Mechanisms for enhanced lignin humification with reduced organic matter loss by goethite in biogas residue composting

A new insight into the straw decomposition associated with minerals: Promoting straw humification and Cd immobilization

Organic matter (OM) derived from the decomposition of crop residues plays a key role as a sorbent for cadmium (Cd) immobilization. Few studies have explored the straw decomposition processes with the presence of minerals, and the effect of newly generated organo-mineral complexes on heavy metal adsorption. In this study, we investigated the variations in structure and composition during the rice straw decomposition with or without minerals (goethite and kaolinite), as well as the adsorption behavior and mechanisms by which straw decomposition affects Cd immobilization. The degree of humification of extracted straw organic matter was assessed using excitation-emission matrix (EEM) fluorescence and Ultraviolet-visible spectroscopy (UV-vis), while employing FTIR spectroscopy and XPS to characterize the adsorption mechanisms. The spectra analysis revealed the enrichment of highly aromatic and hydrophobic components, indicating that the degree of straw decomposition and humification were further intensified during incubation. Additionally, the existence of goethite (SG) accelerated the humification of OM. Sorption experiments revealed that the straw humification increased Cd adsorption capacity. Notably, SG exhibited significantly higher adsorption performance compared to the organic matter without minerals (RS) and the existence of kaolinite (SK). Further analysis using FT-IR spectroscopy and XPS verified that the primary mechanisms involved in Cd immobilization were complexion with -OH and -COOH, as well as the formation of Cd-π binds with aromatic C=C on the surface of solid OMs. These findings will facilitate understanding the interactions of the rice straw decomposing with soil minerals and its remediation effect on Cd-contaminated farmland.

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.

Recent advances review in tea waste: High-value applications, processing technology, and value-added products

Tea waste (TW) includes pruned tea tree branches, discarded summer and fall teas, buds and wastes from the tea making process, as well as residues remaining after tea preparation. Effective utilization and proper management of TW is essential to increase the economic value of the tea industry. Through effective utilization of tea waste, products such as activated carbon, biochar, composite membranes, and metal nanoparticle composites can be produced and successfully applied in the fields of fuel production, composting, preservation, and heavy metal adsorption. Comprehensive utilization of tea waste is an effective and sustainable strategy to improve the economic efficiency of the tea industry and can be applied in various fields such as energy production, energy storage and pharmaceuticals. This study reviews recent advances in the strategic utilization of TW, including its processing, conversion technologies and high value products obtained, provides insights into the potential applications of tea waste in the plant, animal and environmental sectors, summarizes the effective applications of tea waste for energy and environmental sustainability, and discusses the effectiveness, variability, advantages and disadvantages of different processing and thermochemical conversion technologies. In addition, the advantages and disadvantages of producing new products from tea wastes and their derivatives are analyzed, and recommendations for future development of high-value products to improve the efficiency and economic value of tea by-products are presented.

Reducing carbon and nitrogen loss by shortening the composting duration based on seed germination index (SCD@GI): Feasibilities and challenges

Addressing carbon (C) and nitrogen (N) losses through composting has emerged as a critical environmental challenge recently, and how to mitigate these losses has been a hot topic across the world. As the emissions of carbonaceous and nitrogenous gases were closely correlated with the composting process, the feasibility of composting duration shortening on C and N loss needs to be explored. Therefore, the goal of this paper is to find evidence-based approaches to reduce composting duration, utilizing the seed germination index as a metric (SCD@GI), for assessing its efficiency on C and N loss reductions as well as compost quality. Our findings reveal that the terminal seed germination index (GI) frequently surpassed the necessary benchmarks, with a significant portion of trials achieving the necessary GI within 60 % of the standard duration. Notably, an SCD@GI of 80 % resulted in a reduction of CO2 and NH3 by 21.4 % and 21.9 %, respectively, surpassing the effectiveness of the majority of current mitigation strategies. Furthermore, compost quality, maturity specifically, remained substantially unaffected at a GI of 80 %, with the composting process maintaining adequate thermophilic conditions to ensure hygienic quality and maturity. This study also highlighted the need for further studies, including the establishment of uniform GI testing standards and comprehensive life cycle analyses for integrated composting and land application practices. The insights gained from this study would offer new avenues for enhancing C and N retention during composting, contributing to the advancement of high-quality compost production within the framework of sustainable agriculture.

Iron oxyhydroxide catalyzes production of artificial humic substances from waste biomass

Production of artificial humic substances (AHS) from waste biomass will contribute to environmental protection and agricultural productivity. However, there is still a lack of a faster, more efficient and eco-friendly way for sustainable production. In this study, we proposed a method to accelerate the production of AHS from cotton stalks by mild pyrolysis and H2O2 oxidation in only 4 hours, and investigated the formation of AHS during biomass transformation. We found that the process increased the aromatic matrix and facilitated biomass transformation by enhancing the depolymerization of lignin into micromolecular phenolics (e.g., guaiacol, p-ethyl guaiacol, etc.). The optimum conditions of pyrolysis at 250 °C and oxidation with 6 mL H2O2 (5 wt%) yielded up to 19.28 ± 1.30 wt% artificial humic acid (AHA) from cotton stalks. In addition, we used iron oxyhydroxide (FeOOH) to catalyze biomass transformation and investigated the effect of FeOOH on the composition and properties of AHS. 1.5 wt% FeOOH promoted the increased content of artificial fulvic acid (AFA) in AHS from 10.1% to 26.5%, eventually improving the activity of AHS. FeOOH raised the content of oxygen-containing groups, such as carboxylic acids and aldehyde, and significantly increased polysaccharide (10.94%-18.95%) and protein (1.95%-2.18%) derivatives. Polymerization of amino acid analogs and many small-molecule carbohydrates (e.g., furans, aldehydes, ketones, and their derivatives) promoted AFA formation. Finally, carbon flow analysis and maize incubation tests confirmed that AHS were expected to achieve carbon emission reductions and reduce environmental pollution from fertilizers. This study provides a sustainable strategy for the accelerated production of AHS, which has important application value for waste biomass resource utilization.