High efficient removal of 4-aminophenylarsonic acid from aqueous solution via enhanced FeOOH using Mn(VII).

Efficient removal of 4-aminophenylarsonic acid from contaminated water sources is essential to mitigate arsenic pollution. We proposed a competent technique to achieve 4-aminophenylarsonic acid removal via adsorption on enhanced α-FeOOH using various concentrations of Mn(VII). The elimination rate of 4-aminophenylarsonic acid applying FeOOH with Mn(VII) was dependent on acidic conditions. More than 99.9% of 4-aminophenylarsonic acid was eliminated in a 6-min reaction time under acidic conditions. The reaction of 4-aminophenylarsonic acid was fast at 4.0 and 5.0 pH, with its complete oxidation into arsenate and the liberation of manganese Mn(II) in the initial stage of the reaction. Similarly, the reaction rate constant (kobs) decreased from 0.7048 ± 0.02 to 0.00155 ± 0.00007 as the pH increased from 4.0 to 9.0. Oxidation capacity was considerably enhanced via the removal of electrons from 4-aminophenylarsonic acid to Mn(VII) after the creation of its radical intermediate and further change in Mn(III) to Mn(II) in the solution. The results showed that Mn(VII) played a crucial role in 4-aminophenylarsonic acid degradation at a low pH (e.g., 4.0), and the oxidation process proceeded in different manners, namely, electron transfer, hydroxylation, and ring-opening. These results illustrated that Mn(VII) is an effective, economic purification process to mitigate 4-aminophenylarsonic acid generated from poultry waste.

Removal of nickel and copper ions in strongly acidic conditions by in-situ formed amyloid fibrils.

The research investigated a novel strategy that can synchronously remove Ni2+ and Cu2+ by synthesizing amyloid fibrils under harsh conditions. The adsorption capacity of Ni2+ and Cu2+ increased by 18.5% and 34.1% respectively in the in-situ scenario as compared to that Ni2+ and Cu2+ were introduced after amyloid fibrils preparation, meantime, it avoids the generation of acidic waste liquid in the process of preparing amyloid fibrils. The adsorption behaviors of Ni2+ and Cu2+ can be well described by the pseudo-second-order kinetic model and Langmuir isotherm. The functional groups of amide, hydroxyl, and carboxyl played determining roles in the adsorption process. Moreover, when the amyloid fibrils were prepared in the presence of Ni2+ and Cu2+, i.e., the in-situ adsorption scenario, metal ions tended to occupy the functional sites, inhibit protein aggregation, and affect long amyloid fibrils synthesis accordingly. Metal ion-binding site prediction server was used to predict the binding sites of metal ions towards the protein sequence within amyloid fibrils, and the metal ion was observed to preferentially bind to a particular residue such as glutamic acid, cysteine, and serine. The amyloid fibrils be potentially valuable for the removal of heavy metals in strongly acidic wastewater such as acidic mining drainage.

Influence of floc dynamic protection layer on alleviating ultrafiltration membrane fouling induced by humic substances.

Cake layer formation is inevitable over time for ultrafiltration (UF) membrane-based drinking water treatment. Although the cake layer is always considered to cause membrane fouling, it can also act as a "dynamic protection layer", as it further adsorbs pollutants and dramatically reduces their chance of getting to the membrane surface. Here, the UF membrane fouling performance was investigated with pre-deposited loose flocs in the presence of humic acid (HA). The results showed that the floc dynamic protection layer played an important role in removing HA. The higher the solution pH, the more negative the floc charge, resulting in lower HA removal efficiency due to the electrostatic repulsion and large pore size of the floc layer. With decreasing solution pH, a positively charged floc dynamic protection layer was formed, and more HA molecules were adsorbed. The potential reasons were ascribed to the smaller floc size, greater positive charge, and higher roughness of the floc layer. However, similar membrane fouling performance was also observed for the negative and positive floc dynamic protection layers due to their strong looseness characteristics. In addition, the molecular weight (MW) distribution of HA also played an important role in UF membrane fouling behavior. For the small MW HA molecules, the chance of forming a loose cake layer was high with a negatively charged floc dynamic protection layer, while for the large MW HA molecules it was high with a positively charged floc dynamic protection layer. As a result, slight UF membrane fouling was induced.

Influence of sedimentation with pre-coagulation on ultrafiltration membrane fouling performance.

Coagulation plays an important role in effectively alleviating ultrafiltration (UF) membrane fouling due to the existence of flocs. In comparison to traditional filtration, direct filtration (no sedimentation tank) is generally considered to result in less membrane fouling due to the looser cake layer formed on the membrane surface. However, cake layer characteristics are easily influenced by operating conditions (e.g., sedimentation time, temperature), resulting in different fouling loads and the still very limited knowledge about the fouling behavior. Here, a detailed investigation of UF membrane performance was carried out to analyze the differences between traditional filtration and direct filtration. The results showed that a critical settling time indeed existed when flocs gradually settled, leading to severe membrane fouling induced by a dense and thick cake layer. Therefore, the traditional filtration performed worse when the settling time was shorter than the critical time, while it performed better when the settling time was longer. In comparison to room temperature water, the proportion of membrane fouling caused by the cake layer increased at low water temperature due to the contracted membrane pore size, and the cake layer thickness became the main fouling load. The longer the settling time, the fewer pollutants reached the membrane surface, the thinner the cake layer, and the lower the potential for membrane fouling. Thus, traditional filtration performed better than direct filtration, and the critical settling time was not obvious. Although solution pH played an important role in floc properties, the fouling load was influenced little and traditional filtration still performed better. This work shows that the cake layer properties/fouling loads vary with the settling time during the coagulation-UF process, and this finding is of great significance to the improvement of membrane technology in drinking water plants.

Simultaneous oxidation and sorption of highly toxic Sb(III) using a dual-functional electroactive filter.

One of the topics gaining lots of recent attention is the antimony (Sb) pollution. We have designed a dual-functional electroactive filter consisting of one-dimensional (1-D) titanate nanowires and carbon nanotubes for simultaneous oxidation and sorption of Sb(III). Applying an external limited DC voltage assist the in-situ conversion of highly toxic Sb(III) to less toxic Sb(V). The Sb(III) removal kinetics and efficiency were enhanced with flow rate and applied voltage (e.g., the Sb(III) removal efficiency increased from 87.5% at 0 V to 96.2% at 2 V). This enhancement in kinetics and efficiency are originated from the flow-through design, more exposed sorption sites, electrochemical reactivity, and limited pore size on the filter. The titanate-CNT hybrid filters perform effectively across a wide pH range of 3-11. Only negligible inhibition was observed in the presence of nitrate, chloride, and carbonate at varying concentrations. Our analyses using STEM, XPS, or AFS demonstrate that Sb were mainly adsorbed by Ti. DFT calculations suggest that the Sb(III) oxidation kinetics can be accelerated by the applied electric field. Exhausted titanate-CNT filters can be effectively regenerated by using NaOH solution. Moreover, the Sb(III)-spiked tap water generated ∼2400 bed volumes with a >90% removal efficiency. This study provides new insights for rational design of continuous-flow filters for the decontamination of Sb and other similar heavy metal ions.

Effects of bromide on the formation and transformation of disinfection by-products during chlorination and chloramination.

The presence of bromide ion (Br-) complicates the formation of disinfection by-products (DBPs) during chlorination and chloramination greatly. To better illustrate the role of Br-, Br- was introduced at different time intervals, i.e., 0min, 5min, 30min, and 24h, after dosing with chlorine (Cl2) or chloramine (NH2Cl), and the formation of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles, and haloacetones was investigated during these two disinfection scenarios. Ammonia rapidly reacts with chlorine and forms low-reactivity NH2Cl, and this effect inhibits the formation of these DBPs greatly. Br- promotes the formation of THMs, HAAs, and dichloroacetone (DCP) during chlorination, and the later bromide is introduced, i.e., the higher TCl2→Br- is, the more significant the formation of THMs and HAAs observed. Bromide incorporation factors (BIF) increase upon the introduction of Br-, and lower TCl2→Br- is related to higher BIF values. Additionally, Br- inhibits the formation of dichloroacetonitrile (DCAN) and trichloroacetone (TCP), owing to its catalytic degradation effect towards them. In the chloramination process, Br- shows similar effects towards the formation of THMs and HAAs, except that higher TNH2Cl→Br- inhibits their formation. Br- greatly inhibits the formation of DCP, TCP, and DCAN, and the formed haloacetones rapidly degrade upon the introduction of Br-. The results of UV and EEM spectral analysis indicate that the reducing Br- may improve rather than inhibit the oxidation of both the reactive components (DOC1) and the slowly reactive sites (DOC2) within HA, possibly owing to its buffering effect towards chlorine. In chlorination of source water with Br- present, Br- promotes the formation of most DBPs and enhances the incorporation of Br atoms therein, and in this case, DBP formation may be remarkably decreased by dosing with ammonia to transform chlorination to chloramination.

Adsorption combined with superconducting high gradient magnetic separation technique used for removal of arsenic and antimony.

Manganese iron oxide (MnFe2O4), an excellent arsenic(As)/antimony(Sb) removal adsorbent, is greatly restricted for the solid-liquid separation. Through the application of superconducting high gradient magnetic separation (HGMS) technique, we herein constructed a facility for the in situ solid-liquid separation of micro-sized MnFe2O4 adsorbent in As/Sb removal process. To the relative low initial concentration 50.0µgL-1, MnFe2O4 material sorbent can still decrease As or Sb below US EPA's drinking water standard limit. The separation of MnFe2O4 was mainly relied on the flow rate and the amount of steel wools in the HGMS system. At a flow rate 1Lmin-1 and 5% steel wools filling rate, the removal efficacies of As and Sb in natural water with the system were achieved to be 94.6% and 76.8%, respectively. At the meantime, nearly 100% micro-sized MnFe2O4 solid in the continuous field was readily to be separated via HGMS system. In a combination with the experiment results and finite element simulation, the separation was seemed to be independent on the magnetic field intensity, and the maximum separation capacities in various conditions were well predicted using the Thomas model (R2=0.87-0.99).

The removal efficiency and insight into the mechanism of para arsanilic acid adsorption on Fe-Mn framework.

Para arsanilic acid (p-ASA) is extensively used as feed additives in poultry industry, resulting contaminates soil and natural water sources through the use of poultry litter as a fertilizer in croplands. Thus, removal of p-ASA prior to its entering environments is significant to control their environmental risk. Herein, we studied Fe-Mn framework and cubic Fe(OH)3 as promising novel adsorbents for the removal of p-ASA from aqueous solution. The chemical and micro-structural properties of Fe-Mn framework and cubic Fe(OH)3 materials were characterized by X-ray diffraction patterns (XRD), nitrogen adsorption (SBET), zeta (ζ-) potential, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectra (XPS). The maximum adsorption capacity for p-ASA on Fe-Mn framework and cubic Fe(OH)3 was determined to be 1.3mmolg-1 and 0.72mmolg-1 at pH4.0, respectively. Adsorption of p-ASA decreased gradually with increasing pH indicated that adsorption was strongly pH dependent. Azophenylarsonic acid was identified as an oxidation intermediate product of p-ASA after adsorption on Fe-Mn framework. Plausible removal mechanism for p-ASA by Fe-Mn framework was proposed. The obtained results gain insight into the potential applicability of Fe-Mn framework, which can be potentially important for the removal of p-ASA from water.

Enhanced antimony(V) removal using synergistic effects of Fe hydrolytic flocs and ultrafiltration membrane with sludge discharge evaluation.

The integration of adsorbents with ultrafiltration (UF) membranes is a promising method for alleviating membrane fouling and reducing land use. However, a number of problems have become apparent concerning the granular adsorbents used currently, such as high running cost, high chance of causing membrane surface damage, low in situ chemical cleaning efficiency, etc. Herein, to overcome these disadvantages, loose in situ hydrolyzed flocs were directly injected into the membrane tank, providing strong adsorption ability at low cost. To test the feasibility of this method, the heavy metal pollutant antimony (Sb (V)) in a water plant was chosen at a test case, which is similar to arsenic and difficult to remove. We found that Fe-based flocs integrated with an UF membrane showed a large potential advantage in removing Sb(V), even after running for 110 days. We demonstrated that the observed slow transmembrane pressure development could be ascribed to the loose floc cake layer formed, even though some extracellular polymeric substances were induced during operation. We also found that the floc cake layer was easily removed by washing with feed water or dissolved by in situ chemical cleaning under strongly acidic conditions, and many primary membrane pores were clearly observed. In addition, a relative long sludge discharge interval was feasible for this technology and the effluent quality was good, including the turbidity, chromaticity and iron concentration. Based on the excellent performance, these flocs integrated with UF membranes indeed show potential for application in water treatment.

Synthesis of Ce(III)-doped Fe3O4 magnetic particles for efficient removal of antimony from aqueous solution.

Aqueous antimony (Sb) pollution from human activity is of great concern in drinking water due to its adverse health effect. Magnetic Fe3O4 particles, with high separation ability from solution, have been considered as a low-cost Sb adsorbent for contaminants. However, the limited adsorption capacity has restricted its practical application. In this study, a solvothermal approach was developed for doping Ce(III) into Fe3O4, thereby increasing the adsorption efficacy for both Sb(III) and Sb(V). In contrast to un-doped Fe3O4, the adsorption capacity towards Sb(III) and Sb(V) in Ce-doped materials increased from 111.4 to 224.2mg/g and from 37.2 to 188.1mg/g at neutral pH, respectively. Based on the combined results of XPS, XRD, and FTIR, it confirmed that Ce atom successfully doped into the Fe3O4 structure, resulting in the decreased particle size, increased the surface area, and isoelectric point. Furthermore, the vibrating sample magnetometer (VSM) results showed that the Ce doping process had some side effects on the primitive magnetic property, but remaining the high separation potential during water treatment. According to the high removal efficiency and magnetic property, the Ce-doped Fe3O4 of great simplicity should be a promising adsorbent for aqueous Sb removal.