Recycling Of Sludge Research Articles

Extraction and analysis of microplastics in wastewater sludges of a multi-product pulp and paper mill

Pulp and paper wastewater sludges are waste streams produced in major quantities across the world. The recycling of these organic sludges, for example to soil amendments, is desired in the circular economy but carries the risk of potential pollutants to be also introduced into the environment. Pulp and paper wastewater sludges have been scarcely studied matrices in the microplastic research due to their complex composition. In this study, we optimized an extraction process for microplastics from pulp and paper wastewater sludges, and quantified and characterized microplastics down to 20 μm in primary sludge and biosludge generated at the wastewater treatment plant of a multi-product pulp and paper mill in Finland. The occurrence of microplastics was high in primary sludge, 900–1600 microplastics g-1 dry weight, while the maximum number of detected microplastics in biosludge samples remained at 210 g-1 dry weight. Biosludge samples suffered from larger amounts of remaining solids after the extraction process, thus compromising the detection of smaller microplastics (<100 μm) and increasing the uncertainty related to the interpretation of the results. The most prevalent microplastic shape in all samples was fragment, and the most recurring polymer types were polyethylene and polypropylene, while a polystyrene-based copolymer represented approximately 10% of identified microplastics in primary sludge. The present study advances the development of microplastic analysis of the challenging pulp and paper wastewater sludges and brings novel information to the progressing discussion of their circulation potential.

Recycling of water treatment plant sludge for copper adsorption from aqueous solutions

Recent studies have explored various adsorbent materials that are low-cost, available in quantity, and effective for heavy metal removal, one of them is the Water Treatment Plant (WTP) sludge. The study aimed to investigate the potential of recycling Water Treatment Plant sludge into an adsorbent for Cu (II) removal. The sludge adsorbent was carbonized by using a furnace at 600°C for 2 hours. This study was conducted in batch. The adsorbent effectiveness was analyzed by varying the dosage, contact time, and activation of the sludge adsorbent on Cu (II) removal. The adsorption isotherm was analyzed using the Langmuir and Ferundlich models, and the kinetic study used pseudo-first-order and pseudo-second-order model. The results showed the removal efficiency of Cu (II) for both activated and non-activated sludge adsorbents reached 98.6–99.9%. The addition of dosage did not affect the increase in Cu (II) adsorption capacity. Activation of the adsorbent increased the adsorption capacity of Cu (II) with the equilibrium time at 60–90 min, shorter than the non-activated adsorbent at 90–120 min. The adsorption isotherm model for both adsorbent types fitted well to the Langmuir model, indicating the adsorption process occurs in a single layer on a homogeneous surface. The adsorption kinetics followed pseudo-second-order with a high correlation coefficient. Water treatment sludge, an industrial by-product, has the potential to be an effective and low-cost adsorbent material for Cu removal.

A novel lanthanum-modified polytitanium chloride coagulant: Efficient algae removal and enhanced photocatalytic ability of recycled algal sludge

The removal of harmful cyanobacterial blooms (HCBs) and reuse of the resulting algal sludge are pressing issues in current environmental governance and ecological conservation. Aiming at tackling the above-mentioned challenges, titanium (Ti)-based coagulants are promising candidates. However, most of them suffer from poor stability and weak actual algal removal ability, and recycling of the algal sludge usually produces titanium dioxide (TiO2) with low photocatalytic ability. In this work, a lanthanum (La)-modified polytitanium chloride (La-PTC) coagulant is reported. La in the La-PTC coagulant serves a "kill two birds with one stone" strategy in algae removal and algae sludge reuse. Owing to the introduction of La ions, the La-PTC coagulant exhibits ultra-high stability and excellent algae removal capability with an efficiency of 98.71%, which is 7.25% higher than that of PTC coagulant. Moreover, recycling algae sludge can prepare high catalytic (2.45 times the commercial P25 TiO2) La/C-TiO2, where the presence of La enhances its visible light response range and inhibits electron hole recombination. The strategy of this La modified coagulant can not only achieve efficient removal of HCBs, but also transform the recovered algal sludge into photocatalysts with higher catalytic capacity.

Enhancing nitrogen removal in low C/N wastewater with recycled sludge-derived biochar: A sustainable solution

Denitrification is an important biological process in wastewater treatment plants (WWTPs). However, a low carbon-to-nitrogen (C/N) ratio limits the availability of organic carbon, potentially reducing denitrification efficiency. This study investigates the impact of sludge-derived biochar on the nitrogen removal of activated sludge for low C/N ratio municipal wastewater. Sludge-based biochar was characterized by its physicochemical properties, revealing that biochar prepared at 400 °C exhibited the highest specific surface area and the most favorable surface functional groups for electron transfer. The results from batch tests showed that adding 4 g/L of biochar dosage enhanced denitrification rates and total nitrogen (TN) removal efficiency the most. Sequencing batch reactors (SBRs) experiments further confirmed that biochar dosgae improved the removal efficiencies of COD, NH4+-N, and TN, achieving stable values of 97.2 ± 1.2 %, 99.2 ± 0.6 %, and 83.8 ± 2.4 %, respectively. Metabolic and electrochemical analyses revealed that biochar addition enhanced the activity of denitrification enzymes, increasing the ammonia oxidation rate by 12.9 ± 0.7 %, nitrite oxidation rate by 14.7 ± 1.2 %, nitrate reduction rate by 36.9 ± 1.5 %, and nitrite reduction rate by 16.4 ± 0.8 %. The relative abundance of denitrification functional genes (amoA, nirS, nirK, narG, nosZ) increased, and the activities of the corresponding enzymes (AMO, NXR, NAP, NIR) rose by 23±6 %, 53±5 %, 260±15 %, and 55±7 %, respectively. This increase in enzyme activity suggested enhanced denitrification processes, which was further supported by the 60.1 ± 3.7 % increase in electron transfer system activity (ETSA), indicating that biochar acted as an electron shuttle. This study proposes a potential sustainable approach for sludge recycling and enhanced wastewater nitrogen removal under low C/N conditions.

Recycling of Marble Sludge into High Strength and Anti-Efflorescence Geopolymers Through the Synergy of Graphene Oxide and Hydrophobic SiO2 Fillers

Recycling of Marble Sludge into High Strength and Anti-Efflorescence Geopolymers Through the Synergy of Graphene Oxide and Hydrophobic SiO2 Fillers

Studying the Characteristics of Tank Oil Sludge

Oil sludge is one of the main pollutants generated by the oil industry. Due to serious pollution and increasing oil production, problems arise every year in the effective treatment of oil sludge. The current study examines the composition and physicochemical characteristics of oil sludge, as well as traditional and new methods for processing oil sludge. With the tightening of environmental protection requirements, oil sludge quality reduction, recycling, and harmless treatment technologies will become necessary in the future. The primary task was to determine the composition of tank oil sludge, separate it from mechanical impurities, and study the influence of ultrasonic treatment and subsequent atmospheric distillation on the extract. The separation of the concentrate and the composition of the tank oil sludge, using an extracted mixture of hexane and benzene, are considered. The use of modern SEM methods, elemental analysis, NMR analysis, IR, ultrasound, and GC–mass spectrometry made it possible to characterize the organic part of reservoir oil sludge and its distillation products. First, 300 g of tank oil sludge was preheated and mixed with 300 mL of solvent (hexane:benzene = 1:1). After mixing with the solvent, the result mixture was filtered. Then, it was placed in an ultrasonic bath and exposed to ultrasound at a frequency of 100 kHz for 30 min. After processing, it was extracted in a Soxhlet apparatus at a temperature of 65 °C to isolate the extract. The resulting extract was analyzed on a gas chromatograph with mass detection. The composition of the extract was as follows (in %): hexane—83.99; total hydrocarbon isomers—7.12; n-hydrocarbons—2.52; benzene—6.37%. At a temperature of 85 °C, the benzene yield was 65.85%. It has been established that the fractions obtained through the distillation of oil sludge at temperatures of 65–85 °C have improved dissolving capacity. It has also been shown that the use of these fractions promotes an increase in the content of hydrocarbon isomers by 12–13% in the extract composition.

Recycling of Sewage Sludge: Synthesis and Application of Sludge-Based Activated Carbon in the Efficient Removal of Cadmium (II) and Lead (II) from Wastewater.

The limited supply of drinking water has aroused people's curiosity in recent decades. Adsorption is a popular method for removing hazardous substances from wastewater, especially heavy metals, as it is cheap, highly efficient, and easy to use. In this work, a new sludge-based activated carbon adsorbent (thickened samples SBAC1 and un-thickened samples SBAC2) was developed to remove hazardous metals such as cadmium (Cd+2) and lead (Pb+2) from an aqueous solution. The chemical structure and surface morphology of the produced SBAC1 and SBAC2 were investigated using a range of analytical tools such as CHNS, BET, FT-IR, XRD, XRF, SEM, TEM, N2 adsorption/desorption isothermal, and zeta potential. BET surface areas were examined and SBAC2 was found to have a larger BET surface area (498.386 m2/g) than SBAC1 (336.339 m2/g). While the average pore size was 10-100 nm for SBAC1 and 45-50 nm for SBAC2. SBAC1 and SBAC2 eliminated approximately 99.99% of Cd+2 and Pb+2 out the water under all conditions tested. The results of the adsorption of Cd+2 and Pb+2 were in good agreement with the pseudo-second-order equation (R2 = 1.00). Under the experimental conditions, the Cd+2 and Pb+2 adsorption equilibrium data were effectively linked to the Langmuir and Freundlich equations for SBAC1 and SBAC2, respectively. The regeneration showed a high recyclability for the fabricated SBAC1 and SBAC2 during five consecutive reuse cycles. As a result, the produced SBAC1 and SBAC2 are attractive adsorbents for the elimination of heavy metals from various environmental and industrial wastewater samples.

Hierarchical Approach to the Management of Drinking Water Sludge Generated from Alum-Based Treatment Processes

The management of drinking water treatment plant (DWTP) sludge is challenging for water treatment facilities. Previous studies reported mainly on handling sludge through landfilling, release into water bodies, discharge into wastewater treatment plants, onsite disposal, and incineration methods for the treatment of sludge. The limitations of these sludge-handling methods are well documented. This article focuses on the hierarchical approach as an alternative and comprehensive method for handling DWTP sludge. The core of hierarchical management streamlines the minimization of the generated DWTP sludge; treatment of DWTP sludge to reduce toxicity; changing of the physicochemical form of DWTP sludge; and finally, the reuse, recycling, and recovery of DWTP sludge. The premise is to achieve zero landfilling of DWTP sludge, establish a circular economy, generate job opportunities, and preserve the environment. Thus, this study also proposes two main technologies, which are gravity-based sludge separators for fractionating the sludge and photocatalytic membrane reactors (PMRs) as a technology for the treating and/or recovery of nutrients and minerals from DWTP sludge. Until the chemical deductive or minus approach becomes a reality in water treatment, the use of PMRs and gravity-based sludge separators will enhance the management of DWTP sludge when incorporated into the hierarchical approach.

Sludge Recycling from Non-Lime Purification of Electrolysis Wastewater: Bridge from Contaminant Removal to Waste-Derived NOX SCR Catalyst

Catalysts for the selective catalytic reduction (NOX SCR) of nitrogen oxides can be obtained from sludge in industrial waste treatment, and, due to the complex composition of sludge, NOX SCR shows various SCR efficiencies. In the current work, an SCR catalyst developed from the sludge produced with Fe/C micro-electrolysis Fenton technology (MEF) in wastewater treatment was investigated, taking into account various sludge compositions, Fe/C ratios, and contaminant contents. It was found that, at about 300 °C, the NOX removal rate could reach 100% and there was a wide decomposition temperature zone. The effect of individual components of electroplating sludge, i.e., P, Fe and Ni, on NOX degradation performance of the obtained solids was investigated. It was found that the best effect was achieved when the Fe/P was 8/3 wt%, and variations in the Ni content had a limited effect on the NOX degradation performance. When the Fe/C was 1:2 and the Fe/C/P was 1:2:0.4, the electroplating sludge formed after treatment with Fe/C MEF provided the best NOX removal rate at 100%. Moreover, the characterization results show that the activated carbon was also involved in the catalytic reduction degradation of NOX. An excessive Fe content may cause agglomeration on the catalyst surface and thus affect the catalytic efficiency. The addition of P effectively reduces the catalytic reaction temperature, and the formation of phosphate promotes the generation of adsorbed oxygen, which in turn contributes to improvements in catalytic efficiency. Therefore, our work suggests that controlling the composition in the sludge is an efficient way to modulate SCR catalysis, providing a bridge from contaminant-bearing waste to efficient catalyst.

Efficient elimination of antibiotics and antibiotic resistance genes in hyperthermophilic sludge composting

Composting is widely applied in recycling ever-increasing sewage sludge. However, the insufficient elimination of antibiotics and antibiotic resistance genes (ARGs) in conventional compost fertilizer poses considerable threat to agriculture safety and human health. Here we investigated the efficacy and potential mechanisms in the removal of antibiotics and ARGs from sludge in hyperthermophilic composting (HTC) plant. Our results demonstrated that the HTC product was of high maturity. HTC led to complete elimination of antibiotics and potential pathogens, as well as removal of 98.8 % of ARGs and 88.1 % of mobile genetic elements (MGEs). The enrichment of antibiotic-degrading candidates and related metabolic functions during HTC suggested that biodegradation played a crucial role in antibiotic removal. Redundancy analysis (RDA) and structural equation modelling (SEM) revealed that the reduction of ARGs was attributed to the decline of ARG-associated bacteria, mainly due to the high-temperature selection. These findings highlight the feasibility of HTC in sludge recycling and provide a deeper understanding of its mechanism in simultaneous removal of antibiotics and ARGs.

A Critical Review of Systems for Bioremediation of Tannery Effluent with a Focus on Nitrogenous and Sulfurous Species Removal and Resource Recovery

Tanneries generate copious amounts of potentially toxic sludge and effluent from the processing of skins and hides to leather. The effluent requires remediation before discharge to protect the receiving environment. A range of physicochemical methods are used for pre- and post-treatment, but biological secondary remediation remains the most popular choice for the reduction of the organic and macronutrient fraction of tannery effluent. This review provides an update and critical discussion of biological systems used to remediate tannery effluent. While the conventional activated sludge process and similar technologies are widely used by tanneries, they have inherent problems related to poor sludge settling, low removal efficiencies, and high energy requirements. Treatment wetlands are recommended for the passive polishing step of beamhouse effluent. Hybrid systems that incorporate anoxic and/or anaerobic zones with sludge and/or effluent recycling have been shown to be effective for the removal of organics and nitrogenous species at laboratory scale, and some have been piloted. Novel systems have also been proposed for the removal and recovery of elemental sulfur and/or energy and/or process water in support of a circular economy. Full-scale studies showing successful long-term operation of such systems are now required to convince tanneries to modernize and invest in new infrastructure.

Raw material design, sintering temperature optimization and development mechanism investigation of self-foaming porous bricks with high solid waste addition

In recent years, the contradiction between the huge production of municipal sludge and industrial residue and the shortage of landfill space has driven the exploration of novel effective methods to valorize these solid wastes. In this research, blast furnace slag (BFS), municipal sewage sludge (MSS) and kaolin are combined innovatively as precursor materials to manufacture self-foaming porous bricks, and the sintering behavior of bricks under different BFS doses and sintering temperatures is deeply studied to reveal the development mechanism. The results indicate that the formation of Fe2O3-hematite during sintering leads to a reddish-brown appearance of the bricks, while the generation of CaAl2Si2O8-anorthite with lower melting points helps to enhance the vitrification process. Besides, the increase in BFS dose or sintering temperature has significant impacts on the evolution of the brick physicochemical properties. This occurs because changing the dose of BFS or sintering temperature can obviously regulate the internal morphological characteristics of bricks, such as particle consolidation, pore size and structural compactness. Among them, large-sized pores are considered as the weak areas of mechanical strength, which is also the responsibility for the worst compressive strength of bricks sintered at 1300 °C. Finally, under the optimal sintering conditions of 15 % BFS dose and 1250 °C sintering temperature, the compressive strength, water absorption, apparent porosity, bulk density and linear shrinkage of the resulting brick are 65 MPa, 0.45 %, 2.50 %, 2.34 g/cm3 and 19.56 %, respectively. Overall results demonstrate that using recycled sludge and waste slag in brick manufacturing can produce products with desired performance, providing preferable solutions for solid waste valorization and sustainable brick production.

Effect of MgO addition on the structural evolution, crystallization and properties of self-glazed ceramics sintered from granite sludge

Recycling of granite sludge has both economic and environmental benefits. In this paper, high glossiness self-glazed ceramics were prepared from granite sludge with the addition of TiO2, Ca(OH)2 and MgO by combining two-step sintering and low-temperature crystallization. The effect of MgO addition on the phase evolution, crystallization and properties of the glazed ceramics was studied to reveal its role in the diopside precipitation. With increasing MgO content, the reduced glass viscosity accelerates the dissolution of quartz and anorthite into the liquid glass phase, resulting in a decrease in flexural strength above 1 % MgO. Meanwhile, the addition of MgO increases the non-bridging oxygen to lower the glass transition temperature. The increase in the Al/Si ratio of the glass phase and the mixed alkaline earth effect contribute to an increase in the crystallization temperature. After thermal treatment at 950 °C, the precipitated diopside increases the crystallinity of the glazed glass-ceramic from 6.4 % to 19.3 % at 3 % MgO, resulting in a surface glossiness of 99.7 GU and a flexural strength of 64.1 MPa. High glossiness self-glazed ceramics with an aesthetic appearance could be used in decorative building tiles for scalable utilization of granite sludge.

Influence of Ca(OH)2 modification on the pore structure and properties of porous glass-ceramics stepwise sintered from granite sludge

The utilization of granite sludge offers significant economic and environmental advantages. This study focuses on preparing porous glass-ceramics from Ca(OH)2-modified granite sludge through a two-step sintering process comprising dense sintering and high-temperature foaming, with the addition of 1 % SiC powder as a foaming agent. The impact of foaming temperature and Ca(OH)2 addition on the structure, compressive strength, specific strength, and thermal conductivity of the porous glass-ceramics is examined. Incorporating the Ca(OH)2 modifier reduces the glass's viscosity and effectively eliminates micropores on the pore walls. The former promotes foaming and increases porosity, while the latter increases the specific strength of porous glass-ceramics. Increasing both the foaming temperature and the Ca(OH)2 concentration reduces glass viscosity and promotes mineral dissolution, facilitating the foaming process. However, the specific strength of the porous glass-ceramics initially increases before decreasing due to pore coalescence and excessive mineral dissolution. Theoretical evaluations of compressive strength and thermal conductivity indicate that porous glass-ceramics possess a closed-cell pore structure. Porous glass-ceramic made from granite powder containing 3.5 % Ca(OH)2 and foamed at 1240 °C exhibits an apparent density and porosity of 0.73 g/cm3 and 67.1 %, respectively. The compressive strength and thermal conductivity are 14.2 MPa and 0.422 W/(m·K) respectively, with a peak specific strength of 19.4 kN·m/kg. This innovative process enables the scalable recycling of granite sludge into energy-saving building materials.

A Mini Review on Sewage Sludge and Red Mud Recycling for Thermal Energy Storage

Sewage sludge and red mud, as common industrial waste, have become a research hotspot in the field of achieving carbon peaking and carbon neutrality, reducing carbon emissions, and solving environmental problems. However, their treatment and disposal have always been a difficult problem in the environmental field. Utilizing these two materials for thermal energy storage can not only improve energy utilization efficiency but also further reduce carbon emissions during their treatment process, providing a new approach for sustainable development in the industrial sector. This article summarizes the research progress for the resource recovery of sewage sludge and red mud for direct thermal energy recovery and composite phase change energy storage. After proper treatment, sludge and red mud can be directly used as energy storage materials. In addition, sludge and red mud can be combined with phase change materials to prepare composite materials with an excellent energy storage performance. This composite has broad application prospects in fields such as solar energy utilization and building energy efficiency. However, there are still some challenges and issues in this resource recovery and utilization, such as potential environmental pollution during the treatment process, the long-term stability of energy storage materials, and cost-effectiveness, which require further research and resolution. The purpose of this paper is to evaluate the potential of sewage sludge and red mud as energy storage materials, to explore their feasibility and advantages in practical applications, and to reveal the research progress, technical challenges, and future development directions of these two materials in the field of thermal energy storage.

Enhanced dewaterability of waste activated sludge via peroxymonosulfate activation process initiated by magnetic biochar derived from iron-rich sludge

The reduction of water content (WC) in waste activated sludge (WAS) is crucial for the recycling and environmentally-friendly treatment sludge in wastewater treatment plants. A new process of combined conditioning of iron-rich sludge biochar (Fe-BC) and peroxymonosulfate (PMS) was proposed and verified to enhance the dewaterability of WAS. The WC of sludge cake decreased significantly from 85.76% to 76.29% after Fe-BC/PMS treatment. For sludge extracellular polymeric substances (EPS) in sludge, the content of protein and polysaccharide in both TB-EPS and LB-EPS exhibited a decrease after Fe-BC/PMS treatment, whereas the S-EPS demonstrated an increase. Three-dimensional fluorescence (3D-EEM) showed that the fluorescence regions of protein-like and soluble microorganisms in both LB-EPS and TB-EPS were weakened. Through the experiment of free radical quenching, it has been demonstrated that the SO4•− and •OH as the primary oxidant in the Fe-BC/PMS system, effectively degrade proteinaceous components and humic substances present in sludge. The variation of particle size showed that the damaged EPS appeared reflocculation and achieved deep dehydration with Fe-BC as the skeleton. Consequently, a four-step mechanism was proposed for Fe-BC/PMS process, namely, oxidation cracking-sludge biochar flocculation-skeleton support – Fe2+ and Fe3+ reflocculation, which demonstrated the combined process with superior sludge dewatering effect and application potential.

Comprehensive comparison of integrated fixed-film activated sludge (IFAS) and AAO activated sludge methods: Influence of different operational parameters

Due to limited land availability in municipal wastewater treatment plants, integrated fixed-film activated sludge (IFAS) technology offers significant advantages in improving nitrogen removal performance and treatment capacity. In this study, two systems, IFAS and Anaerobic-Anoxic-Oxic Activated sludge process (AAO), were compared by adjusting parameters such as hydraulic retention time (HRT), nitrifying solution recycle ratio, sludge recycle ratio, and dissolved oxygen (DO). The objective was to investigate pollutant removal capacity and differences in microbial community composition between the two systems. The study showed that, at an HRT of 12 h, the IFAS system exhibited an average increase of 5.76%, 8.85%, and 12.79% in COD, NH4+-N, and TN removal efficiency respectively, compared to the AAO system at an HRT of 16 h. The TP concentration in the IFAS system reached 0.82 mg/L without the use of additives. The IFAS system demonstrated superior effluent results under lower operating conditions of HRT, nitrification solution recycle ratio, and DO. The 16S rDNA analysis revealed higher abundance of denitrification-related associated flora, including Proteobacteria, Bacteroidetes, and Planctomycetota, in the IFAS system compared to the AAO system. Similarities were observed between microorganisms attached to the media and activated sludge in the anaerobic, anoxic, and oxic tanks. q-PCR analysis indicated that the incorporation of filler material in the IFAS system resulted in similar abundance of nitrifying bacteria genes on the biofilm as in the oxic tank. Additionally, denitrifying genes showed higher levels due to aeration scouring and the presence of alternating aerobic-anaerobic environments on the biofilm surface, enhancing nitrogen removal efficiency.

Enhancing the recovery of complex amino acids from excess sludge via low-intensity ultrasound-assisted enzymatic hydrolysis

The recovery of high-value products such as complex amino acids from activated sludge is a crucial alternative for the recycling of excess sludge, although several challenges still need to be addressed, especially in terms of extraction efficiency and product quality. Herein, a promising approach involving low-intensity ultrasound-assisted enzymatic hydrolysis (UEH) was utilized to obtain complex amino acids from sludge protein. Compared with the values obtained for single enzymatic hydrolysis (EH), after a 20-minute pre-treatment at ambient temperature using low-intensity ultrasound (0.15 W/mL), the enzyme activity increased by 28.7 %, and the degree of protein hydrolysis (DH) correspondingly rose by 93.3 %. The application of ultrasound during subsequent EH resulted in a decrease in DH, with the extent of the decrease increasing over time. This suggested that the primary cause was conformational changes of enzymes rather than mass transfer. Moreover, both the Michaelis–Menten model (R2 > 0.99) and protein hydrolysis model (R2 > 0.96) accurately simulated EH and UEH, indicating that UEH exhibits superior enzyme–substrate affinity and a higher rate of protein hydrolysis. Furthermore, after separation and purification, the total content of seven essential amino acids in the dry material exceeded that in traditional feed sources such as soybean meal. Additionally, the safety test and energy consumption analysis demonstrated that UEH has good potential for the extraction of complex amino acids from excess sludge.

Facile Preparation of Magnetic Chitosan Carbon Based on Recycling of Iron Sludge for Sb(III) Removal

In this study, following the concept of “treating waste with waste”, magnetic chitosan carbon (MCC) was developed through the pyrolysis of chitosan/iron sludge (CHS) beads created using an embedding method in a closed environment for antimony removal. The results indicate MCC has a good magnetic recovery rate and that its magnetic saturation strength can reach 33.243 emu/g. The iron proportion and acid resistance of MCC were all better than those of CHS, and at 25 °C, its adsorption saturation capacity improved from 24.956 mg/g to 38.234 mg/g. MCC has a quick adsorption equilibrium time, and in about 20 min, 90% of the final equilibrium capacity can be achieved. The primary mechanism of Sb adsorption by MCC is the formation of an inner sphere complex between Fe-O and Sb, while surface complexation, hydrogen bonding, and interaction also play a function. Thus, MCC, a lower-cost and greener adsorbent for Sb removal, has been made using iron sludge. This enabled it to utilize iron sludge as a resource and served as a reference for the sustainable management of water treatment residuals.

Recycle of soda waste sludge as the limestone material for Portland cement: Chemical composition, physical properties and hydration mechanism

Soda waste sludge (SWS) was discharged from the ammonia-soda process for producing sodium carbonate. It is out of effective treatment method but primarily composed of CaCO3. Limestone material is the necessary raw material for the Portland cement production, accounting for more than 80 wt%. Thus, a Portland cement in this study was produced from the SWS with different Cl- content as the substitute for limestone, and its chemical composition, physical properties, and hydration mechanism was investigated. Results demonstrated that when the Cl- in SWS was reduced to 0.26 wt% through water scrubbing, the chlorine-bearing species such as Ca10Mg0.8[(SiO4)3.4(AlO4)0.6O2Cl], C11A7·CaCl2, and Ca3(SiO4)Cl2 in cement clinkers and the 3CaO·Al2O3·CaCl2·10 H2O and Ca10(SiO4)3(SO4)3Cl2 in its hydration products vanished. And the Portland cement produced from 25.64 wt% SWS meets standard requirements for 52.5-grade cement on the flexural and compressive strengths. Its permeability coefficient was increased from 186.27 ×10−13 m/s to 8.65×10−13 m/s, and the mass loss and compressive strength loss were decreased to 6.53% and 7.33%. Also, the mineral phase composition of cement clinker were the 3CaO·SiO2, 2CaO·SiO2, 3CaO·Al2O3, and 4CaO·Al2O3·Fe2O3, the hydration products were the CSH gels, Ca(OH)2, Al(OH)3, and 3CaO·Al2O3·3CaSO4·32 H2O. This work realizes the application of SWS as the substitute for limestone, which is beneficial to the resource treatment of SWS and the reduction of limestone mining.