Search Results (403)

Non-invasive acidic pretreatments using acetic acid (1–5 mM) and citric acid (0.02–0.1 g g⁻¹ TS) were investigated to enhance anaerobic digestion (AD) of waste-activated sludge (WAS). Both pretreatments improved short-term process stability, with pH (6.5–7.1) and alkalinity (1000–5000 mg CaCO₃ L⁻¹) remaining within optimal ranges during 10-day digestion. Acetic acid markedly enhanced solubilization and acidification, increasing volatile fatty acids to ~2500 mg L⁻¹ (+67% vs. control), whereas citric acid achieved ~2000 mg L⁻¹ (+37%). EPS analysis revealed pronounced redistribution of polysaccharides and proteins, with acetic acid inducing stronger disruption of the EPS matrix (SB-EPS polysaccharides up to 34.1 mg eq Glc mL⁻¹). Specific methane yield increased from 28.5 mL CH₄ g⁻¹ VS (control) to 101.7 mL CH₄ g⁻¹ VS with acetic acid (3.6-fold) and to 73.8 mL CH₄ g⁻¹ VS with citric acid (2.5-fold). Gompertz modeling confirmed higher maximum methane potential, ~68% higher maximum methane production rates, and reduced lag phases for both pretreatments. In contrast, pharmaceutical concentrations (31 compounds) were largely unaffected by acid pretreatment, with significant reductions observed only for selected biodegradable molecules. Full article

The study evaluated the feasibility of using the activated sludge process to treat real wastewater from used oil installations containing petroleum hydrocarbons, boron (B), and adsorbable organic halides (AOX). The aim was to determine the maximum ratio of this wastewater that could be added to the influent without impairing treatment efficiency. Tested shares ranged from 0.50% to 1.90%. An initial 1.30% of the tested share caused process instability, reflected in the elevated total nitrogen (TN) levels in treated wastewater. After reducing the share to 0.50%, an adaptation of the activated sludge was observed, manifested by a decrease in TN concentration to below 15.0 mg N/L. For the most favorable share of 1.60% (0.38 ± 0.10 kg_BOD5/kg_MLSS d, 0.51 ± 0.14 kg_COD/kg_MLSS d), the removal efficiencies of chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), TN, and total phosphorus (TP) were 95.0% ± 1.5, 99.1% ± 0.2, 89.3% ± 2.7, and 94.0% ± 5.0, respectively. Increasing the share to 1.90% decreased treatment efficiency and exceedances of COD, BOD₅, TN, and TP occurred. At this ratio, an increase in ammonium nitrogen (NH4⁺-N) and TN concentrations was observed, indicating the inhibition of nitrification. However, the average concentrations of mineral oil index, AOX and B in the treated wastewater remained within permissible levels throughout the study. Full article

Soil contamination by petroleum hydrocarbons represents a significant environmental challenge, especially in industrial and urban areas. This study evaluates the use of three industrial liquid by-products—sludge dewatering sidestream (SD), leftover yeast (LY), and secondary clarifier effluent (SC)—as biostimulant agents for the bioremediation of soils contaminated with gasoline and diesel mixtures. The novelty lies in applying these waste streams within a circular economy framework, with the added advantage that they can be injected directly into the subsurface. Microcosm tests were conducted over 20 weeks, analyzing the degradation of total petroleum hydrocarbons (TPHs) and their aliphatic and aromatic fractions using gas chromatography. The results show that all by-products improved biodegradation compared to natural attenuation. LY was the most effective, achieving 73.2% TPH removal, followed by SD (70.6%) and SC (65.4%). The greatest degradation was observed in short-chain hydrocarbons (C6–C16), while compounds with higher molecular weight (C21–C35) were more recalcitrant. In addition, aliphatic hydrocarbons showed greater degradability than aromatics in heavy fractions. Kinetic analysis revealed that the second-order model best fitted the experimental data, with higher correlation coefficients (R²) and more representative half-lives. Catalase enzyme activity also increased in soils treated with LY and SD, indicating higher microbial activity. Full article

Given the sustainable increase in kitchen waste production, the treatment of organic waste is quite important for both alleviating environmental risks and recovering biomass energy. Anaerobic digestion (AD) could achieve the goals of both organic stabilization and the green energy production of biogas. However, AD conducted at a high organic loading rate can easily suffer from low treatment efficiency due to the accumulation of volatile fatty acids and an imbalance in the microbial community. This study investigated the functional microbial enhancement strategy for enhancing AD performance. The results suggested that adding 10 g of granular sludge every 5 days could enhance AD efficiency. In that case, the daily average methane production rate was increased by 43.21% compared to that in the control group, and the pH and ammonia nitrogen concentration were maintained at the optimal level. Humic acid production was strengthened; it served as an electron shuttle, which facilitated direct interspecies electron transfer. Both Cloacimonadota and Methanobacterium were enriched in the system inoculated with the granular sludge. Metabolomics indicated that the acetyl–CoA conversion was strengthened, and that energy metabolism (complex I and archaeal ATPase) was also enhanced. The granular sludge inoculation also activated the archaeal genetic information processing system. This technology could promote the generation of green energy, which is more conducive to sustainable resource development. This study provides the theoretical basis for a microbial enhancement strategy that can enhance kitchen waste AD. Full article

The article presents the results of a study on the production of a complex chromium–manganese–silicon-containing ferroalloy in a large-scale laboratory ore-thermal furnace using man-made waste—chromium-containing aspiration dust obtained during smelting of high-carbon ferrochrome, fines (−5 mm) of iron–manganese ore currently stored in landfills, and finely dispersed coal sludge formed during enrichment. A single-stage technology for the production of a new complex chromium–manganese–silicon-containing ferroalloy by carbothermal reduction is proposed. A metallurgical assessment of the initial charge materials was carried out by the X-ray diffraction (XRD) phase analysis, and metal samples of the obtained ferroalloy were studied by scanning electron microscopy (SEM) in combination with energy dispersive spectroscopy (EDS). The resulting ferroalloy has a complex microstructure with a predominance of carbide and intermetallic phases. A high degree of extraction of chromium (up to 80%), manganese (up to 75%), and silicon (up to 35%) was recorded. The average chemical composition of the obtained ferroalloy, wt.%: Cr—37.41; Mn—17.31; Si—11.84; C—3.81; P—0.14; S—0.02. The slag formed during the smelting of the ferroalloy has satisfactory technological properties: it is characterized by good fluidity, and it actively exits the furnace by gravity. Entanglement of metal kings in the slag is not observed. The results obtained confirm the technological feasibility of the utilization of technogenic raw materials for the production of complex ferroalloys of the FeCrMnSi type. Full article

The rapid expansion of the salmon industry has generated increasing amounts of waste sludge with negative environmental impacts. Sustainable alternatives, such as using stabilized sludge in agriculture, are needed to mitigate these effects. At the same time, fruit production has grown globally, with hazelnut (Corylus avellana L.) emerging as a crop of high economic importance. However, the effect of salmon sludge application on hazelnut orchards is poorly understood. This study evaluated the application of thermally stabilized fish farming sludge (DS) compared with a slow-release mineral fertilizer (MF) intwo hazelnut varieties, ‘Barcelona’ (B) and ‘Tonda di Giffoni’ (TDG). Growth parameters including trunk cross-sectional area (TCSA), cumulative growth, shoot growth rate, leaf mass area (LMA) and chlorophyll index (SPAD), as well as soil physicochemical properties and enzymatic activities (fluorescein diacetate, β-glucosidase, acid phosphatase) were assessed. No significant differences (p > 0.05) in physiological parameters were found between DS and MF. However, the DS application increased soil pH by up 18%, electrical conductivity by ~48% at peak values, and enzymatic activities by 44% (acid phosphatase in B variety), 38% (β-glucosidase in TDG) and 169% (FDA in TGD), suggesting a great organic matter contribution and enhanced soil metabolic activity. Additionally, the B variety showed superior physiological performance, while TDG exhibited higher enzymatic activity. Overall, these findings provide a preliminary assessment of DS as a sustainable supplement to mineral nitrogen fertilization in hazelnut orchards, supporting both soil quality improvement and circular economy strategies in agriculture and aquaculture. Full article

Mesophilic anaerobic co-digestion of eight distinct substrate mixtures of agroindustrial and food wastes was assessed to determine the most efficient waste mixture for maximizing hydrogen production. To evaluate the impact of adding various mixtures on dark fermentation (DF), batch tests were conducted for 250 h at 37 °C and a pH range between 5.0 and 5.9. Ethanol, butyric, propionic, acetic, and isobutyric acids were identified as the principal fermentation end products. The hydrogen production rate reached in a decreasing order from a mixture comprising 55% Olive Mill Wastewater (OMW), 40% Cheese Whey (CW), and 5% Sewage Sludge (SS) or Liquid Pig Manure (LPM) (38 NmL/gVS) to 55% OMW, 40% CW and 5% diluted Food Waste (FW_dil) (30 NmL/gVS), 60% CW and 40% Grape Residues (GR) (27 NmL/gVS), 80% CW and 20% LPM (13 NmL/gVS), 60% OMW and 40% FW_dil. (10 NmL/gVS), 60% CW and 40% FW_dil, (8 NmL/gVS) and 70% OMW and 30% SS (5 NmL/gVS). These results indicated that H₂ was generated through mixed fermentation pathways, while the addition of OMW > 55% inhibited microbial activity and reduced hydrogen production. The highest hydrogen yield (38 NmL/gVS), accompanied by 27.6%, Volatile Solids (VS) reduction and the highest Volatile Fatty Acids (VFAs) concentration (6.1 g/L). The same substrate mixture resulted in the highest accumulation of acetic and butyric acid in the acidified effluent, indicating the dominance of hydrogen-producing metabolic routes. The data suggest that co-fermentation of the selected residues not only enhances hydrogen production but also creates more stable operational conditions -including improved pH regulation, increased carbohydrate conversion, and greater VFAs accumulation- making the process more robust and viable for practical application. Full article

This study presents an innovative approach to the production of hydrogen from liquids following hydrothermal treatment of biowaste, offering a potential solution for renewable energy generation and waste management. By combining biological and hydrothermal processes, the efficiency of H₂ production can be significantly improved, contributing to a reduced carbon footprint and lower reliance on fossil fuels. The inoculum used was fermented sludge from a wastewater treatment plant, which had been thermally pretreated to enhance microbial activity towards hydrogen production. Kitchen waste, consisting mainly of plant-derived materials (vegetable matter), was used as a substrate. The process was conducted in batch 1-L bioreactors. The results showed that higher pretreatment temperatures (up to 180 °C) increased the hydrolysis of compounds and enhanced H₂ production. However, temperatures above 180 °C resulted in the formation of toxic compounds, such as catechol and hydroquinone, which inhibited H₂ production. The highest hydrogen production was achieved at 180 °C (approximately 66 mL H₂/g_TVSKW). The standard Gompertz model was applied to describe the process kinetics and demonstrated an excellent fit with the experimental data (R² = 0.99), confirming the model’s suitability for optimizing H₂ production. This work highlights the potential of combining hydrothermal and biological processes to contribute to the development of sustainable energy systems within the circular economy. Full article

This work investigated the use of microbial fuel cells (MFCs) for the degradation of polyethylene terephthalate (PET) and the simultaneous generation of electricity. The study implemented two separate single-chamber MFCs, one with a co-culture of Ideonella sakaiensis and Geobacter sulfurreducens (I.S-G.S) and the other with Ideonella sakaiensis and activated sludge (I.S-AS). The effectiveness of microplastic (MP) degradation was assessed based on the electroactivity of the anodic biofilm, the reduction in particle size, and the decrease in PET mass. Both systems achieved a significant reduction in MP size and mass, with the I.S-AS system notably surpassing the I.S-G.S in terms of efficiency and electricity generation. The I.S-AS system achieved a 30% mass reduction and 80% size reduction, along with a peak voltage of 222 mV. The study concludes that MFCs, particularly with the activated sludge co-culture, offer a viable and more environmentally friendly alternative for MP degradation and energy recovery. These findings suggest a promising direction for improving waste management practices and advancing the capabilities of bio-electrochemical systems in addressing plastic pollution. Further research is recommended to optimize the operational conditions and to test a broader range of MP sizes for enhanced degradation efficacy. Full article

The limestone quarrying and processing industry generates huge amounts of waste, with limestone sludge being one of the most prevalent and challenging by-products. This study aims to evaluate the potential of limestone sludge as a sustainable secondary raw material for the mechanochemical synthesis of bioceramics, specifically hydroxyapatite (HA), for high-added-value applications in bone tissue engineering. High-energy milling is innovatively used as the processing route: dry sludge (functioning as the calcium source), a phosphate source, and water were milled with the aim of producing calcium phosphates (in particular, hydroxyapatite) via mechanosynthesis. The industrial sludge was thoroughly analyzed for chemical composition, heavy metals, and mineral phases to ensure suitability for biomedical applications. The mixture of reagents was tailored to comply with Ca/P = 1.67 molar ratio. Milling was carried out at room temperature; the milling velocity was 600 rpm, and milling time ranged from 5 to 650 min. Characterization by XRD, Raman spectroscopy, and SEM confirmed the progressive transformation of calcite into hydroxyapatite through a metastable DCPD intermediate, following logarithmic reaction kinetics. The resulting powders are fine, homogeneous, and phase-pure, demonstrating that mechanosynthesis provides a low-cost and environmentally friendly pathway to convert limestone waste into functional bioceramic materials. This suggests that Moleanos sludge is a viable and sustainable source to produce tailored calcium phosphates and confirms mechanosynthesis as a cost-effective and reliable technology to activate the low-kinetics chemical reactions in the CaCO₃-H₃PO₄–H₂O system. This work highlights a novel circular economy approach for the valorization of industrial limestone sludge, turning a difficult waste stream into a high-value, sustainable resource. Full article

This study investigates the combined effect of wheat straw particle size and mixing ratio on the anaerobic co-digestion (ACD) of waste activated sludge under mesophilic conditions. Ten batch digesters were tested with varying straw-to-sludge ratios (0–1.5%) and particle sizes (5 cm, 1 cm, and <2 mm). Fine straw particles (<2 mm) at 1.5% loading achieved the highest removal efficiencies for TS (43.55%), TVS (47.83%), and COD (51.52%), resulting in a 140% increase in biogas yield and methane content of 60.15%. The energy recovery reached 14.37 kWh/kg, almost double the control. The developed Recurrent Neural Network (RNN) model (3 layers, 13 neurons, 500 epochs) predicted biogas production with 99.8% accuracy, a root mean square error (RMSE) of 0.0038, a mean absolute error (MAE) of 0.0093, and an R² close to 1. These results confirm the potential of integrating agricultural residues into wastewater treatment for renewable energy recovery and emission reduction. This study uniquely integrates mechanical pretreatment of wheat straw with RNN-based modeling to enhance biogas generation and predictive accuracy. It establishes a dual-experimental AI framework for optimizing sludge–straw co-digestion systems. This approach provides a scalable, data-driven solution for sustainable waste-to-energy applications. Full article

This study aimed to investigate the effectiveness of dark fermentation in biohydrogen production from agro-industrial wastes, including apple pomace, brewer’s grains, molasses, and potato powder, subjected to different pretreatment methods. The experiments were conducted at a laboratory scale, using 1000 cm³ anaerobic reactors at a temperature of 35 °C and anaerobic sludge as the inoculum. The highest yield of hydrogen was obtained from pre-treated apple pomace (101 cm³/g VS). Molasses, a less complex substrate compared to the other raw materials, produced 25% more hydrogen yield following pretreatment. Methanogens are sensitive to high temperatures and low-pH conditions. Nevertheless, methane constituted 1–6% of the total biogas under these conditions. The key factor was appropriate treatment of the inoculum, to limit competition from methanogens. Increasing the inoculum dose from 150 cm³/dm³ to 250 cm³/dm³ had no further effect on biogas production. The physicochemical parameters and VFA data confirmed the stability and usefulness of activated sludge as a source of microbial cultures for H₂ production via dark fermentation. Full article

The pollution problem of iron grinding sludge (IS) and polyethylene glycol (PEG) threatens the ecosystem and human health. In this study, an iron-rich catalyst (ISPEG) was prepared by co-pyrolysis of grinding sludge and polyethylene glycol and used to activate peroxydisulfate (PDS) for degrading organic wastewater. In the ISPEG/PDS system, methylene blue (MB) was almost completely removed within 60 min with an apparent rate constant (Kobs) of 0.32 min⁻¹ and a wide range of pH. The effects of IS doping ratio, pyrolysis temperature, catalyst injection, PDS concentration, co-existing ions, and pH on MB removal were investigated. The results showed that ISPEG/PDS had a high removal rate of various organics in the water column. The catalytic mechanism of the ISPEG/PDS system was explored by free radical quenching, electron paramagnetic resonance, and frontier orbital theory studies, in which the main active substance for degrading SDZ was SO₄^•−. Finally, the degradation pathways of MB in the ISPEG/PDS system were analyzed by LC-MS. These results indicate that the ISPEG/PDS system has the potential to treat organic wastewater under the concept of waste control waste. Full article

Soil contamination by heavy metals from industrial and mining activities poses a significant global threat to both environmental and human health, particularly in brownfields—abandoned or underutilized industrial areas that frequently accumulate pollutants. Climate change exacerbates this issue by intensifying extreme events such as floods, which can enhance contaminant mobility and compromise the reliability of conventional remediation methods. This study evaluated the in situ application of a sustainable soil washing technique based on hydrocycloning at a contaminated site in Canoas (Porto Alegre, Brazil), a flood-prone area heavily impacted by the 2024 climate disaster. The method physically separates heavy metals by concentrating them into a fine, high-contamination fraction for controlled disposal. Approximately 3019 m³ of soil was treated, recovering 93.4% of the material (coarse and fine sand) for potential reuse and isolating only 6.6% (200 m³) as hazardous waste. Chemical analyses confirmed that the recovered fractions complied with regulatory limits for heavy metals, while contaminants were effectively retained in the sludge and safely disposed of through landfills. During the April–May 2024 flood events, although the site was inundated, no significant erosion of the backfilled material was registered. The results support hydrocycloning-based soil washing as a robust and climate-resilient approach to adaptive remediation in contaminated environments. Full article

This research is to assess the potential use of phosphate sludge from the Gafsa (Tunisia) phosphate laundries as an alternative raw material for the manufacture of ecological refractory bricks. Feasibility was evaluated through comprehensive physico-chemical and mineralogical characterizations of the raw materials using X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and thermal analysis (TGA-DTA). Bricks were formulated by substituting phosphate sludge with clay and diatomite, then activated with potassium silicate solution to produce geopolymeric materials. Specific formulations exhibited mechanical performance ranging from 7 MPa to 26 MPa, highlighting the importance of composition and minimal water absorption values of approximately 17.8% and 7.7%. The thermal conductivity of the bricks was found to be dependent on the proportions of diatomite and clay, reflecting their insulating potential. XRD analysis indicated the formation of an amorphous aluminosilicate matrix, while FTIR spectra confirmed the development of new chemical bonds characteristic of geopolymerization. Thermal analysis revealed good stability of the materials, with mass losses mainly related to dehydration and dehydroxylation processes. Environmental assessments showed that most samples are inert or non-hazardous, though attention is required for those with elevated chromium content. Overall, these findings highlight the viability of incorporating phosphate sludge into fired brick production, offering a sustainable solution for waste valorization in accordance with the circular economy. Full article