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Sustainable development entails the revival of biopolymer-based membranes for water treatment with the expectation of addressing concerns relevant to the depletion of fossil-based resources and the...

Tea polyphenols (TP) are natural green organic compounds with chelating and reducing properties, which can promote the catalytic reaction, but the mechanism of promotion is still uncertain. In this paper, the chelation and reduction of TP were used to promote the degradation of lincomycin (LCM) by zero-valent iron Fenton-like reaction, and the mechanism of the two properties of TP was analyzed. The results showed that in the Fe0/H2O2 system, the degradation rate of the reaction system was increased from 27% to 100% in two hours after the addition of TP, and the reaction rate was increased about 26 times. Moreover, the parameters of pH, Fe2+, ·OH, oxidation reduction potential (ORP) and so forth indicating that the chelating structure of TP and iron ions was formed under pH = 4–9, which obviously promoted the mutual conversion of Fe3+/Fe2+. It is propitious to the proper amount of iron dissolution in order to facilitate the continuous and efficient Fenton reaction. Under acidic conditions, the TP are more reductive due to the destruction of the chelate structure, which promotes the conversion of Fe3+ to Fe2+ or even zero-valent iron, significantly improves the Fe3+/Fe2+ cycle capacity and increases the amount of OH produced.

Few studies have focused on the effects of biomass feedstocks on the structure–reactivity of magnetic biochar. In this study, four types of magnetic biochar were first prepared using steel pickling waste liquor (serving as iron salt) and sugarcane bagasse (SMBC), rice straw (RMBC), peanut shells (PMBC) and herb residue (HMBC). According to the Langmuir model, the maximum adsorption capacity of Cr(VI) by SMBC was 43.122 mg/g, which was approximately 1.298 times, 3.175 times and 3.677 times higher than that of RMBC, PMBC and HMBC, respectively. The mass balance of chromium indicated that Cr(VI) was removed mainly via reduction. However, the reduction capacity of Cr(VI) differed among the four types of magnetic biochar. The results of characterisations of those magnetic composites before and after reaction demonstrated that the Cr(VI) was electrostatically attracted to the surface of the materials. Consequently, most of the adsorbed Cr(VI) was reduced and the remainder of the Cr(VI) was complexed with C O groups in magnetic biochar. Further, the total iron in magnetic biochar, especially Fe(II), played a dominant role in the removal and reduction of Cr(VI). Finally, correlation analysis showed that the cellulose and ash in the biomass were the main factors that induced the differences in the magnetic biochar’s total iron content. Therefore, this study may provide a reference for the use of magnetic biochar to remove Cr(VI) from aqueous solutions.

The use of plant extracts as reducing agents may be preferable to use of chemical reduction reagent (i.e. sodium borohydride) to synthesis of iron-based nanoparticles for using in wastewater treatment. This report describes the successful synthesis of iron-based nanoparticles (NA-Fe-NPs) using extracts of Nephrolepis auriculata. TEM and XRD indicated that the core of NA-Fe-NPs were amorphous and spherical with size ranging from 40 to 70 nm. Meanwhile, FT-IR revealed that the flavonoids, polyphenols, organic acids in extracts were responsible for reducing Fe3+ and coating/stabilizing the iron-nanoparticles. The removal of Cr(VI) wastewater using NA-Fe-NPs suggested that 90.93% of Cr(VI) were removed, demonstrated the feasibility of the materials for environmental remediation.

Reducing the preparation cost of magnetic biochar is necessary for its large-scale application as an adsorbent. In this study, stainless steel pickling waste liquor and rice straw were successfully applied to synthesize of magnetic biochar (SPWL-MBC). Several iron oxides adhered on the biochar matrix, mainly Fe3O4, Fe2O3 and FeO. SPWL-MBC exhibited superparamagnetism, and its specific surface area was 274.29 m2/g. The material was able to adsorb a model contaminant, crystal violet (CV), with a maximum adsorption capacity of approximately 111.48 mg/g. Adsorption mechanism analysis showed that iron oxides, π-π interaction, hydrogen bonding and electrostatic interaction were responsible for the adsorption of CV. The CV adsorption efficiency of SPWL-MBC remained 71.91% after three adsorption-regeneration cycles. These outcomes illustrate that the magnetic biochar prepared from stainless steel pickling waste liquor can effectively remove CV from wastewater.

Dissolution in an alkali/urea aqueous solution offers a novel way to prepare chitosan membranes via immersion precipitation, whose underlying mechanisms are of fundamental interest to the improvement of filtration performance. This study employed optical coherence tomography (OCT) to in-situ characterize the gelation of chitosan dissolved in a LiOH/urea aqueous solution using pure water as the coagulation bath. The OCT datasets were numerically analyzed to resolve the conversion curves at various depths in the cast film, thereby establishing a method to estimate the phase-inversion rate in terms of the moving gelation front. The periodic competition between the solidification and diffusion of the polymer chains (i.e., the Liesegang phenomenon) was revealed and analyzed in terms of the assumption that the phase inversion should be dominated by the removal of the gelation inhibitors (i.e., the alkali and urea). It was further confirmed by a comparative study that the alkali could play a relatively important role and the porous morphology could be effectively tuned by varying the concentration of alkali in the coagulation bath. All the characterization results provided evidence correlating the reduction in the connectivity of the polymer network with the retarded gelation. This study would shed light on the development of novel methods for fabricating chitosan membranes with optimized geometrical and topological characteristics.

Particulate fouling is detrimental to membrane-based processes for water/wastewater treatment, water reclamation, desalination, and other applications. Although it has been recognized that curved channels can induce Dean vortices (i.e., the secondary flows arising from the centrifugal instability), the effects of the Dean vortices on the deposition of foulant particles remain unclear. 3D optical coherence tomography (OCT) imaging was employed by this study to quantitatively analyze the cake formation in a sinusoidally curved channel by evaluating the surface coverage and the average of the local cake thicknesses as a function of time. The characterization results for the curved channel were compared with those obtained in a straight channel to reveal the interplay between the cake formation and the Dean vortices. The effects of operating conditions were also studied by varying the crossflow rate of the feed solution. In particular, the evolution of cake morphology was analyzed by identifying the relatively active areas of cake growth and removal at various times. All the characterization results suggest that the Dean vortices induced by the sinusoidally curved channel could favor the reduction of the areas covered by the deposits, though this advantage might be partially offset owing to the formation of an extremely uneven cake layer. This work provides in-depth insights into the fouling behavior in a sinusoidally curved channel, which is of great value in optimizing the design of novel spacers for membrane-fouling control.

The use of a membrane with a relatively loose ‘active layer’ opened a new paradigm for the application of osmotically driven processes. An effective way of imparting the osmotic pressure difference across the ‘active layer’ is to employ divalent salts as the draw solute, whose negative effects on the organic fouling have been documented in the literature. This study was targeted on investigating the fouling by clay suspensions when performing the forward osmosis (FO) with a nanofiltration (NF)-like membrane. Optical coherence tomography (OCT) was exploited to analyze the fouling phenomena in a way of determining the critical point of the initial flux, below which the fouling could be completely or partially inhibited. In comparison with the flux-decline measurements, the OCT-based characterization generated a series of digitalized cake layers for numerically evaluating the surface coverage and specific deposit, which provides direct evidence to support the hypothesis that the back diffusion of the draw solute could have significant impact on the initial deposition of the clay particles. That is, the presence of the draw solute in the boundary layer could favor the slow growth of the cake layer even if the initial flux was lower than the critical point. Mapping the local growth rates also indicates that the increase in affinity between the membrane and the clay particles could vary the characteristics of the instability-induced streamwise vortices. In particular, the markedly decreased critical point of the initial flux highlights the role of divalent cations in forming coordinate bonds between the clay particles and the NF-like membrane. All the characterization results offer valuable knowledge to enhance the design of the novel osmotically driven processes.

Magnetic biochars with different iron content were synthesised and used for Cr(VI) removal. The species of iron oxides in that magnetic materials were Fe3O4, Fe2O3 and FeO, which were identified by various instruments. Scanning electron microscope indicated that the iron oxides distributed into the pores or on the surface of the biochar matrix, meanwhile, transmission electron microscopy illustrated that the exposed crystal planes of iron oxides in the magnetic biochar were difference. The maximum adsorption capacity of Cr(VI) by magnetic biochar was up to 71.04 mg/g and the adsorption capacity of Cr(VI) was positively correlated with iron content. Meanwhile, a series of experiments demonstrated that the FeO in the magnetic biochar was the key active component for the removal and reduction of Cr(VI). Finally, the mechanism analysis showed that the removal of Cr(VI) was attributed to the reduction, electrostatic adsorption and complexation, and reduction occupied a leading position. This study provides new insight into the role of iron oxides in magnetic biochar for the removal of Cr(VI).

The effects of the pyrolysis temperature on the Fenton-like catalytic performance of magnetic biochar remain unclear. In this study, magnetic biochar (SMBC300, SMBC400, SMBC500) was synthesised at various temperature (300 °C, 400 °C and 500 °C) and used for the Fenton-like degradation of metronidazole. The characterisation results demonstrated the similarity of functional groups and the species of iron oxides in three types of magnetic biochar. Moreover, the size distribution of iron oxides in these composites were obviously affected by the pyrolysis temperature. Metronidazole was rapidly and completely degraded by SMBC400 coupled with H2O2, and its kinetic rate constant was approximately 1.86 and 3.04 times higher than those of SMBC300 and SMBC500, respectively. Electron spin resonance and free radical quenching experiments showed that obvious differences in the ability of three types of magnetic biochar can heterogeneously activate H2O2 to generate OH, and that surface-bound OH plays a key role in the degradation of metronidazole. The differences in Fe (II) content among the types of magnetic biochar were the main reason for the differences in catalytic performance. The degradation of metronidazole by various species of iron oxides showed that FeO was the key component in the catalytic performance of magnetic biochar. This study confirms that magnetic biochar prepared at 400 °C has the best performance in the Fenton-like degradation of metronidazole.

The removal of contaminants by iron-based nanomaterials was inevitably affected by the natural organic matter (NOM), which is one of the most abundant material on earth and exists in natural waters. This study was performed to investigate the main influence of humic acid (HA, representing NOM) on the behavior and reactivity of Ni/Fe nanoparticles in the removal of deca-brominated diphenyl ether (BDE209). Generally, the inhibitory effect of HA on the removal of BDE209 by Ni/Fe showed greater significance with an increase of HA concentration. The zeta potential and sedimentation experiments showed that the HA enhanced the dispersion and stabilization of Ni/Fe particles; however, the removal of BDE209 was found to be inhibited. Moreover, the corrosion capacity of the Ni/Fe nanoparticles showed a positive correlation with the effect of HA on the reactivity of Ni/Fe nanoparticles. Meanwhile, typical quinone compounds in HA had an adverse effect on the removal of BDE209. Additionally, the competitive adsorption experiments and characterization illustrated that the adsorption of HA by Ni/Fe nanoparticles was superior to BDE209. Overall, it was proposed that the corrosion of Ni/Fe was reduced as the contact between the nanoparticles and H2O was hindered due to the surface of Ni/Fe was occupied by the adsorbed HA, and thus inhibited the reactivity of Ni/Fe nanoparticles in the removal of BDE209.

In this study, Fenton-like catalysts (magnetic biochar) were synthesised by pyrolysis the different biomass pre-impregnated with steel pickling waste liquor. The results of degradation of metronidazole illustrated that the catalytic performance of magnetic biochar was significantly affected by biomass feedstocks. Electron spin resonance (ESR) and radical quenching experiments showed that the hydroxide radicals (OH) were the key reactive oxygen species responsible for the metronidazole removal. Levels of OH varied among different systems consistent with the removal of metronidazole. The activation of H2O2 by carbon-containing components and Fe species (Fe2O3 and Fe3O4) in magnetic biochar were confirmed to be less crucial to the degradation of metronidazole. Moreover, the Fe(II) (FeO) in magnetic biochar played the dominating role in degradation of metronidazole, and the Fe(II) content difference caused by biomass feedstocks was responsible for differences in the catalytic performance of different types of magnetic biochar.

The PKS genes for biosynthesis of the polyether nanchangmycin are organized to encode two sets of proteins (six and seven ORFs, respectively), but are separated by independent ORFs that encode an epimerase, epoxidase, and epoxide hydrolase, and, notably, an independent ACP. One of the PKS modules lacks a corresponding ACP. We propose that the process of oxidative cyclization to form the polyether structure occurs when the polyketide chain is still anchored on the independent ACP before release. 4-O-methyl-L-rhodinose biosynthesis and its transglycosylation involve four putative genes, and regulation of nanchangmycin biosynthesis seems to involve activation as well as repression. In-frame deletion of a KR6 domain generated the nanchangmycin aglycone with loss of 4-O-methyl-L-rhodinose and antibacterial activity, in agreement with the assignments of the PKS domains catalyzing specific biosynthetic steps.

A cluster encoding genes for the biosynthesis of meilingmycin, a macrolide antibiotic structurally similar to avermectin and milbemycin alpha11, was identified among seven uncharacterized polyketide synthase gene clusters isolated from Streptomyces nanchangensis NS3226 by hybridization with PCR products using primers derived from the sequences of aveE, aveF and a thioesterase domain of the avermectin biosynthetic gene cluster. Introduction of a 24.1-kb deletion by targeted gene replacement resulted in a loss of meilingmycin production, confirming that the gene cluster encodes biosynthesis of this important anthelminthic antibiotic compound. A sequenced 8.6-kb fragment had aveC and aveE homologues ( meiC and meiE) linked together, as in the avermectin gene cluster, but the arrangement of aveF ( meiF) and the thioesterase homologues differed. The results should pave the way to producing novel insecticidal compounds by generating hybrids between the two pathways.

Several independent gene clusters containing varying lengths of type I polyketide synthase genes were isolated from ‘Streptomyces nanchangensis’ NS3226, a producer of nanchangmycin and meilingmycin. The former is a polyether compound similar to dianemycin and the latter is a macrolide compound similar to milbemycin, which shares the same macrolide ring as avermectin but has different side groups. Clusters A–H spanned about 133, 132, 104, 174, 122, 54, 37 and 59 kb, respectively. Two systems were developed for functional analysis of the gene clusters by gene disruption or replacement. (1) Streptomyces phage ϕC31 and its derived vectors can infect and lysogenize this strain. (2) pSET152, an Escherichia coli plasmid with ϕC31 attP site, and pHZ1358, a Streptomyces–Escherichia coli shuttle cosmid vector, both carrying oriT from RP4, can be mobilized from E. coli into NS3226 by conjugation. pHZ1358 was shown to be generally useful for generating mutant strains by gene disruption and replacement in NS3226 as well as in several other Streptomyces strains. A region in cluster A (∼133 kb) seemed to be involved in nanchangmycin production because replacement of several DNA fragments in this region by an apramycin resistance gene [aac3(IV)] gave rise to nanchangmycin non-producing mutants.

Shigella flexneri D15 R-plasmid CmR and Escherichia coli 1485 RifR were used to investigate the possible inhibition influence of Honggumycin on conjugative drug resistance R plasmid transfer between bacteria and elimination of R plasmid from the objective bacteria.30 μg/mL of Honggumycin was mixed with S.flexneri D15 R-plasmid CmR or E.coli 1485 RifR,which were separately cultured for 24 h and 48 h on MacConkey agar with or without chloromycetin.The inhibition rate and elimination rate of R plasmid were calculated according to the number of colonies from test group and control group.The results indicated that the transfer rate of R plasmid reached 92.82% and 96.04% in the medium with 30 μg/mL of Honggumycin for 24 h and 48 h,respectively.Besides,there was no significant effect of Honggumycin on elimination of R plasmid from S.flexneri D15 R-plasmid CmR.Therefore,Honggumycin could effectively inhibite conjugative R plasmid transfer from S.flexneri D15 R-plasmid CmR to E.coli 1485 RifR and was impossible to eliminate R plasmid.