Sludge-based Carbon Research Articles

A low-cost assay for hydrogen peroxide using sewage sludge-based carbon nanodots

In this work, sewage sludge is considered for the first time as a colorimetric detection probe for H2O2. This work is beneficial to the management and resource utilization of sewage sludge and the visual detection of H2O2.

Improvement of waste sludge dewaterability by a novel co-conditioning approach with polyaluminum chloride-sludge based carbon-polyacrylamide

A novel sludge conditioning method incorporating sludge-based carbon (SBC) as a filter aid into the coagulation and flocculation co-conditioning process is proposed to strengthen sludge dewaterability, namely the co-conditioning of polyaluminum chloride (PAC)-SBC-polyacrylamide (PAM). The results show that the co-conditioning method can effectively reduce the specific resistance to filtration (SRF), moisture content (MC) of the filter cake and sludge compressibility coefficient (CC), meanwhile increase the net sludge solids yield (YN) of municipal sludge (MS) and textile dyeing sludge (TDS), resulting in a significant improvement in sludge dewatering performance for two types of sludge. The response of sludge dewatering performance to different conditioning agents and the variation characteristics of sludge EPS in co-conditioning process suggest that the co-conditioning mechanism involves a synergistic effect of coagulation, adsorption, and flocculation, which process includes the aggregation and disintegration of microbial cell flocs caused by PAC, the skeleton-building action and biopolymer adsorption by SBC, and sludge floc agglomeration facilitated by PAM. In addition, SBC also optimizes coagulation by electrostatic neutralization, while strengthening flocculation by bridging biopolymers and PAM. Moreover, co-conditioning exhibits a remarkable ability to eliminate dissolved organic matter from the filtrate, leading to an enhancement in the filtrate quality and a reduction in the downstream burden for sludge filtrate treatment. Consequently, the PAC-SBC-PAM co-conditioning emerges as a promising method for sludge pretreatment.

Evaluation of the adsorptive and catalytic properties of sludge-based carbon materials for the efficient removal of antibiotics listed in the European Decision 2020/1161/EU

In this work, sludge from an oily refinery and urban wastewater treatment plant have been used for the synthesis of activated carbons using ZnCl2 and KOH as activating agents. The materials were used as adsorbents and catalysts for the removal of three antibiotics, e.g., sulfamethoxazole (SMX), trimethoprim (TMP) and ciprofloxacin (CPX). The activated carbons have been fully characterized. Thus, the BET surface area of the materials ranged from 183 to 784 m2/g. Qe values of 127.3 mg/g for SMX onto U-ZnCl2; 168.5, and 179.6 mg/g for TMP and CPX, respectively, onto R-KOH were obtained. The best fitting of kinetic data was found by using pseudo-second order (PSO) model, while Freundlich and Liu models successfully fitted the equilibrium adsorption isotherms. SMX, TMP and CPX adsorption mechanisms were governed by pore filling, π-π interactions and H-bonds. R-KOH material was used for wastewater treatment, finding that the adsorption capacity decreased due to a competitive effect. Regarding the Fenton process, the U-ZnCl2 carbon achieved the total SMX degradation after 60 min. In contrast, TMP and CPX showed the highest depletion in only 20 min. The higher performances of the U-ZnCl2 material may be due to a higher C/O ratio and high N and Zn contents. In the experiments with a real aqueous matrix, similar conversions were achieved, although the kinetic constants resulted in slightly lower values. So, it could be stated that adsorption and Fenton oxidation performance were influenced by the different properties of the carbon materials.

Inhibition of aluminum powder explosion by sludge-based carbon nanotubes/phosphorus-nitrogen flame retardant composite powder: Mechanism and kinetic model

Reducing or eliminating aluminum powder explosions is of great significance to preventing and reducing aluminum industry disasters. In order to find an appropriate way to prevent and alleviate the hidden danger of aluminum powder explosion, a sludge-based carbon nanotube (MS@CNTs) carrier with excellent performance was constructed in this paper, and the MPP-MS@CNTs composite powder was prepared by in-situ synthesis technology. The explosion flame propagation and pressure suppression experiments show that the composite powder can more effectively suppress the explosion of aluminum powder. When adding 60 wt% composite detonation inhibitor, the explosion inhibition of aluminum powder can be achieved. Combined with the methods of Redfern, Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose, it was found that the activation energy of aluminum powder increased after adding detonation inhibitor. Its inhibitory effect is theoretically demonstrated. The material properties before and after the explosion were compared and analyzed through characterization tests. Combined with pyrolysis characteristics, the inhibition mechanism of composite powder mainly includes coating inhibition, porous adsorption isolation, decomposition endothermic, and product oxidation, which provides a theoretical and practical basis for the prevention and control of explosion and fire accidents in the aluminum industry.

Carbon sequestration for high-quality sludge-based carbon preparation via K/Na bi-molten salts pyrolysis.

Pyrolysis carbonization of sewage sludge is employed to achieve carbon sequestration and access carbon resources, while the quality of the obtained sludge-based carbon (SBC) is poor due to high ash contents and volatile organic matter. Here, carbonization in KOH/Na2CO3 (K/Na) bi-molten salts was developed for SBC preparation, improvement of carbon exploitation from biomass, and to reduce the contents of ash and volatile organic matter. The results showed that the surface area and pore volume of SBC under optimized conditions reached 1631 m2g-1 and 1.312 cm3g-1 at 700°C, respectively, with a K/Na bi-molten salts/sludge ratio of 2:1 (K:Na = 5:5). Moreover, over fivefold the higher surface area and 43.61% amount of carbon element could be obtained, with a decrease in the mass loss rate for sludge pyrolysis of 25%. The mechanism behind the higher surface area of the SBC was identified and divided into three stages: intense dehydration and dehydrogenation caused by molten salt-enhanced polycondensation of protein and polysaccharide (200-400°C), strongly reduced carbon-oxygen structure after deoxygenation reactions (400-600°C), aromatization and cyclization of long-chain fatty acids triggered by deamidation of tar catalyzed by molten salts (600-900°C). Eventually, 14.63% carbon was sequestered for the high-surface-area SBC prepared by K/Na bi-molten salts system.

Catalysts containing Fe and Mn from dewatered sludge showing enhanced electrocatalytic degradation of triclosan

The present work demonstrates a simple one-step pyrolysis method for the synthesis of a catalytic sludge-based carbon (SBC) biochar containing Fe and Mn from dehydrated sludge with added KMnO4 and Fe(II). The electrocatalytic degradation of triclosan (TCS) in water was evaluated using an Fe/Mn-SBC cathode to promote a heterogeneous Fenton-like reaction. The catalyst generated at 500 °C exhibited an abundant porous structure and a relatively high surface area, and produced an electrode with better conductivity and electron diffusion. The presence of metal oxides changed the surface structure defects of this biochar and enhanced its catalytic performance while increasing the electrochemically active surface area by 72.68 mF/cm2 compared with plain SBC. TCS was degraded (91.3%) within 180 min by oxygen species generated in situ on an Fe/Mn-SBC cathode because the activation energy for oxygen reduction was lowered by 4.62 kJ/mol. The degradation of TCS followed pseudo first-order kinetics and was controlled by TCS diffusion and interfacial chemical reactions between adsorbed TCS and the electrode. Possible TCS degradation pathways were devised based on the main intermediates, and 1O2 was found to be more important than •OH radicals. Through toxicity test and prediction, the toxicity of degradation was gradually reduced. This study demonstrates a simple and ecofriendly method for the electrocatalytic degradation of organic pollutants.

Paper mill sludge-based carbon quantum dots as a specifically ratiometric fluorescent probe for the sensitive and selective detection of coptisine.

Coptisine (COP), one of the bioactive components in Rhizoma Coptidis, has many pharmacological effects. Meanwhile, the determination of COP is essential in pharmacological and clinical applications. Herein, we prepared carbon quantum dots (CQDs) by one-step oil-thermal method using paper mill sludge (PMS) as precursor, and developed a ratiometric fluorescence method for the determination of COP. The structural and optical properties of PMS-CQDs were evaluated through high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), ultraviolet-visible (UV-vis), fluorescence, zeta potential and fluorescence lifetime experiments. Fluorescence intensity ratio at 550 nm and 425 nm (I550 /I425 ) was recorded as an index for quantitative detection of COP. The detection concentration of COP ranges from 0.1 to 50 μM in good linear correlation (R2 =0.9974) with a limit of detection of 0.028 μM (3σ/k). The quenching mechanism was deduced to be inner filter effect and static quenching. The ratiometric fluorescent probe showed impressive selectivity and sensitivity towards COP, and was successfully applied to the detection of COP in human urine with expected recoveries (95.22-111.00%) and relative standard deviations (0.46-2.95%), indicating that our developed method has a great application prospect in actual sample detection.

Enhanced removal of neonicotinoid pesticides present in the Decision 2018/840/EU by new sewage sludge-based carbon materials

Due to the increasingly strict legislation about the disposal of sewage sludge, it is necessary to find sustainable solutions to manage this waste at low-cost conditions. In addition, priority contaminants are now attracting much attention since they are usually detected in WWTP effluents. In this work, five sludge have been used as precursors for the synthesis of activated carbons subsequently tested in the removal by adsorption of three neonicotinoid pesticides listed in the EU Watch List: acetamiprid (ACT), thiamethoxam (THM), and imidacloprid (IMD). Generally, the activated carbons were prepared by chemical activation using ZnCl2 as an activating agent and then the resulting materials were pyrolyzed at 800 °C for 2 h. The synthesized activated carbons showed different textural properties; thus, the best adsorption results were found for AC-Industrial activated carbon, obtained from an industrial origin sewage sludge, with high equilibrium adsorption capacities (qe = 104.2, 137.0, and 119.9 mg g−1), for ACT, THM, and IMD, respectively. Furthermore, it was elucidated that the use of CO2 in the synthesis generated an opening, followed by widening, of the narrowest microporosity, increasing the specific surface area of the carbon materials. The kinetic and isotherm adsorption experimental data were obtained for each of the pesticide-activated carbon systems; thus, the kinetic curves were well-fitted to the pseudo-second-order kinetic model, as well as, Freundlich and Guggenheim-Anderson-de Boer (GAB) empirical models were used for the fitting of the equilibrium adsorption isotherms, finding that GAB model best fitted the experimental data. Additionally, the regeneration of the activated carbons using methanol as a regenerating agent and the single and simultaneous adsorption of a hospital wastewater effluent, fortified with the three studied pesticides have been explored.

Molecular composition and biotoxicity effects of dissolved organic matters in sludge-based carbon: Effects of pyrolysis temperature

Sludge pyrolysis carbonization has shown potential to convert sludge biomass into multifunctional carbon materials. However, ecological risks of dissolved organic matters (DOMs) with obscure molecular characteristics retaining in sludge-based carbons (SBCs) have received little attention. This study investigated the impact of pyrolysis temperatures on the molecular conversion and biotoxicity effects of DOMs in SBCs. The results revealed that DOMs in SBCs300–400 were mainly derived from depolymerization of biopolymers and the polycondensation and cyclization of small intermediate molecules, which mainly consisted of aromatic CHON compounds with 1–3 N atoms, featuring high unsaturation and molecular weights. High-temperature pyrolysis (500–800 °C) promoted the decomposition and ring-opening of aromatic CHON compounds into saturated aliphatic CHO compounds with 2–4 O atoms in SBCs500–800. Noteworthily, SBCs300–400-derived DOMs showed relatively strong biotoxicity on the growth and development of wild-type zebrafish embryos, pakchoi seeds, and Vibrio qinghaiensis Q67, which was significantly related to aromatic amines, phenols, and heterocyclic-N compounds in DOMs of SBCs300–400. SBCs500–800-derived DOMs were mainly straight-chain fatty acids and showed no observable acute biotoxicity. This study highlights the negative impact of DOMs in SBCs on the ecological environment, and provides the theoretical basis for controlling toxic byproducts in sludge pyrolysis process.

Fe/Mn loaded sludge-based carbon materials catalyzed oxidation for antibiotic degradation: Persulfate vs H2O2 as oxidant

Due to the nature of high carbon content in sludge, that is promising to fabricate multi-functional carbon materials with waste activated sludge (WAS). In this study, we report a facile and cost-effective approach to convert waste activated sludge (WAS) into multi-functional sludge-based carbons (Fe/Mn-SBC) through KMnO4-Fe(II) conditioning coupled with pyrolysis strategy. The Fe/Mn-SBC had abundant porous structure and superior catalytic activities towards PS /H2O2, resulting in highly efficient removal of tetracycline (TC) through catalytic oxidation. Meanwhile, •OH radicals played the leading role during TC degradation process in both of Fe/Mn-SBC catalyzed PS and H2O2 systems compared to 1O2 and SO4•- radicals. In addition, the SO4•- produced in Fe/Mn-SBC catalyzed PS system led to higher TC degradation than H2O2 over a wide range of pH, due to its stronger oxidizing and stably properties compared to •OH. Moreover, the different free oxygen radicals were produced from Fe/Mn-SBC catalyzed PS /H2O2, causing formation of different TC degradation products via losing H2O and methyl in amin, or hydroxylation, hydrogenation, and dihydroxylation processes. This study proposed a novel strategy for excess sludge reutilization for preparing carbon-based catalyst with superior oxidative ability for PS /H2O2 activation for organic contaminants degradation.

Coagulation-flocculation followed by catalytic ozonation processes for enhanced primary treatment during wet weather conditions

Combined sewer overflows (CSO), generated during the wet weather flow from the combination of the inflow and stormwater runoff in sewer system, result in an overflow of untreated wastewater from sewer system, which might ultimately contain different micropollutants (MPs). In this study, a coagulation-flocculation-sedimentation (CFS) pretreated CSO spiked with MPs was treated by catalytic ozonation using carbon, iron, and peroxide-based catalysts. The catalysts were characterized and their activity on MPs removal was studied at two different ozone (O3) doses (5 and 10 mg L−1). The effect of the treatment on the spiked CSO effluent was also assessed from the acute toxicity of the effluent using Microtox®, Yeast, and Macrophage cell-line toxicity assay tests. All the carbon-based catalysts showed large surface area, which was strongly influenced by the activation technique in the preparation of the catalysts. The CFS treatment strongly reduced the turbidity (≥60%) but had marginal effect on the UV254, dissolved organic carbon (DOC), and pH. Sludge Based Carbon (SBC) showed strong adsorption capacity (≥60% removal efficiency) for all MPs studied compared to other carbon and iron-based catalysts. Ozonation alone was effective for the degradation of easily oxidizable MPs (sulfamethoxazole, mecoprop, and 2,4-dichlorophenoxyl acetic acid), achieving more than 80% degradation efficiency at 10 mg L−1 of ozone, but not effective for atrazine (≤60% degradation efficiency) at similar O3 dose. Catalytic ozonation (at 10 mg L−1 O3 dose) improved the degradation of the MPs at low catalyst dosage but higher dosage strongly inhibited their degradation. In all cases, the effluents showed negligible acute toxicity, indicating the suitability of the process for the treatment of CSO.

Relationship between the physicochemical properties of sludge-based carbons and the adsorption capacity of dissolved organic matter in advanced wastewater treatment: Effects of chemical conditioning.

Pyrolysis carbonisation is a promising technology to convert organic waste into valuable carbon-based materials. However, sludge is generally highly compressible and difficult to dewater because of its high concentrations of biopolymers; the bound water of sludge is trapped in a network composed of biopolymers. Therefore, chemical conditioning is an indispensable step for improving sludge dewaterability performance. In the present work, the effects of different chemical conditioning agents (polymeric aluminium chloride (PACl), iron(III) chloride (FeCl3), KMnO4-Fe(II) and Fenton's reagent) on the physicochemical properties of sludge-based carbons (SBCs) were systematically studied and the SBCs were further used in advanced wastewater treatment. The adsorption mechanisms of dissolved organic matters (DOMs) by different SBCs were also investigated. The results showed that conditioning with KMnO4-Fe(II) and Fenton's reagent improved the specific surface area of the SBCs, whereas inorganic salt flocculation conditioning reduced the porosity of the SBCs. In addition, we found that the Fenton-SBC and Mn/Fe-SBC performed better than the other investigated SBCs in the removal of organic compounds from secondary effluent and that the pseudo-second-order kinetic model could better describe the process of DOMs adsorption by all of the investigated SBCs. Moreover, three-dimensional fluorescence excitation-emission matrix spectroscopy in combination with an analysis of the physical and chemical fractionation of DOMs showed that all of the SBCs performed well in the adsorption of aromatic substances, hydrophobic acids and hydrophobic neutrals, whereas the Mn/Fe-SBC and Fenton-SBC performed better than the other SBCs in the removal of weakly hydrophobic acids.

Melamine-assisted synthesis of paper mill sludge-based carbon nanotube/nanoporous carbon nanocomposite for enhanced electrocatalytic oxygen reduction activity

Developing efficient and cheap electrocatalysts as substitutes for commercial Pt/C in the oxygen reduction reaction(ORR)is extremely necessary. Herein, paper mill sludge (PMS) was utilized to produce iron, nitrogen and sulfur co-doped carbon nanotube/nanoporous carbon nanocomposite (PMS-CNT/C) by pyrolysis. PMS-CNT/C-b, one of as-prepared PMS-CNT/C exhibited excellent oxygen reduction reaction activity with an onset potential of 0.99 V vs. RHE and half-wave potential of 0.77 V vs. RHE, which was similar to the commercial Pt/C catalyst (onset potential of 0.99 V vs. RHE and half-wave potential of 0.76 V vs. RHE). It had longer-term stability and higher methanol tolerance in alkaline medium than Pt/C. Moreover, the new catalyst also exhibited excellent catalytic performance in neutral solution. The energy output of microbial fuel cells loaded with PMS-CNT/C-b catalyst was also higher than that of commercial Pt/C under neutral condition. The excellent ORR performance of PMS-CNT/C-b was due to the carbon nanotube/nanoporous structure and the synergistic effect of abundant N groups, iron nitrides and thiophene-S. The formation of CNTs in the carbon nanotube/nanoporous carbon nanocomposite was mainly attributed to melamine, which was added into PMS and was at first just considered as a nitrogen source to develop N-doped PMS-based catalysis in this work. The synthesis of paper mill sludge-based carbon nanotube/nanoporous nanocomposite and its excellent ORR activity will make the new catalyst a promising cathodic electrocatalyst alternative for fuel cells.

Study on Preparation of an Oil Sludge-Based Carbon Material and Its Adsorption of CO2: Effect of the Blending Ratio of Oil Sludge Pyrolysis Char to KOH and Urea

How to prepare a low-cost carbon material with a high carbon dioxide (CO2) adsorption performance has attracted much attention worldwide. Oil sludge, a hazardous solid waste, needs to be disposed off properly. Oil sludge pyrolysis has been proven to be an effective method for waste treatment with the production of pyrolysis oil, gas, and char. In this study, nitrogen-doped carbon (NC) was prepared and characterized based on oil sludge pyrolysis char (OSC). Specifically, NCs were generated by mixing OSC with potassium hydroxide and urea under different blending ratios of 1:3:2, 1:3:3, and 1:3:4 at 700 °C. NCs showed good surface morphology and pore structures with large specific surface areas (1056.45–1138.15 m2·g–1), pore volumes (1.54–1.63 cm3·g–1), and a wide range of pore size distribution. The best CO2 adsorption capacity of NCs at room temperature and pressure is 3.3 mmol·g–1 under a blending ratio of 1:3:2. In addition, the CO2/N2 selectivity of NCs is as high as 8.434. The adsorbent synthesized from oil sludge by a simple and low-cost method is a promising material for carbon dioxide adsorption.

Evaluating adsorbent properties of drinking water treatment plant sludge-based carbons activated by K2CO3/CH3COOH: a low-cost material for metal ion remediation

Sludge reclaimed from drinking water treatment plant was carbonized and chemically activated by K2CO3 and CH3COOH. The proposal was to evaluate its adsorbent properties as a low-cost alternative material for metal ion remediation. Morphological, physicochemical, and chemical characteristics have been presented and comprehensively discussed. Main findings revealed a surface area rich in mesopores and loaded with weakly acidic functional groups, also presenting an eroded aspect. Carbonization of the sludge’s organic content increased the concentration of nitrogenic and oxygenated functional surface groups. Chemical activation by K2CO3 and CH3COOH increased adsorption and desorption capacity, pore volume, and pore size by two, three, and over tenfolds, respectively. Uptake of cations increased by 51% and, for anions, around 27%. Association of carbonization with sequenced activation processes converted drinking water treatment plant sludge into an excellent and promising alternative adsorbent material.

Enhancing the sludge-based carbon quality via site-occupied and decomposed process

The sequestration of carbon from the sewage sludge to prepare a useful sludge-based carbon (SBC) could be one of the sustainable alternative methods for the solution of sludge in cities. In this work, a novel method of ‘site-occupied firstly and decomposed subsequently’ was developed to increase the sludge-based carbon (SBC) quality. The urea was designed to generate CO2 and NH3 firstly during the decomposition process around 150–250 °C, and to form HCNO and g-C3N4 at 360 and 550 °C in series. Three times higher BET surface area was observed after 30% urea treated SBC (wurea/wsludge = 3/10, SBC30%u), from 97 ± 4.1 m2/g to 300 ± 7.4 m2/g. The point of zero charge (PZC) of SBC30%u decreased to 3.8 ± 0.23 from 5.4 ± 0.20 (PZC of the untreated SBC) due to the generation of acidic groups. The acidic functional groups generated, such as –CO, –OH, were also confirmed by the FTIR analysis. The SBC obtained was used for the further treatment of leachate effluent, and the corresponding COD removal ratio increased from 21.6% to 50.2% in SBC30%u. It can be concluded that the site-occupied and decomposed process could be a potential process to pyrolysis for the sludge-like complex raw material.

Catalytic pyrolysis coupling to enhanced dewatering of waste activated sludge using KMnO4[sbnd]Fe(II) conditioning for preparing multi-functional material to treat groundwater containing combined pollutants

Sewage sludge, the major by-product during the primary treatment and subsequent biotreatment of wastewater, is increasingly generated around the world. KMnO4Fe(II) consists both oxidation properties of KMnO4 and flocculation ability by in-situ formed Fe(III) and is widely used in water treatment. In this study, KMnO4Fe(II) was used as chemical conditioners to synchronously improve sludge dewatering performance and catalyze the biomass pyrolysis of waste activated sludge for preparing multi-functional material to remedy arsenic containing groundwater. The results showed that the sludge dewaterability was significantly improved due to the moderate pre-oxidation of extracellular polymeric substances by KMnO4, and then the sludge particles were re-flocculated by Fe(III) generated from KMnO4Fe(II). The conditioned sludge cake was then utilized for preparing sludge-based carbon (Fe-Mn-SBC) which was systematically characterized. The surface area of Fe-Mn-SBC was characteristic of high surface area (100.08 m2/g) which had a great adsorption capacity on arsenic. Besides, Fe-Mn-SBC could effectively oxidize As(III) to As(V), and addition of low dose of H2O2 can further improve total arsenic removal due to catalytic peroxidation of Fe-Mn-SBC. Besides, it was found that the presence of humic acid could inhibit the hydroxy iron formation and compete for the active adsorption sites and then resulted in the decrease in arsenic removal, and the co-existing humic acid could also be removed by adsorption of Fe-Mn-SBC. This work proposed a novel sludge treatment process by combining enhanced sludge dewatering with catalytic pyrolysis for preparing multi-functional materials, and they are promising in treatment of water containing combined pollutants.

A novel waste activated sludge multistage utilization strategy for preparing carbon-based Fenton-like catalysts: Catalytic performance assessment and micro-interfacial mechanisms

Waste activated sludge (WAS) contains many anionic functional groups which can interact with heavy metal ions through electrostatic action and complexation reactions. The transition metals adsorbed in WAS can catalyze sludge pyrolysis in anaerobic conditions and improve structural properties of organic matter. In this work, a multistage WAS utilization process for preparing the carbon-based Fenton-like catalysis materials is proposed. More specifically, WAS is firstly used as an adsorbent for heavy metals (Cu and Ni) removal, and then complexes are converted into heterogeneous Fenton-like carbon-based catalysts through oxygen-free pyrolysis. The mechanisms of interactions between extracellular polymeric substances (EPS) and metals are investigated, and the physicochemical properties of sludge-based carbons (SBC) are comprehensively characterized using varies techniques. It is found that WAS is an excellent adsorbent for Cu and Ni removal, which is mainly due to the coordination and electrostatic interactions between EPS and heavy metals. Cu and Ni adsorbed in WAS significantly improved the porous structure of SBC. Both adsorption and catalytic oxidization of Cu/Ni-SBC contribute the removal of E2 in real wastewater. The E2 removal mechanism is explored by electron-spin resonance spectroscopy (ESR) analysis, and it is found that both of .O2− and .OH radicals are responsible for E2 degradation in Cu(II)-SBC-H2O2, while .O2− radicals contributes to E2 degradation in Ni(II)-SBC-H2O2 system, so the former performed better than the latter in total removal of E2. Besides, Cu(II) and Cu(I) are both formed in Cu(II)-SBC during the oxidation process, while only Ni(II) is found in the Ni(II)-SBC-H2O2 process, confirming that different catalytic oxidation reactions are occurred in the Cu(II)-SBC-H2O2 and Ni(II)-SBC-H2O2 processes. This study facilitates a great strategy to the sludge multi-stage circulating utilization and a better understanding about the role of the Cu/Ni existed in SBC during the estrogens removal process.

Characteristics and adsorption study of the activated carbon derived from municipal sewage sludge.

Sewage sludge-based activated carbon is proved to be an efficient and low-cost adsorbent in treatment of various industrial wastewaters. The produced carbon had a well-developed pore structure and relatively low Brunauer-Emmett-Teller (BET) surface area. Adsorptive capacity of typical pollutants, i.e. copper Cu(II) and methylene blue (MB) on the carbon was studied. Adsorptions were affected by the initial solution pH, contact time and adsorbent dose. Results showed that adsorption of Cu(II) and MB on the produced carbon could reach equilibrium after 240 min. The average removal rate for Cu(II) on the carbon was high, up to 97% in weak acidic conditions (pH = 4-6) and around 98% for MB in a very wide pH range (pH = 2-12). The adsorption kinetics were well fitted by the pseudo-second order model, and both Langmuir and Freundlich isotherm models could well describe the adsorption process at room temperature. The theoretical maximum adsorption capacities of Cu(II) and MB on sewage sludge-based activated carbon were 114.94 mg/g and 125 mg/g, respectively. Compared with commercial carbon, the sewage sludge-based carbon was more suitable for heavy metal ions' removal than dyes'.

Facile synthesis of magnetic sludge-based carbons by using Electro-Fenton activation and its performance in dye degradation

Highly stable iron based magnetic carbon were prepared by sequential Electro-Fenton (EF) activation and pyrolysis of sewage sludge. The applied voltage exerts great influence on EF treated sludge flocs and thus poses significant effect on physiochemical properties of the as-prepared carbons. High insertion rate of iron into sludge from EF activation resulted in carbons with highly dispersed iron oxides, which had average size of iron nanoparticles being 4.77nm. The carbon also presented well developed porosity which had Brunauer-Emmett-Teller (BET) surface area attaining 341m2/g. Carbons prepared by traditional Iron Impregnation (IM) were used as comparison to gain further insight into their catalytic role as Fenton-like catalyst. Results showed that EF-activated sludge carbon could yield 96.1% of Methyl Orange (MO) removal in 60min together with only 1.4% of iron leaching. After three cycles, the MO removal can still reach 80% with EF-activated carbons.