Hydrothermal carbonization aqueous phase promotes nutrient retention and humic substance formation during aerobic composting of chicken manure

Recycling C and N from biogas slurry and wastewater of hydrothermal carbonization to rice-paddy systems: Enhanced soil dissolved C and N retention

This study explores a sustainable agricultural approach by mixing biogas slurry (BS) with hydrothermal carbonization aqueous phase (HCAP) to recycle carbon and nitrogen to rice-paddy system. Over two years, the effects of combining swine-derived BS with vegetable-derived HCAP as an alternative for synthesized nitrogen fertilizer in a rice-paddy system were evaluated. Four nitrogen substitution rates were tested: 0 % (control group, CKU), 50 % (low nitrogen substitution rate, BSVL), 75 % (medium nitrogen substitution rate, BSVM), and 100 % (high nitrogen substitution rate, BSVH). Results demonstrated combined application of BS and HCAP significantly improved soil dissolved organic matter (DOM) and total nitrogen content by 28.5-82.5 % and 5.8-7.2 %, respectively, with positive correlations to the increase in nitrogen substitution rate (P < 0.05). The DOM components revealed substantial increases in microbial by-product-like and fulvic acid-like substances in the soil, by 0.6-2.0 folds and 2.8-10.3 folds, respectively. Ammonia volatilization was significantly reduced by 15.6-46.3 % and 2.2-12.6 % across two years, correlating with pH and ammonium levels in floodwater (P < 0.05). Additionally, substituting chemical nitrogen fertilizer with BS and HCAP maintained grain nitrogen content without compromising rice nitrogen uptake. The results of structural equation model indicate that substituting nitrogen with BS and HCAP enhanced the recycling of carbon and nitrogen in paddy soil by improving soil DOM and total nitrogen accumulation. Overall, this study presents a viable strategy for recycling carbon and nitrogen from BS and HCAP into paddy soil, thereby substituting chemical fertilizers and enhancing soil fertility.

Livestock-Crop-Mushroom (LCM) Circular System: An Eco-Friendly Approach for Enhancing Plant Performance and Mitigating Microbiological Risks

Mushroom production using agroforestry biowaste is a great green cycling agriculture alternative. Therefore, the current study explored the Livestock-Crop-Mushroom (LCM) circular production model, starting with co-composting of straw and cow manure as a'St' biofertilizer further used for mushroom cultivation that ultimately produced a'StM' biofertilizer. The two biofertilizers were tested for their impacts on plant growth and potential microbial risks. The results show significant growth of oats stimulated by biofertiliser use. Both'St' and'StM' increased plant biomass, while with the latter, the crude protein content (+5.1%) and root biomass were also higher. Reduced abundances of resistome genes (30%) and pathogens (25%) were observed during the oat growth. Further, metagenomics analysis also indicated a reduction in antibiotic-resistance genes by -20% in soils with oats treated by'St' and -46% in'StM' biofertilizer treatment. The'StM' had a three-fold stronger inhibitory effect on oat rhizosphere soil pathogens than'St'. Moreover, compared to'St','StM' suppressed pathogens in seeds and stems, with specific beneficial biomarker microbes in different plant parts. Overall, the antibiotic resistance gene related to oxytetracycline decreased more than three-fold in the LCM system. This study demonstrates the substantial potential and scalability of the LCM circular system within the agricultural domain.

Aerobic composting with hydrothermal carbonization aqueous phase conditioning: Stabilized active gaseous nitrogen emissions

The losses of reactive gaseous nitrogen (N), including ammonia (NH3) and nitrous oxide (N2O), represent a pressing environmental issue during composting. However, the impact of hydrothermal carbonization aqueous phase (HAP) on compost gaseous N emissions and the underlying mechanisms remain largely unexplored. Herein, Quercus acutissima leaves-derived HAP and its modified HAP (MHAP) were added to the chicken manure compost at 5 % (w/w) and 10 % (w/w) applied rates to observe changes in NH3 and N2O fluxes, compost properties and bacterial communities. Results showed that high application of HAP significantly decreased compost cumulative NH3 volatilization by 23-26 % compared to the control and MHAP. Compost NH3 and N2O emissions were significantly influenced by compost temperature and inorganic N concentrations. Moreover, HAP and MHAP at high rates reduced the relative abundance of Bacteroidota (5-29 %) and Proteobacteria (11-35 %), compared to those at low rates. Compost environmental factors and bacterial diversity were identified as dominant factors affecting gaseous N emissions, with 54 % and 25 % explanatory rates, respectively. Furthermore, high application rates of HAP are expected to reduce annual NH3 emissions from poultry manure compost by 40000 t. These findings provide insights into rational resource utilization of HAP and gaseous N emission reduction from composting.

Hydrothermal treatment of septic sludge: Revealing temperature-sensitive dissolved organic matter and potential toxicity relationships in the hydrothermal liquid

Hydrothermal treatment of septic sludge can result in the transfer of significant amounts of dissolved organic matter (DOM) into the hydrothermal liquid (HL). However, there is a lack of research exploring the relationship between temperature-sensitive fractions of DOM in HL and ecological risks. In this study, spectroscopic techniques combining two-dimensional correlation spectroscopy (2D-COS), self-organizing maps (SOM) and structural equation modeling (SEM), respectively, were employed to investigate temperature-sensitive DOM and its potential correlation with phytotoxicity at five process temperatures (180-340 °C). The findings revealed that DOM content peaked at 260 °C, measuring 7625 mg·CL-1. At peak levels, the concentrations of chemical oxygen demand, ammonium nitrogen, total nitrogen, and total phosphorus in the HL reached 16900 mg L-1, 34.8 mg L-1, 1920 mg L-1 and 756 mg L-1, respectively. Results from EEM-PARAFAC-SOM indicated that temperature significantly influences the variations in fluorescent components within DOM. Additionally, 2D-COS analysis identified conjugated structures and critical turning points at 220 °C and 300 °C. Notably, the -CO-NH- functional group, which is closely associated with aromatic protein II, exhibited the highest sensitivity to temperature changes. Wheat seed germination experiments revealed that the DOM sample at 180 °C exhibited the most pronounced inhibition of wheat root length, while demonstrating the least effect on germination. In contrast, seed growth was most severely impaired at 340 °C. SEM analysis revealed the influence of temperature-both direct and indirect-on the properties of DOM, identifying aromatic protein I as the primary determinant limiting seed germination. This research provides valuable insights for the management and utilization of HL.

Effects of biochar and wood vinegar co-application on composting ammonia and nitrous oxide losses and fertility

Composting faces challenges with nitrogen (N) losses through ammonia (NH3) and nitrous oxide (N2O) emissions. In this study, wood vinegar (WV) and biochar (BC) were applied individually or combined into wheat straw and chicken manure composting. Results showed that BC and WV reduced NH3 volatilizations by 22-23 % individually, but their combined application achieved a 59 % reduction. However, this combination increased N2O emissions by 174 %. The BC + WV treatment improved compost quality, evidenced by increased total N content by 22 % and enhanced the biological index, promoting additional dissolved organic matter production. Overall, BC and WV applications improved compost quality, reduced gaseous N losses, and supported the re-utilization of agricultural residues. The combined use of BC and WV significantly enhances compost quality and reduces NH3 emissions, offering a promising solution for sustainable agricultural residue management.

Enhancing C and N turnover, functional bacteria abundance, and the efficiency of biowaste conversion using Streptomyces-Bacillus inoculation

Microbial inoculation plays a significant role in promoting the efficiency of biowaste conversion. This study investigates the function of Streptomyces-Bacillus Inoculants (SBI) on carbon (C) and nitrogen (N) conversion, and microbial dynamics, during cow manure (10% and 20% addition) and corn straw co-composting. Compared to inoculant-free controls, inoculant application accelerated the compost's thermophilic stage (8 vs 15 days), and significantly increased compost total N contents (+47%) and N-reductase activities (nitrate reductase: +60%; nitrite reductase: +219%). Both bacterial and fungal community succession were significantly affected by DOC, urease, and NH4+-N, while the fungal community was also significantly affected by cellulase. The contribution rate of Cupriavidus to the physicochemical factors of compost was as high as 83.40%, but by contrast there were no significantly different contributions (∼60%) among the top 20 fungal genera. Application of SBI induced significant correlations between bacteria, compost C/N ratio, and catalase enzymes, indicative of compost maturation. We recommend SBI as a promising bio-composting additive to accelerate C and N turnover and high-quality biowaste maturation. SBI boosts organic cycling by transforming biowastes into bio-fertilizers efficiently. This highlights the potential for SBI application to improve plant growth and soil quality in multiple contexts.

Control of nitrogen and odor emissions during chicken manure composting with a carbon-based microbial inoculant and a biotrickling filter

Although aerobic composting is usually utilized in livestock manure disposal, the emission of odorous gases from compost not only induces harm to the human body and the environment, but also causes loss of nitrogen, sulfur, and other essential elements, resulting in a decline in product quality. The impact of biotrickling filter (BTF) and insertion of carbon-based microbial agent (CBMA) on compost maturation, odor emissions, and microbial population during the chicken manure composting were assessed in the current experiment. Compared with the CK group, CBMA addition accelerated the increase in pile temperature (EG group reached maximum temperature 10 days earlier than CK group), increased compost maturation (GI showed the highest increase of 41.3% on day 14 in EG group), resulted in 36.59% and 14.60% increase in NO3--N content and the total nitrogen retention preservation rate after composting. The deodorization effect of biotrickling filter was stable, and the removal rates of NH3, H2S, and TVOCs reached more than 90%, 96%, and 56%, respectively. Furthermore, microbial sequencing showed that CBMA effectively changed the microbial community in compost, protected the ammonia-oxidizing microorganisms, and strengthened the nitrification of the compost. In addition, the nitrifying and denitrifying bacteria were more active in the cooling period than they were in the thermophilic period. Moreover, the abundance of denitrification genes containing nirS, nirK, and nosZ in EG group was lower than that in CK group. Thus, a large amount of nitrogen was retained under the combined drive of BTF and CBMA during composting. This study made significant contributions to our understanding of how to compost livestock manure while reducing releases of odors and raising compost quality.

Electric field-assisted aerobic co-composting of chicken manure and kitchen waste: Ammonia mitigation and maturation enhancement

A low-voltage electric field assisted strategy is considered to be effective in improving compost effect of conventional chicken manure composting (CCMC), but it lacks a critical assessment of NH3 mitigation and suitability for complex initial materials. This study firstly constructed an electric field-assisted aerobic co-composting (EFAC) of chicken manure and kitchen waste to evaluate NH3 mitigation and compost maturity. The results showed that the NH3 emissions of EFAC were 48.73% lower than those of CCMC. The proposed mechanisms suggest that the combined effect of reduced acidity and electric field inhibited the activities and functions related to ammoniation and ammonia-nitrogen conversion. The germination index of EFAC was 54.29% higher than that of CCMC, due to the enhancement of compost maturation. This study demonstrates that the electric field-assisted strategy for co-composting has a broad potential to reduce ammonia emissions and enhance the disposal of complex feedstocks.

Hydrothermal carbonization of biogas slurry and cattle manure into soil conditioner mitigates ammonia volatilization from paddy soil

Hydrothermal carbonization of biogas slurry and animal manure into hydrochar could enhance waste recycling waste and minimize ammonia (NH3) volatilization from paddy fields. In this study, cattle manure-derived hydrochar prepared in the presence of Milli-Q water (CMWH) and biogas slurry (CMBSH), and biogas slurry-based hydrochar embedded with zeolite (ZHC) were applied to rice-paddy soil. The results demonstrated that CMBSH and ZHC treatments could significantly mitigate the cumulative NH3 volatilization and yield-scale NH3 volatilization by 27.9-45.2% and 28.5-45.4%, respectively, compared to the control group (without hydrochar addition), and significantly correlated with pH and ammonium-nitrogen (NH4+-N) concentration in floodwater. Nitrogen (N) loss via NH3 volatilization in the control group accounted for 24.9% of the applied N fertilizer, whereas CMBSH- and ZHC-amended treatments accounted for 13.6-17.9% of N in applied fertilizer. The reduced N loss improved soil N retention and availability for rice; consequently, grain N content significantly increased by 6.5-14.9% and N-use efficiency increased by 6.4-16.0% (P < 0.05), respectively. Based on linear fitting results, NH3 volatilization mitigation resulted from lower pH and NH4+-N concentration in floodwater that resulted from the acidic property and specific surface area of hydrochar treatments. Moreover, NH3-oxidizing archaea abundance in hydrochar-treated soil decreased by 40.9-46.9% in response to CMBSH and ZHC treatments, potentially suppressing NH4+-N transformation into nitrate and improving soil NH4+-N retention capacity. To date, this study applied biogas slurry-based hydrochar into paddy soil for the first time and demonstrated that ZHC significantly mitigated NH3 and increased N content. Overall, this study proposes an environmental-friendly strategy to recycle the wastes, biogas slurry, to the paddy fields to mitigate NH3 volatilization and increase grain yield of rice.