High Humic Acid Content Research Articles

Proton transfer triggered in-situ construction of C=N active site to activate PMS for efficient autocatalytic degradation of low-carbon fatty amine

Removal of low-carbon fatty amines (LCFAs) in wastewater treatment poses a significant technical challenge due to their small molecular size, high polarity, high bond dissociation energy, electron deficiency, and poor biodegradability. Moreover, their low Brønsted acidity deteriorates this issue. To address this problem, we have developed a novel base-induced autocatalytic technique for the highly efficient removal of a model pollutant, dimethylamine (DMA), in a homogeneous peroxymonosulfate (PMS) system. A high reaction rate constant of 0.32 min−1 and almost complete removal of DMA within 12 min are achieved. Multi-scaled characterizations and theoretical calculations reveal that the in situ constructed C=N bond as the crucial active site activates PMS to produce abundant 1O2. Subsequently, 1O2 oxidizes DMA through multiple H-abstractions, accompanied by the generation of another C=N structure, thus achieving the autocatalytic cycle of pollutant. During this process, base-induced proton transfers of pollutant and oxidant are essential prerequisites for C=N fabrication. A relevant mechanism of autocatalytic degradation is unraveled and further supported by DFT calculations at the molecular level. Various assessments indicate that this self-catalytic technique exhibits a reduced toxicity and volatility process, and a low treatment cost (0.47 $/m3). This technology has strong environmental tolerance, especially for the high concentrations of chlorine ion (1775 ppm) and humic acid (50 ppm). Moreover, it not only exhibits excellent degradation performance for different amine organics but also for the coexisting common pollutants including ofloxacin, phenol, and sulforaphane. These results fully demonstrate the superiority of the proposed strategy for practical application in wastewater treatment. Overall, this autocatalysis technology based on the in-situ construction of metal-free active site by regulating proton transfer will provide a brand-new strategy for environmental remediation.

Sludge Biochar Modified by B-doped and Its Adsorption Behavior and Mechanism of 1,2-DCA in Water

Sludge biochar (BC600) and B-doped sludge biochar (BBC600) were prepared with the boric acid doping modified co-pyrolysis method using municipal sludge as precursors, and the materials were structurally characterized by SEM, BET, FTIR, and Zeta potential and static contact angle to investigate the adsorption behavior, mechanism of BC600 and BBC600 on 1,2-DCA in water, and the influencing factors. The results of structural characterization showed that the B element content, specific surface area, and pore volume of biochar increased by 76%, 48%, and 30%, respectively, after the B doping modification; the effect of B doping modification on the surface charge and hydrophobicity of biochar was not significant. The results of adsorption experiments showed that the adsorption of 1,2-DCA by BBC600 was better than that by BC600 due to the larger specific surface area and higher strength of oxygen-containing functional groups of BBC600; the pseudo-first-order kinetic equation could better describe the adsorption of 1,2-DCA by BC600, and the pseudo-second-order kinetic equation could better fit the adsorption of 1,2-DCA by BBC600. The intraparticle diffusion was not the only rate-limiting step affecting the adsorption rate; the biochar material was more dispersed and stable under alkaline conditions, and its oxygen-containing functional groups were deprotonated and had enhanced electron-donating ability, which was beneficial to the adsorption of 1,2-DCA. Humic acid (HA) showed a low concentration-promoting and high concentration-inhibiting effect on the adsorption of 1,2-DCA by BC600, whereas both low and high concentrations of HA showed an inhibitory effect on the adsorption of 1,2-DCA by BBC600. The adsorption of 1,2-DCA by BC600 was inhibited by both low and high concentrations of HA, and HA competed with 1,2-DCA for adsorption; Cl-, SO42-, and NO3- all inhibited the adsorption of 1,2-DCA by biochar, and the degree of inhibition ordered from small to large was Cl-<SO42-<NO3-. The main mechanisms of 1,2-DCA adsorption by biochar were pore filling and π-π interaction.

Hydrothermal pretreatment based on biogas slurry recycling to improve methane yield of typical plant wastes from South China

Lignin content of feedstock contributed more for the biomass recalcitrance despite of the comprehensive effect from multiple physical and chemical characteristics based on the anaerobic digestion analysis of 16 plant wastes from South China. With the objective of improving anaerobic digestion performance of mixed fruit shell, hydrothermal pretreatment based on biogas slurry recycling (HPBSR) was proposed. Compared with traditional hydrothermal pretreatment, the lignin content of mixed fruit shell was reduced by 4.51–21.13% after HPBSR. The soluble chemical oxygen demand of liquid fraction under 200 ℃ increased by 87.45% relative to the control group with biogas slurry. And the cumulative methane yield of anaerobic digestion was 129.97 mL/gVS, which was 45.01% and 18.78% higher than the control group without treatment and the hydrothermal pretreatment group, respectively. Moreover, the HPBSR experimental group did not produce anaerobic digestion inhibitors (furfural and 5-hydroxymethylfurfural), and the higher humic acid concentration would be another possible reason for the improvement of methane yield. The related results will provide insights into the resource utilization of biogas slurry.

Response of nitrogen removal and microbial community to high concentration of humic acid in the anammox biofilm system

The anaerobic ammonium oxidation (anammox) process is highly effective to remove nitrogen from the wastewater with high ammonia concentration, such as landfill leachate and anaerobic digestion. This kind of wastewater generally contains high content of humic acid, and its effect on anammox is not clear. Therefore, this study investigated the effect of humic acid with high concentration (100–1000 mg/L) on the anammox biofilm system. The nitrogen degradation rates were greatly decreased at the high concentration of humic acid and the reaction time was prolonged by 4 h compared with that lacking humic acid. In the anammox biofilm system, the relative abundance of anammox bacteria Candidatus_Brocadia and Candidatus_Kuenenia decreased from 2.1 % and 15.01 % to 0.6 % and 8.32 %, respectively, while the denitrifying bacteria Thauera increased from zero to 8.86 %. Overall, the high humic acid concentration did not obviously inhibit nitrogen removal performance of anammox system, but affected anammox bacteria activity and microbial community structure.

Kinetic Modeling-Assisted Optimization of the Peroxone (O3/H2O2) Water Treatment Process

In this work, we investigate the influence of H2O2 dosage, H2O2 dosing method, and electron-rich dissolved organic matter (DOM) on the performance of the peroxone (O3/H2O2) process using oxalate (OA) as the target organic compound. Our results show that the method used for H2O2 dosing (i.e., single, multiple, and/or continuous injection(s)) has a significant influence on OA removal after 1 h with nearly 100% of OA oxidized by continuous injection of a total of 1 mM H2O2, but only 48 and 80% OA were removed when the same amount of H2O2 (1 mM) is applied in single and multiple injection(s), respectively. Inhibition of futile scavenging of •OH by H2O2 when H2O2 is dosed in smaller amounts either frequently or continuously throughout the process results in a higher efficiency of organic oxidation compared to that achieved with a single injection of a high concentration of H2O2 at the outset. Our results further show that the presence of high concentrations of humic acids (HA, a representative electron-rich DOM) promotes O3 decay and concomitant •OH generation rates and, as a result, significantly enhances the oxidation rate of OA by ozone alone. As such, any enhancement in •OH generation and associated OA oxidation that might be achieved by H2O2 addition in the presence of HA will be dependent on the extent of •OH generation that results from HA-promoted O3 decay. Based on our results, we have developed a mathematical model that can be used to predict •OH generation and OA oxidation by the peroxone process over a range of conditions. The model provides a good description of the influence of various operating parameters (including ozone dosage, H2O2 dosage, H2O2 dosing method, and the presence of HA) on OA oxidation and, potentially, can be used to optimize the choice of operating conditions in full-scale peroxone systems.

Humic Acid-Amended Formulation Improves Shelf-Life of Plant Growth-Promoting Rhizobacteria (PGPR) Under Laboratory Conditions

Plant growth-promoting rhizobacteria (PGPR) is a soil bacterium that positively impacts soil and crops. These microbes invade plant roots, promote plant growth, and improve crop yield production. Bacillus subtilis is a type of PGPR with a short shelf-life due to its structural and cellular components, with a non-producing resistance structure (spores). Therefore, optimum formulations must be developed to prolong the bacterial shelf-life by adding humic acid (HA) as an amendment that could benefit the microbes by providing shelter and carbon sources for bacteria. Thus, a study was undertaken to develop a biofertilizer formulation from locally isolated PGPR, using HA as an amendment. Four doses of HA (0, 0.01, 0.05, and 0.1%) were added to tryptic soy broth (TSB) media and inoculated with B. subtilis (UPMB10), Bacillus tequilensis (UPMRB9) and the combination of both strains. The shelf-life was recorded, and viable cells count and optical density were used to determine the bacterial population and growth trend at monthly intervals and endospores detection using the malachite green staining method. After 12 months of incubation, TSB amended with 0.1% HA recorded the highest bacterial population significantly with inoculation of UPMRB9, followed by mixed strains and UPMB10 at 1.8x107 CFUmL-1, 2.8x107 CFUmL-1and 8.9x106 CFUmL-1, respectively. Results showed that a higher concentration of HA has successfully prolonged the bacterial shelf-life with minimal cell loss. Thus, this study has shown that the optimum concentration of humic acid can extend the bacterial shelf-life and improve the quality of a biofertilizer.

New Insights into the Fouling of a Membrane during the Ultrafiltration of Complex Organic–Inorganic Feed Water

This paper presents an analysis of the fouling of a ceramic membrane by a mixture containing high concentrations of humic acid and colloidal silica during cross-flow ultrafiltration under various operating conditions. Two types of feed water were tested: feed water containing humic acid and feed water containing a mixture of humic acid and colloidal silica. The colloidal silica exacerbated the fouling, yielding lower fluxes (109-394 L m-2 h-1) compared to the humic acid feed water (205-850 L m-2 h-1), while the retentions were higher except for the highest cross-flow rate. For the humic acid feed water, the irreversible resistance prevails under the cross-flow rate of 5 L min-1. During the filtration of an organic-inorganic mixture, the reversible resistance due to the formation of a colloidal cake layer prevails under all operating conditions with an exception. The exception is the filtration of the organic-inorganic mixture of a 50 mg L-1 humic acid concentration which resulted in a lower flux than the one of a 150 mg L-1 humic acid concentration under 150 kPa and a cross-flow rate of 5 L min-1. Here, the irreversible fouling is unexpectedly overcome. This is unusual and occurs due to the low agglomeration at low concentrations of humic acid under a high cross-flow rate. Under lower transmembrane pressure and a moderate cross-flow rate, fouling can be mitigated, and relatively high fluxes are yielded with high retentions even in the presence of nanoparticles. In this way, colloidal silica influences the minimization of membrane fouling by organic humic acid contributing to the control of in-pore organic fouling.

Adsorption of As(V) at Humic Acid-Kaolinite-Bacteria Interfaces: Kinetics, Thermodynamics, and Mechanisms

The immobilization and transformation of arsenic at the mineral-organic interface in soil environments ultimately depend on the soil components and their interactions. Herein, the effect of humic acid (HA) and a typical bacterium (a Gram-positive Bacillus subtilis) coating on the adsorption of arsenate As(V) to kaolinite (Kao) mineral was investigated. The As(V) adsorption reaction kinetics, isotherms, thermodynamics, and mechanism on the clay mineral-organic composites of kaolinite-Bacillus subtilis (Kao-B.s) and humic acid-kaolinite-Bacillus subtilis (Kao-HA-B.s) were investigated. The As(V) adsorption on the composites was better fitted to pseudo-second-order kinetics and the Freundlich model. The adsorption capacity of As(V) followed the order of Kao-HA-B.s &gt; Kao-B.s &gt; B.s &gt; Kao-HA &gt; Kao. The positive ΔH (31.44, 5.87 kJ mol−1) and ΔG (0.10–0.96 kJ mol−1) values confirmed that the adsorption of As(V) by all composites was nonspontaneous and endothermic in character at room temperature. The FT-IR, XRD, and thermodynamic results revealed that the adsorption mechanism of As(V) on the kaolinite–organic interfaces could be attributed to the electrostatic forces between the terminal aluminum or silanol groups of kaolinite and As(V) and the complexation between HA, bacteria, and As(V), which formed an inner-sphere complex and surface complex, respectively. The experimental results showed that the adsorption of As(V) on the Kao-HA or Kao-bacteria system was accompanied by significant additive interactions, while the ternary Kao-HA-bacteria system had a significant inhibitory effect on As(V) binding at a higher HA content due to the shielding effect, with the promotion effect shown at a lower concentration for dispersion effect for HA on the kaolinite particles.

Comparison of lead adsorption on the aged conventional microplastics, biodegradable microplastics and environmentally-relevant tire wear particles

In this study, the adsorption behavior of lead (Pb(II)) onto environmentally-relevant tire wear particles (TWP) gained by natural weathering and mechanical abrasion, ultraviolet-aged polylactic acid microplastics (UV-PLA), and ultraviolet-aged polystyrene microplastics (UV-PS) was compared to investigate the difference of representative microplastics between the adsorption capacity and mechanism. Our results indicated that the aging processes significantly improved the adsorption capacity to Pb(II), and TWP had the highest adsorption amount, followed the order by UV-PLA, UV-PS, PLA and PS. Electrostatic interaction and complexation of oxygen-containing functional groups played crucial roles in the adsorption of Pb(II) onto UV-PLA, the adsorption mechanisms of UV-PS involved electrostatic interaction, complexation and cation-π interaction, while adsorption of TWP was might dominated by the complexation of surface functional groups and properties of the complex rubber co-polymer. Interestingly, the low concentration of humic acid (HA) most significantly improved adsorption capacity of aged microplastics to Pb(II), otherwise it was severely suppressed at higher concentration of HA. Besides, the adsorption behavior of different binary systems between aged microplastics and suspended sediment to Pb(II) had complicated synergistic or suppressive effects with a concentration-dependent and polymer-dependent trend. Furthermore, UV-PLA had the far stronger desorption ability of Pb(II) than that of TWP and UV-PS, suggesting that metal-contaminated biodegradable microplastics posed the higher ecological risks to aquatic organisms. Desorption quantity and rates of Pb(II) from aged microplastics in the simulated sediment system were generally higher than those in turbulent water column. Collectively, these findings provide a wide insight into adsorption capacity and mechanisms of metal ions on the representative aged microplastics and the desorption behavior in complex aquatic environments.

Study on Microstructure of Cemented Organic Soil in Dianchi Lake, China

The organic soil in the Dianchi Lake area contains much humic acid (HA), and the impact of HA on cemented soil has attracted much attention. In this study, test soil is prepared based on the actual HA content of the soil in Dianchi Lake, and cement is added to prepare samples. Unconfined compressive strength (UCS), scanning electron microscopy (SEM), energy-dispersive analysis (EDS), and X-ray diffraction (XRD) tests are conducted on the samples. The strength development and microstructure changes of cemented organic soil are studied. The results show that (1) cemented soil strength decreases with the increase in HA content and increases with the cement mixing ratio; (2) SEM and EDS tests show that with the increase in HA content, the connection between soil particles gradually changed from surface–surface to point–surface, point–edge, or point–point connection. A large overhead structure is inside the cemented soil, and its integrity weakens with increased HA content. However, elements such as Ca, Si, and Al exist in the pores of cemented soil, indicating that cement hydration products are cemented between soil particles. XRD testing shows that with the increase in HA content, the intensity of the diffraction peaks of hydration products in cemented soil gradually decrease. (3) In general, HA will gradually deteriorate the integrity of cemented soil and reduce its strength. When the HA content is more than 15%, the effect of HA on strength is more prominent. However, increasing the cement mixing ratio can effectively weaken HA’s negative effect on cemented soil’s strength. When the cement mixing ratio is between 15% and 25%, the strength of cemented soil with high HA content can be effectively increased. However, this approach is not conducive to the protection of the environment.

Enhanced vector transport of microplastics-bound lead ions in organic matter rich water

ABSTRACT Microplastics act as a vector for toxic trace metals and their surface complexation mechanisms under different environmental conditions are poorly understood. The present study evaluates the interaction mechanisms of pristine and aged polyethylene (PE) microplastics with Pb2+ in water environments in the presence of NaNO3 and humic acid (HA). The influence of pH, contact time, and concentration of Pb2+ on the sorption performances of PE microplastics have also been examined at different ionic strengths (0.001–0.1 M NaNO3), pH (2–9), reaction time (48 h), Pb2+ loading concentrations (1–25 mg L−1), and HA concentrations (0.5–2.5 mg L−1). The Pb2+ adsorption onto both pristine and aged microplastic showed a gradual increase with increasing pH, reaching maximum adsorption at around pH 5–6. Adsorption of Pb2+ onto both PE microplastics decreased at higher ionic strengths and increased at higher HA concentrations suggesting the possible hydrophobic and electrostatic interactions between microplastics and Pb2+ ions. Adsorption kinetic data for pristine PE microplastics were well described by fractional power model indicating time-dependent adsorption, whereas aged PE showed rate-limiting chemisorption by fitting with a pseudo-second-order kinetic model. Isotherm equilibrium data for pristine PE microplastics fitted well for the Freundlich model implying favourable physisorption on the heterogeneous surfaces. Both Hill and Freundlich models were the best-fitted models for aged PE microplastics suggesting the involvement of cooperative multilayer physisorption. Desorption of PE microplastics-bound Pb2+ was greatly influenced by the solution pH. The ascertaining facts elucidated the vector potential of PE microplastics for Pb2+, impacting their migration and destination in water systems where the adsorption could be influenced by the pH, ionic strength, and dissolved organic matter of the water system.

Формирование рекультивационного слоя при открытых разработках

Land reclamation must ensure that the quality of the land complies with environmental quality standards and the requirements of the legislation of the Russian Federation. The pur­pose of this work was to study the process of formation of a reclamation layer in open-cast coal mines. The indicators of the quality of the fertile soil layer should correlate to the quality of the fertile soil layer on average for the region. For effective recultivation, the fertile soil layer should be distinguished by a high content of humic acids and nutrients, as well as a higher degree of saturation with bases. The mechanical composition of the fertile soil layer should be loamy or clayey. Within agriculturally-focused reclamation, the thickness of the reclamation layer should be 0.8—1.5 m, depending on the moisture regime and the type of crop grown. The thickness of the bulk fertile soil layer depends on its availability and should in all cases be at least 0.3 m, in the chernozem zone — 0.4 m. The thickness of the fertile soil layer can be reduced to 0.20 m when arranging hayfields and pastures plots. During forest reclamation, the soil composition of the reclamation layer prepared for trees in the root layer (1.5—2 m) should be optimal for tree growth. Large (more than 0.3 m) stones should not be fixed at ground level (0.4—0.5 m), as this makes mechanization difficult. Also, the amount of fine-grained soil should not be lower than 5—10 %. Otherwise, a fertile soil layer should be ap­plied to the planned surface of the reclamation layer of the required thickness.

Adsorption of antibiotics on different microplastics (MPs): Behavior and mechanism

MPs can adsorb antibiotics to coexist and accumulate in the aquatic environment in the form of complexes, resulting in unforeseeable adverse consequences. The adsorption behavior and mechanism of three antibiotics amoxicillin (AMX), ciprofloxacin (CIP), and tetracycline (TC) by four MPs Polyvinyl chloride (PVC), polystyrene (PS), polypropylene (PP), and polyethylene (PE) were studied. Results showed that the adsorption of antibiotics onto MPs follows the pseudo-second-order kinetic and the Freundlich isotherm model, indicating a multilayer chemical adsorption. Combined with FTIR, XRD, and SEM analyses, the adsorption behavior was simultaneously governed by physical processes. Additionally, the equilibrium adsorption capacity was inhibited in the research concentration range of NaCl from 10 mg/L to 10 g/L. The higher the salt concentration, the more pronounced the inhibition phenomenon was. The high (9) and low (3) pH also inhibited the adsorption of antibiotics to MPs. The humic acid (HA) concentration in the range of 0–20 mg/L generally inhibited the MPs-antibiotics adsorption, but the higher HA concentration showed less inhabitation than the lower one. The adsorption inhibition of TC on the four MPs by SA also followed the above rule. However, the adsorption inhibition of sodium alginate (SA) on AMX and CIP on the four MPs was enhanced with its concentration (0–50 mg/L).

Direct Contact Membrane Distillation for Treatment of Mixed Wastewater of Humic Acid and Reactive Dye: Membrane Flux Decline and Fouling Analysis.

The main waste stream from the textile industry is its wastewater with high color, organic matters, and other contaminants. This study aims to investigate the effect of humic acid in mixed wastewater of humic acid and reactive dye on the treatment performance and permeate flux of a direct contact membrane distillation (DCMD) system. In this research, feed temperature and humic acid concentration were the main input parameters for the analysis of DCMD system operation. The fouling resistances significantly increased with higher humic acid concentrations in the mixed wastewater. As compared with the DI water test, 23% of flux decline occurred when the humic concentration in the wastewater was increased up to 20 mg/L. After the DCMD treatment, the 25 ADMI residual color was detected in the permeate when the mixed wastewater contained 20 mg/L humic acid. The mathematical model, based on the Antione equation, was proposed to predict the membrane flux decline of the DCMD system. The reduced pore size of the cake layer by a dimensionless constant β from the Kelvin equation was also considered for the fouling calculation to describe the transport mechanism.

Microflora for improving the Auricularia auricula spent mushroom substrate for Protaetia brevitarsis production

SummaryMushroom cultivation is a sustainable agricultural waste utilization method, but the lack of high-value utilization of the produced spent mushroom substrate (SMS) has hindered the development of mushroom cultivation-based circular agricultural systems. Conversion and utilization of SMS via Protaetia brevitarsis larvae (PBL) have proven to be a high-value AASMS utilization strategy. However, Auricularia auricula SMS (AASMS), which contains woodchips, is less palatable and digestible for PBL. To solve this problem, in this investigation, we screened out microflora (MF) for AASMS fermentation by comparing the fermentation performance as well as the effect on PBL feed intake, weight gain, and AASMS phytotoxic compound removal efficiency. In addition, by bacterial community analysis, the genera Luteimonas, Moheibacter, and Pseudoxanthomonas were predicted to be functional bacteria for AASMS fermentation and contribute to palatability and digestibility improvement.

Photochemical transformation of sulfadiazine in UV/Fe(II)/sodium citrate Fenton-like system

The persistence and potential hazards of antibiotics in the aquatic environment have attracted worldwide attention. Currently, advanced oxidation technology is considered to be an effective way to degrade antibiotics in the water environment. An enhanced photochemical Fenton-like system was investigated in this study for degradation of antibiotic sulfadiazine (SDZ). The degradation kinetics, pathways, and mechanisms of SDZ in four different photocatalytic systems were studied, including ultraviolet (UV), UV/sodium citrate (SC), UV/Fe(II), and UV/Fe(II)/SC. The highest degradation rate of SDZ was observed in UV/Fe(II)/SC system, and the complexation of SC-Fe(II) promoted photocatalytic efficiency and iron cycling. It was proved that hydroxyl radicals (•OH) were generated in UV/Fe(II)/SC system, but excessive Fe(II) consumed •OH and produced a UV shielding effect, thus reducing the degradation rate of SDZ. In the UV/Fe(II)/SC system, the degradation of SDZ followed pseudo-first-order kinetics, and the reaction rate constant of SDZ reached a maximum of 8.49 × 10−3 min−1, with a degradation efficiency of 97.7%. Even in different real water samples, the removal rate of SDZ can reach about 80%. HCO3−, SO42−, and NO3− in the water environment inhibited the degradation of SDZ, and the order of inhibition was as follows: SO42− > HCO3−>NO3−. With the increase of SDZ concentration and high concentration of humic acid (HA), the degradation rate of the target compound decreased. By identifying the photodegradation products of SDZ, four degradation pathways were proposed, and it revealed that the N–C bond and N–S bond were broken by attacking of hydroxyl groups, where a hydroxyl group replaced the H atom, resulting in the decomposition of SDZ into low molecular weight compounds like SO2, CO2, NO3− and H2O. It suggested that the UV/Fe(II)/SC system has good effect and application prospect in SAs treatment.

Fish populations and biomass in headwater streams of the Lake Tumba Landscape, DR Congo, 2007–2011

The fish biodiversity in the Congo River and its tributaries is extremely rich but the information on fish communities in the headwaters in terms of catch and biomass estimates is rare. Fishes in the running and stagnant waters in this region are of vital importance as a food resource for local residents. This study aimed to describe the fish community, catch, and biomass in the three headwater streams Bambou, Lebomo, and Bongo in the Lake Tumba Landscape (LTL) of the Democratic Republic of the Congo. Such information is of vital importance as a benchmark to understand the sustainability of the fish population for future generations of residents of the LTL. The field data were collected from 2007 through 2011, including dry and wet seasons. Here we present the results of this systematic, multi-annual study which was the first for fishes in streams of this region. In total, 50 species of 15 families were found in the nutrient-poor brown waters of these streams where high concentrations of humic acids cause a low pH. Among abundant species occurring in all three streams were the cyprinid Enteromius holotaenia (Boulenger, 1904), the mormyrid Marcusenius moorii (Günther, 1867), the alestids Clupeocharax schoutedeni Pellegrin, 1926 and Bryconaethiops boulengeri Pellegrin, 1900, and the clariid Clarias angolensis Steindachner, 1866. Bongo Stream was distinguished from the others by a rich abundance of Alestopetersius compressus (Poll et Gosse, 1963). The presence of several species at low pH (between 5.0 and 5.5) is new information that lowers the bottom of the pH interval for these species compared to earlier reports. The maximum total length (TL) of some other species was by 5–20 percentage points higher than those reported earlier. The median weight per unit effort (WPUE) in the streams varied between 30 and 115 g per hour during the dry seasons and between 18 and 86 g per hour during the wet seasons. The fish biomass in the streams varied between 0.05 and 0.7 g ⸱ m–2 with a median 0.14 g ⸱ m–2. This relatively low value compared to other tropical headwaters may be a result of the low pH and dark color of these headwaters. The results of the study serve as a reference point to which future monitoring of fish fauna can be compared for sustainable management of the LTL.

Effect of Humic Acid on the Growth and Metabolism of Candida albicans Isolated from Surface Waters in North-Eastern Poland.

The aim of this study was to determine the effect of humic acid on the growth and metabolism of Candida albicans, a common waterborne pathogenic yeast. At 10–20 mg/L, humic acid caused the greatest increase in biomass and compactness of proteins and monosaccharides, both in cells and in extracellular secretion of the yeast. At higher humic acid concentrations (40–80 mg/L), C. albicans cells still had higher protein levels compared to control, but showed reduced levels of metabolites and inhibited growth, and a significant increase in the activity of antioxidant enzymes, indicating a toxic effect of the humic acid. The increase in protein content in the cells of C. albicans combined with an increase in the activity of antioxidant enzymes may indicate that the studied yeast excels in conditions of high water enrichment with low availability of organic matter. This indicates that Candida albicans is capable of breaking down organic matter that other microorganisms cannot cope with, and for this reason, this yeast uses carbon sources that are not available to other microorganisms. This indicates that this fungus plays an important role in the organic carbon sphere to higher trophic levels, and is common in water polluted with organic matter.

Determination of pesticides and their degradation products in sediment samples by accelerated solvent extraction and solid-phase extraction with high-performance liquid chromatography-high-resolution mass spectrometry.

A new sensitive and selective methods was developed to quantify different types of pesticides and their degradation products in sediment. The method developed was optimized and modified based on the accelerated solvent extraction, followed by the solid-phase extraction clean-up technique. High-performance liquid chromatography coupled with mass spectrometry was used for analysis. The influence of various parameters on the extraction process was investigated, including the extraction temperature, extraction solvent, purification column and purification solvent, etc. Under the optimal conditions, the relative recoveries of the pesticides and their degradation products ranged from 80 to 106% for spiked blank sediment and environmental sediment samples with relative standard deviations of 1-9%. The method displayed low method detection limits for both sediment matrices and achieved good linearity over the tested range of concentrations. The physical and chemical properties of sediment showed that high content of sediment water content and humic acid would affect the extraction efficiency of sample pretreatment. The method was applied to environmental sediment to quantify pesticide residues in the samples. Based on the instrument and method performance validation results, the developed methods can be applied in environmental pesticide residue analysis, thus providing a scientific method for the detection of sediment samples.

Characteristics of Chinese Weathered Coal from Six Geographical Locations and Effects on Urease Activity Inhibition

Weathered coal is known to have potential inhibitory effects on urease activity, thus reducing the loss of nitrogen from fertilizer such as ammonia. This means that it can be used as a urea enhancer to promote urea utilization efficiency. However, the variation in its composition and structure has impeded the optimal utilization of this resource. In this study, we collected Chinese weathered coal from six representative geographical locations and analyzed its elemental and substance composition, as well as determined its chemical structure via Fourier transform infrared spectroscopy and investigated its effects on urease (soybean meal) activity. The results showed evident variation in the composition and structure among the different weathered coal samples, especially in the pH values, humic acid and ash content, and aromaticity. All six weathered coal samples significantly inhibited urease activity, and the inhibitory effect was enhanced with the elevated proportion of weathered coal introduced to urea. When the additive proportion of weathered coal increased, the weathered coal, characterized as having a higher humic acid content and a more aliphatic structure, showed a more rapid increase in the urease activity inhibition rate, while there was only a slight effect when the weathered coal had a low humic acid content and high atomicity. Therefore, the former type of weathered coal was more sensitive to the additive proportion. Furthermore, there was no consistent rule when the same proportion of weathered coal from different geographic locations was blended into urea, which might be attributable to other unexplored factors.