High Humic Acid Research Articles

Effect of humic acid on Se and Fe transformations in soil during waterlogged incubation

Humic acid (HA) serves as electron donor and acceptor in the biogeochemical cycle of Fe and Se in soil. In anoxic condition, a series of redox reactions occur, including reductive dissolution of Fe oxides, decomposition of organic matters, and transformation of trace elements. Thus, this study demonstrates the effect of HA on Se and Fe transformations in soil during waterlogged incubation. Soils were incubated under anoxic condition for 56 days, and pH, redox potential (Eh), and Fe and Se concentrations were measured at specific reaction times (days 2, 4, 8, 15, 28, and 56 of incubation). Moreover, sequential extraction and X-ray photoelectron spectroscopy (XPS) were used to obtain Se and Fe transformations, respectively. High resolution transmission electron microscopy (HR-TEM) was used to observe the morphology properties of soil. Results indicated that 4% HA addition decreased the pH and inhibited Eh decline continuously, and HA addition inhibited the Fe and Se release from soil. The Se concentration in soil solution without and with 4% HA addition at the day 15 of incubation were 1.05 mg L−1 and 0.30 mg L−1, respectively. Moreover, the residual Se fraction in soil with HA addition was evidently more than that in soil without HA addition. XPS of Se3d and Fe2p revealed that the binding energy of the main peak shifted to low values and the peak shape varied with the increase in HA addition. XPS2p3/2 and HR-TEM data indicated that the surface structure of Fe oxides in soil varied with the variations in anoxic incubation time and HA addition amount. HA addition would negatively influence Se and Fe release in soil solution and then reduce their bioavailability. This study aids in understanding the environmental behavior changes of Se and Fe when high HA concentrations enter the soils, especially wetland or paddy soil.

Coagulation and Dissolution of CuO Nanoparticles in the Presence of Dissolved Organic Matter Under Different pH Values

The increased use of copper oxide nanoparticles (CuO NPs) in commercial products and industrial applications raises concerns about their adverse effects on aquatic life and human health. Therefore, the current study explored the removal of CuO NPs from water via coagulation by measuring solubility under various pH values and humic acid (HA) concentrations. The results showed that the media pH significantly affected the coagulation efficiency of CuO NPs (30 mg/L) under various (0–0.30 mM) ferric chloride (FC) dosages. The concentration of dissolved Cu2+ ions at pH 3–6 was (16.5–4.8 mg/L), which was higher than at other studied pH (7–11). Moreover, the simultaneous effect of coagulants and charge neutralization at pH 6–8 enhanced the removal of CuO NPs. At a lower FC (0–0.05 mM) dosage, the higher HA concentration inhibited the aggregation of CuO NPs. However, at the optimum dose of (0.2 mM) FC, the efficiency of turbidity removal and solubility of CuO NPs between pH 8 and 11 was above 98% and 5%, respectively, probably due to coagulant enmeshment. Our study suggested that coagulation was effective in removing the CuO NPs from the complex matrices with pH values ranging from 8–11. The findings of the present study provide insight into the coagulation and dissolution behavior of CuO NPs during the water treatment process.

Control of Membrane Fouling in Organics Filtration Using Ce-Doped Zirconia and Visible Light.

Membrane fouling has been a major issue in the development of more efficient water treatment processes. Specifically in surface waters filtration, organic matter, such as humic-like substances, can cause irreversible fouling. Therefore, this study evaluates the activity of a photocatalytic layer composed of Ce-doped zirconia nanoparticles in improving the fouling resistance during filtration of an aqueous solution of humic acid (HA). These nanoparticles were prepared by hydrothermal and sol–gel processes and then characterized. Before the filtration experiments, the photodegradation of HA catalyzed by Ce-doped zirconia nanoparticles in dispersion was studied. It was observed that the sol–gel prepared Ce-ZrO2 exhibited higher HA removal in practically neutral pH, achieving 93% efficiency in 180 min of adsorption in the dark followed by 180 min under visible-light irradiation using light-emitting diodes (LEDs). Changes in spectral properties and in total organic carbon confirmed HA degradation and contributed to the proposal of a mechanism for HA photodegradation. Finally, in HA filtration tests, Ce-ZrO2 photocatalytic membranes were able to recover the flux in a fouled membrane using visible-light by degrading HA. The present findings point to the further development of anti-fouling membranes, in which solar light can be used to degrade fouling compounds and possibly contaminants of emerging concern, which will have important environmental implications.

Enhanced dispersion of carbon nanotubes in water by plasma induced graft poly(N,N-dimethylacrylamide) and its application in humic acid capture

Humic acid (HA) is the main culprit of producing the carcinogenic, teratogenic, and mutagenic halogenated alkanes. In present work, multi-walled carbon nanotubes (MCNT) were grafted N,N-dimethyl-acrylamide (NDMA) to enhance its type and concentration of the functional groups by using plasma technique. The MCNT/NDMA composites exhibit better dispersion property and higher HA adsorption efficiency. The addition of amide group could strongly enhance the HA adsorption property of MCNT due to less acidic of MCNT/NDMA (pHpzc = 5.0) than MCNT (pHpzc = 4.5). The results highlight the effect of pH values, ionic strength, Pb(II) concentrations and the Pb(II) addition sequences. HA adsorption by MCNT/NDMA obeyed the Langmuir isotherm model, attributed to an outer-sphere surface adsorption mechanism through π–π interactions and coordination of amide group to the functional groups on HA. The presence of Pb(II) significantly effects the HA adsorption in the three difference addition sequences due to different mechanisms.

Performance of granular ferric hydroxide process for removal of humic acid substances from aqueous solution based on experimental design and response surface methodology

Response surface methodology has been used to design experiments and to optimize the effect of independent variables responsible for higher adsorption of humic acid (HA) by granular ferric hydroxide (GFH) from aqueous solutions. The variables of pH (3–11), contact time (15–120 min), adsorbent dose (1–5 g/L) and initial concentration of humic acid (5–20 mg/L) were examined. The adsorption isotherms and kinetics of humic acid substances on granular ferric hydroxide (GFH) were studied. Also the design of the experiments was performed using R software by the CCD (central composite design) method. Variance analysis (ANOVA) was used as the statistical response analysis method. Result of this study proved the optimal values of the independent variables of the adsorbent dose, contact time, initial concentration of humic acid and pH were 4 g/L, 93.75 min, 16.25 mg/L, and 5, respectively. The experimental data followed the Langmuir isotherm and pseudo-second kinetic model. Based on the response surface methodology, higher HA removal efficiencies were obtained with acidic condition, longer reaction time, and appropriated loading amount of GFH.

Humic acid embedded chitosan/poly (vinyl alcohol) pH-sensitive hydrogel: Synthesis, characterization, swelling kinetic and diffusion coefficient

In the present research, humic acid (HA) embedded chitosan (CHT)-poly (vinyl alcohol) (PVA) pH-sensitive hydrogels have been synthesized using glutaraldehyde as a crosslinker. The hydrogels were characterized by Fourier-transform infrared (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) analysis. The effect of HA content, pH, and temperature on the equilibrium solvent uptake has been investigated. With higher HA contents, the equilibrium swelling capacity increases while lower concentrations of acid cause a decrease in the degree of the swelling. The hydrogels have been found to undergo a number of swelling/deswelling cycles when pH of the swelling medium changes from 1.5 to 11.0. Fick’s law, first-order, and second-order kinetic models were applied to the swelling ratio of hydrogels to explain the mass transfer mechanism and specify swelling kinetic parameters. The swelling parameters such as equilibrium swelling capacity, swelling rate constant, swelling exponent, initial swelling rate, diffusion coefficient, etc., have been evaluated.

Fouling process and anti-fouling mechanisms of dynamic membrane assisted by photocatalytic oxidation under sub-critical fluxes

Membrane fouling is often considered as a hindrance for the application of microfiltration/ultrafiltration (MF/UF) for drinking water production. A novel process of photocatalytic membrane reactor/dynamic membrane (PMR/DM), operating in a continuous mode under sub-critical flux, was proposed for the mitigation of membrane fouling caused by humic acids (HAs) in water. The mechanism of membrane fouling alleviation with synergistic photocatalytic oxidation and dynamic layer isolating effect was comprehensively investigated from the characterization of foulant evolution responsible for the reversible and irreversible fouling. The results showed that the PMR/DM utilized photocatalytic oxidation to enhance the porosity and hydrophilicity of the fouling layer by converting the high molecular weight (MW) and hydrophobic HA molecules with carboxylic functional groups and aromatic structures into low-MW hydrophilic or transphilic fractions, including tryptophan-like or fulvic-like substances. The fouling layer formed in the PMR/DM by combination of photocatalytic oxidation and DM running at a sub-critical flux of 100 L·h−1·m−2, was more hydrophilic and more porous, resulting in the lowest trans-membrane pressure (TMP) growth rates, as compared to the processes of ceramic membrane (CM), DM and PMR/CM. Meanwhile, the dynamic layer prevented the foulants, particularly the high-MW hydrophobic fractions, from contacting the primary membrane, which enabled the membrane permeability to be restored easily.

The Role of Lignocellulosic Composition and Residual Lipids in Empty Fruit Bunches on the Production of Humic Acids in Submerged Fermentations.

The aim of this research was to study the production of humic acids (HA) by Trichoderma reesei from empty fruit bunches (EFBs) of palm oil processing, with a focus on the effects of lignocellulosic content and residual lipids. EFBs from two different soils and palm oil producers were previously characterized about their lignocellulosic composition. Submerged fermentations were inoculated with T. reesei spores and set up with or without residual lipids. The results showed that the soil and the processing for removal of the palm fresh fruits were crucial to EFB quality. Thus, EFBs were classified as type 1 (higher lignocellulosic and fatty acids composition similar to the palm oil and palm kernel oil) and type 2 (lower lignocellulosic content and fatty acids composition similar to palm oil). Despite the different profiles, the fungal growth was similar for both EFB types. HA production was associated with fungal growth, and it was higher without lipids for both EFBs. The highest HA productivity was obtained from type 1 EFB (approximately 90mgL-1 at 48h). Therefore, the lignocellulosic composition and the nature of the residual lipids in EFBs play an important role in HA production by submerged fermentation.

The role of dissolved organic carbon concentration and composition on nickel toxicity to early life-stages of the blue mussel Mytilus edulis and purple sea urchin Strongylocentrotus purpuratus

Nickel (Ni) emissions resulting from production and transportation raise concerns about the impact of Ni exposure to marine ecosystems. Ni bioavailability models are established for FW systems, but the influence of chemical parameters (e.g. dissolved organic carbon (DOC)) on Ni toxicity within marine systems is less well understood. To examine the effects of DOC concentration and composition on Ni toxicity, acute toxicity tests were conducted on early life-stages of blue mussels (Mytilus edulis) and sea urchin embryos (Strongylocentrotus purpuratus) in full strength sea water (32 ppt). Nine different field collected samples of water with varying concentration (up to 4.5 mg C/L) and composition of DOC were collected from the east coast of the United States. Organic matter compositional analysis included molecular fluorescence and absorbance spectroscopy. The different DOC sources had different protective effects against embryo toxicity. The control (no DOC) Ni 48 h-EC50 for Mytilus embryos was 133 µg/L (95% confidence interval (C.I.) of 123–144 µg/L), while Strongylocentrotus embryos displayed control 96-h EC50 values of 207 µg/L (167–247 µg/L). The most significantly protective sample had high humic acid concentrations (as determined from fluorescence spectroscopy), which yielded an EC50 of 195 µg/L (169–222 µg/L) for Mytilus, and an EC50 of 394 µg/L (369–419 µg/L) for S. purpuratus. Among all samples, protection was related to both DOC quantity and quality, with fluorescence-resolved humic and fulvic acid concentrations showing the strongest correlations with protection for both species. These data suggest that DOC is protective against Ni toxicity in M. edulis and S. purpuratus, and that accounting for a DOC quality factor will improve predictive toxicity models such as the biotic ligand model.

Dissolved oxygen inhibits the promotion of chlorothalonil photodegradation mediated by humic acid

Chlorothalonil (CT) is widely used to control fungal diseases, and it is commonly detected in the environment. Phototransformation is an important process which removes CT from aquatic environments. The kinetics and mechanisms of CT photodegradation in solutions with and without humic acid (HA) were investigated, and the influence of dissolved oxygen (DO) on the photodegradation process was also considered. The rate constant observed in pure water was only 0.017 h−1, but it increased to 0.083 h−1 with 5.0 mgC L−1 of HA present. Reactive species generated by HA were shown to play an important role. Moreover, the degradation of CT was promoted at higher HA concentrations. But higher DO concentrations inhibits CT degradation because of the reaction between DO and excited triplet state CT (3CT*) or HA (3HA*). The contributions of the reactive species tested were in the sequence 3HA* > 1O2 > H2O2/O2− ≈ OH in a nitrogen-saturated system, but in an oxygen-saturated system the order was OH ≈1 O2 > H2O2/O2− > 3HA*. 3CT* was confirmed as the active form of CT during degradation, with 4-hydroxy-chlorothalonil and 2,4,5-trichloroisophthalonitrile as the main products. Compared to direct photodegradation, CT photodegradation mediated by HA can decrease the toxicity of an aquatic environment as demonstrated through tests with Scenedesmus obliquus.

Effect of Phosphate on Ultrafiltration Membrane Performance After Predeposition of Fe3O4

The effect of predeposition of Fe3O4 on ultrafiltration (UF) processes has been widely studied in recent years. However, there have been no reports of effects of phosphate on the predeposition process. In this article, the fluxes of humic acid (HA) solutions filtered by Fe3O4+UF and Fe3O4+H2PO4−+UF were studied and filtered water was analyzed. Results indicate that the optimum concentration of Fe3O4 for the predeposition process was 0.45 g/L. Filtration fluxes of HA solutions using UF, Fe3O4+UF, and Fe3O4+H2PO4−+UF were 0.32, 0.52, and 0.41, respectively, after 10 min. Removal efficiencies of HA filtrated by UF, Fe3O4+UF, and Fe3O4+H2PO4−+UF were 32.6%, 41.1%, and 35.8%, respectively, according to dissolved organic matter results. After Fe3O4 adsorbed phosphate, the effect of Fe3O4 predeposition on removal of high and medium molecular weight HA was weaker. However, Fe3O4 predeposition enhanced removal of low molecular weight HA. Scanning electron microscopy and atomic force microscopy demonstrated that phosphate decreased compactness of the Fe3O4 predeposition layer. These data provide new insights into use of Fe3O4 predeposition in UF applications.

Synthesizing Ag/PDA/PES Antibacterial Membrane for Natural Organic Molecules Removal

Silver nanoparticles (NP) was successfully immobilized on polydopamine (PDA) supported polyethersulfone (PES) membrane via a redox reaction. Polyvinylpyrrolidone (PVP) was added into membrane dope solution as a pore-forming agent. Four pieces of membranes (M1, M2, M3 and M4) were fabricated with different active layer coatings to compare their morphological and performance properties. The differences between each sample were highlighted as follow: M1 (pristine PES), M2 (PES+PVP), M3 (PDA/PES+PVP) and M4 (Ag/PDA/PES+PVP). All membranes were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction and contact angle analysis. The membrane performance was examined using pure water permeability (PWP) test, antibacterial test and humic acid (HA) rejection test. Pristine M1 membrane showed that PWP of 27.16 LMH/bar and HA rejection of 84 %. In this study, it was found that the addition of PVP as a pore agent into the membrane M2 increased water flux but slightly deteriorated HA rejection. Coating of PDA on M3 and immobilizing silver NP on M4 membrane surface have improved HA rejection but compromised PWP. The results showed that membrane M4 carried excellent antibacterial property and highest HA rejection among all fabricated membranes.

Adsorption of Cu(II) and Cd(II) from aqueous solutions by ferromanganese binary oxide–biochar composites

Remediation of heavy metal–contaminated soil and water bodies necessitates the continuous development of effective decontamination techniques. To address this issue, ferromanganese binary oxide–biochar composites (FMBC) were prepared using impregnation/sintering methods, and their physicochemical properties and morphologies were examined. Kinetic modeling and adsorption isotherms were used to characterize the adsorption of Cu(II) and Cd(II) on FMBC, revealing that adsorption was well represented by pseudo-second-order kinetics (R2>0.99) and the Langmuir isotherm model. The prepared FMBC exhibited maximum Cu(II) and Cd(II) adsorption capacities of 64.9 and 101.0mg/g, respectively, exceeding the corresponding values of biochar (21.7 and 28.0mg/g, respectively). Moreover, adsorption was favored by increased pH and high humic acid concentration. X-ray photoelectron spectroscopy and Fourier transform infrared analyses confirmed that the heavy metal ions adsorbed on FMBC were divalent, indicating that the uptake of Cu(II) and Cd(II) was mainly due to the formation of strong mono- or multidentate inner-sphere complexes (e.g., COO–M (M=Cu or Cd) and Fe–Mn–O–M). Thus, the prepared composites exhibited potential applications as excellent adsorbents for Cu(II) and Cd(II) removal from contaminated water.

Super-hydrophilic and fouling resistant PVDF ultrafiltration membranes based on a facile prefabricated surface

The hydrophilicity of PVDF membrane is playing an enormously important role in its widespread water treatment fields considering the excellent intrinsic properties of PVDF raw materials. Rather than the conventional surface modification or hybridization, herein, we report a novel approach to prepare super-hydrophilic PVDF ultrafiltration (UF) membrane by creating a prefabricated super-hydrophilic surface of inorganic TiO2 nanoparticles (NPs). The resultant membrane [prepared by prefabrication surface adhesion of TiO2 NPs on PVDF-PEG-TiO2 hybrid membrane (SaT-PPT)] has a uniform distribution of TiO2 NPs not only on the membrane surface but also within membrane matrix, this will maximize the super-hydrophilic feature throughout the membrane: from inner porous structures to outer surfaces, and will avoid “dead-corner” to block fast water pass through. The performances of SaT-PPT membrane as compared with the control membranes (PVDF-PEG, and PVDF-PEG with TiO2 anchored only at surface) were investigated in terms of humic acid (HA) rejection, flux and flux decline in lab-made cross flow UF experiments with and without UV irradiation. It indicated that SaT-PPT membrane exhibited the highest hydrophilicity and flux, lowest flux decline and total resistance, but still with the highest HA rejection rate. In addition, SaT-PPT membrane showed the highest flux recovery after simple physical cleaning to extend the longer life span of membrane. It is reasonable to believe that our developed SaT-PPT membranes will provide insightful engineering practices to benefit the broad water treatment applications.

Interaction of Humic Acid with Cu/Pb-Zn Tailings of Different Degrees of Weathering

Aggregation of tailings is instrumental for developing a physical environment permitting water infiltration, aeration, and root penetration. Previous research found that microaggregation of Cu-Pb-Zn tailings was stimulated by amendment of composted sugarcane residues. The present study aimed to identify organic functional groups in humic acids (HA) involved in the aggregation of Cu-Pb-Zn tailings, which were considered to be formed from long-term organic matter decomposition in the engineered tailing-soil. The adsorption of HA by the weathered (WT) and freshly deposited (FT) tailings was evaluated at a range of pH conditions in tailing-HA suspension. Humic acid adsorption decreased with increasing pH from 5.0 to 9.0. The FT was found to contain more oxy-(hydr)oxides, particularly poorly crystalline Fe and Al oxy-(hydr)oxides than the WT, which was one of the factors attributing to FT’s higher HA affinity. The Fourier transform infrared spectroscopy analysis of tailing particles before and after HA adsorption indicated that carboxylic and phenolic groups of HA preferentially interacted with tailing mineral particles, probably through ligand exchange, polyvalent cation bridge and electrostatic attraction. The pH-dependent HA adsorption indicated the potential role of functional groups of organic matters in microaggregation of Cu/Pb-Zn tailings. Moreover, the presence of abundant Al/Fe oxyhydroxides promoted organo-mineral interactions. The present findings will contribute toward developing field application to engineer functional Technosols from the tailings by selecting organic matter rich in functional groups.

Comparison of Metagenomic DNA Extraction Methods for Soil Sediments of High Elevation Puga Hot Spring in Ladakh, India to Explore Bacterial Diversity

ABSTRACTExtraction of good-quality metagenomic DNA from extreme environments is quite challenging, particularly from high elevation hot spring sediments. Low microbial load, high humic acid content and other contaminants complicate the process of extraction of metagenomic DNA from hot spring sediments. In the present study, efficacy of five manual DNA extraction protocols with modifications has been evaluated for metagenomic DNA extraction from boron–sulfur rich high elevation Puga hot spring sediments. Best suited protocol was identified based on the cell lysis efficiency, DNA yield, humic acid content, PCR reproducibility and representation of bacterial diversity. Quantity as well as quality of crude metagenomic DNA differed remarkably between various protocols used and were not pure enough to give PCR amplification using 16S rRNA bacterial and archaeal primers. Crude metagenomic DNA extracted using five different DNA extraction protocols was purified using spin column based purification method. Even after purification, only three protocols C, D and E yielded metagenomic DNA that could be amplified using both archaeal and bacterial primers. To evaluate the degree of microbial diversity represented by protocols C, D and E, phylogenetic genes amplified were subjected to amplified ribosomal DNA restriction analysis (ARDRA) and denaturing gradient gel electrophoresis analysis (DGGE) analysis. ARDRA banding pattern of amplicons generated for all the three extraction protocols, i.e., C, D and E were found to be similar. DGGE of protocol E derived amplicons resulted in the similar number of dominant bands but a greater number of non-dominant bands, i.e., the highest microbial diversity in comparison to protocols C and D, respectively. In the present study, protocol E developed from Yeates et al. protocol has been found to be best in terms of DNA yield, DNA purity and bacterial diversity depiction associated with boron–sulfur rich sediment of high elevation hot springs.

Removal of humic acid from aqueous solution by magnetic multi-walled carbon nanotubes decorated with calcium

Abstract Multi-walled carbon nanotubes (MWCNTs) were magnetized with hybrids of iron oxides and modified with calcium by one step chemical co-precipitation method to prepare magnetic nanocomposite for removal of humic acid (HA) from aqueous solution. The nanocomposite was characterized by field emission scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, specific surface area and vibrating-sample magnetometer, respectively. The results showed that MWCNTs were coated with magnetic iron oxide and CaCO 3 . The magnetic MWCNTs coated calcium (MMC) was used to remove humic acid and the influence of exposure time and pH of solution on the removal rate was examined. The MMC had excellent properties in removal of HA, when MMC dosage was 0.5 g L − 1 the HA removal rate achieved 90.27% at HA initial concentration of 20 mg L − 1 and pH = 7.0 ± 0.2 for contacting time of 30 min. The pH slightly affected the removal efficiency of HA. The studies of adsorption kinetics indicated that pseudo-second-order kinetics model was suitable for describing the adsorption. The adsorption isothermal equations were analyzed and results revealed that the adsorption of HA on MMC followed Temkin equation. Thermodynamics analysis of the adsorption showed that Δ G 0 and Δ H 0 were negative, suggesting that the adsorption was a spontaneous and exothermic process, associated with mainly chemical adsorption. The negative enthalpy Δ S 0 illustrated that the randomness decreased after adsorption. The HA removal efficiency increased after calcium was coated on MWCNTs, which was attributed to coordination of calcium with HA by the interaction of metal cation bridging and ligand. MMC were regenerated by using pre-ultrasonic microwave technology and could remain high HA removal efficiency of 89.20% after 5 cycles of adsorption- regeneration.

Implications of humic acid, inorganic carbon and speciation on fluoride retention mechanisms in nanofiltration and reverse osmosis

The impact of pH and humic acid (HA) on the retention of fluoride (F) and inorganic carbon (IC) by nanofiltration (NF) and reverse osmosis (RO) membranes was determined. Synthetic waters were prepared using realistic ranges of F, IC and HA for carbonaceous waters found for example in the fluoride rich waters in Tanzania. These waters were filtered using NF270 and BW30 membranes to determine retention mechanisms.IC changes speciation with pH. The dominant species at pH<6, 6–10 and >10 are H2CO3, HCO3− and CO32− respectively. This results in changes in charge and size of the hydrated ion radius. The mechanism for IC retention by the NF270 and BW30 membranes are charge repulsion and size exclusion, respectively. F retention increases with pH. IC influenced F retention at pH>10 where IC exists as divalent CO32− and is retained more easily than the monovalent F−.HA enhances the retention of F by NF/RO membranes under certain conditions. The enhancement effect is more pronounced at neutral than at acidic pH and basic pH. The mechanism for the enhancement is attributed to the change in surface charge of the membranes by adsorption of HA. At high HA concentration the F retention enhancement is annulled by deposit formation on the membrane.The results obtained in this study indicate the complexity of retention in real surface- and ground waters that can alter significantly in pH as well as IC and HA content. The research is situated in the context of developing membrane technologies for autonomous systems in remote locations where water quality is variable and mechanisms of membrane performance are poorly understood.

Effect of reduced humic acid on the transport of ferrihydrite nanoparticles under anoxic conditions

Humic acid (HA) occurs ubiquitously in the subsurface environments and is well-known to play a critical role in the fate and transport of ferrihydrite nanoparticles (NPs) and NPs-associated contaminants. Under anoxic conditions, HA can readily be reduced by microorganisms or geochemical reducing species, and the mechanisms and kinetics of ferrihydrite reduction by reduced HA (HAred) are well-documented; however, the role of these redox reactions on the transport of ferrihydrite NPs is largely underestimated. This study provides new knowledge regarding the role of HA (both reduced HA (HAred) and oxidized HA (HAox)) of environmentally relevant concentrations (0–50 mg C/L) on the transport of ferrihydrite NPs in anoxic sand columns. Our findings show that, regardless of the redox state, the presence of a low concentration of HA (3 mg C/L) inhibited ferrihydrite NP's transport due to enhanced aggregation (and deposition) between positively charged ferrihydrite NPs and negatively charged HA molecules. In contrast, higher HA (both HAred and HAox) concentration (≥10 mg C/L) significantly enhanced the mobility of ferrihydrite NPs, primarily due to the enhanced electrostatic and steric stabilization originating from excessively adsorbed HA molecules. Interestingly, the transport of ferrihydrite NPs is substantially lower in the presence of HAred than in the presence of HAox. This distinct effect (HAred vs. HAox) on the particle transport is attributed to the fact that reductive dissolution of ferrihydrite NPs occurs in the presence of HAred (ferrihydrite dissolves and thus total breakthrough decreases), but not in the presence of HAox. Furthermore, the abatement extent of ferrihydrite NPs transport triggered by the presence of HAred is dependent on dissolved HAred concentration. Taken together, our findings provide direct, and much needed insights into the distinct roles of redox state of HA on the transport of redox-sensitive metal-bearing NPs in porous media.

Bioremoval of humic acid from water by white rot fungi: exploring the removal mechanisms.

Twelve white rot fungi (WRF) strains were screened on agar plates for their ability to bleach humic acid (HA). Four fungal strains were selected and tested in liquid media for removal of HA. Bioremediation was investigated by HA color removal and changes in the concentration and molecular size distribution of HA by size exclusion chromatography. Trametes versicolor and Phanerochaete chrysosporium showed the highest HA removal efficiency, reaching about 80%. Laccase and manganese peroxidase were measured as extracellular enzymes and their relation to the HA removal by WRF was investigated. Results indicated that nitrogen limitation could enhance the WRF extracellular enzyme activity, but did not necessarily increase the HA removal by WRF. The mechanism of bioremediation by WRF was shown to involve biosorption of HA by fungal biomass and degradation of HA to smaller molecules. Also, contradicting previous reports, it was shown that the decolorization of HA by WRF could not necessarily be interpreted as degradation of HA. Biosorption experiments revealed that HA removal by fungal biomass is dependent not only on the amount of biomass as the sorbent, but also on the fungal species. The involvement of cytochrome P450 (CYP) enzymes was confirmed by comparing the HA removal capability of fungi with and without the presence of a CYP inhibitor. The ability of purified laccase from WRF to solely degrade HA was proven and the importance of mediators was also demonstrated.