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

Lithium ion batteries have been undergoing rapid development in the global market due to their superior performance. However, the soaring number of lithium ion batteries in the market presents serious disposal challenges at the end of life. Moreover, continuous mining processes are harmful to the environment. From the viewpoint of cleaner production and green chemistry, the efficient recovery and reutilization of spent lithium ion batteries are necessary. In this perspective, the overall process of lithium ion battery recycling, especially the recent advances of hydrometallurgical methods, are summarized, focusing on the leaching, separation, and purification processes. The proper disposal of the waste discharged during the recycling process is proposed, highlighting the mitigation of secondary pollution. In addition, the environmental impact of recycling processes is summarized and thoroughly evaluated by recent life cycle assessment studies, revealing the key role of recycling strategic metal elements toward sustainability in an anthropogenic cycle. Finally, the current challenges in this area are pointed out and perspectives on sustainable approaches, cleaner production, and life cycle assessment are proposed.

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.

Extracellular polymeric substance (EPS) is recognized as a critical component that determines sludge dewaterability. In this study, a layer by layer degradation of EPS was confirmed for the first t...

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

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

This study compared effects of three different valent iron (Fe0, Fe(II) and Fe(III)) on enhanced anaerobic sludge digestion, focusing on the changes of oxidation reduction potential (ORP), dissolved organic nitrogen (DON), and microbial community. Under the same iron dose in range of 0–160 mg/L after an incubation period of 30 days (d), the maximum methane production rate of sludge samples dosed with respective Fe0, Fe(II) and Fe(III) at the same concentration showed indiscernible differences at each iron dose, regardless of the different iron valence. Moreover, their behavior in changes of ORP, DON and microbial community was different: (1) the addition of Fe0 made the ORP of sludge more negative, and the addition of Fe(II) and Fe(III) made the ORP of sludge less negative. However, whether being more or less negative, the changes of ORP may show unobservable effects on methane yield when it ranged from −278.71 to −379.80 mV; (2) the degradation of dissolved organic nitrogen, particularly proteins, was less efficient in sludge samples dosed with Fe0 compared with those dosed with Fe(II) and Fe(III) after an incubation period of 30 d. At the same dose of 160 mg/L iron, more cysteine was noted in sludge samples dosed with Fe(II) (30.74 mg/L) and Fe(III) (27.92 mg/L) compared with that dosed with Fe0 (21.75 mg/L); (3) Fe0 particularly promoted the enrichment of Geobacter, and it was 6 times higher than those in sludge samples dosed with Fe(II) and Fe(III) at the same dose of 160 mg/L iron.

A microbial fuel cell-photocatalysis system with a novel photocatalytic air-cathode (MFC-PhotoCat) was proposed for synergistic degradation of 2,4,6-trichlorophenol (TCP) with simultaneous electricity generation. Stable electricity generation of 350 mV was achieved during 130 days of operation. Besides, 50 mg L−1 TCP was completely degraded within 72 h, and the rate constant of 0.050 h−1 was 1.8-fold higher than MFC with air-cathode without N-TiO2 photocatalyst. Degradation pathway was proposed based on the intermediates detected and density functional theory (DFT) calculation, with two open-chain intermediates (2-chloro-4-keto-2-hexenedioic acid and hexanoic acid) detected. Furthermore, hierarchical cluster and PCoA revealed significant shifts of microbial community structures, with enriched exoelectrogen (55.2% of Geobacter) and TCP-degrading microbe (7.1% of Thauera) on the cathode biofilm as well as 61.8% of Pseudomonas in the culture solution. This study provides a promising strategy for synergic degradation of recalcitrant contaminants by intimate-coupling of MFC and photocatalysis.

Biological wastewater treatment generates a large quantity of sewage sludge that requires proper treatments. In this study, the biochar pyrolyzed by sludge conditioned with Fenton's reagent and lime (referred to as Fenton-lime system) was first used as an efficient silicon fertilizer for rice cultivation. When the pyrolysis temperature was 750 °C, the dissolved silicon and available silicon contents in biochar derived from sludge conditioned with Fenton-lime system were much higher than those in raw sludge derived biochar without conditioning (3.49 vs. 0.72, 77.25 vs. 2.33 mg/g dry solid, respectively). The enhanced available silicon content was attributed to the newly formed calcium aluminosilicate from the reactions between the added lime and silicon-rich phases in sludge. The rice cultivated with biochar derived from Fenton-lime conditioned sludge showed improved biomass of stem and root by 76.85% and 36.11%, respectively, compared to blank group without the addition of Si source. Heavy metals and the reactive oxygen species (ROS) accumulation in rice were not observed after a culture period of 30 days in the application of sludge-derived biochar as silicon fertilizer. This study provides a promising approach for sewage sludge recycling as an efficient silicon fertilizer in silicon-deficiency land.

Many studies have investigated the effects of different pretreatments on the performance of anaerobic digestion of sludge. However, the detailed changes of dissolved organic nitrogen, particularly the release behavior of proteins and the byproducts of protein hydrolysis-amino acids, are rarely known during anaerobic digestion of sludge by different pretreatments. Here we quantified the changes of three types of proteins and 17 types of amino acids in sludge samples solubilized by ultrasonic, thermal, and acid/alkaline pretreatments and their transformation during anaerobic digestion of sludge. Tryptophan protein, aromatic protein I, aromatic protein II, and cysteine were identified as the key dissolved organic nitrogen responsible for methane production during anaerobic digestion of sludge, regardless of the different pretreatment methods. Different from the depletion of other amino acids, cysteine was resistant to degradation after an incubation period of 30 days in all sludge samples. Meanwhile, the “cysteine and methionine metabolism (K00270)” was absent in all sludge samples by identifying 6755 Kyoto Encyclopedia of Genes and Genomes assignments of genes hits. Cysteine contributed to the generation of methane and the degradation of acetic, propionic, and n-butyric acids through decreasing oxidation-reduction potential and enhancing biomass activity. This study provided an alternative strategy to enhance anaerobic digestion of sludge through in situ production of cysteine.

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

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

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

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

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

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

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

A geopolymer material was synthesized from alkali-thermal pretreated Fe-rich Bayer red mud (RM) and fly ash. Dissolution efficiencies of Al2O3 and SiO2 in the RM in alkaline solutions were improved by pretreatment. The transformation of mineral phases in the RM during synthesis of geopolymer was investigated by the alkaline leaching test, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The role of Fe species in geopolymerization was investigated by Mossbauer spectra. The results showed that binding energies of Al-O and Si-O increased in geopolymerization; the coordinated Fe3+ replaced Al3+ in the aluminosilicate structure of geopolymer.

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.

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

Leady oxide samples with various Fe contents were recovered from simulated spent lead paste with the addition of various dosages of iron oxides as simulated Fe impurities via hydrometallurgical process with sodium citrate-acetic acid solution. More than 75 wt% of the Fe element in simulated spent lead paste remained in the recovered leady oxide. The recovered leady oxide samples were used to prepare positive plates in order to illuminate the effect of Fe impurities on the phase composition of positive material. When the Fe content in recovered leady oxide was > 223 mg kg−1, the generation of 4PbOPbSO4 (4BS) during curing procedure was inhibited. The specific surface area, α-PbO2 content, and hydrated PbO2 content of positive active mass (PAM) after formation procedure decreased with the increase of Fe content. As a result, larger PbSO4 crystals formed in Fe-containing PAMs after cell discharge, which hindered the transfer of H2SO4 electrolyte and destroyed the interconnected PbO2 skeleton. The negative effect of Fe impurities on cell cycle performance was observed when the PAM was manufactured from the leady oxide containing only 49 mg kg−1 Fe element, with the cell capacity decreased from 2.2 to 1.0 Ah after only 230 charge-discharge cycles.

Electroplating sludge is a hazardous waste produced in large quantities in the electroplating industry during production. It is rich in heavy metal resources and can be recovered as value-added heavy metal products. To recover Zn in electroplating sludge, Fe/Al/Ca impurities were effectively removed as hematite, boehmite, and calcium sulfate, respectively, via a facile hydrothermal method with reduction of nitric acid by addition of glucose. After the sludge was dissolved in nitric acid, the generated solution contained 6.1 g/L of Zn, 2.2 g/L of Fe, 2.5 g/L of Al, and 2.9 g/L of Ca. First, approximately 100% Fe was extracted as hematite nanoparticles containing 94.6 wt% Fe2O3 after the solution was treated at 190 °C for 6 h. Second, when the temperature was elevated to 270 °C, nearly 99% Al was isolated as boehmite particles containing 95.2 wt% Al2O3. Third, more than 98% Ca was removed as anhydrite, which contained 95.9 wt% CaSO4, by adding sulfuric acid. During the steps, the total loss of Zn was less than 3%, and 5.75 g/L of residual Zn was recovered as zincite containing 92.2 wt% ZnO by adjusting the pH to 8. The dissolved Fe, Al, and Ca impurities were successfully removed as purified hematite, boehmite, and anhydrite, respectively, through the stepwise separation method by adjusting reaction temperatures and pH. The high content of Zn in the electroplating sludge was finally purified as zincite.

Microplastic accumulation in agricultural soils can stress plants and affects quality of the products. Current research on the effects of microplastics on plants is not consistent and the underlying mechanisms are yet unknown. Here, the molecular mechanisms of the stress response were investigated via metabolomic and transcriptomic analyses of rice Oryza sativa L. II Y900 and XS123 under the exposure of polystyrene microplastics (PS-MPs) in a field study. Distinct responses were obtained in these two rice subspecies, showing decreased head rice yield by 10.62% in Y900 and increase by 6.35% in XS123. The metabolomics results showed that PS-MPs exposure inhibited 29.63% of the substance accumulation-related metabolic pathways and 43.25% of the energy expenditure-related metabolic pathways in the Y900 grains; however, these related pathways were promoted in the XS123 grains. The transcriptomics results indicated that the expression of genes encoding proteins involved in the tricarboxylic acid cycle in the Y900 grains was inhibited, but it was enhanced in the XS123 grains. The XS123 subspecies could response against microplastic exposure stress through the metabolite accumulation and energy expenditure pathways, while the Y900 could not. The results provide insight into the perturbation of rice grains in farmlands with microplastics contamination.

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.

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

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

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

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

In this study, 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.

Enzymes have important advantages in sludge dewatering, but their catalytic performance is limited by their poor activity and stability. To address this issue, we develop a series of immobilized enzymes (immobilized acid protease, IE 1; immobilized pectinase, IE 2; immobilized laccase, IE 3) prepared by the electrostatic interaction between the Fe3O4@SiO2-NH2 as immobilized carrier and the free enzyme, and used for sludge dewatering. As-obtained immobilized enzymes endowed high efficiency and stable sludge dewatering performance in a wide pH range, and had the best dewatering performance when the pH was 5. Specifically, the specific resistance filtration (SRF) performance of the immobilized enzyme at pH 5 was better than that of the control group, and the order was FE 3, 3.84 × 1013 m kg−1 > FE 1, 2.52 × 1013 m kg−1 > CL 1, 2.16 × 1013 m kg−1 > CL 2, 1.34 × 1013 m kg−1 > FE 2, 2.06 × 1013 m kg−1 > IE 2, 0.89 × 1013 m kg−1 > IE 1, 0.82 × 1013 m kg−1 > IE 3, 0.73 × 1013 m kg−1. Such improvement is attributed to two respects: Firstly, the immobilized enzyme has good activity, stability, and abundant functional groups on the surface, which is conducive to the attachment and continuous decomposition of organic matter. Secondly, the solid immobilized carrier can construct the skeleton structure in situ and effectively promote the release of water in sludge. This study provides a feasible way for the practical application of biological enzyme in sludge dewatering.

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.

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

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

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

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

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

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

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

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