Solid Waste Treatment Research Articles

The Impacts of Cellulose on Volatile Fatty Acid Production and the Microbial Community in Anaerobic Fermentation of Sludge at High and Medium Temperatures.

During large-scale sewage treatment, a large amount of excessive sludge is produced, which will cause serious pollution in the environment. In recent years, anaerobic digestion technology has been widely promoted because it can achieve better sludge reduction, and the products and byproducts after anaerobic digestion can be fully utilized as resources. In this study, cellulose was added as the co-fermentation substrate during the fermentation process at 30 ℃ and 50 ℃ to enhance the production of VFAs. The result indicated that cellulose could significantly increase the yield of VFAs in both 30 ℃ and 50 ℃. Meanwhile, COD and reducing sugar generation in the fermentation process were also measure. Analysis of the microbial community structure at the class and genus levels revealed that the proportion of several genus closely related with cellulose degradation such as Cellvibrio, Fibrobacter, and Sporocytophaga were significantly increased with the addition of cellulose. Co-fermentation was recognized as an economic and environmental friendly strategy for sludge and other solid waste treatment. The analysis of the effect of cellulose as a substrate on the production of VFAs at high and medium temperatures is highly important for exploring ways to increase the production of VFAs in anaerobic fermentation.

Catalytic Valorization of Organic Solid Waste: A Pilot-Scale Run of Sugarcane Bagasse

Organic solid waste treatment is crucial for enhancing environmental sustainability, promoting economic growth, and improving public health. Following our previous organic solid waste upgrading technique, a further two-step pilot-scale run, using sugarcane bagasse as the feedstock, has been successfully conducted with long-term stability. Firstly, the sugarcane bagasse was treated under mild conditions (400 °C and 1 bar of CH4), and this catalytic Methanolysis treatment resulted in a bio-oil with a yield of 60.5 wt.%. Following that, it was subjected to a catalytic Methano-Refining process (400 °C and 50 bar of CH4) to achieve high-quality renewable fuel with a liquid yield of 95.0 wt.%. Additionally, this renewable fuel can be regarded as an ideal diesel component with a high cetane number, high heating values, a low freezing point, low density and viscosity, and low oxygen, nitrogen, and sulfur contents. The successful pilot-scale catalytic upgrading of sugarcane bagasse further verified the effectiveness of this methane-assisted organic solid waste upgrading technique and confirmed the high flexibility of this innovative technology for processing a wide spectrum of agricultural and forestry residues. This study will shed light on the further valorization of organic solid waste and other carbonaceous materials.

Synthesis of mixed-base active material from drilling fluid solid waste and biomass for oil wastewater adsorption and its mechanism

To address the issues of high energy consumption, high cost and the risk of secondary pollution in drilling fluid solid waste treatment methods, this study prepared a mixed-based active material using drilling fluid solid waste and biomass materials as raw materials. The mixed-based active material is characterized by its abundant pore structure and high pore volume, demonstrating excellent adsorption performance for heavy metal ions and residual oil in industrial wastewater. Thermogravimetric and basic physical property analyses indicated a synergistic effect between drilling fluid solid waste and biomass materials, showing that joint pyrolysis of the two can enhance the yield of active materials. The adsorption performance of mixed-base active materials for heavy metal ions and residual oil were was tested. It was found that the removal rate of four heavy metal ions (Cr6+, Mn2+, Cu2+, and Zn2+) from the solution could reached 57.1 %, 96.3 %, 99.0 % and 94.1 %, respectively, at a concentration of 0.5 g/L of mixed-base active materials. Characterization revealed that the mixed-base activated carbon has a well-developed pore structure and numerous types of functional groups. The isothermal adsorption process of heavy metal ions by the active material is consistent with the Langmuir model and belongs to the monomolecular layer adsorption. The adsorption rate model of residual oil in wastewater by active materials conforms to the pseudo-second-order equation. The adsorption performance of mixed-base active materials primarily stems from physical adsorption enabled by their well-developed internal pore structure, along with chemical adsorption facilitated by oxygen- and nitrogen-containing functional groups on the surface.

Establishment and evaluation of dynamic viscoelasticity constitutive model for asphalt mixtures based on PCA model: Utilizing coal-based synthetic natural gas slag and phosphogypsum whisker as substitute fillers

To promote the secondary utilization of solid waste in asphalt pavement and reduce resource waste and environmental damage, the fine solid waste powder from the secondary treatment of solid waste was used as a substitute filler to prepare asphalt mixtures. To more precisely characterize the effects of filler type and substitution ratio on the dynamic viscoelastic mechanical characteristics of asphalt mixtures, the dynamic modulus test was conducted on asphalt mixtures, while the dynamic modulus master curve of asphalt mixtures was established based on the time-temperature equivalent principle and the Sigmoidal function. The improved generalized Sigmoidal (IGS) model, five-parameter fractional Zener (FFZ) model, six-parameter fractional Zener (SFZ) model and ten-parameter fractional Zener (TFZ) model were used to construct the shrinkage frequency curves of different asphalt mixtures under different constitutive relationships, whereas the applicability of the constitutive models was further evaluated by the principal component analysis (PCA) model. The research results showed that the dynamic modulus and phase angle of the mixture exhibited a similar change rule with the variation of temperature and frequency, and the use of solid waste-based fillers could effectively reduce the effect of frequency variation on the viscoelasticity of the mixture. The dynamic modulus master curve constructed by Sigmoidal function could accurately describe the functional relationship between the dynamic modulus with loading frequency and temperature, and the variation trend of dynamic modulus in a wider frequency range was flattened with the increase in frequency, and this change rule was not affected by the substitution ratio of the filler, while the use of solid waste-based filler could reduce the dependence of the mixture on the temperature. Compared to several fractional constitutive models, the IGS model exhibited a higher fitting accuracy for the dynamic viscoelasticity of several mixtures, and with the use of solid waste-based fillers, the deviation of fitting curves gradually decreased. A comparative study showed that the fractional constitutive model was difficult to accurately describe the dynamic viscoelasticity of the mixture, and the IGS model was preferred to be recommended as a calculation model to investigate the constitutive relationship on the dynamic viscoelasticity of the mixture.

Data-driven multi-objective intelligent optimal control of municipal solid waste incineration process

The municipal solid waste incineration (MSWI) process has become the primary technology for municipal solid waste (MSW) treatment worldwide due to its advantages of harmlessness, reduction, and resource recovery. However, the automatic combustion control (ACC) system developed in developed countries are often not effectively applicable to other countries, particularly China, due to regional differences in MSW composition. To achieve intelligent development of MSWI plants, it is crucial to develop intelligent optimal control technology tailored to national conditions to reduce comprehensive pollutant emission concentration (CPEC) and improve combustion efficiency (CE). This article proposes a data-driven multi-objective intelligent optimal control strategy. Firstly, based on the analysis of the whole process, the Tikhonov regularization-least regression decision tree (TR-LRDT) algorithm is used to establish a MSWI whole process model, incorporating serial controlled objects and parallel pollutant indicators, to support a multi-objective optimization model. Then, leveraging the ACC system and expert experience, a multi-input multi-output loop controller is established using the single neuron adaptive PID (SNA-PID) algorithm to achieve stable control of key controlled variables. Next, a mutation crossover strategy and termination condition are integrated with the multi-objective particle swarm optimization (MOPSO) algorithm to solve the multi-objective optimization model, and domain expert rules are applied to determine the optimal setpoints for key controlled variables in the Pareto front, aiming to reduce CPEC and improve CE. Finally, the effectiveness of the proposed intelligent optimal control strategy is validated using actual data. The experimental results demonstrate that this strategy not only maintains the stability of key controlled variables but also decreases CPEC by 1.82% and increases CE by 2.38%, laying a foundation for further research into intelligent optimization control of the MSWI process. Further, the software system based on the proposed strategy is developed and validated on a hardware-in-loop simulation platform.

Co-incineration of multiple inorganic solid wastes towards clean disposal: Heat and mass transfer modeling, pollutant generation, and machine learning based proportioning

The co-disposal of solid waste by industrial kilns is presently attracting increasing attention. In this study, we investigate the co-disposal of solid waste, i.e. converter ash (CA), sintered ash (SA), blast furnace bag ash (BA), and municipal solid waste incineration fly ash (MSWIFA), under simulated blast furnace ironmaking conditions. The results show that it is feasible to use blast furnace to treat MSWIFA, but the stability of temperature field should be controlled in the process of co-disposal. With the increase of temperature, the conversion rate of NO decreased to 16.4%, and ZnFe2O4 became the main mineral composition, accounting for 75.53%. Corresponding to the flue gas corrosion condition of solid waste treatment, it is found that the corrosion resistance of the furnace material TH347H is better than 20G. Finally, based on the experimental data, the nested optimization algorithm of machine learning model is established to achieve the reverse output of optimal conditions. Overall, the study provides theoretical support and methodology guidance for the co-disposal of solid waste in blast furnaces in providing support for the further development of co-disposal of solid waste in industrial kilns.

Sustainable tourism in the Tremiti Islands (South Italy)

An analysis of the pressure factors that influence the sustainable tourism in the Tremiti Islands (TI) has been performed. Tourist’s fluxes have been investigated in terms of monthly arrival and presences showing a high value of the territorial exploitation index with high number of arrivals, particularly in August, and low occupancy rate. Effects of climatic change has been analyzed in TI with reference to the increase of average air and sea temperature in the islands. Some measures of contrast to climate change and to favour sustainable tourism have been discussed also. The CO2 emissions by ferries transport, solid waste and wastewater treatment have been calculated. Environmental taxation for sustainable tourism aimed tat CO2 content reduction is also assessed identifying the value in 1.47 €/capita on the basis of the tourist arrivals and presences considering the environmental cost for CO2 removal and showing that tourism taxation should be well accepted if funds are destined to environmental purposes.

The waste of nations: Household trash and the affective politics of recycling in Israel

Solid waste treatment is an acute concern for countries facing waning landfilling capacity, increasingly strict controls on waste transport and treatment, and the persistent threat of climate change. These challenges are typically met by neoliberal and technocratic solutions that privatize public services while encouraging curbside recycling. I examine such an effort to promote curbside recycling in Israel. Drawing on extensive fieldwork in the Israeli recycling world, and on anthropology, geography, science and technology studies and critical waste studies literatures, I interrogate the affective politics of household waste recycling in Israel over the past decade and attempts to configure a Europeanized and moral national space through recycling. I describe the cultural and ethnonational repertoires through which curbside recycling was naturalized in the Israeli landscape, how recycling was mutually animated with a range of sociopolitical concerns that far exceeded its financial or environmental significance, and how these mutually shaped waste as a social–environmental problem. I argue that social and material conditions gave rise to a dual process, in which both the problem of waste, and its necessary solutions, were actively and mutually constructed. This paper contributes to comparative literatures on national cultures of waste recycling, shedding light on how a project of Western ecological modernization was translated and became locally meaningful in Israel's settler-colonial context, how household waste was ontologically coproduced in this process, and how its stakes were experienced, voiced, and materialized.

Analysis of Solid Waste Treatment and Management in Typical Chinese Industrial Parks with the Goal of Sustainable Development and Future Suggestions

Solid waste disposal and management have become a global problem, which is particularly tricky in China with its large population and rapid urbanization. This study focused on the disposal status of multi-source solid waste as well as the park management of some typical cities of China. Firstly, the main technical methods for solid waste disposal were summarized as follows: landfill, incineration, anaerobic digestion and aerobic compost. Secondly, the network analysis method was applied to seek an optimized method for solid waste disposal and management. Thirdly, typical demonstration parks for solid waste disposal and management were analyzed to study their respective operating modes and strategies for synergistic development in terms of resources, environment and economy and to explore the sustainable development potential of the Guangdong–Hong Kong–Macao operating mode. The results showed that the collaborative disposal and recycling of solid waste are important for cities (especially megacities) to achieve resource conservation and environmental protection. The NIMBY effect and environmental pollution risks caused by decentralized construction could be reduced through the construction of circular industrial parks. Advanced technologies and the national policy for solid waste disposal and recycling in industrial parks of small–medium cities, large–medium cities and megacities were systematically analyzed so as to explore a self-operating management mode of industrial parks. Finally, reasonable suggestions, such as sharing, saving and cycling and propaganda education, as well as green and low-carbon solutions were put forward for solid waste disposal and management in typical industrial parks, effectively resolving the contradiction between economic development and environmental protection so as to help urban sustainable development.

Efficacy and Economic Benefits of Nano TiO2 Photocatalytic Advanced Oxidation Technology in Solid Waste Treatment

In order to assess the application value of nano TiO2 photocatalytic advanced oxidation technology in the field of solid waste treatment and improve the efficiency of waste disposal, this study investigates the preparation of TiO2/ZnIn2S4 composite photocatalysts using an in-situ growth method. Subsequently, this photocatalyst is applied to urban solid waste treatment schemes to degrade solid waste and organic pollutants in wastewater. The results indicate that, at a pH value of 7.5, the composite material exhibits the optimal photocatalytic degradation performance, achieving a degradation rate of 90%. Following the urban solid waste treatment scheme, the greenhouse gas emissions per ton of municipal solid waste range from 50 to 100 kg, resulting in a 90% reduction in greenhouse gas emissions. The calculated payback period for this waste treatment scheme is 5 years. The findings suggest that this treatment approach effectively reduces greenhouse gas emissions, enhances resource recovery rates, and demonstrates favorable economic benefits for application in small to medium-sized urban areas. This research provides valuable insights for the application of nano TiO2 photocatalytic technology in the field of solid waste treatment.

Microbial electrochemical enhanced composting of sludge and kitchen waste: Electricity generation, composting efficiency and health risk assessment for land use

To realize the energy and resource utilization from organic solid waste, a two-phase microbial desalination cell (TPMDC) was constructed using dewatered sludge and kitchen waste as the anode substrate. The performance of electricity generation and composting efficacy was investigated, along with a comprehensive assessment of the potential health risks associated with the land use of the resulting mixed compost products. Experimental outcomes revealed a maximum open-circuit voltage of 0.893 ± 0.005 V and a maximum volumetric power density of 0.797 ± 0.009 W/m³. After 90 days of composting enhanced by microbial electrochemistry, a significant organic matter removal rate of 31.13 ± 0.44 % was obtained, and the anode substrate electric conductivity was reduced by 30.02 ± 0.04 % based on the anode desalination. Simultaneously, there was an increase in the content of available nitrogen, phosphorus, and potassium, as well as an improvement in the seed germination index. The forms of heavy metals shifted from bioavailable to stable residual states. The non-carcinogenic hazard index (HI) values for heavy metals and polycyclic aromatic hydrocarbons (PAHs) during the land use of compost products were less than 1, and the total carcinogenic risk (TCR) values for heavy metals and PAHs were below the acceptable threshold of 10−4. The occupational population risk of infection from five pathogens was higher than that of the general public, with all risk values ranging from 8.67 × 10−8 to 1, where the highest risk was attributed to occupational exposure to Legionella. These outcomes demonstrated that the mixture of dewatered sludge and kitchen waste was an appropriate anode substrate to enhance TPMDC stability for electricity generation, and its compost products have promising land use suitability and acceptable land use risk, which will provide important guidance for the safe treatment and disposal of organic solid waste.

Solid waste management and resource recovery during the 4-crew 180-day CELSS integrated experiment

In order to explore the management and treatment methods of solid waste in the Controlled Ecological Life Support System (CELSS) of future lunar bases, during the 4-crew 180-day integrated experiment, the Solid Waste Management and Treatment System (SWMTS) was built, in which the treatment of recyclable solid waste such as inedible plant parts and human excrement was completed through a combination of biological aerobic composting and high-temperature oxidation. Basic data on the types and amounts of solid waste generated during the 4-crew 180-day experiment mission were obtained. There were six types of solid wastes, including the work support wastes, the household support wastes, the plant cultivation wastes, the plant-based wastes, and crew feces. The daily average production was 0.67, 1.4, 0.32, 8.48, 0.534 kg/d, respectively. The proportion of plant-based wastes was high as 74.3 %, indicating that it was the most important part. By closed-loop air drying and graded crushing, all 1526.97 kg of plant-based waste was treated, with water recovery (about 1163.87 kg), as well as volume reduction and stabilization treatment. By incineration and aerobic composting treatment, 67.3 % (244.4 kg) of the plant-based wastes (dry weight) and all of the feces (96.26 kg) were converted, providing 339.54 kg carbon dioxide for plant growth. And 90.6 kg organic fertilizer was obtained. The fertilizer was highly mature, met safety requirements, and effectively improved lettuce yield. The recycling rate of renewable solid waste during the experiment reached 89.8 %. The efficient circulation of solid waste had been achieved during the 4-crew 180-day integrated experiment. The long-time experimental results have shown that the established solid wastes management and treatment system can timely treat biomass solid waste such as inedible parts of plants and crew feces, achieve timely recovery of water in such solid waste, and recycle carbon and other elements, which effectively improved the material closure of the system and ensured the successful 4-crew 180-day experiment. This work also maybe lay the foundation for the construction and operation of an ecological life support system for future lunar bases.

Anaerobic co-digestion of food waste and excess sludge by humus composites: Characteristics and microbial community structure

Volatile fatty acids (VFA) produced during the anaerobic co-digestion (Co-AD) an Manual removal of impurities such as bones, fish spines, napkins, etc., after collection at the food waste collection sited hydrolysis of food waste (FW) and excess sludge (ES) are important factors affecting the stability of the digestion and biogas production. This study aimed to use humus composites (HS) to mediate the Co-AD system of FW and ES, investigate their effects on VFA conversion, and analyze the microbial community structure using high-throughput sequencing technology to reveal the mechanism of action of HS in mediating the Co-AD system from a microbial perspective. The amount of HS was positively correlated with the accumulation of VFA produced by the hydrolysis of co-digested substrates, and in the Co-AD system with 5.00 g/L HS, the accumulation of VFA increased by approximately 1.1 times, whereas the pH and oxidation reduction potential of the system tended to be in the benign range, offering a favoring condition for enhancing the stability of the system. The biogas production increased by 46.3 % compared with that of the blank group. HS significantly increased the relative abundance values of Synergistota, a mutualistic symbiont with acetic acid-producing bacteria, and Proteobacteria, a mutualistic symbiont with methanogenic bacteria, thus promoting VFA conversion and strengthening the Co-AD efficacy of FW and ES. This study provides a simple and effective method to improve the Co-AD efficacy of FW and ES, as well as a new approach for the anaerobic resource treatment of other organic solid wastes.

Combined preparation and application of geopolymer pavement materials from coal slurry-slag powder-fly ash mining solid waste: A case study

The solid waste treatment problem generated in the process of coal mining has always been an important factor restricting safe and environmentally friendly production, and the coal slurry from the coal mine road surface is a new type of mine solid waste, so it is of great significance to treat and efficiently utilize the coal slurry. Currently, a common method of solid waste utilization is to add modifying reagents to prepare functional materials. Select coal slurry, slag powder and fly ash as raw materials, and sodium sulfate and sodium hydroxide were used as alkali exciters to prepare coal slurry based geopolymer pavement material (CSGPM). Response surface methodology was used to establish regression equations between the design optimization objectives (coagulation time, compressive strength) and the variables (mass fraction, mass ratio of slag powder to fly ash, mass ratio of sodium sulfate to sodium hydroxide). The effects of two-by-two interactions of the factors on the optimization objective were explored, and the use of different raw materials was obtained. Under the optimal proportioning parameters, the coagulation time of CSGPM was 33 min and the compressive strength of 24 h of curing was 11.20 MPa. In addition, the generation mechanism of AFt and C-S-H gel substances inside the specimen was explained with the help of microscopic scanning. CSGPM showed good mechanical properties in both load-bearing numerical simulations and acoustic emission tests. Numerical simulation was used to establish the relationship between the design objective of the roadbed (maximum subsidence of the roadbed after bearing) and the design variable (thickness of CSGPM paving). Comparative analyses yielded an optimal subgrade surface layer design thickness of 5 cm, with a maximum subsidence of 0.0033 m after bearing vehicles. Synchronization of roadbed material and concrete damage in combined specimen acoustic emission tests with uniform load transfer. The final coal mine pavement was successfully paved and the total cost of CSGPMD is 63.2 per cent of C30 concrete. Those results are important for the preparation of new pavement functional materials.

Dual roles of odor cleaners and pollutant producers for chemical scrubbing and biological treatment: Evidence in a food waste anaerobic digestion plant

The odor generated during municipal solid waste and wastewater treatment is a major source of public complaints worldwide. Chemical scrubbing and biological treatment are commonly used to control the odor. However, in this study, such odor control measures were found to produce derived odorous compounds and greenhouse gases, leading to reduced efficiency or uncertainty in odor treatment. In a food waste anaerobic digestion plant, a series of site and lab investigations were conducted on the odor control performance and mechanisms, as well as secondary pollutants of chemical scrubbing and biotrickling. Methanethiol, hydrogen sulfide (H2S), propanethiol, and acetaldehyde were identified as the top four odor contributors to the gas collected in the plant. The mechanisms of acetaldehyde and propanethiol removal in the chemical scrubbers were studied using gas-washing bottles. Acetaldehyde was mainly removed via physical absorption, whereas propanethiol could be completely removed via oxidation by sodium hypochlorite (NaClO). However, acetaldehyde was desorbed from the absorption solution and generated from the oxidation of ethanol by NaClO in the chemical scrubbers, leading to low, or even negative removal efficiency. H2S, methanethiol, propanethiol, and acetaldehyde could be abated by the biotrickling filters. However, H2S, methanethiol, propanethiol, and greenhouse gases could be also produced under anaerobic conditions, particularly when the packings were compacted. Furthermore, acetaldehyde could be produced from ethanol by bacteria possessing dehydrogenase under aerobic conditions. Both chemical scrubbers and biotrickling filters demonstrated the dual roles of odor removal and pollutant production.

Assessment of 150 TPD mechanical biological treatment (MBT) based municipal solid waste treatment and disposal facility

Assessment of 150 TPD mechanical biological treatment (MBT) based municipal solid waste treatment and disposal facility

Improving the stabilization/solidification performance of Pb-containing alkali-activated slag via incorporation of superabsorbent polymer

Alkali-activated materials (AAM) have garnered significant attention for the treatment of Pb-contaminated solid waste, attributed to their low carbon footprint and superior stabilization/solidification (S/S) capabilities. However, recent concerns arise regarding their long-term S/S performance, especially when exposed to rainwater environments and considering the inherent shrinkage and potential cracking of AAM. This research delves into the feasibility of enhancing the S/S efficacy of alkali-activated slag (AAS) through the integration of super absorbent polymers (SAP). Findings reveal a marked improvement in the S/S performance of Pb-laden AAS upon SAP addition. Specifically, incorporating 0.5 wt% and 1 wt% SAP curtailed Pb leaching in AAS samples (cured for 90 days) by 47 % and 75 %, respectively. Comprehensive analyses using XRD, TGA, MIP, BSEM, EDX, XPS and MAS NMR suggest that the bolstered S/S performance of SAP-augmented AAS is not rooted in alterations to the reaction degree, pore structure, or reaction products of AAS. Instead, it hinges on the innate capacity of SAP to absorb and retain Pb. Leaching tests reveal that, in AAS cured for 90 days, approximately 1.72 mg of Pb ions were retained per gram of SAP. This investigation furnishes a novel vantage point for refining and deploying alkali-activated materials (or other cementitious materials) as effective S/S agents.

Integrated assessment of environmental and economic impact of municipal solid waste incineration for power generation: A case study in China

Municipal solid waste incineration for power generation is significant for reducing and reusing solid waste. The study conducted an integrated assessment of environment and economy on municipal solid waste incineration in China, from a “cradle to grave” perspective using 1 tonne of municipal solid waste incineration as the functional unit. The environmental impacts of each month are also calculated to analyze the dynamic change throughout one year. The results indicate that the environmental impacts are mainly concentrated in marine ecotoxicity, freshwater ecotoxicity, human carcinogenic toxicity, and human non-carcinogenic toxicity. Flue gas purification, waste incineration and transportation are the key processes, which account for 65.61 %, 18.50 %, and 11.93 % of the overall environmental impact, respectively. Urea, activated carbon, chelating agent (EDTA) and diesel fuel for transportation are key factors. The life cycle cost (LCC) is 132.26 RMB/t of waste, of which the initial capital causes the largest economic cost. When considering power generated from municipal solid waste incineration to replace electricity supply from the power grid, it achieves significant environmental benefits and the normalized environmental impact value changes from 0.85 to −12.19. The findings provide references for municipal solid waste treatment to mitigate the environmental impact and reduce the economic burden across the entire life cycle.

Mechanical Response and Deterioration Mechanisms in Freeze–Thaw Environments for Crushed Stone Stabilized with Industrial Solid Waste

The conflict between industrial solid waste treatment and environmental protection in Inner Mongolia is becoming increasingly prominent. Using industrial solid waste such as mineral powder, fly ash and wet calcium carbide slag as raw materials, using the alkali excitation method to prepare geopolymer, and replacing part of the cement for pavement base can effectively absorb industrial solid waste and realize the dual goals of waste utilization and environmental protection. Through mechanical properties tests before and after a freeze–thaw cycle and micro tests such as scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP), the strength variation rule and mechanism of geopolymer-cement stabilized aggregate under freeze–thaw cycles were deeply investigated. The relationship between different porosity indexes and mechanical properties in mercury intrusion porosimetry (MIP) was established by grey relation analysis. The results prove that a mixture with impaired properties after freeze–thaw cycles and the anti-freezing performance of the mixture with 20% geopolymer content are better than that of the mixture with no geopolymer content and 40% geopolymer content. The loss rates of unconfined compressive strength (UCS) after 5, 10 and 20 freeze–thaw cycles were 9.5%, 27.6% and 36.4%, respectively. The appropriate addition of geopolymer can enhance the anti-freezing performance of a stable aggregate. Following freezing and thawing cycles, the unconfined compressive strength (UCS) damage of the mixture is mainly influenced by a rise in total porosity, and the grey correlation degree is 0.75. The increase in more harmful pores and total porosity mainly results in an indirect tensile strength (ITS) loss. The grey correlation degree is 0.91. The compressive rebound modulus (CRM) is not affected by the change in pores but decreases with a rise in the geopolymer dosage.

Enhanced production of hydrogen-rich gas from municipal sewage sludge gasification using a CaO-RM composite catalyst

Hydrogen-rich gas, characterized by high yield and purity, can be effectively generated through the steam gasification of sewage sludge (SS), offering substantial benefits for organic solid waste treatment and resource conservation. This study evaluated the gasification performance in a horizontal moving-bed reactor employing a wet-mixed CaO-red mud (CaO-RM) composite catalyst. The effects of CaO loading rate (CaO/RM), catalyst-to-SS ratio (CaO-RM/SS), and reaction temperature on the syngas yield, lower heating value (LHV), carbon conversion ratio, H2 to CO (H2/CO) ratio, and H2 yield were investigated. Results indicated that red mud loaded with a calcium-based catalyst significantly enhanced syngas production, particularly for hydrogen generation, during SS gasification. A maximum hydrogen molar fraction of 50.84% and a yield of 7.07 mol/kg were achieved with a CaO/RM of 40% and a CaO-RM/SS of 30% at 750 °C. With the reaction temperature increase from 700 to 900 °C, the catalytic performance for secondary tar cracking and steam reforming was further enhanced. The total syngas yield, H2 yield, hydrogen molar fraction, LHV of syngas, and carbon conversion rate peaked at 0.79 m³/kg, 19.30 mol/kg, 54.41%, 10,249.48 kJ/kg, and 65.67%, respectively, at 900 °C.