Lanthanum molybdate/magnetite for selective phosphate removal from wastewater: characterization, performance, and sorption mechanisms.

Lanthanum molybdate/magnetite (M-La2(MoO4)3) with various LaCl3/Fe3O4 mass ratios was synthesized and optimized for selective phosphate removal from wastewater. M-La2(MoO4)3 (2:1) was selected on the basis of phosphate sorption capacity for further experiments and characterized by a variety of methods. The phosphate sorption kinetics, isotherms, and matrix effect were studied. The maximum sorption capacity at initial pH 7 indicates the possible applicability M-La2(MoO4)3 (2:1) in removing phosphate from the aquatic environment. Phosphate removal by M-La2(MoO4)3 (2:1) with high selectivity was achieved in the presence of other co-existing anions, while calcium and magnesium ions were found to inhibit the sorption process. The sorption isotherm study showed that Freundlich and Sips models fit better the Langmuir model, indicating that heterogeneous multilayer sorption was dominant during the phosphate sorption process. Sorption kinetic results showed that the pseudo-first-order kinetic model can describe well the phosphate sorption process by M-La2(MoO4)3 (2:1). Consecutive sorption-desorption runs showed that M-La2(MoO4)3 (2:1) could be reused for a few cycles. Simultaneous removal of phosphate and organic matter was achieved in real wastewater by using M-La2(MoO4)3 (2:1). The sorption mechanism was inner-sphere complexation.

A novel hydrogel for highly efficient adsorption of Cu(II): synthesis, characterization, and mechanisms.

Among the Cu(II) removal methods, adsorption is a favorable technique and has attracted large attention because of its effectiveness and low cost. In quest of seeking for a favorable adsorbent with a high Cu(II) adsorption capacity and excellent reusability, researchers have paid much attention to hydrogels with three-dimensional networks. In this study, a novel hydrogel (P(AMPS-co-VDT) hydrogel) based on free-radical polymerization was synthesized with ionic monomer sodium 2-acrylamido-2-methylpropane sulfate (AMPS-Na+) and 2-vinyl-4, 6-diamino-1, 3, 5-triazine (VDT) and applied for Cu(II) adsorption in aqueous solutions. The hydrogel was characterized for swelling performance, surface morphology, functional groups, thermal gravimetric behavior, and elements. The maximum Cu(II) adsorption capacity (175.75 mg/g) was relatively high compared with other hydrogels. The P(AMPS-co-VDT) hydrogel also was found to have a relatively good Cu(II) desorption and reuse behavior. The adsorption mechanism could be chelation and ion exchange. This work provides a new hydrogel for effective Cu(II) removal in the future.

Comparative adsorption of emerging contaminants in water by functional designed magnetic poly(N-isopropylacrylamide)/chitosan hydrogels.

The magnetic poly(N-isopropylacrylamide)/chitosan hydrogel with interpenetrating network (IPN) structure was designed based on the functional groups of targeted emerging contaminants, represented by hydrophilic sulfamethoxazole (SMZ) and hydrophobic bisphenol A (BPA). The average particle size, specific surface area, and total pore volume of the hydrogel were turned out to be 103.7 µm, 60.70 m2/g and 0.0672 cm3/g, respectively. Adsorption results indicated that the maximum adsorption capacity occurred at the pH where SMZ was anionic and BPA was uncharged. When the adsorption temperature increased from 25 °C to 35 °C, the amount of adsorbed SMZ hardly changed, but that of BPA increased by two times. The adsorption capacity of the binary system (i.e., with both SMZ and BPA) was almost the same as that of the single system, indicating that simultaneous adsorption of SMZ and BPA was achieved. The adsorption equilibrium was reached quickly (within 5 min) for both SMZ and BPA. For adsorption isotherm, the Freundlich model fitted well for SMZ at 25, 35 and 45 °C. However, the adsorption of BPA exhibited the sigmoidally shaped isotherm at 25 °C with the Slips model fitting well, and both the Freundlich isotherm and the Slips isotherm fitted the data well at 35 °C and 45 °C, suggesting that the adsorption force was initially weak but greatly enhanced with an increase in adsorbate concentration or ambient temperature. The main adsorption mechanism was inferred to be electrostatic interactions for SMZ, and hydrophobic interactions as well as hydrogen bonding for BPA. The hydrogel adsorbent maintained favorable adsorption capacity for BPA after five adsorption-desorption cycles. These findings may provide a strategy for designing high performance adsorbents that can remove both hydrophilic and hydrophobic organic contaminants in the aquatic environment.

Ultraviolet/persulfate (UV/PS) pretreatment of typical natural organic matter (NOM): Variation of characteristics and control of membrane fouling.

The effects of ultraviolet/persulfate (UV/PS) pretreatment on ultrafiltration (UF) membrane fouling caused by typical natural organic matter (NOM) fractions including humic acid (HA), sodium alginate (SA), and bovine serum albumin (BSA) were investigated. UF membrane fouling during the filtration of different NOM fractions after UV/PS pretreatment was compared through the evaluation of normalized membrane flux decline and membrane fouling reversibility. The fouling mitigation mechanisms were investigated through the characterization of ultraviolet absorbance (UV254), dissolved organic matter, zeta potential, particle size distribution, fluorescence excitation-emission matrix spectra, and fitness of four classic fouling models. Furthermore, the fouled membranes were characterized by Fourier-transform infrared spectroscopy and scanning electron microscopy. The results showed that UV/PS pretreatment significantly alleviated membrane fouling caused by HA, SA, and HA-SA-BSA mixture, and the fouling control performance improved at high PS doses. However, either UV alone or UV/PS pretreatment at low PS dose (10 mg/L) significantly aggravated BSA fouling with the normalized flux at the end of first filtration cycle being 8% and 15%, respectively. The increased particle size of BSA after UV/PS pretreatment was attributed to the formation of aggregates, which mainly accumulated in membrane pores and aggravated membrane fouling. Modeling results suggest that the mitigation of membrane fouling derived from SA and mixed organic fractions was primarily ascribed to the control of cake filtration, while the mitigation of HA fouling was attributed to the declined contribution of standard blocking.

Enhanced degradation of organic contaminants by zero-valent iron/sulfite process under simulated sunlight irradiation.

Degradation of propranolol (PrP) by a combined zero-valent iron and sulfite system under simulated sunlight irradiation (ZVI/sulfite/photo) was investigated. Simulated sunlight irradiation enhanced the degradation of PrP by accelerating the decomposition of ferric sulfite complex as a result to producing sulfite radical (SO3•-). As bubbles would block the transport of photons in the reaction solution, mechanical aeration rather than purging air was suggested to sustain the essential dissolved oxygen. The degradation of PrP increased with the elevation of initial ZVI concentration from 0.05 to 0.5 mM, but decreased a little with further increasing ZVI concentration to 1.0 mM. The degradation of PrP raised from 68.5% to 98.7% while sulfite dose increased from 0.1 to 2.0 mM. High removal efficiencies were always achieved when the initial PrP concentration ranged from 10 to 40 µM. As HSO3- which can efficiently complex Fe(II) and transfer Fe(III) to Fe(II) is the dominant species of sulfite at pH 4.0-6.0, the highest removal of PrP was achieved at pH 4.0-6.0. The presence of bicarbonate and humic acid significantly retarded the removal of PrP, while chloride ions could promote the removal of PrP to some extent. SO4•-, HO• and SO5•- were suggested to account for PrP removal, while SO4•- was evidenced to be the dominant radicals. Good reuse of ZVI in the system was also achieved as the removal of PrP kept higher than 80% after repeatedly used for 5 times. Possible degradation pathways of PrP in the ZVI/sulfite/photo system were accordingly proposed based on LC-MS and density functional theory calculation. The removal of amitriptyline, nitrobenzene, imipramine and methylparaben in the ZVI/sulfite/photo system was also evaluated. As a reducing agent, sulfite is expected to consume the possible formed bromine-containing intermediates as a result to inhibiting the formation of bromate, which is better than the activated persulfate system.

Efficient degradation of imipramine by iron oxychloride-activated peroxymonosulfate process.

Synthesized iron oxychloride (FeOCl) was firstly applied to activate peroxymonosulfate (PMS) to degrade imipramine (IMI), a tricyclic antidepressant. Compared to some other Fe-based materials including zero valent iron, Fe2O3, Fe3O4 and ferric ions, FeOCl presented an impressive catalytic activity on PMS at near-neutral condition due to its unique structure containing abundant unsaturated iron atoms and oxo-bridged configuration. With an increase of FeOCl dose, PMS dose or initial pH in ranges of 0.02 - 0.5 g/L, 0.1 - 2.5 mM and 4.0 - 8.0, the degradation efficiency of IMI was effectively raised by 64.0%, 48.5% and 50.6%, respectively. The presence of either bicarbonate or chloride stimulated the removal of IMI. Moreover, 70.4% of IMI was degraded under the background of real water with 2 mM PMS. The possible reactive species were identified as sulfate and hydroxyl radicals. The formed hypochlorite through the reaction of PMS and the released chloride ions may also contribute to the degradation of IMI. Among the oxidants, sulfate radical was proven to be the dominate one in the system. Additionally, the FeOCl/PMS system can overall effectively degrade six other organic compounds including amitriptyline, desipramine, propranolol, nitrobenzene, methyl-paraben and ethyl-paraben, further suggesting the possible application of this system in treatment of vast aquatic micro-organic pollutants.

The activated iron system for phosphorus recovery in aqueous environments.

Finding a good sorbent for phosphorus (P) recovery from the aquatic environment is critical for preventing eutrophication and providing P resources. The activated iron system (mainly consisted of zero-valent iron (ZVI), Fe3O4 and Fe2+) has been reported to exhibit a favorable performance towards various contaminants in wastewater, but its effect on P recovery has not been studied systematically. In this study, we used Fe2+-nitrate pretreatment reaction to prepare the activated iron system and then applied it to P recovery. Results show that more than 99% P was removed from water in 60 min; co-existing anions (NO3-, Cl- and SO42-) and natural organic matter (NOM) had little effect on P removal. The P removal capacity of activated iron system is very high compared with currently reported sorbents. Externally-supplied Fe2+ plays an important role on P removal in the system. Regeneration study shows that the activated iron system exhibited stable P recovery ability by using 0.1 M NaOH solution. Various methods were applied to characterize the ZVI and iron corrosion, and results conclude that sorption precipitation, and co-precipitation contribute to P removal. This method will be promising and have an application potential in the field for efficient and cost-effective recovery of P with cheap microscale zero valent iron.