Sewage Sludge Incineration Research Articles

Lightweight aggregates produced from low-temperature sintering of multiple solid wastes for heavy metals removal: Adsorption kinetics and stabilization

Solid wastes, including incinerated sewage sludge ash (ISSA), waste bentonite, and waste glass powder (WGP), were recycled and sintered at a low temperature (680°C) to produce lightweight aggregates (WSA). WGP acted as a fluxing agent to significantly lower sintering temperature of 1000-1200°C in other studies. WSA demonstrated an excellent mechanical strength of 3.76 MPa. The adsorbent dosage, initial pH, kinetics and isotherm on heavy metals adsorption were evaluated in batch adsorption experiments. The isothermal data exhibited a good correlation with the Langmuir model, and the maximum adsorption capacity was approximately 9.26 mg/g at 296 K. Pb(II) removal was dominated by precipitation and cation exchange. Breakthrough curves were determined for fixed-bed adsorption. At 50% breakthrough, the maximum adsorption capacity was 1.82 mg/g. The WSA after heavy metals adsorption were then reused to replace river sand (10-50%) in producing lightweight mortars. The solidification of spent WSA in the lightweight mortars could significantly reduce the leaching of Pb(II) by 98.5%. Moreover, the reuse of spent WSA resulted in low density and low thermal conductivity of cement mortars. This study demonstrates total waste management for municipal solid wastes: upcycling of waste–utilization–permanently stored as construction materials.

Functionalizing heavy metal contained incinerated sewage sludge ash in recycled glass-based alkali-activated materials for sewer environment

This study evaluates the performance of alkali-activated cement (AAC) mortars in an artificial sewage environment. The mortars, initially prepared with waste glass powder (GP) and ground granulated blast furnace slag (GGBS) in a 50:50 mass ratio, were modified by replacing 10 wt% of GGBS with incinerated sewage sludge ash (ISSA) with the goal of offering a biocidal effect. Comparisons were made with calcium aluminate cement (CAC), metakaolin (MK), and MK combined with zinc ferrite nanoparticles, each at a similar GGBS replacement level. The results showed that only incorporating CAC improved the strength development, achieving compressive and flexural strengths of 62.7 MPa and 7.4 MPa, respectively, at 28 days, while introducing ISSA or MK reduced the compressive strength to 47 MPa and flexural strength to 4.5 MPa. Although heavy metal ions from ISSA or zinc ferrite nanoparticles minimized biofilm thickness, they could not compensate for the reduced strength and increased alkalis leaching. Among all the tested mixtures, the 50GP40GGBS10CAC mixture exhibited superior biogenic acid resistance, possibly due to its Al-rich C-N-A-S-H gel phases (Ca/Si = 0.4, Na/Al = 0.8, Si/Al = 3.4) and refined pore structure (porosity = 3.4 %), making it the most microbial acid-resistant option for sewer rehabilitation.

Production of hydroxyapatite utilizing calcium and phosphorus in sewage sludge incineration ash

Sewage sludge incineration ash (SSIA), enriching the most of phosphorus (P), could be named as promising P source for P recycling and management. The novel strategy including extraction of P from SSIA by acid (HCl), purification and separation to obtain Ca liquid and Al-P liquid that could produce hydroxyapatite was investigated in this study. The P acid leaching rate was 97.9 % from SSIA at 0.2 mol/L HCl for 2 h. In P purification, P combined with Fe and Al to form precipitation (Al-P and Fe-P) with the increase of pH (<4.0). At a pH of around 4.0, the separation of Ca in the liquid phase was maximized, while Al-P and Fe-P precipitated out. Then, the Al-P precipitation could be dissolved in NaOH solution (0.2 mol/L) to separate Fe-P precipitation, that obtaining the Al-P liquid. What’s more, the high P content (P2O5, 25.5 %) in P product could be produced directly under 1.5 Ca/P molar ratio, which could be used in P fertilizer. The heavy metal content in the P product were far below the Chinese, American and EU fertilizer regulation, indicating that its environment safety. The Ca and P elements leached out during the acid leaching process were eventually recombined to form hydroxyapatite by wet-chemical purification. The cost of P recovery from SSIA was $3.06/kg P product demonstrating commercial potential of this strategy.

Исследование экологической безопасности автоклавного золопенобетона, полученного с использованием золы от сжигания осадка сточных вод

The article presents the research of ecological safety of autoclaved ash-foam concrete using ash from sewage sludge incineration in the constructed and operated production building. It is shown that after more than eighteen years of operation, the building made of autoclaved ash-foam concrete obtained using ash from sewage sludge incineration plant turned out to be environmentally safe for humans. Purpose: ash from sewage sludge incineration has high average specific radioactivity (radium and thorium), which strongly limits its further use. Earlier it was found that the use of ash from sewage sludge incineration as a raw material in autoclaved ash-foam concrete in different proportions affects the content of natural radionuclides in the finished product. The paper considers the environmental safety of autoclaved ash-foam concrete after prolonged operation. Methods: the research was carried out at the operating facility using a verified dosimeter-radiometer ATOMEX MKC-AT6130. Results: it was found that in all samples of autoclaved ash-foam concrete produced with ash from sewage sludge incineration the generated radiation background was below the norm, on the border of threshold values. Practical significance: the results of the work are important for construction, as they expand the ideas about the peculiarities of autoclaved ash-foam concrete and the possibility of safe use of ash from sewage sludge incineration in construction.

Sustainable reuse of modified incineration sewage sludge ash (M-ISSA) for stabilization of highly As-contaminated soil

Arsenic (As) is an environmental hazardous contaminant, seriously threatening human health. Chemical activation can effectively enhance As adsorption performance of incinerated sewage sludge ash (ISSA). Through modification, the iron (mainly present as hematite) in the ISSA was rearranged to KFeO2. Based on the results of the present study, addition of modified ISSA (M-ISSA) in contaminated soil had a positive effect on As immobilization. A set of laboratory batch experiments including toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP), and sequential extraction procedure (SEP) were carried out to investigate effects of M-ISSA dosages and curing time on immobilization of As contaminated soil (100, 500, 1000 mg As/kg soil). Results indicated that a higher addition amount of M-ISSA enhanced the effectiveness of stabilization and significantly reduced the As leachability after a stabilization period of 28 d. Particularly, in 1000 mg As/kg soil, M-ISSA reduced the labile As concentration in the TCLP test from 21.45 to 0.73 mg/L and in the SPLP test from 27.75 mg/L to 7.83 mg/L. M-ISSA transformed As in soil to more stable forms that were bounded to amorphous iron hydrous oxides. The number of stable fractions saw a sharp rise from 31% to 60%, when the M-ISSA addition was 5%. Different characterizations were conducted including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM), in order to demonstrate the stabilization behavior and mechanism of As and M-ISSA. The main stabilization mechanism was associated with adsorption and coprecipitation processes. Overall, this study proposed a novel recycling method for ISSA that could be chemically modified into a reliable and efficient additive for the immobilization of As contaminated soil.

Synergistic recycling of MSWI fly ash and incinerated sewage sludge ash into low-carbon binders

This study proposed a novel method for synergetic recycling of municipal solid waste incineration fly ash (IFA) and incinerated sewage sludge ash (ISSA) to produce low-carbon binders. The hydration mechanism, physical properties, and environmental risks associated with the designed binders were thoroughly evaluated. The results revealed a compositional complementary effect between IFA and ISSA, with ettringite being identified as the main crystal product resulting from the reaction between Ca2+ and SO42- in IFA and reactive aluminates in ISSA. The chlorides in raw IFA were effectively immobilized by the formation of various Cl-containing products, and all potentially toxic elements were immobilized in the binder system, exhibiting low leachability. Besides, CaO was found to be a highly efficient activator, providing additional reactive Ca2+ for the formation of more abundant and larger ettringite crystals, which consequently led to the high compressive strength (> 40 MPa) of the designed binders. Overall, this study provided a feasible approach for the upcycling of IFA and ISSA, contributing to the realization of “Zero-waste city” and the advancement of sustainable construction materials.

Valorization of sewage sludge incineration ash as a novel soilless growing medium for urban agriculture and greenery

Limited open areas for urban agriculture and greenery have led to the search for innovative, sustainable growing media to strengthen the food supply and improve atmospheric quality for a resilient city. Rampant land developments have caused soil to become increasingly scarce. Sewage sludge incineration ash (SSIA), the by-product of waste-to-energy (WtE) incineration of sewage sludge, is a major municipal waste containing phosphorus-fertilizing nutrients. For the first time, we investigated the novel application of SSIA as a soilless plant-growing medium with built-in fertilizer. SSIA outperformed topsoil in bulk density, water-holding capacity, porosity, and nutrient content. However, it was found that SSIA has a high salinity and should be treated first. Wheatgrass (Triticum aestivum L.), a fast-growing glycophyte, thrived in the desalinated SSIA, showing growth and nutrient content comparable to the topsoil case. Simultaneously, it demonstrated phytoremediation. The SSIA residue was then recycled into cementitious materials, using desalinating water for mixing. SSIA upcycle into a growing medium facilitates urban resource management by utilizing nutrients in sewage waste for eco-friendly plant cultivation, benefiting urban agriculture and greenery. It is also a prudent valorization step before further recycling SSIA to reduce landfill requirements.

Accelerated de-chelation of EDTA-metal complexes: A novel and versatile approach for wastewater and solid waste remediation

Industrial waste, including wastewater and solid waste, often contains toxic heavy metals that necessitate extraction and separation prior to safe disposal or reusing them. Sewage sludge incineration ash (SSIA), a non-incinerable waste, holds significant amounts of heavy metals such as iron, zinc, copper, nickel, chromium, and lead. Recovery and reuse of heavy metals from SSIA and further application of treated SSIA sludge remain challenging. Ethylenediaminetetraacetic acid (EDTA) is widely used for heavy metals chelation in different applications. While its chelation with heavy metals is rapid and easy to achieve, the de-chelation of the metal complexes is otherwise slow (∼3 days) and challenging due to their high stability constants. In this study, we investigate the recovery of heavy metals from SSIA through chelation using EDTA, and develop, for the first time, a method to rapidly de-chelate the EDTA-metal complexes through the facile chilling process (1 – 3 h) that accelerates the separation of EDTA and metal ions. A sequential precipitation of high-purity heavy metals from the EDTA-metal complexes was demonstrated with and without de-chelation. This novel and versatile method allows the separation of many valuable compounds from the treated SSIA, including regenerated EDTA, potassium hexafluorosilicate, iron phosphate, iron(III) hydroxide, iron silicate, titanium phosphate, calcium phosphate, copper(I) thiocyanate, nickel bis(dimethylglyoximate), lead(II) sulfate, and zinc sulfide. This approach opens doors for more sustainable waste management and the recovery of valuable resources from industrial waste.

Ex Situ Stabilization/Solidification Approaches of Marine Sediments Using Green Cement Admixtures.

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.

Synergistic recovery of aluminum phosphorus from incinerated sewage sludge ash via acid and alkaline treatment

The “phosphorus (P) crisis” has increased interest in improving P recovery methods and their efficiency. Incineration of sewage sludge ash is a recognized method for efficient P recovery, but challenges persist because of low recovery efficiency using thermochemical or biological methods and the issue of heavy-metal contaminants. Traditional wet-chemical processes, which yield calcium phosphate as the main product, are complex and costly. In contrast, aluminum (Al) phosphate (AlP) not only serves as a slow-release phosphate fertilizer but also has diverse high-value industrial applications, such as its use in battery coatings. To address these challenges, we developed a novel recovery route based on AlP extraction from Al-rich incinerated sewage sludge ash via acid leaching and alkaline precipitation. Our findings indicate that nitric acid (HNO3) achieves the highest Al leaching efficiency. The leaching kinetics of PO43− and metals follow second-order kinetics. Furthermore, pH adjustment with NaOH showed that the P precipitation efficiency from oxalic acid leachate was lower than that from hydrochloric acid, sulfuric acid (H2SO4), and HNO3 (88.0%–99.8%) because of buffering effects. These results underscore the potential of Al-rich ash for effective P recovery and considerably broaden the range of applications for P products.

Performance improvement of glass-based lightweight aggregates through thermodynamic modelling design and lightweight mortar validation

To reduce environmental impact of sintered lightweight aggregates (LWAs), in this study, novel glass-based LWAs were produced from municipal solid wastes at 900 °C. The mix was designed by thermodynamic modelling to optimize the phase composition, liquid phase properties, and microstructure of the LWAs. Results demonstrated that the inclusion of incinerated sewage sludge ash (ISSA) increased the viscosity of the liquid phase, resulting in a refined pore structure characterized by smaller, more isolated pores, and thicker pore walls. Additionally, ISSA facilitated the formation of various crystalline phases (e.g. wollastonite) to stabilize the pore structure, thereby enhancing densification and matrix strength. Leaching behaviour tests confirmed the suitability of glass-based LWAs for environmentally safe lightweight products. Lightweight mortars incorporating developed LWAs exhibited a high 28-day compressive strength (up to 57.9 MPa) with a low density of 1688 kg/m3 and a low thermal conductivity of 1.0 W/(m·K). The energy simulation revealed substantial reductions in energy consumption when the lightweight mortars were utilized in the building compared with the reference building using normal-weight C30 concrete, underscoring its promising role in conserving energy and reducing carbon emissions.

Binary solid wastes derived clinker: Raw feed system design validation and thermodynamic simulation investigation

Solid waste derived clinker design methodology was established based on thermodynamic simulation and experiment validation via the recycling of incinerated sewage sludge ash (ISSA) and recycled concrete fine (RCF). Compared with 1000 °C and 1100 °C, 1200 °C was the optimum temperature for C2S-rich clinker synthesis due to the highest simulated belite content after sintering. A utilization rate of 95 % was achieved, accomplishing the maximization of solid waste recycling. Due to the CaCO3 phase formation by the reaction of high-content belite (46.8 %) with CO2, carbonated 1200ARS eco-cement showed higher compressive strength than OPC and other eco-cements. The lowest porosity (18.1 %) with dense microstructure was also obtained by carbonated 1200ARS. Benefiting from the high CO2 reactivity of belite, 1200ARS displayed the optimum CO2 sequestration capacity with a higher carbonation degree (30.1 %) than other batches, providing a promising direction for future development of the low-carbon cement industry to achieve environmental sustainability.

Circular economy approach: Nutrient recovery and economical struvite production from wastewater sources by using modified biochars

The enrichment of phosphorus (P) and nitrogen (N) in aquatic systems can cause eutrophication. Moreover, P rocks may become exhausted in the next 100 years. A slow-release fertilizer called struvite (MgNH4PO4.6H2O) can reduce surface runoff. However, the high cost of raw material or chemicals is a bottleneck in their economical production. Therefore, incinerated sewage sludge ash, food wastewater, and bittern were combined as the sources of P, N, and Mg, respectively. Sawdust biochar was used to enhance the adsorptive recovery of nutrients. First, recovery kinetics was studied by comparing bittern-impregnated biochar (BtB) with the Mg-impregnated biochar (MgB). Subsequently, the synergistic physical and chemical interactions were observed for P and N recovery. Almost complete PO43–P recoveries were achieved within 10 min for both biochars. However, NH4+-N recovery was stable after 2 h, with 26% recovery by MgB and 20% recovery by BtB. Biochars activated with steam (steam-activated biochar) and KOH (KOH-activated biochar) gave superior activities to those of unactivated biochars and activated carbon (AC) nutrient recovery and struvite purity. Moreover, the activated biochars showed a lower risk of surface runoff, similar to that of AC. Therefore, activated biochars can be used as an alternative to AC for economical struvite production from a combination of wastewater sources.

Hydrothermally Stimulated Molecular Interfaces for Augmented Electron Delocalization in Wet-Chemical Phosphorus Recovery from Incineration Ash of Sewage Sludge.

Wet-chemically recovering phosphorus (P) from sewage sludge incineration ash (SSIA) has already become a global initiative to address P deficit, but effectively isolating P from these accompanying metals (AMs) through adsorption in a SSIA-derived extract remains elusive. Here, we devised a hydrothermal stimulus-motivated thermodynamic and kinetic enhancement to gain anionic ethylenediaminetetraacetic acid (EDTA) molecular interfaces for AM enclosure to resolve this conundrum. A new dosage rule based on the EDTA coordination ratio with AMs was established for the first time. Upon hydrothermal extraction at 140 °C for 1 h, the P extraction efficiency reached 96.7% or higher for these obtained SSIA samples, and then exceptional P sequestration from these EDTA-chelated AMs was realized by the peculiar lanthanum (La)-based nanoadsorbent (having 188.86 mg P/g adsorbent at pH ∼ 3.0). Relevant theoretical calculations unraveled that these delocalized electrons of tetravalent EDTA molecules boosted the enclosure of liberated AMs, thereby entailing a substantially increased negative adsorption energy (-408.7 kcal/mol) of P in the form of H2PO4- through intruding lattice-edged carbonates to coordinate La with monodentate mononuclear over LaCO5(1 0 1). This work highlights the prospect of molecular adaptation of these common extractants in wet-chemical P recovery from various P-included wastes, further sustaining global P circularity.

Investigation on solidified/stabilized behavior of marine soil slurry by lime-activated incinerated sewage sludge ash-ground granulated blast furnace slag under multifactor conditions

This study aims to evaluate the possibility of reusing treated marine clayey soils by stabilization/solidification (S/S) technology as geomaterial in reclamation projects from the aspects of engineering strength, chemical modification and environmental risk assessment. The lime-activated incinerated sewage sludge ash (ISSA) together with ground granulated blast furnace slag (GGBS) was employed as the binder. The multi-controlling factors including water content, curing time, salinity, and chemical compositions of mixing solution were taken account to identify the S/S treated Hong Kong marine deposit (HKMD) slurry based on the strength tests, pH measurement, thermo-gravimetric (TG) analysis, X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS) and toxicity characteristic leaching procedure (TCLP) tests, etc. The results show that the S/S treatment using lime-activated ISSA-GGBS can effectively enhance the strength of marine soil at initial water content of 110% and 200%. The water content and curing time have a significant impact on the S/S treated HKMD. The pH of treated soils is higher than 11.1, which proves an alkaline environment for the reactions in the treated soil. A special case is the treated HKMD at 200% water content hydrated by MgCl2 solution, which has a low pH of 10.23 and maintains a slurry state. Based on the TCLP results, the leaching concentration of heavy metals from S/S treated HKMD is environmentally safe and meets Hong Kong standard for reusing treated soil with a low level of <0.2 mg/L. The content of main products such as calcium/magnesium silicate hydrate, ettringite or Friedel's salt depends on the chemical additions (e.g. distilled water, seawater, NaCl and Na2SO4). The products in the specimens mixed with MgCl2 solutions are mainly composed of Mg(OH)2, M-S-H and MgCO3, which is distinct with the neoformations in the other cases. Therefore, this study proves that the S/S treated soil slurry could be reused as geomaterials in reclamation projects, and the S/S process is greatly affected by water content, curing time and solution compositions, etc.

Understanding particle adhesion of sewage sludge incineration ash at high temperatures: Effect of physical characteristics

Ash particle adhesion at high temperatures in thermochemical processes is a serious problem, and adhered ashes cause operational problems for processing plants, resulting in inefficient and unstable operation. A major mechanism of adhesion is the formation of a liquid phase due to melting of the ash components with low melting points, which results in a liquid bridge force, which is an attractive force. Therefore, the chemical characteristics of the ashes have been carefully studied to understand the adhesion phenomenon. However, each ash is also characterized by its physical properties such as particle size and packing ability. In this study, we focused on the physical characteristics of sewage sludge incinerated ashes collected from commercial incineration plants and carefully examined their relationship to adhesion. We found good correlations between particle size or porosity of the powder bed and adhesiveness at both ambient temperature and 800 °C. Understanding particle adhesion based on physical characteristics is simpler than considering complicated chemical characteristics and is useful for predicting particle adhesion at high temperatures.

N2O emission factors in bubbling fluidized bed incineration of municipal sewage sludge: The China case

The N2O emissions resulting from sludge incineration are estimated using the default values published by the Intergovernmental Panel on Climate Change (IPCC), which may differ significantly from the actual emissions. In this investigation, N2O emissions from four sludge incineration lines in two plants were monitored for varying durations. The variation in N2O emission factors (EFs) between incineration lines of the same plant was much smaller than the difference between different plants. Data on N2O EFs obtained from brief monitoring may contain variabilities of up to 30%. N2O EFs were more sensitive to temperature changes at low temperatures, necessitating extended monitoring periods to improve the reliability of N2O monitoring outcomes in cases of low furnace temperatures. Excessive use of the SNCR system to reduce NOx emissions resulted in concentrations of N2O and NH3 in the exhaust gases exceeding NOx levels. In the case of furnace temperature control and advanced reburning technology, it is advisable to utilize actual monitoring data or the smaller default values provided by the IPCC in China. Otherwise, the estimated N2O emissions may exceed the actual emissions.

Migration of trace elements and radioisotopes to various fractions of solid wastes generated as a result of the sewage sludge incineration process

The research was aimed at providing new knowledge in the field of chemical characteristics of solid waste generated in the process of combustion of sewage sludge in fluidized bed furnaces. The research material consisted of disposed fluidized beds (DFB), sewage sludge ash (SSA) and air pollution control residues (APC) from three Polish installations for the thermal treatment of sewage sludge. Natural radionuclides as well as anthropogenic isotope 137Cs were determined in the tested materials and the migration of a wide spectrum of trace elements to various waste fractions generated in the process of sewage sludge combustion was examined. It was observed that both radioisotopes and most of the trace elements determined accumulate in SSA and DFB, while the APC fraction contains a much smaller amount of them. The exceptions are mercury and selenium, whose volatile compounds migrate to the exhaust gas dedusting system and accumulate in the APC fraction (up to 40 mg/kg and 13 mg/kg, respectively). A potential threat from the 226Ra isotope in SSA is identified in the context of the management of this waste in the production of building materials because the typical activity of 226Ra in SSA collected from areas with very low Ra content in natural environment exceeds 1.5–6 times the activity of this isotope in conventional cement mixtures. When managing SSA and DFB, special attention should be paid to the content of metalloids such as As, B and Se, due to the high content of mobile forms of these elements in the mentioned materials.

Enhancing Sewage Sludge Treatment with Hydrothermal Processing: A Case Study of Adana City

As a byproduct of municipal wastewater treatment systems, sewage sludge has traditionally been treated in low-value applications such as landfilling, posing significant environmental risks due to its pollutant content. However, there is a growing interest in utilizing the energy potential of sewage sludge through thermochemical conversion methods. Among these methods, hydrothermal liquefaction (HTL) has come to the fore as a promising green approach, offering an environmentally friendly means of extracting bio-oils and biochemicals from sewage sludge. In this study, the HTL method, regarded as an innovative approach among sewage sludge treatment methods apart from incineration, pyrolysis, and landfilling, is comparatively investigated in terms of greenhouse gas (GHG) emissions alongside other methods. In particular, this study analyzes the projected amount and various characteristics of sewage sludge that could potentially be generated by 2030 for the city of Adana, which currently produces approximately 185 tons of sewage sludge per day. The findings indicate that without intervention, sludge production is projected to reach 68,897 tons per year by 2030. Moreover, this research demonstrates that the utilization of HTL for sludge treatment results in a reduction of emissions by approximately 7-fold compared with incineration of sewage sludge.

Recycling of incinerated sewage sludge ash and waste glass powder in alkali-activated slag for sewer rehabilitation

A new era has dawned in the manufacturing of cement-free binders with appropriate mechanical strengths and durability to combat CO2 emissions. However, the assessment of their performance in extreme conditions is ongoing. Here, we attempted to use incinerated sewage sludge ash (ISSA), a waste product of sewage sludge incineration that contains limited amounts of heavy metals, along with waste glass powder (GP) and ground granulated blast furnace slag (GGBS), as precursors to produce cement-free binders through alkali-activation. The alkali-activated materials (AAMs) were then subjected to an intensified sewage corrosion test for 6 months. The aim was to utilize the heavy metals in the ISSA as biocides to resist the biogenic acid attack on the AAMs. The experimental results indicated that superior performance was achieved by using a ternary binder prepared with ISSA, GP, and GGBS under biogenic acid simulation. Such enhanced durability can be attributed to the low Ca content in the resulting alkali-activated gels, which also reduced the grain size of gypsum formed and prevented expansion deterioration. Furthermore, the slow release of heavy metals from the AAMs prepared with the ISSA, evidenced by the leaching test results, was able to inhibit microbial growth.