Structural characteristic and ammonium and manganese catalytic activity of two types of filter media in groundwater treatment

Two types of filter media in groundwater treatment were conducted for a comparative study of surface structure and catalytic performance. Natural filter media was adopted from a conventional aeration–filtration groundwater treatment plant, and active filter media as a novel and promising filter media was also adopted. The physicochemical properties of these two kinds of filter media were characterized using numerous analytical techniques,such as X-Ray diffraction（XRD）, scanning electron microscope（SEM）, energy dispersive X-ray（EDX）, X-ray photoelectron spectroscopy（XPS） and Zeta potential. The catalytic activities of these filter media were evaluated for ammonium and manganese oxidation.XRD data showed that both active filter media and natural filter media belonged to birnessite family. A new manganese dioxide（Mn O2） phase（PDF#72-1982） was found in the structure of natural filter media. The SEM micrograph of natural filter media showed honeycomb structures and the active filter media presented plate structures and consisted of stacked particle. These natural filter media presented lower level of some trace elements such as calcium and magnesium, lower degree of crystallinity, lower Mn（III） content and lattice oxygen content than that of active filter media, which were associated with its poor ammonium and manganese catalytic activities. In addition, some γ-Fe2 O3 and Mn CO3 were found in the coating which may hinder the ammonium and manganese catalytic oxidation. This study provides a thorough and comprehensive understanding about the most commonly used filter media in water treatment, which can provide a theoretical guide to practical applications.

A comparison study of the start-up of a MnO_x filter for catalytic oxidative removal of ammonium from groundwater and surface water

As an efficient method for ammonium（NH4~＋）removal,contact catalytic oxidation technology has drawn much attention recently,due to its good low temperature resistance and short start-up period.Two identical filters were employed to compare the process for ammonium removal during the start-up period for ammonium removal in groundwater（Filter-N）and surface water（Filter-S）treatment.Two types of source water（groundwater and surface water）were used as the feed waters for the filtration trials.Although the same initiating method was used,Filter-N exhibited much better ammonium removal performance than Filter-S.The differences in catalytic activity among these two filters were probed using X-ray diffraction（XRD）,scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）,and compositional analysis.XRD results indicated that different manganese oxide species were formed in Filter-N and Filter-S.Furthermore,the Mn3p XPS spectra taken on the surface of the filter films revealed that the average manganese valence of the inactive manganese oxide film collected from Filter-S（FS-MnOx）was higher than in the film collected from Filter-N（FN-MnOx）.Mn（IV）was identified as the predominant oxidation state in FS-MnOxand Mn（III）was identified as the predominant oxidation state in FN-MnOx.The results of compositional analyses suggested that polyaluminum ferric chloride（PAFC）used during the surface water treatment was an important factor in the mineralogy and reactivity of MnOx.This study provides the theoretical basis for promoting the wide application of the technology and has great practical significance.

Removal of ammonium ion from water by Na-rich birnessite:Performance and mechanisms

Na-rich birnessite（NRB） was synthesized by a simple synthesis method and used as a high-efficiency adsorbent for the removal of ammonium ion（NH＋4） from aqueous solution.In order to demonstrate the adsorption performance of the synthesized material,the effects of contact time,pH,initial ammonium ion concentration,and temperature were investigated.Adsorption kinetics showed that the adsorption behavior followed the pseudo second-order kinetic model.The equilibrium adsorption data were fitted to Langmuir and Freundlich adsorption models and the model parameters were evaluated.The monolayer adsorption capacity of the adsorbent,as obtained from the Langmuir isotherm,was 22.61 mg NH＋4-N/g at283 K.Thermodynamic analyses showed that the adsorption was spontaneous and that it was also a physisorption process.Our data revealed that the higher NH＋4adsorption capacity could be primarily attributed to the water absorption process and electrostatic interaction.Particularly,the high surface hydroxyl-content of NRB enables strong interactions with ammonium ion.The results obtained in this study illustrate that the NRB is expected to be an effective and economically viable adsorbent for ammonium ion removal from aqueous system.

Remediation of arsenic contaminated soil by sulfidated zero-valent iron

In this study,the influences of sulfidation on zero-valent iron(ZVI)performance toward As(Ⅴ)immobilization in soil were systemically investigated.It was found that,compared to unamended ZVI,sulfidated ZVI(S-ZVI)is more favorable to immobilize As(Ⅴ)in soil and promote the conversion of water soluble As to less mobile Fe-Mn bound As.Specifically,under the optimal S/Fe molar ratio of 0.05,almost all of the leached As could be sequestrated by>0.5 wt.%S-ZVI within 3 h.Although the presence of HA could decrease the desorption of As from soil,HA inhibited the reactivity of S-ZVI to a greater extent.Column experiments further proved the feasibility of applying S-ZVI on soil As(Ⅴ)immobilization.More importantly,to achieve a good As retention performance,S-ZVI should be fully mixed with soil or located on the downstream side of As migration.The test simulating the flooding conditions in rice culture revealed there was also a good long-term stability of soil As(Ⅴ)after S-ZVI remediation,where only 0.7%of As was desorbed after 30 days of incubation.Magnetic separation was employed to separate the immobilized As(Ⅴ)from soil after S-ZVI amendment,where the separation efficiency was found to be dependent of the iron dosage,liquid to soil ratio,and reaction time.Toxicity characteristic leaching procedure(TCLP)tests revealed that the leachability of As from soil was significantly reduced after the S-ZVI amendment and magnetic separation treatment.All these findings provided some insights into the remediation of As(Ⅴ)-polluted soil by ZVI.

Weak magnetic field accelerates chromate removal by zero-valent iron

Weak magnetic field（WMF） was employed to improve the removal of Cr（VI） by zero-valent iron（ZVI） for the first time. The removal rate of Cr（VI） was elevated by a factor of 1.12-5.89 due to the application of a WMF, and the WMF-induced improvement was more remarkable at higher Cr（VI） concentration and higher p H. Fe2＋was not detected until Cr（VI） was exhausted, and there was a positive correlation between the WMF-induced promotion factor of Cr（VI） removal rate and that of Fe2＋release rate in the absence of Cr（VI） at pH 4.0-5.5. These phenomena imply that ZVI corrosion with Fe2＋release was the limiting step in the process of Cr（VI） removal. The superimposed WMF had negligible influence on the apparent activation energy of Cr（VI） removal by ZVI, indicating that WMF accelerated Cr（VI）removal by ZVI but did not change the mechanism. The passive layer formed with WMF was much more porous than without WMF, thereby facilitating mass transport. Therefore,WMF could accelerate ZVI corrosion and alleviate the detrimental effects of the passive layer, resulting in more rapid removal of Cr（VI） by ZVI. Exploiting the magnetic memory of ZVI, a two-stage process consisting of a small reactor with WMF for ZVI magnetization and a large reactor for removing contaminants by magnetized ZVI can be employed as a new method of ZVI-mediated remediation.

Simultaneous removal of arsenate and fluoride from water by AI-Fe （hydr）oxides

A1-Fe （hydr）oxides with different A1/Fe molar ratios （4：1, 1：1, 1：4, 0：1） were prepared using a co- precipitation method and were then employed for simultaneous removal of arsenate and fluoride. The 4A1 ： Fe was superior to other adsorbents for removal of arsenate and fluoride in the pH range of 5.0-9.0. The adsorption capacity of the A1-Fe （hydr）oxides for arsenate and fluoride at pH 6.50.3 increased with increasing A1 content in the adsorbents. The linear relationship between the amount of OH released from the adsorbent and the amount of arsenate or fluoride adsorbent by 4A1 ： Fe indicated that the adsorption of arsenate and fluoride by A1- Fe （hydr）oxides was realized primarily through quantita- tive ligand exchange. Moreover, there was a very good correlation between the surface hydroxyl group densities of A1-Fe （hydr）oxides and their adsorption capacities for arsenate or fluoride. The highest adsorption capacity for arsenate and fluoride by 4A1 ： Fe is mainly ascribed to its highest surface hydroxyl group density besides its largest pHpzc. The dosage of adsorbent necessary to remove arsenate and fluoride to meet the drinking water standard was mainly determined by the presence of fluoride since fluoride was generally present in groundwater at much higher concentration than arsenate.

Co-present Pb(Ⅱ)accelerates the oxidation of organic contaminants by permanganate:Role of Pb(Ⅲ)

The permanganate(Mn(VII))oxidation has emerged as a promising technology for the remediation and treatment of the groundwater and surface water contaminated with the organic compounds.Nonetheless,only a few studies have been conducted to explore the role of the heavy metals(especially the redox-active ones)during the Mn(VII)oxidation process.In this study,taking Pb(II)as an example,its influence on the Mn(VII)decontamination performance has been extensively investigated.It was found that,with the presence of Pb(II),Mn(VII)could degrade diclofenac(DCF),2,4-dichlorophenol,and aniline more effectively than without.For instance,over a wide pH range of 4.5–8.0,the dosing of 10μmol/L Pb(II)accelerated the DCF removal rate from 0.006–0.25 min–1 to 0.05–0.46 min–1 with a promotion factor of 1.9–9.4.Although the UV-vis spectroscopic and high resolution transmission electron microscopy analyses suggested that Mn(VII)could react with Pb(II)to produce Mn(IV)and Pb(IV)at pH 6.0–8.0,further experiments revealed that Pb(II)did not exert its enhancing effect through promoting the generation of MnO_(2),as the reactivity of MnO_(2)was poor under the employed pH range.At pH below 5.0,it was interesting to find that,a negligible amount of MnO_(2)was formed in the Mn(VII)/Pb(II)system in the absence of contaminants,while once MnO_(2)was generated in the presence of contaminants,it could catalyze the Pb(II)oxidation to Pb(IV)by Mn(VII).Collectively,by highlighting the conversion process of Pb(II)to Pb(IV)by either Mn(VII)or MnO_(2),the reactive Pb(III)intermediates were proposed to account for the Pb(II)enhancement effect.