Humic Acid Concentration Research Articles

Magnetic nanoparticle modified moss Biochar: A novel solution for effective removal of enrofloxacin from aquaculture water.

The presence of residual antibiotics in water constitutes a potential threat to aquatic environments. Therefore, designing environmentally friendly and efficient biochar adsorbents is crucial. Aquaculture by-product moss (bryophyte) was transformed into biochar, which can eliminate antibiotics from wastewater through adsorption. This study successfully fabricated moss biochar (BC) and magnetically modified moss biochar (MBC), and explored their adsorption performance for enrofloxacin (ENR). Characterization analyses revealed that the specific surface area, total pore volume, and the quantity of functional groups of the MBC were significantly larger than those of the BC. The Langmuir isotherm model suggests that the maximum adsorption capacities of BC and MBC for ENR are 7.24mgg⁻1 and 11.62mgg⁻1. The adsorption process conforms to a pseudo-second-order kinetic model. Studies carried out at different temperatures disclose the spontaneous and endothermic thermodynamic characteristics of the system. Under neutral conditions, the adsorption efficiency attains its peak. The existence of various coexisting ions in water exerts a negligible influence on the adsorption process; furthermore, when the concentration of humic acid (HA) ranges from 0 to 20mg/L, the removal rate remains above 90%. In actual water samples, the antibiotic removal rate can be as high as 96.84%. After three cycles of reuse, the structure of MBC remains unchanged while maintaining a high removal efficiency. The primary mechanisms for antibiotic adsorption by MBC involve electrostatic interactions, hydrophobic interactions, pore-filling effects, hydrogen bonding, and π-π interactions. This reusable magnetic moss biochar provides a promising research direction for effectively eliminating antibiotics from water sources.

Bioaugmentation strategies in co-composting anaerobically digested food waste with agricultural by-products: Enhancing fertilizer quality and microbial communities.

Effective management of urban solid waste is critical for achieving sustainable development goals. One key aspect of this challenge is the recycling of anaerobically digested residues from anaerobic digestion of food waste, which plays a pivotal role in promoting sustainability. However, there is a gap in understanding the feasibility and effectiveness of converting these digested residues into valuable fertilizers through composting. Addressing this gap, the present study explored the potential of composting anaerobically digested residue and evaluated the quality of the co-compost products. In this study, we investigated the composting process using a mixture of rice straw, food waste, sheep manure and mature composted residues (RFM group) alongside the anaerobically digested residues. The results demonstrated that the composting process quickly reached the thermophilic stage, during which NH+4-N concentrations increased and C/N ratio decrease. The RFM group exhibited the highest humic acid content compared to other groups. Additionally, microbial analysis revealed key species such as Clostridium, Moheibacter, Bacillus, Thermobacillus, and Pseudogracilibacillus as major contributors to the composting process. The germination index (GI) test indicated that the co-composted residues were non-toxic to plants, suggesting their suitability as a fertilizer. All these works indicated that the addition of rice straw, food waste, and mature composted residues to anaerobically digested materials significantly enhanced the composting process, resulting in a high-quality co-compost. This approach not only provided a promising method for recycling food waste but also contributed to the broader goal of sustainable solid waste management.

Unraveling the mechanisms of post-treatment to enhance humification and Cd remediation in compost through EDTA-Fenton-Like systems.

This study aimed to enhance humification and cadmium (Cd) remediation in compost by investigating the effects of three post-treatments: ultrapure water, citric acid, and ethylenediaminetetraacetic acid disodium (EDTA). The results revealed that the EDTA post-treatment significantly enhanced humification by facilitating an EDTA-Fenton-like system within compost comprising rice straw and river sediment to remediate Cd-contaminated sediment. EDTA post-treatment not only promoted humic substances and humic acid concentrations of up to 66.30g/kg and 30.40g/kg, respectively, but also led to a reduction in the Cd content and bioavailability factor by 75.02% and 9.76%, respectively. In addition, parallel factor analysis revealed two distinct components, while two-dimensional correlation spectroscopy showed that the polysaccharides and carboxyl groups in humic acid were preferentially bound to Cd. Overall, this study proposes a promising approach for enhancing humification and Cd remediation in compost by the EDTA post-treatment.

Study on the influence of soil properties on fluorescence intensity of polycyclic aromatic hydrocarbons.

The properties of soil matrix have an impact on the fluorescence intensity of polycyclic aromatic hydrocarbons (PAHs), which restricts the application of fluorescence spectral technology in detecting PAHs in soil. The present study explored the mechanism of the influence of soil matrix properties on the fluorescence intensity of PAHs from the perspective of specific surface area (SSA). A three-factor three-level experimental design was adopted for investigating the relationship between soil matrix properties, PAH fluorescence intensity, and soil SSA. The typical benzo[ghi]perylene pollutant in soil as the research object, 27 soil samples with different sand content, moisture content, humic acid content, and given benzo[ghi]perylene concentration (2mg/g) were prepared. On the basis of obtaining the fluorescence spectra and SSA data of soil samples, statistical analyses of fluorescence intensity and SSA were investigated in relation to the soil matrix properties. The statistical results showed that the soil matrix properties had a significant influence (P < 0.05) on the fluorescence intensity and SSA. Furthermore, combined with the technology of fluorescence microscopy imaging, the influence mechanism of soil matrix properties on fluorescence intensity was revealed. The soil matrix properties affected the soil SSA, resulting in a change of benzo[ghi]perylene concentration in the soil surface at the probe window, thereby affecting the fluorescence intensity.

Reduced soil water repellency suggests the need for timely replenishment of soil organic matter in long-term traditional farming

Long-term land use and management practices can affect soil organic matter (SOM) and cause changes in soil water repellency (SWR), the extent of which is related to SOM content and composition. Many studies have focused on explaining the generation of SWR and have emphasized the relation between the occurrence and persistence of SWR and SOM; however, few studies have attempted to revisit the amount and quality of SOM based on changes in SWR. In this 10-year study, SWR and SOM were evaluated after traditional tillage versus a one-time straw return, and the effect of traditional tillage on SOM was illustrated through changes in SWR. The findings indicated that SOM and humic acid (HA) contents and the degree of humification decreased by 8.58 %, 24.93 %, and 20.44 %, respectively, after 10 years of traditional tillage. Furthermore, the H/C molar ratio of HA decreased by 13.38 %, and the aliphatic/aromatic C ratio and the hydrophobic/hydrophilic C ratio decreased by 24.05 % and 31.08 %, respectively, resulting in a weakening of HA hydrophobicity. The primary cause for the decline in SWR over extended periods of traditional tillage was the reduction in both the amount and quality of SOM and the decreased hydrophobicity of HA. By contrast, during the initial phase of one-time straw return, there was a notable increase in the amount and quality of SOM and HA hydrophobicity, resulting in a slight water repellency of the soil; however, this increase only lasted for 3 years. The decrease in the degree and persistence of SWR reflects the decrease in the amount and quality of SOM after long-term traditional tillage, which should be supplemented SOM promptly. We recommend supplementing straw again after 3 years of the one-time straw return. By illustrating the correlation between SWR and SOM, we hope to provide land managers with new perspectives regarding SOM, which is negatively affected by long-term land use, especially in soils under long-term traditional tillage.

Biostimulants for enhancing productivity, bioactive components, and the essential oils of garlic with the potential antifungal activity

To feed the world’s growing population, the agriculture sector has recently had to strike a balance between reducing its detrimental effects on ecosystems and human health and boosting resource efficiency and production. In reality, pesticides and fertilizers are vital to agriculture and are useful instruments that farmers can employ to increase yield and guarantee steady productivity throughout the seasons under both favorable and unfavorable conditions. Therefore, in the present study, fertilizing with potassium citrate as a foliar spray and humic acid (HA) as a soil application allowed for the evaluation of vegetative growth parameters (plant height, number of leaves/plant), total phenolic content, total carbohydrate, antioxidant activity, the essential oil (EO) composition, and bulb yield of garlic (Allium sativum L.). These were carried out in two field experiments throughout the 2020–2021 and 2021–2022 growth seasons. A gas chromatography-mass spectroscopy (GC-MS) apparatus was performed to determine the chemical composition of the isolated EOs. The antifungal activity of the EOs was assessed against two fungi, Fusarium proliferatum and Macrophomina phaseolina, that cause geranium plants to wilt and decay. The findings indicated that applying HA at a rate of 2 g/L with potassium citrate at a rate of 5 or 10 mL/L produced garlic bulbs with the highest levels of productivity and diameter. The diverse treatments between HA with potassium citrate resulted in significant variations in the bioactive components, such as total phenol content, antioxidant activity, total carbohydrate, and sulfur content. The analysis of the EOs revealed the presence of dimethyl trisulfide, diallyl disulfide, methyl 2-propenyl trisulfide, allitridin, and methyl allyl disulfide and allyl tetrasulfide as main compounds. By gradually increasing the concentration of the garlic EO to 4000 µg/mL compared to the control, the inhibition percentage of fungal growth of F. proliferatum and M. phaseolina was increased. In conclusion, a high concentration of HA with potassium citrate (5 or 10 mL/L), may be suitable and highly appreciated as a fertilizer application to enhance the productivity and EOs content of garlic plants.

Effect of Fenton-Based Processes on Arsenic Removal in the Presence of Humic Acid.

Geogenic arsenic (As) contamination in groundwater poses a significant public health risk in many regions worldwide. Previous studies have reported hydrogen peroxide (H2O2) concentrations ranging from 5.8 to 96 μmol L-1 in rainwater, which may contribute to the oxidation and removal of As. However, the influence of natural organic matter, such as humic acid (HA), on rainwater-borne H2O2-induced Fenton processes for the oxidation and removal of As remains unclear. In this study, the Fenton process was employed to investigate changes in As(V), As(III), and their mixtures, both in the presence and absence of HA. The results showed that low concentrations of HA (0-10 mg/L) promoted the oxidation of As(III) and removal of As(V) when As(V) and As(III) were present individually. However, when As(V) and As(III) coexisted, HA inhibited the Fenton process for As(V) removal. This inhibition was likely due to As(III) competing strongly with HA for hydroxyl radicals in the Fenton reaction system. Additionally, the presence of HA hindered the Fe(III)-driven removal of As(V), a product of the Fenton reaction. These findings further enhance our understanding of the potential role of rainwater-borne H2O2 in the transformation of As species in open water environments.

Novel pretreatment technologies for sludge dewatering and dissolution: Humic acid combine with sodium percarbonate and different iron species

Large amounts of waste activated sludge are generated daily worldwide, posing significant environmental challenges. A promising sludge management method is urgently needed. This study innovatively introduces humic acid (HA) into a sodium percarbonate (SPC) sludge treatment system to enhance dewatering and dissolution processes. Therein, SPC was activated by dissolved iron (Fe(II) or Fe(III)) or solid phase iron (zero-valent iron or magnetite (Fe3O4)). Results confirmed that Fe(III)/SPC/HA could improve the dewaterability of sludge without pH adjustment, with the capillary suction time decreasing from 123.6 ± 1.32 s (control) to 58.10 ± 4.35 s, which was comparable with that of the Fe(III)/SPC at pH 3.0. Meanwhile, Fe3O4/SPC/HA significantly enhanced sludge dissolution, and the released protein and polysaccharide levels were 2.98 and 7.08 times higher than that in the control. Both Fe(III)/SPC/HA and Fe3O4/SPC/HA reduced heavy metals and pathogens in the sludge while increasing HA content in filtrates, all of which were beneficial for subsequent sludge disposal and HA recycling, offering cost-effective technologies for sludge treatment.

Influence of Organic Matter and Speciation on the Dynamics of Trace Metal Adsorption on Microplastics in Marine Conditions.

Dissolved organic matter (DOM), primarily in the form of humic acid (HA), plays a crucial role in trace metal (TM) speciation and their subsequent adsorption dynamics on microplastics (MP) in aquatic environments. This study evaluates the impact of environmentally relevant concentrations of HA on the adsorption behaviors of essential (Co, Cu, Ni, and Zn) and toxic (Cd and Pb) TMs onto polyethylene (PE) and polypropylene (PP) pellets, as well as PP fibers under marine conditions, during a six-week experiment. The HA concentrations were 0.1, 1, and 5 mg/L, while all metals were in the same amounts (10 µg/L). Results reveal that HA significantly influences the adsorption of Cu, Pb, and Zn on MP, particularly on PP fibers, which exhibited the greatest TM adsorption dynamics. The adsorption patterns correspond to the concentrations of these metals in seawater, with the sequence for pellets being Zn > Cu > Pb > Ni > Co~Cd, and for fibers Cu > Zn > Pb > Co~Ni > Cd. Speciation modeling supported these findings, indicating that Cu, Pb, and Zn predominantly associate with HA in seawater, facilitating their adsorption on MP, whereas Cd, Co, and Ni mainly form free ions and inorganic complexes, resulting in slower adsorption dynamics. Statistical analysis confirmed the influence of HA on the adsorption of Cd, Pb, Cu, and Ni. By investigating the dynamics of TM adsorption on plastics, the influence of DOM on these two contaminants under marine conditions was evaluated. The presented results can help in forming a better understanding of synergistic plastic and trace metal pollution in marine systems that are relevant at the global level, since both contaminants pose a serious threat to aquatic ecosystems.

Performance of co-composting Pholiota nameko spent mushroom substrate and pig manure at different proportions: Chemical properties and humification process

Co-composting is the controlled aerobic degradation of organics, using more than one feedstock. By combining the spent mushroom substrate of Pholiota nameko (SMS) and pig manure (PM), the benefits of each could be used to optimize the composting process and the final product. This study introduced a comprehensive evaluation strategy aimed at identifying the optimal co-composting ratio for these two substrates. A 120-day composting trial was conducted, blending SMS and PM in various ratios to evaluate the benefits of co-composting SMS-PM. The results indicated that dissolved organic matter (DOM) in SMS-derived compost primarily originated from plants, whereas PM-derived compost predominantly consisted of microbial metabolic products, and co-composting combined both sources. An increase in aromaticity and humification degree of DOM occurred during the composting process itself rather than being derived from autochthonous origin. Carbohydrates like phenols and alcohols broke down during composting, and microbes utilized polysaccharides as an energy source for humus formation. As co-composting progressed, the treatments with varying mass ratios of SMS to PM, including 8:2, 7:3, 6:4, 5:5, 4:6, and 3:7 were observed to result in a decline in aliphatic hydroxylated chains alongside an enhancement in aromaticity within the compost. Additionally, there was a conversion from organic carbon (C) to carboxyl C within humic acid (HA) due to oxidation and dehydrogenation processes that facilitated the formation of stable nitrogen-containing compounds characterized by condensed aromatic structures. Following thorough evaluation, it was determined that optimal composting efficacy occurred at a mass ratio of SMS to PM equal to 6:4. Post-compost analysis revealed increases in nutrient content; specifically, germination index (GI) value reached 132.7%, while organic matter content attained 45.3%. Conversely, electrical conductivity (EC), C contents of water-soluble substances and humin (Cwss and CHu) decreased by approximately 11.8%, 73.4%, and 29.8% respectively; meanwhile, C contents of humic-extracted acid and HA (CHE and CHA), along with degree of polymerization (DP), increased by 17.3%, 20.3% and 9.9% respectively. The proposed co-compost formula not only facilitated simultaneous recycling of both SMS and PM waste but also transformed them into high-quality organic fertilizers suitable for soil enrichment—effectively addressing challenges faced by both edible fungi cultivation and livestock industries while augmenting organic fertilizer sources for Black land protection.

Sesame Stalk Compost in Soil Revitalization and Long-term Sustainable Crop Productivity in Organic Sesame (Sesamum indicum L.)

ABSTRACT Resource depletion is one of the primary concerns of modern agriculture farmers, which needs to be considered for long term sustainability. To assess the effect of sesame stalk compost on the growth, yield, and quality of sesame under organic cultivation, long-term (four years) field experiments were conducted for eight seasons consecutively from 2020 to 2023. The inoculated composts collected after 90 days of composting contain N (1.45–1.50%), P (0.22–25%), K (0.23–0.25%), Fe (510–514 ppm), Zn (150–154 ppm), Cu (286–288 ppm), and Mn (540–542 ppm), which was higher than the uninoculated sesame stalk. Similarly, the humic acid content (122 mg/g of compost), fulvic acid (23–24 mg/g of compost), total humic substances (145–146 mg/g of compost), and CO2–C evolution (186–188 mg/100 g of compost) were significantly higher with microbial inoculated composts than uninoculated compost. The results of the long-term field experiment indicated that application of sesame stalk compost @ 5 t/ha significantly increased the soil organic carbon (6.30 g/kg), soil organic carbon (SOC) stock (11.8 mg/ha), raised the pH to neutralize the acidic pH in red lateritic soil (6.8 to 7.2), reduced the soil bulk density (1.38 to 1.34), penetration resistance (720 kpa to 630 kpa), and available N, P, and K. As a result, the sesame grain yield obtained with application of sesame stalk compost @ 5 t/ha (778–782 kg/ha) was comparable with recommended doses of chemical fertilizers (794 kg/ha). Significant improvement in grain quality (24.2% of protein, 418–422 ppm of Ca, 12.4–12.6 ppm of Zn, 9.6 ppm of Fe and 2.6 ppm of Cu) and oil yield (364.1–367.5 kg/ha) was also observed due to the application of microbial inoculated sesame stalk compost.

Microplastics Meet Metoprolol in Natural Water: Sorption Behavior and Mechanism

As an ideal carrier for the spread of pollutants in the aquatic environment, microplastics (MPs) can adsorb pharmaceutical β-blockers, which can affect their migration and lead to some unpredictable adverse consequences. In this paper, the sorption behaviors and mechanism of MPs (polyvinyl chloride (PVC) and polypropylene (PP)) for typical β-blocker metoprolol (MTL) were investigated. The effects of pH, salinity and humic acids (HAs) on the sorption were studied, which proved that the sorption behavior was different under different environmental conditions. Both low pH and high salinity inhibited the sorption of MTL by the MPs. Specifically, the sorption capacity of MTL increased, with pH increase from 3 to 10. When pH = 10, the sorption capacities of MTL on PVC (1.75 mg/g) and PP (3.34 mg/g) reached the maximum. After pH &gt; 10, the amount of MTL adsorbed on PVC was slightly decreased, while that on PP was essentially the same. The addition of salt ions inhibited the sorption in the concentration range of 5–250 mg/g for both NaCl and CaCl2, with the inhibitory effect of Ca2+ being stronger than that of Na+. Moreover, the presence of HAs promoted the sorption of MPs for MTL. In the absence of HAs, the sorption capacities of PP and PVC for MTL were 0.34 mg/g and 0.79 mg/g, respectively. When HA concentration was 100 mg/L, the highest sorption capacities of PP and PVC reached 0.79 mg/g and 1.37 mg/g, respectively. This indicated that the promoting effect of HAs on PP was stronger than that on PVC. In general, based on the study of the sorption behavior of MTL and the characterization of the MPs, the sorption mechanism was speculated to consist mainly of electrostatic interactions, cation exchange, hydrophobic interaction and halogen bonding. The sorption kinetics of MTL on the two MPs were well-fitted by the pseudo-second-order model with R2 &gt; 0.99. The sorption isotherms both fitted the Freundlich model, which substantiated that the sorption of MTL on the MPs (PVC and PP) was multilayered and heterogeneous. Collectively, these findings provided a theoretical basis for revealing the complex interactions between MPs and MTL in natural water and a new insight into the fate and migration of MPs and β-blockers in the environment.

Synergistic mechanisms of humic acid and biomineralization in cadmium remediation using Lysinibacillus fusiformis.

Heavy metal pollution, particularly cadmium, poses severe environmental and health risks due to its high toxicity and mobility, necessitating effective remediation strategies. While both microbially induced carbonate precipitation (MICP) and humic acid adsorption are promising methods for heavy metal mitigation, their combined effects, particularly the influence of humic acid on the MICP process, have not been thoroughly investigated. This study explores the interaction between humic acid and MICP, revealing that humic acid significantly inhibits the MICP process by reducing urease activity, with the 10% humic acid treatment resulting in a 23.8% reduction in urease activity compared to the control. Additionally, while higher concentrations of humic acid did not significantly reduce cadmium ion concentrations, they did result in a slight increase in organically bound cadmium, indicating an interaction that could alter metal speciation in the soil. These findings provide important insights into the mechanisms by which humic acid affects MICP, offering a foundation for optimizing combined remediation approaches. Future research should aim to fine-tune the balance between MICP and humic acid to enhance the overall efficiency of cadmium remediation strategies. This study contributes to the development of more effective and sustainable methods for addressing cadmium contamination.

A comparative study on the stability and coagulation removal of aged vs. nonaged nanoplastics in surface water

Nanoplastics (NPs) are released into surface water due to the widespread use of plastics, undergoing aging from environmental and human factors that alter their physical and chemical characteristics. However, detecting NPs remains challenging, resulting in limited research on their behavior in surface water and their removal efficiency by drinking water treatment. This study utilizes palladium-doped polystyrene nanoplastics (PSNPs) as tracers to enable precise detection and quantification through ICP-MS, thereby overcoming the limitations of conventional detection methods. PSNPs are aged using solar irradiation and ozone to simulate both natural and artificial aging processes, affecting the physical and chemical properties of NPs, which in turn influence their behavior in water treatment systems. Moreover, the study investigates the impact of various coagulation conditions, including different coagulants (AlCl3 and PACl), pH levels (4−9), and humic acid (HA) concentrations (0–10 mg/L), on the of both aged and nonaged NPs. The results demonstrate solar aging triggers significant morphological changes in PSNPs, while ozone aging induces more oxygen functional groups on PSNPs (CIozone=20.99; CIsolar=0.70), increasing sensitivity to HA concentrations and resulting in reduced removal efficiencies for ozone aged PSNPs by AlCl3 (68.68 %) and PACl (74.74 %). In addition, PACl achieves higher PSNPs removal efficiencies (REmin=88.59 %) than that of AlCl3 (REmin=85.57 %) under varied pH levels. This research fills a gap in understanding aged NPs behavior in surface water and offers practical solutions for optimizing coagulation for NPs removal, enhancing our ability to predict NPs environmental fate and manage NPs pollution to ensure drinking water safety.

Ultrasound-assisted bisphenol AF degradation using in situ generated hydrogen peroxide

Bisphenol AF (BPAF) is degraded through the ultrasound-assisted in situ generation and activation of hydrogen peroxide (H2O2) by the copper(II) catalysed oxidation of hydroxylamine (NH2OH) with dioxygen (O2). Compared to added H2O2, in situ generated H2O2 significantly improves the degradation of BPAF from 46.7% to 94.8% in ∼15 min. The reaction follows a pseudo-first-order kinetic model. This study examines the influence of solution pH, anions, humic acid, and different concentrations of the reactants on BPAF degradation. Mass spectrometry was used to identify the BPAF degradation products, and a degradation pathway is proposed. This work advances the understanding of in situ hydrogen peroxide generation and activation in advanced oxidation (Fenton-like) processes (AOPs).

Humic Substances from Waste-Based Fertilizers for Improved Soil Fertility

This research explores how different organic waste transformation methods influence the production of humic substances (HSs) and their impact on soil quality. Using olive and orange wastes as substrates, the study compares vermicomposting, composting, and anaerobic digestion processes to determine which method produces the most humic-substance-rich products. The characterization of HSs in each product included analyses of total organic carbon (TOC), humic and fulvic acid content, humification rate, humification degree, and E4/E6 ratio, with HSs extracted using potassium hydroxide (KOH) and analyzed via Diffuse Reflectance Infrared Fourier-Transform (DRIFT) spectroscopy to assess structural complexity. The results revealed that the chemical composition of the input materials significantly influenced the transformation dynamics, with orange by-products exhibiting a higher humification rate and degree. Vermicomposting emerged as the most efficient process, producing fertilizers with superior humic content, greater microbial biodiversity, and enhanced cation exchange capacity, thus markedly improving soil quality. Composting also contributed to the stabilization of organic matter, albeit less effectively than vermicomposting. Anaerobic digestion, by contrast, resulted in products with lower levels of HSs and reduced nutrient content. Aerobic processes, particularly vermicomposting, demonstrated the most rapid and effective transformation, producing structurally complex, stable humus-like substances with pronounced benefits for soil health. These findings underscore vermicomposting as the most sustainable and efficacious approach for generating HS-rich organic fertilizers, presenting a powerful alternative to synthetic fertilizers. Furthermore, this study highlights the potential of organic waste valorization to mitigate environmental pollution and foster circular economy practices in sustainable agriculture.

Enhancing Oxygen-Dissolving Capacity of Rotary Drum Food Waste Composting: Tumbling Process Optimization and Experimental Validation with Discrete and Finite Element Methods

An optimized tumbling process can significantly improve the oxygen dissolving capacity of composting and fertilizer quality: by increasing the fluffiness of the lower layer of the pile, localized anaerobic fermentation can be avoided, thereby enhancing compost quality. This paper presents a method for improving the oxygen dissolving capacity of rotary drum food waste composting through a combination of simulation optimization and experimental validation. First, the discrete element method was used to optimize the key parameters of the tumbling process. The response surface method was then employed to analyze the composting test results and determine the optimal conditions. To ensure the reliability of the equipment under this method, failure risk analysis was conducted using the finite element method. The simulation optimization results showed that with a rotary drum reactor speed of 3.5 r/min, a horizontal angle of inclination of 2.5°, a mixing blade angle of inclination of 43°, and a blade pitch of 580 mm, the fluffiness of the lower layer of the pile increased by 8.515%, achieving the best tumbling and indirectly enhancing oxygen dissolving capacity. The maximum deformation of the load-bearing components was only 0.0548 mm, and the minimum safety factor was 4.408 (≥1 is considered safe). A 14-day composting experiment was conducted to validate the optimized parameters. The results showed that the maximum temperature of the compost pile reached 68.34 °C (lasting 7 days), with the pH, moisture content, C/N ratio, humus substances, humic acid, and fulvic acid contents of the fertilizer all meeting or exceeding the levels recommended by Chinese national standards. These findings indicate that the optimized tumbling device effectively improved the stability and dissolved oxygen efficiency of food waste composting, providing valuable practical insights and a research foundation for enhancing oxygen efficiency in the composting of other organic wastes.

Characteristics and pollution indices of leachates from municipal solid waste landfills in Iranian metropolises and their implications for MSW management

Leachate from municipal solid waste landfills poses a significant threat to aquatic ecosystems due to poor management practices. This study evaluated thirty leachate samples from Iranian metropolises using the Leachate Pollution Index (LPI). Various parameters, including BOD₅, COD, TDS, pH, EC, heavy metals, turbidity, PAHs, phthalates, and humic acid, were analysed. The BOD₅ levels ranged from 350 to 20,000 mg/L, and the COD levels ranged from 2,000 to 90,000 mg/L. The TDS content varied between 14.7 and 67 g/L, while the turbidity ranged from 15 to 186 NTU. Heavy metals were present but within standard limits. The phthalate concentrations ranged from 6 to 150.8 mg/L, and the humic acid concentrations ranged from 135 to 2,200 mg/L. Naphthalene was the most frequent hydrocarbon detected. The LPIs were less than 30 for all the samples, with the highest in Ahvaz and the lowest in the treated samples from Tehran. This study highlights the presence of persistent organic and hazardous contaminants in Iran’s municipal landfills, emphasizing the need for effective leachate treatment and improved waste management practices. Enhanced final disposal methods, increased waste recovery, and improved solid residue separation are crucial for preventing further leachate production and environmental contamination.

Prediction of the impact of tobacco waste hydrothermal products on compost microbial growth using hyperspectral imaging combined with machine learning.

The insufficient understanding of the impact of hydrothermal products on the growth characteristics of compost microorganisms presents a significant challenge to the broader implementation of hydrothermal coupled composting for tobacco waste. Traditional biochemical detection methods are labor-intensive and time-consuming, highlighting the need for faster and more accurate alternatives. This study investigated the effects of hydrothermal treatment on tobacco straw products and their influence on compost microorganism growth, using hyperspectral imaging (HSI) technology and machine learning algorithms. Sixty-one tobacco straw samples were analyzed with a hyperspectral camera, and image processing was used to extract average spectra from regions of interest (ROI). Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were applied to assess four key variables: nicotine content, total humic acid content, Penicillium chrysogenum H/C ratio, and Bacillus subtilis OD600 ratio. The effects of hydrothermal treatment on compost were classified as promoting, inhibiting, or neutral regarding microbial growth. The Competitive Adaptive Reweighted Sampling (CARS) method identified the most influential wavelengths in the 900-1700 nm spectral range. The Random Forest (RF) model outperformed SVM, KNN, and XGBoost models in predicting microbial growth responses, achieving R c = 0.957, RMSE = 3.584. Key wavelengths were identified at 1096 nm, 1101 nm, 1163 nm, 1335 nm, and 1421 nm. The results indicate that hyperspectral imaging combined with machine learning can accurately predict changes in the chemical composition of tobacco straws and their effects on microbial activity. This method provides an innovative and effective means of improving the resource usage of tobacco straws in composting, enhancing sustainable waste management procedures.

Characteristics of dissolved organic matter and their role in membrane fouling during simultaneous sludge thickening and reduction using flat-sheet membranes.

Four parallel simultaneous sludge thickening and reduction reactors using flat-sheet membranes were employed for the aerobic digestion of sludge to explore the characteristics of dissolved organic matter and its membrane fouling effect. During the initial 8 days of using flat-sheet membranes for simultaneous sludge thickening and reduction (MSTR), a notable increase was observed in the concentrations of humic acids and compounds that resemble soluble microbial by-products in the effluent. Subsequently, a fluctuating trend in humic acid levels ensued, accompanied by a gradual decline in soluble microbial by-product-like substances. Post the initial 8-day period, the capillary suction time (CST) rose from approximately 400s to over 800s, the viscosity increased from 20mPas to 38mPas, and the membrane resistance increased from roughly 6.0e+11m-1 to approximately 9.0e+11m-1. This phenomenon can be attributed to the clogging of pores by foulants whose size is similar to that of the membrane pores leading to the accumulation and deposition of macromolecules and larger particulates forming gel layers and cake layers. The interplay among diverse microorganisms engenders functional modules, collectively influencing the distribution and characteristics of dissolved organic matter within the MSTR. These microorganisms exert their metabolic effects individually and interact reciprocally, creating synergistic and inhibitory mechanisms. Notably, the synergistic interactions among microorganisms predominated, culminating in an enhanced effluent quality within the system.