Search Results (1,663)

Waste activated sludge (WAS), a byproduct of livestock wastewater treatment, poses significant disposal challenges due to its low biodegradability and potential environmental impact. Anaerobic digestion (AD) offers a sustainable approach for methane recovery and sludge stabilization. This study evaluates the biomethane potential (BMP) of WAS and its co-digestion with swine slurry (SS), water lily (Nymphaea spp.), and lotus (Nelumbo nucifera) shoot biomass to enhance methane yield. Batch BMP assays were conducted at substrate-to-inoculum (S/I) ratios of 1.0 and 0.5, with methane production kinetics analyzed using the modified Gompertz model. Mono-digestion of WAS yielded 259.35–460.88 NmL CH₄/g VS_added, while co-digestion with SS, water lily, and lotus increased yields by 14.89%, 10.97%, and 16.89%, respectively, surpassing 500 NmL CH₄/g VS_added. All co-digestion combinations exhibited synergistic effects (α > 1), enhancing methane production beyond individual substrate contributions. Lower S/I ratios improved methane yields and biodegradability, highlighting the role of inoculum availability. Co-digestion reduced the lag phase limitations of WAS and plant biomass, improving process efficiency. These findings demonstrate that co-digesting WAS with nutrient-rich co-substrates optimizes biogas production, supporting sustainable sludge management and renewable energy recovery in livestock wastewater treatment systems. Full article

Electrocoagulation (EC) processes have emerged as an efficient solution for different inorganic and organic effluents. The main characteristics of this versatile process are its ease of operation and low sludge production. The literature indicates that EC can be successfully used as a single process or a step within a combined treatment system. If used in a combined system, this process could be employed as a pre-, a post-, or middle treatment step. Additionally, the EC process has been used in both continuous and batch modes. In most studies, EC has achieved significant improvements in the treated water quality and relatively low total energy consumption. This review presents a comprehensive evaluation and analysis of standalone and combined continuous EC processes. The influence of key operational parameters on continuous EC performance is thoroughly discussed. Furthermore, recent advancements in reactor design, modeling, and process optimization are addressed. The benefits of integrating other treatment processes with the EC process, such as advanced oxidation, membranes, chemical coagulation, and adsorption, are also evaluated. The performance of most standalone and combined EC processes used for organic pollutant treatment and published in the last 25 years is critically analyzed. This review is expected to give researchers many insights to improve their treatment scenario with recent and efficient environmental experiences, sustainability, and circular economy. The clearly presented information is expected to guide researchers in selecting efficient, cost-effective, and time-saving treatment alternatives. The findings ensure the considerable potential of continuous EC treatment processes for organic pollutants. However, more research is warranted to enhance process design, operational efficiency, scale-up, and economic viability. Full article

Anaerobic digestion (AD) is a sustainable and widely adopted technology for the treatment of organic solid wastes (OSWs). However, AD efficiency varies significantly across different substrates, primarily due to differences in the microbial community and metabolic pathways. This review provides a comprehensive summary of the AD processes for four types of typical OSWs (i.e., sewage sludge, food waste, livestock manure, and straw), with an emphasis on their universal characteristics across global contexts, focusing mainly on the electron transfer mechanisms, essential microbial communities, and key metabolic pathways. Special attention was given to the mechanisms by which substrate-specific structural differences influence anaerobic digestion efficiency, with a focused analysis and discussion on how different components affect microbial communities and metabolic pathways. This study concluded that the hydrogenotrophic methanogenesis pathway, TCA cycle, and the Wood–Ljungdahl pathway serve as critical breakthrough points for enhancing methane production potential. This research not only provides a theoretical foundation for optimizing AD efficiency, but also offers crucial scientific insights for resource recovery and energy utilization of OSWs, making significant contributions to advancing sustainable waste management practices. Full article

In the process of producing ferroalloys, a large amount of secondary raw materials is formed, including slag, aspiration dusts and sludge. The recycling of secondary raw materials can create resources and bring environmental and economic benefits. Wet secondary raw materials (WSRMs) are characterized by a high chromium oxide content (averaging 24%), but due to their high moisture levels, they cannot be directly used in arc furnaces. As a strategic approach, mixing WSRMs with drier, more chromium-rich dusts (up to 45% Cr₂O₃) has been proposed. This not only reduces the overall moisture content of the mixture but also enhances the metallurgical value of the charge material. This paper presents the results of laboratory studies on the agglomeration of secondary wet raw materials using briquetting, extrusion and pelletizing methods. The main factors influencing the quality of the resulting product were analyzed, including the method of agglomeration, the composition of the mixture, as well as the type and dosage of the binder component. The strength characteristics of the finished agglomerated samples were evaluated in terms of resistance to splitting, impact loads and falling. Notably, the selected binders are organic and polymer substances capable of complete combustion under metallurgical smelting conditions. Full article

Sewage sludge (SS) is commonly applied as a soil amendment. This practice has raised concern about the dissemination of emerging pollutants (EPs). EPs include compounds such as flame retardants, plasticizers, pharmaceuticals, and personal care products, among others, which may pose risks to human health and ecosystems. The complexity of the SS matrix, combined to the absence of an international legislation framework, makes it necessary to evaluate the techniques available for detecting these contaminants. Detection is typically performed using sensitive analytical techniques; however, the extraction strategy selected remains a crucial step. This review aims to compile different methodologies for the determination of EPs in SS, focusing on extraction strategies reported between 2010 and 2025. Ultrasound-assisted extraction (UAE), pressurized liquid extraction (PLE), and microwave-assisted extraction (MAE) are the most widely used strategies for EPs. UAE is considered the most preferable option, as it enables the extraction of a wide range of compounds without the need for expensive equipment. Among novel techniques, the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method is especially promising, as it is applicable to multiple target compounds. This review provides up-to-date information that can support the development of routine and standardized methodologies for the characterization of EPs in SS. Full article

Flocculants are indispensable in water and wastewater treatment, enabling the aggregation and removal of suspended particles, colloids, and emulsions. However, the conventional development and application of flocculants rely heavily on empirical methods, which are time-consuming, resource-intensive, and environmentally problematic due to issues such as sludge production and chemical residues. Recent advances in machine learning (ML) have opened transformative avenues for the design, optimization, and intelligent application of flocculants. This review systematically examines the integration of ML into flocculant research, covering algorithmic approaches, data-driven structure–property modeling, high-throughput formulation screening, and smart process control. ML models—including random forests, neural networks, and Gaussian processes—have successfully predicted flocculation performance, guided synthesis optimization, and enabled real-time dosing control. Applications extend to both synthetic and bioflocculants, with ML facilitating strain engineering, fermentation yield prediction, and polymer degradability assessments. Furthermore, the convergence of ML with IoT, digital twins, and life cycle assessment tools has accelerated the transition toward sustainable, adaptive, and low-impact treatment technologies. Despite its potential, challenges remain in data standardization, model interpretability, and real-world implementation. This review concludes by outlining strategic pathways for future research, including the development of open datasets, hybrid physics–ML frameworks, and interdisciplinary collaborations. By leveraging ML, the next generation of flocculant systems can be more effective, environmentally benign, and intelligently controlled, contributing to global water sustainability goals. Full article

Pseudo-persistent organic pollutants, such as pharmaceuticals, personal care products (PPCPs), and organic dyes, are a major issue in current environmental engineering. Considering the limitations of traditional wastewater treatment plant methods and degradation technologies for organic pollutants, the search for new technologies more suitable for treating these new types of pollutants has become a research hotspot in recent years. Membrane filtration, adsorption, advanced oxidation, and electrochemical advanced oxidation technologies can effectively treat new organic pollutants. The electro-advanced oxidation process based on sulfate radicals is renowned for its non-selectivity, high efficiency, and environmental friendliness, and it can improve the dewatering performance of sludge after wastewater treatment. Therefore, in this study, octyl methoxycinnamate (OMC) was selected as the target pollutant. A new type of electrochemical filtration device based on the advanced oxidation process of sulfate radicals was designed, and a new type of modified carbon nanotube material electrode was synthesized to enhance its degradation effect. In a mixed system of water and acetonitrile, the efficiency of the electrochemical filtration device loaded with the modified electrode for degrading OMC is 1.54 times that at room temperature. The experimental results confirmed the superiority and application prospects of the self-designed treatment scheme for organic pollutants, providing experience and a reference for the future treatment of PPCP pollution. Full article

Per- and polyfluoroalkyl substances (PFAS) are synthetically produced chemicals that are causing a major One Health crisis. These “forever chemicals” are widely distributed globally in air, water, and soil, and because they are highly mobile and extremely difficult to degrade in the environment. They cause additional health concerns in a circular bioeconomy and food system that recycles and reuses by-products and numerous types of waste materials. Uptake of PFAS by plants and food-producing animals ultimately leads to the consumption of PFAS-contaminated food that is associated with numerous adverse health and developmental effects in humans. Contaminated meat, milk, and eggs are some of the main sources of human PFAS exposure. Although there is no safe level of PFAS exposure, maximum tolerable PFAS consumption guidelines have been established for some countries. However, there is no international PFAS monitoring system, and there are no standardized international guidelines and mechanisms to prevent the consumption of PFAS-contaminated foods. Urgent action is needed to stop PFAS production except for critical uses, implementing effective water-purification treatments, preventing spreading sewage sludge on land and pastures used to produce food, and requiring marketers and manufacturers to use packaging that is free of PFAS. Full article

This study treated the NaOH component in red mud sludge, an industrial by-product generated at 300,000 tons annually in Korea, with sulfuric and nitric acids to produce NaSO₄ and NaNO₃, respectively. The effects of acid-treated liquid red mud (LRM) on the hydration reactions and early strength development in cement mortar were investigated. Properties such as flow, setting time, hydration heat, and compressive strength were evaluated alongside hydration product analysis using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The neutralization of LRM stabilized the pH between 7 and 8. Mortars containing neutralized red mud (NRM) and sulfuric-treated red mud (SRM) exhibited shorter initial setting times and similar final setting times compared to untreated red mud (LM). After one day, XRD confirmed the presence of Ca(OH)₂ in NRM and SRM but not in LM, while SEM revealed reduced pore sizes in NRM and SRM. Depending on dosage, the compressive strength of SRM increased by 35–60% compared to Plain mortar. These results demonstrate that LRM treated with nitric or sulfuric acid has significant potential as a setting accelerator for cement mortar. Full article

In this study, the effects of graphene-based nanomaterials—specifically graphene nanoplatelets (GNPs) and graphene oxide (GO) nanosheets—on methane (CH₄) production during anaerobic digestion (AD) of thermally hydrolyzed sewage sludge were investigated. Anaerobic digestion was carried out over a 40-day period under mesophilic conditions in batch digesters with a volume of 2.65 L. The influence of various dosages of GNPs and GO nanosheets on methane yields was assessed, including a comparison between GNPs with different specific surface areas (320 m²/g and 530 m²/g). The highest CH₄ yield (194 mL/g-VS_added) was observed with a GNP dosage of 5 mg/g-TS and a surface area of 530 m²/g, showing an increase of 3.08% compared to the control. This treatment group had the greatest positive effect also on the degradation of organic matter, with total solids (TS) and volatile solids (VS) removal reaching 34.35% and 44.18%, respectively. However, the GO dosages that significantly decreased cumulative CH₄ production were determined to be 10–15 mg/g-TS. Graphene oxide at dosages of 10 and 15 mg/g-TS reduced specific cumulative CH₄ yields by 4.03% and 5.85%, respectively, compared to the control, indicating CH₄ yield inhibition. This lab-scale study highlights the potential for integrating GNPs into full-scale, continuously operated wastewater treatment anaerobic digesters for long-term use in future applications. Full article

This study evaluates the agronomic potential of two types of vermicompost—one produced solely from wine industry residues (WIR) and one incorporating sewage sludge (WIR + SS)—under rainfed and deficit irrigation conditions in Mediterranean vineyards. The vermicompost was obtained through a two-phase process involving initial thermophilic pre-composting, followed by vermicomposting using Eisenia fetida for 90 days. The conditions were optimized to ensure aerobic decomposition and maintain proper moisture levels (70–85%) and temperature control. This resulted in end products that met the legal standards required for agricultural use. However, population dynamics revealed significantly higher worm reproduction and biomass in the WIR treatment, suggesting superior substrate quality. When applied to grapevines, WIR vermicompost increased soil organic matter, nitrogen availability, and overall fertility. Under rainfed conditions, it improved vegetative growth, yield, and must quality, with increases in yeast assimilable nitrogen (YAN), sugar content, and amino acid levels comparable to those achieved using chemical fertilizers, as opposed to the no-fertilizer trial. Foliar analyses at veraison revealed stronger nutrient uptake, particularly of nitrogen and potassium, which was correlated with improved oenological parameters compared to the no-fertilizer trial. In contrast, WIR + SS compost was less favorable due to lower worm activity and elevated trace elements, despite remaining within legal limits. These results support the use of vermicompost derived solely from wine residues as a sustainable alternative to chemical fertilizers, in line with the goals of the circular economy in viticulture. Full article

Petroleum oily sludge (OLS), a hazardous by-product of the petroleum industry, and high-alkali lignite (HAL), an underutilized low-rank coal, pose significant challenges to sustainable waste management and resource efficiency. This study systematically investigated the combustion behavior, reaction pathways, and gaseous-pollutant-release mechanisms across varying blend ratios, utilizing integrated thermogravimetric-mass spectrometry analysis (TG-MS), interaction analysis, and kinetic modeling. The key findings reveal that co-combustion significantly enhances the combustion performance compared to individual fuels. This is evidenced by reduced ignition and burnout temperatures, as well as an improved comprehensive combustion index. Notably, an interaction analysis revealed coexisting synergistic and antagonistic effects, with the synergistic effect peaking at a blending ratio of 50% OLS due to the complementary properties of the fuels. The activation energy was found to be at its minimum value of 32.5 kJ/mol at this ratio, indicating lower reaction barriers. Regarding gas emissions, co-combustion at a 50% OLS blending ratio reduces incomplete combustion products while increasing CO₂, indicating a more complete reaction. Crucially, sulfur-containing pollutants (SO₂, H₂S) are suppressed, whereas nitrogen-containing emissions (NH₃, NO₂) increase but remain controllable. This study provides novel insights into the synergistic mechanisms between OLS and HAL during co-combustion, offering foundational insights for the optimization of OLS-HAL combustion systems toward efficient energy recovery and sustainable industrial waste management. Full article

The fatigue resistance of cement-stabilized macadam (CSM) plays a vital role in ensuring the long-term durability of pavement structures. However, limited cementitious material (CM) content often leads to high packing voids, which significantly compromise fatigue performance. Existing studies have rarely explored the coupled mechanism between pore structure and fatigue behavior, especially in the context of solid-waste-based CMs. In this study, a cost-effective alkali-activated sludge gasification slag (ASS) was proposed as a sustainable CM substitute for ordinary Portland cement (OPC) in CSM. A dual evaluation approach combining cross-sectional image analysis and fatigue loading tests was employed to reveal the effect pathway of void structure optimization on fatigue resistance. The results showed that ASS exhibited excellent cementitious reactivity, forming highly polymerized C-A-S-H/C-S-H gels that contributed to a denser microstructure and superior mechanical performance. At a 6% binder dosage, the void ratio of ASS–CSM was reduced to 30%, 3% lower than that of OPC–CSM. The 28-day unconfined compressive strength and compressive resilient modulus reached 5.7 MPa and 1183 MPa, representing improvements of 35.7% and 4.1% compared to those of OPC. Under cyclic loading, the ASS system achieved higher energy absorption and more uniform stress distribution, effectively suppressing fatigue crack initiation and propagation. Moreover, the production cost and carbon emissions of ASS were 249.52 CNY/t and 174.51 kg CO₂e/t—reductions of 10.9% and 76.2% relative to those of OPC, respectively. These findings demonstrate that ASS not only improves fatigue performance through pore structure refinement but also offers significant economic and environmental advantages, providing a theoretical foundation for the large-scale application of solid-waste-based binders in pavement engineering. Full article

This study evaluates the agronomic and environmental performance of pelletized compost derived from olive mill waste as a sustainable alternative to mineral fertilizers for cultivating wheat (Triticum turgidum L.) under conventional tillage methods. A field experiment was conducted in semi-arid Spain, employing three fertilization strategies: inorganic (MAP + Urea), sewage sludge (SS), and organic compost pellets (OCP), each providing 150 kg N ha⁻¹. The parameters analyzed included wheat yield, grain quality, soil properties, and greenhouse gas (GHG) emissions. Inorganic fertilization yielded the highest productivity and nutrient uptake. However, the OCP treatment reduced grain yield by only 15%, while improving soil microbial activity and enzymatic responses. The SS and OCP treatments showed increased CO₂ and N₂O emissions compared to the control and inorganic plots. However, the OCP treatment also acted as a CH₄ sink. Nutrient use efficiency was greatest under mineral fertilization, though the OCP treatment outperformed the SS treatment. These results highlight the potential of OCP as a circular bio-based fertilizer that can enhance soil function and partially replace mineral inputs. Optimizing application timing is critical to aligning nutrient release with crop demand. Further long-term trials are necessary to evaluate their impact on the soil and improve environmental outcomes. Full article

Sewage sludge, characterized by its high organic matter and nutrient content, as well as the presence of microbial pathogens and other contaminants, requires proper management due to its significant generation rate. The table olive sector, which is highly significant in Spain as a global leader in production and export, generates various waste streams such the Organic Solid By-Products from Table Olive Processing (OSBTOP), which are mainly derived from the olive pit after the pitting process. The main aim of this study was to enhance the methane production performance of sewage sludge through co-digestion with OSBTOP as a co-substrate. Batch assays demonstrated that employing OSBTOP as a co-substrate increased methane content by 35–41% across all tested mixtures. While the highest methane yield was produced at a 40:60 (sludge:OSBTOP) ratio, a 60:40 mixture proved to be a more advantageous option for scale-up and practical application. This is attributed to factors such as the higher availability of sludge and its inherent buffering capacity, which counteracts the accumulation of volatile fatty acids and promotes process stability, thereby contributing to the study’s objective of significantly enhancing methane production from sewage sludge through co-digestion. In semi-continuous operation, methane yields in the co-digestion scenario exceeded those of mixed sludge digestion, showing a yield of 180 versus 120 LCH₄⁻¹ · kgVS_added⁻¹, representing a 50% improvement. This study highlights the potential of anaerobic digestion as a strategy for valorizing OSBTOP, a by-product with no prior studies, while demonstrating that its co-digestion with sewage sludge enhances methane generation, offering a sustainable approach to organic waste treatment. Full article