Search Results (39)

The carbon emissions from the cement industry account for approximately 8% of global carbon emissions, which exerts significant pressure on the environment. In this paper, the microbial-induced calcium carbonate precipitation (MICP) technology was introduced into the carbonization modification research of recycled hardened cement powder (RHCP), and the carbon sequestration performance of RHCP under different pressures was studied. The physicochemical properties of the carbonated products were characterized by microscopic testing methods, and the carbon sequestration mechanism under different pressures was obtained. Subsequently, carbonated RHCP (C-RHCP) was tested as a partial cement substitute for solidified sludge to evaluate its mechanical and durability properties. The results show that when the pressures were 0.3 and 0.5 MPa, the carbon sequestration capacity of RHCP was relatively good, reaching 59.14 and 59.82 g/kg, respectively. Since the carbon sequestration amounts under the two pressures were similar, and considering the energy consumption, in this study, a reaction pressure of 0.3 MPa was selected to prepare C-RHCP. Compared with pure cement, the 28-day unconfined compressive strength (UCS) of the sludge cured with 30% C-RHCP increased by 12.08%. The water stability coefficient of the solidified sludge in the C-RHCP group was greater than 1 after soaking for 7, 14, and 21 days, while the water stability coefficient of the cement group decreased to 0.92 at 14 days. After 20 freeze–thaw cycles, the mass losses of the cement group, the RHCP group, and the C-RHCP group were 31.43%, 38.99%, and 33.09%, respectively. This research not only provides an environmentally friendly strategy for the resource utilization of RHCP but also pioneers a new synergistic model that combines microbial mineralization with the modification of industrial solid waste. It demonstrated significant scientific value and engineering application prospects in reducing carbon emissions in the cement industry and promoted sustainable geotechnical engineering practices based on the “waste–waste” principle. Full article

Microbially induced carbonate precipitation (MICP) is the precipitation of CaCO₃ crystals, induced by microbial metabolic activities such as ureolysis. Various applications of MICP have been proposed as innovative biocementation techniques. This study aimed to verify the feasibility of ureolysis-driven MICP applications in deep-subsurface environments (e.g., enhanced oil recovery and geological carbon sequestration). To this end, we screened sludge collected from a high-temperature anaerobic digester for facultatively anaerobic thermophilic bacteria possessing ureolytic activity. Then, we examined the ureolysis-driven MICP using a representative isolate, Bacillus haynesii strain SK1, under aerobic, anoxic, and strict anaerobic conditions at 30 °C, 40 °C, and 50 °C. All cultures showed ureolysis and the formation of insoluble precipitates. Fourier transform infrared spectroscopy analysis revealed precipitates comprising CaCO₃ at 30 °C, 40 °C, and 50 °C under aerobic conditions but only at 50 °C under anoxic and strict anaerobic conditions, suggesting efficient MICP at 50 °C. Interestingly, an X-ray diffraction analysis indicated that calcium carbonate crystals that were produced under aerobic conditions were in the form of calcite, while those that were produced under anoxic and strict anaerobic conditions at 50 °C were mostly in the form of vaterite. Thus, we demonstrated ureolysis-driven MICP under high-temperature and O₂-depletion conditions, suggesting the potential of MICP applications in deep-subsurface environments. Full article

This paper presents a study on the ring formation phenomenon in lime kilns using simulation. The research focuses on the chemical recovery cycle integrated into the pulp production process at a pulp mill, with particular emphasis on the calcium cycle within the lime kilns. Lime kilns are critical components, as their unavailability can significantly impact the overall cost-effectiveness of the facility. The calcination of lime sludge occurs in a rotary kiln, where calcium carbonate in the lime sludge is converted into calcium oxide (lime). Under certain conditions, material can progressively accumulate, leading to ring formation and eventual kiln clogging, resulting in operational downtime. To investigate this issue, the authors developed a physics-based model using a finite-dimensional, one-dimensional approach that considers only longitudinal variation. Several approximations were made to maintain a reasonable simulation time without compromising accuracy. Simulations based on real operational data identified fluctuations in fuel flow rate and sulfur content from non-condensable gases as key contributors to ring formation. The results showed that these fluctuations caused instability in the temperature profiles of the solids and gas beds, leading to periods of cooling before the lime sludge reaches the outlet to the coolers. This cooling promotes the recarbonation of lime and, consequently, the formation of rings. The findings highlight that stabilizing fuel flow and managing sulfur content could mitigate ring formation and improve kiln efficiency. The developed model provides a valuable tool for predictive analysis and process optimization, potentially supporting the development of a digital twin to enhance real-time monitoring and operational control. Full article

The pyrolysis process of residues has emerged as a sustainable method for managing organic waste, producing biochars that offer significant benefits for agriculture and the environment. These benefits depend on the properties of the raw biomass and the pyrolysis conditions, such as washing and drying. This study investigated biochar production through slow pyrolysis at 300 °C, using eight biomass types, four being plant residues (PBR)—sugarcane bagasse, filter cake, sawdust, and stranded algae—and four non-plant-based residues (NPBR)—poultry litter, sheep manure, layer chicken manure, and sewage sludge. The physicochemical properties assessed included yield, carbon (C) and nitrogen (N) content, electrical conductivity, pH, macro- and micronutrients, and potentially toxic metals. Pyrolysis generally increased pH and concentrated C, N, phosphorus (P), and other nutrients while reducing electrical conductivity, C/N ratio, potassium (K), and sulfur (S) contents. The increases in the pH of the biochars in relation to the respective biomasses were between 0.3 and 1.9, with the greatest differences observed for the NPBR biochars. Biochars from sugarcane bagasse and sawdust exhibited high C content (74.57–77.67%), highlighting their potential use for C sequestration. Filter cake biochar excelled in P (14.28 g kg⁻¹) and micronutrients, while algae biochar showed elevated N, calcium (Ca), and boron (B) levels. NPBR biochars were rich in N (2.28–3.67%) and P (20.7–43.4 g kg⁻¹), making them ideal fertilizers. Although sewage sludge biochar contained higher levels of potentially toxic metals, these remained within regulatory limits. This research highlights variations in the composition of biochars depending on the characteristics of the original biomass and the pyrolysis process, to contribute to the production of customized biochars for the purposes of their application in the soil. Biochars derived from exclusively plant biomasses showed important aspects related to the recovery of carbon from biomass and can be preferred as biochar used to sequester carbon in the soil. On the other hand, biochars obtained from residues with some animal contributions are more enriched in nutrients and should be directed to the management of soil fertility. Full article

As an industrial waste residue, Electrolytic Manganese Residue (EMR) can greatly promote sludge dewatering and further particle-size optimization can significantly strengthen sludge dewaterability. In this study, the effects of ammonium sulfate, calcium sulphate dihydrate, and manganese carbonate in EMR on sludge dewatering performance were investigated using the response surface optimization method. It was found that the optimized ratio of three components in EMR was 1.0:1.6:2.2 based on capillary suction time (CST), specific resistance of filtration (SRF), and zeta potential of dewatered sludge. The composition ratio of particle-size optimized EMR was modified based on the above optimization, resulting in a significant increase in sludge dewatering performance (CST and SRF reduced by 8.7% and 11.2%, respectively). Compared with those in original sludge, the content of bound extracellular polymeric substances in the conditioned sludge with optimized ratio was drastically reduced while that of soluble extracellular polymeric substances was slightly increased, which was in accordance with the decline of fluorescence intensity. These findings indicated the disintegration of extracellular polymeric substances, the enhancement of hydrophobicity, and dewatering properties of the sludge. In summary, optimized EMR can effectively intensify the dewaterability of sludge, providing a competitive solution for dewatering and further disposal of sludge. Full article

Sewage sludge can be used as an organic amendment as long as it is ensured that there is no risk of environmental contamination or risk to public health. In this study, sewage sludge from two wastewater treatment plants (WWTPs) subjected to two disinfection and stabilization treatments [40% (mass/mass), calcium oxide, and calcium hydroxide] and their respective untreated sewage sludge were used. Three control treatments were also added: conventional farmyard manure (FYM), a nitrogen (N) mineral fertilizer (ammonium nitrate 34.5% N) applied at a rate of 50 kg N ha⁻¹ (N50) (the same rate of all organic amendments), and an unfertilized control (N0), totaling nine treatments. Lettuce (Lactuca sativa L.) was cultivated in pots for two growing cycles. The dry matter yield (DMY) was higher in the N50 treatment (13.5 and 10.6 g plant⁻¹ in the first and second growing cycles, respectively), followed by sewage sludge (10.8 to 12.4 and 8.4 to 8.7 g plant⁻¹), FYM (8.5 and 7.2 g plant⁻¹), and the control (7.7 and 6.0 g plant⁻¹). The DMY was related to the N provided by the different treatments, assessed by the N and nitrate concentrations in tissues, N uptake, and apparent N recovery (ANR). Sewage sludge, due to its high N concentration and low carbon (C)/N ratio, mineralized rapidly, providing a significant amount of N to plants, as well as other nutrients, such as phosphorus (P) and boron (B). FYM, with a higher C/N ratio, provided less N to plants, also due to the short duration of the lettuce growing cycle. Alkalized sewage sludge increased soil pH and calcium (Ca) availability for plants. Fertilizer treatments minimally influenced cationic micronutrients. Heavy metals in the initial sewage sludge were below the threshold values established in international legislation, and the levels in soil and lettuce tissues were generally not higher than those in other treatments. Both of the sewage sludges used in this study showed high fertilizing value and very reactive behavior, making nutrients available much more quickly than FYM. This information is relevant to consider in defining their agricultural use. Full article

This article presents the results of studies on the distribution of rare metals among the products of the alkali sulfate processing of nepheline syenites. In response to the limited reserves of Bayer bauxite in the alumina industrial production region of Kazakhstan, the feasibility of using alternative alumina-containing nonbauxite raw materials was investigated. The most promising nonbauxite raw materials in Kazakhstan are nepheline and kaolinite clays. At present, there is no effective technology for processing nepheline ores. This article describes a proposed complex technology involving nepheline processing with the associated extraction of gallium and vanadium. The technology includes the activation of raw materials, followed by two-stage leaching, where potassium is extracted in the first stage. The sludge and solution obtained from the second stage of the leaching process are utilized for calcium silicate production and two-stage carbonization, respectively. In the first stage, aluminum hydroxide is extracted, and, in the second stage, a concentration of rare metals, such as gallium and vanadium, is obtained. Vanadium is extracted from the solution via crystallization, and gallium is extracted via electrodeposition. Overall, 38.48% of the Ga₂O₃ and 56.12% of the V₂O₅ are recovered from raw nepheline syenite. A technological scheme of the developed technology is presented in this article. Full article

Sewage sludge should primarily find use in agriculture, reducing the quantity directed towards alternative disposal methods like incineration or deposition in municipal landfills. This study evaluated the agronomic value and the risk of soil and plant tissue contamination with heavy metals in sewage sludge obtained from two wastewater treatment plants (WWTP). The experiment was arranged as a 2 × 5 factorial (two sewage sludges, five sanitation treatments), involving lettuce cultivation in pots over two growing cycles. The two sewage sludges were sourced from the WWTPs of Gelfa and Viana do Castelo and underwent five sanitation and stabilization treatments (40% and 20% calcium oxide, 40% and 20% calcium hydroxide, and untreated sewage sludge). The Gelfa sewage sludge, characterized by a higher initial nitrogen (N) concentration, resulted in greater dry-matter yield (DMY) (12.4 and 8.6 g plant⁻¹ for the first and second growing cycles, respectively) compared to that from Viana do Castelo (11.0 and 8.1 g plant⁻¹), with N release likely being a major factor influencing crop productivity. The high N concentration and the low carbon (C)/N ratio of sewage sludge led to rapid mineralization of the organic substrate, which additionally led to a higher release of other important nutrients, such as phosphorus (P) and boron (B), making them available for plant uptake. Alkalizing treatments further stimulated sewage sludge mineralization, increasing soil pH and exchangeable calcium (Ca), thereby enhancing Ca availability for plants, and indicating a preference for use in acidic soils. Cationic micronutrients were minimally affected by the sewage sludge and their treatments. The concentrations of heavy metals in the sewage sludge, soils, and lettuce tissues were all below internationally established threshold limits. This study highlighted the high fertilizing value of these sewage sludges, supplying N, P, and B to plants, while demonstrating a low risk of environmental contamination with heavy metals. Nevertheless, the safe use of sewage sludge by farmers depends on monitoring other risks, such as toxic organic compounds, which were not evaluated in this study. Full article

Pyrolysis is an energy recovery technique with significant potential for managing wastewater treatment plant byproducts. This research aims to investigate the physicochemical and thermal properties of Moroccan sludge, as well as the behavior of its decomposition during pyrolysis at three different heating speeds (5, 10, and 20 K/min). Characterization of the sludge before pyrolysis through ultimate analysis, proximate analysis, FTIR spectroscopy, and XRD revealed that the sludge consists predominantly of organic matter, with a volatile matter rate of 48%, an ash rate of 37%, and a higher heating value (HHV) of 15 MJ/kg. The TGA-DTG curves identified four distinct stages in the sludge decomposition process: drying, decomposition of organic matter, degradation of calcium carbonate, and decomposition of inorganic matter. Using TG-MS analysis, the principal gases identified during pyrolysis were H₂O, H₂, CH₄, CO₂, CO, NO, and SO. The average activation energies (E_a) determined through kinetics models were found to be 413.4 kJ/mol for the Kissinger–Akahira–Sunose (KAS) model, 419.6 kJ/mol for the Flynn–Wall–Ozawa (FWO) model, and 416.3 kJ/mol for the Starink model. The values of E_a and the pre-exponential coefficient (A) obtained through the KAS, FWO, and Starink techniques are consistent with ΔG values ranging between 152 and 155 KJ/mol. The positive ΔS values range from 0.003 to 1.415 kJ/mol.K, indicating the complexity of the sludge response during pyrolysis and the spontaneity of the chemical reaction at high temperatures. The kinetic data obtained serves as a pillar for the development and improvement of sewage sludge pyrolysis systems, reinforcing their role in sustainable energy production. Full article

The results of experiments on manganese pellets based on beneficiated manganese-containing sludge and the melting of ferromanganese alloy with their use are presented. Via beneficiating manganese-containing sludge (16.32% Mn), a concentrate with a manganese content of 35.2% was obtained. The composition of the charge used to prepare manganese pellets is proposed, and the conditions affecting their strength are determined. It was established that manganese is present in the composition of calcined pellets in the form of jacobsite MnFe₂O₄ and hausmannite Mn₃O₄. The formation of a phase of ferrobustamite (Ca_0.79Fe_0.21)SiO₃, a ferrosilico-calcium binder that helps increase the strength of pellets, was found. Ferromanganese alloy was obtained as a result of the melting of calcined manganese pellets in a high-temperature Tamman-type unit. The Fe-Mn-Si alloy corresponds to the DIN 17 564 as-grade FeMn70Si in terms of manganese (63.76%) and silicon (17.21%) contents. The content of limiting impurity elements—carbon and phosphorus—in ferromanganese alloy is within acceptable limits. The structure of Fe-Mn-Si alloy and slag formed during their smelting process were studied. Full article

The possibility of deep radiochemical purification of Li₂CO₃ has been examined in the context of the purification program of the AMoRE collaboration. In this experiment, commercial Li₂CO₃ was converted into LiNO₃. Co-precipitation with inorganic salt-based carriers followed by membrane filtration and sorption using MDM inorganic sorbent methods were tested for the removal of alkaline-earth and transition metals, potassium, magnesium, aluminum, uranium, thorium, and radium. The calcium molybdate-based carrier was the most efficient for removing Th, U, and K. Subsequently, the radium, calcium, and barium contamination was removed with MDM sorbent. After the impurities’ removal, the final Li₂CO₃ product was synthesized with NH₄HCO₃ sludge. The separation factors were derived by means of ICP-MS and HPGe analyses of the initial material and the intermediate and final products. The study showed the optimum conditions of co-precipitation and sorption to reach a high yield and radiopurity of lithium carbonate used for low-radioactive-background experiments. The developed method is an important step toward performing next-generation large-scale (1-ton) neutrino experiments using Li-containing detectors. Full article

In this work, authigenic microbial mineral formation in groundwater near the uranium sludge storage at SC Chepetsky Mechanical Plant (ChMP) (Glazov, Russia) was analysed in field and laboratory experiments using thermodynamic modelling when the microbial community was activated by a mixture of acetate, glucose and whey. It was found that the mineral basis of the barrier consisted of aggregated soil particles with freshly deposited phases of carbonate and sulphide minerals of different degrees of crystallinity. An important factor in the formation of calcium phases is microbial denitrification, which is accompanied by an increase in pH values of the medium. The main factors of uranium immobilisation in the biogeochemical barrier were revealed, including its reduction to insoluble forms of uranium dioxide, adsorption on ferrous and sulphide-ferrous minerals, as well as the formation of phosphate phases through the addition of phosphorus-containing whey and co-precipitation or co-crystallisation in calcite phases. Full article

Biogas represents a source of renewable energy that could provide a replacement for fossil fuels to meet the increasing demand for energy. The upgrading of biogas through the removal of CO₂ to a content of 95–97% of CH₄ is necessary to increase its calorific value. This review focuses on biogas upgrading technologies using wastes or residues that enable the performing of mineral carbonation. In this research, we analyzed a natural biogas or synthetic one with a content of about (40–50%) of carbon dioxide. The chemical absorption is also briefly described in this study, due to its being the first step in innovative absorption and regeneration processes using mineral carbonization. Wastes with high calcium contents, i.e., ashes, steel-making slags, and stabilized wastewater anaerobic sludge, were considered for direct carbonization, taking into account the leaching of particles from carbonated wastes/residues. Moreover, the different types of reactors used for mineral carbonation have been described. The presented technological solutions are easy to use and economical, and some of them also take into account the regeneration of reagents. However, in the context of their direct use in biogas plants, it is necessary to consider the availability of wastes and residues. Full article

Phosphate ore is a non-renewable resource, so finding a replacement is necessary. Municipal sludge has significant recycling potential because of its high phosphorus content and large discharge characteristics. The migration and transformation of phosphorus in municipal sludge treated with different concentrations of HCl were studied using the standards, measurements, and testing phosphorus extraction protocol from two aspects: phosphorus complexation and mineral form. After the hydrothermal carbonization treatment without HCl, the hydrochar retained 99.7% of phosphorus in the sludge, and the organophosphorus percentage was about 30%. In the hydrothermal carbonization treatment with the addition of 0.5–2.5% HCl, the phosphorus content in the hydrochar decreased gradually from 99.5% (46.18 mg/g) to 91.8% (64.17 mg/g) that of the original sludge, and the proportion of non-apatite inorganic phosphorus increased from 34% to 94%. Hydrochloric acid provides a low-pH environment and promotes the dissolution of calcium-related phosphorus precipitates and enhances the dehydration reaction. This study provides technical support for the recovery of phosphorus resources from municipal sludge. Full article

Mine water usually contains heavy metals and other inorganic and organic pollutants that contaminate water bodies. Reverse osmosis (RO) techniques are capable of producing purified water that meets discharge regulations. However, the problem of RO concentrate disposal and utilization is still not solved. The well-known zero liquid discharge (ZLD) process provides total concentrate utilization at the power industries but seems unreasonably expensive for the treatment of large amounts of mine water due to required chemical softening and the evaporation of concentrate. In the present article, a new approach to increase the recovery of reverse osmosis and to avoid high operational costs is demonstrated and discussed. The new technique involves radical RO concentrate flow reduction and withdrawal, together with dewatered sludge. The idea to “hide” concentrate in dewatered sludge is proposed and demonstrated during experiments. The article demonstrates results of the conducted experimental program aimed at reduction of volumes of all liquid wastes produced during mine water treatment using a new approach to concentrate it with a cascade of nanofiltration membranes and to reach a TDS value of 110–120 g per liter. The obtained concentrate is mixed with the wet sludge, which is further dewatered and withdrawn together with the dewatered sludge. Experiments are conducted that demonstrate a reduction in calcium in the concentrate due to deposition of calcium carbonate on the “seed crystals” in the circulation mode. Another distinguishing feature of the new technique is the separation of concentrate into two streams containing high concentrations of monovalent ions (sodium and ammonium chlorides) and divalent ions (calcium, magnesium and copper sulphates). Flow diagrams of the processes are presented to demonstrate the water treatment technique used to produce deionized water and two types of sludges: sludge after clarification and sludge after calcium carbonate deposition. Full article