Reuse of Fenton sludge as an iron source for NiFe_2O_4 synthesis and its application in the Fenton-based process

The potentially hazardous iron-containing sludge from the Fenton process requires proper treatment and disposal, which often results in high treatment cost. In this study, a novel method for the reuse of Fenton sludge as an iron source for the synthesis of nickel ferrite particles(NiFe_2O_4) is proposed. Through a co-precipitation method followed by sintering at 800°C, magnetic NiFe_2O_4 particles were successfully synthesized, which was confirmed by powder X-ray diffraction(XRD), scanning electronic microscopy(SEM), energy dispersive spectroscopy(EDS), Fourier transform infrared spectroscopy(FT-IR) and Raman spectroscopy. The synthesized NiFe_2O_4 could be used as an efficient catalyst in the heterogeneous Fenton process. In phenol degradation with H_2O_2 or NiFe_2O_4 alone, the phenol removal efficiencies within the reaction time of 330 min were as low as 5.9% ± 0.1% and 13.5% ±0.4%, respectively. However, in the presence of both NiFe_2O_4 and H_2O_2, phenol removal efficiency as high as 95% ± 3.4% could be achieved, indicating the excellent catalytic performance of NiFe_2O_4 in the heterogeneous Fenton process. Notably, a rapid electron exchange between_Ni II and_Fe III ions in the NiFe_2O_4 structure could be beneficial for the Fenton reaction. In addition, the magnetic catalyst was relatively stable, highly active and recoverable, and has potential applications in the Fenton process for organic pollutant removal.

Coupled biodegradation of p-nitrophenol and p-aminophenol in bioelectrochemical system:Mechanism and microbial functional diversity

Biodegradation mechanisms and microbial functional diversity during coupled pnitrophenol(PNP)and p-aminophenol(PAP)degradation were studied in a bioelectrochemical system.PNP in the biocathode and PAP in the bioanode were almost completely removed within 28 hr and 68 hr respectively.The degradation followed the steps including hydrating hydroxyalkylation,dehydrogenating carbonylation,and hydrolating ring cleavage,etc.Metagemomic analysis based on the KEGG and egg NOG database annotations revealed the microbial composition and functional genes/enzymes related to phenol degradation in the system.The predominant bacteria genera were Lautropia,Pandoraea,Thiobacillus,Ignavibacterium,Truepera and Hyphomicrobium.The recognized biodegradation genes/enzymes related to pollutant degradation were as follows:pmo,hbd,&ppo for phenol degradation,nzba,amie,&badh for aromatic degradation,and CYP&p450 for xenobiotics degradation,etc.The co-occurrence of ARGs(antibiotic resistant genes),such as ade F,Mex J,Erm F,PDC-93 and Escherichiacolimdf A,etc.,were annotated in CARD database during the biodegradation process.The Proteobacteria&Actinobacteria phylum was the primary host of both the biodegradation genes&ARGs in this system.The microbial functional diversity ensured the effective biodegradation of the phenol pollutants in the bioelectrochemical system.

Partial aging can counter-intuitively couple with sulfidation to improve the reactive durability of zerovalent iron

Sulfated zero-valent iron(SZVI)has shown promising applications in wastewater treatment.However,the rapid decline in the reactivity of SZVI with time limits its real practice.To mediate this problem,partial aging was proposed to improve the reactive durability of SZVI.Taking Cr(VI)as the target contaminant,we found that the aged ZVI(AZVI)gradually lost reactivity as aging time increased from 0.5 to 2 d.Counter-intuitively,the partially aged SZVI(ASZVI)showed greater reactivity than SZVI when exposed to oxygenated water for a period ranging from 0.5 to 14 d.In addition,the ASZVI with 0.5 d of aging time(ASZVI-0.5)not only maintained reactivity in successive runs but also increased the Cr(VI)removal capacity from 9.1 mg/g by SZVI to 19.1 mg/g by ASZVI-0.5.Correlation analysis further revealed that the electron transfer from the Fe0 core to the shell was mediated by the conductive FeS and FeS2 in the subshell of ASZVI.Meanwhile,the lepidocrocite and magnetite on the surface of ASZVI facilitated Cr(VI)adsorption and subsequent electron transfer for Cr(VI)reduction.Moreover,the iron(hydr)oxide shell could retain the conductive FeS and FeS2 in the subshell,allowing ASZVI to reduce Cr(VI)efficiently and sustainably.In general,partial aging can enhance the reactive durability of ZVI when coupled with sulfidation and this synergistic effect will be beneficial to the application of SZVI-based technology for wastewater treatment.

Solar evaporation for simultaneous oil-water separation and electricity generation with Janus wood-based absorbers

Oily wastewater from ocean oil spills endangers marine ecosystems and human health. Therefore, developing an effective and sustainable solution for separating oil-water mixtures is urgent. Interfacial solar photothermal evaporation is a promising approach for the complete separation of two-phase mixtures using only solar energy. Herein, we report a carbonized wood-based absorber with Janus structure of comprising a hydrophobic top-layer and an oleophobic bottom-layer for simultaneous solar-driven oil-water separation and electricity generation. Under sunlight irradiation, the rapid evaporation of seawater will induce a separation of oil-water mixtures, and cause a high salt concentration region underlying the interface, while the bottom “bulk water” maintains in a low salt concentration, thus forming a salinity gradient. Electricity can be generated by salinity gradient power. Therefore, oil-water separation efficiency of > 99% and derived extra electricity power of ~0.1 W/m2 is achieved under solar radiation, demonstrating the feasibility of oil-water separation and electricity production synchronously directly using solar energy. This work provides a green and cost-effective path for the separation of oil-water mixtures.

Confinement of Fe atoms between MoS_(2) interlayers drives phase transition for improved reactivity in Fenton-like reactions

Phase manipulation of MoS_(2) from thermodynamically stable 2H phase to the unstable but more reactive 1T phase represents a crucial strategy for improving the reactivity in many reactions.The widely adopted wet chemistry approach uses intercalating entities especially alkali metal ions to achieve the phase transition;however,these entities are normally inert for the target reaction.Here,we describe the first use of iron atoms for the intercalation of 2H-MoS_(2) layers,driving the partial transition from 2H to 1T phase.Interestingly,in the peroxymonosulfate(PMS)-based Fenton-like reactions,the interlayered confinement of Fe atoms not only activates the inert basal plane,but also adds more reactive Fe sites for the formation of metal-PMS complex as primary reactive species for pollutant removal.In the degradation of a model pollutant carbamazepine(CBZ),the Fe-intercalated MoS_(2) exhibits a first order rate constant 13.3 times higher than 2H-MoS_(2).This strategy is a new direction for manipulating the phase composition and boosting the catalytic reactivity of MoS_(2)-based catalysts in various scenarios,including environmental remediation and energy applications.

Reductive transformation and detoxification mechanism of 2,4-dinitrochlorobenzene in combined zero valent iron and anaerobic-aerobic process

A combined zero valent iron (ZVI) and anaerobic-aerobic process was adopted for the treatment of 2,4-dinitrochlorobenzene (DNCB)-containing wastewater. The transformation pathway, reduction of acute toxicity and enhancement of biodegradability were investigated. After pretreatment by ZVI, DNCB in wastewater could be completely converted into 2,4-diaminochlorobenzene (DACB). The ratio of BOD5/COD increased from 0.005±0.001 to 0.168±0.007, while EC 50, 48 hr (V/V) increased from 0.65% to 5.20%, indicating the enhancement of biodegradability and reduction of acute toxicity with the pretreatment by ZVI. DACB was further dechlorinated to m-phenylenediamine during the anaerobic process using methanol as electron donor, with EC50, 48 hr increasing from 5.20% to 48.2%. After the subsequent anaerobic-aerobic process, m-phenylenediamine was degraded completely, with effluent COD of 67.5±10.8 mg/L. This effluent of the subsequent anaerobic-aerobic process was not toxic to zebrafish. The combined ZVI and anaerobic-aerobic process offers bright prospects for the treatment of chlorinated nitroaromatic compound-containing wastewater.

3D dahlia-like NiAl-LDH/CdS heterosystem coordinating with 2D/2D interface for efficient and selective conversion of CO_(2)

Developing photocatalyst with high activity,superior stability and prominent selectivity for CO_(2)conversion is of great importance for the target of carbon neutralization.Herein,3 D dahlia-like NiAl-LDH/CdS heterosystem is developed through in-situ decoration of exfoliated CdS nanosheets on the scaffold of NiAl-LDH and the on-spot self-assembly.The formation of a hierarchical architecture collaborating with well-defined 2 D/2 D interfacial interaction is constructed by optimizing the ratio of CdS integrated in the formation of the heterojunction.The light-harvesting capacity of NiAl-LDH/CdS is improved by this unique scaffold,and the charge transfer between NiAl-LDH and CdS is effectively facilitated by virtue of the unique 2 D/2 D interface.As a result,the 3 D hierarchical NiAl-LDH/CdS heterosystem presents 12.45μmol g^(-1)h^(-1)of CO production(3.3 and 1.6 folds of pristine NiAl-LDH and CdS) with 96% selectivity and superior stability.This 3 D hierarchical design collaborating with 2 D/2 D interfacial interaction provides a new avenue to develop ideal catalysts for artificial photosynthesis.

Weakly hydrophobic nanoconfinement by graphene aerogels greatly enhances the reactivity and ambient stability of reactivity of MIL-101-Fe in Fenton-like reaction

In the pursuit of heterogeneous catalysts with high reactivity,metal organic framework(MOF)nanomaterials have received tremendous attentions.However,many MOF catalysts especially Fe-based MOFs need to be utilized immediately after synthesis or being activated using high temperature,because of the easy loss of reactivity in humid environments resulting from the occupation of active Fe sites by water molecules.Here,we describe an inspiring strategy of growing MIL-101-Fe nanoparticles inside the three-dimensional confined space of graphene aerogel(GA),generating shapeable GA/MIL-101-Fe nanocomposite convenient for practical use.Compared to MIL-101-Fe,GA/MIL-101-Fe as catalyst demonstrates much higher reactivity in Fenton-like reaction,attributing to smaller MIL-101-Fe particle size,presence of active Fe(II)sites,and abundant defects in GA.Strikingly,the weakly hydrophobic nature of the composite greatly inhibits the loss of catalytic reactivity after being stored in humid air and accelerates the recovery of reactivity in mild temperature,by resisting the entrance of water molecules and helping to exclude water molecules.This work demonstrates that a delicate design of nanocomposite structure could not only improve the reactivity of the catalytic component,but also overcome its intrinsic drawback by taking advantage of the properties of host.We hope this functional nanoconfinement strategy could be extended to more scenarios in other fields.

Formable porous biochar loaded with La-Fe(hydr)oxides/montmorillonite for efficient removal of phosphorus in wastewater:process and mechanisms

The development of biochar-based granule-like adsorbents suitable for scaled-up application has been attracting increasing attention in the field of water treatment.Herein,a new formable porous granulated biochar loaded with La-Fe(hydr)oxides/montmorillonite(LaFe/MB)was fabricated via a granulation and pyrolysis process for enhanced phosphorus(P)removal from wastewater.Montmorillonite acted as a binder that increased the size of the granulated biochar,while the use of Fe promoted the surface charge and facilitated the dispersion of La,which was responsible for selective phosphate removal.LaFe/MB exhibited rapid phosphate adsorption kinetics and a high maximum adsorption capacity(Langmuir model,52.12 mg P g^(−1)),which were better than those of many existing granulated materials.The desorption and recyclability experiments showed that LaFe/MB could be regenerated,and maintained 76.7%of its initial phosphate adsorption capacity after four adsorption cycles.The high hydraulic endurance strength retention rate of the developed material(91.6%)suggested high practical applicability in actual wastewater.Electro-static attraction,surface precipitation,and inner-sphere complexation via ligand exchange were found to be involved in selective P removal over a wide pH range of 3-9.The thermodynamic parameters were determined,which revealed the feasibility and spontaneity of adsorption.Based on approximate site energy distribution analyses,high distribution frequency contributed to efficient P removal.The research results provide a new insight that LaFe/MB shows great application prospects for advanced phosphate removal from wastewater.

Fungal diversity and its mechanism of community shaping in the milieu of sanitary landfill

Land filling is the main method to dispose municipal solid waste in China.During the decomposition of organic waste in landfills,fungi play an important role in organic carbon degradation and nitrogen cycling.However,fungal composition and potential functions in landfill have not yet been characterized.In this study,refuse and leachate samples with different areas and depths were taken from a large sanitary landfill in Beijing to identify fungal communities in landfills.In high-throughput sequencing of ITS region,474 operational taxonomic units(OTUs)were obtained from landfill samples with a cutoff level of 3%and a sequencing depth of 19962.The results indicates that Ascomycota,with the average relative abundance of 84.9%,was the predominant phylum in landfill fungal communities.At the genus level,Family Hypocreaceae unclassified(15.7%),Fusarium(9.9%)and Aspergillus(8.3%)were the most abundant fungi found in the landfill and most of them are of saprotrophic lifestyle,which plays a big role in nutrient cycling in ecosystem.Fungi existed both in landfilled refuse and leachate while both the richness and evenness of fungal communities were higher in the former.In addition,fungal communities in landfilled refuse presented geographic variances,which could be partly attributed to physical habitat properties(pH,dissolved organic carbon,volatile solid,NH_(4)^(+),NO_(2)^(−)and NO_(3)^(−)),while NO_(3)^(−)was considered the most significant factor(p<0.05)in shaping fungal community.

Unraveling natural aging-induced properties change of sludge-derived hydrochar and enhanced cadmium sorption site heterogeneity

Hydrochar has potential applications in soil improvement and heavy metal remediation.Hydrochar would undergo the process of aging when introduced into the soil,altering its properties.However,recent studies have focused mainly on the artificial aging of hydrochar,which could not reveal the cumulative effect of multiple environmental factors.Therefore,the periodical monitoring of the property and sorption behavior of hydrochar after amending soils is necessary to better understand the multifaceted mechanisms associated with the natural aging of hydrochar.This study selected the sludge-derived hydrochar(SLHC)as a typical hydrochar and applied a 16-month rice-wheat-rice rotation to mimic the natural aging of hydrochar,focusing on changing properties and cadmium(Cd)sorption and literature contrast between aging strategies and biochar types.The porosity,O abundance,and ash content of 16-month aged SLHC increased by 37%,47%,and 8.5%,respectively,facilitating Cd sorption due to surface complexation,pore sorption,and precipitation.The sorption percentage of Cd to SLHC was in the range of 11-14%for SLHC-A0 and increased to 17-31%for SLHC-A4 and 20-32%for SLHC-A16 after natural aging.The natural aging of SLHC induced by ash content played an essential role in Cd sorption site heterogeneity.Linear regression analysis showed that aging strategies on sorption behavior significantly differed between biochars.Thus,studies involving natural aging with multiple environmental factors are preferred over those involving chemical or biological aging.Future studies should continue to explore the mechanisms of natural aging-induced heavy metal sorption between hydrochar and pyrochar.These results improve insights to appraise the potential of SLHC as soil amendments to alleviate the adverse effects of heavy metal contamination and provide an essential basis for researchers and staff in soil management and environmental prevention.

A hybrid fuel cell for water purification and simultaneously electricity generation

The development of highly efficient energy conversion technologies to extract energy from wastewater is urgently needed,especially in facing of increasing energy and environment burdens.Here,we successfully fabricated a novel hybrid fuel cell with BiOCl-NH_(4)PTA as photocatalyst.The polyoxometalate(NH_(4)PTA)act as the acceptor of photoelectrons and could retard the recombination of photogenerated electrons and holes,which lead to superior photocatalytic degradation.By utilizing BiOCl-NH_(4)PTA as photocatalysts and Pt/C air-cathode,we successfully constructed an electron and mass transfer enhanced photocatalytic hybrid fuel cell with flow-through field(F-HFC).In this novel fuel cell,dyes and biomass could be directly degraded and stable power output could be obtained.About 87%of dyes could be degraded in 30 min irradiation and nearly 100%removed within 90 min.The current density could reach up to~267.1μA/cm^(2);with maximum power density(Pmax)of~16.2μW/cm^(2) with Rhodamine B as organic pollutant in F-HFC.The power densities were 9.0μW/cm^(2),12.2μW/cm^(2),and 13.9μW/cm^(2) when using methyl orange(MO),glucose and starch as substrates,respectively.This hybrid fuel cell with BiOCl-NH_(4)PTA composite fulfills the purpose of decontamination of aqueous organic pollutants and synchronous electricity generation.Moreover,the novel design cell with separated photodegradation unit and the electricity generation unit could bring potential practical application in water purification and energy recovery from wastewater.

Removal of phosphate from wastewater using alkaline residue

Alkaline residue(AR) was found to be an efficient adsorbent for phosphate removal from wastewater. The kinetic and equilibrium of phosphate removal were investigated to evaluate the performance of modified alkaline residue. After treatment by NaOH(AR-NaOH), removal performance was significantly improved, while removal performance was almost completely lost after treatment by HCl(AR-HCl). The kinetics of the removal process by all adsorbents was well characterized by the pseudo second-order model. The Langmuir model exhibited the best correlation for AR-HCl, while AR was effectively described by Freundlich model. Both models were well fitted to AR-NaOH. The maximum adsorption capacities calculated from Langmuir equation were in following manner: AR-NaOH > AR > AR-HCl. Phosphate removal by alkaline residue was pH dependent process. Mechanisms for phosphate removal mainly involved adsorption and precipitation, varied with equilibrium pH of solution. For AR-HCl, the acid equilibrium pH(< 6.0) was unfavorable for the formation of Ca-P precipitate, with adsorption as the key mechanism for phosphate removal. In contrast, for AR and ARNaOH, precipitation was the dominant mechanism for phosphate removal, due to the incrase on pH(> 8.0) after phosphate removal. The results of both XRD and SEM analysis confirmed CaHPO4·2H2O formation after phosphate removal by AR and AR-NaOH.

Simultaneous pyridine biodegradation and nitrogen removal in an aerobic granular system

Simultaneous pyridine biodegradation and nitrogen removal were successfully achieved in a sequencing batch reactor(SBR) based on aerobic granules. In a typical SBR cycle, nitritation occurred obviously after the majority of pyridine was removed, while denitrification occurred at early stage of the cycle when oxygen consumption was aggravated. The effect of several key operation parameters, i.e., air flow rate, influent NH_4^+-N concentration,influent p H and pyridine concentration, on nitritation, pyridine degradation and total nitrogen(TN) removal, was systematically investigated. The results indicated that high air flow rate had a positive effect on both pyridine degradation and nitritation but a negative impact of overhigh air flow rate. With the increase of NH_4^+ dosage, both nitritation and TN removal could be severely inhibited. Slightly alkaline condition, i.e., pH 7.0–8.0, was beneficial for both pyridine degradation and nitritation. High pyridine dosage often resulted in the delay of both pyridine degradation and nitritation. Besides, extracellular polymeric substances production was affected by air flow rate, NH_4^+ dosage, pyridine dosage and p H.In addition, high-throughput sequencing analysis demonstrated that Bdellovibrio and Paracoccus were the dominant species in the aerobic granulation system. Coexistence of pyridine degrader, nitrification related species, denitrification related species, polymeric substances producer and self-aggregation related species was also confirmed by highthroughput sequencing.

Nanoscale zero-valent iron supported on biochar for the highly efficient removal of nitrobenzene

The application of nanoscale zero-valent iron (nZVI) in the remediation of contaminated groundwater or wastewater is limited due to its lack of stability, easy aggregation and iron leaching. To address this issue, nZVI was distributed on oak sawdust-derived biochar (BC) to obtain the nZVI/BC composite for the highly efficient reduction of nitrobenzene (NB). nZVI, BC and nZVI/BC were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). For nZVI/BC, nZVI particles were uniformly dispersed on BC. nZVI/BC exhibited higher removal efficiency for NB than the simple summation of bare nZVI and BC. The removal mechanism was investigated through the analyses of UV-Visible spectra, mass balance and XPS. NB was quickly adsorbed on the surface of nZVI/BC, and then gradually reduced to aniline (AN), accompanied by the oxidation of nZVI to magnetite. The effects of several reaction parameters, e.g., NB concentration, reaction pH and nZVI/BC aging time, on the removal of NB were also studied. In addition to high reactivity, the loading of nZVI on biochar significantly alleviated Fe leaching and enhanced the durability of nZVI.

Graphene enhancedα-MnO_(2) for photothermal catalytic decomposition of carcinogen formaldehyde

Formaldehyde(HCHO)causes increasing concerns due to its ubiquitously found in indoor air and being irritative and carcinogenic to humans.Photothermal-catalysis developed in recent years has been considered as a significant strategy for enhancing catalytic activity.Manganese oxides,compared with its strong thermocatalytic activity,generally suffer from much lower photocatalytic activity make its photochemical properties less concerned.Herein,α-MnO_(2)nanowires were composited with the graphene oxide(GO)via mechanical grinding and co-precipitating method,respectively.α-MnO_(2)/GO nanohybrids prepared by co-precipitating method exhibits excellent activity,achieving 100%decomposition of HCHO with the solar-light irradiation at ambient temperature.It is found that,besides the photo-driven thermocatalysis,the photocatalysis mechanism made a major contribution to the decomposition of HCHO.The incorporation of GO,on the one hand,is beneficial to improve the optical absorption capacity and photothermal conversion efficiency;on the other hand,is conductive to electron transfer and effective separation of electrons and holes.These synergistic effects significantly improve the catalytic activity ofα-MnO_(2)/GO nanohybrids.This work proposes a new approach for the utilization of solar energy by combining manganese oxides,and also develops an efficient photothermal-catalyst to control HCHO pollution in indoor air.