The transformation of heavy metal speciation during rapid high-temperature aerobic fermentation of food waste and their potential mechanisms

Optimizing extraction conditions to enhance the humification and soil remediation potential of compost-derived dissolved organic matter

Compost tea (CT), primarily composed of dissolved organic matter derived from compost, is widely used in various environmental and agricultural applications. Nevertheless, limited information is available regarding how extraction parameters influence the quality of CT and its efficacy in soil remediation. In this study, a multi-factor orthogonal design L16 (43) was employed to investigate the effects of compost-to-water ratio (CWR), extraction time (ET), and aeration pattern (AP) on nutrient extraction and humification of CT, aiming to optimize the extraction conditions. Results showed that N, P2O5, and K2O extraction efficiencies in all treatments ranged from 10 to 25 %, 10-20 %, and 50-85 %, respectively. The comprehensive humification score was in the range of 1.27-1.60. Among the three parameters, ET showed the most significant influence on CT quality. The optimal treatment for nutrient extraction was T15 (CWR 1:60, ET 48 h, and stirring), while T17 (CWR 1:30, ET 48 h, and aeration) exhibited superior performance on humification. Furthermore, the total Cd removal efficiency of T17 was 83.64 % after multiple washing cycles, which was attributed to an increased number of hydroxyl, carboxyl, and carbonyl functional groups that provided additional binding sites for Cd.

Phosphate-coupled high-carbon ferromanganese particles synergistically regulate co-composting of seaweed and corn starch residue: Improving nitrogen cycling and accelerating humification

A substantial amount of seaweed waste, rich in plant-stimulating properties, holds great potential for composting. However, without proper catalysts or additives, composting and humification are slow and inefficient, causing carbon and nitrogen losses. This study explores a novel approach to enhance composting efficacy by coupling phosphate with high-carbon ferromanganese particles (HCFMP). The results indicate that the phosphate-HCFMP coupling promotes humus precursor transformation, as evidenced by dynamic changes in reducing sugars, amino acids, and polyphenols. Additionally, ultraviolet characteristic parameters and Parallel Factor (PARAFAC) analysis show that the coupled treatment improves both the rate and degree of humification. By the end of composting, this treatment exhibited the highest HA/FA (4.38), with the HA/FA on day 21 surpassing other treatments on day 35. While the phosphate-only group achieved a relatively high degree of humification, the process was slower and accompanied by substantial NH3 volatilization. The HCFMP-only group reduced NH3 emissions, but the oxidative performance of HCFMP was enhanced under lower pH conditions, reducing organic matter participation in humus formation. Compared to phosphate alone, the coupled treatment reduced NH3 emissions by 48.6% and increased nitrate content by 12%. Further analysis suggests that the enhancement mechanisms may include: (1) phosphate stimulating humus precursor production; (2) HCFMP mainly acting as a catalyst under higher pH to promote precursor polymerization; and (3) HCFMP's acidic sites adsorbing NH3/NH4+ and facilitating nitrification. In conclusion, coupling HCFMP with phosphate enhances composting efficacy, and the resulting products, with plant-stimulating properties, offer a feasible solution for sustainable green agriculture development.

A review of volatile fatty acids production from organic wastes: Intensification techniques and separation methods

High value-added products from organic waste fermentation have garnered increasing concern in modern society. VFAs are short-chain fatty acids, produced as intermediate products during the anaerobic fermentation of organic matter. VFAs can serve as an essential organic carbon source to produce substitutable fuels, microbial fats and oils, and synthetic biodegradable plastics et al. Extracting VFAs from the fermentation broths is a challenging task as the composition of suspensions is rather complex. In this paper, a comprehensive review of methods for VFAs production, extraction and separation are provided. Firstly, the methods to enhance VFAs production and significant operating parameters are briefly reviewed. Secondly, the evaluation and detailed discussion of various VFAs extraction and separation technologies, including membrane separation, complex extraction, and adsorption methods, are presented, highlighting their specific advantages and limitations. Finally, the challenges encountered by different separation technologies and novel approaches to enhance process performance are highlighted, providing theoretical guidance for recycling VFAs from organic wastes efficiently.

Evaluating the role of salinity in enhanced biogas production from two-stage anaerobic digestion of food waste by zero-valent iron

Salts including NaCl are the most common food flavoring agents so they are often accumulated in food waste (FW) and have potential impact on anaerobic digestion (AD) of FW. In this study, the enhanced biogas production from two-stage anaerobic digestion (TSAD) of FW by microscale zero-valent iron (ZVI) under different salinity (3, 6, 9, and 15 g NaCl/L) was evaluated. Under salinity stress, ZVI becomes a continue-release electron donor due to the enhanced corrosion and dissolution effect and the slow-down surface passivation, further improving the performance of TSAD. Experimental results revealed that the biogas production including H2 and CH4 from TSAD with 10 g/L ZVI addition was promoted under salinity stress. The maximum H2 and CH4 yield (303.38 mL H2/g-VS and 253.84 mL CH4/g-VS) were observed at the salinity 9 g NaCl/L. Compared with that of zero salinity, they increased by 40.94% and 318.46%, respectively. Additionally, Sedimentibacter, an exoelectrogen that can participate in the direct interspecies electron transfer, also exhibited the highest relative abundance (34.96%) at the salinity 9 g NaCl/L. These findings obtained in this study might be of great importance for understanding the influence of salinity on the enhanced AD by ZVI.