Recovery of Ni(II) from real electroplating wastewater using fixed-bed resin adsorption and subsequent electrodeposition

Resin adsorption and subsequent electrodeposition were used for nickel recovery. Treated wastewater can meet the Electroplating Pollutant Discharge Standard. The spent resin is completely regenerated by 3 BV of 4% HCl solution. 95.6% of nickel in concentrated eluent was recovered by electrodeposition. Effective recovery of high-value heavy metals from electroplating wastewater is of great significance, but recovering nickel ions from real electroplating wastewater as nickel sheet has not been reported. In this study, the pilot-scale fixed-bed resin adsorption was conducted to recover Ni(II) ions from real nickel plating wastewater, and then the concentrated Ni(II) ions in the regenerated solution were reduced to nickel sheet via electrodeposition. A commercial cation-exchange resin was selected and the optimal resin adsorption and regeneration conditions were investigated. The resin exhibited an adsorption capacity of 63 mg/g for Ni(II) ions, and the average amount of treated water was 84.6 bed volumes (BV) in the pilot-scale experiments. After the adsorption by two ion-exchange resin columns in series and one chelating resin column, the concentrations of Ni(II) in the treated wastewater were below 0.1 mg/L. After the regeneration of the spent resin using 3 BV of 4% (w/w) HCl solution, 1.5 BV of concentrated neutral nickel solution (>30 g/L) was obtained and used in the subsequent electrodeposition process. Using the aeration method, alkali and water required in resin activation process were greatly reduced to 2 BV and 3 BV, respectively. Under the optimal electrodeposition conditions, 95.6% of Ni(II) in desorption eluent could be recovered as the elemental nickel on the cathode. The total treatment cost for the resin adsorption and regeneration as well as the electrodeposition was calculated.     

Synthesis of vinasse-dolomite nanocomposite biochar via a novel developed functionalization method to recover phosphate as a potential fertilizer substitute

• Nanocomposites were prepared by adding dolomite to vinasse at different ratio. • Textural and morphological features of adsorbents were studied in detail. • CCD based RSM was used for investigation of P ion removal by nanocomposite. • The q_m based on Langmuir model for modified vinasse biochar was 178.57 mg/g. • P loaded nanocomposite improved plant growth and could be utilized as P-fertilizer. The effectiveness of phosphate (P) removal from aqueous solutions was investigated by novel low-cost biochars synthesized from vinasse and functionalized with calcined dolomite. The vinasse-derived biochar, synthesized via pyrolysis at different temperatures, showed easy preparation and a large surface area. The novel vinasse biochar nanocomposites were prepared by adding dolomite to the vinasse biochars with different weight percentages (10, 20 and 30%). The characteristics of the prepared materials were identified for further understanding of the inherent adsorption mechanism between P ions and vinasse biochars. Vinasse-dolomite nanocomposite was very effective in the adsorption of P species from aqueous media. The effect of the operational factors on Vinasse-dolomite nanocomposite was explored by applying response surface methodology (RSM). According to RSM results, the optimum condition was achieved to be contact time 90 (min), 250 (mg/L) of P concentration and pH 7. Thermodynamic isotherm and kinetic studies were applied on experimental data to understand the adsorption behavior. The Vinasse-dolomite nanocomposite revealed preferential P species adsorption in the presence of co-existing anions. The P species could be recovered by 1.0 M HCl where the efficiency was not affected up to the fifth cycle. The P-loaded Vinasse-dolomite nanocomposite was successfully tested on a plant; it significantly improved its growth and proved its potency as a P-based fertilizer substitute.     

Ammonia and phosphorus removal from agricultural runoff using cash crop waste-derived biochars

• Orange tree residuals biochar had a better ability to adsorb ammonia. • Modified tea tree residuals biochar had a stronger ability to remove phosphorus. • Partially-modified biochar could remove ammonia and phosphorus at the same time. • The real runoff experiment showed an ammonia nitrogen removal rate of about 80%. • The removal rate of total phosphorus in real runoff experiment was about 95%. Adsorption of biochars (BC) produced from cash crop residuals is an economical and practical technology for removing nutrients from agricultural runoff. In this study, BC made of orange tree trunks and tea tree twigs from the Laoguanhe Basin were produced and modified by aluminum chloride (Al-modified) and ferric sulfate solutions (Fe-modified) under various pyrolysis temperatures (200°C–600°C) and residence times (2–5 h). All produced and modified BC were further analyzed for their abilities to adsorb ammonia and phosphorus with initial concentrations of 10–40 mg/L and 4–12 mg/L, respectively. Fe-modified Tea Tree BC 2h/400°C showed the highest phosphorus adsorption capacity of 0.56 mg/g. Al-modified Orange Tree BC 3h/500°C showed the best performance for ammonia removal with an adsorption capacity of 1.72 mg/g. FTIR characterization showed that P = O bonds were formed after the adsorption of phosphorus by modified BC, N-H bonds were formed after ammonia adsorption. XPS analysis revealed that the key process of ammonia adsorption was the ion exchange between K⁺ and NH₄⁺. Phosphorus adsorption was related to oxidation and interaction between PO₄^3– and Fe³⁺. According to XRD results, ammonia was found in the form of potassium amide, while phosphorus was found in the form of iron hydrogen phosphates. The sorption isotherms showed that the Freundlich equation fits better for phosphorus adsorption, while the Langmuir equation fits better for ammonia adsorption. The simulated runoff infiltration experiment showed that 97.3% of ammonia was removed by Al-modified Orange tree BC 3h/500°C, and 92.9% of phosphorus was removed by Fe-modified Tea tree BC 2h/400°C.     

Mercury removal from aqueous solution using petal-like MoS2 nanosheets

• Synthesized few-layered MoS₂ nanosheets via surfactant-assisted hydrothermal method. • Synthesized MoS₂ nanosheets show petal-like morphology. • Adsorbent showed 93% of mercury removal efficiency. • The adsorption of mercury is attributed to negative zeta potential (-21.8 mV). Recently, different nanomaterial-based adsorbents have received greater attention for the removal of environmental pollutants, specifically heavy metals from aqueous media. In this work, we synthesized few-layered MoS₂ nanosheets via a surfactant-assisted hydrothermal method and utilized them as an efficient adsorbent for the removal of mercury from aqueous media. The synthesized MoS₂ nanosheets showed petal-like morphology as confirmed by scanning electron microscope and high-resolution transmission electron microscopic analysis. The average thickness of the nanosheets is found to be about 57 nm. Possessing high stability and negative zeta potential makes this material suitable for efficient adsorption of mercury from aqueous media. The adsorption efficiency of the adsorbent was investigated as a function of pH, contact time and adsorbent dose. The kinetics of adsorption and reusability potential of the adsorbent were also performed. A pseudo-second-order kinetics for mercury adsorption was observed. As prepared MoS₂ nanosheets showed 93% mercury removal efficiency, whereas regenerated adsorbent showed 91% and 79% removal efficiency in the respective 2^nd and 3^rd cycles. The adsorption capacity of the adsorbent was found to be 289 mg/g at room temperature.     

Crosslinking acrylamide with EDTA-intercalated layered double hydroxide for enhanced recovery of Cr(VI) and Congo red: Adsorptive and mechanistic study

• Functional groups of AM and EDTA in composite increased removal of Cr(VI) and CR. • Removal process reached equilibrium within 30 min and was minimally affected by pH. • Elimination of Cr(VI) was promoted by coexisting CR. • Adsorption process of CR was less influenced by the presence of Cr(VI). • Mechanisms were electrostatic attraction, surface complexation and anion exchange. We prepared ethylenediaminetetraacetic acid (EDTA)-intercalated MgAl-layered double hydroxide (LDH-EDTA), then grafted acrylamide (AM) to the LDH-EDTA by a cross-linking method to yield a LDH-EDTA-AM composite; we then evaluated its adsorptive ability for Congo red (CR) and hexavalent chromium (Cr(VI)) in single and binary adsorption systems. The adsorption process on LDH-EDTA-AM for CR and Cr(VI) achieved equilibrium quickly, and the removal efficiencies were minimally affected by initial pH. The maximum uptake quantities of CR and Cr(VI) on LDH-EDTA-AM were 632.9 and 48.47 mg/g, respectively. In mixed systems, chromate removal was stimulated by the presence of CR, while the adsorption efficiency of CR was almost not influenced by coexisting Cr(VI). The mechanisms involved electrostatic attraction, surface complexation, and anion exchange for the adsorption of both hazardous pollutants. In the Cr(VI) adsorption process, reduction also took place. The removal efficiencies in real contaminated water were all higher than those in the laboratory solutions.     

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

• Biochar supported nanoscale zero-valent iron composite (nZVI/BC) was synthesized. • nZVI/BC quickly and efficiently removed nitrobenzene (NB) in solution. • NB removal by nZVI/BC involves simultaneous adsorption and reduction mechanism. • nZVI/BC exhibited better catalytic activity, stability and durability than nZVI. 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.     

Ammonia removal from low-strength municipal wastewater by powdered resin combined with simultaneous recovery as struvite

• Powdered resin was employed for ammonia recovery from municipal wastewater. • Powdered resin achievedefficient ammonia removal under various working conditions. • Co-existing cations indicated competitive adsorption of ammonia. • Ammonia was recoveredby two-stage crystallization coupled with ion exchange. Low-strength municipal wastewater is considered to be a recoverable nutrient resource with economic and environmental benefits. Thus, various technologies for nutrient removal and recovery have been developed. In this paper, powdered ion exchange resin was employed for ammonia removal and recovery from imitated low-strength municipal wastewater. The effects of various working conditions (powdered resin dosage, initial concentration, and pH value) were studied in batch experiments to investigate the feasibility of the approach and to achieve performance optimization. The maximum adsorption capacity determined by the Langmuir model was 44.39 mg/g, which is comparable to traditional ion exchange resin. Further, the effects of co-existing cations (Ca²⁺, Mg²⁺, K⁺) were studied. Based on the above experiments, recovery of ammonia as struvite was successfully achieved by a proposed two-stage crystallization process coupled with a powdered resin ion exchange process. Scanning electron microscopy (SEM) and X-ray diffractometry (XRD) results revealed that struvite crystals were successfully gained in alkaline conditions (pH= 10). This research demonstrates that a powdered resin and two-stage crystallization process provide an innovative and promising means for highly efficient and easy recovery from low-strength municipal wastewater.     

Influence of phosphate on deposition and detachment of TiO2 nanoparticles in soil

We examined influence of phosphate on transport of TiO₂ NPs in soil. Deposition was reduced at higher pH and by adsorption of phosphate in soil. Release was more for NPs initially deposited at higher pH. Release was more for NPs initially deposited in the presence of phosphate. Surface roughness and charge heterogeneity play a role in the deposition/ release. The widespread use of TiO₂ nanoparticles (NPs) makes inevitable their release into the soil. Phosphate is also widespread within soil, and is likely copresent with TiO₂ NPs. However, the influence of phosphate on deposition/release— and thereby on transport— of TiO₂ NPs in soil is yet to be elucidated. In this study we conducted saturated column experiments to systematically examine the transport of TiO₂ NPs in soil amended with phosphate at different ionic strengths (ISs) (1, 10, 100 mmol/L NaCl) and pHs (4 and 9). Results show that the deposition of TiO₂ NPs decreased with decreasing IS, increasing pH, and when soil absorbed phosphate. These observations are qualitatively in agreement with Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy calculations, because the repulsive energy barrier is larger and secondary minimum depth is smaller at a lower IS, higher pH, and in the presence of phosphate. Accordingly, both primary- and secondary-minimum deposition were inhibited. Interestingly, although the deposition was less at higher pH and in the presence of phosphate, the subsequent spontaneous detachment and detachment by reduction of solution IS in these cases were greater. In addition, the presence of phosphate in the solution can cause a small quantity of attached TiO₂ NPs to detach, even without perturbations of physical and chemical conditions. Our study was the first to investigate the influence of phosphate on detachment of TiO₂ NPs and the results have important implication for accurate prediction of fate and transport of TiO₂ NPs in subsurface environments.     

Dibutyl phthalate adsorption characteristics using three common substrates in aqueous solutions

• DBP adsorption was tested using three kinds of substrates in constructed wetlands. • The DBP adsorption capacity followed the order: steel slag>gravel>shell sand. • High temperatures increased the DBP adsorption capacity in the substrates. • DOM consistently inhibited the DBP adsorption onto steel slag and gravel. In recent years, the presence and adverse impacts of phthalic acid esters in aquatic environments have gained increasing attention. This work investigated the adsorption behavior of a typical phthalic acid ester, dibutyl phthalate (DBP), onto steel slag, gravel, and shell sand (substrates commonly used in constructed wetlands). The influence of dissolved organic matter (DOM) on DBP adsorption was investigated using humic acid as a proxy for DOM. The results demonstrated that the adsorption of DBP to three substrates reached equilibrium within 96 h, and the adsorption kinetics were well fitted by a pseudo-second-order model. The DBP adsorption isotherms were best fitted by the Langmuir adsorption model. The DBP adsorption capacity decreased in the order of steel slag>gravel>shell sand, with values of 656 mg/kg, 598 mg/kg, and 6.62 mg/kg at 25°C, respectively. DBP adsorbed to the surface of all substrates in a monolayer via an endothermic process. The DBP adsorption capacities of steel slag and gravel decreased as the DOM content increased. The DBP adsorption mechanisms to steel slag and gravel mainly involved the surface coordination of DBP with –OH or –COOH groups and electrostatic interactions. The results of this work suggest that steel slag and gravel may be ideal substrates for use in constructed wetlands to treat wastewater polluted with DBP.     

In situ formation of bimetallic FeNi nanoparticles on sand through green technology: Application for tetracycline removal

• In situ preparation of FeNi nanoparticles on the sand via green synthesis approach. • Removal of tetracycline using GS-FeNi in batch and column study. • Both reductive degradation and sorption played crucial role the process. • Reusability of GS-FeNi showed about 77.39±4.3% removal on 4th cycle. • TC by-products after interaction showed less toxic as compared with TC. In this study, FeNi nanoparticles were green synthesized using Punica granatum (pomegranate) peel extract, and these nanoparticles were also formed in situ over quartz sand (GS-FeNi) for removal of tetracycline (TC). Under the optimized operating conditions, (GS-FeNi concentration: 1.5% w/v; concentration of TC: 20 mg/L; interaction period: 180 min), 99±0.2% TC removal was achieved in the batch reactor. The removal capacity was 181±1 mg/g. A detailed characterization of the sorbent and the solution before and after the interaction revealed that the removal mechanism(s) involved both the sorption and degradation of TC. The reusability of reactant was assessed for four cycles of operation, and 77±4% of TC removal was obtained in the cycle. To judge the environmental sustainability of the process, residual toxicity assay of the interacted TC solution was performed with indicator bacteria (Bacillus and Pseudomonas) and algae (Chlorella sp.), which confirmed a substantial decrease in the toxicity. The continuous column studies were undertaken in the packed bed reactors using GS-FeNi. Employing the optimized conditions, quite high removal efficiency (978±5 mg/g) was obtained in the columns. The application of GS-FeNi for antibiotic removal was further evaluated in lake water, tap water, and ground water spiked with TC, and the removal capacity achieved was found to be 781±5, 712±5, and 687±3 mg/g, respectively. This work can pave the way for treatment of antibiotics and other pollutants in the reactors using novel green composites prepared from fruit wastes.     

Degradation of metronidazole by dielectric barrier discharge in an aqueous solution

The discharge characteristics during the degradation of MNZ by DBD were investigated. Increasing the discharge frequency can promote the degradation of MNZ. MNZ removal reaches 99.1% at the initial concentration of 40 ppm within 120 min. Coexisting organic matter inhibits the degradation of MNZ. The energy efficiency of DBD for MNZ removal is higher than other technologies. Degradation of metronidazole (MNZ) which is a representative and stable antibiotic by dielectric barrier discharge (DBD) in an aqueous solution has been studied. Effects of initial MNZ concentration, solution pH and coexisting organics on the degradation were investigated. The results illustrated that increasing the input power and the discharge frequency can improve the removal of MNZ. At low initial concentration, the removal of MNZ can reach up to 99.1%. Acidic and neutral conditions are more favorable for MNZ removal than alkaline condition in the early stage of degradation. However, the difference in MNZ removal between those in acidic or neutral media and that in alkaline one could be neglected with prolonging of the treatment time. Therefore, this method can be applied to MNZ degradation with a wide pH range. Coexisting organic matter in water can attenuate the removal to some extent. This study could provide valuable references for the degradation of nitroimidazole antibiotics by DBD.     

Impacts of advanced treatment processes on elimination of antibiotic resistance genes in a municipal wastewater treatment plant

The distributions of ARGs were monitored in a WWTP in Harbin during six months. CASS had the best removal efficacy of ARGs compared to other processes in the WWTP. UV disinfection could effectively control the HGT. AGAC significantly remove ARGs and organics due to its high absorption capacity. Combination of ozone and AGAC significantly improve removal of ARGs and organics. Antibiotic resistance genes (ARGs) pose a serious threat to public health. Wastewater treatment plants (WWTPs) are essential for controlling the release of ARGs into the environment. This study investigated ARG distribution at every step in the treatment process of a municipal WWTP located in Harbin for six consecutive months. Changes in ARG distribution involved in two advanced secondary effluent treatment processes, ozonation and granular activated carbon (GAC) adsorption, were analyzed. Biological treatment resulted in the highest ARG removal (0.76–1.94 log reduction), followed by ultraviolet (UV) disinfection (less than 0.5-log reduction). Primary treatment could not significantly remove ARGs. ARG removal efficiency increased with an increase in the ozone dose below 40 mg/L. However, amorphous GAC (AGAC) adsorption with a hydraulic retention time (HRT) of 1 h showed better removal of ARGs, total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) than ozonation at a 60 mg/L dose. UV treatment could efficiently reduce the relative ARG abundance, despite presenting the lowest efficiency for the reduction of absolute ARG abundance compared with GAC and ozone treatments. The combination of ozone and AGAC can significantly improve the removal of ARGs, TOC, TN and TP. These results indicate that a treatment including biological processing, ozonation, and AGAC adsorption is a promising strategy for removing ARGs and refractory organic substances from sewage.     

Enhanced triallyl isocyanurate (TAIC) degradation through application of an O3/UV process: Performance optimization and degradation pathways

• UV/O₃ process had higher TAIC mineralization rate than O₃ process. • Four possible degradation pathways were proposed during TAIC degradation. • pH impacted oxidation processes with pH of 9 achieving maximum efficiency. • CO₃^2– negatively impacted TAIC degradation while HCO₃^– not. • Cl^– can be radicals scavenger only at high concentration (over 500 mg/L Cl^–). Triallyl isocyanurate (TAIC, C₁₂H₁₅N₃O₃) has featured in wastewater treatment as a refractory organic compound due to the significant production capability and negative environmental impact. TAIC degradation was enhanced when an ozone(O₃)/ultraviolet(UV) process was applied compared with the application of an independent O₃ process. Although 99% of TAIC could be degraded in 5 min during both processes, the O₃/UV process had a 70%mineralization rate that was much higher than that of the independent O₃ process (9%) in 30 min. Four possible degradation pathways were proposed based on the organic compounds of intermediate products identified during TAIC degradation through the application of independent O₃ and O₃/UV processes. pH impacted both the direct and indirect oxidation processes. Acidic and alkaline conditions preferred direct and indirect reactions respectively, with a pH of 9 achieving maximum Total Organic Carbon (TOC) removal. Both CO₃^2– and HCO₃^– decreased TOC removal, however only CO₃^2– negatively impacted TAIC degradation. Effects of Cl^– as a radical scavenger became more marked only at high concentrations (over 500 mg/L Cl^–). Particulate and suspended matter could hinder the transmission of ultraviolet light and reduce the production of HO· accordingly.     

Removal and recovery of toxic nanosized Cerium Oxide using eco-friendly Iron Oxide Nanoparticles

• Eco-friendly IONPs were synthesized through solvothermal method. • IONPs show very high removal efficiency for CeO₂ NPs i.e. 688 mg/g. • Removal was >90% in all synthetic and real water samples. • >80% recovery of CeO₂ NPs through sonication confirms reusability of IONPs. Increasing applications of metal oxide nanoparticles and their release in the natural environment is a serious concern due to their toxic nature. Therefore, it is essential to have eco-friendly solutions for the remediation of toxic metal oxides in an aqueous environment. In the present study, eco-friendly Iron Oxide Nanoparticles (IONPs) are synthesized using solvothermal technique and successfully characterized using scanning and transmission electron microscopy (SEM and TEM respectively) and powder X-Ray diffraction (PXRD). These IONPs were further utilized for the remediation of toxic metal oxide nanoparticle, i.e., CeO₂. Sorption experiments were also performed in complex aqueous solutions and real water samples to check its applicability in the natural environment. Reusability study was performed to show cost-effectiveness. Results show that these 200 nm-sized spherical IONPs, as revealed by SEM and TEM analysis, were magnetite (Fe₃O₄) and contained short-range crystallinity as confirmed from XRD spectra. Sorption experiments show that the composite follows the pseudo-second-order kinetic model. Further R²>0.99 for Langmuir sorption isotherm suggests chemisorption as probable removal mechanism with monolayer sorption of CeO₂ NPs on IONP. More than 80% recovery of adsorbed CeO₂ NPs through ultrasonication and magnetic separation of reaction precipitate confirms reusability of IONPs. Obtained removal % of CeO₂ in various synthetic and real water samples was>90% signifying that IONPs are candidate adsorbent for the removal and recovery of toxic metal oxide nanoparticles from contaminated environmental water samples.     

In situ synthesis of FeS/Carbon fibers for the effective removal of Cr(VI) in aqueous solution

• FeS/carbon fibers were in situ synthesized with Fe-carrageenan hydrogel fiber. • The double helix structure of carrageenan is used to load and disperse Fe. • Pyrolyzing sulfate groups enriched carrageenan-Fe could easily generate FeS. • The adsorption mechanisms include reduction and complexation reaction. Iron sulfide (FeS) nanoparticles (termed FSNs) have attracted much attention for the removal of pollutants due to their high efficiency and low cost, and because they are environmentally friendly. However, issues of agglomeration, transformation, and the loss of active components limit their application. Therefore, this study investigates in situ synthesized FeS/carbon fibers with an Fe-carrageenan biomass as a precursor and nontoxic sulfur source to ascertain the removal efficiency of the fibers. The enrichment of sulfate groups as well as the double-helix structure in ι-carrageenan-Fe could effectively avoid the aggregation and loss of FSNs in practical applications. The obtained FeS/carbon fibers were used to control a Cr(VI) polluted solution, and exhibited a relatively high removal capacity (81.62 mg/g). The main mechanisms included the reduction of FeS, electrostatic adsorption of carbon fibers, and Cr(III)-Fe(III) complexation reaction. The pseudo-second-order kinetic model and Langmuir adsorption model both provided a good fit of the reaction process; hence, the removal process was mainly controlled by chemical adsorption, specifically monolayer adsorption on a uniform surface. Furthermore, co-existing anions, column, and regeneration experiments indicated that the FeS/carbon fibers are a promising remediation material for practical application.     

TiO2@palygorskite composite for the efficient remediation of oil spills via a dispersion-photodegradation synergy

• A novel and multi-functional clay-based oil spill remediation system was constructed. • TiO₂@PAL functions as a particulate dispersant to break oil slick into tiny droplets. • Effective dispersion leads to the direct contact of TiO₂ with oil pollutes directly. • TiO₂ loaded on PAL exhibits efficient photodegradation for oil pollutants. • TiO₂@PAL shows a typical dispersion-photocatalysis synergistic remediation. Removing spilled oil from the water surface is critically important given that oil spill accidents are a common occurrence. In this study, TiO₂@Palygorskite composite prepared by a simple coprecipitation method was used for oil spill remediation via a dispersion-photodegradation synergy. Diesel could be efficiently dispersed into small oil droplets by TiO₂@Palygorskite. These dispersed droplets had an average diameter of 20–30 mm and exhibited good time stability. The tight adsorption of TiO₂@Palygorskite on the surface of the droplets was observed in fluorescence and SEM images. As a particulate dispersant, the direct contact of TiO₂@Palygorskite with oil pollutants effectively enhanced the photodegradation efficiency of TiO₂ for oil. During the photodegradation process, •O₂⁻and •OH were detected by ESR and radical trapping experiments. The photodegradation efficiency of diesel by TiO₂@Palygorskite was enhanced by about 5 times compared with pure TiO₂ under simulated sunlight irradiation. The establishment of this new dispersion-photodegradation synergistic remediation system provides a new direction for the development of marine oil spill remediation.     

Biogenic palladium prepared by activated sludge microbes for the hexavalent chromium catalytic reduction: Impact of relative biomass

• Pd nanoparticles could be reduced and supported by activated sludge microbes. • The effect of biomass on Pd adsorption by microbes is greater than Pd reduction. • More biomass reduces Pd particle size, which is more dispersed on the cell surface. • When the biomass/Pd add to 6, the catalytic reduction rate of Cr(VI) reaches stable. Palladium, a kind of platinum group metal, owns catalytic capacity for a variety of hydrogenations. In this study, Pd nanoparticles (PdNPs) were generated through enzymatic recovery by microbes of activated sludge at various biomass/Pd, and further used for the Cr(VI) reduction. The results show that biomass had a strong adsorption capacity for Pd(II), which was 17.25 mg Pd/g sludge. The XRD and TEM-EDX results confirmed the existence of PdNPs associated with microbes (bio-Pd). The increase of biomass had little effect on the reduction rate of Pd(II), but it could cause decreasing particle size and shifting location of Pd(0) with the better dispersion degree on the cell surface. In the Cr(VI) reduction experiments, Cr(VI) was first adsorbed on bio-Pd with hydrogen and then reduced using active hydrogen as electron donor. Biomass improved the catalytic activity of PdNPs. When the biomass/Pd (w/w) ratio increased to six or higher, Cr(VI) reduction achieved maximum rate that 50 mg/L of Cr(VI) could be rapidly reduced in one minute.     

Highly efficient and selective removal of phosphate from wastewater of sea cucumber aquaculture for microalgae culture using a new adsorption-membrane separation-coordinated strategy

● A new adsorption-membrane separation strategy is used for phosphate removal. ● PVC/Zr-BT shows a selective adsorption ability to low-concentration phosphate. ● Low concentration of P below 0.05 mg/L was achieved in actual wastewater treatment. ● Algal biomass production served as a demonstration of phosphorus recycling. Enhanced phosphorus treatment and recovery has been continuously pursued due to the stringent wastewater discharge regulations and a phosphate supply shortage. Here, a new adsorption-membrane separation strategy was developed for rational reutilization of phosphate from sea cucumber aquaculture wastewater using a Zr-modified-bentonite filled polyvinyl chloride membrane. The as-obtained polyvinyl chloride/Zr-modified-bentonite membrane was highly permeability (940 L/(m²·h)), 1–2 times higher than those reported in other studies, and its adsorption capacity was high (20.6 mg/g) when the phosphate concentration in water was low (5 mg/L). It remained stable under various conditions, such as different pH, initial phosphate concentrations, and the presence of different ions after 24 h of adsorption in a cross-flow filtration system. The total phosphorus and phosphate removal rate reached 91.5% and 95.9%, respectively, after the membrane was used to treat sea cucumber aquaculture wastewater for 24 h and no other water quality parameters had been changed. After the purification process, the utilization of the membrane as a new source of phosphorus in the phosphorus-free f/2 medium experiments indicated the high cultivability of economic microalgae Phaeodactylum tricornutum FACHB-863 and 1.2 times more chlorophyll a was present than in f/2 medium. The biomass and lipid content of the microalgae in the two different media were similar. The innovative polyvinyl chloride/Zr-modified-bentonite membrane used for phosphorus removal and recovery is an important instrument to establish the groundwork for both the treatment of low concentration phosphate from wastewater as well as the reuse of enriched phosphorus in required fields.     

The treatment of black-odorous water using tower bipolar electro-flocculation including the removal of phosphorus,turbidity, sulfion,and oxygen enrichment

• An innovative bubble column tower BPE was designed to treat the black-odorous water. • PO₄³⁻, S²⁻ and turbidity were removed, and dissolved oxygen was enriched in the BPE. • An aluminum bipolar electrode gave the best oxygen enrichment and pollutant removal. • Changes of microorganisms confirmed the improvement in water quality achieved. The large amount of municipal wastewater discharged into urban rivers sometimes exceeds the rivers’ self-purification capacity leading to black-odorous polluted water. Electro-flocculation has emerged as a powerful remediation technology. Electro-flocculation in a bubble column tower with a bipolar electrode (BPE) was tested in an attempt to overcome the high resistance and weak gas-floatation observed with a monopolar electrode (MPE) in treating such water. The BPE reactor tested had a Ti/Ta₂O₅-IrO₂ anode and a graphite cathode with an iron or aluminum bipolar electrode suspended between them. It was tested for its ability to reduce turbidity, phosphate and sulphion and to increase the concentration of dissolved oxygen. The inclusion of the bipolar electrode was found to distinctly improved the system’s conductivity. The system’s electro-flocculation and electrical floatation removed turbidity, phosphate and sulphion completely, and the dissolved oxygen level improved from 0.29 to 6.28 mg/L. An aluminum bipolar electrode performed better than an iron one. Changes in the structure of the microbial community confirmed a significant improvement in water quality.     

Distribution and removal of antibiotic resistance genes during anaerobic sludge digestion with alkaline,thermal hydrolysis and ultrasonic pretreatments

Sludge digestion is critical to control the spread of ARGs from wastewater to soil. Fate of ARGs in three pretreatment-AD processes was investigated. UP was more efficient for ARGs removal than AP and THP in pretreatment-AD process. The total ARGs concentration showed significant correlation with 16S rRNA gene. The bacteria carrying ARGs could be mainly affiliated with Proteobacteria. Sewage sludge in the wastewater treatment plants contains considerable amount of antibiotic resistance genes (ARGs). A few studies have reported that anaerobic digestion (AD) could successfully remove some ARGs from sewage sludge, but information on the fate of ARGs in sludge pretreatment-AD process is still very limited. In this study, three sludge pretreatment methods, including alkaline, thermal hydrolysis and ultrasonic pretreatments, were compared to investigate the distribution and removal of ARGs in the sludge pretreatment-AD process. Results showed that the ARGs removal efficiency of AD itself was approximately 50.77%, and if these three sludge pretreatments were applied, the total ARGs removal efficiency of the whole pretreatment-AD process could be improved up to 52.50%–75.07%. The ultrasonic pretreatment was more efficient than alkaline and thermal hydrolysis pretreatments. Although thermal hydrolysis reduced ARGs obviously, the total ARGs rebounded considerably after inoculation and were only removed slightly in the subsequent AD process. Furthermore, it was found that the total ARGs concentration significantly correlated with the amount of 16S rRNA gene during the pretreatment and AD processes, and the bacteria carrying ARGs could be mainly affiliated with Proteobacteria.