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Fenton and Fenton-like sludge conditioning processes have been studied intensively due to their superior efficiency in improving sludge dewaterability. But these processes inevitably produce a large quantity of Fe-rich sludge cake that induces challenges for disposal. Herein a sustainable sludge recycling strategy has been developed by using sludge-derived Fe-rich biochar as an iron source and catalyst to enhance sludge dewatering via advanced oxidation processes. Both homogeneous Fenton reactions initiated by the leached Fe2+ from the biochar, and heterogeneous Fenton reactions initiated by the bonded iron, in forms of Fe3O4, on the surface of the biochar, are revealed to contribute to the increase the amount of OH generation during sludge conditioning, which further improved the release of bound water and sludge dewaterability. The stability of the dewatering performance using the new strategy is demonstrated via three consecutive reuse cycles, in which a stable water contents of dewatered sludge cakes of approximately 46.38 wt% ± 2.88 is obtained. The iron content of the biochar becomes stable after the 2nd round recycle. A reduction of 28.39% on the total operating cost of sludge treatment could be realized when compared with the Fenton conditioning system without sludge recycling. The proposed sustainable sludge recycling strategy could realize zero disposal Fe-containing sludge, and meanwhile produce biochar that can be beneficially reused as valuable functional materials for other applications.

Mercapto-functionalized attapulgite (MATP) could efficiently adsorb Cd from aqueous solution, achieving adsorption equilibrium within 30 min with the maximum adsorption capacity of 120 mg g−1 at pH 6.7, 7.89-fold higher than that of ATP. Density functional theory (DFT) calculations revealed that the formed S–Cd–S and Cd–S bonds on MATP had lower adsorption energy (−3.75 and −2.84 eV) and higher bond order (1.14 and 0.39) than the corresponding values of Cd–O (−1.02 eV and 0.26) on ATP, which resulted in higher adsorption affinity of MATP toward Cd than ATP. The adsorption capacity increased by 7 times with the increasing of pH from 2.0 to 6.7. The positive-charged surface and protonation of MATP inhibited its adsorption for Cd at strong acid condition (pH

The catalytic capabilities of copper doped attapulgite (Cu/ATP) and silicon carbide (Cu/SiC) nanocomposites for p-nitrophenol (PNP) were characterized under microwave (MW) irradiation. Higher catalytic performance of Cu/SiC was obtained than that of Cu/ATP due to higher production rate of reactive oxygen species (ROS) as well as higher MW absorptivity. The electron (e−) – hole (h+) pairs were related to the generation of ROS on Cu/SiC. The modification Cu with SiC had an enhancement on the band gap and large EVB absolute values, which promoted the catalytic activity of Cu/SiC. An ROS-producing copper-redox cycle between CuI and CuII of Cu/ATP was responsible for PNP degradation. The produced CuI via thermal dissociation of [Cu–O–Cu]n species in Cu/ATP activated molecular oxygen, followed by Fenton-like reactions to produce ROS. The reusability of the catalysts and negligible phase transformation of Cu species after five rounds of cycle verified the catalyst stability. Based on Density functional theory (DFT) calculation and catalytic experimental analyses, the denitro-hydroxylation of PNP was the initial oxidation reaction step followed by further oxidation to form short-chain carboxylic acids. OH oxidation was predominant whereas O2− was not involved in the OH addition on the meta-position due to lower oxidation energy than the corresponding activation energies. Other than reactive species attack, the “hot spots” on the surface of Cu/SiC was responsible for thermal stabilization of PNP/intermediates in soil. In this study, MW-assisted Cu/ATP and Cu/SiC catalytic degradation of PNP was proved to be an efficient technology for wastewater treatment and soil remediation.

The migration of long chain soluble lithium polysulfides through the separator to the anode, the so called “shuttle effect”, is one of the major issues responsible for the capacity degradation of lithium-sulfur (Li-S) batteries. In this work, N and S co-doped mesoporous carbon was prepared by a novel egg shell template method and utilized to modify the separator for high performance Li-S batteries. The discharge capacity of the second cycle retained at 1467 mAh g −1 at 1 C after 200 cycles and decayed at 0.20% per charge-discharge cycle, and a reversible capacity of 561 mAh g −1 was achieved even at 5 C rate after 200 cycles. The prepared material showed a porous hollow sphere morphology with larger surface area and N and S co-doped that can provide great electrochemical property as well as surface chemistry for the adsorption of the intermediate polysulfides. After separator modification, XPS analysis revealed that pyrrolic-type N, pyridinic-like N, and thiosulphate were the major factors contributing to the superior electrochemical performance of the CS/S cathode. This work also provided a rational design strategy for the modification of separator to effectively utilize the active sulfur and to retard the migration of dissolved polysulfides, which enhanced the performance of high energy density Li-S batteries with long cycling life.

Electro-dewatering (EDW) is an innovative method for volume reduction of sewage sludge before re-utilization and disposal. In this study, dewaterability limit and energy consumption in sludge electro-dewatering process were directly explored using in-situ linear sweep voltammetry (LSV) analysis by a high-voltage electrochemical workstation instead of a traditional DC power source. Dewaterability limits of biosolids EDW were identified under a constant-voltage dewatering mode with different applied voltages at 10, 20, 30, 40, and 50 V, independently. The LSV tests reveal that the dewaterability limit of sludge is attributed to the higher electrical resistance of the sludge layer near the anode. The mass of the filtrate flow was linearly proportional to the total amount of electric charge corresponding to the energy consumption in EDW, which elucidated the principal mechanism of EDW. Under a constant-voltage dewatering mode, the applied voltage is a key factor in controlling the energy consumption. Reducing the applied voltage while extending the dewatering time is proposed to reduce the energy consumption and obtain a good dewatering result. As the applied voltage decreased from 50 to 10 V, the energy consumption could be reduced from 403.6 to 80.3 kWh/m 3 removed water, the dewatering times was increased from 6.4 to 85.4 min, and the dry solids content of dewatered cake increased from 16.1 to 34.4 wt%. Those results indicate that LSV is an effective method to reveal the mechanism of EDW and optimize the operation parameters to reduce energy consumption.

A novel nano-scale ferrite (MgFe 2 O 4 ) was employed for hexachlorobenzene (HCB) removal in soil with microwave (MW) treatment. MW-generated hole (h + )/electron pair could activate water and oxygen adsorbed on the surface of MgFe 2 O 4 to produce OH and O 2 − . Radical scavenging tests confirmed it was OH but not h + and O 2 − that directly oxidized HCB. O 2 − was a responsible oxidant of intermediates decomposition. Thus the co-existing of water and molecular oxygen had significant enhancement on HCB catalytic oxidation, showing high degradation (80%) and dechloriantion (93%) after 20 min of MW radiation. Electron spin resonance analysis demonstrated that O 2 − and OH radicals were aroused from MW-induced h + /electron activation of molecule oxygen and water, but not from the lattice oxygen and –OH groups in the structure of ferrites. Thermal desorption of HCB occurred at the wide temperature of the surface soil at the range of 90–500 °C, and obviously catalytic oxidation happed at a temperature range of 90–620 °C in the water/oxygen-contained system. Complicated pyrolytic reactions happed at 90–670 °C in the absence of water and oxygen. The addition of MgFe 2 O 4 with MW radiation elevated soil temperature, leading to HCB pyrolysis that fitted well with the first order kinetics model. When soil was vitrified at >670 °C, with the process of thermal fixation, changes of the soil structure took place.

The mechanism of clay colloids promoting arsenite (AsIII) adsorption on iron oxide particles (Fe2O3) was studied. Fe2O3 on attapulgite (Fe/ATP) showed 8.30–fold higher adsorption capacity per unit area than the pristine Fe2O3 (0.200 mg m−2 g−1) at neutral condition. Compared with Fe2O3, the higher adsorption affinity of Fe/ATP to AsIII was obtained based on the lower adsorption energies of the formed AsIII surface complexes on Fe/ATP by density functional theory (DFT) calculations. The increased AsIII adsorption capacity and affinity on Fe/ATP were attributed to the enhanced Fe chemical activity in Fe/ATP where the stronger delocalization of Fe led to stronger hybridization of the Fe–3d orbital with the O–2p orbital in AsIII. ATP played an important role in facilitating Fe activity through electron transfer from Al and O atoms of ATP to enhance the electronic property of the loaded Fe, which was beneficial to the adsorption of AsIII as electron acceptor. The introduction of ATP provided Fe2O3 with more surface activity and availability to AsIII, which is of great significance for understanding the fate and transport of AsIII in the coexistence water system of clay and iron oxide particles.