Fulvic Acid Concentration Research Articles

Effects of organic wastes on structural characterizations of fulvic acid in semiarid soil under plastic mulched drip irrigation

Poor soil has restricted the crop production in semiarid soil. Fulvic acid (FA) is considered to play an significant role in soil fertility. The amount and structure of FA after application of different organic wastes (OWs) was assessed in this work. Six treatments were involved in this experiment: chemical fertilizer combined with chicken manure (CM), sheep manure (SM), maize straw (MS), fodder grass (FG), and tree leaves (TL), while chemical fertilizer only was used as control (CK). The soil FA content (P < 0.05) after the application of TL was the highest than other OWs. The E4/E6 ratios, ΔlogK values, aliphatic C/aromatic C ratios of soil FA after the application of TL were the lowest than other OWs, whereas the C/H ratio was the highest. The specific fluorescence intensities (SFI) of peak A (Ex/Em 260–265/415-430 nm) and peak B (Ex/Em 310–315/415-430 nm) from EEM fluorescence spectrum of FA were the lowest after the application of TL. In conclusion, the application of TL was the most effective for improving FA accumulation, and making FA complex and stability. Thus, TL is the recommended OW for use in semiarid soil under plastic mulched drip irrigation conditions.

Effects of Ca2+ and fulvic acids on atrazine degradation by nano-TiO2: Performances and mechanisms

In this study, the adsorption and UV photocatalytic degradation of atrazine using nano-TiO2 particles were studied systematically, and the colloidal stability of nano-TiO2 particles in solution was also investigated to reveal the removal mechanism. Experiments which contained the first 6.0 hours darkness and 4.0 hours UV illumination later were conducted at different concentrations of Ca2+ and/or fulvic acids (FA) at pH = 7.0. Results showed that the adsorption rate of atrazine onto nano-TiO2 particles decreased with the increase of Ca2+ and/or FA concentrations, which could be explained well by the colloidal stability of nanoparticles. When the solution contained Ca2+ or Ca2+-FA, the nanoparticles were aggregated together leading to the decrease of the contact surface area. Besides, there existed competitive adsorption between FA and atrazine on the particle surface. During photocatalytic degradation, the increase of Ca2+ and/or FA concentration accelerated the aggregation of nano-TiO2 particles and that reduced the degradation efficiency of atrazine. The particle sizes by SEM were in accordance with the aggregation degree of nanoparticles in the solutions. Sedimentation experiments of nano-TiO2 particles displayed that the fastest sedimentation was happened in the CaCl2 and FA coexistent system and followed by CaCl2 alone, and the results well demonstrated the photodegradation efficiency trends of atrazine by nano-TiO2 particles under the different sedimentation conditions.

Influence of fulvic acid on Pb(II) removal from water using a post-synthetically modified MIL-100(Fe)

HypothesisModification of MIL-100(Fe) with ethanediamine (ED) is expected to improve the removal percentage of Pb(II) ions from aqueous solution. Nevertheless, the adsorption performance of ED-MIL-100(Fe) in natural waters will be affected by natural organic matter such as fulvic acids (FA). Hence, it is necessary to study the influence of FA on the physicochemical property, adsorption behavior and mechanisms of ED-MIL-100(Fe) towards the removal of Pb(II) from water. ExperimentsBatch adsorption experiments were conducted to compare adsorption capacity of MIL-100(Fe) and ED-MIL-100(Fe) for Pb(II). In addition, XRD, FTIR, SEM and XPS techniques were applied to investigate the characteristics, adsorption isotherms, and kinetics in the presence and absence of FA. FindingsED-MIL-100(Fe) enabled 99% removal of Pb(II) from water at or below 60 mg L−1, whereas the MIL-100(Fe) hardly adsorbed any Pb(II). Additionally, the adsorption percentage of the Pb(II) ions (76%) outcompeted that of other metal ions (i.e. Co, Cu, Ni, Zn, and Cd) (each ≤ 25%) in the mixed solution. The negative surface charge of ED-MIL-100(Fe) was not affected by FA. Increasing FA concentration steadily increased the functional groups surrounding the ED-MIL-100(Fe) via electrical interaction, thus facilitating the Pb(II) ions adsorption.

Root diameter controls the accumulation of humic substances in decomposing root litter

The humification of plant litter is a crucial step for the buildup of soil organic matter in terrestrial ecosystems. Yet, how environmental change and substrate quality affect root humification still remains poorly understood. A two-year litterbag experiment was conducted to assess the root mass remaining and accumulation of humic substances in roots of three diameter classes (0–2, 2–5 and 5–10 mm) of two common subalpine tree species (Picea asperata and Abies faxoniana) at two elevations (3037 m and 3580 m) on the eastern Tibetan Plateau. No significant differences were found between elevation treatments in the concentration of humic substances. Both root mass loss and concentrations of humic substance, humic acid and fulvic acid decreased with increasing root diameter. Both fulvic acid concentration and humification degree declined as root decomposition progressed but humic acid concentration exhibited an opposite trend. Our results reveal that the diameter-associated variations in accumulation of humic substances were substantially stronger than altitudinal and interspecific differences in decomposing root litters. These findings have important implications for carbon sequestration via root humification in the subalpine forests experiencing snow-covered winter.

Research on the Presence of Phaeozems in the Suceava Plateau

Phaeozems are in class cernisols and has a wide spread in the Suceava Plateau. These soils have been the objective of many pedo-geographical studies, being firstly interpreted as exhausted chernozems (Obrejeanu et al., 1958), as exhausted brown forest soils (Bucur, 1967), and then as pratozems or chernozems like soils (Florea and Muica, 1962), presently being known under the name mentioned above. To achieve its purpose were established following objectives have been achieved in the field and laboratory: the study of the natural formation of phaeozems Suceava Plateau; the morphological, chemical and physical phaeozems (for which the characteristic of the space searched areas have been opened in the soil profiles were taken samples); determining the favorability of different crops. Among the pedogenetic factors, the relief played a very important role in the formation and development of the phaeozem type soils from this part of the country. The process of soil formation is manifested as the chernozems by intense accumulation of humus at the top of the soil profile, but at a lower level and having a higher content of fulvic acids than the chernozems. It follows horizon Amolic (Am), dark and quite deep.

Organic matter and mineralization of river waters in mountains of Russia and adjacent countries

The article examines general regularities of the formation of dissolved organic matter (DOM), salinity (∑), the acid-alkaline indicators (pH) river waters in the mountains with various types of altitudinal zonation in Russia and CIS countries. The analysis is based on the results of many years of experimental studies in the network of the Roshydromet. The reaction of water of rivers in a southerly direction in accordance with changes in landscape-geochemical conditions are sequentially changed from acidic in the tundra of the Arctic to neutral in the tundra and taiga, slightly alkaline in forest-meadow and alkaline in a desert and subtropical mountains. The average annual salinity water of the mountain rivers in two Northern types of vertical zones is 42 and 74 mg/l, in two Southern types – 140 and 450 mg/l. The average annual values of permanganate (PO) and bichromate (BO) oxidation, and color of river water in xerophytic desert-subtropical mountains are small (3 and 7), and increase to medium and slightly increased grades into humid tundra and taiga, tundra of the Arctic, and the forest meadow mountains (7–8 and 13–18 mg O/l). Relationships PO:BO change from 62% in the tundra of the Arctic up to 50%, 41% and 35% in the tundra and taiga, forest-meadow and desert-subtropical mountains. The content of humic (HA) and fulvic (FA) acids is also maximum in two Northern types of vertical zones (0.224 and 1.80 mg/l) and decreases in the two Southern types to 0.013 and 0.067, 0.373 and 0.637 mg/l. The relationship of contents of HA and FA decreases to the South in forest-grassland and desert-subtropical mountains in 1.3 and 3.7 times.

Dynamics of the Organic Matter Content of Bottom Sediments along the Razdolnaya River–Amur Bay Boundary (Sea of Japan)

The contents of Corg, humiс acids (HA), and fulvic acids (FA) in soil and riverine and marine bottom sediments have been investigated along a transect between the Razdolnaya River and Amur Bay. The revealed higher Corg content of soil compared to that of riverine and marine sediments is associated with peatlands. The increased HA content of sediments compared to the FA content, corresponding to the initial period of water mixing, is explained by flocculation. The identified riverine sediments with increased FA, Fe, and Mn contents indicate active processes of flocculation and the formation of Fe and Mn oxyhydroxides. Soil shows significantly larger amounts of humified organic matter than marine sediments. Marine sediments contain mostly biochemically unrecycled organic matter.

Application of fulvic acid to seedlings influencing root growth and productivity of iceberg lettuce

Humic substances are used in agriculture as promoters of plant growth, especially of the root system. The objective of the work was to evaluate the effect of the application of different doses of fulvic acid on the growth and productivity of American lettuce, Raider Plus cultivar. The experimental design used was entirely randomized, with five treatments of fulvic acid 0, 1, 2, 4, 8 mL·L-1 and four repetitions, applied at the time of transplanting. Two experiments were conducted simultaneously: one in the greenhouse, where fresh and dry mass of the aboveground and root parts, length and volume of the roots were evaluated; and the other in the field, where, at the end of the cycle, fresh and dry mass of the aboveground parts, number of leaves, stem length and average head circumference were evaluated. The application of different doses of fulvic acid promoted the growth of lettuce plants, especially the root system. The emission of roots, with predominance, of those of smaller diameter, was found in the higher concentrations of fulvic acid. The number of leaves and the average circumference of the head expressed responses in the concentrations of fulvic acid.

Effect of fulvic acid on methane hydrate formation and dissociation in mixed porous media

In this work, the effect of fulvic acid (FA) concentration and memory effect on methane hydrate formation and dissociation in mixed sand-clay porous media were studied at 15 MPa and 8.0 ºC. The mixed sand-clay porous media were prepared based on the marine sediments composition of the South China Sea. The results demonstrated that the hydrate formation in porous media includes rapid formation stage and slow formation stage, and there is no obvious difference in fresh and memory solution systems. The low mass concentration of FA (2.0 wt.% FA) has a slightly acceleration effect for the hydrate formation and the hydrate formation time is shorter than that in pure water system. The high mass concentration of FA evidently inhibit the hydrate formation, especially for the 10.0 wt.% FA, the amounts of hydrate formation is significantly less than that in pure water system. The FA solutions can significantly accelerate the hydrate dissociation, and the gas released rate from hydrate increases with the increase of FA concentration. In addition, the gas recovery rate can be improved effectively by high concentrated FA.

Sorption Mechanism and Performance of Peat Soil Humin for Methylene Blue and &lt;i&gt;p&lt;/i&gt;-Nitrophenol

The responsible mechanism and performance of peat soil humin for the sorption of methylene blue (MB) and p-nitrophenol (p-NP) have been investigated. Humin was obtained from peat soil of Siantan, West Kalimantan, Indonesia, after removing the content of humic and fulvic acids into a NaOH solution using the recommended procedure of International Humic Substances Society (IHSS). The obtained humin was then purified by rigorous stirring in a mixed solution of HCl 0.1 M and HF 0.3 M. Ash content in humin after the purification abruptly decreased from 36.84 to 1.26 wt.% indicating that minerals and other inorganic impurities were mostly removed. Phenolic –OH and carboxyl (–COOH) functional groups contributing to the acidity of humin were in the level of 3.44 and 2.10 mmol/g, respectively. At optimum medium pH of 6.20 for MB and 7.00 for p-NP, –COO– as the deprotonated product of –COOH was the most responsible active site in sorbing MB and p-NP through electrostatic interaction and hydrogen bonding, respectively. The homogeneity of –COO– as the active site for the sorption of MB and p-NP implied that the surface of humin sorbent was energetically uniform and thereby the sorption of both MB and p-NP followed better the Langmuir than the Freundlich isotherm model with sorption capacity of 0.19 and 0.26 mmol/g and sorption energy of 32.92 and 27.27 kJ/mol, respectively.

Photodegradation of novel brominated flame retardants (NBFRs) in a liquid system: Kinetics and photoproducts

The photolysis of four typical NBFRs decabromodiphenyl ethane (DBDPE), bis(2-ethylhexyl) tetrabromophthalate (TBPH), pentabromotoluene (PBT) and hexabromobenzene (HBB) were first explored under different sources of light, two temperatures, organic solvents and the presence of humic substance (HS). Degradation could be described by pseudo-first-order kinetic model. Under different irradiation sources, the degradation rates were in order of UVC (0.0616–0.137 min−1) > UVB (0.0348–0.0810 min−1) > sunlight (0.0102–0.0370 min−1) > UVA (almost no degradation). Under UVB irradiation, the half-life of NBFRs was the lowest in tetrahydrofuran (6.16–22.77 min), and the longest (93.42–>120 min) in acetone, indicating that organic solvents greatly affected the degradation kinetics. HS could influence the degradation, and DBDPE or TBPH respectively declined 13.92–30.68% and 12.17–59.41% at 240 min, while the degradation of PBT and HBB were highly inhibited. TBPH photolysis was affected by humic acid (HA) or fulvic acid (FA) concentration, but DBDPE degradation barely showed significant difference (p < 0.05) in the presence of 1 and 10 mg L−1 of HA. Photolytic products of the four NBFRs were identified by GC-NCI/EI-MS, indicating that the photodegradation process was mainly stepwise debromination from high- down to low-bromine-substituted NBFRs. 2,4,6-triBT and 2,4,5-triBT were identified as products of PBT. PBB, 1,2,4,5-tetraBB, 1,2,4-triBB, 1,3,5-triBB and 1,3/1,2-diBB were identified as products of HBB. Our observations could provide a few insights into the removal of NBFRs in a liquid environment.

Grape pomace compost as a source of organic matter: Evolution of quality parameters to evaluate maturity and stability

The Pisco and wine industry in Chile generates about 400,000 tonnes/year of grape pomace as organic wastes (OWs). This material can be composted and used as organic fertilizer or amendment in grape orchards located in inceptisol soils with a very low organic matter as a strategy to increase soil and grape quality. The maturity and the stabilization of compost define the potential use of OWs as an amendment. Therefore, the objectives of the present study were focused to evaluate the evolution of chemical, microbiological, biochemical and phytotoxicity parameters during the composting process using grape marc and other components. The experimental study consisted of nine opened piles constituted by grape pomace, goat or horse manure. The piles were evaluated for 180 days in winter-spring seasons and mechanical turns were carried out every 10 days. The results indicated that humic to fulvic acids content ratio (Ha/Fa) could be used as process evolution indicator. The potential enzymatic activity of alkaline phosphatase and β-glucosidase, and microbiological functional groups like cellulolytic, amylolytic and phosphate solubilizing bacteria were strongly correlated with production of fulvic and humic acids (p ≤ 0.01). The compost derived from treatments complies with Chilean National Standard - NCh 2880/04, 2016 for the quality of organic amendments including low phytotoxicity with a radish germination %> 92% and absence of Salmonella sp., and fecal coliforms <1000 NMP/g. In conclusion, quality parameters evaluated showed sensitivity to evaluate both the composting process and compost quality.

Improve quality and productivity of some faba bean cultivars with foliar application of fulvic acid

BackgroundTwo field experiments were carried out at the Research and Production Station of the National Research Centre, Nubaria region, Behira Governorate, Egypt, during two winter seasons of 2014/2015 and 2015/2016. The aim of this study was to investigate the response of vegetative growth, yield, yield components, and some metabolic constituents of four faba bean (Vicia faba L.) cultivars “Nubaria 2, Sakha 1, Sakha 3, and Sakha 4” to foliar application of fulvic acid (FA) at 0.0, 3, 6, and 9 gL− 1.ResultsThe results show that all applications of FA increased all vegetative characters (i.e., plant height, number of branches and leaves, and total dry weight/plant, fourth leaf area and leaf area index, specific leaf weight, and crop growth rate), as well as, yield and its components (i.e., number of pods/plant, weight of pods/plant, seed and straw yield/plant, seed and straw yield/feddan, and seed index) of all studied faba bean cultivars, comparing to untreated plants. The results also show the total photosynthetic pigments content in leaves were increased by increasing FA concentration up to 9 gL−1. Treatment FA at 9 gL−1, significantly improved the nutritional value and quality of seeds by increasing total carbohydrates, crude protein, minerals (nitrogen, phosphorus, and potassium) content, arginine, lysine, phenylalanine, and tryptophan.ConclusionsGenerally, foliar application of FA at 9 gL−1, singly or interaction with Sakha 4 effectively increased seed yield and quality. In conclusion, the growth and yield contributing characters and quality of four bean cultivars could be improved with foliar application of FA treatments.

Effects of fulvic acid and fulvic ions on Escherichia coli survival in river under repeated freeze-thaw cycles

The effects of fulvic acid (FA) and ions on mesophilic pathogenic bacteria survival under freeze-thaw (FT) stress in natural water and its resistant mechanisms are rarely understood. Therefore, survival patterns of Escherichia coli in river water added with various concentrations of FA or FA-ion under FT stress were studied in this work. Meanwhile, cell surface hydrophobicity (CSH), unit activities of superoxide dismutase (SOD) and catalase (CAT) were determined and Escherichia coli morphologies were observed to explore the bacterial resistant mechanisms against FT stress. The results demonstrated that FT cycles significantly reduced bacterial quantities as sampling time, i.e. freeze-thaw cycle time increased. And the biggest reducing rate was observed after the first FT cycle in every system. Ttd values, time needed to reach detection limit under FT stress decreased under FT stress as FA was added into water, while the changes of ttd values were quite complicated when FA and various ions existed together. Generally, the ttd values of FA-cation systems exceeded that of FA system except FA-Ca2+ systems, but it was opposite for FA-anion systems. CSH was heightened after FT cycles and reached peak value at last sampling time in every system. Mechanical constraint from extracellular ice crystals and high CSH induced bacterial aggregation, which protect inner cells of aggregation from extracellular ice crystals. And the unit activities of SOD were significantly higher than those of CAT. Unit activities of SOD and CAT in large part of tested systems increased with sampling time under FT stress, which reduced reactive oxygen species produced from repeated FT cycles. Thus, these could improve the resistance of Escherichia coli to freeze-thaw stress and promote their survival. This work explored the survival pattern and strategy of Escherichia coli in natural water under FT stress.

Fulvic acids generated in municipal waste landfills in Promnik

Landfill leachates are resistant to biodegradation, contain substances harmful to the environment, which is why they are troublesome in the water and sewage management. The study tested the leachate from the municipal waste landfill in Promnik, whose age of waste disposal is 33 years. The research consisted of extracting from average leachates (with a volume of 800 m3) fulvic acids resistant to biodegradation. The extraction of acids was carried out using a hydrophobic and hydrophilic ionite in a hydrogen form. The extracted fulvic acids (FAs) was subjected to qualitative analysis on the content of micro-pollutants and the content of elementary elements forming the structure of the FAs molecule, their infrared and UV-VIS spectra were examined. Then, a full analysis of the obtained values was carried out in order to determine the properties of the obtained extractant and demonstrate the convergence of its features with humus substances that are common in the environment, which are an important element of soils, affect their quality and participate in the transport of plant nutrients. It was demonstrated that the concentration of FAs in the effluent is 905.6 mg/l.

Formation of soil humus profile under long-derivative forests on the Vasyugan Plain (West Siberia, Russia)

Humus profile formation in southern Vasyugan plain is closely related to its parent rocks ranging from carbonaceous clays and heavy loams. Carbonates ensure slowing down of restoration cycles of the indigenous vegetation at the stage of grass deciduous forests (for more than one generation), because well developed grass cover dominated by bunch grasses impedes restoration of dark coniferous species. This gives an insular pattern to some features of climatic zonality due to different soil-vegetation relationship between zonal and successional derivative communities. Plant and soil cover determine local conditions for soil drainage and leaching. In contrast to zonal forest communities with tree storey composed of dark conifers, growing&nbsp; on sod podsolic soils with residual humus horizons, under revegetating deciduous forests soil formation takes place under higher soil biological activity due to differing quantity and quality of plant matter input. The well drained areas under aspen and birch forest with understorey dominated by herbs and grasses (the most abundant species being&nbsp; Betula pubescens, Populus tremula, Carex macroura, Aegopodium podagraria, Calamagrostis obtusata, Equisetum pratense, Rubus saxatilis) are occupied by organic matter accumulating soddy podzolized soils with carbonate-containing layers close to the surface. In semihydromorphic and hydromorphic biotopes under smallreed aspen-birch forests (the most abundant species being Betula pubescens, Populus tremula, Calamagrostis phragmitoides Carex globularis, Equisetum sylvaticum, Filipendula ulmaria) organic matter accumulating soils with varying thickness of the humus/peat horizons are common. The species composition of such plant communities corresponds to the one typical for the southern taiga, but their production characteristics are closer to those common for the more southern communities of the northern forest-steppe with 3–5 t/ha (dry mass) of phytomass. Phytomass mineralization rate is higher, and leaves and grass decomposition products are less acidic as compared with zonal forests, where plant litter is rich in needles and mosses. As a result, organic matter accumulating soils under such communities developed some features, more common for their southern counterparts, distinguishing them from the soddy podzolic soils and making them more like the humus-accumulating soils in the northern forest-steppe. These soils have weak granulometric differentiation and well developed structure of the humus horizon. Humus content in quite high, reaching in the southernmost part of the soil area 6–8% in humus accumulating horizons (AU) 50 cm thick. The northernmost parts of the area see the decreased thickness of the dark humus horizon where the latter is substituted with brownish-gray (AY) horizon common for the taiga soils with 4–6% humus content. Organic matter accumulating soil profiles were found to be contrasting in pH(H2O), as the latter increased from 5.5–6.0 in layers immediately below the litter to the neutral values of 6.0-7.0 in humus horizons and 7.0–7.5 in subsoil horizons. High location of carbonates and solonetz properties of parent rock results in high (75-95%) saturation of soil absorbing complex with basic elements, also preventing drastic degradation of humus profile, as only the topmost part of the humus horizon was found to be affected by acidic products of forest litter decomposition. The relic part of the soil profile can be seen in all studied soils. The radiocarbon age of the relic horizons, as determined by humic acids, ranged 4,000–6,000 years. Humus quality reflects differences in humus horizon genesis. Contemporary horizon of soddy podzolised soils is formed due to climatic conditions of the southern taiga zone and has humic to fulvic acids ratio of 1.2–1.4 and low content of Ca-bound acids, while residual humus horizons were found to have increased humic acid content, decreased fulvic acids content of aggressive 1 and 1a fractions, the highest ratio of humic to fulvic acid carbon of 1.8–2.1 and increased content of their Ca-bound fractions. These features, as well as a very low boundary of humus horizon indicate relic humus formation under more southern, i.e. forest-steppe, environmental conditions. The microbiomorph fraction of humus horizons was found to be dominated by plant detritus and phytoliths. The phytoliths assemblages of the contemporary and relic humus horizons were quite similar with notable absence of coniferous phytoliths. All these suggest that organic matter accumulating soils formation under different climatic conditions in late Holocene was related to phytocenoses similar to grassy deciduous forests. The study revealed that both contemporary humus accumulation and relic humus preservation are negatively correlated with eluvial process rate. So successional dynamics of forest communities determines the pendulum nature of soil evolution. The stage of native dark coniferous forests is characterized by humus horizon degradation under acidic forest litter. The restoration stage of grassy birch forests accelerates humus accumulation and partial restoration of both contemporary and relic humus profiles, which is more explicit with the longer duration of this successional stage.

Enhancement of pig bristles waste bioconversion by inoculum of keratinolytic bacteria during composting

The objective of this study was to evaluate the effect of keratinolytic B. cereus PCM 2849 inoculum on the process of composting pig bristles, in the mixture with sawdust and lignite dust. The process was conducted in closed, static and dynamic reactors. The impact of the composting technique and inoculum on the mineralization and maturity indices during active stage of composting was evaluated. A beneficial effect of the inoculum was confirmed during composting with the application of a static technique and with the dynamic technique. The introduction of bacterial inoculum enhanced transformation of mineral compounds and had a positive effect on maturity, as established with maturity indexes i.e. C/N ratio, carbon solubility, oxidation index of mineral forms of nitrogen, humification ratio or content of humic and fulvic acids. Products after the active stage of composting, especially inoculated compost variants, were characterized by beneficial contents of minerals and met safety standards regarding occurrence of heavy metals. Moreover, inoculated variants, left on prisms for further maturation, reached a more advanced level of matter decomposition and stabilization, as compared to composts obtained after the active phase of composting. The use of B. cereus inoculum for composting pig bristles turned out to be an effective method for accelerating the biodegradation of this hard-to-degrade waste and enabled to produce a valuable fertilizing product.

Effects of fulvic acids and electrolytes on colloidal stability and photocatalysis of nano-TiO2 for atrazine removal

The colloidal stability and photocatalysis of nano-TiO2 particles were investigated in the presence of fulvic acids (FA) and electrolytes (NaNO3, Na2SO4, Na3PO4) at different pH. Results showed that increasing FA concentration, the absolute value of zeta potential of nano-TiO2 increased and particle size decreased at all pH which promoted the colloidal stability of nano-TiO2. Particle size of nano-TiO2 was larger with the coexistence of FA and electrolytes than with FA only as the concentration of electrolytes was greater than or equal to 0.01 mol/L. The largest particle size occurred in the presence of Na3PO4, followed by Na2SO4 and NaNO3. Particle size of nano-TiO2 decreased with higher pH and stability further increased in the presence of FA and/or electrolytes. Nano-TiO2 stabilization was enhanced by increasing FA concentration when the solution pH was 7.0. However, the removal efficiency of atrazine by nano-TiO2 decreased with the increase in FA concentration. Adding electrolytes (0.01 mol/L), atrazine removal by nano-TiO2 further decreased, albeit slightly. The inhibitory effect of electrolytes on nano-TiO2 removal of atrazine was highest for Na3PO4, followed by Na2SO4, and NaNO3, which were consistent with the results of colloidal stability of nano-TiO2. These findings help to better understand the mechanisms and correlation between colloidal stability and photocatalysis of nano-TiO2 in the presence of FA and electrolytes.

Nitrogen additions stimulate litter humification in a subtropical forest, southwestern China

Despite the importance of nitrogen (N) deposition for soil biogeochemical cycle, how N addition affects the accumulation of humic substances in decomposing litter still remains poorly understood. A litterbag experiment was conducted to assess the potential effects of N addition (0 kg·N·ha−1·year−1, 20 kg·N·ha−1·year−1 and 40 kg·N·ha−1·year−1) on mass remaining and humification of two leaf litter (Michelia wilsonii and Camptotheca acuminata) in a subtropical forest of southwestern China. After one year of decomposition, litter mass was lost by 38.1–46.5% for M. wilsonii and 61.7–74.5% for C. acuminata, respectively. Humic substances were declined by 12.1–23.8% in M. wilsonii and 29.1–35.5% in C. acuminata, respectively. Nitrogen additions tended to reduce mass loss over the experimental period. Moreover, N additions did not affect the concentrations of humic substances and humic acid in the early stage but often increased them in the late stage. The effect of N addition on the accumulation of humic substances was stronger for C. acuminate litter than in M. wilsonii litter. Litter N and P contents showed positive correlations with concentrations of humic substances and fulvic acid. Our results suggest that both litter quality and season-driven environmental changes interactively mediate N impacts on litter humification. Such findings have important implications for carbon sequestration via litter humification in the subtropical forest ecosystems experiencing significant N deposition.

Geochemical scaling potential simulations of natural organic matter complexation with metal ions in cooling water at Eskom power generation plants in South Africa

The modified database in the pH, redox equilibrium calculations code (PHREEQC) with a Tipping and Hurley database (T_H.DAT) coupled with the Windermere’s humic acid model (WHAM) was used to simulate scale formation potential in cooling water circuitry, at Eskom power generating stations in South Africa. This study reports a semi-empirical simulative approach in which organic matter fractions, metals and anions in raw and cooling water were used as modelling experimental inputs. By using the saturation index profiles of Ca2+/ Mg2+ with fulvic acid in a modified Tipping and Hurley (T_H.DAT) database, fulvate complex species such as CaFulvate, MgFulvate, and geochemical modelling predictions, mineral phases that potentially precipitate are discussed. Speciation calculations showed that the increase in fulvic acid levels decreased saturation indices of scaling metal phases due to reduced levels of Ca2+ and Mg2+ in the water. Furthermore, if the concentrations of fulvic acid are known, semi-empirical calculations using the geochemical PHREEQC code with a modified T_H.DAT arepossible. Consequently, mineral phase equilibria outputs may give an indication of how the pH and temperature is to be manipulated to optimally predict and control the incidence of scaling.