N2O production was still lacking. Here, the pot experiment of pakchoi (Brassica chinensis) with a gradient of BR or BRC application rates (0, 30%, 60%, 100% w/w) was carried out to simulate different N fertilizer substitution rates. The results showed that the pakchoi yield had no difference between BR or BRC and control treatments; BRC had more advantages than BR in maintaining or increasing the pakchoi yield. BR and BRC could all reduce N2O production potential in vegetable soils. But BRC had a stronger ability to inhibit denitrification while BR had a stronger ability to inhibit nitrification compared with each other. The results showed that BR and BRC had different regulatory pathways for pakchoi yield and N2O production. BR regulated the pakchoi yield majorly through nitrification, but BRC majorly through denitrification. It suggested that BR and BRC could partially or completely replace inorganic fertilizers without reducing pakchoi yield. BRC combined with chemical fertilizers was a higher intelligence strategy in vegetable systems to improve pakchoi yield and N2O production compared with BR. It provided a theoretical basis for the application of BR and BRC to nutrient cycling and microbial processes in the soil‐vegetable system.

Application of Biogas Residues in Circular Agricultural Ecological Parks: Food Security and Soil Health

Application of Biogas Residues in Circular Agricultural Ecological Parks: Food Security and Soil Health

The simultaneous addition of chitosan and peat enhanced the removals of antibiotics resistance genes during biogas residues composting

Direct reuse of biogas residue (BR) has the potential to contribute to the dissemination of antibiotic resistance genes (ARGs). Although high-temperature composting has been demonstrated as an effective method for the harmless treatment of organic waste, there is few researches on the fate of ARGs in high-temperature composting of BR. This research examined the impact of adding 5% chitosan and 15% peat on physicochemical characteristics, microbial communities, and removal of ARGs during BR-straw composting in 12 Biolan 220L composters for 48 days. Our results showed that the simultaneous addition of chitosan and peat extended the high-temperature period, and increased the highest temperature to 74 °C and germination index. These effects could be attributed to the presence of thermophilic cellulose-decomposing genera (Thermomyces and Thermobifida). Although the microbial communities differed compositionally among temperature stages, their dissimilarity drastically reduced at final stage, indicating that the impact of different treatments on microbial community composition decreases at the end of composting. Peat had a greater impact on aerobic genera capable of cellulose degradation at thermophilic stage than chitosan. Surprisingly, despite the total copy number of ARGs significantly decreased during composting, especially in the treatment with both chitosan and peat, intl1 gene abundance significantly increased 2 logs at thermophilic stage and maintained high level in the final compost, suggesting there is still a potential risk of transmission and proliferation of ARGs. Our work shed some lights on the development of waste resource utilization and emerging contaminants removal technology.

A systematical comparation of Cu (II) adsorption behavior and mechanism between biomass fly ash and biogas residue pyrolysis char

Biomass fly ash (BFA) and biogas residues are the main by-products of biomass direct-fired power generation and biogas production. This study compares the Cu(II) adsorption mechanisms of BFA and biogas residue pyrolysis char (BRPC) through systematic tests. BFA exhibited a significantly higher adsorption capacity (75.34 mg/g) than BRPC (42.80 mg/g). The pseudo-first-order kinetic model best described BFA, while the Elovich model was optimal for BRPC. Both materials fit the Freundlich isotherm model. BFA's superior mineral co-precipitation and ion-exchange capacity are due to its rich mineral content, particularly calcium. BRPC benefits from an additional functional group complex adsorption due to its pyrolytic charcoal content. Variations in pore structure of BFA and BRPC did not demonstrate a significant effect on the adsorption. The results of this study provide essential data support for the potential of high-value utilization of BFA and BRPC and the innovative modification of high-performance biomass-based heavy metal adsorbent materials.

Organic waste recycling application increases N availability and mitigates N2O emission without crop yield penalty in the North China Plain.

Agricultural organic waste recycling can supply nutrients for crop production and partially replace chemical nitrogen fertilizers, which is beneficial for waste management and environmental protection. Nevertheless, comprehensive evaluation of the effects of different organic materials applications on crop yield and the environment is limited. Therefore, in this study, a comprehensive investigation of the synergistic effects of straw, pig manure, and biogas residue recycling on the wheat (Triticum aestivum L.) and maize (Zea mays L.) systems was carried out in the North China Plain. Field experiments were conducted from 2019 to 2021, comprising five treatments: straw (ST), pig manure (PM), and biogas residue (BR) partially replacing chemical nitrogen fertilizer, sole application of chemical nitrogen fertilizer (CF), and a control with no nitrogen application (WN). The results showed that organic materials significantly increased soil total nitrogen (3.04%-9.10%) and N recovery efficiency (REN; 42.21%-44.99%), but pig manure was more beneficial in increasing crop yields (3.50%), especially wheat yields (8.72%), and REN was significantly higher than that of the other treatments. Organic materials performed differently in wheat and maize seasons, and wheat yield could be improved by organic materials return. Organic materials stimulated N2O emission in wheat season (4.28%-32.20%), while biogas residue inhibited the N2O emission in maize season (47.47%). The negative effect of straw and biogas residue on yield decreased with increasing years of return, and pig manure continued to contribute to yield. In conclusion, pig manure is the optimal alternative that can increase crop yield, soil N content, and REN without stimulating N2O emissions.

The new strategies of using nitrogen and iron modified hydrochar to enhance methane production during co-anaerobic digestion of cow manure and corn straw

The traditional hydrochar shows limited ability to promote methane production during anaerobic digestion of organic solid waste. This study explored the effect of hydrochar modified using nitrogen and iron on methane production and microbial communities during the co-anaerobic digestion (co-AD) of cow manure and corn straw. Compared with unmodified hydrochar prepared from biogas residue (BHC), iron and nitrogen-iron modified hydrochar (BHC-Fe and BHC-N) improved the specific surface area (SSA) and proportion of oxygen-containing functional groups (OCFGs) related to direct interspecies electron transfer. The results showed that, compared to the control group (without hydrochar addition), the total methane production increased by 30 %, 36 %, and 46 % in the BHC, BHC-Fe, and BHC-N groups, respectively. The addition of modified hydrochar improved the microbial diversity and enrichment of Methanobacterium, Methanobrevibacter, and Methanosarcina spp., with BHC-N being the most effective. COD and Methanobrevibacter showed the highest explanation for methane production in AD performance indexes and archaeal genera (66.4 % and 29.3 %). Surface OCFGs of hydrochar had a more significant and direct effect on methane production than the SSA and archaeal genera. Therefore, the addition of BHC-N contributes more to promote methane production during the co-AD of cow manure and corn straw. This study could provide the new strategies for improving the co-AD of cow manure and corn straw performance, further promoting the resourcing and disposal of cow manure and corn straw.

Sequential carbonization of pig manure biogas residue into engineered biochar for diethyl phthalate removal toward environmental sustainability

Manure biogas residue has attracted increasing attention in waste recycling but faces substantial challenges because of its low carbon content, high ash content, and high heavy metal content. A novel sequential carbonization approach was proposed for recycling biogas residue; this approach consisted of pre-pyrolysis, activation with Ca(OH)2, and then activation with KOH. Pig manure-derived biogas residue was upcycled into engineered biochar (EB) with a high yield (26 %) and showed excellent performance in removing a typical plasticizer, diethyl phthalate (DEP). The proportion of carbon content greatly increased from 18 % (biogas residue) to 67 % (EB); however, the ash content decreased from 50 % (biogas residue) to 24 % (EB). The concentration of heavy metals decreased, and Zn had the largest decrease from 713 mg kg−1 to 61 mg kg−1 (p < 0.001). The sorption of DEP onto EB was rapid and reached equilibrium within 20 h. The developed specific surface area of EB was 1247 m2/g and provided abundant sorption sites for DEP; additionally, the sorption quantity reached 309 mg/g. The sorption capacity was dominated by surface adsorption. The oxygen-containing functional groups, graphene structure, porous structure, and hydrophobicity of EB contributed to the pore filling, hydrogen bonding, π–π stacking, and partitioning processes. Furthermore, the EB showed excellent practical application potential and great cycling stability. A sequential carbonization strategy was proposed to upcycle manure biogas residue into the EB for DEP removal; moreover, this strategy can aid in the attainment of environmental sustainability, including sustainable waste management and environmental pollution mitigation.

Distribution of microplastics and phthalic acid esters during dry anaerobic digestion of food waste and potential microbial degradation analysis

Food waste (FW) and its biogas residue were considered as sources of terrestrial microplastics (MPs) and phthalic acid esters (PAEs) contamination. However, there was a lack of research and understanding of the MPs and PAEs pollution problem in FW dry anaerobic digestion process (DADP). The MPs and PAEs in three stages of the DADP with the largest monomer disposal scale in China were identified. At the biogas residue extrusion stage, MPs abundance and PAEs concentration reached the highest values, which were 3.63 ± 0.45 × 103 N·kg-1 and 3.62 ± 0.72 mg·kg-1, respectively. Furthermore, there was a significant positive correlation between MPs and PAEs throughout the process (p < 0.05). Although bacteria and fungi with plastic degradation potential were present in all stages, the contamination problem of MPs and PAEs cannot be completely solved through DADP. This study provides a scientific basis for preventing and controlling the pollution of MPs and PAEs.

The effects of fertilizer pretreatment on nitrogen cycling in an intensively managed temperate grassland

Effective nitrogen (N) management is essential for minimizing fertilizer nutrient losses and maximizing N use efficiency. This study, conducted over two years on permanent grassland sites in Schleswig-Holstein, Germany, explored the effects of urea treatment with a urease inhibitor and digestate acidification on N-cycling and yield performance in a temperate maritime grassland context. Micro plots within these grasslands received varying N rates via acidified (with sulphuric acid) or non-acidified digestate (biogas residues), urea treated with- or without urease inhibitor (N-(n-butyl) thiophosphoric triamide) or calcium ammonium nitrate. Parameters measured included dry and N matter accumulations, NH3 volatilization, N2O emissions, NO3--N leaching, methane (CH4), and total greenhouse gas (GHG) emissions from soils. The findings demonstrated that the acidified digestate consistently enhanced metabolizable energy (ME), N yields (up to 47 %) and the apparent N recovery (ANR). While the acidified digestate and treated urea concurrently reduced NH3 emissions, the treated urea did not significantly affect (p> 0.05) dry matter (DM) and N yields, ANR, or total GHG emissions. Thus, digestate acidification or urea N stabilization could effectively mitigate the environmental impact of forage grass production while maintaining higher or comparable yields. However, higher risks of pollution swapping to groundwater bodies may result from higher N input rates. Applying acidified digestate or stabilized urea N to grasslands at a 120 kg mineral N ha−1 rate offers a practical approach, yielding appreciable N and ME while minimizing N losses.

Effect of agricultural management system (“cash crop”, “livestock” and “climate optimized”) on nitrous oxide and ammonia emissions

AbstractThe study aimed to measure soil-atmosphere N2O fluxes and their controlling factors, as well as NH3 emissions and yields for two soils (silt loam and clay loam) in three management systems over two years under subsequent wheat and maize cultivation. The management systems were characterized as follows: (1) cash crop (C) with mineral fertilizer and conventional tillage; (2) livestock (L) with biogas residue fertilization and its incorporation prior to sowing in maize and reduced tillage; and (3) climate optimized (O) with minimum tillage, 8-year crop rotation, with biogas residue fertilization, in maize without incorporation in clay loam soil or incorporation by strip-tillage prior to seeding in silt loam soil. Stable isotope ratios of N2O and mineral N were determined to identify N2O processes. Within the organically fertilized maize treatments, cumulative N2O fluxes were highest in the O-system treatments of both sites (4.0 to 9.4 kg N ha− 1 a− 1), i.e. more than twice as high as in the L-system (1.5 to 3.1 kg N ha− 1 a− 1). Below root-strip till fertilizer application did not enhance N2O fluxes. Fluxes with mineral fertilization of wheat (1.1 to 3.1 kg N ha− 1 a− 1) were not different from those with organic fertilization. Isotopic values of emitted N2O revealed that bacterial denitrification dominated most of the peak flux events, while the N2O/(N2 + N2O) ratio of denitrification was mostly between 0.1 and 0.5. It can be concluded that, contrary to the intention to lower greenhouse gas fluxes by the O-system management, the highest N2O fluxes occurred in the O-system without biogas digestate incorporation in maize. With respect to NH3 fluxes, we could confirm that the application of digestate application in growing crops without incorporation or late incorporation in fertilization before sowing induces high fluxes. The beneficial aspects of the O-system including more stable soil structure and resource conservation, are thus potentially counteracted by increased N2O and NH3 emissions.

Preparation of bacterial fertilizer from biogas residue after anaerobic co-digestion of kitchen waste and residual sludge.

Azotobacter chroococcum and Bacillus subtilis were selected as fermentation strains, and biogas residue after anaerobic digestion of kitchen waste and residual sludge was used as fermentation substrate. A single factor optimization test was used to optimize the solid-state fermentation parameters of biogas residue with the number of viable bacteria and the number of spores as indexes. The results showed that the optimum inoculation conditions involved the following: 55% initial moisture content, 15% initial inoculation amount, 30 ℃, and 1:1 initial inoculation ratio for 13days. Pot experiment showed that the prepared three kinds of bacterial fertilizers could not only effectively promote the growth of white clover, improve the composition of soil nutrients, but also change the structure of soil bacterial community, which is of great significance to the health of soil ecosystem in white clover.

Enhanced energy efficiency and fast co-pyrolysis characteristics of biogas residues and long-flame coal using infrared heating and TG-FTIR-MS

Co-pyrolysis may enhance the energy efficiency of anaerobic digestion waste (biogas residues), while simultaneously facilitating the clean utilization of coal. A thermogravimetric analyzer (TG), TG-FTIR-MS, and infrared heating technique were employed to investigate the rapid co-pyrolysis properties of long-flame coal (LFC) and biogas residues (BR) in this study. Meanwhile, the effects of temperature on the co-pyrolysis product distributions and compositions were studied in reactors that were heated with electric heating and rapid infrared heating. The co-pyrolysis of LFC and BR had the potential to decrease greenhouse gas emissions, as indicated by the TG-FTIR/MS findings. The co-pyrolysis kinetics were calculated using two models (KAS and FWO); the average Eα values are 176.09 and 187.26 kJ/mol, respectively. Tar yields increased initially in IH (electric heating) and EH (infrared heating) reactors, before declining as the temperature rose. The tar yields are greatest for EH at 500 °C (16.12 wt%) and IH at 600 °C (16.02 wt%). Tar yields generated via infrared heating were greatly higher than those generated by EH at 600–700 ℃. IH has a higher tar yield due to the fact that there are significant synergistic effects between coal and lignin, protein, and lipid at high temperatures. The GC-MS results indicate that IH has promoted the aromatization and ketonization reactions. Moreover, more monocyclic aromatic and bicyclic aromatic products are generated by infrared heating, suggesting an indication of tar quality improvement. An elevated co-pyrolysis temperature results in a greater degree of graphitization in char.

Synthesis of surficial-modified green biochar catalyst generated by biogas residue biochar and potential application for catalytic ozonation degradation of ciprofloxacin

This study synthesized novel, green, and easily recoverable surface-modified economical catalysts via hydrothermal treatment (HT) successfully, utilizing biogas residue biochar (BRB), a food waste product from anaerobic fermentation, pyrolyzed at 500 °C for 50 min. Using autoclaves, a total of six solutions were prepared, each having 1 g fine-grinded BRB, surficial modified by adding glycerol (GL) (10 or 20 mL) and SDI water (70 or 60 mL), and heated in an oven at 240 °C, 180 °C, and 120 °C for 24 h. Afterward, the catalysts showed the potential for degradation of widely used emerging pollutants like ciprofloxacin. Taking advantage of catalytic surface modification, the catalytic ozonation degradation was more effective than that of a single ozonation. However, under similar conditions, catalyst amount 0.20 g, ozone dose 15 mg L−1, and ciprofloxacin 80 mg L−1, the performance of the 10 mL GL-180 °C catalyst was excellent. It showed a 92.45%–94.41% optimum removal rate in the 8–10 min interval. After five continuous cycles, the 10 mL GL-180 °C catalyst exhibited excellent stability and reusability. XPS, FT-IR, BET, XRD, and SEM before and after the reaction confirmed the successful synthesis and degradation mechanism. A possible degradation pathway was unrevealed based on a liquid chromatography-mass spectrometer (LC-MS) and scavenger test, proving the significant roles of superoxide radicals (O2•-), hydroxyl radicals (•OH), and singlet oxygen (1O2). Further, Electron paramagnetic resonance (EPR) analysis confirmed the presence of active oxygen species. Subsequently, 10 mL GL-180 °C showed promising degradation for the actual water environment, such as groundwater (73.55%) and river water (64.74%). This work provides a valuable economic strategy to convert biogas residue biochar into a low-cost catalyst for organic pollutant decomposition.

Low concentration adsorption of ammonia using metal halide loaded biogas residue-based carbon materials

Treating wastewater with elevated ammonia nitrogen levels in garbage treatment plants is a global concern, with blow-off recognized as an efficient process for nitrogen removal. However, this method generates low-concentration ammonia, presenting a challenge for adequate recovery. This study addresses this issue by impregnating metal halides onto K2CO3-activated biogas residue to create composite materials tailored for adsorbing low-concentration ammonia. We systematically investigated the impact of activation parameters, metal halide type, loading capacity, and environmental conditions on the adsorption properties of the materials. Notably, at an activation temperature of 700 °C, utilizing copper chloride with a loading capacity of 30 %, the material exhibited a saturation adsorption capacity of 29.32 mg/g for 200 ppm NH3, with a breakthrough time of 45.6 min, significantly surpassing the untreated sample and demonstrated excellent regeneration performance. SEM, BET, and FTIR analyses revealed that the material provided dispersion sites for metal halides, promoted the complexation of metal halides and ammonia and retained pores for ammonia diffusion, thereby enhancing adsorption efficiency. This innovative approach contributes to waste utilization and ensures efficient ammonia recovery through metal halide-ammonia complexation.

Preparation of mesoporous biogas residue biochar via a self-template strategy for efficient removal of ciprofloxacin: Effect of pyrolysis temperature

Biochar preparation and application is an anticipated pathway for the resource utilization of biogas residue. In this study, biochars were prepared by the pyrolysis of biogas residue from food waste anaerobic digestion (named as BRBCs) under various pyrolysis temperatures (300, 500, 700, and 900 °C), and the effect of pyrolysis temperatures on the physicochemical characteristics of BRBCs was examined. The adsorption performance toward ciprofloxacin (CIP), a typical antibiotic in waterbodies, was also investigated. The results showed that pyrolysis temperature significantly changed the physicochemical properties of BRBCs. In addition, the minerals in the biogas residue, especially SiO2, were rearranged to form a mesoporous structure in biochar through a self-template strategy (without activator). BRBC prepared at 900 °C exhibited a high specific surface area and pore volume, well-developed mesopore structure, and more carbon structure defects, and exhibited the largest CIP adsorption capacity with 70.29 mg g−1, which was ascribed to the combined interaction of pore diffusion, π–π interactions, hydrogen bonding, complexation, and electrostatic forces. Furthermore, the adsorption of CIP by BRBC900 was well described by two-compartment kinetic and Langmuir isotherm models. BRBC900 showed good adsorption performance toward CIP at pH 7–9. The adsorption of CIP by BRBC is a spontaneous, exothermic, entropy-increasing process. Moreover, BRBC also presented a good recycling potential. Therefore, the preparation of mesoporous biochar based on a self-template strategy not only provides an option for the resource utilization of biogas residue but also offers a new option for the treatment of antibiotic wastewater.

A potential slow-release fertilizer based on biogas residue biochar: Nutrient release patterns and synergistic mechanism for improving soil fertility

The large yield of anaerobic digestates and the suboptimal efficacy of nutrient slow-release severely limit its practical application. To address these issues, a new biochar based fertilizer (MAP@BRC) was developed using biogas residue biochar (BRC) to recover nitrogen and phosphorus from biogas slurry. The nutrient release patterns of MAP@BRC and mechanisms for enhancing soil fertility were studied, and it demonstrated excellent performance, with 59% total nitrogen and 50% total phosphorus nutrient release rates within 28 days. This was attributed to the coupling of the mechanism involving the dissolution of struvite skeletons and the release of biochar pores. Pot experiments showed that crop yield and water productivity were doubled in the MAP@BRC group compared with unfertilized planting. The application of MAP@BRC also improved soil nutrient levels, reduced soil acidification, increased microbial populations, and decreased soil heavy metal pollution risk. The key factors that contributed to the improvement in soil fertility by MAP@BRC were an increase in available nitrogen and the optimization of pH levels in the soil. Overall, MAP@BRC is a safe, slow-release fertilizer that exhibits biochar-fertilizer interactions and synergistic effects. This slow-release fertilizer was prepared by treating a phosphorus-rich biogas slurry with a nitrogen-rich biogas slurry, and it simultaneously addresses problems associated with livestock waste treatment and provides a promising strategy to promote zero-waste agriculture.

Effects of food waste biogas residue composting on soil aggregates and its organic matter content in relocation site

Understanding the effects of food waste biogas residue composting and chemical amendments on soil aggregates composition of different particle sizes, stability, and organic matter distribution in relocation sites could provide primary data for improving soil quality and land utilization of food waste biogas residue composting. We analyzed the characteristics of soil aggregates distribution, stability of aggregates, and organic matter content in different particle sizes under treatments with different application amounts of food waste biogas residue composting, chemical amendments (β-cyclodextrin, calcium sulfate and ferric oxide were mixed at a mass ratio of 1:1:1), and control (100% soil). The results showed that 20% (soil: biogas residue composting=8:2) and 30% (soil: biogas residue composting =7:3) biogas residue composting significantly decreased the micro-aggregates content with the particle size of <0.106 mm and increased the large aggregates content with the particle size of 0.5-1.0 mm. All treatments significantly increased large aggregates content with the particle size of ≥2.0 mm, soil aggregate structure content, and mean weight diameter, but reduced the percentage of aggregate destruction. Among all the treatments, the effect of mixes application of 20% biogas residue composting and chemical amendments was the best. Biogas residue composting treatments significantly affected the distribution of organic matter in soil aggregates, with the strongest effect under 30% biogas residue composting treatment. Biogas residue composting treatments significantly increased soil organic matter content in all aggregates, with the maximal increase of organic matter content in soil micro-aggregates with the particle size of 0.106-0.25 mm. In conclusion, biogas residue composting could increase organic matter content of soil aggregates in different particle sizes, promote the formation of large soil aggregates, and improve the stability of aggregation. Specifically, the mixed application of biogas residue composting and chemical amendments performed better on soil improvement in relocation site.