High Humic Acid Content Research Articles

Efficient degradation of carbamazepine by organo-montmorillonite supported nCoFe2O4-activated peroxymonosulfate process

Carbamazepine (CBZ) is one of most frequently detected pharmaceutical contaminants in water ecosystem, which cannot be removed efficiently by traditional techniques. Degradation of CBZ by peroxymonosulfate (PMS) activated with organo-montmorillonite supported nCoFe2O4 (nCoFe2O4/OMt) was investigated in this study. The degradation efficiency of CBZ (5 mg L−1) was 93% within 60 min in the presence of 0.4 g L−1 nCoFe2O4/OMt and 0.5 mM PMS at pH 6.8 and 25 °C, following a pseudo-first order kinetics. High PMS concentration and low initial pH could enhance CBZ degradation. The presence of Cl−, NO3− and HCO3− showed marked enhancement, slight suppression and obvious inhibition of CBZ degradation, respectively. High concentration of humic acid could decrease the CBZ degradation. X-ray photoelectron spectroscopy of nCoFe2O4/OMt before and after reaction revealed that both Co2+/Co3+ and Fe2+/Fe3+ were involved in PMS activation during the CBZ degradation. Electron paramagnetic resonance and radical scavenger experiments confirmed that both OH and SO4− played a predominant role on the CBZ degradation. The degradation products were identified by LC–MS/MS to understand the possible pathways.

Effective removal of inorganic mercury and methylmercury from aqueous solution using novel thiol-functionalized graphene oxide/Fe-Mn composite.

A novel thiol-functionalized graphene oxide/Fe-Mn (SGO/Fe-Mn) was investigated for aqueous Hg2+ and CH3Hg+ removal. Mercury were removed mainly through ligand exchange and surface complexation with surface active sites (i.e., -SH, OH, OCO, CC, SiO, and ππ bond). SH had the strongest binding ability with mercury, forming sulfur-containing organic matter or polymers with Hg2+, and sulfur-containing organometallic compounds or thiolate-like species with CH3Hg+. The BET sorption isotherm model well simulated the sorption isotherm data of Hg2+ (R2=0.995, qm=233.17 mg/g) and CH3Hg+ (R2=0.997, qm=36.69 mg/g), indicating a multilayer adsorption process. The mercury uptake was promoted with the increase of 3-MPTS content, adsorbent dosage, and pH (<5.5), whereas the uptake was inhibited by high pH (>5.5) and high concentrations of humic acid and electrolytes. SGO/Fe-Mn demonstrated high mercury uptake in simulated surface water/groundwater and in the presence of Pb, Cu, Ni, Sb, Cd and Zn. The mercury-laden SGO/Fe-Mn can be successfully regenerated and reused for three times with 98.1% and 67.0% of original Hg2+ and CH3Hg+ sorption capacity when 5% thiourea + 2 M KI was used as the desorbing agent. This study demonstrates potential and viability of SGO/Fe-Mn for mercury remediation.

Enhanced immobilization of U(VI) using a new type of FeS-modified Fe0 core-shell particles

Sulfur-modified zero valent iron (S-ZVI) particles have been reported to show improved reactivity and selectivity than conventional ZVI. However, current methods for ZVI sulfidation do not fully utilize the advantages of the material, and S-ZVI has not been tested for U(VI) immobilization. In this work, we synthesized a new type of FeS-modified ZVI core-shell particles (FeS@Fe0) through a facile two-step reaction approach, and then tested for reductive sequestration of U(VI) in water. X-ray diffraction, Scanning transmission electron microscopy, and physical property analyses confirmed the formation of the core-shell structure, surface compositions and magnetic properties. Batch kinetic tests showed that FeS@Fe0 with an Fe0/FeS molar ratio of 1:1 offered the highest U(VI) reduction rate, prolonged reactive life than pristine ZVI, and the reduced uranium was most resistant to re-oxidation when exposed to oxygen. The retarded first-order kinetic model was able to adequately interpret the experimental rate data. FeS@Fe0 performed well over the pH range 5.5–9.0, with higher pH more favoring the reaction. High concentrations (5–10 mg/L) of humic acid, bicarbonate (1–5 mM) and Ca2+ (1 mM) showed only modest inhibition to the U(VI) reduction. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and extraction studies indicated that U(VI) was immobilized via both direct adsorption and reductive precipitation, where Fe0 was the main electron source, with Fe0, sorbed Fe(II) and structural Fe(II) acting as the electron donors. FeS@Fe0 may serve as an improved material for efficient immobilization of U(VI) and other redox-active contaminants in water.

Sequestration of pertechnetate using carboxymethyl cellulose stabilized FeS nanoparticles: Effectiveness and mechanisms

Technetium (99Tc) typically exists as pertechnetate (TcO4−) and hydrated oxide (TcO2·nH2O) in soil and groundwater. While the former, Tc(VII), is very soluble and mobile in the environment, the latter is considered sparingly soluble and immobile. Consequently, immobilization of Tc(VII) can be achieved through conversion of Tc(VII) into Tc(IV). In this study, carboxymethyl cellulose (CMC) stabilized FeS nanoparticles (CMC-FeS) were prepared and tested for reductive immobilization of Tc(VII). Effects of nanoparticle dosage and water chemistry, including pH, humic acid and Ca2+ ions, were examined. At a dosage of 100 mg/L of CMC-FeS as Fe, CMC-FeS rapidly removed >96% of 1.2 μM of Tc(VII) within 1 h, with a retarded first-order rate constant (ka) of 150.32 h-1. Higher pH in the range of 5.0–9.0 favored the reaction, with an optimal pH range of 8.0–9.0. While Ca2+ (up to 2 mM) only modestly affected the Tc(VII) removal, high concentrations of humic acid (up to 10 mg/L as TOC) showed increased inhibition on the Tc(VII) removal rate. FTIR and XPS analyses indicated that CMC-FeS immobilized TcO4− through reductive conversion of TcO4− into TcO2(s) and formation of Tc2S7 precipitate. The immobilized Tc remained insoluble when aged for 100 days under anoxic conditions, whereas up to 22.9% of the immobilized Tc was remobilized when it was exposed to air for 100 days.

Chromium uptake by lettuce as affected by the application of organic matter and Cr(VI)-irrigation water: Implications to the land use and water management

Toxic chromium [(Cr(VI)] in food chain has created an alarming situation for human life and ecosystems. The present study through a greenhouse pot experiment aims to (a) investigate the ability of organic matter in reducing Cr uptake by lettuce (Lactuca sativa L.) from a sandy loam soil irrigating with Cr(VI)-water, (b) to provide a way for the restriction of Cr transfer from contaminated soils and irrigation water to plants/crops and (c) to contribute to the better management of soil (land) and water use, without reduction of the agricultural production.Since soil and groundwater contamination by Cr is a potential risk in a worldwide scale, due to industrial activities and/or natural processes, organic carbon may play a key role in the mobility of added Cr(VI) to soil via irrigation water, in a significant way. The cultivation of lettuce, using organic matter in the form of leonardite (10 and 30 wt%) and Cr(VI)-irrigation water (100, 200 and 300 mgL−1), showed that the uptake of Cr in both shoots and roots increased with increasing concentration of Cr in the irrigation water. The highest Cr values in shoots (average = 10 mg/kg) and in roots (average = 28 mg/kg) were recorded in those plants cultivated in soil after the addition of Cr(VI)- water without organic matter, whereas the lowest Cr values in shoots (average = 0.44 mg/kg) and in roots (average = 0.7 mg/kg) were recorded in those plants cultivated in soil with addition of 30 wt% organic matter.The used leonardite as organic matter that is an oxidized form of lignite, due to its high content of humic acid is considered to be a useful organic fertilizer that provides possibilities for combining food production with soil protection. Therefore, the application of the natural organic material leonardite, as a land management technique, seems to be a cost-effective method consistent to related protocols for the protection of the soil quality.

Hydrophilic nanofiltration membranes with reduced humic acid fouling fabricated from copolymers designed by introducing carboxyl groups in the pendant benzene ring

In this study, strategy of designing new polymers by copolymerization of carefully chosen monomers was explored to synthesize high performance nanofiltration membranes. A series of copolymers with different content of carboxyl groups were successfully synthesized by polymerization of 2-(bis(4-hydroxyphenyl)methyl)benzoic acid (BHPBA), 4,4′-dichlorodiphenyl sulfone (DCDPS). These copolymers have a high glass transition temperature and decomposition temperature, although a large amount of carboxyl groups was introduced in the chains of copolymers. Membranes fabricated from these polymers kept a reasonable tensile strength, even when 100% carboxyl groups were introduced in the polymer. Furthermore, Prepared membranes had a hydrophilic surface, and a high rejection of dyes and salts with relatively large flux. The antifouling measurements demonstrated that the fouling of both humic acid and BSA were greatly reduced with an increasing amount of carboxyl groups in the copolymer. These copolymer membranes exhibited superhigh antifouling of humic acid with a flux recovery ratio (FRR) of 100%, making them promising to be applied in the treatment of water with high content of humic acid.

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.

Structural Memory Effect of Mg-Al and Zn-Al layered Double Hydroxides in the Presence of Different Natural Humic Acids: Process and Mechanism.

The structural memory effect of layered double hydroxides (LDHs) is one of the important reasons for their extensive use in environmental remediation. In this study, humic acid (HA) was extracted from black soil and sediments and characterized to determine their structures. The regeneration mechanisms of calcinated LDHs (CLDHs) including different divalent metals (Mg-CLDH and Zn-CLDH) in deionized water and different HA solutions were carefully elucidated, and the reasons for the behavior differences in the two materials were explained. The presence of the HAs significantly increased the dissolution rate of Mg2+ ions from Mg-CLDHs and subsequent regeneration of Mg-LDH. Because of the diverse functional groups in the HAs, these groups were complexed with metallic ions such as Mg2+ on the surface of Mg-CLDH in the beginning. During the process, the HAs adsorbed the regenerated LDHs on the surfaces. Therefore, the crystallinity, morphology, and specific surface area of the regenerated Mg-LDH significantly changed, especially in the presence of high concentrations of HA. In the case of Zn-CLDH, the regeneration rate of the LDH increased in the presence of HA, but the surface of Zn-CLDH was covered with regenerated Zn-LDH and HA. Then, the inside of the particles could not transform to LDH, leading to poor crystallinity and a significant increase in the ZnO content of the HA system.

Sample Preparation for Metaproteome Analyses of Soil and Leaf Litter.

Soil and litter metaproteomics, assigning soil and litter proteins to specific phylogenetic and functional groups, has a great potential to shed light on the impact of microbial diversity on soil ecosystem functioning. However, metaproteomic analysis of soil and litter is often hampered by the enormous heterogeneity of the soil matrix and high concentrations of humic acids. To circumvent these challenges, sophisticated protocols for sample preparation have to be applied. This chapter provides the reader with detailed information on well-established protocols for protein extraction from soil and litter samples together with protocols for further sample preparation for subsequent MS analyses.

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.

MIRES OF THE ALTAI REPUBLIC: DISTRIBUTION, FEATURES OF PEAT DEPOSITION, PROPERTIES OF PEAT DEPOSITS, USES

Physico-geographical conditions in the territory of the Altai Republic determine the degree of peat formation in North, Central and South-Eastern regions and the properties of peats. A distinctive feature of the deposits is the high ash content of peat throughout the profile, up to the formation of mineral layers. The deposit thickness ranges from 0.3 to 4.5 meters. Peat forms over the eluvium or eluvium-deluvium of dense crystalline rocks. Peculiarities of the water and mineral nutrition of alpine mires define the distinctive properties of their peat as compared to West Siberian mires: a high degree of decomposition, good supply of nutrients, as well as a high content of humic acids. Such a pattern is typical for both eutrophic and mesotrophic mires. Peat properties change towards the SouthEastern region of the Altai Republic for a higher alkalinity, increase in total exchangeable bases, and an increase in humic acids in organic matter. At the same time, the thickness of peat deposits declines.

The analysis of phytophagous mammals’ excretory activity in forest ecosystems

In this paper the author considers the excretory activity as one of zoocenosis environment-transforming activity types. The paper presents the results of experimental data on the effect of phytophagous animals excreta on the soil-forming processes through adding organic substances to the soil in the process of decomposing the undigested plant residues. The organic substance (humus) is a source of mineral elements necessary for plant organisms. The value of phytophagous animals excreta is in their peculiar properties such as high content of humic acids performing a number of important functions in the biosphere. In this paper one of these functions accumulative has been considered. Decomposition of the organic substance in the form of the excreta of the elk (Alces alces, L.) as the largest phytophagous animal of the north-west proceeded in the course of the experiment in natural and laboratory conditions. Anthropogenically disturbed areas of the Vologda Region have been chosen as natural conditions. The excreta decomposition took place on medium-loamy and strongly podzolic soils on the cutting site after clear felling in the sorrel spruce forest. In laboratory conditions the experiments on excreta decomposition have been carried out in microlysimeters. Thereby we have chosen the three factor experiment with subsequent developing mathematical models (regression equations). We have used the winter variety of the elks excreta which differs in composition from the summer variety. Winter excreta appear as a result of digesting the coarse woody feeds. In the paper the results of the research on the group composition of humus and agrochemical NPK-complex have been given. As a result of decomposition it has been revealed that the content of the humus components under study and NPK have been influenced by the size of particles in the soil, microconditions and the time of organic substance decomposition.

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.

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.

Low humic acids promote in vitro lily bulblet enlargement by enhancing roots growth and carbohydrate metabolism.

Bulblet development is a problem in global lily bulb production and carbohydrate metabolism is a crucial factor. Micropropagation acts as an efficient substitute for faster propagation and can provide a controllable condition to explore bulb growth. The present study was conducted to investigate the effects of humic acid (HA) on bulblet swelling and the carbohydrate metabolic pathway in Lilium Oriental Hybrids 'Sorbonne' under in vitro conditions. HA greatly promoted bulblet growth at 0.2, 2.0, and 20.0 mg/L, and pronounced increases in bulblet sucrose, total soluble sugar, and starch content were observed for higher HA concentrations (≥2.0 mg/L) within 45 d after transplanting (DAT). The activities of three major starch synthetic enzymes (including adenosine 5'-diphosphate glucose pyrophosphorylase, granule-bound starch synthase, and soluble starch synthase) were enhanced dramatically after HA application especially low concentration HA (LHA), indicating a quick response of starch metabolism. However, higher doses of HA also caused excessive aboveground biomass accumulation and inhibited root growth. Accordingly, an earlier carbon starvation emerged by observing evident starch degradation. Relative bulblet weight gradually decreased with increased HA doses and thereby broke the balance between the source and sink. A low HA concentration at 0.2 mg/L performed best in both root and bulblet growth. The number of roots and root length peaked at 14.5 and 5.75 cm, respectively. The fresh bulblet weight and diameter reached 468 mg (2.9 times that under the control treatment) and 11.68 mm, respectively. Further, sucrose/starch utilization and conversion were accelerated and carbon famine was delayed as a result with an average relative bulblet weight of 80.09%. To our knowledge, this is the first HA application and mechanism research into starch metabolism in both in vitro and in vivo condition in bulbous crops.

Impact of natural organic matter on bromate removal in the sulfite/UV-L advanced reduction process

Advanced reduction processes (ARPs) are treatment processes that involve combining reducing reagents and activating tools to produce highly reactive reducing free radicals. The process has proven effective for treating oxidized contaminants, and the effects of process variables on the degradation kinetics of various target contaminants have been investigated in our previous studies. In natural environments, natural organic matter (NOM) is found in surface or ground water. NOM absorbs UV light and can react with photochemically produced radicals, thus affecting target contaminant photochemical reactions and further influencing the efficiency of ARP. This study examines the impact of humic acid (HA) and Suwanee River NOM on bromate reduction rates with UV irradiation using a low-pressure mercury UV lamp. The effects of the sulfite dose, solution pH, and light intensity are studied and the pseudo-first-order rate constants in the presence of HA (kobs,HA) are compared to those observed in the absence of HA (kobs). At low HA concentrations of 1 mg L−1, kobs,HA was larger than kobs; however, kobs,HA was less than kobs at higher HA concentrations. Furthermore, kobs,HA did not increase with increasing sulfite doses in the presence of HA, which is unlike the behavior of kobs.

Substantial Humic Acid Adsorption to Activated Carbon Air Cathodes Produces a Small Reduction in Catalytic Activity.

Long-term operation of microbial fuel cells (MFCs) can result in substantial degradation of activated carbon (AC) air-cathode performance. To examine a possible role in fouling from organic matter in water, cathodes were exposed to high concentrations of humic acids (HA). Cathodes treated with 100 mg L(-1) HA exhibited no significant change in performance. Exposure to 1000 mg L(-1) HA decreased the maximum power density by 14% (from 1310 ± 30 mW m(-2) to 1130 ± 30 mW m(-2)). Pore blocking was the main mechanism as the total surface area of the AC decreased by 12%. Minimization of external mass transfer resistances using a rotating disk electrode exhibited only a 5% reduction in current, indicating about half the impact of HA adsorption was associated with external mass transfer resistance and the remainder was due to internal resistances. Rinsing the cathodes with deionized water did not restore cathode performance. These results demonstrated that HA could contribute to cathode fouling, but the extent of power reduction was relatively small in comparison to large mass of humics adsorbed. Other factors, such as biopolymer attachment, or salt precipitation, are therefore likely more important contributors to long-term fouling of MFC cathodes.

Decreased solubilization of Pu(IV) polymers by humic acids under anoxic conditions

Pu(IV) polymer has a very low solubility (log[Pu(IV)aq]total=−10.4 at pH 7.2 and I=0). However, some aspects of their environmental fate remain unclear. Humic acids are able to complex with Pu4+ ions and their dissolved species (<10kD) in the groundwater (neutral to alkaline pH) may cause solubilization of the polymers. Also, humic acids have the native reducing capacity and potentially reduce the polymeric Pu(IV) to Pu(III)aq (log[Pu(III)aq]total=−5.3 at pH 7.2 and I=0). Solubilization and reduction of the polymers can enhance their mobility in subsurface environments. Nevertheless, humic acids readily coat the surfaces of metal oxides via electrostatic interaction and ligand exchange mechanisms. The humic coatings are expected to prevent both solubilization and reduction of the polymers. Experiments were conducted under anoxic and slightly alkaline (pH 7.2) conditions in order to study whether humic acids have effects on stability of the polymers. The results show that the polymeric Pu(IV) was almost completely transformed into aqueous Pu(IV) in the presence of EDTA ligands. In contrast, the dissolved humic acids did not solubilize the polymers but in fact decreased their solubility by one order of magnitude. The humic coatings were responsible for the decreased solubilization. Such coatings limited the contact between the polymers and EDTA ligands, especially at the relatively high concentrations of humic acids (>0.57mg/L). Solubilization of the humic–coated polymers was thus inhibited to a significant extent although EDTA, having the great complexation ability, was present in the humic solutions. Reduction of Pu(IV) polymers by the humic acids was also not observed in the absence of EDTA. In the presence of EDTA, the polymers were partially reduced to Pu(III)aq by the humic acids of 0.57mg/L and the percentage of Pu(III)aq accounted for 51.7% of the total aqueous Pu. This demonstrates that the humic acids were able to reduce the aqueous Pu(IV), instead of the polymeric Pu(IV). Such a demonstration is supported by the very positive redox potential of aqueous Pu(IV)-EDTA complex: Eho′(PuL24-/PuL25-)=154.3mV >>Eh(PuO2(am)/Pu3+)=−182.7mV calculated at 10−10mol/L Pu3+ and pH 7.2. At the higher humic concentrations (>0.57mg/L), the polymers were reduced to a lesser extent because the much denser humic coatings resulted in lower concentrations of the aqueous Pu(IV). Consequently, humic acids make Pu(IV) polymers pretty stable unless the artificial ligands such as EDTA are present in the groundwater.

Comparison of Antibiotic Resistance Removal Efficiencies Using Ozone Disinfection under Different pH and Suspended Solids and Humic Substance Concentrations

This study mainly evaluated the effectiveness of ozonation toward the enhancement of the removal efficiencies of antibiotic-resistant bacteria (ARB), pB10 plasmid transfer, and pB10 plasmids under different pH and suspended solids (SS) and humic acid concentrations. First, chlorination was tested as a reference disinfection process. Chlorination at a very high dose concentration of Cl2 (75 mg L(-1)) and a long contact time (10 min) were required to achieve approximately 90% ARB and pB10 plasmid transfer removal efficiencies. However, even these stringent conditions only resulted in a 78.8% reduction of pB10 plasmid concentrations. In case of ozonation, the estimated CT (concentration × contact time) value (at C0 = 7 mg L(-1)) for achieving 4-log pB10 plasmid removal efficiency was 127.15 mg·min L(-1), which was 1.04- and 1.25-fold higher than those required for ARB (122.73 mg·min L(-1)) and a model nonantibiotic resistant bacterial strain, E. coli K-12, (101.4 mg·min L(-1)), respectively. In preventing pB10 plasmid transfer, ozonation achieved better performance under conditions of higher concentrations of humic acid and lower pH. Our study results demonstrated that the applicability of CT concept in practice, conventionally used for disinfection, might not be appropriate for antibiotic resistance control in the wastewater treatment process. Further studies should be conducted in wastewater engineering on how to implement multiple barriers including disinfection to prevent ARB and ARG discharge into the environment.