Search Results (51)

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 sustainable management of sewage sludge (SS) requires comparative evaluations that capture both environmental impacts and the trade-offs associated with emerging and established treatment routes. This study applies life cycle assessment (LCA) to compare hydrothermal carbonization (HTC), rotary kiln pyrolysis, and incineration using SS from the Salitre WWTP in Bogotá, Colombia, based on a life cycle inventory that integrates experimental characterization, Aspen Plus simulations, and Ecoinvent datasets modeled in EASETECH. Thirteen ILCD midpoint impact categories were assessed, and uncertainty was evaluated through global sensitivity analysis (GSA) and Monte Carlo simulations. The results show that the three technologies distribute their impacts differently across categories, as follows: HTC yields reductions in several categories due to carbon storage and fertilizer substitution but presents toxicity-related impacts linked to heavy metal transfer to soils; pyrolysis produces a pyrochar with metal retention and nutrient recovery potential that influences climate and resource-related categories while remaining sensitive to sludge composition; and incineration influences climate categories without the potential toxic effects of using chars in soils, reduces sludge volume, and facilitates subsequent nutrient recovery processes from ash, with lower uncertainty due to its technological stability. These results support circular economy strategies in low- and middle-income countries by clarifying the environmental conditions under which carbonized materials or ash-derived recovery pathways can be incorporated into sludge treatment systems. Full article

The rising demand for sustainable agriculture and circular resource management has intensified interest in converting wastewater sludge into value-added products. This review explores the transformation of sewage sludge into slow- and controlled-release fertilizers (CRFs), with a focus on biochar production and encapsulation technologies. Sewage sludge is rich in essential macronutrients (N, P, K), micronutrients, and organic matter, making it a promising feedstock for agricultural applications. However, its use is constrained by challenges including compositional variability, presence of heavy metals, pathogens, and emerging contaminants such as microplastics and PFAS (Per- and Polyfluoroalkyl Substances). The manuscript discusses a range of stabilization and conversion techniques, such as composting, anaerobic digestion, pyrolysis, hydrothermal carbonization, and nutrient recovery from incinerated sludge ash. Special emphasis is placed on coating and encapsulation technologies that regulate nutrient release, improve fertilizer efficiency, and reduce environmental losses. The role of natural, synthetic, and biodegradable polymers in enhancing release mechanisms is analyzed in the context of agricultural performance and soil health. While these technologies offer environmental and agronomic benefits, large-scale adoption is hindered by technical, economic, and regulatory barriers. The review highlights key challenges and outlines future perspectives, including the need for advanced coating materials, improved contaminant mitigation strategies, harmonized regulations, and field-scale validation of CRFs. Overall, the valorisation of sewage sludge into CRFs presents a viable strategy for nutrient recovery, waste minimization, and sustainable food production. With continued innovation and policy support, sludge-based fertilizers can become a critical component of the green transition in agriculture. Full article

Small-scale thermal treatment systems can provide environmentally improved sewage sludge treatment due to processing sludge locally, which lowers transport costs and emissions. However, the combined effect of confined volume and complex sludge properties makes achieving strict regulations on flue gas emissions and end-ash composition challenging. System development thus requires the use of advanced, 3D CFD simulation supported studies. An important step forward regarding these is the application of combustion models which introduce tailored surrogate fuels and apply detailed chemical kinetics to achieve a high-fidelity combustion description in confined volumes. In relation to this, the paper presents an innovative computationally efficient sewage sludge surrogate-based combustion model capable of defining surrogates, tailored to sewage sludge, and capable of providing detailed insight into reaction zone evolution in small-scale sludge incineration systems. The validity of the proposed model and surrogates is confirmed via simulated temperatures differing from measurements in the small-scale system for less than 30 K. The validated model of a small-scale system is used in the parametric analysis of variable air–fuel ratios, higher fuel moisture presence, varying bed temperature, and varying thermal power to enable unprecedentedly accurate and efficient definition of design features of small-scale systems and to provide key guidelines for operation optimization. Full article

The main aim of the research was to evaluate the feasibility of using recycled ceramics and ash from municipal sewage sludge as concrete fillers. As part of the study, standard cylindrical and cubic samples were investigated. The samples consisted of waste ceramic aggregate fractions 0–4 mm and 4–8 mm, which were sourced from used products manufactured by a sanitary fittings factory, as well as ash from one of the Polish sewage treatment plants. The chemical composition and morphology of recycled materials used to produce concrete were examined. The research itself focused on determining the strength properties of the produced composites under both normal conditions and after initial heat treatment. Microstructural tests of the produced composites were also carried out. The results demonstrated that selected recycled materials can successfully replace materials previously used in concrete production. The obtained strength results do not differ significantly from the strength of concrete made of traditional materials. Research has confirmed the possibility of using waste materials as concrete fillers. Full article

The effectiveness of the stabilisation/solidification process depends upon a number of factors, the most significant of which are the type of binder, contaminants, and soil undergoing treatment. In accordance with the principles of sustainable construction, alternatives to cement are sought after, with the objective of achieving the lowest environmental impact while maintaining a high level of strength and effective binding of the contaminant. In the study of the stabilisation/solidification of zinc-contaminated loess, incinerated sewage sludge fly ash with reactive magnesia was selected as the binder, and the UCS of the mixtures and microstructure was verified after 28 days of treatment. The values obtained were related to the strength of a reference sample and exhibited by S/S products using Portland cement. The findings verified the effectiveness of the selected materials in the S/S process. Following a 28-day treatment with 30 and 45% IFA and MgO in a 2:1 ratio, the samples were classified as a hard subgrade, suitable for civil engineering purposes, due to the UCS values achieved, ranging from 0.52 to 0.9 MPa. Furthermore, a correlation between the UCS values and the water content was identified, and the mineralogical composition of S/S products was determined with the use of the XRD technique. Full article

This paper examines the properties of sewage sludge ashes (SSAs) from the incineration of sewage sludge with added limestone for toxic gas treatment. It also evaluates the potential valorization of SSA in cement composites as supplementary cementitious materials (SCMs). The work involves a thorough characterization of four SSAs, including physical, chemical, and mineralogical properties. It also includes assessing the behavior of SSA in water solution through electrical conductivity measurements. The reactivity of ashes was evaluated using the R³ method and mechanical properties. The results revealed that all SSAs present comparable mineralogical and chemical properties, with varying proportions. Major elements such as Ca, Si, Fe, P, and S are predominant in the ashes, with traces of heavy metals. In an aqueous solution, a gradual formation of ettringite was detected only for two SSA. The heavy metal leachability was negligible, confirming that SSA is a non-hazardous waste. Finally, the reactivity and strength activity index assessments revealed a low and slow reactivity of SSA compared to metakaolin or slag. The SSA that favored ettringite formation in aqueous solution presented the lowest compressive strength at 28 days after incorporation in mortar. Despite originating from different incineration sites, these ashes fall under the same category of SCM reactivity. Full article

This study aimed to determine the level of immobilization and the mechanism of leaching of heavy metals (Cd, Cr, Cu, Pb and Zn) from self-hardening slurries (SHSs) based on ash from municipal sewage sludge incineration. To mimic the character of the SHS operation in the cut-off wall, the author’s leaching method—a filtration leaching test based on the percolation test—was used. In addition, this paper briefly described the factors affecting the level of heavy metal release from cement composites, as well as the chemical mechanisms and physical processes responsible for this phenomenon. This study showed that SHSs immobilized heavy metals at high levels (≥98.18%), and the aqueous extracts from the samples had a high pH (≥12.9%). Statistically significant correlations were obtained between the concentration of some metals and pH (positive correlation for Cr and Zn), test duration (positive correlation for Cd) and the liquid-to-solid ratio (negative correlation for Cd and Cr). For some of the metals tested, it was possible to determine the release mechanisms: dissolution and wash-out for Cd and Pb, and dissolution for Cr and Zn. Full article

The routine dredging of waterways produces huge volumes of sediments. Handling contaminated dredged sediments poses significant and diverse challenges around the world. In recent years, novel and sustainable ex situ remediation technologies for contaminated sediments have been developed and applied. This review article focuses on cement-based binders in stabilizing contaminants through the stabilization/solidification (S/S) technique and the utilization of contaminated sediments as a resource. Through S/S techniques, heavy metals can be solidified and stabilized in dense and durable solid matrices, reducing their permeability and restricting their release into the environment. Industrial by-products like red mud (RM), soda residue (SR), pulverized fly ash (PFA), and alkaline granulated blast furnace slag (GGBS) can immobilize heavy metal ions such as lead, zinc, cadmium, copper, and chromium by precipitation. However, in a strong alkali environment, certain heavy metal ions might dissolve again. To address this, immobilization in low pH media can be achieved using materials like GGBS, metakaolin (MK), and incinerated sewage sludge ash (ISSA). Additionally, heavy metals can be also immobilized through the formation of silicate gels and ettringites during pozzolanic reactions by mechanisms such as adsorption, ion exchanges, and encapsulation. It is foreseeable that, in the future, the scientific community will increasingly turn towards multidisciplinary studies on novel materials, also after an evaluation of the effects on long-term heavy metal stabilization. Full article

Struvite crystallization can recover nitrogen and phosphorus simultaneously from various kinds of wastewaters as a slow-release fertilizer. However, the enhancement of the removal efficiency of NH₄-N is challenging because the molar concentration of NH₄-N is higher than that of PO₄-P in many types of sewage including digested sludge filtrate. In this study, phosphorus eluate was recovered from sewage sludge incineration ash (SSA) and applied to the struvite crystallization process to increase the removal efficiency of NH₄-N for the digested sludge filtrate. Under acidic conditions, a maximum of 98.4% of phosphorus was eluted from SSA; in alkaline conditions, a maximum of 51.2% was eluted; and in sequential elution conditions with (NaOH+H₂SO₄), a maximum of 98.0% was eluted. Jar tests were performed by injecting three types of eluates (H₂SO₄ 1 N_elulate, NaOH 1 N_elulate, and (NaOH+H₂SO₄)_eluate), and PO₄-P was stably removed (>86%) under all tested conditions. When the NaOH 1 N_eluate was injected, the NH₄-N removal efficiency was highest at 84.4%, followed by 78.4% with the (NaOH+H₂SO₄)_eluate, and 58.7% with the H₂SO₄ 1 N_eluate at the molar ratio of Mg:P:N of 1.5:1.5:1. In addition, the sequential jar tests were conducted by injecting both the NaOH 1 N_eluate and (NaOH+H₂SO₄)_eluate. In the pH range of 8.5–9.5, the PO₄-P and NH₄-N removal efficiencies reached 92.3–94.5% and 97.9–99.1%, respectively. X-ray diffraction analyses confirmed that the majority of the crystal phases were struvite forms. Therefore, the combined application of both the NaOH 1 N_eluate and (NaOH+H₂SO₄)_eluate was adequate to enhance not only the phosphorus recovery but also the removal efficiencies of PO₄-P and NH₄-N. SSA recovering PO₄-P could be utilized as a new phosphorus source in the struvite crystallization process. Full article

The European Union’s initiative to reduce carbon dioxide emissions has paved the way for the exploration of innovative building materials that are environmentally friendly and meet all requirements of durability and strength. These criteria can be met by combining natural resources used in the production of building materials with waste materials that would otherwise be landfilled, having a negative impact on the environment. This study focuses on such materials and presents the results of recent research conducted at the Warsaw University of Life Sciences. The aim was to develop a new generation of materials fully compliant with the principles of the circular economy and sustainable development. Simultaneously, these materials should have no adverse effects on human health and be strong enough to carry the required loads. This study proposes the combination of a natural raw material—in the form of clay—with fly ash from the incineration of sewage sludge to produce a new generation of materials. Several samples were prepared using fly ash from two sources and then were fired at 950 °C. The resulting composites underwent physico-chemical and strength tests. These tests not only confirmed the high strength and durability of the obtained product but also the neutralization of the heavy metals originally present in the fly ash. Full article

Sewage sludge (SS) is an organic waste that may potentially be used as a slow-release source of phosphorus (P), despite the necessity for pre-treatment and its lower P content compared to soluble mineral fertilizers. For these reasons, composted sewage sludge was used to manufacture pelletized organomineral fertilizers, by mixing it with the inorganic sources monoammonium phosphate (MAP) and AshDec^® (ASD) (thermochemically incinerated SS). The fertilizers were physiochemically characterized and evaluated for their P solubilization dynamics and lability in the soil. The sources tested were as follows: organic compost of sewage sludge powder (SSC) and its pelletized form (SCP), pelletized organomineral SSC + MAP (S + MAP) and SSC + ASD (S + ASD), ASD alone, compared conventional MAP and a control (nil-P). These fertilizers were applied to columns containing 50 g of soil at the dose of 100 mg P column⁻¹ and were leached daily with 30 mL of water or 2% citric acid for 30 days. We analyzed the leachates for pH and P content. Pelletizing process resulted in denser products and promoted more gradual P release. The organomineral S + MAP was the most water-soluble recycled source, solubilizing about 70% of the total P, while the others presented much lower solubilization (<20%). In contrast, all fertilizers showed high solubility in 2% citric acid (except for S + ASD). After leaching, soil P fractionation disclosed that the P leftover in the soil remained mostly in the labile and moderately labile pools. Composting and the ASD process produced materials with slow P solubilization, being favored in acidic soils and in plant’s rhizosphere. In turn, S + MAP resulted in a promising product with intermediate P solubility, better synchronized with crop demand, potentially increasing P-use efficiency. Our results shed light in the physico-chemical properties and on the solubilization dynamics of novel organomineral products in tropical soil conditions. Full article

There is much organic waste that comes from by-products of agriculture and product processing, solid waste from livestock, and municipal waste. Conventional methods that are widely used for the treatment and management of organic fractions of waste are landfilling, composting, anaerobic digestion, incineration, gasification, and pyrolysis. Among the above methods, pyrolysis is a relatively simple, robust, and scalable technology for transforming diverse organic waste feedstock into renewable energy products. Recently, the electrochemical conversion of biochar into electricity in direct carbon fuel cells (DCFC) has also been investigated and shown to be feasible and highly efficient. This paper focuses on the utilization of organic waste as a fuel and the investigation of their characteristics during electrochemical reactions in molten hydroxide direct carbon fuel cells (MH-DCFCs). Organic waste of different origins (the food-processing industry, urban and suburban areas, municipal solid organic waste, sewage sludge) with diversified characteristics was used as the main feedstock. The lowest power density was determined for sewage sludge (5.1 mW cm⁻²), and the best results were obtained for peanut shells (53.14 mW cm⁻²). This study concludes that higher elemental carbon, lower ash content and the presence of reactive surface oxygen functional groups in biochar obtained from organic waste might contribute to better cell performance. Moreover, the research establishes the potential of carbonized organic waste as a prospective alternative fuel source for power generation in an MH-DCFC. Full article

This review provides an overview of methods to extract valuable resources from the ash fractions of sewage sludge, municipal solid waste, and wood biomass combustion. The resources addressed here include critical raw materials, such as phosphorus, base and precious metals, and rare earth elements for which it is increasingly important to tap into secondary sources in addition to the mining of primary raw materials. The extraction technologies prioritized in this review are based on recycled acids or excess renewable energy to achieve an optimum environmental profile for the extracted resources and provide benefits in the form of local industrial symbioses. The extraction methods cover all scarce and valuable chemical elements contained in the ashes above certain concentration limits. Another important part of this review is defining potential applications for the mineral residues remaining after extraction. Therefore, the aim of this review is to combine the knowledge of resource extraction technology from ashes with possible applications of mineral residues in construction and related sectors to fully close material cycle loops. Full article

The sustainable development of construction materials is an essential aspect of current worldwide trends. Reusing post-production waste in the building industry has numerous positive effects on the environment. Since concrete is one of the materials that people manufacture and use the most, it will continue to be an integral element of the surrounding reality. In this study, the relationship between the individual components and parameters of concrete and its compressive strength properties was assessed. In the experimental works, concrete mixes with different contents of sand, gravel, Portland cement CEM II/B-S 42.5 N, water, superplasticizer, air-entraining admixture, and fly ash from the thermal conversion of municipal sewage sludge (SSFA) were designed. According to legal requirements in the European Union, SSFA waste from the sewage sludge incineration process in a fluidized bed furnace should not be stored in landfills but processed in various ways. Unfortunately, its generated amounts are too large, so new management technologies should be sought. During the experimental work, the compressive strength of concrete samples of various classes, namely, C8/10, C12/15, C16/20, C20/25, C25/30, C30/37, and C35/45, were measured. The higher-class concrete samples that were used, the greater the compressive strength obtained, ranging from 13.7 to 55.2 MPa. A correlation analysis was carried out between the mechanical strength of waste-modified concretes and the composition of concrete mixes (the amount of sand and gravel, cement, and FA), as well as the water-to-cement ratio and the sand point. No negative effect of the addition of SSFA on the strength of concrete samples was demonstrated, which translates into economic and environmental benefits. Full article