High Efficient Removal of Trace Molybdenum from Water by FeCl_3:Effects of p H and Affecting Factors in the Presence of Co-existing Background Constituents

The effect of FeCl_3 coagulation-filtration on the removal of trace Mo(Ⅵ) from water is investigated in the p H range of 4. 00 to 9. 00 and the effects of sulfate,silicate,phosphate and humic acid( HA) on the process were determined. Overall,the removal of Mo(Ⅵ) is determined by two factors: the content of Fe intercepted from water( Intercepted Fe) and the affinity between Mo(Ⅵ)( or co-existing background constituents) and adsorption sites. At low p H,where the agglomeration of the iron flocs is limited,the former factor is dominant,so the methods that can promote the agglomeration of the iron flocs,such as increasing the p H,adding co-existing constituents( sulfate,phosphate or HA),can increase the removal of Mo(Ⅵ). While at high p H,the second factor dominated. Increasing the p H weakens the affinity between Mo(Ⅵ) and the iron flocs,and co-existing background constituents( sulfate,phosphate,silicate or HA) compete with Mo(Ⅵ) for adsorption sites,both effects result in a decrease in Mo(Ⅵ) removal. The Mo(Ⅵ) removal efficiency of FeCl_3 in natural water decreases as the p H increases from 4. 00 to 9. 00,and it is better to operate the coagulation process at p H 5.00 in the practical water treatment engineering.

Influence of extracellular polymeric substances from activated sludge on the aggregation kinetics of silver and silver sulfide nanoparticles

Extracellular polymeric substances(EPS)in activated sludge from wastewater treatment plants(WWTPs)could affect interactions between nanoparticles and alter their migration behavior.The influence mechanisms of silver nanoparticles(Ag NPs)and silver sulfide nanoparticles(Ag_(2)S NPs)aggregated by active EPS sludge were studied in monovalent or divalent cation solutions.The aggregation behaviors of the NPs without EPS followed the Derjaguin-Landau-Verwey-Overbeek(DLVO)theory.The counterions aggravated the aggregation of both NPs,and the divalent cation had a strong neutralizing effect due to the decrease in electrostatic repulsive force.Through extended DLVO(EDLVO)model analysis,in NaNO3 and low-concentration Ca(NO_(3))_(2)(<10 mmol/L)solutions,EPS could alleviate the aggregation behaviors of Cit-Ag NPs and Ag_(2)S NPs due to the enhancement of steric repulsive forces.At high concentrations of Ca(NO_(3))_(2)(10‒100 mmol/L),exopolysaccharide macromolecules could promote the aggregation of Cit-Ag NPs and Ag_(2)S NPs by interparticle bridging.As the final transformation form of Ag NPs in water environments,Ag_(2)S NPs had better stability,possibly due to their small van der Waals forces and their strong steric repulsive forces.It is essential to elucidate the surface mechanisms between EPS and NPs to understand the different fates of metal-based and metal-sulfide NPs in WWTP systems.

Impact of dissolved oxygen on the production of nitrous oxide in biological aerated filters

Polymerase chain reaction-denaturing gradient gel electrophoresis （pCR-DGGE） and microelectrode technology were employed to evaluate the Nitrous oxide （N2O） production in biological aerated filters （BAFs） under varied dissolved oxygen （DO） concentrations during treating wastewater under laboratory scale. The average yield of gasous N2O showed more than 4-fold increase when the DO levels were reduced from 6.0 to 2.0 mg·L^-1, indicating that low DO may drive N2O generation. PCRDGGE results revealed that Nitratifractor salsuginis were dominant and may be responsible for N2O emission from the BAFs system. While at a low DO concentration （2.0 mg·L^-1）, Flavobacterium urocaniciphilum might playa role. When DO concentration was the limiting factor （reduced from 6.0 to 2.0 mg·L^-1） for nitrification, it reduced NO2^--N oxidation as well as the total nitrification. The data from this study contribute to explain how N2O production changes in response to DO concentration, and may be helpful for reduction ofN2O through regulation of DO levels.

Release of deposited MnO2 nanoparticles from aqueous surfaces

Changes in solution chemistry and transport conditions can lead to the release of deposited MnO2 nanoparticles from a solid interface,allowing them to re-enter the aqueous environment.Understanding the release behavior of Mn02 nanoparticles from naturally occurring surfaces is critical for better prediction of the transport potential and environmental fate of Mn02 nanoparticles.In this study,the release of Mn02 nanoparticles was investigated using a quartz crystal microbalance with dissipation monitoring(QCM-D),and different environmental surface types,solution pH values and representative macromolecular organics were considered.Mn02 nanoparticles were first deposited on crystal sensors at elevated NaN03 concentrations before being rinsed with double-deionized water to induce their remobilization.The results reveal that the release rate of Mn02 depends on the surface type,in the decreasing order:SiO2>Fe304>Al2 O3,resulting from electrostatic interactions between the surface and particles.Moreover,differences in solution pH can lead to variance in the release behavior of Mn02 nanoparticles.The release rate from surfaces was significantly higher at pH 9.8 that at 4.5,indicating that alkaline conditions were more favorable for the mobilization of Mn02 in the aquatic environment.In the presence of macromolecular organics,bovine serum albumin(BSA)can inhibit the release of Mn02 from the surfaces due to attractive forces.In presence of humic acid(HA)and sodium alginate(SA),the Mn02 nanoparticles were more likely to be mobile,which may be associated with a large repulsive barrier imparted by steric effects.

Highly inhibited transport of dissolved thallium(I) in manganese oxide-coated sand: Chemical condition effects and retention mechanisms

Thallium contamination in water can cause great danger to the environment.In this study,we synthesized manganese oxide-coated sand(MOCS)and investigated the transport and retention behaviors of Tl(I)in MOCS under different conditions.Characterization methods combined with a two-site nonequilibrium transport model were applied to explore the retentionmechanisms.The results showed that Tl(I)mobility was strongly inhibited in MOCS media,and the retention capacity calculated from the fitted model was 510.41 mg/g under neutral conditions.The retention process included adsorption and oxidative precipitation by the manganese oxides coated on the sand surface.Cotransport with the same concentration of Mn(II)led to halving Tl(I)retention due to competition for reactive sites.Enhanced Tl(I)retention was observed under alkaline conditions,as increasing pH promoted electronegativity on the media surface.Moreover,the competitive cation Ca^(2+)significantly weakened Tl(I)retention by occupying adsorption sites.These findings provide new insights into understanding Tl(I)transport behavior in water-saturated porous media and suggest that manganese oxide-coated sand can be a cost-effective filter media for treating Tl-contaminated water.