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The dramatic increase in global generation of e-wastes has become a great challenge for sustainable development, and strategies for efficient and environmental-friendly recycling and disposal of e-waste are of great demand. A cost-effective strategy of crushing pretreatment combined with pyrolysis to recover metals from waste printed circuit boards (WPCBs) has been developed. Effects of particle size and pyrolysis temperature on metal recovery were explored. The optimal combination of less energy consumption and higher metal recovery was obtained when the pretreated particle size was 4.0 cm and pyrolysis temperature was 330 °C. The Cu and Sn were recovered as zero-valent copper and tin-copper alloy with the recovery efficiency of 92.38 and 99.80 wt%, respectively. Brominated pollutants are easily controlled when pretreated particle size is larger than 2.0 cm and pyrolysis temperature is below 400 °C. Under the optimal crushing pretreatment and pyrolysis conditions, the bromine contents in the pyrolysis products of solid residues, liquid tar, and gas were 45.45 wt%, 38.70 wt%, and 15.85 wt%, respectively. The structure of WPCBs was destroyed at 275–525 °C due to decomposition of brominated epoxy resins (BERs), which could be accurately characterized by 8 dominating reactions through pyrolysis kinetics analysis. The main reactions took place at conversion of 0.14 and 0.15, corresponding to a pyrolysis temperature of 306–342 °C. Thus, the interlayer bonding force of WPCBs significantly decreased, contributing to effective separation of metals in WPCBs.

Modification of exoelectrogens with conjugated polymers is an efficient strategy to improve extracellular electron transfer (EET) from individual cells to electrode. However, due to the hydrophobic nature of conductive polymers, improving cell-electrode adhesion needs to be addressed. In this research, we report the modification of Shewanella oneidensis MR-1 by successively in situ coating individual cells with polypyrrole (PPy) and adhesive polydopamine (PDA). The PPy-PDA modified cells display improved conductivity and adhesion. We employ PPy-PDA modified cells as anode in microbial fuel cells (MFCs) and find that electro-activity of anode is greatly improved as direct EET is improved, and riboflavin secretion which is conducive to indirect EET is enhanced. The maximum power density of MFCs employing PPy-PDA modified cells is 11.8 and 4.8 higher than that of PPy modified and unmodified cells, respectively. Our results indicate this in situ modification of exoelectrogens with PPY-PDA offers a facile and promising strategy for performance improvement of MFCs.

A novel method to enhance sludge dewaterability with ammonium sulfate ((NH4)2SO4) was proposed, and the potential reuse of dewatered sludge cake and filtrate as nitrogen fertilizers was evaluated. Compared with raw sludge, 87.91% reduction of capillary suction time (CST) and 88.02% reduction of specific resistance to filtration (SRF) after adding 80% (m/m) (NH4)2SO4 were achieved, with 38.49% of protein precipitated simultaneously. The (NH4)2SO4 dose destroyed cell membrane, resulting in the release of intracellular water by converting bound water into free water, thus enhancing sludge dewaterability. In the solid phase, the content of protein-N increased, and larger protein aggregates were formed. The (NH4)2SO4 dose destroyed the hydration shell, making proteins to exhibit hydrophobic interactions, and to be aggregated, and precipitated from the liquid phase. When incubated Pennisetum alopecuroides L. with the dewatered sludge cake and filtrate after dewatering and conditioning with (NH4)2SO4, the germination rate of grass seed and shoot lengths both increased while compared with those incubated with dewatered sludge cake and filtrate of the raw sludge. This study might provide insights into sustainable sludge treatment by integrating sludge dewatering and the potential reuse of dewatered sludge cake and filtrate as nitrogen fertilizer via treatment with (NH4)2SO4.

This study investigated the pyrolytic performances of deep-dewatered sludge cakes which were previously conditioned with Fenton's reagent and red mud. The pyrolytic products, including fuel gas, tar and solid char, were characterized by GC, GC-MS and FTIR. The results showed that pyrolysis of sludge cakes conditioned with Fenton's reagent and red mud produced more gas, especially higher H2 yield, compared with pyrolysis of raw sludge. In addition, red mud promoted PAHs formation and tar re-formation through side-chain-cleaving, dehydrogenation, polycondensation and aromatization of hydrocarbon during the pyrolysis, resulting in enhancement of the H2 yield. The sharp decrease in the absorbance of C Haromatic group of chars from the conditioned cakes implied that red mud could intensify the cracking and re-formation of aromatics. The higher the iron oxide content in red mud was, the better catalytic efficiency in the decomposition of organics and tar re-formation was, which led to more H2 production.

The effect of pH was investigated in a hydrometallurgical method for recycling spent lead-acid batteries with citric acid. The pH in this novel procedure was adjusted with a cheap and conveniently available alkalescent reagent-ammonia. The desulphurization efficiency of spent lead paste could be increased dramatically up to 99 wt% at a weaker acidic pH of 5.5, compared with only 20 wt% without pH adjustment using a fixed leaching at more acidic pH of 2.1 for the duration time of 180 min. The mechanism of the improvement of desulphurization efficiency at adjusted weaker acidic pH was proposed as the demolition of the core-shell structure. The dissolution of lead citrate (shell) will make the lead sulphate particles (core) released and available to react. The chemical formula of the lead citrate product was either Pb(C 6 H 6 O 7 )·H 2 O at more acidic pH of 3.3, or Pb 3 (C 6 H 5 O 7 ) 2 ·3H 2 O at weaker acidic pH of 5.5 and 6.2. The pH value will also notably affect the final concentrations of the main impurities in the obtained lead citrate products. A more acidic pH was more favorable for the elimination of the main impurities such as Fe, Ba, Sb, Cu, Zn and Al, by forming soluble species that remained in the leaching solution, which results in cleaner solid lead citrate products. This study has emphasized the availability of pH as a key factor in a novel hydrometallurgical route for recycling spent lead acid batteries.

This article reviews recent studies on the recycling of spent lead paste and describes novel technologies. Although the pyrometallurgical process has been dominant in the secondary lead recycling processes, there has been growing pressure to achieve sustainable greener recycling methods to address the environmental pollution issues caused by emissions of lead particulates and sulfur oxides in the traditional smelting route. The electrowinning process has been studied for many years, but high energy-consumption and emissions of toxic components such as fluoride compounds have caused concerns and hindered rapid growth in industrial application. In last 10 years, many sustainable and environmental friendly processes, such as paste-to-paste recycling and hydrogen-lead oxide fuel cell method have been proposed for recycling spent lead paste from discarded lead acid batteries. Ultrafine leady oxide could be prepared from spent lead pastes via newly developed novel hydrometallurgical routes, and then applied as active materials in the cathode and the anode for making high-performance lead acid batteries. It is a green alternative for recycling of spent lead acid battery and other secondary lead.

Sludge samples taken from different sources and times may have different characteristics that could affect dewatering performance. In this study, 20 sludge samples from five wastewater treatment plants and different seasons in 1 year were characterized. Pearson correlation analysis indicated that solid content (SC), total suspended solid (TSS), polysaccharides and proteins contents had positive correlations with the capillary suction time (CST), whereas volatile suspended–solid/total suspended solid (VSS/TSS) exhibited negative correlations with CST. Moreover, no correlations between CST and specific resistance to filtration were found among these different sludge samples. The principal component analysis confirmed that only two group variables could represent most of the sludge characteristic parameters. The first set of variables represents the particulate nature of the biotic factors (SC, VSS/TSS, SCOD, TSS, polysaccharides and proteins), and the second set is the pH. CST could not be a reasonable indicator of dewaterability in sludge deep dewatering by Fe2+/S2O8 2−-phosphogypsum composite conditioning. Furthermore, the results of diaphragm filter press dewatering showed that initial SC and VSS/TSS were the most dominant sludge characteristics affecting the solid content of dewatered cake (R p = 0.610, p = 0.016; R p = −0.838, p = 0.000, respectively) with Fe2+/S2O8 2−-phosphogypsum composite conditioning. Results from this study suggest that dewatering performance is predictable by sludge characteristics parameters for Fe2+/S2O8 2−-phosphogypsum conditioning.

Electrodeposition and electrodissolution reactions of the Pb2+/Pb electrode were studied on a glassy carbon rotating disk electrode in aqueous solutions of CH3SO3H and Pb(CH3SO3)2. The electrolytic parameters, kinematic viscosity and ionic conductivity, were determined with various concentrations of CH3SO3H and Pb(CH3SO3)2. The diffusion coefficient of Pb2+ in this electrolyte prepared with CH3SO3H was determined by the Levich Equation. Both the concentrations of CH3SO3H and Pb(CH3SO3)2 were found responsible for the equilibrium potential shifts and exchange current density variations. The electrochemical processes at the Pb2+/Pb electrode were identified as being under mixed ohmic-diffusion control. The electrolyte conductivity and the ionic activity of Pb2+ were recognized as important parameters for designing the soluble lead redox flow cells. During constant current charge–discharge measurement, the specific capacity of the Pb2+/Pb electrode was about 253 mAh g−1Pb, about 98 % of the theoretical value. The impurity elements Fe, Ba, Al, and Zn in the Pb2+ electrolytes prepared with recycled lead exhibited insignificant influences on the Pb2+/Pb reactions. It is reasonable to believe that the recycled lead can be applied in soluble lead redox flow batteries, and the cost may be further reduced with recycled lead because expensive impurity-control processes seemed to be avoidable.

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.

One-part geopolymer was synthesized from alkali–thermal activated Bayer red mud (RM) with addition of silica to optimize its composition. The RM was pretreated through alkali–thermal activation and turned to geopolymer precursor, which could be used by only adding water in blending process. However the long-term strength of the binder with only RM was poor because of the unstable polymerization due to the low SiO 2 /Al 2 O 3 molar ratio (1.41). Silica fume (SF) was chosen to increase the SiO 2 /Al 2 O 3 molar ratio of the geopolymer formulation. By adding 25 wt% of SF, the 28 d compressive strength of the geopolymer with a SiO 2 /Al 2 O 3 molar ratio of 3.45 could reach 31.5 MPa at a water/solid ratio of 0.45. Sodium aluminosilicate in the activated RM dissolved in water and formed an alkaline environment to dissolve SF. The dissolved silica participated in geopolymerization, leading to a satisfactory geopolymer composition. Typical amorphous geopolymer matrices were formed in the binder completely cured.

A novel nanostructured leady oxides comprising porous carbon skeleton has been synthesized by thermal decomposition of lead citrate precursor, recovered from spent lead-acid battery paste. The influences of O 2 percentage in the calcination atmosphere (O 2 /N 2 mixture) and the temperature on leady oxide product characteristics are studied by chemical analysis, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The major crystalline phases of the products are identified as lead oxides, metallic Pb, and carbon. Porous carbon is observed as skeletons within the leady oxide (PbO containing some Pb metal) particles. Mass percentage of Pb metal in the leady oxide increases with increasing the proportion of oxygen in the calcination atmosphere. However, the amount of carbon decreases from approximately 8.0 to 0.3 wt%, and the porous carbon skeleton structure is gradually damaged with oxygen concentration increasing. A model about the thermal decomposition of lead citrate precursor is firstly proposed to elucidate these observations. The nanostructured leady oxides combined with porous carbon can be directly used as precursor of active materials in a new lead acid battery.

Aerobic granular sludge (AGS) was cultivated in a bench scale sequencing batch reactor within 21 days. Strategy of the rapid startup was inoculated with part of mature AGS during cultivation, while aerobic biological selector was implemented for the inhibiting outgrowth of filamentous bacteria and fast selection of zoogloea bacteria. Then, the cultivated AGS was employed for the treatment of solvent recovery raffinate. Stable AGS was successfully domesticated after 55 days under strategy of gradually increase the proportion of real wastewater in influent. The domesticated AGS was orange, irregular shape, smooth and compact. SVI, SV 30 /SV 5 , MLVSS/MLSS, EPS, PN/PS, average particle size, granulation rate, (SOUR) H and (SOUR) N of AGS were 19.06 mL/g, 0.97, 0.55, 30.05 mg/g MLVSS, 1.10, 1.28 mm, 98.87%, 32.47 and 7.97 mg O 2 /h g VSS respectively. Finally, COD, TIN, NH 4 + –N and TP of the effluent were lower than 25.9 mg/L, 1.64 mg/L, 1.13 mg/L and 0.21 mg/L, and their removal rate was more than 98.43%, 97.12%, 98.02% and 98.09% respectively. Thus, COD, TP removal, nitrification and denitrification were realized in a single bioreactor. The result indicated that the feasibility of AGS for high C/N ratio industrial wastewater treatment.

In this study, a granular adsorbent was prepared from phoenix tree leaf powder with bentonite as the binder. The granular adsorbent was characterized by TG, BET and SEM analyses. The maximum specific surface area and pore volume were 166.3 m2 g−1 and 0.276 cm3 g−1, respectively, after the granular adsorbent was calcined at 500 °C. Effects of pH, adsorption time and initial metal ion concentration on the adsorption of Pb2+ by 500 °C calcined granular adsorbent were investigated in batch experiments. Higher pH was favorable for the adsorption process and significant release of Na+, K+ and Mg2+ were observed, assuming the predominant Pb2+ adsorption mechanism was ion exchange. The adsorption could attain equilibrium within 24 h with a gradual increase of the solution pH. The kinetics data were analyzed using three adsorption kinetic models: the pseudo-first-order, pseudo-second-order and intraparticle diffusion equations. Results show that intraparticle diffusion or chemical adsorption is the rate-limiting step depending on the adsorption time. The adsorption isotherms best fitted the Langmuir–Freundlich model and the maximum Langmuir adsorption capacity was found to be 71 mg g−1. This novel granular adsorbent has proven to be a potential inexpensive adsorbent for Pb2+ removal from aqueous solutions.

Catalytic wastewater treatment is confronted by varied challenges like catalyst stability and efficiency in aqueous media due to the complex chemistry during organic compound degradation. Herein, we attempt to address this challenge by creating a synergistically stable and active bimetallic CuCoOx–LDH catalyst via facile copper ion hydrothermal impregnation in a CoOx–LDH catalyst. Different instrumental techniques like BET, XRD, FTIR, SEM, XPS and electrochemical studies etc. were conducted to investigate the properties of the catalyst before and after impregnation of copper ions. It was found that the changes in the electrochemistry and redox properties of the CuCoOx–LDH catalyst based on cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) appeared in the form of enhanced activity and excellent stability. In the bicarbonate activation of hydrogen peroxide (BAP) system, the synthesized CuCoOx–LDH catalyst can efficiently degrade 200 ppm 4-chlorophenol (4-CP) with 84% COD and 78% TOC removal in less than 40 minutes, and even 1000 ppm of 4-CP in hours, while the CoOx–LDH and CuOx–LDH catalysts or their physical mixtures are apparently sluggish. This catalyst can also effectively degrade various substituted phenols including 2,4-dichlorophenol (DCP), 2,4,4-trichlorophenol (TCP), 2-chlorophenol (2-CP), phenol, and chlorobenzene with significant COD removal. The findings from fluorescence, scavengers, electron paramagnetic resonance (EPR), XPS, and electrochemical studies suggest collectively the generation of ˙OH, 1O2, and ˙O2− species and that the regeneration of active sites may be part of the degradation process. This approach based on CV, EIS and XPS studies has provided novel knowledge about the intrinsic origins of synergetic acceleration of catalyst activity.

Barium sulfate (BaSO4) is a common impurity in recycled lead paste that is challenging to eliminate completely during hydrometallurgical recycling of spent lead acid batteries, so the effect of this impurity in positive active materials on the performance of recycled lead acid batteries was investigated. The BaSO4 doped lead oxide composite was used as a positive active material in positive plates of lead acid batteries with theoretical capacities of 2.0 A h. BaSO4 was retained in the solid phase throughout the battery fabrication process. Different BaSO4 dosages affected the phase of the positive plates during the curing process, with the highest content of metallic lead obtained at a BaSO4 dosage of 0.06 wt%. Morphology analysis indicated that aggregates were formed in the positive plates and the particles became rougher with increasing addition of BaSO4 during the formation process. BaSO4 also demonstrated a large impact on charge/discharge cycles with 100% DOD in battery testing. Analysis of disassembled failed batteries indicated that the expansion and shedding-off of the positive active material were mainly responsible for the failure of these batteries, and this could be attributed to the non-uniform growth of lead oxide on the BaSO4 nucleus, and the accumulation of internal stress.

A novel ultrasensitive, selective and low cost electrochemical sensor based on a hollow sphere bismuth oxide doped mesoporous carbon aerogel nanocomposite derived from a sustainable biomass material was successfully fabricated for simultaneous Pb2+ and Cd2+ detection at picomolar levels. In this nanocomposite material, we successfully brought together the advantages of an extraordinarily large surface area biomass derived carbon matrix with mesopores for analyte pre-enrichment and the excellent electroanalytical activity of the bismuth oxide hollow sphere structure for highly sensitive heavy metal sensing. Under optimized conditions, this electrode material exhibited a very low detection limit of 1.72 pM for Pb2+ and 1.58 pM for Cd2+ under ambient conditions, the lowest ever limit of detection recorded for the detection of both Pb2+ and Cd2+ using activated carbon. Furthermore, two wide linear ranges from 0.5 pM to 10 pM and from 10 pM to100 pM were observed due to the differences of adsorption dynamics at different metal ion concentration ranges. The nanocomposite sensor material demonstrated excellent reproducibility and great resistance to interference. Furthermore, the application for real water analysis was demonstrated and the result was highly consistent with the measurement from inductively coupled plasma optical emission spectroscopy (ICP-OES).

Aerobic granular sludge (AGS) was successfully cultivated in a double column cyclic aerobic granular reactor (DCCAGR) within 18 days by inoculating with 30% (w/w) mature aerobic granules and 70% activated sludge, while granulation process and reactor performance was investigated in the continuous flow reactor. The AGS cultivated was white or pale yellow, while granule’s SVI, average particle size, granulation rate, extracellular polymeric substances, polysaccharides/proteins ratio and water content were about 46 mL/g, 1.2 mm, 92%, 37 mg/g MLVSS, 1.4 and 98.3% on the 20th day. Observed from the microscopic structure of the cultivated AGS, a large number of microorganisms tightly adhered together inhibited inside the granules, including coccus, bacillus and protozoa. Finally, effluent chemical oxygen demand, total inorganic chemical demand, ammonium nitrogen and total phosphorus of the system were 33 mg/L, 8.46 mg/L, 7.3 mg/L and 1.26 mg/L, and their removal rates were 97%, 88%, 90% and 87% respectively. Effective hydraulic selection pressure can be created in DCCAGR, while inoculated AGS had positive significance to the agglomeration of other flocculent sludge, which greatly reduced the startup time and consumption of mature aerobic granules.

Geopolymers have been introduced as a promising strategy for the solidification/stabilization (s/s) of heavy metals due to its sustainability and environmental friendliness. However, it usually takes a long curing time to achieve a rational mechanical strength, and the stability of heavy metals in geopolymer needs to be further enhanced to reduce possible environmental risks. Here we introduced a microwave (MW) strategy for the s/s of real lead slag with geopolymer technology. The stabilization of lead slag (LS) with different addition ratios were characterized, and the effect of microwave power as well as irradiation time were also examined to optimize the geopolymer strength and the leaching of Pb. The geopolymerization process was drastically enhanced, showing shortened polymerization period from 28 days to 15 min with an optimum compressive strength of 18.8 MPa and s/s efficiency of 98.73%. It was revealed that physical embedding was the main stabilization mechanism proved by lead speciation, X-Ray Diffraction (XRD), Fourier Transform Infrared Spectrometry (FTIR), Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometry (EDS) analysis. It suggested that the combined effects of local heating and enhanced dehydration with MW irradiation would benefit the stabilization of lead slag in geopolymers.

Reuse of sludge-derived Fe-rich biochar as sludge conditioner is an attractive route for management of waste activated sludge at source. Homogeneous and heterogeneous Fenton reactions have been proved in sludge conditioning with Fe-rich biochar activating H2O2 to enhance sludge dewaterability. The FeAl2O4 phase in Fe-rich biochar was first identified during pyrolysis of sewage sludge after adding both Fe2O3 and Al2O3, since Fe and Al elements are two of major metal elements in Fe-rich sludge. Compared with the Fe-rich biochar that did not comprise FeAl2O4 phase, the capillary suction time (CST) and specific resistance to filterability (SRF) of the sludge conditioned with the Fe-rich biochar comprising FeAl2O4 phase could be efficiently decreased by 23% and 44%, respectively. The results indicated that FeAl2O4 phase in Fe-rich biochar could improve sludge dewaterability by enhancing heterogeneous Fenton reaction. Synergistic effect between Fe and Al in FeAl2O4 contributed to weak the O-O bond in H2O2 and reduce the activation energy of H2O2 decomposition for enhancing ·OH generation, which could be explained by density functional theory (DFT) calculations for the first time. Thus, the decomposition rate of H2O2 and the amount of ·OH generation were obviously promoted by FeAl2O4 phase in sludge-derived biochar during sludge conditioning, attributing to the destruction of sludge flocs, the release of bound water, and the improvement of sludge dewaterability.

An innovative cathodic algal biofilm microbial fuel cell equipped with a bioactive oxygen consuming unit (AB-OCU-MFC) was proposed for enhancing the leachate treatment containing biorefractory organic matters and high strength of ammonium nitrogen. The proposed AB-OCU-MFC performed better with regard to COD, NH4+-N, TN removals and algal biomass yield than standalone algal biofilm-MFC and control reactors. AB-OCU-MFC with OCU of 2 cm thickness removed more than 86% of COD, 89.4% of NH4+-N, 76.7% of TN and produced a maximum voltage of 0.39 V and biomass productivity of 1.23 g·L−1·d−1. The High-throughput sequencing of DNA showed a significant change in microbial community of reactors implemented with OCU, in which the ratio of exoelectrogenic bacteria of anode and denitrifying bacteria on cathode were significantly increased. The results obtained by cathodic algal biofilm MFC with low cost and bioactive barrier of OCU, would provide a new sight for practical application of MFC.

Fe-rich biochar with multivalent iron compounds (Fe0, Fe0.95C0.05, Fe3O4, and FeAl2O4) pyrolyzed from sludge cake conditioned with Fenton's reagent and red mud was utilized as an efficient Fenton catalyst for the degradation of 4-chlorophenol (4-CP). Effects of pyrolysis temperature and sludge conditioner composition on the transformation of iron compounds were studied. Both homogeneous Fenton reaction initiated by Fe2+ leached from both low-valent Fe0 and Fe0.95C0.05, and heterogeneous Fenton reaction initiated by solid iron phases of Fe3O4 and FeAl2O4 were revealed to contribute to the degradation of 4-CP. The removal efficiency of 4-CP remained 100% after five successive degradation rounds. The homogeneous Fenton reaction mainly works in the first degradation round, and the heterogeneous Fenton reaction dominates in subsequent degradation rounds. The findings of this study suggest that sewage sludge derived Fe-rich biochar could be utilized as an efficient Fenton catalyst for recalcitrant organics degradation.

The novel catalyst LaCu0.5Fe0.5O3-δ with oxygen vacancies (OVs) was prepared and demonstrated excellent stability and activity for the degradation of bisphenol A. The removal rate of 92.1 % and H2O2 utilization efficiency of 70.4 % were obtained due to the efficient hydroxyl radical generation mediated by OVs. The density functional theory calculation showed that the substitution of Cu and formation of OVs significantly increases the charge density near the active sites. Bader charge analysis revealed that the charge offset accelerated the reduction of Fe. The elevation of electron transfer efficiency also promotes the valence transition of copper and iron atoms. The reversible electronic transition between Fe2+ ⇆ Fe3+, Cu+ ⇆ Cu2+ and Cu2+ ⇆ Fe2+ involved in this reaction were considered to be enhanced and the homolytic bond clearage of H2O2 was simultaneously promoted, facilitated by the electron-rich region combined with OVs on the surface of LaCu0.5Fe0.5O3-δ.

A coupled microbial electrolysis cell - anaerobic granular sludge system (MEC-AGS) was established to explore the degradation efficiency of 2,4,6-trichlorophenol (TCP) with synchronous biogas production. Results showed that MEC-AGS yielded a higher proportion of CH4 than MEC (83.8 ± 0.4% vs 82.0 ± 1.0%, P

A novel technique for phosphorus recovery from the liquid phase of anaerobic digestate was developed using biochar derived from iron−rich sludge (dewatered sludge conditioned with Fenton’s reagent). The biochar pyrolyzed from iron−rich sludge at a low temperature of 300 °C (referred to as Fe−300 biochar) showed a better phosphorus (P) adsorption capacity (most of orthophosphate and pyrophosphate) than biochars pyrolyzed at other higher temperatures of 500–900 °C, with the maximum P adsorption capacity of up to 1.843 mg g−1 for the liquid phase of anaerobic digestate. Adsorption isotherms study indicated that 70% P was precipitated through chemical reaction with Fe elements, i.e., Fe(II) and Fe(III) existed on the surface of the Fe−300 biochar, and other 30% was through surface physical adsorption as simulated by a dual Langmuir-Langmuir model using the potassium dihydrogen orthophosphate (KH2PO4) as a model solution. The seed germination rate was increased up to 92% with the addition of Fe−300 biochar after adsorbing most of P, compared with 66% without the addition of biochar. Moreover, P adsorbed by the chemical reaction in form of iron hydrogen phosphate can be solubilized by a phosphate-solubilizing microorganism of Pseudomonas aeruginosa, with the total solubilized P amount of 3.045 mg g−1 at the end of an incubation of 20 days. This study indicated that the iron−rich sludge−derived biochar could be used as a novel and beneficial functional material for P recovery from the liquid phase of anaerobic digestate. The recovered P with biochar can be re-utilized in garden soil as an efficient P−fertilizer, thus increasing the added values of both the liquid phase of anaerobic digestate and the iron−rich sludge.

Novel leady oxides with different particle sizes are prepared via pyrolysis of lead citrate in rotary kiln and subsequent ball-milling. The mechanism of how particle size influences the phase transition route of novel leady oxides during soaking process is investigated. PbO with larger particle size (D50 diameter = 22.4 μm) is converted to 3PbO∙PbSO4, and 3PbO∙PbSO4 is then partially transformed to PbO∙PbSO4 while PbO∙PbSO4 are gradually converted to PbSO4. PbO with smaller particle size (D50 diameter = 8.3 μm) is directly converted to PbSO4, and 3PbO∙PbSO4 is partially transformed to PbO∙PbSO4. Phase compositions after the soaking process determine the PbO2 content in positives plates because PbO2 is the oxidation product of PbSO4 in the sequent formation process. Particle size of leady oxides determines the initial capacity of testing cells through affecting the soaking process and a linear correlation between the initial capacity and PbO2 content in positive plates is obtained (R2 = 0.78). Therefore, leady oxides with larger particle size requires higher sulfuric acid density (1.045 g cm−3) to achieve an optimized initial capacity (2.17 Ah), while a lower sulfuric density (1.015 g cm−3) is recommended for small particle leady oxides to achieve an optimized capacity of 2.58 Ah.

Hydrometallurgical process for recovery of spent lead-acid battery paste shows great advantages in reducing SO2 and lead particulates emissions than traditional pyrometallurgical process. However, the hydrometallurgical process usually has drawbacks of high consumption of chemical reagents and difficulty in removing impurities (especially Fe and Ba elements) from the recovered product. In this paper, a closed-loop ammonium salt system is proposed for spent lead-acid battery paste recovery. Both recirculation of leaching reagents and preparation of low-impurity recovered products have been realized. The spent lead paste is first leached by a mixed solution of ammonium acetate, acetic acid and hydrogen peroxide. After filtration, the separated lead acetate solution is reacted with ammonium carbonate to generate lead carbonate via precipitation process. The impurity elements are efficiently removed by pH control and complexation between acetate ions and impurity elements in the leaching and precipitation processes. The soluble SO42− separated from the precipitation process is removed by adding barium acetate to generate solid BaSO4 by-product. At the same time, the regenerated ammonium acetate filtrate is separated and re-used in the next-round leaching process in order to realize a closed-loop process. In the 5th round of filtrate recirculation processes, the leaching ratio of lead is maintained at levels higher than 92.7 wt%. Furthermore, high-purity lead tetroxide is prepared by calcination of lead carbonate in air at 450 °C. The contents of Fe and Ba in the final recovered lead tetroxide product are as low as 2.7 and 5.2 mg/kg, respectively. The recovered lead tetroxide product meets the specifications for use as an additive in the positive active materials for making a new lead-acid battery. This study provides a feasible technology for high-value utilization of spent lead paste.

Suspended solids (SS) are one of major pollutants that deteriorate water quality. The high-rate clarifier is commonly used as the tertiary treatment by coagulation to agglomerate particles, thus achieving a high SS removal and making effluents acceptable for discharge. Currently the control of average residence time in operation of high-rate clarifier is challenging: With limited residence time, the particles fail to form flocs in the mixing tank, causing inefficient solid/liquid separation; while with prolonged residence time, SS sedimentation would accumulate at the bottom of the tank. In this study, a liquid-solid two-phase computational fluid dynamics (CFD) model has been developed to simulate the distributions of flow field and SS in a high-rate clarifier. The CFD model was successfully validated against experimental results in a full-scale operation, with the normalized standard error on SS less than 1.24 %. The results showed that the height of under-through channel affected the flow field more significantly rather than its width. This study also indicated that with the height of under-through channel decreasing from 2000 to 500 mm and the height of baffle increasing from 3300 to 5213 mm, the average SS concentration at the bottom of reaction tank would decrease by 34.95 % and the average residence time would be shortened by 4.77 %, which can be helpful for prolonging dredging cycle and avoiding unnecessary dredging costs.

MFC toxicity sensor has major hindrances that limit its practical application, such as the poor concentration-response relationship and inferior recovery capability after high toxicity shock. Till now, the direct influence of intrinsic properties on the performance of MFC toxicity sensor has not been well understood. Quorum sensing (QS) is a cell-to-cell communication strategy that indirectly affects the intrinsic properties of electroactive biofilms. In this work, commercially available QS autoinducers (AHLs) were applied to MFC toxicity sensor to manipulate anode biofilm for better sensing performance. The results showed that the addition of AHLs (C6-HSL, 3-OXO-C12-HSL) led to higher sensing linearity to a wider range of Pb2+. The voltage of MFC sensors with AHLs addition fully recovered even after 10 mg/L Cu2+ shock, indicating an enhanced recovery capability of MFC toxicity sensor. It was found that higher live/dead cells ratio and increased exoelectrogen Geobacter abundance were responsible for the superior sensing linearity and recovery capability of MFC toxicity sensor. Our work presented a novel and effective way to advance the process of MFC toxicity sensor application from the perspective of EABs.

Selective capture and maximum recovery of Ag(I) from wastewater is of great significance for a sustainable future. In this work, novel rhodanine (Rd)-functionalized UiO-66 adsorbents (i.e., UiO-66-Rd and UiO-66-NH2-Rd) were designed and synthesized. Different from previously reported UiO-66 derivatives with single metal coordination sites, the as-synthesized UiO-66-Rd and UiO-66-NH2-Rd have dual coordination sites, resulting in higher capacity and outstanding selectivity. The maximum capacities of UiO-66-Rd and UiO-66-NH2-Rd are 112 and 163 mg·g−1, nearly 5.6 and 8.2 times higher than that of UiO-66, respectively. Impressively, the maximum selectivity coefficient of UiO-66-NH2-Rd is approximately 1795 and 1173 folds higher than that of UiO-66 and UiO-66-NH2. The experimental characterizations and theoretical calculations indicate that the Rd-induced enhancement in the adsorptivity and selectivity are mainly attributed to the dual coordination sites (i.e., C S and C S bonds), which collectively coordinate with Ag(I) in the form of Ag mono-coordinated with S. Compared with the UiO-66-Rd, UiO-66-NH2-Rd possesses excellent recyclability and durability due to the vital role of amide bonds generated from NH2 group in the functionalization of UiO-66 with Rd. Furthermore, UiO-66-NH2-Rd can almost completely remove Ag(I) from the actual wastewater with complex matrix, satisfying the national integrated wastewater discharge standard and industrial wastewater emission standard, highlighting a great potential of practical application.

Sewage sludge dewatering is an efficient approach to reduce the volume of sludge for the subsequent disposal. In this study, a novel one-step acidification sludge dewatering method was developed with using oxalic acid as a conditioner. In laboratory-scale experiments with the dosage of 200 mg/g dry solid (DS), the normalized capillary suction time and the specific resistance to filtration were respectively decreased by 78.7% and 60.0% after 30 min of oxalic acid conditioning, much more efficient than those conditioned with sulfuric acid and hydrochloric acid at the same pH value. This superior dewatering performance was attributed to two factors. One was that oxalic acid could more efficiently promote the hydrolysis of polysaccharide, especially pectins, to release bound water. The other was that OA could dissolve more Fe3+ and Al3+, as well as form precipitate with Ca2+ in sludge, which may act as flocculants or co-precipitator for the subsequent sludge particles coagulation. In pilot-scale experiments, the water content of oxalic acid conditioned sludge cake was reduced to 60% under the optimum conditions, while the reagent cost was as low as 110.0 USD/t DS. This work provides a cost-effective and easy-operated sewage sludge disposal technique, and also sheds light on the potential of oxalic acid in environmental waste treatment.

Converting sewage sludge into functional environmental materials has become an attractive sewage sludge disposal route. In this study, we synthesize a sewage sludge-based material via a facile one-pot hydrothermal carbonization method and construct a visible light molecular oxygen activation system with hydrothermally carbonized sewage sludge (HTC-S) and oxalate to degrade various organic pollutants. It was found that iron species of HTC-S could chelate with oxalate to generate H2O2 via molecular oxygen activation under visible light, and also promote the H2O2 decomposition to produce •OH for the fast organic pollutants degradation. Taking sulfadimidine as the example, the apparent degradation rate of HTC-S/oxalate system was almost 5–20 times that of iron oxides/oxalate system. This outstanding degradation performance was attributed to the presence of iron-containing clay minerals in HTC-S, as confirmed by X-ray diffraction measurements and Mossbauer spectrometry. In the oxalate solution, these iron-cont...

The nitrogen-containing gases pyrolyzed from sewage sludge can be converted into NO

A facile one-pot solvothermal method was applied to synthesize a magnetic biochar composite (MB) using phoenix tree leaves-derived biochar as the carbon matrix. The structure of MB was optimized by varying the load ratio and particle size of Fe3O4 nanoparticles on biochar. Time-dependent structure and composition evolution of solid and liquid phases during heterogeneous solvothermal process were investigated to understand the formation mechanism of MB. Firstly, Fe2+/Fe3+ ions were coordinated by oxygen-containing groups on biochar and part of them were hydrolyzed to form iron hydroxides. Then, those iron-containing precursors were thermally decomposed and reduced to iron oxides; and finally Fe3O4 nanoparticles were generated. The MB had an adsorption capacity for Cr(VI) of 55.0 mg/g in an aqueous solution, which exceeds those of biochar (39.8 mg/g) and Fe3O4 nanoparticles (26.5 mg/g). The adsorption mechanism study reveals that biochar as a carbon skeleton mainly provided binding sites for Cr(VI) and electron-donor groups for reduction of Cr(VI), while Fe3O4 nanoparticles mainly involved in the immobilization of newly formed Cr(III) through formation of Fe(III)-Cr(III) hydroxide. MB exhibited a stable structure with a lower Fe leakage at pH 2.0 than that of a comparable magnetic biochar sample prepared by conventional co-precipitation method. Recycling experiments suggested that MB could keep 84% of its initial removal capability for Cr(VI) even after seven cycles. The results indicate that solvothermal method is a promising alternative to prepare magnetic biochar for adsorption of heavy metal-containing wastewater.

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. H

A magnetic adsorbent (MA) was synthesized from wasted iron mud of a groundwater treatment plant using a novel one-step hydrothermal method. The results showed that Fe content of MA was 41.8 wt%, 2.5 times higher than that of iron mud, which was caused by hydrothermal dissolution of non-ferrous impurities under alkaline condition, such as quartz and albite, regardless of addition of ascorbic acid or not. Ferrihydrite was 92.7% in dry iron mud before adding ascorbic acid and gradually decreased to 58.1% by increasing the molar ratio of ascorbic acid to Fe following hydrothermal treatment. The strongest saturation magnetization of 16.29 emu/g was observed in the prepared MA-4 when the ascorbic acid to Fe molar ratio was 1. The highest surface site concentration of 1.31 mmol/g was observed in MA-2 when the ratio was 0.02. The mechanism of hydrothermal conversion of wasted iron mud to MA was reductive dissolution of ferrihydrite to form siderite, which was then reoxidized to maghemite. When 12.5 g/L of MA-2 was applied to treat smelting wastewater, over 99% removal of Cu2+, Zn2+, Pb2+, and Cd2+ was achieved. The major mechanisms of Cu2+ and Zn2+ adsorption by the adsorbent were cationic exchange.

Fenton's reagent has been widely used to enhance sludge dewaterability. However, drawbacks associated with hydrogen peroxide (H2O2) in Fenton's reagents exist, since it is a hazardous chemical and shows carcinogenicity, explosivity, instability, and corrosivity. Moreover, initial acidification and subsequent neutralization are needed as optimal conditions for homogeneous Fenton conditioning and final filtrate discharge. In this study, a Fenton-like process for the enhanced dewaterability of waste activated sludge with in-situ generation of H2O2 and without extra pH adjustment was firstly proposed, namely citric acid (CA)-assisted oxygen activation in an air/nano zero-valent iron (nZVI) system and chemical re-coagulation with polydiallyldimethylammonium chloride (PDMDAAC). Using the response surface methodology (RSM), the optimal doses of CA, nZVI, and PDMDAAC were determined to be 13, 33, and 9 mg g−1 dry solids (DS), respectively. This composite conditioner showed a good dewatering capability compared with the raw sludge, e.g. the capillary suction time decreased from 130.0 to 9.5 s. The enhanced sludge dewaterability was further confirmed by laboratory-scale diaphragm filter press dewatering tests, which produced a lower cake moisture content compared with the raw sludge, and the final pH of the filtrate was close to neutrality. The citric acid promoted the production of H2O2 and Fe(II)/Fe(III) species, the degradation of protein in tightly-bound extracellular polymeric substances, and the decomposition of protein-N in the solid phase of sludge, resulting a greater conversion of bound water to free water. The results of electron spin resonance indicated that the hydroxyl radicals were mainly responsible for the decomposition of proteinaceous compounds. The subsequent chemical re-coagulation with PDMDAAC can make the zeta potential of sludge samples less negative, reduce the repulsive electrostatic interactions, and agglomerate the smaller particles into larger aggregates, thus enhancing sludge dewaterability.

Fe

High water affinity of extracellular polymeric substances (EPS) and high compressibility of sewage sludge solids have negative impacts on sludge dewatering. In this study, a composite conditioner, Fe 2+ –activated sodium persulfate (denoted as Fe 2+ /SPS) combined with thermal–pretreated phosphogypsum (PG), was used to improve the sludge dewaterability. The mechanism of the composite conditioning of sewage sludge was elucidated: the proteins in tightly bound EPS were transferred into the filtrate and loosely bound EPS, and the polysaccharides in loosely and tightly bound EPS were transferred into the filtrate; the bound water was released and reduced from 2.60 g/g DS (dry solid) initially to 0.81 g/g DS; specific resistance to filtration and capillary suction time were reduced by 91.6% and 88.4%, respectively. Radical quenching experiment indicated that sulfate radical (SO 4 − ) is the dominant free radical and plays an important role in determining the oxidation–reduction potential during conditioning. Moreover, both the XRD and SEM results clearly showed that Fe 2+ /SPS combined with PG promoted the generation of column–shaped dihydrate gypsum in the conditioned sludge. Thus, the dihydrate gypsum crystals could act as skeleton builders, which create a more permeable and rigid lattice structure of the sludge cake. The improvement of sludge dewatering was confirmed by diaphragm filter press dewatering process, which yielded 45.7 wt% cake moisture content and 91.7% dewatering efficiency.

BACKGROUND Lead citrate is an attractive precursor for the preparation of ultrafine leady oxide from the paste in spent lead-acid batteries through a novel hydrometallurgical process, since the recovered lead oxide could be recycled for the production of new lead acid batteries. RESULTS Two different metal organic complexes were synthesized from lead sulfate from the paste of spent lead-acid batteries in a leaching solution at two different initial pH values. Single crystals of the two precursors were obtained by conditioning and filtering from the leached solutions, and used for single crystal XRD analysis. At an initial pH of 3.5, the chemical formula of Precursor-I is deduced to be Pb(C6H6O7)·H2O while at an initial pH of 5.2, the chemical formula of Precursor-II is Pb3(C6H5O7)2·3H2O. CONCLUSIONS Both Precursor-I and Precursor-II crystallize in the triclinic crystal system, with space group P-1. This structural study on precursors sheds light on the mechanism of a paste-to-paste recovery route for the recovery of spent lead paste. © 2014 Society of Chemical Industry

Pilot-scale sewage sludge dewatering experiments were conducted using two composite conditioners: FeCl3 + lime (Fe-lime) and Fenton's reagents + red mud (Fenton-RM). Mass balance analysis was performed on Cu, Zn, Pb, Cd, and Cr during the conditioning and dewatering processes to investigate their transformation and distribution. Speciation of heavy metals was also investigated by the Tessier sequential extraction method. Results show that (1) most of the heavy metals were retained in the solid cake during the dewatering process, especially Cu and Cr; (2) in the sludge cakes, more than 87 wt% of Cu and Cr existed in organic bound and residual forms, and the contents of the bioavailable fractions (exchangeable, carbonate bound and Fe–Mn oxides bound form) for Zn, Pb, and Cd were larger in the Fenton-RM system than those in the Fe-lime system; (3) the main factors affecting the distributions of these heavy metals are pH and chemical speciation in two conditioning processes. Generally, heavy metal concentrations in filtrate and dewatered sludge cakes in both systems were below the corresponding standards, and heavy metals in the dewatered sludge cake could be more effectively immobilized in the Fe-lime system than in that of the Fenton-RM system.

Joint application of Fenton’s reagent and CaO can dramatically enhance sludge dewaterability, thus are also likely to affect subsequent thermal drying process. This study investigated the synergistic effects of the two conditioners on the thermal drying behavior of sewage sludge and the emission characteristics of main sulfur-/nitrogen-containing gases. According to the results, Fenton peroxidation combined with CaO conditioning efficiently promoted sludge heat transfer, reduced the amounts of both free and bound water, and created porous structure in solids to provide evaporation channels, thus producing significant positive effects on sludge drying performance. In this case, the required time for drying was shortened to one-third. Additionally, joint usage of Fenton’s reagent and CaO did not increase the losses of organic matter during sludge drying process. Meanwhile, they facilitated the formation of sulfate and sulfonic acid/sulfone, leading to sulfur retention in dried sludge. Both of Fenton peroxidation and CaO conditioning promoted the oxidation, decomposition, and/or dissolution of protein and inorganic nitrogen in sludge pre-treatment. As a consequence, the emissions of sulfurous and nitrogenous gases from dewatered sludge drying were greatly suppressed. These indicate that combining Fenton peroxidation with CaO conditioning is a promising strategy to improve drying efficiency of sewage sludge and to control sulfur and nitrogen contaminants during sludge thermal drying process.

A novel green recycling process is investigated to prepare lead acetate trihydrate precursors and novel ultrafine lead oxide from spent lead acid battery pastes. The route contains the following four processes. (1) The spent lead pastes are desulphurized by (NH4)2CO3. (2) The desulphurized pastes are converted into lead acetate solution by leaching with acetic acid solution and H2O2; (3) The Pb(CH3COO)2·3H2O precursor is crystallized and purified from the lead acetate solution with the addition of glacial acetic acid; (4) The novel ultrafine lead oxide is prepared by the calcination of lead acetate trihydrate precursor in N2 or air at 320–400 °C. Both the lead acetate trihydrate and lead oxide products are characterized by TG-DTA, XRD, and SEM techniques. The calcination products are mainly α-PbO, β-PbO, and a small amount of metallic Pb. The particle size of the calcination products in air is significantly larger than that in N2. Cyclic voltammetry measurements of the novel ultrafine lead oxide products show good reversibility and cycle stability. The assembled batteries using the lead oxide products as cathode active materials show a good cyclic stability in 80 charge/discharge cycles with the depth of discharge (DOD) of 100%.

In this study, anaerobic granular sludge (AGS) was used as a novel adsorbent for hexavalent chromium (Cr (VI)) removal from aqueous solutions. Factor experiments were conducted to find out the effects of different variables on the biosorption process. Among these terms, the impact of three main independent variables (contact time, initial pH and AGS dosage) on the removal efficiency of Cr (VI) was modeled using a well-fitting polynomial equation (R2 = 0.9044), by conducting 20 batch experiments designed by a central composite. The experimental isotherm data were successfully described by the Freundlich isotherm and the pseudo-second-order kinetic model was more suitable for explaining the kinetics process of adsorption. The AGS can be disposed using 0.1 M NaOH with 96.4% desorption efficiency. The results of the analyses (X-ray photoelectron spectroscopy and Fourier transformed infrared spectroscopy) suggested that Cr (VI) adsorption most likely involved electrostatic adsorption, redox reaction and complexation.

With increasing awareness of reduction of energy and CO2 footprint, more waste is considered recyclable for generating value-added products. Here we reported the negatively-valued iron mud, a waste from groundwater treatment plant, was successfully converted into magnetic adsorbent. Comparing with the conventional calcination method under the high temperature and pressure, the synthesis of the magnetic particles (MPs) by Fe2+/Fe3+ coprecipitation was conducted at environment-friendly condition using ascorbic acid (H2A) as reduction reagent and nitric acid (or acid wastewater) as leaching solution. The MPs with major component of Fe3O4 were synthesized at the molar ratio (called ratio subsequently) of H2A to Fe3+ of iron mud ≥ 0.1; while amorphous ferrihydrite phase was formed at the ratio ≤ 0.05, which were confirmed by vibrating sample magnetometer (VSM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). With the ratio increased, the crystalline size and the crystallization degree of MPs increased, and thus the Brunauer-Emmett-Teller (BET) surface and the cation-exchange capacity (CEC) decreased. MPs-3 prepared with H2A to Fe3+ ratio of 0.1 demonstrated the highest methylene blue (MB) adsorption of 87.3 mg/g and good magnetic response. The adsorption of MB onto MPs agreed well with the non-linear Langmuir isotherm model and the pseudo-second-order model. Pilot-scale experiment showed that 99% of MB was removed by adding 10 g/L of MPs-3. After five adsorption-desorption cycles, MPs-3 still showed 62% removal efficiency for MB adsorption. When nitric acid was replaced by acid wastewater from a propylene plant, the synthesized MPs-3w showed 3.7 emu/g of saturation magnetization (Ms) and 56.7 mg/g of MB adsorption capacity, 2.8 times of the widely used commercial adsorbent of granular active carbon (GAC). The major mechanism of MPs adsorption for MB was electrostatic attraction and cation exchange. This study synthesized a magnetic adsorbent from the negatively-valued iron mud waste by using an environment-friendly coprecipitation method, which had a potential for treatment of dye wastewater.

Organic content of sludge is a major factor influencing its dewaterability. Conditioning sewage sludge with oxidation reagents (Fenton's reagent or Fe2+/persulfate) can effectively improve sludge dewaterability. In traditional conditioning process of sewage sludge, the optimization of conditioner dosage were commonly based on volume of sludge (referred as mg/L) or mass of dry solid (DS) of sludge (referred as mg/g DS). However, inconsistency of the oxidation dose mode existed for different sewage sludge sources. In this study, sludge samples of different volatile solids (VS) contents were used to derive optimal dosages of Fenton's reagent and Fe2+/persulfate, using the response surface methodology (RSM). For the case of Fenton's reagent, the optimal dosages of Fe2+ and H2O2 were 107–110 mg/g VS and 86–88 mg/g VS, respectively. For Fe2+/persulfate, the optimal dosages of Fe2+ and persulfate were 49 mg/g VS and 269–271 mg/g VS, respectively. The optimal dosages of the oxidation reagents based on VS contents were proved to be consistent and effective for different sewage sludge with different organic matter contents from different wastewater treatment plants (WWTPs). In contrast, the optimal dosages of oxidation reagents, based on DS, fluctuated significantly for different sludge sources. Furthermore, sewage sludge dewaterability was significantly related to the degradation and the content of loosely bound extracellular polymeric substances (LB-EPS) in the organic matters of conditioned sludge (R2 > 0.9, p

Air sparging (AS) is one of the most efficient techniques for remediating saturated soils and groundwater contaminated with volatile organic compounds. Most studies have focused on how the subsurface conditions control the AS process; however, the “side-effects” of AS that feed back to subsurface environment have not been well addressed. This paper studied the perturbation of porous media induced by AS and the consequent multi-parameter changes with the support of Miller soil box and resistivity test, and Darcy experiment and tracer breakthrough test. The Miller soil box test shows that the resistivity response can be credibly used as a non-intrusive method to indicate the porosity change, and that the porosity-resistivity data can be well fitted using Archie equation (R 2 > 0.98). Based upon the electricity measurement and above quantitive relationship, it was found that the porosity increased near the air injection point and decreased near the upper boundary of the column due to the upward-transport of particles during air sparging. The changes in porosity were found to be directly proportional to the air injection rate, and the maximum absolute variation of porosity was up to 0.104 at the air flow rate of 20 ml/min, while it did not change in the absence of AS. Both the hydraulic conductivity and dispersion coefficient increased after AS perturbation as the preferential flow pathway formed. The two parameters changed from 3.40 m/d and 0.110 to 6.13 m/d and 0.288, respectively, at 20 ml/min. This work provides useful insight into the changes in flow and transport properties of porous media induced by AS, which then help to understand the instability of air flow and the parameter-uncertainty analysis in related AS model.

Lead citrate is a key precursor for the green recycling of spent lead acid battery paste in a citric acid/sodium citrate (CA/SC) solution. In this study, the main paste component, PbSO4, was leached and crystallized to yield lead citrate. Results showed that the leaching of PbSO4 in citric acid/sodium citrate solution was remarkably enhanced by an increase in temperature from 35 °C to 95 °C and an increase in sodium citrate (SC) concentration from 50 to 650 g/L. In comparison, increasing the citric acid/sodium citrate molar ratio inhibited this leaching. Controlled crystallization through cooling the solution or adjusting the pH of the solution can effectively produce lead citrate crystals. The X-ray diffraction patterns of four products obtained in a comparison test were all consistent with Pb3(C6H5O7)2. However, the scanning electron microscopy analysis suggested that the morphology was distinct from rods to sheets, which were mainly affected by the temperature variation.

A novel method involving the fabrication of Mo–W mixed oxide (MoxW1–xO3) is proposed to modify the modest reaction kinetics and poor cycling stability of MoO3 material. By a simple coelectrodeposition method, a series of MoxW1–xO3 oxides is deposited on a TiO2 nanotube array substrate. Because of the differences between Mo6+ and W6+ in nature, there is significant distortion existing in the mixed oxides, leading to their decreased crystallite size and enlarged lattice space, which facilitates ion diffusion in the solid. As results, the mixed oxides show much better balance between specific capacitance and cycling stability than the bare MoO3 or WO3 sample, which suffers from either poor cycling stability or low electrochemical activity. Impressively, the optimal Mo–W mixed oxide exhibits a high specific capacitance of 517.4 F g–1 at 1 A g–1, and, moreover, it retains 89.3% of the capacitance even at a high current density of 10 A g–1, demonstrating ultrahigh rate capability. These findings reveal the pote...

Lithium-sulfur batteries have attracted great attention because of their high energy density, environmental friendliness, natural abundance and intrinsically low cost of sulfur. However, their commercial applications are greatly hindered by rapid capacity decay due to poor conductivity of electrode, fast dissolution of the intermediate polysulfides into the electrolyte, and the volume expansion of sulfur. Herein, we report a novel composite MWCNTs@TiO2-S nanostructure by grafting TiO2 onto the surface of MWCNTs, followed by incorporating sulfur into the composite. The inner MWCNTs improved the mechanical strength and conductivity of the electrode and the outer TiO2 provided the adsorption sites to immobilize polysulfides due to bonding interaction between TiO2 and polysulfides. The MWCNTs@TiO2-S composite with a mass ratio of 50% (MWCNTs in MWCNTs@TiO2) exhibited the highest electrochemistry performance among all compositing ratios of MWCNTs/TiO2. The performance improvement might be attributed to the downward shift of the apparent Fermi level to a more positive potential and electron rich space region at the interface of MWCNTs-TiO2 that facilitates the reduction of lithium polysulfide at a higher potential. Such a novel hybrid structure can be applicable for electrode design in other energy storage applications.