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A novel mechanochemically assisted persulfate activation method was proposed in this study to enhance the leaching of valuable metals from lithium-ion batteries by combining ball-milling, advanced oxidation processes and sucrose reduction. By optimizing leaching parameters including temperature, pH, milling time and solid-to-liquid ratio, high leaching efficiencies of 97.1%, 94.0%, 87.6% and 93.8% can be achieved for Li, Ni, Co and Mn respectively. In the mechanochemical process, the breakage of covalent bonds in cathode material is facilitated by free radicals generated from zero valent iron activated ammonia persulfate as well as mechanochemical activation. To further explore the role of free radicals, the mechanism of ammonia persulfate activation by zero valent iron was elucidated, and SO

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.

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.

Hemin has attracted considerable interest as an efficient catalyst recently, however, its direct application is inefficient due to severe molecular aggregation. Immobilizing hemin on various supports is a feasible approach to address this issue. In this work, a CNTs-hemin catalyst was prepared by loading hemin onto multiwalled carbon nanotubes (CNTs) through ball milling. Compared with hemin, CNTs-hemin demonstrates remarkably enhanced performance in the peroxymonosulfate system, with a 650-fold improvement of apparent rate constant, reaching 97.8% degradation of sulfathiazole in 5 min. High-valent iron-oxo porphyrin cation ((Porp)

Arsenic-alkali residue (AAR) from antimony production can pose significant health and environmental hazards due to the risk of arsenic (As) leaching. In this study, geopolymer composite synthesized from fly ash (FA) was investigated for efficient stabilization of high-arsenic-containing AAR (As

This study investigated the effects of electrical signaling disruption induced by adding tetraethylammonium (TEA, a potassium channel blocker) on the formation of mixed-cultured electroactive biofilms, especially the relative abundance of Geobacter over time. Results showed that TEA addition decelerated the biofilm formation, but selectively enriched Geobacter over time (45.8% on Day 32, 67.7% on Day 60 and 78.1% on Day 90), thus resulting in higher final extracellular electron transfer (EET) efficiency. Redundancy analysis (RDA) confirmed that TEA and operation time were significant factors for the selective enrichment of Geobacter. Moreover, increase in cellular processes and signal processing by PICRUSt analysis indicated adaptive responses of electrogenic biofilms to electrical signaling disruption. Furthermore, qRT-PCR indicated the compensatory roles of key cytochromes and pilA in electrochemical communication, which induced Geobacter enrichment. This work provided a broader understanding of electroactive biofilm regulation and potential applications for electricity generation and biosensor in the future.

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.

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

Massive realgar tailings abandoned in mining areas in China have caused serious arsenic (As) pollution seeking for urgent disposal. Stabilization treatment is a feasible strategy, however, stabilization technologies for realgar tailings, that are Fe-deficient, Ca-rich and S-rich, have not been well developed to date. In this study, we conducted a pilot-scale stabilization treatment of realgar tailings via ferrous sulfate addition to evaluate the transformation of As during stabilization. We found that Si, As, Ca, and S were the predominant elements in the raw realgar tailings with a low content of Fe, and realgar (AsII4S4) and pharmacolite (CaHAsVO4·2H2O) were the main As-bearing minerals. After the ferrous sulfate treatment, the As leaching concentration of realgar tailings was successfully reduced from 135 mg/L to a level below the Chinese regulatory limit (2.5 mg/L). Based on the results of leaching tests, sequential extraction analysis, XRD, SEM-EDS, XPS, and thermodynamic modeling, we concluded that ferrous sulfate addition enhanced the transformation of Ca–As and S–As species to more stable Fe–As species, e.g., crystalline symplesite and amorphous Fe–As complex. Dissolution of pharmacolite was facilitated by H+ and SO42− derived from the hydrolysis and oxidation of ferrous sulfate, and oxidation of realgar could be promoted by reactive oxygen species (ROSs) from Fe(II) oxygenation. This study improved our understanding of As transformation pathways in realgar tailings during ferrous sulfate treatment, which could serve as an alternative scheme for realgar tailings stabilization.

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.

From extraction to use, crude oil undergoes a series of processes such as transportation and refining that inevitably lead to the contamination of soil by the oil. The conventional bioremediation of petroleum in soil is circumscribed by the low activity of functional microbes, scarcity of electron acceptors, and inefficient electron transfer. This study investigated the effects and mechanism of plants, carbon sources, and surfactants on petroleum and polyaromatic hydrocarbon (PAH) degradation using enhanced plant-microbial fuel cells (P-MFCs) in soil. The degradation rate of PAHs (phenanthrene and pyrene) significantly increased with increasing surfactant concentration and the addition of plants. Compared with the co-metabolism of glucose, the addition of β-cyclodextrin more strongly enhanced oil remediation in soil. The charge-transfer resistance values in the MFCs were significantly reduced with the addition of plants, glucose, and β-cyclodextrin. The synergistic action of the plants and surfactants significantly enhances the efficiency of the MFC system in the removal of petroleum from soil, and recommends the applications of P-MFCs for the in situ remediation of petroleum-contaminated soils.

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

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.

Hydrometallurgical route normally has lower energy consumption and less carbon dioxide emission than high-temperature smelting route. However, efficient removal of impurities is a common challenge for hydrometallurgical process. A facile recovery route of spent lead-acid battery pastes, including efficient desulfurization and pH-controlled acid leaching, is proposed. Effects of two typical desulfurizers (NaOH and Na2CO3) on desulfurization efficiency and removals of major impurities (Ba and Fe elements) were comparatively investigated for the first time. NaOH was more effective than Na2CO3 with a higher desulfurization efficiency of 99.3 wt% in 10 min. Approximately 26.2 wt% of BaSO4 in the raw spent lead paste was converted into BaCO3 in the Na2CO3 desulfurization system, causing more Ba element entered into the acid leaching solution. The significant decrease of pH in the acid leaching solution caused a high concentration of Fe element impurity, which was efficiently removed by further pH adjustment. The optimal conditions were determined to be: a NaOH/PbSO4 molar ratio of 2.0 in the desulfurization step, a HNO3/Pb molar ratio of 2.2 in the acid leaching step, and followed by adjusting the pH of the acid leaching solution to about 3.48. Up to 98.4 wt% of the Pb was recovered, while 99.8 wt% of Ba and 99.9 wt% of Fe element impurities were removed. The obtained low-impurity lead nitrate solution was further converted into high-purity PbCO3 and α-PbO products, providing a viable alternative for the recovery of the spent lead pastes.

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.

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.

This study investigated a novel sodium iron chlorophyllin-H2O2 (SIC–H2O2) sludge pretreatment strategy before anaerobic digestion to enhance methane production. The efficiencies and mechanism of the proposed strategy to enhance sludge biodegradability were explored. The SIC–H2O2 pretreatment could enhance the oxidation performance for sludge floc disintegration to dissociate TB-EPS into S-EPS increased SCOD to 521.38 mg/L. The increase of solubilization and release of EPS with the pretreatment facilitate the biogas production at 702 L kg−1 VS, which was 3-folds of the control and significantly higher than other pretreatments. The result of excitation–emission matrix and parallel factor (EEM-PARAFAC) analysis showed that the SIC–H2O2 pretreatment enhanced the dissociation of TB-EPS fractions, especially the protein-like and soluble microbial by-product-like substances. Electron paramagnetic resonance (EPR) results provided evidence for homolytic catalysis H2O2 for the generation OH and the production of high-valent (Por)FeIV(O) intermediates. Synergistic effects of reactive oxygen species ( OH, H2O2 and /HO2) and (Por)FeIV(O) enhanced the EPS disintegration during SIC–H2O2 pretreatment. The mixed-acid type fermentation provided continuous VFAs supply under the enrichment of Chloroflexi and Actinobacteria and multiplication Methanosaeta also promoted methane production. This research provides a feasible pretreatment strategy increase sludge biodegradability and enhance biogas production in the anaerobic digestion process.

The utilization of recycled biochar combined with chemical leaching is an appropriate method to remove cadmium (Cd) from paddy soil. Some Cd-rich soil clay particulates (particulate Cd) are reported to be removed via biochar adsorption and the potential impact of biochar on soil properties need further study. The removal efficiencies and mechanisms of Cd from soil by using floatable hydroxyapatite modified biochar (HBC) combined with CaCl2 were studied. Synergetic removal efficiencies of total Cd (46.5%) and bioavailable Cd (37.9%) from the paddy soil were achieved with 2% HBC and 1 mM CaCl2. The increased soluble Cd in soil pore water by CaCl2 leaching could be efficiently adsorbed on HBC, and removed by HBC collection, reducing the risk of the residual soluble Cd in soil pore water to rice plants caused by the inefficient drainage in the field. The suspendability of clay particulates in overlying water was little affected by the low-level CaCl2 based on Derjaguin-Landau-Verwey-Overbeek (DLVO) calculation. Moreover, low-level CaCl2 facilitated the accumulation of particulate Cd on the floating HBC via decreasing the interaction energy (by 25%) between clay particulates and HBC. HBC-mediated Cd migration contributed ~70% of total Cd removal, while soluble and particulate Cd removed through the drainage accounted for ~30%. Soil clay proportion maintained at 25.3% due to the replenishment of HBC residues. In addition, soil nutrient and physicochemical conditions were improved with HBC residues. This work provides a novel soil remediation method by using floatable biochar combined with low-level CaCl2 for Cd-contaminated paddy soil remediation.

In this study, preparation of hierarchically porous biochar (PB) and simultaneous nutrient recovery from sewage sludge were realized through three steps of KHCO3-activated pyrolysis, water leaching and acid leaching. The prepared PB samples were applied as adsorbents for the removal of 4-chlorophenol (4-CP) from aqueous solutions. Effect of pyrolysis temperature on the physicochemical properties of PB samples was investigated. The PB prepared at 900 °C (PB-900) had the highest surface area (1476.0 m2/g) and total pore volume (1.138 cm3/g). The formation mechanism of porous structure of PB-900 was revealed by investigating the phase transformation, element distribution and pore structure evolution during its whole preparation process. PB-900 showed a high 4-CP adsorption rate of 14.4 mg/(g∙min), and its maximum adsorption capacity for 4-CP was up to 192.4 mg/g. The mechanism of 4-CP removal by PB-900 was mainly physical adsorption, and its strong aromaticity strengthened its interaction with 4-CP through π-π bonding. The water leaching solution in the preparation process of PB-900 contained a lot of nutrient elements (K, Si, P), which was recovered for grass seeds germination. Compared with the samples cultured with ultrapure water only, the seed germination rate of samples cultured with ultrapure water added with 20% of pretreated water leaching solution increased from 63% to 80%, and the average shoot length of grass grown for 7 days increased by 51.4%. The findings of this study suggest that KHCO3 is an alternative activator to prepare hierarchically porous biochar adsorbent from sewage sludge and realize simultaneous nutrient recovery.

The evaluation of ecological risks of contaminant mixtures to organisms is very challenging due to the non-linear response of organisms to each component, especially under the co-existence of both stimulators and inhibitors. Whether the stimulatory effect can reduce or even offset the inhibitory effect would be critical to the risk assessment and the treatment measures of mixed pollutants. Here, the combined toxicity of sodium fluoride (NaF), a stimulator with stimulation rate >100%, and six compounds that cannot induce hormesis (four ionic liquids (ILs) and two pesticides) were studied. The time-dependent toxicity of each toxicant on Vibrio qinghaiensis sp.-Q67 was investigated at 0.25, 2, 4, 6, 8, 10 and 12 h. Results showed that four ILs and two pesticides failed to induce hormesis, while NaF induced hormesis from 2 to 6 h and induced stimulation only after 6 h and reached its maximum (650%) at 12 h. All mixture rays with NaF induced hormesis at different times. In the four NaF-IL mixture systems, the absolute value of maximum stimulation demonstrated an upwards and then a downwards trend with the increasing of mixture ratio of IL. In two NaF-pesticide systems, the maximum stimulation effect declined with the increasing of the mixture ratio of pesticide. The toxicities of the mixture were successfully predicted by the improved inverse distance weighted interpolation, which are not able to be predicted by the commonly used concentration addition or independent action models. This paper shed lights on evaluating the hormesis of mixtures and the ecological risk of fluoride.

Deep dewatering of sewage sludge pretreated with advanced oxidation processes (AOPs) is a strategy for efficient sludge reduction and subsequent disposal. The pretreatment and dewatering performance of sludge conditioned with three types of AOPs (Fe2+/H2O2, Fe2+/Ca(ClO)2, and Fe2+/Na2S2O8), compared with sludge conditioned with traditional conditioner (Fe3+/CaO), were investigated in both bench and pilot-scale tests. All of those conditioner systems could reduce the water content of dewatered sludge cake to below 60 wt% in bench-scale (about 16 kg raw sludge per round) and pilot-scale (approximate 800 kg raw sludge per round) diaphragm filter press dewatering. Compared with raw sludge, the deep-dewatering filtrate after different conditioning and dewatering processes had higher ammonia nitrogen (NH4+-N) and chemical oxygen demand (COD) contents due to the degradation of organic matter, and much lower total phosphorus (TP) content due to the formation of iron phosphate precipitate. A better biodegradability (i.e. higher BOD5/COD ratio) was found in the deep-dewatering filtrate of sludge conditioned with Fe2+/H2O2 (25.2 %) and Fe2+/Ca(ClO)2 (17.4 %). Most of the heavy metals (Cr, Cu, Ni, and Pb) (>79 wt%) have remained in the dewatered sludge cake, and most of the Cl element (>90 wt%) in the sludge pretreated by Fe2+/Ca(ClO)2 and Fe3+/CaO was kept in the filtrate, rather than the dewatered sludge cake. Based on the pilot-scale experimental results, if all the filtrate in the deep-dewatering process returned to the influent of WWTP, the loading ratios of TP, NH4+-N, COD in the four conditioner systems were less than 3 wt%. The above results proved that the AOPs conditioned sludge could achieve deep-dewatering in pilot-scale and the direct recirculation of deep-dewatering filtrate to the influent of wastewater treatment plant was feasible.

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).

Fractional pretreatment of lignocellulose is compelling to synergistically enhance its carbohydrate and lignin outputs for the extension of renewable energy sources. A two-stage approach using hydrothermal and ionic liquid (1-butyl-3-methylimidazoliumacesulfamate, [bmim]Ace) pretreatments was evaluated for hierarchically extracting hemicelluloses and lignin from Tamarix austromongolica, while providing a cellulose-rich fraction that could be readily hydrolyzed by cellulase for the recovery of fermentable glucose and residual lignin. Autohydrolysate-derived xylooligosaccharides (XOS), high-quality lignin, and accessible cellulose were successively acquired at the end of the process. The molecular weights, structural characteristics, functional groups and transitional fate of hemicelluloses and lignin were thoroughly explored towards a waste-free concept. This integrated biorefinery removed the amorphous portions, disrupted the rigid structure and altered cellulose I to II, thereby improving the enzymatic digestibility from 11.6 to 90.2%. Results confirmed that 60.98 mg/g XOS (DP 2–6), 352 mg/g glucose and 178.2 mg/g lignin were harvested via this coupled process. In-depth HSQC and 31P NMR techniques signified that the lignins contained large amounts of β-aryl ether units and hydroxyl groups, rendering them essentially suitable for depolymerizing into aromatic chemicals from biomass to energy. It was reasonable to diversify the energy-oriented product portfolio as a function of this sequential process, such as high-purity XOS, fermentable glucose and lignin, which can remarkably boost the feasibility of bioenergy.

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.

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.

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.