Evaluation of adsorption and coagulation characteristics of humic acids preceded by alternative advanced oxidation techniques

Humic substances mainly humic acids constitute the major fraction of natural organic matter in water supplies. Humics express diverse actions primarily related to the formation of potentially harmful disinfection by products (DBPs). Therefore, the removal of DBP precursors through numerous treatment techniques gains high importance. Besides the conventional treatment processes, the applications of advanced oxidation techniques are considered as effective tools for the elimination of humic acids (HAs) from natural waters. In the present study, both the adsorption and coagulation characteristics of humic acid samples are evaluated subsequent to pretreatment by photocatalytic oxidation and ozonation. The changes in preoxidized humic acid solutions are assessed in relation to the alterations induced in the UV-vis and fluorescence spectroscopic properties. The removal efficiency of color in terms of Color₄₃₆ and aromaticity with respect to UV₂₅₄ are presented relevant to each treatment step. Major key parameters such as the selection of coagulant types (alum and ferric chloride), coagulant aids (ionic and non-ionic polyelectrolyte) and optimum coagulant dose were comparatively discussed. The adsorption characteristics of powdered activated carbon (PAC) and granular activated carbon (GAC) were investigated.     

Evaluation of humic acid photocatalytic degradation by UV–vis and fluorescence spectroscopy

Photodegradation of humic substances causes drastic changes in the UV–vis absorption and fluorescence properties of humic acids. In this study it is intended to fulfill the lack of knowledge about the spectral changes of humic acids during photocatalytic oxidation processes and elucidate the effects observed on the molecular size distribution of humic acid focusing on their analysis by UV–vis and fluorescence spectroscopy.

As confirmed by the spectroscopic evaluation of the molecular size distribution data, photocatalytic degradation of humic acid leads to the formation of lower molecular size (small fractions) and higher UV absorbing compounds. For fractions less than 10 kDa, UV₂₅₄ absorbing moieties in treated humic acid samples become higher than that of raw humic acid designating the generation of new species during photocatalysis. UV–vis spectroscopic changes were also evaluated by the parameters relating to the concomitant removal of the total organic carbon as well as by the ratios using absorption values at discrete wavelengths. Moreover, the fluorescence spectra of treated humic acid samples show decreasing intensity profiles with increasing photocatalytic irradiation time.     

MIEX和PAC对微污染水源水的水质净化效果比较

研究了MIEX和PAC两种水处理吸附剂对微污染水源水的水质净化性能。实验分别考察了MIEX和PAC对DOC和UV₂₅₄的去除效率,并通过凝胶渗透色谱和三维荧光光谱分析,研究了MIEX和PAC对不同相对分子质量区间以及不同种类有机物的去除规律。在正常的吸附剂投加量下(MIEX 5~8 ml·L^-1,PAC 30~50 mg·L^-1),MIEX对DOC和UV₂₅₄的平均去除率比PAC高23%和20%。但随着吸附剂投加量的增加,两者去除效率差别逐渐减小,MIEX对DOC和UV₂₅₄的最大去除率仅比PAC高6%~8%。与PAC相比,MIEX去除的有机物相对分子质量分布范围更广,特别是对中等分子量(5000~50000)有机物,其去效率明显高于PAC。MIEX对腐殖酸和富里酸类有机物的去除率略高于PAC,而对蛋白质类有机物的去除率则远高于PAC。动力学分析表明,MIEX和PAC对DOC的吸附去除过程符合准二级动力学,MIEX对有机物的吸附速率是PAC的40倍左右。     

Catalytic removal of perchloroethylene (PCE) over supported chromium oxide catalysts

The oxidation of perchloroethylene (PCE) was investigated over chromium oxide catalysts supported on SiO₂, SiO₂–Al₂O₃, activated carbon, mordenite type zeolites, MgO, TiO₂ and Al₂O₃. Supported chromium oxide catalysts were more active than any other metal oxide catalysts including noble metal examined in the present study. PCE removal activity of chromium oxide catalysts mainly depended on the type of supports and the content of metal loaded on the catalyst surface. TiO₂ and Al₂O₃ containing high surface areas were effective for the high performance of PCE removal, since the formation of well dispersed Cr(VI) active reaction sites for the present reaction system, was enhanced even for the high Cr loading on the catalyst surface. CrO_x catalysts supported on TiO₂ and Al₂O₃ also exhibited stable PCE removal activity at a low feed concentration of PCE of 30 ppm up to 100 h at 350°C. However, significant catalyst deactivation was observed at high PCE concentration of 10 000 ppm. CrO_x/TiO₂ revealed stronger water tolerance than CrO_x/Al₂O₃ due to the surface hydrophobicity.     

改性镍铁渣吸附剂对Cr(VI)吸附性能的影响及机理分析

以镍铁渣为原料,加入硝酸和表面活性剂对其矿物相改性,制备改性镍铁渣吸附剂,考察表面活性剂种类、十六烷基三甲基溴化铵(CTAB)掺量、吸附剂掺量、溶液初始pH值、Cr(VI)浓度对Cr(VI)吸附效果的影响。结果表明:镍铁渣经改性后可制得结构疏松、比表面积高达180.6 m²/g的无定形SiO₂;改性镍铁渣对Cr(VI)的吸附率在10 min内可达到90%,吸附等温线符合Langmuir模型,最大理论吸附容量为42.55 mg/g,吸附动力学符合拟二级动力学模型。改性镍铁渣吸附剂对Cr(VI)的吸附机理主要是物理吸附和氧化还原,即吸附剂表面范德华力将HCrO ^-₄吸附至吸附剂表面,CTAB提供的电子对将Cr(VI)还原为Cr(III)。对镍铁渣改性获得的高比表面积无定形SiO₂不仅可以有效吸附净化Cr(VI),同时可以实现镍铁渣资源化利用,达到以废治污的目的,具有良好的环境效应和经济效益。     

Adsorption characteristics of metal-capture-agent immobilized PAC for low concentration Cr(Ⅵ) in water at low temperature

针对低温微污染水中(275 K)低浓度Cr(Ⅵ)离子(0.500 mg·L^-1),制备基于表面负载食品级单宁酸为金属捕获剂的改性PAC(TA-PAC),以HNO₃、NaOH氧化改性PAC为对照,研究了TA-PAC的表面物理化学特性和吸附性能,并进行了pH影响和吸附等温线拟合研究。结果表明:TA-PAC的比表面积、总孔容积和表面极性大小最佳。TA-PAC对低温水中Cr(Ⅵ)及总铬的去除效果优于N-PAC和OH-PAC。酸性范围内(pH=3.0~6.0)TA-PAC对Cr(Ⅵ)及总铬的去除率均大于碱性范围(pH=7.0~10.0)。Freundlich 双参数吸附等温式对TA-HNC吸附水中低浓度总铬的吸附等温线拟合效果最好(R²=0.9941)。TA-PAC吸附低温水中低浓度Cr(Ⅵ)是一个极为复杂的过程,主要吸附机理可能包括表面还原作用、酯化/螯合作用和离子交换作用等。     

Different N-containing functional groups modified mesoporous adsorbents for Cr(VI) sequestration: Synthesis, characterization and comparison

Ordered mesoporous SBA-15 has been functionalized by aminopropyl, imidazole and triazole groups by one or two-step post-grafting route and investigated as adsorbents of hexavalent chromium in aqueous solutions. XRD, N₂ adsorption–desorption measurements, FT-IR, solid state NMR and element analysis techniques have been employed to prove the ordered mesoporous structures of the functionalized SBA-15 and the successful immobilization of the organic functional moieties on SBA-15. The Cr(VI) adsorption behavior on the resultant adsorbents were examined by a batchwise method. The results show that all adsorbents exhibit the fast adsorption rate and the excellent adsorption capacity. Electrostatic interaction between the adsorbents and adsorbate plays an important role in the adsorption process. Equilibrium data were well fitted to the Langmuir and Freundlich adsorption models.     

Insight into the effect of surface carboxyl and amino groups on the adsorption of titanium dioxide for acid red G

In this study, TiO₂ functionalized with organic groups were prepared to study the effect of carboxyl and amino groups on the adsorption behavior of TiO₂ for the removal of acid red G (ARG) as an anionic dye from aqueous solution. TiO₂ was successfully modified with carboxyl and amino groups by using the hydrolysis method with oxalic acid (OAD, with two carboxyl groups), ethylenediamine (EDA, with two amino groups) and DL-alanine (DLA, with one carboxyl group and one amino group) at low temperature (65 °C) and labeled as OAD-TiO₂, EDA-TiO₂ and DLA-TiO₂, respectively. The ARG uptake by the functionalized TiO₂ samples was largely dependent on the functional groups. The interaction between ARG and the functional organic groups on the TiO₂ samples plays an important role in the adsorption process, which leads to the excellent adsorption performance (higher capacity and faster adsorption rate) of the functionalized TiO₂ samples than that of P25 (commercial TiO₂ without modification). Furthermore, there is no obvious loss of the adsorption capacity for the functionalized TiO₂ even after 5 adsorption-desorption cycles, which indicated the good reusability of the modified TiO₂ samples for anionic dye removal from aqueous solution.     

Immobilization of chromium (VI) evaluated by binding isotherms for ground granulated blast furnace slag and ordinary Portland cement

The interaction mechanisms of the Cr(VI) ion in presence of GGBFS and OPC were evaluated by chromium binding isotherms and by pore solution analysis. The chromium in the final leaching solution was measured and the solid samples were investigated by SEM and by XRD. GGBFS was more efficient than OPC in fixing Cr ions at lower initial concentrations. However, from an initial Cr(VI) concentration of 2000 and 5000 mg/L, OPC was more efficient.

For an initial Cr(VI) concentration of 50 000 mg/L, around 145 mg Cr/g was fixed by OPC and only 8 and 55 mg Cr/g were fixed by GGBFS in alkaline and water-based immersion solutions, respectively. The Cr-bearing phases identified by XRD and SEM are: CaCrO₄ and CaCrO₄·2H₂O, C–S–H and calcium aluminate phases. The pore solution chemistry indicates that a value around 92% of chromium was retained by GGBFS and 87% by OPC.     

纳米腐殖酸动态吸附废水中镉离子及其洗脱特性

在静态法研究纳米腐殖酸吸附模拟含镉废水基础上搭建考察模拟含镉废水中镉离子在吸附剂上动态吸附及洗脱特性的吸附柱实验装置,考察镉离子溶液浓度、吸附(脱附)温度、共存离子和进料流速对穿透吸附量和饱和吸附量的影响,运用Thomas模型研究了纳米腐殖酸柱吸附过程动力学机理,测定了再生后纳米腐殖酸的穿透吸附量和饱和吸附量,结果表明:初始镉离子浓度150 mg·L^-1和流速10 ml·min^-1下,其饱和吸附量分别为426.3 mg·g^-1和405.5 mg·g^-1;Thomas模型所得饱和吸附量q_em分别为364.1、436.1和441.9 mg·g^-1;洗脱峰镉离子浓度分别为3.3、12.0和22.0 g·L^-1;共存离子SO₄^2-浓度增加,纳米腐殖酸对镉离子的穿透吸附量和饱和吸附量降低;吸附和脱附均可常温工况进行。经30次吸附和再生后,穿透吸附量和饱和吸附量无明显降低。用红外光谱仪(FT-IR)、扫描电镜(SEM)及X射线能谱仪(EDS)对纳米腐殖酸吸附再生前、后性能进行表征,结果表明:纳米腐殖酸物化性能稳定,形貌基本无变化,尺度发生一定程度减小,表面及内部的氨基、羟基等对吸附镉离子均发挥有效作用,该材料可满足重复使用。     

不同无机酸对聚吡咯/TiO2复合物的吸附性能影响

考察了不同无机酸对PPy/TiO₂复合物吸附性能的影响。首先分别在HNO₃、H₂SO₄和H₃PO₄体系中合成了聚吡咯(PPy)/TiO₂复合物(分别简写为N-PPy/TiO₂、S-PPy/TiO₂和P-PPy/TiO₂)。以红外光谱、热重分析、Zeta电位、比表面积分析和扫描电镜等测试方法对复合物的物理化学性能进行了表征。接着以几种合成的复合对阴离子染料酸性红G和阳离子染料亚甲基蓝进行吸附研究,发现无机酸对合成的复合物的吸附性有较大的影响。几种复合物均可在30min内达到吸附平衡,并且可以重复使用6次以上吸附量没有明显的降低。其中S-PPy/TiO₂的吸附性能最好,其对ARG和MB的最大吸附量分别达到218.34mg/g和314.68mg/g。复合物对染料的吸附过程符合准二级动力学模型和Langmuir吸附等温式。对S-PPy/TiO₂进行吸附热力学研究表明,其对染料的吸附过程为熵增的自发过程。     

腐植酸与不溶性腐植酸吸附铬的对比研究

通过对不溶性腐植酸和末处理的腐植酸对六价铬吸附作用的研究,确定了最佳反应条件,说明不溶性腐植酸的作用效果.试验表明,在反应接触时间60 min、酸性pH10左右的水溶液条件下,不溶性腐植酸对铬离子去除率可达98%.试验主要研究了不溶性腐植酸对铬离子的反应动力学和吸附等温线及其作用机理.     

The nature of low temperature deactivation of CoCr2O4 and CrOx/γ-Al2O3 catalysts for the oxidative decomposition of trichloroethylene

The CoCr₂O₄ and CrO_x/γ-Al₂O₃ catalysts were used for the oxidative decomposition of trichloroethylene (TCE). Both catalysts showed an initial deactivation at low temperatures around 280 °C, mainly due to the dissociative adsorption of reactant TCE. This was confirmed by the temperature programmed oxidation of TCE where the carbon oxides were formed up to a temperature below 300 °C. Possible changes in the oxidation state of chromium species were observed with XANES and ESR. During the oxidation reaction at low temperatures, the Cr(VI) species were reduced to Cr(III) species, which seemed to be coupled with TCE adsorption. At higher temperatures, however, the Cr(VI) species appeared again and the catalytic activity was completely recovered.     

Effect of silver on the photocatalytic degradation of humic acid

In this study, humic acid was mineralized and degraded photocatalytically in presence of bare TiO₂ and silver loaded TiO₂ (0.5–5.0 at.% Ag). X-ray diffraction (XRD) and inductive coupled plasma (ICP) analysis confirm the complete photodeposition of silver over TiO₂ by photodeposition method. X-ray photoemission spectroscopy (XPS) studies confirmed the presence of Ag⁰ in all Ag–TiO₂ samples and the absence of Ag⁺ ions. Silver loading over TiO₂ improved the rate of mineralization and degradation of humic acid with a maximum loading of 1.0 at.% Ag. Ninety percent carbon from humic acid was mineralized to CO₂ only after 60 min by using bare TiO₂ as a photocatalyst. However, this conversion was possible within 40 min by using 1.0 at.% Ag-loaded TiO₂. This observation verifies that coating of metals like silver over TiO₂ acts as an electron sink and can improve the redox reaction by preventing electron–hole recombination reaction. The optimum 1.0 at.% Ag loading in the current work is indicative that the blocking of the TiO₂ surface active sites by silver also plays an important role in the photocatalytic mineralization and degradation of humic acid. As the silver loading is increased, less number of active site are available over the surface of photocatalyst TiO₂ for redox reaction. This finding was supported by the TEM analysis of the photocatalyst samples.     

Hydrothermal doping method for preparation of Cr-TiO2 photocatalysts with concentration gradient distribution of Cr

Cr³⁺-doped anatase titanium dioxide photocatalysts were prepared by the combination of sol–gel process with hydrothermal treatment. The samples were characterized by UV–vis diffuse reflectance spectroscopy, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area (S_BET), transmission electron microscopy (TEM), atomic absorption flame emission spectroscopy (AAS), electron paramagnetic resonance (EPR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was confirmed that Cr substitutes Ti⁴⁺ in TiO₂ lattice in trivalent ionic state, and the concentrations of dopants Cr³⁺ decrease from the exterior to the interior of doped TiO₂. The photocatalytic activity of Cr-TiO₂ was investigated for the photocatalytic degradation of XRG aqueous solution both under UV and visible light irradiation. Due to the excitation of 3d electron of Cr³⁺ to the conduction band of TiO₂, Cr-TiO₂ shows a good ability for absorbing the visible light to degrade XRG. Doping of chromium ions effectively improves the photocatalytic activity under both UV light irradiation and visible light irradiation with an optimal doping concentration of 0.15% and 0.2%, respectively. The special distribution of dopants Cr³⁺ seems having a good effect on enhancing the photocatalytic activity of Cr-TiO₂.     

光催化协同TiO2动态膜去除水中腐植酸及膜污染特性

针对物理扰动模式控制动态膜污染使涂膜层脱落方面的局限性,提出光催化氧化技术协同动态膜降低膜污染,对比了陶瓷微滤膜、动态膜、光催化协同动态膜处理含腐植酸废水及含腐植酸/TiO₂混合废水过程中的膜通量、污染物去除率及膜污染阻力分布的变化趋势。结果表明:光催化协同作用可有效提高动态膜过滤腐植酸溶液过程中的膜通量、总有机碳(TOC)及UV₂₅₄的去除率,并同时降低可逆污染阻力及不可逆污染阻力,其中可逆污染阻力明显大于其他部分阻力,可逆污染是造成膜通量衰减的主要原因。光催化预处理时间越长,稳态膜通量、TOC及UV₂₅₄去除率增幅越显著,控制膜污染越有效。光催化预处理2h和8h再动态膜过滤时TOC去除率分别可达到80%和90%以上,UV₂₅₄去除率都可达95%以上。     

Adsorption performance and physicochemical mechanism of MnO2-polyethylenimine-tannic acid composites for the removal of Cu(II) and Cr(VI) from aqueous solution

In this work, an adsorbent, which we call MnPT, was prepared by combining MnO₂, polyethylenimine and tannic acid, and exhibited efficient performance for Cu(II) and Cr(VI) removal from aqueous solution. The oxygen/nitrogen-containing functional groups on the surface of MnPT might increase the enrichment of metal ions by complexation. The maximum adsorption capacities of MnPT for Cu(II) and Cr(VI) were 121.5 and 790.2 mg·g⁻¹, respectively. The surface complexation formation model was used to elucidate the physicochemical interplay in the process of Cu(II) and Cr(VI) co-adsorption on MnPT. Electrostatic force, solvation action, adsorbate–adsorbate lateral interaction, and complexation were involved in the spontaneous adsorption process. Physical electrostatic action was dominant in the initial stage, whereas chemical action was the driving force leading to adsorption equilibrium. It should be noted that after adsorption on the surface of MnPT, Cr(VI) reacted with some reducing functional groups (hydroxylamine-NH₂) and was converted into Cr(III). The adsorption capacity declined by 12% after recycling five times. Understanding the adsorption mechanism might provide a technical basis for the procedural design of heavy metal adsorbents. This MnPT nanocomposite has been proven to be a low-cost, efficient, and promising adsorbent for removing heavy metal ions from wastewater.     

氯胺及其与二氧化氯联用对原水管道溶解性有机物降解的影响

采用环状反应器模拟原水输水管道, 考察氯胺(NH₂Cl)及其与二氧化氯联用(NH₂Cl/ClO₂)对溶解性有机物(DOM)、溶解性有机碳(DOC)和UV₂₅₄降解以及有机物荧光特性的影响。结果表明:NH₂Cl或NH₂Cl/ClO₂对DOC、UV₂₅₄和DOM的降解均产生较大的影响。相比NH₂Cl, NH₂Cl/ClO₂的影响更大, 但是有机物降解的恢复速度没有明显差异, DOC、UV₂₅₄和DOM的降解分别在停止投加氧化剂的第5 d、4 d和1 d恢复。投加氧化剂后, 芳香族有机物以向易生物降解的极性有机物的转化为主, 溶解性有机物的可生物降解能力增加。NH₂Cl和NH₂Cl/ClO₂作用后, 类蛋白质物质以及紫外区类腐殖质类物质明显减少。NH₂Cl/ClO₂更易破坏有机物中的芳香族化合物的结构, 而NH₂Cl氧化使得有机物分子结构中羰基、羟基、羧基和胺基等官能团增加, 从而有机物可生物降解能力较强。NH₂Cl和NH₂Cl/ClO₂作用后, 有机物降解作用可恢复至比未加氧化剂更高的水平, 基于卤代副产物生成的考虑, 相比NH₂Cl, NH₂Cl/ClO₂更适合用于原水输水管道的氧化。     

不溶性腐殖酸吸附Cr(Ⅵ)的研究

研究了不溶性腐殖酸对六价铬的吸附作用。进行了反应接触时间、pH值、IHA投加量、光照条件、温度等对反应的影响研究,确定了最佳反应条件,同时应用未处理的腐殖酸进行对比研究,说明不溶性腐殖酸的作用效果。试验表明在反应接触时间60 min、pH值为7左右、不溶性腐殖酸投加量为5 g/L和Cr(Ⅵ)的质量浓度为5.36 mg/L的条件下,不溶性腐殖酸对铬离子去除可达95%,比未处理的腐殖酸对铬离子去除提高近1倍。并绘制了不溶性腐殖酸对铬离子的反应动力学曲线和吸附等温线。     

TiO2改性石墨烯电极电吸附去除污水中NH4+

通过水热法制备得到TiO₂改性石墨烯复合材料（RGO/TiO₂）,考察了其形貌结构和电化学性能。将其组装成电极,对比未改性石墨烯（RGO）电极和RGO/TiO₂电极的电吸附NH₄⁺性能。重点考察外加电压、循环流速、初始浓度等工艺参数对RGO/TiO₂电极电吸附NH₄⁺的影响,并对其电吸附NH₄⁺特性和对模拟实际含NH₄⁺废水深度脱NH₄⁺效果进行研究。结果表明：RGO/TiO₂复合材料具有三维孔洞结构,比表面积为382.08 m²·g^-1,比电容量在扫速为0.01 V·s^-1时达到325.80 F·g^-1,优于RGO材料。RGO/TiO₂电极的初次电吸附量较RGO电极提升了28.3%,循环再生吸附10次后,RGO/TiO₂电极的NH₄⁺吸附量仅降低了5.87%,循环再生吸附性能优于RGO电极。外加电压2.0 V、循环流速35 ml·min^-1和NH₄⁺初始浓度1.0 mmol·L^-1为RGO/TiO₂电极的最佳NH₄⁺电吸附条件。RGO和RGO/TiO₂电极电吸附NH₄⁺过程符合准一级动力学模型和Freundlich等温吸附模型,电吸附NH₄⁺为非均匀表面的多层吸附行为,以物理吸附为主。RGO/TiO₂电极4级串联时对模拟实际含NH₄⁺炼油净化水的去除率达到86.84%。