Search Results (442)

Urbanisation-driven housing demand and the environmental burden of sewage sludge disposal highlight the need for low-carbon, circular construction materials. This study evaluates incinerated sanitary sludge ash (ISSA) as a supplementary cementitious material in stabilised earth blocks, aiming to reduce the use of cement and lime while valorising waste sludge. Lateritic soil blocks were produced with a binder-to-soil ratio of 1:7 by mass, in which ISSA partially replaced the primary stabilising binder (cement or lime) at a replacement level of 10–40% within the binder fraction. ISSA’s mineralogical characteristics were analysed using XRD and XRF. The compressive strength and density of earth blocks were measured at 7 and 28 days under curing conditions (29–36 °C; 60–75% humidity). Cement-stabilised blocks were water-cured to support cement hydration, whereas lime-stabilised blocks were air-cured to promote carbonation and pozzolanic reactions. The results, therefore, compared practical binder-specific curing regimes rather than strictly identical curing environments. ISSA exhibited moderate pozzolanic potential, and its incorporation enabled substantial partial replacement of both binders. Cement-stabilised blocks achieved higher strengths, up to 7.7 MPa, after 28 days of curing, whereas lime-stabilised blocks developed strength more gradually, reaching 4.8 MPa. Optimal mixtures were identified at 40% cement + 60% ISSA and 30% lime + 70% ISSA, balancing mechanical performance and binder reduction. A positive density–strength relationship was observed, but chemical bonding predominated over densification effects. ISSA-based stabilised earth blocks show promising structural performance and reduced binder use, but durability and life-cycle assessment need further evaluation before large-scale implementation. Full article

The valorization of drinking water treatment sludge (DWTS) and eggshell waste represents a promising route for reducing landfill disposal and developing alternative stabilized materials for geotechnical applications. This study aimed to evaluate the mechanical and microstructural behavior of DWTS stabilized with commercial lime (CL) and eggshell-derived hydrated lime (EHL), including alkali-activated EHL systems. EHL was produced from locally collected eggshell waste through washing, drying, grinding, calcination at 1000 °C for 4 h, hydration, drying, and sieving. The mixtures were prepared with lime contents of 5%, 8%, 11%, and 14%, while NaOH solutions of 0.5, 1.0, and 1.5 M were used for the activated systems. A total of 120 cylindrical specimens were compacted under controlled dry unit weight and moisture content and cured for 7 and 28 days. The stabilized DWTS was evaluated through unconfined compressive strength (q_u), SEM–EDS analysis, and multifactorial ANOVA. The highest q_u for CL-treated specimens was 4561.72 kPa at 14% lime and 28 days, while EHL reached its best response at 11% lime and 7 days, with a q_u of 3195.13 kPa. In general, EHL showed a competitive performance at intermediate and high lime contents, although increasing NaOH molarity tended to reduce strength. Full article

Sewage sludge management is increasingly shifting from a liability-focused “treat-and-dispose” approach toward resource recovery, where digestion residues and their liquid fractions are treated as secondary feedstocks for nutrient, water, and energy recovery. In Europe, the recast Urban Wastewater Treatment Directive strengthens performance and monitoring requirements and reinforces the need for efficient sludge treatment and downstream valorization routes. This review synthesizes evidence on how pretreatment-induced changes in digestate properties translate into membrane performance outcomes and maps practical design implications for selecting pretreatment-membrane trains for nutrient recovery and reclaimed water production. Pressure-driven membrane methods (MF/UF/NF/RO), together with membrane distillation and electrodialysis, are central candidates for producing clarified water streams and concentrating nutrients; however, their performance is governed by digestate rheology, colloidal stability, and the composition of soluble microbial products and inorganic ions, which collectively shape fouling and scaling risks. Pretreatments such as thermal hydrolysis and microwave conditioning can modify floc structure and solubilize organics, with potential benefits for dewaterability and mass transfer, but can also shift particle size distributions toward fines and increase fouling propensity if not coupled with appropriate solid–liquid separation and conservative flux control. Emphasis is placed on mechanisms and operational trade-offs rather than single-point performance claims, highlighting where evidence is robust and where further comparability and full-scale validation remain necessary. Full article

This study explores the case of the Wuhan East Lake National Independent Innovation Demonstration Zone (East Lake High-Tech Zone), investigating an advanced-scale stormwater and sewage co-treatment system alongside a “low-position, differentiated, vacuum” sewage collection approach. These systems operate within the framework of the “five-builds-one-management” model, which covers sewage collection, treatment, sludge disposal, reclaimed water utilization, tailwater discharge, and operation and maintenance management. The proposed system was associated with measurable before–after improvements: the sewage collection rate increased by 17%, the influent BOD₅ concentration at the sewage treatment plant rose from approximately 92 mg/L to 112 mg/L (~+22%), and water level fluctuations in the tailwater receiving area were reduced by 75%. This planning framework offers a valuable reference for similar urban areas, though calibration based on local hydrological conditions, industrial structure, and population size is essential. Full article

In the face of the raw materials crisis and environmental concerns, sustainable waste management has become a priority for current and future generations. Recycling waste from wastewater treatment plants in a closed loop protects natural resources, reduces landfill volumes, and lowers disposal costs. This paper presents the results of tests on the physical, filtration, and mechanical properties of mixtures of washed mineral waste (WMW) from grit chambers with fly ash from the thermal treatment of municipal sewage sludge (SSA) in a fluidized bed furnace. Additionally, radiological tests of the mixture components were conducted. Based on the conducted tests, the possibility of sustainable use in civil engineering, such as soil backfills and embankment construction materials, was assessed. The possibility of safely using waste materials in the indicated construction solutions was demonstrated for mixtures with dominant WMW content (90% and 70% by total weight). The waste mixtures correspond to poorly or medium-grade sands with a small amount of silt (uniformity coefficients of 3.33, 3.50, and 8.00). They are characterized by maximum dry densities of 1.542, 1.770, and 1.780 g/cm³; optimal moisture contents of 12.54, 12.86, and 20.25%; permeability coefficients of 0.08, 0.22, and 0.39 m/d; and internal friction angles of 38.4, 39.5, and 40.1°. The values of the determined parameters of some mixtures are similar to those of natural sands used as construction aggregates. All mixtures meet the geotechnical criteria for use in road embankments, below frost depth, and in flood embankment bodies. Mixtures with a 90% mass fraction of WMW were also approved for application as backfill for installation trenches. However, none of the mixtures met the hydraulic conductivity threshold required for the upper layers of embankments nor for backfill of abutments and retaining structures without the use of an additional binder (cement or lime), which is considered a prerequisite for these applications. Full article

While there is some agreement on estimating construction cost contingency for “known unknowns,” there is little consensus on estimating management reserves for “unknown unknowns.” Definitions of risk and uncertainty also differ between the economics and finance literature and the cost engineering literature. This paper examines how cost engineering guidance on estimating management reserves is applied in government-sponsored project cost estimates. This lack of consensus is evident in a specific program: the management, treatment, and disposal of 212,000 cubic meters of mixed radioactive and hazardous chemical waste generated by plutonium production at the Hanford Nuclear Site. Over $30 billion has been invested in treatment facilities, vitrification plants, and laboratories analyzing gases, liquids, sludges, and salt cake from 177 aging storage tanks. The remaining construction and operating costs are highly uncertain, with estimates ranging from $300 billion to $640 billion. Analyses of alternatives for constructing Hanford waste treatment facilities assume 15% contingencies and 40% management reserves. A method is presented to compute the implicit moments of Extreme Value distributions of cost estimates for different options, helping determine whether one alternative’s cost estimate stochastically dominates others. Adopting industry definitions of contingency and management reserves by federal government agencies could improve construction cost estimation in government-financed programs. Full article

The problem of industrial waste disposal is becoming increasingly pressing. For a long time, one of the primary methods of managing hazardous industrial waste was to dispose of it for long periods (decades) in engineered landfills. However, over time, due to various climatic, geological, and other changes, landfills begin to cause significant harm to the environment and human health. Old landfills, many built in the mid-20th century, pollute the air, soil, and groundwater. Therefore, the issue of decommissioning “old” landfills is becoming increasingly pressing. This study aimed to develop technological solutions for the safe extraction and processing of hazardous liquid waste from an aged industrial landfill. An integrated treatment chain was designed, comprising extraction, multi-barrier water treatment, vacuum evaporation, and lithification. Optimal lithification compositions were identified: for the salt concentrate–sludge–spent media mixture, a ratio of 68.2% sorbent D, 28.0% salt concentrate, and 3.8% dewatered sludge/spent media yielded a loose granular geocomposite; for oil-containing waste, the optimal ratio using lime and opoka was 1:0.9:0.5 (bottom sediments/CaO/opoka). Biotesting confirmed that the lithified waste is Hazard Class V (non-hazardous), whereas the untreated waste is Class III (moderately hazardous). The resulting geocomposite is suitable for on-site technical reclamation, closing the material cycle. Full article

Following the completion of the installation and commissioning of a solar sludge drying system serving the largest wastewater treatment plant on the island of Tenerife, a study has been carried out on the possibilities of implementing this type of infrastructure in other important plants in the Canary Archipelago. To this end and given the favorable climatic conditions found in the Canary Islands for this type of facility, the availability of land and possible impacts on surrounding areas have been studied. There are potential implementations on the islands. Thanks to these facilities, the volume of sludge to be transported to disposal or reuse areas is drastically reduced. The major drawback of these systems is the significant amount of land required, which is not always available on densely populated islands with rugged terrain. Full article

Accurate and rapid determination of moisture content in waste sludge is essential for optimizing dewatering processes, reducing disposal costs, and minimizing environmental impact. This study investigates the use of Fourier Transform Near-Infrared (FT-NIR) spectroscopy combined with Partial Least Squares Regression (PLS-R) for predicting the moisture content of dewatered sludge. A total of 96 sludge samples, with dry matter contents ranging from 12.4% to 24.6%, were collected from two treatment plants. FT-NIR spectra were acquired over the 800–2500 nm range, and chemometric models were developed to correlate spectral information with gravimetrically determined moisture content. The optimized PLS-R model demonstrated strong predictive performance, achieving a cross-validated coefficient of determination (R²_CV) of 0.87, a root mean square error of cross-validation (RMSECV) of 0.92%, and a residual predictive deviation (RPD) of 2.73. Independent test set validation confirmed the robustness of the model (R²_Test = 0.88, RMSEP = 0.88%, RPD = 2.92), supported by strong calibration results (R²_CT = 0.95, RMSEE = 0.60%, RPD = 4.46). Principal component analysis indicated that spectral variability observed in sludge samples was primarily associated with wastewater treatment plant (WWTP)-specific characteristics, reflecting moisture–organic matter interactions. These results demonstrate that FT-NIR spectroscopy is a promising tool for sludge moisture prediction. Full article

Sludge electro-dewatering has emerged as a research hotspot in advanced sludge treatment due to its ability to effectively remove interstitial water that is difficult to separate by mechanical dewatering. This paper systematically reviews the fundamental principles, key influencing factors, evolution of electrode materials, and engineering applications of electro-dewatering technology. Emphasis is placed on analyzing the effects of sludge properties, electric field parameters, and electrochemical reactions on dewatering efficiency. The characteristics and applicable scenarios of three generations of electrode materials—from conventional metal electrodes and carbon-based materials to dimensionally stable anodes (DSA)—are summarized. Current challenges include insufficient electrode stability, the trade-off between energy consumption and efficiency, limited understanding of underlying micro-scale mechanisms, and difficulties in process scale-up. Future efforts should focus on the development of high-performance electrode materials, investigation of multi-field coupling enhancement mechanisms, establishment of machine learning-based intelligent control strategies, and engineering design of continuous electro-dewatering equipment to promote its large-scale application in sludge treatment and disposal. Full article

The escalating challenge of solid waste disposal necessitates innovative recycling strategies. This study aims to constructed technosols from bulk solid wastes (fly ash, straw and sewage sludge) for the dual purpose of sustainable waste management and the rehabilitation of degraded land. Following a 150-day incubation period, six resulting technosols were systematically evaluated for aggregate stability, bacterial community structure, and biological safety to assess their viability as functional soil materials. All constructed technosols had a pH of 7.44–7.71 and were enriched in soil organic matter, nitrogen, and phosphorus. Aggregate stability (R_0.25: 46.6–64.0%) surpassed that of typical Chinese soils. Bacterial analysis revealed a stable consortium of 165 core genera, accounting for 92.93–98.11% of the total relative abundance, and were dominated by six phyla (Proteobacteria, Bacteroidota, Planctomycetota, Gemmatimonadota, Firmicutes, Actinobacteriota). The addition of straw modulated phylum structure, elevating Bacteroidota and reducing Proteobacteria. The bacterial communities exhibited clear functional hierarchy at class and order levels, with dominant groups forming a complementary carbon–nitrogen–phosphorus cycling network. Functional prediction further indicated distinct differentiation in carbon and nitrogen metabolic pathways. The technosols were non-phytotoxic and significantly enhanced the growth of Portulaca oleracea, increasing plant height (4.9–86.7%), dry weight per plant (67.3–605.4%), and SPAD values (8.1–15.9%), respectively. This study provides a sustainable strategy for repurposing solid wastes into functional technosols, aligning with circular economy principles and offering a viable solution for the ecological restoration of degraded lands such as mining areas. Full article

Waste tyres, with their high carbon content and heating value that is greater than that of coal and biomass, present a potential feedstock for energy recovery. Similarly, automotive paint sludge (APS) is a hazardous waste rich in volatile and inorganics compounds, making it difficult to dispose of safely, but it also has potential for thermochemical conversion. Gasification is a thermochemical process which can turn such wastes into syngas, a mixture mainly composed of carbon monoxide and hydrogen that can be utilized to generate power and produce liquid fuels. To deal with challenges of single feedstock gasification, co-gasification combines two or more feedstocks, taking advantage of synergistic interactions to enhance syngas yield and overall efficiency. In this work, Aspen Plus simulation software is used to develop a model for the co-gasification of waste tyres and automotive paint sludge. Sensitivity analysis was performed with the aim of investigating and optimizing the overall process conditions of waste tyre and APS co-gasification. This study investigated the effect of air (ER) and water feed (SFR) and blend ratios on the adiabatic reaction temperature, product gas composition and heat value of the product syngas. Optimal operating ranges were identified as ER = 0.35–0.40 and SFR = 1.0–1.2 for tyre gasification, ER ≈ 0.50–0.55 for APS-only gasification, and ER = 0.40–0.48 with SFR = 0.8–1.0 for co-gasification blends. Adiabatic temperatures under recommended conditions were typically 700–800 °C. The LHV of syngas decreased with increasing ER, SFR, and APS fraction, falling from ~13 MJ/kg for tyre gasification to below 10 MJ/kg for APS-rich cases due to oxidation and dilution by CO₂ and ash. No positive synergistic effect in syngas quality was observed under thermodynamic equilibrium conditions. APS primarily acted as an ash-rich, low-carbon diluent, reducing CO concentration, heating value and adiabatic temperature. However, potential catalytic interactions from APS mineral matter, which are not represented in the equilibrium model, may produce synergistic effects in practical gasifiers. Full article

Sewage sludge management remains a critical challenge in Greece, where increasing regulatory pressure, environmental constraints, and limited stakeholder participation complicate regional decision-making. In particular, the revision of regional Waste Management Plans requires decision-support approaches that are both technically robust and socially legitimate. This study develops and applies a participatory, data-driven multi-criteria decision analysis framework to evaluate sustainable sewage sludge management strategies in the Region of Eastern Macedonia and Thrace. The framework combines structured stakeholder participation with quantitative performance assessment, enabling transparent, reproducible, and systematic comparison of alternative sewage sludge management options. Four realistic sludge management alternatives—composting fr agriculture, forestry use, land restoration, and thermal drying with energy recovery were assessed against fifteen economic, environmental, and social sub-criteria. Data were collected through structured questionnaires administered to forty-four representatives from five stakeholder groups: utilities (water and sewerage service providers), local authorities, scientists/experts, end-users, and citizens. Group preferences were aggregated using equal group weighting to ensure balanced representation. The results show that environmental and economic criteria outweigh social aspects. The highest mean weights were assigned to compliance with environmental requirements for products derived from the disposal method (0.105) and compliance with stricter national environmental legislation (0.104), followed by energy intensity (0.097), installation cost (0.065), and operation and maintenance (O&M) cost (0.061). Overall rankings identified composting and thermal drying as the most preferred options, followed by land restoration and forestry use; sensitivity analysis (±10% variation in sub-criterion weights) confirmed ranking stability. The proposed framework enhances decision transparency by embedding measurable criteria and stakeholder inputs within a structured analytical process. From a policy perspective, it addresses participation gaps in Greek waste planning and offers a transferable decision-support tool for future regional planning. Further extensions may include integration with life cycle assessment and cost–benefit analysis to support adaptive updates under circular economy objectives. Full article

Industrial wastewater containing heavy metals such as iron (Fe) and copper (Cu) remains a major environmental concern in Malaysia, since industrial effluents significantly contribute to national water pollution loads. Without proper treatment, these contaminants can accumulate in the ecosystem and pose long term risks to human health and aquatic life. This study evaluates the performance, sludge characteristics, and cost implications of alkaline precipitation using sodium hydroxide (NaOH) and calcium oxide (CaO) in the presence and absence of a polymeric flocculant (SW204) for heavy metal removal. Experimental findings reveal that both NaOH and CaO effectively removed heavy metals, where NaOH achieved removal efficiencies of 91.6% for Fe and 93.5% for Cu, while CaO removed 98.9% of Fe and 99.17% of Cu. The addition of polymer improved the treatment efficiency where removal up to 99.73% Fe and 99.80% Cu was achieved with the CaO and polymer system. Settling time improved drastically from 30 min when using NaOH to 2 min when using CaO and the polymer system, indicating the formation of denser and more compact flocs. The specific gravity and sludge weight also increased by approximately 4% with polymer addition, which may influence the disposal costs. Economic analysis revealed that CaO treatment is substantially more cost-effective than NaOH, yielding savings of approximately RM 15.77 per m⁻³ of effluent treated. Therefore, the combination of CaO and polymers provided the best balance of removal efficiency, settling performance, and cost reduction. The findings support the use of CaO-based systems as sustainable, high-efficiency alternatives for industrial wastewater treatment, all of which aligns with UN Sustainable Development Goals 6 (Clean Water and Sanitation) and 12 (Responsible Consumption and Production). Full article

Activated sludge treatment is plagued by high secondary pollution risks, and ship antifouling paint particles (APPs) as hazardous heavy metal-rich solid wastes generated from hull derusting wastewater, pose severe environmental threats and intractable disposal dilemmas. This study developed a novel pilot-scale activated sludge reduction process coupling APPs-derived carbon-based catalysts with ultrasound-Fe²⁺/peroxydisulfate (PDS) advanced oxidation. Columnar catalysts were fabricated via direct carbonization-molding using waste APPs from an 82,000 deadweight bulk carrier were used as the sole raw material to prepare columnar catalysts via direct carbonization-molding; single-factor and orthogonal experiments optimized process parameters, Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) characterized catalyst and sludge properties, free radical quenching experiments elucidated reaction mechanisms and a 90-day continuous pilot run assessed catalytic stability. The process achieved a 43.5% sludge removal rate under optimal conditions, accompanied by 100% toluene and 92.3% phenolic compound degradation, as well as efficient total phosphorus (TP) and total nitrogen (TN) removal. Mechanistic studies via characterization and quenching experiments confirmed the catalyst enhanced PDS activation through free/non-free radical synergy and accelerated Fe²⁺/Fe³⁺ redox cycling. A 90-day continuous pilot operation demonstrated excellent long-term catalytic stability, with sludge removal rate remaining above 38%. This “waste treating waste” technology realizes high-value APPs resource utilization, provides a low-carbon sludge disposal pathway, and offers a scalable solution for collaborative pollution control in the wastewater treatment and shipping industries. Full article