Residual Sludge Research Articles

Integrated process for zero discharge of coking wastewater: A hierarchical cycle-based innnovation

The wastewater from coke making is characterized by high toxicity, high concentration of pollutants and complex composition. Therefore, it is difficult to treat using conventional methods such as advanced oxidation and ion exchange processes. In this study, a zero-discharge integrated process (ZDIP) composed of pre-physicochemical – oxic – hydrolytic & denitrification – oxic – post-physicochemical (A/O/H/O/A) biological, pre-processing, membrane and end-processing units was created to treat coking wastewater. The results showed that most of the chemical oxygen demand, sulfide, cyanide and NH4+-N in the coking wastewater were removed in A/O/H/O/A biochemical unit. Hardness, F− and turbidity were further eliminated in the pre-processing unit, while more than 98 % of the effluent was reused in the membrane unit. Finally, zero discharge treatment of residual liquid and sludge was realized in the end-processing unit. The operating cost was about 2.49 USD/m3 and the carbon emissions 9.17 kg CO2-eq/m3 of influent for the entire ZDIP. Theoretically, the ZDIP based on hierarchical cycle drive, which is applicable to handling complex wastewaters, cutting carbon emissions and recycling water, can be taken as an effective wastewater treatment process in the next decade.

Economic Analysis of Thermal–Catalytic Process of Palm Oil (Elaeis guineesensis, Jacq) and Soap Phase Residue from Neutralization Process of Palm Oil (Elaeis guineensis, Jacq)

Palm oil is, from an economic, environmental, and social point of view, a vegetable oil with great potential and the state of Pará-Brazil is Brazil’s great producer. In addition, soap phase residue or palm oil neutralization sludge (PONS), a byproduct of the neutralization step of the chemical refinement of palm oil, is produced, posing a huge problem for waste disposal and management in the production process of refined palm oil (RPO). In this context, this work aims to systematically investigate the economic analysis of the thermal–catalytic process of crude palm oil (CPO) and palm oil neutralization sludge (PONS). The thermocatalytic processes of CPO and PONS carried out at pilot scale and their economic feasibility were analyzed. The yields of biofuels produced by fractional distillation were also presented. The physicochemical properties of CPO and PONS, as well as those of organic liquid products obtained by the thermal–catalytic process of CPO and PONS were taken into account in the economic analysis. In addition, the chemical composition organic liquid products obtained by thermal–catalytic process of CPO and PONS, as well as its distillation fractions (green gasoline, green kerosene, green light diesel and heavy diesel), used as key factors/indicators on the economic analysis. The analysis of the key factors/indicators from the thermocatalytic processes of CPO and PONS showed economic viability for both crude palm oil (Elaeis guineensis, Jacq) and palm oil neutralization sludge. The minimum fuel selling price (MFSP) obtained in this work for the biofuels was 1.59 USD/L using crude palm oil (CPO) and 1.34 USD/L using palm oil neutralization sludge (PONS). The best breakeven point obtained was of 1.24 USD/L considering the PONS. The sensibility analysis demonstrated that the pyrolysis and distillation yields are the most important variables that affect the minimum fuel-selling price (MFSP) in both economic analyses.

Residual sludge catalyzed by hydrolysis of thermophilic bacteria

In order to improve the utilization rate of the surplus sludge, this experiment investigated the efficient hydrolysis of the residual sludge, explored the effect of sludge nitrogen source, analyzed the influence on the content of protein, amino acid, polypeptide and particle size of the sludge hydrolysis index, and the extraction conditions were optimized by response surface analysis. The maximum protein extraction rate of the residual sludge at the reaction pH of 60°C and =7. Here, the particle size of S sludge was gradually reduced, reduced by 1.1% by 500 m-100 um, 7.5% by 30-50 μ m, 5.4% by 10 μ m-30 μ m, and 0-10 μ As m decreases 13% and sludge increased 13% Nt particles become thinner, larger than surface area and more developed pore structure.

Research on residual sludge disposal and resource utilization technology of urban sewage treatment plant

Urban sewage treatment plants play a pivotal role in the process of urban sewage treatment in China, but due to the implementation of the daily urban sewage treatment process will appear a large number of residual sludge, if not timely and properly disposed of, it will affect the surrounding natural environment, and even endanger human health. Therefore, taking effective measures, such as reasonable treatment of sludge, can efficiently convert waste into resources and achieve efficient use of resources. This paper aims to deeply explore the most commonly used sludge treatment technologies, and compare and analyze the advantages and disadvantages of various technologies, in order to provide useful suggestions and references for environmental protection and engineering applications.

Adsorptive Pattern Using Drinking Water Treatment Residual for Organic Effluent Abatement from Aqueous Solutions.

Zeolite (ZSM-12) is a unique material obtained from the drinking water treatment plants' residual "alum sludge", as a result of using aluminum sulphate as a primary coagulant in the plants. Herein, alum sludge (AS) is initially dewatered and subjected for various calcination temperatures 400 °C, 600 °C and 800 °C and the corresponding materials are named as AS400, AS600 and AS800, respectively. Such calcination is provided to attain ZSM-12, which is considered a highly adsorptive material. The material characterization and morphology were investigated using scanning X-ray diffraction (XRD) and electron microscope (SEM) that confirm the presence of ZSM-12 and porosity of such prepared materials. Thereafter, such materials are introduced for phenol remediation from aqueous solution. The experimental data reveal that AS400 had the largest adsorption capacity (275 mg-phenol/g), in comparison to the commercial adsorbent materials during 2 h of isotherm time. Such a result confirms the suitability of alum sludge residue to be a good candidate for environmental remediation. Furthermore, adsorption isotherm models were applied, and the data are well-fitted to the Langmuir isotherm model. In addition, thermodynamic parameters are investigated which verify the physisorption adsorption process and exothermic nature with a spontaneous reaction system.

Characterization and quality analysis of biomass pellets prepared from furfural residue, sawdust, corn stalk and sewage sludge

Searching and exploring for new biomass sources is essential for biofuels production. Furfural residue pellets (FRPs), sawdust pellets (SPs), corn stalk pellets (CSPs) and sewage sludge pellets (SSPs) were produced using single pellets press, their quality was analysed and compared. Proximate and ultimate parameters varied for all pellets depending on their chemical composition. FRPs had the highest relaxed density (1.431 g/cm3) than SPs and CSPs at 130 °C and strength (∼6 MPa) than CSPs and SSPs at 200 °C. Among all pellets, SPs achieved higher strength of 10.38 MPa. Porosity (3.42 v%) and moisture absorption (7.68%) of FRPs were found lower than SPs, CSPs, and SSPs. Compression energy for FRPs (24.15 J/g) and SSPs (18.64 J/g) was found to be lower than SPs and CSPs, making more economic sense and indicating the potential of biomass wastes for co-pelletization with other biomass sources. Higher heating value of FRPs (22.45 MJ/kg), SPs and CSPs (∼20 MJ/kg) were found satisfactory and met the set standards. FRPs had higher volumetric energy density (32.06 kJ/cm3) compared to other pellets. There were no or very less heavy metals contents in FRPs, SPs and CSPs than SSPs. From overall ranking, FRPs were found higher in rank, followed by SPs.

Anaerobic co-digestion of bovine manure and residual sludge from tilapia fish (Oreochromis niloticus) breeding ponds

Tilapia production was 4.2 million tons in 2016, and almost half of the production came from aquaculture. At the same time, organic waste from breeding increases as the demand for tilapia production. An alternative to using such waste is the production of energy and organic fertilizers. The use of a co-substrate can help to achieve the moisture content necessary to feed the digester. The aim of this study was to determine the effect of the anaerobic co-digestion of bovine manure with residual sludge from tilapia fish breeding ponds in the production of sludge. Methane and CO2 production, chemical oxygen demand (COD), total solids (TS), total fixed solids (TFS), total volatile solids (TVS), volatile fatty acids (VFA), total nitrogen (TN), total phosphorus (TP) content, and microbiological parameters (fecal coliforms and salmonella) during composting were determined. The organic fertilizer obtained was evaluated by a germination and seedling growth assay. The results of this study showed that the mixture of bovine manure and residual sludge from tilapia fish breeding ponds (1:1) produced high methane and low CO2 in the composting process compared to the when these raw materials were composted individually. Alfalfa germination and seedling growth were significantly boosted by the application of sludge from the mixture of bovine manure with residual sludge from tilapia fish breeding ponds.

Information-logical model of the influence of the composition of soil structures of the newly created agricultural landscape on the yield and nutritional value of crops

The studies conducted on establishing the impact of introducing various norms of sewage sludge on the yield and nutritional value of agricultural crops when creating an agrolandscape of a reclaimed municipal solid waste landfill were carried out on such crops as triticale, festulolium, awnless brome. The amount of nutrients supplied to the experimental variants depended on the application rate of sewage sludge or soil. No further nutrients were added. The conducted information-logical analysis showed the presence of a direct close relationship between the yield of triticale, festulolium, awnless brome and variants of the field experiment. The share of the influence of the introduction of sewage sludge according to the variants of the experiment on the yield of festulolium was 31.64%. The share of the influence of the introduction of sewage sludge according to the variants of the experiment on the yield of triticale is 54.4%. The share of the influence of the introduction of WWS according to the variants of the experiment on the yield of awnless rump was 77.2%. Based on the result of the information-logical analysis, a model of the influence of the residual sewage sludge on crop yields was compiled.

Recycling of residual sludge from aluminum anodizing in fired clay bricks

The article presents the results of research aimed at assessing the possibility to use the waste sludge produced in the aluminium anodizing process as an additive to ceramic masses used in the manufacture of building bricks. The physicochemical characteristics of the sludge were determined and the influence of adding the waste to the raw material mixture on the physical and mechanical properties of fired construction ceramics with a porous body was tested on a laboratory scale. The required test specimens were formed from plastic ceramic masses containing 9 – 50% of the waste. After firing at temperatures ranging from 900 to 1000 o C, the linear shrinkage, apparent density, open porosity, water absorption and compressive strength of the obtained materials were determined. The results of the conducted research indicate that adding up to 23% of the sludge to the mix allows obtaining materials with physical properties similar to those of commercial products. • Effect of aluminium anodizing sludge addition on main properties of fired clay ceramic was investigated. • An addition of up to 23 wt% of the dried aluminium anodizing sludge to the raw material mixture used in the industrial production of building bricks allows obtaining a material with physical properties similar to those of commercial products.

Isoproterenol loading transesophageal echocardiography in atrial fibrillation.

In patients with sludge or severe spontaneous echo contrast (SEC) in the left atrial appendage (LAA), cases with isoproterenol loading transesophageal echocardiography (ISP-TEE) have been reported to identify the presence of thrombus in the LAA. This study aimed to assess the validity and hemodynamic changes of ISP-TEE in the LAA. We prospectively enrolled patients with atrial fibrillation (AF) who underwent ISP-TEE. The degree of sludge/SEC was categorized as being either absent (grade 0), mild SEC (grade 1), moderate SEC (grade 2), severe SEC or sludge (grade 3). The hemodynamic evaluation was performed by measuring LAA flow velocity, LAA tissue Doppler imaging (LAA-TDI) velocity, and pulmonary vein systolic forward flow velocity (PVS). In total, 35 patients (mean age 71 ± 7years; 71% male) underwent ISP-TEE. Among 35 patients, 30 patients had grade 3 or 2 SEC, 5 patients had grade 1 SEC. After ISP loading, 23 patients (66% of all patients) showed improved sludge/SEC and one patient was diagnosed with thrombus in the LAA. There were 25 patients with grade 1 SEC, or no SEC (classified as Group1), 10 patients had residual sludge or grade 2 to 3 SEC (classified as Group2) after ISP administration. LAA flow, LAA-TDI, and PVS velocities were significantly higher in group 1 than in group 2 after ISP administration. There was no complication during the examination and after 24h and 3months. ISP infusion may be a potential tool to recognize LAA thrombus under the sludge/SEC during TEE in AF.

One-pot synthesis of a magnetic Zn/iron-based sludge/biochar composite for aqueous Cr(VI) adsorption

Using the traditional Chinese medicine residual (TCMR) as biomass, and the iron-based waterworks sludge (IBWS) and Zinc chloride (ZnCl 2 ) as modified materials, this study synthesized IBWS/ZnCl 2 /TCMR-derived biochar composite (Fe-Zn@BC) in one-pot technique for aqueous Cr(VI) adsorption. Batch experiments of Cr(VI) adsorption were carried out with the Fe-Zn@BC as an adsorbent. The pH research revealed that acidic conditions (pH < pHzpc) were in favor of Cr(VI) adsorption, with the highest removal observed at pH 2. The maximum adsorption capacity of Fe-Zn@BC was about 27.04 mg/g at 35 °C. Based on the examination of kinetics, isotherm, the adsorption process by Fe-Zn@BC was consistent with the equation of pseudo-second-order and the Langmuir model, which had a monolayer adsorption nature. Anions have negative effects on Cr(VI) reduction by Fe-Zn@BC, the negative effects order followed Cl − < SO 4 2 − < PO 4 3 − , which were positive correlated with the concentration and the charge of anions. Potential removal mechanism was investigated with various characterization techniques, indicating that the major mechanisms of Cr(VI) adsorption by Fe-Zn@BC were physical and chemical adsorption, including the reaction of Cr(VI) to Cr(III). IBWS was calcined to impart magnetism of composite, and ZnCl 2 generated magnetic zinc ferrite (ZnFe 2 O 4 ) while activating the composite, endowing the composite with enhanced Cr(VI) adsorption capability and stronger magnetism. Therefore, Fe-Zn@BC appears to be a viable material for removing Cr(VI) in wastewater. • A promising material was prepared in one-pot technique for Cr(VI) adsorption. • Synthesis and characterization of a new Zn/iron-based sludge/biochar composite. • A recycle method of Chinese medicine residual and iron-based waterworks sludge (IBWS). • IBWS provided great magnetism for composite through calcining. • The adsorption fitted the pseudo-second-order model and Langmuir isotherm model.

Fabrication of biodegradable chicken feathers into ecofriendly-functionalized biomaterials: characterization and bio-assessment study

This study aims to investigate novel applications for chicken feather waste hydrolysate through a green, sustainable process. Accordingly, an enzymatically degraded chicken feather (EDCFs) product was used as a dual carbon and nitrogen source in the production medium of bacterial cellulose (BC). The yield maximization was attained through applying experimental designs where the optimal level of each significant variable was recorded and the yield rose 2 times. The produced BC was successfully characterized by FT-IR, XRD and SEM. On the other hand, sludge from EDCFs was used as a paper coating agent. The mechanical features of the coated papers were evaluated by bulk densities, maximum load, breaking length, tensile index, Young’s modulus, work to break and coating layer. The results showed a decrease in tensile index and an increase in elongation at break. These indicate more flexibility of the coated paper. The coated paper exhibits higher resistance to water vapor permeability and remarkable oil resistance compared to the uncoated one. Furthermore, the effectiveness of sludge residue in removing heavy metals was evaluated, and the sorption capacities were ordered as Cu ++ > Fe ++ > Cr ++ > Co ++ with high affinity (3.29 mg/g) toward Cu ++ and low (0.42 mg/g) towards Co ++ in the tested metal solution.

A novel multi-components hierarchical porous composite prepared from solid wastes for benzohydroxamic acid degradation

In this study, a novel carbon-wrapped-iron hierarchical porous catalyst (Fe/C-Mn800) was prepared from electrolytic manganese residue (EMR) and sewage sludge (SS), which showed outstanding degradation ability toward benzohydroxamic acid (BHA, nearly 90 % was removed within 60 min) with low metal leaching rate. Mechanism exploration found transition metal ions (Fe and Mn) can serve as electron acceptors and facilitate the generation of persistent free radicals (PFRs). These transition metal ions and PFRs mainly participated in the single-electron pathway via activating PMS to generate a large amount of reactive oxygen species (ROS). While the electron negative graphitic N and CO groups not only improve the electronegatively of catalyst, but also acted as the electron sacrificers to favor the electron transfer and directly oxidized the absorbed BHA through the ternary activated outer-sphere complexes. Eley–Rideal (E-R) and Langmuir–Hinshelwood (L-H) analysis further demonstrated the crucial role of pre-adsorption during the degradation process. This work provided a deep insight into the degradation mechanism of metal/carbon composite and promising opportunity widened the horizon of the high-value utilization of EMR and SS.

Effect of a micronization method on the particle-size distribution and eluted phosphate-ion concentration for methane fermentation residue sludge

Micronized methane fermentation residue sludge can be used as a liquid fertilizer because the micronized solid particles can be directly sprayed. Thus, the objective of this study was to clarify the effect of the micronization method on the particle-size distribution and eluted phosphate-ion concentration of sludge micronized by ultrasonication or ball milling. Although the average particle size in the sludge micronized by ball milling was ~15 µm smaller than that micronized by ultrasonication, many finer particles (<10 µm) were observed in the ultrasonication-micronized sludge. Compared with untreated sludge, the concentration of the eluted phosphate ions of ultrasonication-micronized sludge was almost 15% higher, whereas that of the ball-milled sludge changed insignificantly. These results indicate that the particle sizes in the ball-milled and ultrasonication-micronized sludge were different, resulting in different phosphate ion elution behavior. Thus, the particle size and phosphate ion concentration can be controlled by changing and/or combining micronization techniques and optimizing their operating conditions. Effect of a micronization method on the particle-size distribution and eluted phosphate-ion concentration for methane fermentation residue sludgeAll authorsTakamasa Mori , Yui Komiya & Mitsuyasu Yabehttps://doi.org/10.1080/23311916.2022.2138869Published online:27 October 2022Display full size

Quantitative microbial risk assessment with nasal/oral breathing pattern for S. aureus bioaerosol emission from aeration tanks and residual sludge storage yard in a wastewater treatment plant.

A large number of pathogenic bioaerosols are generated during the treatment process of wastewater treatment plants (WWTPs), and they can pose potential risks to human health. Therefore, this study systematically analyzed the emission characteristics of Staphylococcus aureus bioaerosols released from an inverted umbrella aeration tank, a microporous aeration tank, and a residual sludge storage yard in a WWTP, and quantitatively evaluated the health risks of four kinds of exposed populations with nasal/oral breathing patterns under optimistic and conservative estimations. The results displayed that the bioaerosol concentration in inverted umbrella aeration tank was higher than that in microporous aeration tank and residual sludge storage yard. Aerosolization ratio in residual sludge storage yard was an order of magnitude lower than that in aeration tanks. Sludge workers were at higher health risks than the other three exposed populations. The health risks of nasal breathers (infection risk: 1.62 × 10-5-2.56 × 10-3 pppy; disease burden: 4.24 × 10-8-6.72 × 10-6 DALYs pppy) were 0.61-0.63 times higher than those of oral breathers (infection risk: 9.95 × 10-6-1.59 × 10-3 pppy; disease burden: 2.61 × 10-8-4.18 × 10-6 DALYs pppy). For female field engineers using oral breathing, laboratory technicians, and researchers without personal protective equipment (PPE), infection risk and disease burden had the opposite results, which indicated that satisfying one certain benchmark did not mean absolute safety. In addition, health risks of exposed populations were reduced by an order of magnitude after wearing PPE. This study can provide a reliable theoretical basis for the risk prevention of bioaerosols and supply data support for the strategies of health risk control perspectives for local sewage utilities.

Insight into the synergistic effect and products distribution during co-pyrolysis of phytoremediation residue and municipal sewage sludge through experiment and reaction force field simulation

We co-pyrolyzed municipal sewage sludge (MS) and Sedum Alfredii L. (SA, a heavy metal hyperaccumulator plant) for the first time to solve their disposal issue. Experimental and simulation results show that synergistic effects exist during the co-pyrolysis process. The thermal decomposition mechanism, kinetics, and product distribution of MS and SA at different mixing ratios (1:0, 3:1, 1:1, 1:3, 0:1) were investigated by thermogravimetric analysis and co-pyrolysis experiments. According to thermogravimetric results, the decomposition of all feedstocks can be divided into three stages. FWO method and Master plot method were used to calculate the activation energy and determine the reaction mechanism. When the addition ratio of SA was 75 %, the difference between theoretical and practical activation energies was greatest, indicating that the best synergy could be achieved at this mixing ratio. Co-pyrolysis experiment shows that more bio-oil and gas were produced. The synergistic effect between MS and different fractions of SA was studied using Reaction Force Field simulation, revealing that the free radicals generated by MS and SA advance the MS decomposition time while increasing the decomposition degree of SA. In addition, we built an artificial neural network with a 3 × 21 × 1 structure to predict the degradation process of various mixtures, which exhibits a high agreement with the experimental results. This study can provide a new idea for the disposal of SA and MS, i.e., co-pyrolysis, by solving their disposal issue while obtaining valuable products.

Preparation of Iron Salt-Modified Sludge Biochar and Its Uptake Behavior for Phosphate

Residual sludge is a significant waste resource, and the preparation of biochar achieves sludge disposal. Biochar has a high uptake capacity for phosphate. To prepare a sludge biochar adsorbent for phosphate, sludge was chemically and anaerobically treated in the presence of iron salts and pyrolyzed. We investigated the effects of the pyrolysis temperature and iron salt on the phosphate uptake capacity, finding that the pretreatment of the sludge with iron salts removed intrinsic phosphate, thus improving the uptake ability. The optimal adsorbent, denoted SB-B-Fe, was prepared by pyrolysis at 700 °C and subsequently modified with a 20 g/L iron-containing solution, yielding a phosphate uptake capacity of 0.5 mg/g. Further, the performance of SB-B-Fe remains high at pH 5–9 and is less affected by interfering anions. The sorption kinetics are consistent with the pseudo-second-order kinetic model, suggesting uptake by chemisorption, and the Langmuir model has a saturation capacity of 0.85 mg/g for uptake and prefers monolayer molecular uptake. The characterization showed that the adsorbent surface provided many uptake sites for phosphate and a high specific surface area. We hope that these findings will encourage the development of other value-added waste-based materials for environmental remediation.

Energetic, bio-oil, biochar, and ash performances of co-pyrolysis-gasification of textile dyeing sludge and Chinese medicine residues in response to K2CO3, atmosphere type, blend ratio, and temperature

Hazardous waste stream needs to be managed so as not to exceed stock- and rate-limited properties of its recipient ecosystems. The co-pyrolysis of Chinese medicine residue (CMR) and textile dyeing sludge (TDS) and its bio-oil, biochar, and ash quality and quantity were characterized as a function of the immersion of K2CO3, atmosphere type, blend ratio, and temperature. Compared to the mono-pyrolysis of TDS, its co-pyrolysis performance with CMR (the comprehensive performance index (CPI)) significantly improved by 33.9% in the N2 atmosphere and 33.2% in the CO2 atmosphere. The impregnation catalyzed the co-pyrolysis at 370°C, reduced its activation energy by 77.3 kJ/mol in the N2 atmosphere and 134.6 kJ/mol in the CO2 atmosphere, and enriched the degree of coke gasification by 44.25% in the CO2 atmosphere. The impregnation increased the decomposition rate of the co-pyrolysis by weakening the bond energy of fatty side chains and bridge bonds, its catalytic and secondary products, and its bio-oil yield by 66.19%. Its bio-oils mainly contained olefins, aromatic structural substances, and alcohols. The immersion of K2CO3 improved the aromaticity of the co-pyrolytic biochars and reduced the contact between K and Si which made it convenient for Mg to react with SiO2 to form magnesium-silicate. The co-pyrolytic biochar surfaces mainly included -OH, -CH2, C=C, and Si-O-Si. The main phases in the co-pyrolytic ash included Ca5(PO4)3(OH), Al2O3, and magnesium-silicate.

Vitrification of petrochemical sludge for rapid, facile, and sustainable fixation of heavy metals

Highly effective re-utilization of hazardous petrochemical wastes plays important roles in the fields of energy science, environmental remediation, and chemical engineering. To overcome the problems caused by high temperature and long-term molten ablation to the refractory material in the furnace during the vitrification of petrochemical residual sludge, here we present a facile strategy to promote the quick vitrification of petrochemical residual sludge through the temperature-stage disposal of raw sludge, followed by the addition of other doping materials such as SiO2, B2O3, and CaO to form binary SiO2/B2O3- and trinary SiO2/B2O3/CaO-doped slag materials. The obtained results indicate that the sintered slag exhibited quicker vitrification (15 min) against that of the raw sludge (more than 110 min). In addition, the slag reveals higher fixation efficiency towards every heavy metal than sludge, and it is found that the slag exhibited more than 80% enhancement towards the fixation of Zn and As than raw sludge. Based on the obtained results, we propose potential mechanisms on the vitrification and metal fixation of petrochemical sludge and slag. The sustainability of the temperature-stage disposal of sludge is further evaluated using the Sustainability Footprint method (an evaluation method based on sustainability). It is expected that the methods and findings shown in this work are helpful for readers to develop facile techniques to promote the re-utilization of hazardous wastes in the fields of materials science, chemical engineering, as well as energy and environmental science.

Removal and recovery of uranium (VI) from aqueous solutions by residual sludge and its biochars.

The removal and recovery of uranium (VI) from water solutions are critical for energy and environmental security. In this study, hydrochar at 100, 150, and 190°C (HC100, HC150, and HC190) and pyrochar at 250°C (BC250) were prepared from residual sludge (RS). The uranium (VI) adsorption behavior, recovery, and heavy metal risk of RS and its biochars were assessed. The sorption distribution coefficient of RS was higher than those of its biochars within the tested concentration range. The maximum adsorption capacity of uranium (VI) by HC190 was 121.26mg/g at acidic pH (pH 4.5), which was higher than those of other tested biochars, previously reported unmodified biochars, and activated carbon. The zeta potential, FTIR, and XPS results implied that the adsorption of uranium (VI) by RS and its biochars was regulated by electrostatic attraction and the complexation with oxygen- and phosphorus-containing functional groups. Besides, partial reduction of uranium (VI) into uranium (IV) happened during the process of adsorption. More than 86% of the adsorbed uranium (VI) was recovered by 0.01M hydrochloric acid and 100% by 0.01M sodium carbonate. The leaching amount of heavy metals was greatly reduced after the sludge was converted to biochar, indicating that hydrothermal carbonization and pyrolysis can promote the stabilization of heavy metals. This work demonstrates that RS and its biochars can be implemented as low-cost, environment-friendly, and high-efficient materials for the purification of uranium (VI)-containing solutions by means of adsorption and desorption.