Humic Acid Removal Research Articles

Ultrasound irritation enhanced activation of peroxymonosulfate with Fe0 for humic acid removal: less formation of Fe-HA complex

Ultrasound irritation enhanced activation of peroxymonosulfate with Fe0 for humic acid removal: less formation of Fe-HA complex

Investigation of Anti-fouling and UV-Cleaning Properties of PVDF/TiO2 Mixed-Matrix Membrane for Humic Acid Removal.

Natural organic matters (NOMs) have been found to be the major foulant in the application of ultrafiltration (UF) for treating surface water. Against this background, although hydrophilicity has been demonstrated to aid fouling mitigation, other parameters such as membrane surface morphology may contribute equally to improved fouling resistance. In this work, with humic acid solution as the model substance, the effects of titanium dioxides (TiO2) types (PC-20, P25, and X500) on membrane anti-fouling and defouling properties were comparatively analysed. The aims are (1) to determine the correlation between membrane surface morphology and membrane fouling and (2) to investigate the anti-fouling and UV-cleaning abilities of PVDF/TiO2 mixed-matrix membranes with different membrane topographies and surface energy conditions. The mixed-matrix membrane with P25 TiO2 exhibited the most significant UV-defouling ability, with a high irreversible flux recovery ratio (IFRR(UV)) of 16.56 after 6 h of UV irradiation, whereas that with X500 TiO2 exhibited both superior anti-fouling and defouling properties due to its smoother surface and its highly reactive surface layer.

Synthesis of Mg/Al-LDH nanoflakes decorated magnetic mesoporous MCM-41 and its application in humic acid adsorption

In this study, Mg/Al-LDH nanoflakes decorated magnetic mesoporous MCM-41 (magMCM-LDH) was prepared, and the materials were used as an adsorbent for the removal of humic acid (HA) from aqueous solution. The preparation, morphology, composition and magnetic properties of magMCM-LDH were characterized by various techniques. The results suggested that the Mg/Al-LDH nanoflakes have successfully decorated on the magMCM-41. Various batch experiments were conducted to investigate the influence of contacting time, initial concentration, solution pH and ions concentration. The results suggested that the adsorption process of HA onto 10-magMCM-LDH was spontaneous and endothermic, which conformed to the pseudo-second-order and Langmuir isotherm models. The maximum adsorption capacity of 10-magMCM-LDH was 181.14 mg/g at the temperature of 298 K. A lower pH and a higher ion concentration of the solution can be beneficial to the adsorption process. The adsorbent processed an excellent practical application and regeneration ability. Finally, FT-IR, XRD, XPS analyses proved that the electrostatic interactions and ion-exchange may play an important role in the adsorption process.

Mixed-Matrix Membranes Comprising of Polysulfone and Porous UiO-66, Zeolite 4A, and Their Combination: Preparation, Removal of Humic Acid, and Antifouling Properties.

High-performance Mixed-Matrix Membranes (MMMs) comprising of two kinds of porous fillers UiO-66 and Zeolite 4Aand their combination were fabricated with polysulfone (PSf) polymer matrix. For the very first time, UiO-66 and Zeolite 4A were jointly used as nanofillers in MMMs with the objective of complimenting synergistic effects. The individual and complimentary effects of nanofillers were investigated on membrane morphology and performance, pure water flux, humic acid rejection, static humic acid adsorption, and antifouling properties of membranes. Scanning Electron Microscopy (SEM) analysis of membranes confirmed that all MMMs possessed wider macrovoids with higher nanofiller loadings than neat PSf membranes and the MMMs (PSf/UiO-66 and PSf/Zeolite 4A-UiO-66) showed tendency of agglomeration with high nanofiller loadings (1 wt% and 2 wt%). All MMMs exhibited better hydrophilicity and lower static humic acid adsorption than neat PSf membranes. Pure water flux of MMMs was higher than neat PSf membranes but the tradeoff between permeability and selectivity was witnessed in the MMMs with single nanofiller. However, MMMs with combined nanofillers (PSf/Zeolite 4A-UiO-66) showed no such tradeoff, and an increase in both permeability and selectivity was achieved. All MMMs with lower nanofiller loadings (0.5 wt% and 1 wt%) showed improved flux recovery. PSf/Zeolite 4A-UiO-66 (0.5 wt%) membranes showed the superior antifouling properties without sacrificing permeability and selectivity.

Coagulation behaviors of aluminum salts towards humic acid: Detailed analysis of aluminum speciation and transformation

The hydrolysis of Al-based coagulants, especially aluminum speciation and transformation, is necessary for organic matter removal by the coagulation process. The goal of this study was to investigate the efficiency and mechanism of hydrolyzed Al species in the coagulation of humic acid (HA) removal. Three aluminum coagulants have been applied to investigate HA coagulation, which are aluminum chloride AlCl3 dominated by monomeric aluminum species Ala, polyaluminum chloride PACl1 dominated by medium polymer species Alb, and commercial polyaluminum chloride PACl2 dominated by larger polymer species and/or colloidal aluminum species Alc. Results showed that the best coagulation effect on HA removal (higher than 90%) occurred at pH 6 for three aluminum coagulants and their effect decreased in the order: PACl1 > AlCl3 > PACl2. Except that, the in situ hydrolyzed aluminum species produced by AlCl3 had synergistic effects on various sites of HA, and showed good adaptability to raw water and coagulant dosage. Hydrolyzed larger polymeric aluminum species of PACl1 could selectively bind to the HA site with strong binding, especially Al13 under the weak acidic condition. While for PACl2, complexation of small and median polymeric aluminum species, charge neutralization effect of Al13, and the effect of sweep coagulation of large polymeric aluminum species were involved. Moreover, diversity of hydrolyzed aluminum species in the coagulation process presented a significantly impact on flocs characteristics. This study provided a new insight into the relationship between HA and aluminum speciation and transformation for Al-based coagulants, which can be indicative to select suitable coagulants according to the water quality in the coagulation process.

Synthesis and evaluation of activated carbon from rice husks for removal of humic acid from water

Activated carbon was synthesized from the New Rice for Africa (NERICA) rice husk variety, followed by its evaluation for removal of humic acid from water. Product values of carbon yield, C and total specific surface area, as,BET were employed as the performance criterion. The best physically activated carbon resulted from char activation at 800 °C for 10 min, leading to as,BET and C×as,BET values of 756.8 and 402.7 m2 g−1, respectively. The best chemically activated carbon resulted from 30 wt% H3PO4 activation of rice husk at 400 °C for 30 min, leading to as,BET and C×as,BET values of 2258.4 and 1058.7 m2 g−1, respectively. Despite the higher as,BET value, the maximum adsorption capacity of the best chemically activated carbon (5.3 mg g−1) was found lower than 8.9 and 27.2 mg g−1 exhibited by the chemically activated carbons prepared at 500 and 600 °C, respectively. The best adsorption conditions included carbon dose of 0.5 g, solution pH of 2, and contact time of 60 min. The adsorption capacity of the prepared activated carbons (27.2 mg g−1) was comparable to that of the commercial activated carbon (30.40 mg g−1). The analyses of the adsorption isotherms and kinetics revealed that the experimental data fits well the Langmuir isotherm model, as well as the pseudo-second-order kinetic model. The latter suggests that the adsorption of humic acid onto the activated carbon was controlled by the chemisorption process. Overall, the study revealed that the NERICA rice husk variety has good prospects for preparation of activated carbons for humic acid adsorption.

Adsorption of humic acid from aqueous solutions onto shellfish ash: Kinetic and isotherm studies and artificial neural network modeling

Background: Natural organic matters such as humic acid react with chlorine and produce disinfection by products such as trihalomethanes that are carcinogenic. In this study, shellfish ash was used as a novel adsorbent for removal of humic acid. Methods: The present study was performed under various laboratory conditions including pH, adsorbent dose, contact time, and initial concentration of humic acid. Residual concentrations of humic acid in the samples were determined by a UV-Vis spectrophotometer at 254 nm wavelength. Artificial neural network (ANN) modeling studies were also performed. Results: Elemental analysis showed that the shellfish ash was 98% pure calcium. It was indicated that the maximum adsorption capacity was achieved in acidic conditions (pH = 3) and pHzpc was found to be 10.3. The adsorption data followed the Langmuir model (R2 > 0.9). The adsorption of humic acid followed the pseudo-second-order kinetic (R2 = 0.999). ANN modeling also provided the accurate prediction of humic acid adsorption for testing data (R2 = 0.989). Conclusion: According to the results, shellfish ash is recommended as an effective biosorbent for removal of organic pollutants such as humic acid. Keywords: Adsorption, Humic substances, Kinetics, Shellfish, Neural network

Towards enhanced fouling resistance of PVC ultrafiltration membrane using modified montmorillonite with folic acid

The main aim of this study is to develop the highly permeable and fouling resistant polyvinyl chloride (PVC) ultrafiltration membranes consisting different amounts of natural and modified montmorillonites with folic acid (Mt-FA). Mt. was modified with folic acid to achieve the better dispersion in the PVC matrix. Mt-FA was confirmed by XRD, FTIR and TGA. The effect of the Mt. and Mt-FA on the membrane morphology, porosity, hydrophilicity, roughness, mechanical strength, pure water flux and antifouling property in humic acid removal were investigated. XRD patterns revealed the formation of exfoliated clay mineral layers in 0.5 and 1.0 wt% loading of Mt-FA and the intercalated structure for the upper concentration of Mt-FA and the PVC/Mt-0.5 membrane. All the nanocomposite membranes showed higher hydrophilicity and roughness than the neat PVC membrane. The results demonstrated that the pure water flux, porosity and mechanical strength of the membranes were enhanced with the addition of Mt-FA up to a loading of 1.5 wt%. The PVC/Mt-FA-1.0 membrane exhibited high flux recovery ratio (FRR) and humic acid rejection of 92% and 90%, respectively. This was due to the exfoliated structure, surface hydrophilicity and electrostatic repulsion between negative charge of Mt-FA and humic acid. In addition, the reusability of the optimum membrane was evaluated for the filtration of the surface water in five permeation-cleaning cycles and the results confirmed that the modified membrane with 1.0 wt% Mt-FA can offer the excellent FRR as well as the reversible fouling ratio (RFR) in the filtration process.

Transformation of acetaminophen in solution containing both peroxymonosulfate and chlorine: Performance, mechanism, and disinfection by-product formation

With the fast development of peroxymonosulfate (PMS)-dominating processes in drinking water and wastewater treatment, residual PMS is easy to come across chlorine as these processes are usually followed by secondary chlorine disinfection. The synergistic effect of PMS and chlorine on the degradation of micro-organic pollutants is investigated by selecting acetaminophen (ACT) as a reference compound for the first time in this study. Unlike conventional PMS or chlorine activation which generates reactive species such as hydroxyl radical (HO•), sulfate radical (SO4•−), chlorine radical (Cl•), and singlet oxygen (1O2), the efficient ACT removal is attributed to the direct catalytic chlorination by PMS due to the significantly enhanced consumption of chlorine along with negligible change of PMS concentration at neutral condition, and the same reaction pathways in both PMS/chlorine and chlorine processes. The kinetic study demonstrates that ACT oxidation by PMS/chlorine follows second order reaction, and the degradation efficiency can be promoted at alkaline conditions with peak rate constants at pH 9.0−10.0. The presence of chloride can enhance the removal of ACT, while ammonium and humic acid significantly retard ACT degradation. Higher formation of selected disinfection by-products (DBPs) is observed in the PMS/chlorine process than in the sole chlorination. This study highlights the important role of PMS in organic pollutants degradation and DBPs formation during the chlorination process.

Dynamic regulation of Al-based floc cake layers by spiral rotation during ultrafiltration in drinking water treatment

Integrated ultrafiltration (UF) membrane-based processes are promising drinking water treatment technologies. However, the membrane module always remains static, resulting in membrane fouling through the gradual formation of a thick cake layer. As floc-based cake layers are loose, in the present study, a membrane module spiral rotation was introduced with the aim of regulating the cake layers. The cake layer thickness readily decreased and the UF membrane fouling was alleviated. The results showed that Al-based flocs were not easily removed from the membrane surface during rotation due to its low density; as a result, the likelihood of humic acid (HA) reaching the membrane surface was low. Computational fluid dynamics indicated that a strong shearing force was generated with high rotation height. Thus, the cake layer thickness was easily regulated, and the UF membrane fouling was further alleviated. However, the floc-based cake layer could be broken by strong shearing forces, thereby allowing HA molecules to directly reach the membrane surface and further aggravating membrane fouling. In comparison to alkaline condition, the UF membrane performed better under acidic conditions, particularly in terms of HA removal, due to the smaller floc size and higher positive charge. Additionally, excellent UF membrane performance was also observed when treating raw water, indicating the potential application.

Enhanced Treatment of Pharmaceutical Wastewater by an Improved A2/O Process with Ozone Mixed Municipal Wastewater

A pilot-scale experiment is carried out for treating mixed wastewater containing pharmaceutical wastewater (PW) and domestic wastewater (DW), by a process that is a combination of hydrolysis acidification-ozone-modified anaerobic–anoxic–aerobic-ozone (A2/O) (pre-ozone) or hydrolysis acidification-modified A2/O-ozone (post-ozone). The effects of different mixing ratios of PW and DW and pre-ozone treatment or post-ozone treatment on the removal of nitrogen and phosphorus and chemical oxygen demand (COD) are compared and studied. The optimal ratio of PW in mixing wastewater is 30%, which has the optimal COD removal efficiency and minimum biotoxicity to biological treatment. The pre-ozone treatment shows more advantages in removing nitrogen and phosphate but the post-ozone treatment shows more advantages in COD removal. Analysis of dissolved organic matter (DOM) demonstrates that post-ozone treatment has a more significant effect on the removal of fulvic acid and humic acid than the effect from the pre-ozone treatment, so the COD removal is better. Overall DOM degradation efficiency by post-ozone treatment is 55%, which is much higher than the pre-ozone treatment efficiency of 38%. Microbial community analysis reveals that the genus Thauera and the genus Parasegetibacter take great responsibility for the degradation of phenolics in this process. All the results show that the post-ozone treatment is more efficient for the mixed wastewater treatment in refractory organics removal.

Removal of humic acid from aqueous solutions by a novel hydrogarnet/zeolite composite

Removal of humic acid from aqueous solutions is pivotal to protect water from environmental and health concerns. Slurry consisting of silica gel, alumina, calcium hydroxide, and zeolite A was hydrothermally treated to prepare a hydrogarnet/zeolite composite for humic acid removal from water. The amount of hydrogarnet formed and the partial disorder in the zeolite structure affected the porous properties of the composite. The zeolite content in the slurry influenced the humic acid adsorption capacity. The composite hydrothermally treated for 2 h showed improvement in higher humic acid adsorption capacity (9.0 mg g−1) than the composites hydrothermally treated for 6 and 24 h (7.4 and 5.9 mg g−1) based on the pseudo-second-order model. The adsorption capacity of the composite was related to its crystal phase and the lattice distortion of the hydrogarnet, not the amount of hydrogarnet formed.

Efficiency of Zeolite Coated with Zero-Valent Iron Nanoparticles for Removal of Humic Acid from Aqueous Solutions

The most important effect of natural organic materials in water is reacting with disinfectants and creating disinfectant by-products that are mostly carcinogenic. The aim of this study was to determine the optimum conditions for removal of humic acid (HA) by zeolite coated with nZVI nanoparticles (Zeolite/nZVI) from aqueous solutions. In this study, after synthesis of zeolite/nZVI, its structure and morphology were examined using FTIR, BET, XRF, and FESEM techniques. The effects of HA concentration, composite content, pH, and reaction time were evaluated. The experimental data were analyzed by Langmuir and Freundlich isotherm and pseudo-first-order and second-order kinetic models. Finally, the thermodynamic parameters of enthalpy (ΔΗ°), entropy (ΔS°), and Gibbs free energy (ΔG°) were calculated. The results of the analyses confirmed the accuracy of the composite structure. Its specific surface area by using BET method was 203.43 m2/g. The HA removal efficiency was obtained at 92.98% in optimum conditions of 50 mg/L concentration, 2 g/L composite dose, pH = 3, and reaction time of 60 min. The results of the isotherm and kinetic study showed that the HA adsorption process follows the Langmuir isotherm (R2 = 0.9707) and pseudo-second-order kinetic. The maximum adsorption capacity of the composite was determined at 23.36 mg/g by Langmuir model. Thermodynamic parameters indicate that the adsorption of HA endothermic and the reaction cannot be done spontaneously. Zeolite/nZVI composite had good removal efficiency after five times of recycling. The present study showed that zeolite/nZVI can be used as an effective adsorbent for removal of HA from aqueous solutions.

Low-Pressure Membrane for Water Treatment Applications

Three ultrafiltration membranes were prepared using phase separation techniques. The membranes were characterized by scan electron microscope, porosity, pore size distribution measurement, and mechanical properties. The membrane performance was carried out using synthetic solutions from humic acid and tap water to express the contaminated drinking water. The polyvinylidene difluoride (M2) has the highest tensile strength 33.2 MPa with elongation of 52.3%, while polyacrylonitrile (M3) has the lowest mechanical properties, tensile strength 16.4 MPa with elongation of 42.7%. Polyethersulfone membrane (M1) provides the highest removal of humic acid, which was 99.5, 98.8, and 98.2% using feed concentrations 0.1, 0.3, and 0.5 g/l, respectively, while M3 provides the highest permeate flux which was 250, 234.4, and 201.4 l/m2 h using feed concentrations 0.1, 0.3, and 0.5 g/l, respectively. Analysis of water samples indicates that the prepared membranes can be used to treat the contaminated drinking water which produced the high quality of drinking water after treatment.

PHOTOCATALYTIC ACTIVITY OF IN-SITU FE-DOPED TIO2 FOR NATURAL ORGANIC MATTER REMOVAL

Humic acids represent a major fraction of natural organic matter (NOM) in aquatic environments. Having undefined composition and complex ill-defined structures, their presence in natural waters is undesirable. In this study, solar photocatalytic activity of synthesized Fe-doped TiO2 photocatalysts was investigated for the degradation of a 100 kDa molecular size fraction of humic acid. For this purpose, catalysts comprised of 5 different molar ratios of Fe/Ti were prepared by in-situ sol gel method and characterized by FTIR and Raman spectroscopy. Optimum loadings of the catalysts were determined and the kinetics of humic acid removal was investigated focusing on UV–vis spectroscopic parameters. Moreover, fluorescence techniques such as excitation-emission matrix (EEM) were also acquired for elucidating induced structural changes of humic acid during photocatalytic degradation. Results revealed that, using photocatalysts prepared by in-situ sol-gel method 20 to 25% removal of humic acid could be attained after photocatalytic treatment of 120 min.

Electrocatalytic degradation of humic acid using particle electrodes of activated carbon loaded with metallic cobalt

A column granular electrode loaded with metallic cobalt was prepared using powder activated carbon (namely Co/AC) and used in a continuous electrochemical reactor to degrade humic acid (HA). The results of XRD indicated that the form of catalyst prepared at 600 °C for 4 h mainly consisted of Co0, whereas it consisted of CoO when prepared at 450–500 °C for 4 h. The Co0 possessed better catalytic effects in the degradation of HA than CoO. When C0 of HA was 200 mg L−1, the C/C0 approached 0.06–0.12 under 0.1 A, pH of 7.0, 0.01 M Na2SO4, and 20 min of hydraulic retention time (HRT). The current, HRT, initial pH, electrolyte type and concentration influenced the degradation of HA. The ESR signals indicated that both H∗ and OH were catalytically generated by Co/AC electrode. Compared to AC electrodes, the Co/AC electrodes showed a faster reaction Tafel slope (68 mV dec−1) and larger electrochemical double-layer capacitance (Cdl = 1.93 mF cm−2). The degradation and removal of HA was achieved by both the electro-oxidation and electro-reduction in the Co/AC electrode system.

Potential of using green adsorbent of humic acid removal from aqueous solutions: equilibrium, kinetics, thermodynamic and regeneration studies

ABSTRACT The natural organic matter in water resources poses many problems, such as unpleasant taste and colour in the water, and is one of the most important precursors to the formation of disinfection byproducts (DBPs) during water treatment. This study was performed to evaluate the efficiency of activated carbon (AC) and activated carbon coated with nZVI nanoparticles (AC-nZVI) to remove humic acid from aqueous solutions. To end this, the effect of some operational factors including pH, contact time, humic acid concentration and adsorbent dose was studied in removal of humic acid from aqueous solutions in the presence of AC and AC-nZVI. The structure of the adsorbents and their morphology were characterized by FTIR, BET, SEM and XRD analyzes. The adsorption isotherm was determined using Langmuir, Freundlich and kinetic adsorption models by studying quasi-first-order and quasi-second-order models. The thermodynamic parameters of the adsorption system such as changes in enthalpy (ΔH0), entropy (ΔS0) and free energy of Gibbs (ΔG0) were also measured and evaluated. The results showed that the removal efficiency is directly associated with the dose of adsorbent and has a reverse association with pH and humic acid concentration. The optimal removal of humic acid at the adsorbent dosage of 1.6 g/L, the humic acid concentration of 50 mg/L and the contact time of 45 min was found 84.7% and 95.68% for AC and AC-nZVI, respectively. The SBET and total pure volume for the AC-nZVI were 821.52 m2/g and 0.631 cm3/g respectively. The removal rate by AC-nZVI as significantly high, indicating the effective role of nanoparticle stabilisation on activated carbon. As a result, it is possible to find an effective and highly efficient adsorbent by stabilising the nanoparticles on activated carbon that can be used to remove humic acid.

Ultra-high synergetic intensity for humic acid removal by coupling bubble discharge with activated carbon

Humic acid (HA) removal research focuses on the global water treatment industry. In this work, efficient HA degradation with an ultra-high synergetic intensity is achieved by combined bubble discharge with activated carbon (AC). Adding AC to the discharge greatly improves HA removal efficiency and degradation speed; the synergetic intensity reaches 651.52% in the combined system, and the adsorption residual on AC is 4.52%. After 90 min of treatment, the HA removal efficiency reaches 98.90%, 31.29%, and 7.61% in the plasma-AC combined, solo bubble discharge, and solo AC adsorption systems, respectively. During the plasma process, the number of pore structures and active sites and the amount of oxygen-containing functional groups on the AC surface increase, resulting in a higher adsorption capacity to reactive species (H2O2 and O3) and HA and promoting interactions on the AC surface. For HA mineralization, the presence of AC greatly promotes the destruction of aromatic structures and chromophoric HA functional groups.

Facile synthesis of polyethyleneimine modified magnetic graphite: An effective adsorbent for the removal of humic acid from aqueous solution

In this study, a simple method was introduced to synthesize polyethyleneimine modified magnetic graphite (Fe3O4@GR-PEI(50)), which was used to adsorb humic acid (HA) from aqueous solution. The obtained materials were characterized by field emission scanning electron microscope, X-Ray diffraction, Fourier transform-infrared, and thermogravimetric analysis. The results showed that Fe3O4@GR-PEI(50) was synthesized successfully and PEI uniformly covered on Fe3O4@GR-PEI(50) surface. The adsorption performance was evaluated at different concentration, temperature, pH, and cationic concentration. The maximum adsorption capacity of Fe3O4@GR-PEI(50) was 49.87 mg/g at 293 ± 1 K and it was greatly affected by the solution pH and the additional cations. This is mainly due to the strong electrostatic interactions between the negatively charged HA molecules and the positively charged adsorbents. The adsorption kinetics were examined using pseudo-first-order, pseudo-second-order and intra-particle diffusion model. The equilibrium adsorption data were analyzed by Langmuir and Freundlich models. The results revealed that the pseudo-second-order model and Freundlich isotherm fit the kinetics and equilibrium data, respectively. Furthermore, Fe3O4@GR-PEI(50) exhibited a good performance of regeneration and reuse, which maintained a high adsorption capacity after six consecutive times of regeneration.

The Investigation of Oxidation Flocculation Characteristics of Ferrate Solution

The fresh ferrate solution was prepared by in situ electrolysis method and directly added into the simulated surface micro-polluted water to proceed purification and pretreatment process. To explore the influence on the dosage of ferrate and pH of raw water, the simulated water sample was treated by single factor change coagulation experiment. Combining with turbidity, ammonia nitrogen, humic acid removal rate as the judgment index, and the fractal dimension of floc was calculated by using the platform of floc morphology analysis, the optimal dosage of the ferrate solution and reaction pH range were confirmed. This work revealed profoundly the correlation of turbidity, ammonia nitrogen, humic acid removal rate and flocculation fractal dimension.