Sludge-derived Carbon Research Articles

Waste to functions: Construction of a novel solar-thermal conversion material based on sludge-derived carbon dots via Ca-in-situ-functionalization for efficient solar-driven water evaporation

Solar interface water evaporator (SIWE) based on waste-derived carbon dots (CDs) are highly promising for large-scale production applications in the future, due to their low-cost, eco-friendly, and tunable structure and properties. However, there are still obstacles, including limited performance, blind selection of waste materials, and unknown underlying mechanisms between waste properties and the physicochemical properties of derived CDs. In this study, a novel CDs-based wooden SIWE derived from paper mill sludge (PMS) was constructed (called ESCDs-wood). Under 1 sun, ESCDs rapidly heated up from 15.6 °C to 53.5 °C and reached stability within 10 mins. The solar-thermal conversion efficiency of ESCDs was as high as 137.58 %, and the ESCDs-wood achieved a high evaporation rate of 2.94 kg m-2h−1. Moreover, the ESCDs-wood cost about $9 to complete 1 m2 evaporation. Meanwhile, the ESCDs-wood exhibited long-term stability, after 20 cycles, its solar-thermal conversion efficiency and water evaporation rate remained at 84.21 % and 85.03 % of the initial test, respectively. Moreover, the Ca-doping was found to be a key factor in effectively enhancing the solar-thermal conversion and the thermal stability of ESCDs, and the exact role of Ca-doping on the solar-thermal conversion performance enhancement of CDs was validated and revealed. Therefore, this study not only constructed a cost-effectiveness, high performance, sustainability, chemical-free, and eco-friendly SIWE, but also innovatively proposed the functionalization mechanism of Ca-doping for CDs and thus provided a new sight for the targeted regulation and design of CDs.

A comparison of hydrothermal carbonization versus pyrolysis-activation for sludge-derived carbon materials on physiochemical properties and electrochemical performance

Sludge-derived carbons were prepared by hydrothermal carbonization and pyrolysis-activation. In this work, the physiochemical properties and electrochemical performance of these carbons were compared in detail. The structure of pyrochar (PC) has been fully developed that layered porous skeleton was formed during activation process. Thus, obtained the pyrolysis-activated carbon (PAC) had excellent specific surface area (463.2 m2/g) and pore volume (0.36 m3/g), which were higher than these of hydrothermal carbonization-activated carbon (HCAC-300) (364.1 m2/g, 0.18 m3/g). Due to the high nitrogen content of sludge, there were abundant N functional groups (N-5, N-6, N-Q) on the surface of PAC and HCAC. The self-doping of nitrogen was beneficial for improving the carrier concentration and charge transport capacity of carbons, and forming the pseudocapacitance via the redox reaction. Owing to the remarkable physiochemical properties, PAC exhibited highest specific capacitance of 114.7 F/g at 1 A/g, which led to a large amount of charge storage and rapid diffusion of electrons/ions. However, hydrothermal carbonization performed a high economic advantage in disposing the high-humidity feedstock such as sludge. Therefore, the exploration on improving the pore structure in hydrothermal carbonization process thus obtaining high performance carbon material would be of significance and of prospects.

Iron containing sludge-derived carbon towards efficient peroxymonosulfate activation: Active site synergy, performance and alternation mechanism

Converting industrial sludge into catalytic materials for water purification is a promising approach to simultaneously realize effective disposal of sludge and resource of water. However, manipulating the high efficiency remains a huge challenge due to the difficulty in the active sites control of the sludge. Herein, we proposed a constitutive modulation strategy by the combination of hydrothermal and pyrolysis (HTP) for the fabrication of defects-assistant Fe containing sludge-derived carbon catalysts on upgrading performance in peroxymonosulfate (PMS) activation for pollutant degradation. Adjustable defects on dyeing sludge-derived carbon catalysts (DSCC) were achieved by introducing oxygen or nitrogen functional precursors (hydroquinone or p-phenylenediamine) during hydrothermal processes and by further pyrolysis, where O was detrimental while N was beneficial to defect generation. Compared to the DSCC with less defects (DHSC-O), the defect-rich sample (DHSC-2N) exhibited superior catalytic performance of PMS activation for bisphenol A (BPA) elimination (k = 0.45 min−1, 2.52 times of DHSC-O), as well as 81.4% total organic carbon (TOC) removal. Meanwhile, the degradation capacity was verified in wide pH range (2.1–8.1) and various aqueous matrices, reflecting the excellent adaptability and anti-interference performance. Furthermore, the continuous-flow experiments on industrial wastewater showed synchronous BPA and chemical oxygen demand (COD) removal, implying great potential for practical application. Solid electron paramagnetic resonance (EPR) and 57Fe Mösssbauer spectra analysis indicated that the defects acted as secondary active sites for Fe sites, which were beneficial to accelerating the electron transfer process. The only Fe active sites preferred the radical pathway. The controllable reaction tendency provides possibilities for the on-demand design of sludge-based catalysts to meet the requirements of practical wastewater treatment under Fenton-like reaction.

Novel hydrophobic hierarchical porous carbon from sewage sludge for the efficient capture of gaseous iodine

Finding an inexpensive and efficient porous adsorbent to capture the gaseous radioiodine generated during spent fuel reprocessing has been challenging. Herein, we present a design philosophy for waste control to develop porous carbon for gaseous iodine capture from sewage sludge waste. Among them, the novel in situ etching of polytetrafluoroethylene was employed to improve pore accessibility. The hazards of the conventional preparation of sludge-derived carbon using highly corrosive NaOH and HF solutions were overcome. Polytetrafluoroethylene etched porous carbon with large specific surface area (1103 m2/g), interconnected hierarchical porous structure, and excellent hydrophobicity (water contact angle 126.52°), providing efficient adsorption of gaseous iodine in hot (30–150 °C) and humid (50–96% relative humidity [RH]) environments. The iodine adsorption of hierarchical porous carbon was tested under static and dynamic conditions, and high records have been achieved. Notably, due to the structural advantage of hydrophobicity, a considerable dynamic adsorption capacity (1746.77 mg/g) was also maintained in a mixed iodine gas stream containing water vapor in a humid (50% RH) hot (75 °C) condition. This study is the first to use an in situ etching strategy for polytetrafluoroethylene, which opens a new avenue for converting sludge waste into low-cost porous carbon and provides an attractive option for capturing iodine in hot and humid environments.

Sludge-derived hierarchically porous carbon electrode prepared via CaCO3-assisted dual crosslinking for enhanced phosphate electrosorption

Electrosorption is considered a promising technology to remove charged pollutants in an efficient and green way, wherein the electrode materials are crucial for achieving its high performance. In this study, a Zr-containing hierarchically porous carbon electrode (ZHPC-1-Ca) tailored for phosphate removal was synthesized based on alginate-like exopolysaccharides (ALE), a biomass extract of excess sludge. The gel-forming ability of ALE provided a basis for obtaining a conductive carbon matrix with well-dispersed metal active sites, and the pore structure of ALE-derived electrodes was simply regulated via a dual-crosslinking strategy. In the synthesis, CaCO3 acted as both the hard template and the crosslinker, while Zr facilitated pore formation during the secondary crosslinking process. ZHPC-1-Ca exhibited a maximum electrosorption capacity of 12.40 mg g−1 at 1.2 V, with a low energy consumption of 3.166 kWh kg−1-P. The electrosorption behavior was well fitted with the pseudo-first-order kinetics and the Langmuir isotherm model. Moreover, ZHPC-1-Ca maintained stable electrosorption performance under pH 4–10 and during twenty capture-release cycles (85.2%). The electrosorption mechanisms were primarily elucidated as electrostatic attraction, ligand exchange, and Lewis acid-base interaction, contributing to the enhanced and selective phosphate removal. This study achieves a simple and controllable synthesis of hierarchically porous carbon electrodes using sludge biopolymers, which extends the application of sludge-derived carbon in phosphate electrosorption.

Carbon source recovery from waste sludge reduces greenhouse gas emissions in a pilot-scale industrial wastewater treatment plant.

Carbon cycle regulation and greenhouse gas (GHG) emission abatement within wastewater treatment plants (WWTPs) can theoretically improve sustainability. Currently, however, large amounts of external carbon sources used for deep nitrogen removal and waste sludge disposal aggravate the carbon footprint of most WWTPs. In this pilot-scale study, considerable carbon was preliminarily recovered from primary sludge (PS) through short-term (five days) acidogenic fermentation and subsequently utilized on-site for denitrification in a wool processing industrial WWTP. The recovered sludge-derived carbon sources were excellent electron donors that could be used as additional carbon supplements for commercial glucose to enhance denitrification. Additionally, improvements in carbon and nitrogen flow further contributed to GHG emission abatement. Overall, a 9.1% reduction in sludge volatile solids was achieved from carbon recovery, which offset 57.4% of external carbon sources, and the indirect GHG emissions of the target industrial WWTP were reduced by 8.05%. This study demonstrates that optimizing the allocation of carbon mass flow within a WWTP has numerous benefits.

Study on amino-directed modification of oil sludge-derived carbon and its adsorption behavior of bisphenol A in water

In order to remove bisphenol A (BPA) in wastewater, this paper reported an amino-functionalized oily sludge-derived carbon (GP-H-OSC) obtained by grafting amino groups using oily sludge as a precursor, which could quickly adsorb BPA in the wastewater. The adsorption results showed that the grafting modification method was more likely to form effective adsorption sites on the surface than the impregnation modification. FT-IR and Boehm titration results indicated that the oxidation modification strategy was beneficial in generating more carboxyl groups on the surface of the oily sludge-derived carbon, which could provide intermediate connection groups for the subsequent grafting. The SEM and BET results revealed that the polyethyleneimine (PEI) would form a dense mesoporous structure on the surface during the grafting process, which was conducive to the transport of pollutants. The adsorption process of BPA by GP-H-OSC conformed to the pseudo-second-order kinetic model and the Langmuir isotherm model. The maximum extent of BPA adsorption was 393.2 mg/g based on the Langmuir isotherm model. Based on the analysis of FT-IR and XPS, GP-H-OSC mainly trapped BPA in water through the formation of hydrogen bonds between the functional amino groups on the surface and the hydroxyl groups on BPA. Moreover, primary amines were more likely to form hydrogen bonds with hydroxyl groups on BPA than imines. The removal rate of GP-H-OSC for low concentration BPA wastewater could reach 95% within 1 h, and it still had strong adsorption performance after recycling experiments. In summary, it was feasible to graft PEI on the surface of sludge-derived carbon, and the obtained amino-functionalized carbon material could adsorb BPA quickly and efficiently, showing great potential in practical wastewater treatment.

Municipal sludge-derived carbon dots-decorated, N-doped hierarchical biocarbon for the electrochemical reduction of carbon dioxide

Uncontrolled emission of carbon dioxide (CO2) from various industries, which poses a severe threat to the environment and induces climate change, CO2 electroreduction is an advanced technology for converting waste CO2 and closing anthropogenic carbon cycle. However, developing novel, affordable and high-performance electrocatalysts for converting CO2 to value-added hydrocarbons remains highly challenging. Herein, a carbon dots-decorated, N-doped hierarchical biocarbon material is developed from municipal sludge, which can work as an effective and robust carbocatalyst for the electrochemical reduction of CO2. More importantly, such hierarchical biocarbon catalyzes the electrochemical conversion of CO2 to value-added organic products, including methane, methanol and ethanol, with excellent stability and total Faraday efficiency of 90.14% at about -0.71 V vs. RHE. Reasons for the carbocatalyst electroactivity toward efficient and selective production of ethanol is proposed to be the carbon dots and the doped N sites (especially pyridinic-N and pyrrolic-N), which is also validated by density functional theory calculations (DFT). A possible route for the electrochemical reduction of CO2 is also unraveled. This study is a significant step forward to the exploitation of biomass wastes for harvesting greenhouse gasses and electrochemical energy conversion.

Pulp mill sludge-derived carbon activated with an alternative source of chemicals and its application in wastewater treatment – An approach for byproducts valorization

The purpose of this study was to investigate pulp mill by-products valorization through activated carbon (AC) production and its application in wastewater treatment. Bio-sludge is a known promising precursor for AC production. The mill's chemical recovery stage generates an effluent (electrostatic precipitator ash leachate - EPAL) with high levels of potassium and sodium, which motivate studies regarding its viability as a chemical source for carbon activation. Bio-sludge and EPAL are problematic by-products and this research line would allow their return to the productive chain, as an adsorbent for the wastewater treatment. Two carbonization heating rates (3.5, 15 °C/min), three activation agents (NaOH, KOH, EPAL) and two activator:bio-sludge ratios (1:1, 2:1) were used for AC production. The best ACs in terms of surface area were those produced at 3.5 °C/min, with KOH or EPAL in 2:1 proportion. ACs produced under these conditions and commercial activated carbon (CAC) were used in adsorption tests with industrial wastewater. For color removal, KOH-activated carbon presented the greatest efficiency (80.45 %), followed by CAC (76.74 %) and EPAL-activated carbon (70.13 %). For COD removal, EPAL-activated carbon presented greater efficiency (53.49 %), followed by CAC (40.84 %) and KOH-activated carbon (36.86 %). Freundlich's model best described the experimental adsorption data. The KOH results were expected to be satisfactory, since KOH is proven to be effective for carbon activation. The EPAL-activated carbon results were remarkable, especially for COD removal, showing that EPAL can be used as an activator and that the by-products have potential for valorization according to the circular economy principles.

Direct Z-scheme SiNWs@Co3O4 photocathode with a cocatalyst of sludge-derived carbon quantum dots for efficient photoelectrochemical hydrogen production

Solar driven photoelectrochemical (PEC) hydrogen production has attracted considerable attention, but the design of highly efficient, robust and low-cost photocathode still remains a significant challenge. Herein, we report a novel SiNWs@Co3O4Z-scheme heterojunction photocathode with carbon quantum dots eco-friendly derived from sludge (SCQDs) as the co-catalyst. The photocathode not only leads to effective separation of electron–hole pair, lower transmission resistance, and longer lifetime of charge carriers, but also elevates the stability by preventing direct contact between the SiNWs and the electrolyte as well as the self-oxidation. Simultaneously, the excellent electron transport properties of the SCQDs further improved the PEC performance. Correspondingly, a maximum current density of 14.88 mA·cm−2 was obtained at −0.67 V with the applied bias photon-to-current efficiency (ABPE) achieving 8.4% under visible light irradiations at pH = 7. This work provides a promising scheme for Si-based photocathodes for PEC hydrogen production with a high performance, reliable stability, and low-cost.

The behavior of surface acidity on photo-Fenton degradation of ciprofloxacin over sludge derived carbon: Performance and mechanism

Sludge derived carbon (SC) has been widely used in advanced oxidation processes as an effective and economic catalyst. In this study, we applied surface modified SC for the first time to catalyze the heterogeneous photo-Fenton process with ciprofloxacin, a highly concerned emerging contaminant, as a model substance. H2SO4 was used to acidify the SCs under varying acid dosages, temperatures, and reaction time lengths. The surface acidity of SCs was quantitatively characterized with NH3-TPD. A strong correlation between the surface acidity and the catalytic activity was clearly demonstrated. The highest catalytic activity was obtained with SC whose acidity was 0.149 mmol·g−1 after being modified with 6 mol·L−1 H2SO4 at −20 ℃ for 24 h. In addition, XRD, XRF, BET, XPS, and HRTEM were also used to characterize the obtained SC. ·OH radicals were found to be the main reactive species by EPR. Ten transformation products were identified by GC–MS, based on which three possible reaction pathways were proposed.

Dissolved organic matter byproducts from combined low-level alkaline and mechanical treatment of sludge: species, and their bioavailability.

Low-level alkalinity (pH 9-10) coupled with ultrasonic or mechanical cutting with different energy input for obtaining carbon sources were tested for sludge pretreatment process before anaerobic sludge digestion. The differences between the primary sludge (PS) and waste activated sludge (WAS)-derived dissolved organic matter (DOM) species were evaluated for their bioavailability and affinity (in the form of amino acids) to the bio-nutrient removal (BNR) biomass. Soluble microbial by-product-like substances as the predominant DOM components in the raw PS and WAS increased by 23 and 22%, respectively, after low-level alkaline treatment (pH 9-10) and ultrasonication. In addition, the protein components were degraded further as free amino acids (FAAs). The sludge-derived aspartate, glutamate, followed by arginine were the most commonly used FAAs by the BNR biomass. The pattern of recovering this special sludge-derived carbon source to enhance P removal and recovery in the BNR process is depicted.

Sewage sludge-derived Fe- and N-containing porous carbon as efficient support for Pt catalyst with superior activity towards methanol electrooxidation

In this work, a facile Fe- and N-containing porous carbon derived from sewage sludge was prepared and served as the support of Pt nanoparticles for the electrooxidation of methanol. Both the sludge-derived carbon (denoted as SC) and the resultant Pt/SC catalyst was physically characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The electrocatalytic performance for methanol oxidation reaction (MOR) of the Pt/SC was examined by cyclic voltammetry (CV) and chronoamperometric method. The results showed that the Pt/SC possessed slightly larger Pt particle size (5.5 nm) and lower electrochemical active surface area (ECA) compared to common Pt/C catalyst. However, the mass activity of Pt/SC for MOR was up to 201 mA mg−1, which was much higher than that of Pt/C (93 mA mg−1), indicating the synergistic effect of the sewage sludge-derived carbon with Fe and N species on methanol electrooxidation. Furthermore, Pt/SC showed enhanced durability towards MOR compared to common Pt/C, implying its potential for using in direct methanol fuel cell (DMFC) for energy conversion, which also demonstrated a promising solution for the utilization of sewage sludge resources.

Phosphate recovery from wastewater using sludge-derived carbon as uranium decontaminant

Phosphate recovery from wastewater using sludge-derived carbon as uranium decontaminant

Hydrothermal route-enabled synthesis of sludge-derived carbon with oxygen functional groups for bisphenol A degradation through activation of peroxymonosulfate

A considerable amount of sewage sludge (SS) is generated from wastewater treatment process, which is hazardous to the environment and in urge to be disposed. In this study, for the first time, we prepared carbocatalyst with abundant surface oxygen functional groups using the hazardous waste of SS as precursor via a facile hydrothermal coupled pyrolysis process. The hydrothermal treatment was found to be crucial for enhancing the oxygen content of sludge carbon (SC), most of which existed as ketonic groups. Catalytic performances of the developed SCs were examined by activating peroxymonosulfate (PMS) to degrade bisphenol A (BPA). Sample with more ketonic group performed better for BPA degradation. Under optimal reaction conditions, 100 % of BPA and 69.53 % of TOC could be removed in 20 min. Singlet oxygen (1O2) was suggested to be the main reactive oxygen species for degrading BPA and a BPA degradation pathway was proposed. The BPA solution showed decreased bio-toxicity after the oxidation process according to the acute ecotoxicity test. This study demonstrated the importance of surface functional groups on carbocatalyst for advanced oxidation process, which could be induced by a facile hydrothermal treatment. The feasibility of utilizing hazardous SS for advanced carbocatalyst fabrication was also revealed.

Determination and toxicity evaluation of the generated byproducts from sulfamethazine degradation during catalytic oxidation process

Sulfamethazine (SMZ), a kind of sulfonamide antibiotics, can exist for a long periods of time and has been widely detected in the environment, which could pose a potential health threat to human beings. In this study, sludge-derived carbon (SC) catalyst was modified and applied to degrade SMZ during catalytic oxidation process. Degradation products and possible transformation pathways were investigated based on data of GC–MS. The toxicity evolution of SMZ degradation after catalytic oxidation process was tested with zebrafish and microbial degradation respirometer. As a consequence, SC modified with nitric acid (SCHNO3) exhibited highly catalytic efficiency reached 92.2% SMZ conversion and 75.2% total organic carbon (TOC) removal rate after 480 min. Ten kinds of possible products were identified by GC–MS during degradation process of SMZ, indicating two possible pathways. No pronounced malformation was observed in the toxicity experiments with zebrafish until 120 h post fertilization (hpf). However, further analysis showed that zebrafish incubated with SMZ solution had higher mortality, lower hatching rate, slower spontaneous movement and shorter body length, compared with the group used normal nutrient solution, while the water after treatment had lower toxicity effects on zebrafish. The toxicity experiments with microbial degradation respirometer showed that SMZ solution had lower value of oxygen uptake, which indicated that SMZ solution had higher values of toxicity and inhibition of pharmaceutical compounds. This study provides a catalyst with low cost and high catalytic efficiency for degradation process of SMZ and gives a deeper insight into the ecotoxicity of treated water.

Oxytetracycline degradation and toxicity evolution by catalytic oxidation process over sludge derived carbon

The degradation behavior of oxytetracycline (OTC) in aqueous solution using sludge derived carbon (SC) was investigated in this paper. SC treated with different kinds of acids were characterized by BET and thermogravimetric analysis. The results showed that SC-H2SO4 exhibited higher catalytic activity than SC-HCl and SC. The maximum removal of OTC and total organic carbon (TOC) after catalytic oxidation process at 60 °C was 92.6% and 70.2%, respectively. The safety of antibiotics after advanced oxidation processes (AOPs) has attracted much attention due to the possibility of toxicity increasing. Seven intermediate products were identified by GC–MS and four pathways were proposed. Furthermore, the toxicity of OTC degradation was investigated by zebrafish embryos for the first time. Zebrafish incubated with OTC solution (TE2) had haemagglutination, pericardial edema and showed significant changes in heartbeat, body length, and roaming frequency compared with the normal nutrient solution (TE1). Moreover, all zebrafish embryos had condensation phenomenon and did not hatch out in the treated OTC solution (TE3). In contrast, the zebrafish could hatch out without abnormality cultured with the treated OTC solution adjusted to the neutral pH (TE4). Results indicated that the treated OTC solution after catalytic oxidation process should be adjusted to the neutral pH to reduce the toxicity to the ecology.

Preliminary investigation of the degradation mechanism of o, m and p-cresol using sludge-derived carbon nanosheets by catalytic oxidation based on quantum chemistry

Advanced oxidation technology is widely used to oxidize organic compounds in the liquid phase by OH conventionally. Here, we prepared a sludge-derived carbon nanosheets, which was applied in the catalytic wet air oxidation (CWAO), catalytic wet peroxide oxidation (CWPO) and catalytic wet ozone oxidation (CWOO) systems. Because of its abundant oxygen-containing functional groups, the catalytic activity of nanosheets was much higher than some conventional catalysts. It was found that the first-order reaction model did not have similar characteristics as expected. Combining with molecular descriptors calculated by the DFT method and PLS analysis, we try to explain this phenomenon for the first time and proposed possible mechanisms for the three advanced oxidation technologies.

Heterogeneous fenton-like degradation of ofloxacin over sludge derived carbon as catalysts: Mechanism and performance

In this study, heterogeneous Fenton-like degradation of ofloxacin (OFX) was investigated by sludge derived carbon (SC). The effects of SC catalyst, temperature and pH on the efficiency of ofloxacin degradation were investigated. SC treated with sulfuric acid (SC-H2SO4) performed high catalytic activity, indicating that sulfate group produced low pH of the surface and was beneficial for heterogeneous Fenton-like degradation. The removal of ofloxacin and TOC was 91.5% and 62.3%, respectively, after 180 min adsorption and 540 min oxidation, at pH 6 and a dosage of 138 mg L−1 H2O2. It was found that OFX conversion increased with the decrease of pH and OFX was degraded under the wide range of pH (3–6) by SC-H2SO4. These promising results clearly demonstrate the potential of the heterogeneous Fenton-like process for the effective degradation of ofloxacin by SC-H2SO4. Based on intermediated products identified by gas chromatography–mass spectrometry, a possible OFX oxidation pathway in Fenton-like reaction was proposed.

Activation of persulfate by CuO-sludge-derived carbon dispersed on silicon carbide foams for odorous methyl mercaptan elimination: identification of reactive oxygen species.

In this work, sludge-derived carbon (SC) was innovatively integrated with copper oxide (CuO) on macroporous silicon carbide foams to construct a distinctive catalyst (CuO/SC) with strong catalytic activity, which can effectively activate persulfate (PS) for the removal of methyl mercaptan (CH3SH). The structure and morphology of CuO/SC were investigated by means of XRD, SEM, and EDS. The effects of initial pH values, copper contents, PS dosages, and flow rates on CH3SH removal were also investigated. Under optimal condition, more than 90% of CH3SH was removed by CuO/SC-PS combined system within 10-min reaction due to the synergistic function of CuO and SC. More importantly, on the basis of reactive species trapping and ESR spectroscopy, it is revealed that the responsible reactive species for catalytic CH3SH composition were ·SO4-, ·OH, 1O2, and ·O2- in CuO/SC-PS system. Finally, the possible PS activation scheme of CuO/SC samples was proposed.