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Sewage sludge (SS) dewatering is a key step in sludge disposal, which plays an important role in reducing sludge volume, facilitating transportation and subsequent treatment. In this paper, a facile hydrothermal-alkaline treatment for SS was proposed, which can be used for sludge dewatering and humic acid (HA) recycling at the same time. Response surface methodology (RSM) was used to determine the optimal conditions, and a mathematical model was established to accurately predict the changes of sludge water content and the extraction rate of HA. Under the optimal conditions of 170 °C/42 min/0.05 (for hydrothermal temperature, hydrothermal time, and mass ratio of KOH to wet sludge, respectively), the water content decreased to 46.7% and the extraction rate of HA (with a purity of 96.2%) was 89.1%. The improvement of the dewatering performance effectively facilitates the subsequent disposal of the sludge. The hydrothermal-alkaline method not only realizes the efficient dehydration of the sludge, but also obtains HA from the sludge extract. The obtained HA has potential economic value in the fields of agriculture, biological medicine, environment, and the like.

Owing to the development of urbanization, the amount of sewage sludge generated through biological activated sludge process has increased dramatically. Anaerobic fermentation of sludge is recognized as an expedient and efficient treatment process, widely applied for biogas generation, resource recovery, and volatile fatty acid production. Volatile fatty acids are one of the most widely used carbon sources and have great use in biological nutrient removals. Volatile fatty acids production in anaerobic sludge fermentation is affected by sludge properties, metabolic pathways, and operating parameters. This paper aims to present an overview of the recent advancement in volatile fatty acids production from waste activated sludge. Standalone and hybrid pretreatment methods prior to the sludge fermentation were introduced and assessed based on VFAs accumulation rate and system performance. In addition, different metabolic steps involved in anaerobic fermentation (i.e. hydrolysis, acidification, and methanogenesis) were deeply evaluated. More importantly, the effects of humic substances were evaluated, among which, the electron transfer, the enzyme activity of microbial species, and the interaction between exogenous electron transporters and humic substances were illustrated. Furthermore, the influence of nitrogen and phosphorus ingredients in sludge fermentation and volatile fatty acids production was introduced. It was found that the additives and pretreatment of waste activated sludge are energetically preferred for the hydrolysis improvement and accelerating the volatile fatty acids accumulation. It was concluded that different structures of humic substances may have different effect on the fermentation process and volatile fatty acids production. The synergistic addition of hydrolytic enzymes assisted to reverse the negative effect of humic acids in some cases, and mitigated the adverse effect of humic substances on the inhibition of bacterial growth. The composition and properties of waste activated sludge may limit its biodegradability and hamper the volatile fatty acids production.

Power overshoot that presents in the power curves of microbial fuel cells (MFCs) is one of the main reasons for the deterioration of MFC performance over the high current region. In this research, the mechanisms of power overshoot were investigated with single-chamber MFCs integrated with carbon cloth anode and Fe/N-doped carbon cathodes possessing varied capacitance properties. It was revealed that insufficient anodic current produced at high potential is responsible for power overshoot generation, which could be eliminated with higher capacitive cathode (7.79 F) compared with the one with lower capacitive cathode (3.74 F). This elimination can be ascribed to the improvement of MFC capacitance induced by cathode capacitance, which was proved by MFC charge-discharge test. However, cathode capacitance can only increase the MFC capacitance to a limited extent, as power overshoot can still occur when applying long stabilization time for polarization test.

Cathode oxygen reduction reaction (ORR) performance is crucial for power generation of microbial fuel cells (MFCs). The current study provides a novel strategy to prepare Fe/N-doped carbon (Fe/N/C) catalyst for MFCs cathode through high temperature pyrolyzing of biomass capsuling melamine resin polymer. The obtained Fe/N/C can effectively enhance activity, selectivity and stability toward 4 e– ORR in pH neutral solution. Single chamber MFC with Fe/N/C air cathode produces maximum power density of 1166 mW m−2, which is 140% higher than AC cathode. The improved performance of Fe/N/C can be attributed to the involvement of nitrogen and iron species. The excellent stability can be attributed to the preferential structure of the catalyst. The moderate porosity of the catalyst facilitates mass transfer of oxygen and protons and prevents water flooding of triple-phase boundary where ORR occurs. The biomass particles encapsulated in the catalyst act as skeletons, which prevents catalyst collapse and agglomeration.

The effects of sludge aging on improving sludge electro-dewatering (SED) performance were studied, with the sludge properties variation during aging process investigated. Sludge electro-dewatering performances were explored by constant voltage method (25 V) on various samples. The organic matter in the extracellular polymeric substances (EPS) was gradually consumed and decomposed during sludge aging process. Under identical electro-dewatering conditions, dewaterability and time-space yield of aged sludge achieved 49.33% solid content and 223.46 kg m−2 h−1 respectively. Such results indicate the beneficial effects of sludge aging process in terms of SED performances, which needs further exploration into fundamental mechanisms.

Groundwater treatment sludge is an industrial waste that is massively produced from groundwater treatment plants. Conventional methods for treatment of this sludge, such as discharge into deep wells or the sea, or disposal at landfills, are not environmentally sustainable. Here, we demonstrate an alternative strategy to recycle the sludge by preparing a magnetic maghemite adsorbent via a one-step hydrothermal method with NaOH solution as the only solvent. With this method, the weakly magnetized sludge, which contained 33.2% iron (Fe) and other impurities (e.g., silicon (Si), aluminum (Al), and manganese (Mn)), was converted to magnetic adsorbent (MA) with the dissolution of Si/Al oxides (e.g., quartz and albite) into the liquid fraction. At a NaOH concentration of 2 mol·L−1, approximately 18.1% of the ferrihydrite in the Fe oxides of the sludge was converted into 11.2% maghemite and 6.9% hematite after the hydrothermal treatment. MA2 (i.e., MA produced by a 2 mol·L−1 NaOH concentration) exhibited a good magnetic response of 8.2 emu·g−1 (1 emu = 10−3 A·m2), and a desirable surface site concentration of 0.75 mmol·g−1. The synthesized MA2 was used to adsorb the cationic pollutant tetracycline (TC). The adsorption kinetics of TC onto MA2 fitted well with a pseudo-second-order model, and the adsorption isotherms complied well with the Langmuir model. The maximum adsorption capacity of MA2 for TC was 362.3 mg·g−1, and the main mechanism for TC adsorption was cationic exchange. This study is the first to demonstrate the preparation of an MA from recycled sludge without a reductant and/or exogenous Fe source. The prepared adsorbent can be used as a low-cost adsorbent with high capacity for TC sorption in the treatment of TC-containing wastewater. Keywords: Groundwater treatment sludge, Maghemite, Cationic exchange, Adsorption, Tetracycline

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.

A facile, environmentally friendly and scalable method was reported to synthesize highly dispersed Bi-BiOCl nanoparticles dispersed on three dimensional porous networks of carbon nanosheet using NaCl as template and citric acid as carbon source. The novel 3D architecture demonstrated easily accessible porous structure, large surface area, superior electrical conductivity and good mechanical flexibility, which was capable of accelerating three dimensional diffusion of ions and transport of electrons in the whole electrode. In addition, the highly dispersed Bi-BiOCl nanoparticles on the carbon backbone could facilitate the utilization of these active materials in electrochemical sensing. Under optimized conditions, Bi-BiOCl@C-3 modified glassy carbon electrode exhibited preeminent electroanalytical performance for the simultaneous sensing of Pb2+ and Cd2+ in the linear range of 1–60 μg L−1, with sensitivities of 0.38 and 0.49 μA L μg−1, respectively. The developed protocol has shown limits of detection (S/N = 3) of 0.2 and 0.4 μg L−1 for Pb2+ and Cd2+, respectively, which complies with the limits set by the World Health Organization (WHO). Moreover, high resistance to interference, long-term stability, good reproducibility and satisfactory testing recoveries were realized for real water sample, suggesting that the proposed 3D Bi-BiOCl@C-3 nanocomposite could be utilized as a promising candidate for the fabrication of high-performance electrochemical sensor.

Wet chemical approach is widely applied for P extraction from incinerated sewage sludge ash (ISSA) due to the relatively simple process and low lost. In this study, H2SO4 and H2C2O4 were compared to recover P from ISSA through three steps of acid leaching, cation exchange resin (CER) purification and precipitation. Transformations of P speciation and mineral phases in ISSA from 600 to 900 °C were studied. The results showed that the ISSA samples were mainly composed of inorganic P (IP), and part of non-apatite IP (NAIP, mainly AlPO4) would transform to apatite P (AP, Ca3(PO4)2) with the increase in temperature. The ratio of NAIP to IP dropped from 71.9% at 600 °C to 53.7% at 900 °C. Effect of acid concentration on the leaching efficiency of P from the ISSA samples incinerated at different temperatures by H2SO4 and H2C2O4 was investigated, and the leaching behaviors of key elements of P, Ca, Al and Fe were compared. H2C2O4 exhibited a better performance than H2SO4 for the leaching efficiency of P. Severe sintering of ash particles occurred at temperature >800 °C inhibited the P leaching by H2SO4. During CER purification, the impurity elements in the H2SO4 leachate were easily removed by CER, whereas the Al and Fe elements in the H2C2O4 leachate were hardly removed due to the formation of anionic complexes between Al3+/Fe3+ and oxalic ions. Finally, high-purity struvite product was synthesized from the purified H2SO4 leachate, which could be directly utilized as a fertilizer with negligible environmental risk. Amorphous aluminum and iron hydroxyphosphates were obtained from the H2C2O4 leachate. This study provides insights for P recovery from ISSA samples by different acid leaching systems.

In this study, a method to reduce the emission of NOx precursors (e.g., hydrogen cyanide (HCN) and ammonia (NH3)) while simultaneously reclaim more plant-available P was proposed through pyrolyzing ferric sludge (sludge conditioned by Fenton's reagents) rather than raw sludge. The nitrogen and phosphorus transformation at different pyrolysis temperatures was investigated. The results indicated that in comparison with the pyrolysis of raw sludge, the remaining iron compounds in ferric sludge can fix char-N in more stable forms (e.g., appearance of pyrrole-N at 900 °C). The secondary cracking of amine-N compounds in tar-N (e.g., 81.67% increase of amine-N at 900 °C) can be inhibited. Hence, more amine-N was remained and less heterocyclic-N and nitrile-N compounds were generated in tar N. Less generation of NH3-N and HCN-N was also observed in NOx precursors (e.g., 5.46% decrease of NH3-N and 6.91% decrease of HCN-N at 900 °C). Moreover, the results of X-ray diffractometry, liquid 31P nuclear magnetic resonance spectroscopic, X-ray photoelectron spectroscopic, and chemical analyses collectively indicated that iron present in ferric sludge also favored reclamation of more plant-available P. In comparison with the pyrolysis of raw sludge, an increase in the total phosphorus pool was noted (18.06–36.26 versus 15.54–30.59 mg g−1 dry solids). A decrease in mobility with the predominant P as sodium hydroxide (NaOH)-P, and an increase in plant-available P can be also obtained. This study indicated that pyrolysis of ferric sludge was a feasible way to simultaneously reduce emission of NOx precursors, reclaim plant-available P, and reuse ferric sludge.

Pre-oxidation is effective in enhancing sludge dewaterability. Different types and doses of oxidants are used to improve sludge dewaterability in pre-oxidation. Rapid evaluation of the sludge dewaterability is vital for optimizing the type and dose of oxidants in pre-oxidation. It normally takes more time to evaluate sludge dewaterability by measuring typical indicators such as specific resistance to filtration (SRF), content of bound water, and composition of EPS. This study presented a rapid parameter, oxidation-reduction potential (ORP), to correlate it with the dewaterability of pre-oxidized sludge samples. An index of ΔORP (ΔORP = ORPt=0.5 min–ORPt=0 min) showed positive correlations with SRF (r = 0.89, p

Mn-containing sludge from groundwater treatment was converted to magnetic particles (MPs) via a one-step hydrothermal method using sodium ascorbate (SA) as the reductant. The MPs were characterized by X-ray diffraction spectroscopy, Mossbauer spectroscopy, X-ray fluorescence spectroscopy, magnetometry and Gran titration and the results showed that magnetic jacobsite was obtained as an intermediate product in transformation of Fe/Mn oxides to siderite and rhodochrosite. When the molar ratio of SA to Mn in the sludge was two, the produced MPs-2 contained a mixture of ferrihdyrite, hematite, jacobsite and Si/Al oxides, and could magnetize at 2.4 emu/g. Ferrihydrite content in MPs decreased with increase of the SA/Mn molar ratio, leading to decrease of the surface sites concentration (Hs). Thus, MPs-2 contained optimized Hs of 6.7 mmoL/g and a desirable adsorption capacity of Cu(II) (73.1 mg/g). The adsorption isotherms of MPs-2 on Cu(II) complied with the Langmuir model and the adsorption kinetics fitted well with the pseudo-second-order model. The major mechanism of adsorption was cationic exchange of the coordinated H and Na ions on MPs-2 surface sites with the Cu(II) ions. This study was the first time to report preparation of MPs by recycling Mn-containing sludge, which could be used as a high-capacity and low-cost adsorbent in treatment of heavy metal-containing wastewater.

How to exert the value-added superiority was a key link in the development of biomass valorization that heightens an appeal for a waste-minimized protocol. The fractional use of three building blocks in biomass became an urgent challenge to be faced. Herein, we report an autohydrolysis-aided biorefinery for the sequential conversion of wheat straw hemicelluloses, cellulose and lignin into xylooligosaccharides (XOS), fermentable glucose and lithium-sulfur cathode at the end of the process, respectively. The yield of XOS (DP of 2–6) reached up to 24.06% (w/w) of xylan and 6.19% (w/w) of the initial biomass. The hydrothermal treatment removed the amorphous portion and disrupted the rigid structure, thereby improving the cellulose digestibility from 14.1 to 88.9%. The molecular weights, functional groups and structural features of residual lignin after enzymatic hydrolysis were thoroughly explored for the cathode of lithium-sulfur batteries via the carbonizing process. Because of the considerable surface area, the covalent linkage between the lignin-derived carbon (LC) and sulfur, and the uniform dispersion of sulfur particles, the developed LC@S cathode exhibited excellent rate capability, and the specific capacity of 1238, 1085 and 1035 mA h g−1 at 0.1, 0.2 and 0.5 C, respectively. The LC@S cathode retained 596 mA h g−1 after 200 cycles at 0.5 C with a coulombic efficiency of 92%. The present study provides a systematic strategy that bears the primary responsibility for exploiting biomass into a potential feedstock with worthwhile functions in the thriving domains of chemicals, biofuels and energy storage devices.

Novel PbO@C composite is synthesized through an optimized mechano-chemical method and used as negative active materials for enhanced performance of lead-carbon battery. Mechanical ball-milling of solid lead acetate, sodium hydroxide and carbon additives (Vulcan-72) would generate uniform composite of lead oxide and carbon (PbO@C) via chemical reactions and mechanical dispersion. The constant mechanical impact and friction during ball-milling leads to lattice distortion and enables intimate connection between Pb and C in the synthesized PbO@C composite, which is proved to be critical for the enhanced battery performance. The specific capacity is higher than battery with direct addition of carbon as additives (126.5 vs. 118.9 mAh g−1), and the cycle performance under high rate partial-state-of-charge duty is also improved. Batteries with the utilization of PbO@C composite accomplished 15119, 11296, 9882, 8336 and 7038 cycles within five consecutive cycle-sets of cycle test, with a decreasing rate of 19.12%, which was drastically lower than battery with direct addition of VC 72 (30.14%). The proposed research provides a promising strategy for feasible synthesis of negative active materials for lead-carbon batteries.

The nitrogen-containing gases pyrolyzed from sewage sludge can be converted into NOx compounds, which would cause severe environmental pollution. This study developed a new strategy to reduce the emission of NOx precursors such as ammonia (NH3) and hydrogen cyanide (HCN) using red mud. The highest reduction efficiencies (15.10% for NH3 and 24.72% for HCN) were achieved at 900 °C while compared with those pyrolyzed from raw sludge without the addition of red mud. The transformation and distribution of nitrogenous compounds in three-phase pyrolysates were studied at 400–800 °C for pyrolysis process of a model soybean protein compound. The nitrogenous compounds, i.e., amine-N, heterocyclic-N, and nitrile-N, were identified as the three main intermediates related with the production of NOx precursors. Ferric oxide (Fe2O3) and calcium oxide (CaO) presented in red mud were identified as the driving force which facilitated nitrogen stabilization in char (e.g., at 800 °C, 21.63% increase of char-N after addition of Fe2O3, and 41.54% increase of char-N after addition of CaO). These metal oxides possibly reacted with protein-N to form FexN and CaCxNy, inhibited the secondary cracking of amine-N compounds in tar (e.g., at 800 °C, 2.33% increase of amine-N after addition of Fe2O3, and 0.38% increase of amine-N after addition of CaO), and reduced the production of nitrile-N (e.g., at 800 °C, 30.41% reduction of nitrile-N after addition of Fe2O3, and 27.40% reduction of nitrile-N after addition of CaO) and heterocyclic-N compounds (e.g., at 800 °C, 21.60% reduction of heterocyclic-N after addition of Fe2O3, and 13.98% reduction of heterocyclic-N after addition of CaO). Hence, the emission of NH3 and HCN in gas phase can be controlled. Moreover, Fe2O3 showed better capability in controlling the emission of NOx precursors than CaO (higher reduction of NH3-N and higher reduction of HCN-N). These results indicate that red mud is an efficient catalyst to reduce emission of NOx precursors through controlling intermediates at 400–800 °C.

Cell lysis in sludge pretreatment by advanced oxidation process (AOP) has a great effect on sludge dewaterability. Cell lysis caused by reactive radicals (e.g. hydroxyl radical) was dependent on the reaction site of AOP. However, little is known about the accurate radical generation site of AOP in sludge pretreatment. In this study, two kinds of oxidation behaviors from different oxidants (HOCl vs. H2O2) catalyzed by ferrous iron were comparatively investigated. Higher amount of living cells (84.3%) and hydroxyl radicals (9.86 × 10−5 M), and more fragmentized sludge flocs (particle sizes of D50 was 50.1 vs. 57.3 μm of RS) were detected in sludge conditioned by Fe2+/H2O2, which implied that Fenton reaction mainly happened at surface and outside of sludge flocs (such as EPS layer and liquid phase). Thus, it could be regarded as “extracellular oxidation”. Fewer living cells (undetectable), fewer amount of hydroxyl radicals (undetectable in sludge), and more integrated sludge flocs (particle size of D50 was 56.1 vs. 57.3 μm of RS) were determined in sludge conditioned by Fe2+/Ca(ClO)2. Hence, it could be regarded as “Intracellular oxidation”. In addition, sludge pretreatment based on Fe2+/Ca(ClO)2 could achieve simultaneous deep-dewatering performance and total coliforms inactivation. Based on response surface methodology, the optimal dosages of Fe2+ and Ca(ClO)2 were proposed as 106.1 and 234.5 mg/g volatile solids respectively, without any acidification of sludge. Under these optimal dosages, the water content of dewatered sludge cake was 51.9 ± 0.1 wt% and the pH of the final filtrate was 5.8 ± 0.2. Total coliforms of sludge could be inactivated in 10 s after Fe2+/Ca(ClO)2 addition.

As the biological recognition element of microbial fuel cell (MFC) toxicity “shock” sensors, the electrode biofilm is perceived to be the crucial issue that determines the sensing performance. A carbon felt and indium tin oxide (ITO) film anode were utilized to examine the effects of anodic biofilm microstructure on MFC toxicity sensor performance, with Pb2+ as the target toxicant. The carbon felt anode based MFC (CF-MFC) established a linear relationship of Pb2+ concentration (CPb2+) vs. voltage inhibition ratio (IR2h) at a CPb2+ range of 0.1 mg L−1 to 1.2 mg L−1. The highest IR2h was only 38% for CF-MFC. An ITO anode based MFC (ITO-MFC) also revealed a linear relationship between CPb2+ and IR2h at CPb2+ of 0.1 mg L−1 to 1.5 mg L−1 but better sensing sensitivity compared with the CF-MFC. The IR2h of ITO-MFC gradually approached 100% as CPb2+ further increased. The enhanced sensing sensitivity for the ITO anode possibly originated from the thin biofilm that resulted in the efficient exposure of exoelectrogens to Pb2+. The employment of 2D conductive metal oxide with a smooth surface as the anode was able to increase the MFC sensing reliability in real wastewater.

Bio-electro-Fenton (BEF) system holds great potential for sustainable degradation of refractory organics. Activated carbon (AC) air cathode was modified by co-pyrolyzing of AC with glucose and doping with nano-zero-valent iron (denoted as nZVI@MAC) in order to promote two-electron oxygen reduction reaction (2e- ORR) for enhanced oxidizing performance. Single chamber microbial fuel cells (SCMFCs) with nZVI@MAC cathode was examined to degrade landfill leachate. It was revealed that nZVI@MAC cathode SCMFC showed higher degradation efficiency towards landfill leachate. Six landfill leachate treatment cycles indicated that nZVI@MAC cathode SCMFC exhibited higher COD removal efficiencies over AC and nZVI@AC and greatly enhanced columbic efficiency compared to AC and nZVI@AC cathode. Anti-biofouling effect was found on nZVI@MAC cathode because of the high Fenton oxidation effects at the vicinity of the cathode. Electrochemical characterizations indicated that MAC cathode had superior 2e- ORR capability than AC and nZVI@AC cathode, which was further evidenced by higher H2O2 production from nZVI@MAC cathode in SCMFC. Graphitic structure of MAC was evidenced by High Resolution Transmission Electron Microscopy, and glucose pyrolysis also resulted in nano carbon spheres on the activated carbon skeletons. Raman spectra indicated more defects were generated on MAC during its co-pyrolyzation with glucose.

An integrated two-step process, comprising vacuum chlorinating and hydrothermal synthesis, is developed for direct recovery of the three-dimensional lead sulfide (PbS) dendrite product from the lea...

A hybrid electrochemical conditioning strategy for enhanced sewage sludge dewatering was proposed. A water content of 47.2 wt.% for the dewatered sludge cake was achieved at an applied voltage of 20 V for 30 min, which was significantly lower than previously reported results. The capillary suction time (CST) and specific resistance to filtration (SRF) were decreased by 75.6% and 90.9%, respectively. Four simultaneous processes, including electrooxidation, the electro-Fenton process, molecular oxygen activation via zero valent iron (ZVI) and Fe(III) flocculation, had synergetic effects on the degradation of extracellular polymeric substances (EPS) to enhance sludge dewaterability. The in situ generation of ZVI on the cathode electrode facilitated the reduction of Fe(III) to Fe(II) via activation of molecular oxygen. The sludge pH decreased spontaneously and remained acidic due to the competitive reaction of ZVI generation to hydrogen evolution as well as the Fe(III) flocculation process, which further guaranteed the high efficiency of hydroxyl radical generation. Changes in the physiochemical properties of the sludge (particle size distribution, zeta potential, viscosity and EPS characteristics) induced by the hybrid conditioning process were further explored. In addition, the economic potential of the hybrid system was preliminarily assessed (USD$ 127.6/ton dry sludge).

Microbial fuel cell (MFC) sensor exhibits attractive prospects for online monitoring of water toxicity as an early warning device. However, the accumulation of dead cells in anode biofilm might decrease the sensing sensitivity of MFC during long term operation. In addition, with repeated exposure to toxins, the microbial community of anode biofilm would also adjust to build up higher endurance to environmental toxicity. In this study, the long term sensing sensitivity of MFC sensor and the microbial community changes were characterized with Pb2+ as the target toxin. The results show that newly formed biofilm with higher live/dead cell ratio exhibited higher sensitivity than mature biofilm. Modification of anodic biofilm via high current stimulation was applied to increase the ratio of live cells, which led to enhanced sensing sensitivity of MFC with mature anode biofilm. However, the enhancement was relatively limited for biofilm that was previously exposed to repeated Pb2+ shocks. Microbial community analysis revealed that the proportions of microbial species possessing higher environmental robustness, such as Hyphomicrobiaceae and Cloacibacillus, significantly increased in the anode biofilm after long term repeated Pb2+ shocks.

Oxidation ditches (ODs) are often used for wastewater treatment. However, limitations of ODs like high energy expenditure and increased sludge sedimentation hinder its wide application. In this study, the computational fluid dynamics (CFD) model integrated with Activated Sludge Model No. 2 (ASM2) was proposed and applied in a full-scale OD. The integrated model provided heterogeneous information on the characteristics of hydrodynamics and biokinetics of OD, especially with respect to the simulation of total phosphorus removal by CFD-ASM2 integration model for the first time. The simulated values of flow velocities, suspended solids (SS), dissolved oxygen, chemical oxygen demand, total nitrogen, ammonium nitrogen, and total phosphorus concentrations were well validated with the measured results, with the standard deviation errors of less than 5.56%, 0.28%, 0.74%, 7.39%, 3.17%, 5.27%, and 7.40%, respectively. Based on the integrated model, four different operational strategies were simulated. The proposed operational strategy of operating 7 surface aerators and 10 submerged impellers not only met the standard discharge requirements (GB 18918-2002) but also consumed less energy by 22.3%, compared with the original strategy of operating 9 surface aerators and 13 submerged impellers. Meanwhile, this proposed operational strategy also reduced the SS concentrations in the second and fourth channels, which was beneficial to elimination of sludge sedimentation. Moreover, the proposed operational strategy was successfully applied and validated in full-scale OD. The foregoing results collectively suggest that the CFD-AMS2 integration model is numerically capable to optimize the operational strategy of ODs.

How to efficiently improve waste activated sludge (WAS) dewaterability is a common challenge in WAS treatment and management throughout world. The interaction energy of sludge flocs is of great importance for sludge dewaterability. In this study, the relationship among the repulsive force of sludge flocs, hydrophilic/hydrophobic characteristics of sludge flocs, and sludge dewaterability have been quantitatively and qualitatively investigated based on extended Derjaguin-Landau-Verwey-Overbeek theory for the first time. The energy barrier of sludge flocs has good correlations with sludge dewaterability (p 0.05). Trivalent cations (Al

A hybrid sludge conditioning strategy with electrooxidation and Fe(II) addition was used for heavy metal removal from sewage sludge and industrial sludge, with simultaneous sludge dewatering and stabilization. With the addition of 82 mg/g DS Fe(II) and treatment time of 4.5 h, heavy metal removals of 72.95% and 78.49% for Cu, 66.29% and 84.26% for Zn, and 36.52% and 36.99% for Pb were achieved from sewage sludge and industrial sludge samples respectively. The system pH decreased to 2.33 and 2.98 and the oxidation–reduction potential (ORP) values increased to 435.90 mV and 480.60 mV in sewage sludge and industrial sludge samples, respectively, which was conducive to the desorption and dissolution of heavy metals from sludge structures and the degradation of the organic compounds that complexed with heavy metals. In addition, the hybrid conditioning process demonstrated excellent dewatering performance due to the efficient electrochemical disintegration of sludge flocs together with the coagulation of sludge particles by Fe(III) generated via electrooxidation. The strong acidic and oxidative environment produced by the enhanced electrooxidation process was also responsible for pathogen inactivation.

Over half of century, sanitary landfill was and is still the most economical treatment strategy for solid waste disposal, but the environmental risks associated with the leachate have brought attention of scientists for its proper treatment to avoid surface and ground water deterioration. Most of the treatment technologies are energy-negative and cost intensive processes, which are unable to meet current environmental regulations. There are continuous demands of alternatives concomitant with positive energy and high effluent quality. Microbial fuel cells (MFCs) were launched in the last two decades as a potential treatment technology with bioelectricity generation accompanied with simultaneous carbon and nutrient removal. This study reviews capability and mechanisms of carbon, nitrogen and phosphorous removal from landfill leachate through MFC technology, as well as summarizes and discusses the recent advances of standalone and hybrid MFCs performances in landfill leachate (LFL) treatment. Recent improvements and synergetic effect of hybrid MFC technology upon the increasing of power densities, organic and nutrient removal, and future challenges were discussed in details.

Large amounts of microplastics accumulate in the agricultural soil. Microplastics would stress the crops but the underlying mechanism remains unclear. Herein, a laboratory exposure and field trials were carried out to investigate the response of rice (Oryza sativa L. II You. 900) to stress induced by polystyrene microplastics (PS-MPs) using a metabolomic approach. After laboratory exposure for 21 days, the decreases in shoot biomass of rice exposed to low, medium and high doses of PS-MPs were 13.1% (CV = 4.1%), 18.8% (CV = 3.7%), and 40.3% (CV = 9.2%), respectively, while the antioxidant enzymes showed an inverted upper-U shape when exposed to PS-MPs. A total of 24 samples from three exposure dose levels were included in the metabolic analysis. The metabolites of 12 amino acids, 16 saccharides, 26 organic acids and 17 others (lipids and polyols) in leaves decreased after the exposure to both 50 mg L−1 and 250 mg L−1 PS-MPs doses with hydroponically-cultured. The inhibition of perturbed biological pathway causes the biosynthesis of amino acids, nucleic acids, fatty acids and some secondary metabolites decreased which indicate that the energy expenditure exceeded the substance accumulation. In order to further validate the effects of PS-MPs on rice leaves obtained from the laboratory-scale experiments, a field-trial experiment was conducted. After 142 days of cultivation in farmland, the results with a maximum of 25.9% lower biomass in the crops exposed with PS-MPs. As such, the presence of PS-MPs may affect rice production by altering the metabolic systems of rice. Long-term exposure of PS-MPs to rice might be a potential risk to rice safety and quality.

In this study, the efficiency of the combined zerovalent iron (ZVI) and ozone (O3) treatment at a pH of 2 (acid-ZVI-O3) for simultaneous improvement of sludge dewaterability and pathogen inactivation was investigated. The results showed that the ozone treatment alone deteriorated sludge dewaterability, while the introduction of acid-ZVI into the ozone treatment could significantly enhance the sludge dewaterability. At the optimal conditions with 30 mg O3 g–1 of total solid (TS) and 63 mg ZVI g–1 of TS at a pH of 2, the capillary suction time of conditioned sludge was 1.63 s L g–1 TS, which was much smaller than those of raw sludge (10.45 s L g–1 TS), the single ozonation treated sludge (16.07 s L g–1 TS), and the acid-ZVI-treated sludge (6.98 s L g–1 TS). The acid-ZVI-O3 treatment promoted the generation of hydroxyl radicals and showed synergistic effects in removing key hydrophilic substances which would deteriorate sludge dewaterability, i.e., humic acid-like compounds and soluble microbial byproduct-li...

Cadmium (Cd) in soil was stabilized using copper loaded attapulgite (Cu/ATP) in a microwave (MW) system. Excellent Cd stability in soil was achieved with Cu/ATP addition due to higher adsorption energy (1.38 eV) of Cu/ATP for Cd than that of ATP (∼1 eV), confirmed by density functional theory calculations. The strong hybridization of the s, p-orbitals of Cd with the s, p, d-orbitals of Cu on ATP contributed to the strong interactions between Cd and Cu/ATP. The stability performance of Cd in Cu/ATP-treated soil was further enhanced after MW irradiation through a series of phase transformation to more stable Cd-bearing crystalline minerals. The transformation was initiated by MW-induced "hot spots", which created cationic vacancy on Cu/ATP surface and enhanced the solid-state reactions between Cd and Cu/ATP framework. The total bond orders of Cd in the formed CdAl4O7 crystalline mineral elevated to 3.38, which was 5-fold higher than that for Cd on Cu/ATP, ensuring the long-term stability of Cd even after 360 curing days. Cd contaminated soil from a former industrial electroplating site was successfully stabilized with the proposed strategy. The research provides an effective stabilization strategy as well as a comprehensive understanding of the mechanism of long-term Cd stabilization.

A method to improve bromine fixation by co-pyrolysis of non-metallic fractions (NMFs) of waste printed circuit boards (WPCBs) with Bayer red mud (RM) has been developed. More than 78.59 wt% of bromine was fixed into the solid residues with an addition of 15 wt% RM after co-pyrolysis at 500 °C, comparing with 36.42 wt% without the RM addition. Metal oxides (Fe2O3, Al2O3, TiO2, and Na2O, etc.) in the RM contributed significantly to the bromine fixation. The bromine fixation percentages were 62.94, 65.05, 47.24, and 49.05 wt% with an individual addition of 15 wt% Fe2O3, Na2O, Al2O3, and TiO2, respectively. Metal oxides in the RM showed synergistic effects on the bromine fixation, and this can be attributed to the secondary reaction of Na2O and bromine decomposed from FeBr3. The mechanisms of bromine fixation by RM are formation of Br-M (M: Fe, Al, Ti, and Na) and O H bonds generated from the direct elimination and a two-step of dissociative adsorption and β-H elimination reactions between metal oxides and bromide.

A delaminated MXene-bismuth (Bi@d-Ti3C2) nanocomposite was synthesized for the construction of a microgrid electrochemical sensor via mechanical milling. The Bi@d-Ti3C2 nanocomposite was synthesized by accumulation of Bi(III) on the surface of delaminated Ti3C2 nanosheets through electrostatic attraction and subsequent in-situ growth of bismuth nanorods. Under optimized experimental conditions, the sensor exhibits (a) linear responses to Pb(II), Cd(II) and Zn(II) in the concentration range from 1 to 20 μg L−1, (b) well separated peak potentials at −0.54 V, −0.76 V and − 1.15 V vs. Ag/AgCl, (c) sensitivities of 0.98, 0.84 and 0.60 μA L μg−1, and (d) detection limits of 0.2, 0.4 and 0.5 μg L−1, respectively. This performance is attributed to the uniform dispersion of Bi nanorods on electrically conductive delaminated Ti3C2 MXene, and to the enhanced diffusion due to the microgrid structure.

During advanced oxidation treatment for enhancing sludge dewaterability, the peptide chains of protein can be decomposed into amino acids. Protein exhibits a great impact on sewage sludge dewaterability. However, the role of amino acids in sludge dewatering remains unclear. In this study, among the 23 types of amino acids investigated, tryptophane (Trp) and lysine (Lys) were identified as the key amino acids affecting sludge dewaterability during Fenton oxidation treatment. The content of lysine showed positive correlations with capillary suction time (CST), specific resistance to filtration (SRF), and bound water content, and the concentrations of total protein, low molecular weight protein, amines and amides, and 3-turn helix of proteinaceous compounds in bound extracellular polymeric substances (EPS), while the content of tryptophane showed negative correlations with the above parameters. The amino acids may be sourced from damage of the membrane and ribosomal proteins by hydroxyl radicals, and the peptide bonds connected with tryptophane were more inclined to be decomposed than other amino acids. Particularly, more amino acids of tryptophane can result in more hydrophobic interaction, and less necessary energy barrier for aggregation of particles. As such, regulating protein degradation towards production of tryptophane may be related with enhanced sludge dewaterability by Fenton oxidation treatment.

Fe3O4@SiO2-NH2 magnetic particles with core-shell structure were attached on carboxylated biochar derived from phoenix tree leaves to synthesize a novel magnetic biochar for removing Cr(VI) ions from acidic solutions. FSEM, FTEM, XRD characterizations of the synthesized magnetic biochar revealed that the Fe3O4@SiO2-NH2 magnetic particles distributed uniformly on the surface or macrospores of carboxylated biochar by strong chemical bonding. The Cr(VI) ions adsorption capacity of magnetic biochar was 27.2mg·g-1, surpassing original carboxylated biochar (18.2mg·g-1). VSM and XPS characterizations demonstrated that the attached Fe3O4@SiO2-NH2 magnetic particles not only endowed biochar with perfect magnetic property (23emu·g-1) but also provided complexing sites for binding Cr(III) cations reduced from Cr(VI) anions. The Cr(VI) ions removal by magnetic biochar contained three steps: (1) adsorption of Cr(VI) anions by protonated functional groups; (2) reduction of Cr(VI) anions to Cr(III) cations by electron-donor groups; and (3) chelation of Cr(III) cations by amine groups. The adsorption recycling test showed that magnetic biochar kept 85% of its initial Cr(VI) adsorption capacity at the sixth cycle, and the Fe leakage under pH1.0 was smaller than 0.25mg·L-1. The results indicated that this novel magnetic biochar was applicable for the practical treatment of Cr(VI)-containing wastewater.

Electro-dewatering (EDW) is an energy-efficient method for sludge dewatering. In this study, effects of piecewise electric field operation on EDW were investigated by experiments and simulation. Operational parameters were studied mainly in terms of sludge resistance variation during electro-dewatering process, which were evaluated by linear sweep voltammetry (LSV) analysis. Simulation of the sludge cake electro-dewatering processes was developed and validated, based upon time-dependent experimental data of electric currents and filtrate weights. The modeling results were in good agreement with experiments. It was proved by experimental and modeling results that the piecewise operation has positive effects on key performances of EDW devices, that is, limited water content, space-time yield, and mass specific energy consumption.

Rational design and facile synthesis of thiol-modified metal–organic frameworks (MOFs) for the efficient capture of highly toxic mercuric ions from water has attracted great attention. However, the corresponding adsorption mechanism is not well understood. In this paper, a thiol-modified Zr-based MOF (Zr-DMBD) with free-standing and accessible thiol groups was prepared. It exhibited remarkable performance in the capture of Hg(II), and its maximum adsorption capacity was 171.5 mg·g–1, approximately 9 times that of the pristine UiO-66. Impressively, the maximum value of the selective coefficient was as high as 28899.6. Additionally, 99.64% of Hg(II) could be eliminated by Zr-DMBD from the actual wastewater, rendering the concentration of Hg (II) below 0.05 ppm (Emission Standard of Mercury (GB30770-2014)). The excellent adsorption capacity and outstanding selectivity were ascribed to the remarkable coordination between S2– and Hg(II), as supported by the results of FT-IR and XPS. Unexpectedly, a good correl...

The catalytic mechanism of red mud (RM) on the pyrolysis of sewage sludge was investigated. The thermogravimetric data were used to study the kinetic characteristics by using a discrete distributed activation energy model (DAEM) to clarify the effects of three main components (Fe2O3, Al2O3, SiO2) in the RM on the pyrolysis of organic matters in sewage sludge. The modeling results showed that the pyrolysis of organic matters, especially at the higher temperature stage, was promoted by Fe2O3 and Al2O3 in the RM. Adding Fe2O3 or the RM alone could reduce the mean activation energy of sewage sludge pyrolysis by 13.9 and 20.1 kJ mol−1, respectively. The modeling results were validated by pyrolysis experiments of raw sludge with different additives at 600, 700, 800, and 900 °C. The experimental results showed that the addition of Al2O3, Fe2O3 or the RM could produce more gas than the addition of SiO2, especially at high temperatures. Fe2O3 and Al2O3 acted as catalysts in the tar decomposition by in-situ catalyzing the cracking of C C and C H bonds to produce more gases. Especially, Fe2O3 and Al2O3 increased the H2 yield from sewage sludge pyrolysis at 700, 800, and 900 °C by 268.5 and 50.7%, 111.1 and 56.0%, 10.9 and 10.3%, respectively. The char obtained from pyrolysis of sewage sludge with the RM possessed magnetic property, which has various potential applications. The research indicates that the RM is an efficient catalyst in the pyrolysis of sewage sludge.

Water from different sources generally contains different kinds of suspended particles, which introduces the challenge of how to control physical clogging during managed aquifer recharge (MAR). Suspended solid concentration (SS) and turbidity (NTU) are widely recognized as indicators of physical clogging potential. The aims of this study were to examine the degree of physical clogging caused by organic and inorganic suspended particles and elaborate the different mechanisms that controlled clogging under specific SS and NTU conditions. Column experiments were performed by continuous suspended particle injection through a saturated porous medium under stable physicochemical and hydrodynamic conditions. Three sets of transport tests were carried out. One test was conducted with chlorinated-secondary wastewater (CSW), which SS was 17.59 ± 0.44 mg L−1 corresponding to 3.09 ± 0.05 NTU. The other two tests were silica-particle wastewater (SPW) with the same SS (1.73 ± 0.03 NTU) and the same NTU (29.21 ± 0.57 mg L−1 SS) as the CSW, abbreviated to SPW-SS and SPW-NTU, respectively. The particle breakthrough curves (BTCs), spatial deposition profiles, and variations in hydraulic conductivity were measured. The transport model, DLVO theory, and O’Melia and Ali clogging model were applied to explain the mechanisms of physical clogging in different systems. The retention of inorganic particles was greater than that of organic particles; 56.02% of organic particles were retained in CSW, while 87.62 and 86.36% of inorganic particles were retained in SPW-SS and SPW-NTU, respectively. The distribution of organic particles was less uniform than that of inorganic particles. However, the variation of the relative hydraulic conductivity (K/K0) was more significant for organic particles than for inorganic particles, with decreased by just 1.80 ± 0.64% in SPW-SS and 4.03 ± 1.64% in SPW-NTU, but decreased by 85.86 ± 1.22% in CSW. This study explained the results with the support of classical models and the DLVO theory. The physicochemical characteristics of suspended particles determined whether and how physical clogging occurred. Suspended particles with different properties follow different transport-deposition processes and have different tendencies to cause physical clogging. Especially for organic particles, clogging degree is quite noticeable. Our results imply that the same SS and NTU threshold values cannot be applied to different types of source water during recharge to prevent physical clogging, even in the same controlled environmental conditions. Physicochemical characteristics of suspended particles need to be considered when developing physical clogging indicators.

A complex chitosan/β-cyclodextrin polymer was synthesized by bridging with maleoyl chains followed by cross-linking with glutaraldehyde. The adsorption performance of the synthetic polymer was investigated for selective removal of methyl orange (MO) from aqueous solution. The kinetic behavior was well fitted by the pseudo-second order model, while the adsorption process at equilibrium followed the Langmuir isotherm model. The thermodynamic parameters suggested that the adsorption was exothermic and spontaneous. Under optimal adsorption conditions, the capacity for MO reached 392mg/g with the dosage of 10mg/50mL. Based on the analysis from FTIR, 1H NMR, TGA and zeta potential, the adsorption mechanism could be explained by the synergistic effect of electrostatic attraction of amino groups from chitosan and host-guest interaction from β-cyclodextrin. This adsorbent also demonstrated high selectivity towards MO due to the unique structure of cross-linked chitosan/β-cyclodextrin polymer that are complementary to that of MO molecule.

Microbial fuel cells (MFCs) are promising biotechnologies tool to harvest electricity by decomposing organic matter in waste water, and the anode material is a critical factor in determining the performance of MFCs. In this study, chestnut shell is proposed as a novel anode material with mesoporous and microporous structure prepared via a simple carbonization procedure followed by an activation process. The chemical activation process successfully modified the macroporous structure, created more mesoporous and microporous structure and decreased the O−content and pyridinic/pyrrolic N groups on the biomass anode, which were beneficial for improving charge transfer efficiency between the anode surface and microbial biofilm. The MFC with activated biomass anode achieved a maximum power density (23.6 W m−3) 2.3 times higher than carbon cloth anode (10.4 W m−3). This study introduces a promising and feasible strategy for the fabrication of high performance anodes for MFCs derived from cost-effective, sustainable natural materials.

Spent lithium ion batteries are potential environmental hazards and if not re-cycled waste natural resources. One of the difficulties for recovery is the recycling cost high and restricting the economic drivers. In this research, a process is developed to directly reuse nickel-manganese-cobalt oxides from spent lithium ion batteries to prepare air electrodes based on a simple thermal treatment method. 100% value metals (cobalt, nickel and manganese) were regenerated from the cathode. By heated at 600 °C, the Ni-Co-Mn oxides experienced a significant phase change from an α-NaFeO2-type structure to spinel structure. Electrochemical tests revealed that the regenerated nickel-manganese-cobalt oxides exhibited remarkable bifunctional catalytic activities towards the oxygen evolution and oxygen reduction reactions in aqueous KOH electrolyte. The nickel-manganese-cobalt oxide powders were applied in an air battery, the energy efficiency was 75% at a current density of 10 mA cm−2, which was better than commercal zinc-air batteries.

In this study, we compared the transport characteristics of Bacillus subtilis cells and their spores in saturated porous media. Both the bacteria cells and spores were readily transported under lower ionic strengths (IS) (1 mM), featuring high mass recovery rates (> 75%). The bacteria cells recovery rate declined to 58.05% when the IS increased to 100 mM; but the spores recovery rate remained at 74.54%. Spores appear to be more mobile than bacterial cells over wide range of IS. Surface properties and breakthrough curves analysis of the two bio-particles (cells and spores) indicated that attachment, straining and blocking mechanisms contribute differently to deposition processes. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory further indicated that the particles attachment may primarily occurred at the secondary energy minimum. More important, XDLVO calculations showed that the dominant forces changed with IS, altering the efficiency of particles attachment. The electric double layer repulsion mainly controlled particle deposition at 1 mM. In contrast, the van der Waals attraction and Lewis acid-base interactions dominated particle deposition at 100 mM. This study showed that spores are more mobile than bacteria cells in subsurface environment. Given that spores form under harsh environmental conditions, we must consider spore formation and transport when groundwater microbial contamination occurs.

NiMn layered double hydroxide (NiMn LDH) and NiMn LDH/reduced graphene oxide (rGO) with flower-like 3D composite were synthesized by a simple solvothermal process. The electrochemical properties of NiMn LDH/rGO composite with different contents of rGO were studied, resulting in enhanced capacitance due to the incorporation of rGO compared with pristine NiMn LDH. The NiMn LDH/rGO composite containing 4.46 wt% rGO (LDH/rGO-4) exhibited the highest specific capacitance of 1500 F g −1 at 1 A g −1 with an excellent cyclic stability of 90.5% over 5000 charging and discharging cycles at 20 A g −1 . The asymmetric supercapacitor assembled with LDH/rGO-4 and rGO electrodes exhibited a high specific capacitance of 82.5 F g −1 at 0.5 A g −1 and superior energy density of 29.3 Wh kg −1 . These results illustrate that the LDH/rGO-4 composite is a promising material for supercapacitor applications.

The ZnO/g-C 3 N 4 photocatalyst was prepared by ball milling and demonstrated enhanced photocatalytic degradation of RhB under visible light irradiation. The photocatalyst is consisted of ZnO and g-C 3 N 4 heterojunctions formed by the shear stress during the mechanical treatment. The addition of g-C 3 N 4 can improve the photocatalytic performance of ZnO under visible light. The heterojunction formed between ZnO and g-C 3 N 4 decreased the recombination rate of photogenerated carriers and improved the photocatalytic activity of the ZnO/g-C 3 N 4 hybrids. The optimal ZnO/g-C 3 N 4 photocatalyst with 10 wt% g-C 3 N 4 showed a degradation efficiency of 51.3% for RhB under visible light, which is 2.1 times higher than that of pristine ZnO. The electron paramagnetic resonance (EPR) measurement showed that the OH radicals are the dominant active species in photocatalytic process under both full solar spectrum and visible light irradiation. And the OH radical generation is much more efficient under full solar spectrum than that under visible light due to the UV response of ZnO. This work provides a simple method for the design and preparation of novel heterojunction photocatalysts.

In this study, the influence of Na2SO4 on electro-dewatering (EDW) of waste activated sludge (WAS) was investigated. The highest water removal efficiency of 42.5% was achieved at the optimum Na2SO4 dosage of 12.5 g kg−1 DS during EDW process at a constant voltage of 20 V. The migration and distribution of water, organic matters and Na+ at different Na2SO4 dosages were investigated through layered experiments. The results indicated the entire EDW process followed the S curve model, and it can be divided into three stages: (1) initial desalination stage: at the initial few min of EDW process, the rate of electroosmosis was extremely slow while electromigration of ions like Na+ was intense, and the electromigration was more obvious with increased Na2SO4 dosage; (2) dewatering stage: the dewatering efficiency increased dramatically via electroosmosis; (3) the dewaterability limit stage: the maximum value of dewatering efficiency has been achieved, while the water removal efficiency and dry solids content remained constant. During the EDW process, the possible electrolysis resulted in a pH gradient in the sludge cake. With the addition of Na2SO4 in the EDW, the pH gradient was intensified, and the migration rate of organic matters moving from cathode to anode increased while compared with the raw WAS. This study provided insights into the mechanism of EDW process at different dosages of Na2SO4.

Sustained molecular oxygen activation by iron doped silicon carbide (Fe/SiC) was investigated under microwave (MW) irradiation. The catalytic performance of Fe/SiC for norfloxacin (NOR) degradation was also studied. Rapid mineralization in neutral solution was observed with a pseudo-first-order rate constant of 0.2239 min −1 under 540 W of MW irradiation for 20 min. Increasing Fe/SiC rod and MW power significantly enhanced the degradation and mineralization rate with higher yield of reactive oxygen species (ROS). Fe shell corrosion and subsequent Fe 0/II oxidation by molecular oxygen with MW activation was the key factor for NOR degradation through two-electron-transfer by Fe 0 under acidic conditions and single-electron-transfer by Fe II under neutral-alkaline solution. Removal rate of NOR was significantly affected by solution pH, showing higher degradation rates at both acidic and alkaline conditions. The highest removal efficiencies and rates at alkaline pH values were ascribed to the contribution of bound Fe II species on the Fe shell surface due to the hydroxylation of Fe/SiC. ·OH was the main oxidizing specie for NOR degradation, confirmed by density functional theory (DFT) calculations and radical scavenger tests. DFT calculations were conducted on the reaction/activation energies of the transition/final states of NOR/degradation products, combined with intermediate identification with high performance liquid chromatography coupled with a triple-quadruple mass spectrometer (HPLC-MS/MS), the piperazinyl ring was the most reactive site for ·OH attack, followed by further ring-opening and stepwise oxidation. In this study, Fe/SiC were proved to be an excellent catalyst for the treatment of fluoroquinolone antibiotics with MW activation.

In this work, a hierarchical Ni3S2@MoS2 hybrid structure was synthesized by an effective strategy with a combined hydrothermal route and subsequent annealing treatment. When tested as supercapacitor electrodes, the Ni3S2@MoS2 composites exhibited high specific capacitance of 1418.5 F g−1 at 0.5 A g−1, which also showed a good capacitance retention of 75.8% at 5 A g−1 after 1250 cycles. The Ni3S2@MoS2 composites demonstrated 1.9 fold higher specific capacitance compared to the amorphous shell counterpart (NixSy@MoS2). Furthermore, the assembled asymmetric supercapacitor (Ni3S2@MoS2//rGO) also demonstrated a capacitance of 61 F g−1 at 0.5 A g−1, with energy and power densities of 21.7 Wh kg−1 at 400 W kg−1 and 12 Wh kg−1 at 2400 W kg−1 under an operating window of 1.6 V. The asymmetric supercapacitor also showed a favorable cycle stability with 72% capacity retention over 4000 cycles at 10 A g−1. The improved electrochemical performance is attributed to the synergetic effect of the large accessible surface area and optimal contacts between the MoS2 and the electrolyte, as well as high capacitance of the metallic Ni3S2 core.

Kinetic studies on the pyrolysis process for non-metallic fraction (NMF) of waste printed circuit boards (WPCBs) were conducted using both the isoconversional SKAS method and the discrete distributed activation energy model (discrete DAEM). The pyrolysis process of the NMF sample could be classified into three stages, and a large mass loss was observed from 98 to 570 °C, attributed to thermal degradation of epoxy resins in the NMF sample. The kinetic parameters, including activation energies (E i), pre-exponential factors (A i), and contributed fractions (f i,0), were determined. It indicated that the discrete DAEM could predict the pyrolysis process of the NMF more accurately and completely when compared with the isoconversional SKAS method. In the discrete DAEM, E i and A i values were evaluated at 99 equally spaced intervals of conversion. The E i and A i (in the form of lnA i) transformed with reaction progress, ranging from 80.9 to 240.5 kJ/mol and 19.07 to 39.55 s−1, respectively, with the conversion increased from 0.01 to 0.99. The pyrolysis of the NMF of WPCBs could be accurately characterized as 17 dominating reactions from f i,0 results.

Reaction mechanism of one-part geopolymer formation using red mud (RM) was explored in this study. Leaching test, X-ray photoelectron spectroscopy (XPS), Mossbauer spectroscopy and nitrogen isothermal adsorption (NIA) were conducted to study transformations of Na, Al, Si, Fe species, binding energies of Al O and Si O, and pore structure, respectively. The alkali-thermal-activated RM could dissolve in water to release large amounts of soluble Na, Al and Si species for geopolymerization. But more dissolved Si is needed from added silica fume (SF) to form stable geopolymer gels. The binding energies of Al O and Si O bonds in the geopolymer increased with the polymerization of reactive SiO2 and Al2O3. The coordinated Fe3 + in RM played a role like Al3 + by replacing it in the aluminosilicates structure, and exerted no obvious impact on geopolymerization. The dissolved SF took part in the geopolymerization to form dense geopolymer matrices in long-term curing.