Migration and transformation behaviors of antibiotics in water-sediment system under simulated light and wind waves.

Antibiotics can generally be detected in the water-sediment systems of lakes. However, research on the migration and transformation of antibiotics in water-sediment systems based on the influences of light and wind waves is minimal. To address this research gap, we investigated the specific impacts of light and wind waves on the migration and transformation of three antibiotics, norfloxacin (NOR), trimethoprim (TMP), and sulfamethoxazole (SMX), under simulated light and wind waves disturbance conditions in a water-sediment system from Taihu Lake, China. In the overlying water, NOR was removed the fastest, followed by TMP and SMX. Compared to the no wind waves groups, the disturbance of big wind waves reduced the proportion of antibiotics in the overlying water. The contributions of light and wind waves to TMP and SMX degradation were greater than those of microbial degradation. However, the non-biological and biological contributions of NOR to degradation were almost equal. Wind waves had a significant impact on the microbial community changes in the sediment, especially in Methylophylaceae. These results verified the influence of light and wind waves on the migration and transformation of antibiotics, and provide assistance for the risk of antibiotic occurrence in water and sediments.

Influence by varying organic matter content and forms in suspended particulate matter: impacts on the adsorption of tetracycline and norfloxacin.

Antibiotics are commonly detected in natural waters. The organic matter (OM) in suspended particulate matter (SPM) has a critical impact on the adsorption of antibiotics in water. We investigated the contribution of OM content and form to the adsorption of tetracycline (TC) and norfloxacin (NOR) in the SPM of Taihu Lake. To change the content and form of OM in SPM, the samples were subjected to pyrolysis at 505 ˚C and oxidization with H2O2, respectively. Combustion almost completely removed OM, while oxidation removed most of the OM and transformed the remaining OM. Regardless of whether the OM changed or not, the adsorption of NOR and TC by SPM was more in line with the pseudo-second-order kinetic model instead of pseudo-first-order. The fitting of the intraparticle diffusion model showed that the removal of OM had a certain degree of change in the adsorption process. The isothermal adsorption of TC in all samples was more in line with the Temkin model. The isothermal adsorption of NOR in the oxidized sample conformed to the Temkin model, while it conformed to the Langmuir model in the original sample and the sample removed OM via combustion. The adsorption capacity of SPM with almost complete removal of OM significantly decreased, while conversely, the adsorption capacity of SPM after oxidation increased. This indicates that both the content and form of OM affect the adsorption of antibiotics by SPM, and the form of OM has a greater impact. The contribution of OM to NOR adsorption was greater than that of TC. In conclusion, the results verify the importance of OM in adsorbing antibiotics onto SPM, which may provide basic data for antibiotic migration in surface water.

Peroxymonosulfate activation by nitrogen-doped herb residue biochar for the degradation of tetracycline.

Biochar is an environmentally friendly material with potential applications in water purification. In this study, herb residue nitrogen-doped biochar (N-BC) was fabricated and used to activate peroxymonosulfate (PMS). Characterization and density-functional theory (DFT) studies were conducted to explore the influence of nitrogen doping. Radical scavenging activity and electron paramagnetic resonance (EPR) spectroscopy revealed that non-radical singlet oxygen (1O2) is the main reactive oxidative species. Additionally, pyridinic-N was shown to play a pivotal role in the 1O2-dominated pathway. Three possible degradation pathways were proposed based on the identified degradation intermediates. Batch experiments confirmed that N-BC showed excellent catalytic performance and reusability. The best condition for tetracycline (TC) degradation efficiency (>99%) in 60 min was obtained when the dosage of N-BC was 1 g/L and the concentration of PMS was 5 mM. Furthermore, N-BC showed approximately 65.5% degradation efficiency within 4 cycles. Furthermore, the toxicity of degradation intermediates was examined using ECOSAR and T.E.S.T procedures. This study brings forth a feasible strategy to synthesize biochar. Furthermore, the proposed approach will facilitate the use of biochar in water purification.

Radix Astragali residue-derived porous amino-laced double-network hydrogel for efficient Pb(II) removal: Performance and modeling.

Valorizing solid waste for heavy metal adsorption is highly desirable to avoid global natural resources depletion. In this study, we developed a new protocol to valorize Radix Astragali residue (one of the Chinese medicine residues) into a low-cost, chemically robust, and highly permeable (ca. 90%) amino-laced porous double-network hydrogel (NH2-CNFs/PAA) for efficient Pb(II) adsorption. The NH2-CNFs/PAA showed (i) excellent Pb(II) adsorption capacity (i.e., 994.5 mg g-1, ~4.8 mmol g-1), (ii) fast adsorption kinetics (kf = 2.01 ×10-5 m s-1), (iii) broad working pH range (2.0-6.0), and (iv) excellent regeneration capability (~15 cycles). (v) excellent performance in various real water matrices on Pb(II) removal. Moreover, its high selectivity (distribution coefficient Kd ~2.4 ×106 mL g-1) toward Pb(II) was owing to the present of abundant amino groups (-NH2). Furthermore, the fix-bed column test indicated the NH2-CNFs/PAA can effectively remove 114.6 bed volumes (influent concentration ~5000 µg L-1) with an enrichment factor 10.9. The full-scale system modeling (i.e., pore surface diffusion model (PSDM)) has been applied to predict the NH2-CNFs/PAA performance on Pb(II) removal. Overall, we have provided an alternative "win-win" scenario that can resolve the Chinese medicine residues disposal issue by valorizing it into high performance gel-based adsorbents for efficient heavy metal removal.

Effects of suspended particulate matter from natural lakes in conjunction with coagulation to tetracycline removal from water.

Coagulation is a common method used to remove suspended particulate matter (SPM) from the water supply. SPM has preferable adsorption ability for antibiotics in water; therefore, SPM adsorption and coagulation may be a possible way to remove tetracycline (TC) from water. This study carried out coagulation experiments combining SPM collected from a natural lake at a location with three common coagulants-polyaluminum sulfate, polyaluminum chloride, and polyferric sulfate-under different pH values, exploring the adsorption of TC by SPM, coagulation of SPM with TC, and the primary influencing factors of this process. The maximum removal rate of TC can reach 97.87% with an SPM concentration of 1000 mg/L. Multi-factor analysis of variance showed the importance of various TC removal factors, which were ranked as follows: SPM concentration â‰« initial TC concentration > type of coagulant > pH values. The higher the SPM concentration, the better the TC removal (p < 0.001). Fourier infrared spectroscopy results demonstrated the strong adsorption effect of SPM on TC after being combined with a coagulant, and scanning electron microscopy also indicated that SPM becomes effective nuclei in the coagulation process, which is a possible reason for better TC removal. However, the effluent turbidities under 1000 mg/L SPM concentrations were high without coagulant aid. With the addition of coagulant aid anion polyacrylamide, the TC removal remained unchanged, effluent turbidity significantly reduced, and the TC desorption became low. These results indicate that applying SPM from natural lakes in the coagulation process could potentially remove TC in water.

Electrolysis-sulfate-reducing up-flow sludge bed-biological contact oxidation reactor for Norfloxacin removal from wastewater with high sulfate content.

This study investigated the treatment of 100-mg/L Norfloxacin (NOR) wastewater containing high concentrations of sulfate through a combination of electrolysis, sulfate-reducing up-flow sludge bed (SRUSB), and biological contact oxidation reactor (BCOR) treatments. Results revealed that after 62 h, the reaction system had processed over 97% of the NOR. Additionally, electrolysis with sodium sulfate as the electrolyte transformed 87.8% of the NOR but only 33.5% of the total organic carbon (TOC). In the SRUSB, the TOC and SO42- contents were simultaneously reduced by 87.4% and 95.6%, respectively, providing a stable environment to the BCOR. In the BCOR, 36.3% and 85.9% of the NOR and TOC were degraded. High-performance liquid chromatography-tandem mass spectrometry analysis identified three possible degradation pathways under the attack of -OH during electrolysis, including defluorination, piperazinyl ring transformation, and quinolone ring transformation. Furthermore, the Illumina HiSeq sequencing results demonstrated that the sulfate-reducing bacteria (represented by Desulfobacter and Desulfobulbus) in the SRUSB and the sulfate-oxidizing bacteria (mainly consisting of Gammaproteobacteria and Alphaproteobacteria) in the BCOR played important roles in carbon chain oxidation and benzene ring opening and thoroughly degraded the electrolysis products. Thus, this method effectively overcomes the incomplete degradation and low removal efficiency issues associated with single electrolysis or biological methods in traditional processes.

Degradation of tetracycline in water by biochar supported nanosized iron activated persulfate.

Biochar supported nanosized iron (nFe(0)/BC) was synthesized and used as a persulfate (PS) activator to degradation tetracycline (TC). The influence of the initial pH values, PS and nFe(0)/BC dosage, initial TC concentration, and coexist anions were investigated. In the nFe(0)/BC-PS system, TC could be effectively removed at various pH values (3.0-9.0). The degradation efficiency of TC (100 mg/L) was 97.68% using nFe(0)/BC (0.4 g/L) and persulfate (1 mM) at pH 5.0. Coexisting ions (HCO3- and NO3-) had an inhibitory effect on TC degradation. The removal of TC could be fitted by a pseudo-second-order model. Electron-Spin Resonance (ESR) analysis and scavenging tests suggested that sulfate radicals (SO4·-) and hydroxyl radicals (HO·) were responsible for TC degradation. Details of the advanced oxidation process (AOP)-induced degradation pathways of TC were determined based on liquid chromatography mass-spectrometry (LC-MS) analysis. The nFe(0)/BC could still maintain 86.38% of its original removal capacity after five cycles. The findings of this study proved that nFe(0)/BC can be applied to activate PS for the treatment of pollution caused by TC.

Impact of sediment characteristics on adsorption behavior of typical antibiotics in Lake Taihu, China.

Sediment adsorption is one of the main fates of antibiotics in aquatic environments. However, few studies have compared the physicochemical properties of sediments from the same aquatic ecosystem but at different locations and correlated them with antibiotic adsorption efficiency. To predict the adsorption of antibiotics in water-sediment systems more accurately, this study conducted experiments with tetracycline (TC) and oxytetracycline (OTC) in tetracyclines, ciprofloxacin (CIP) in fluoroquinolones, and roxithromycin (ROX) in macrolides. Sediments from different locations in Lake Taihu, China, were collected to determine the adsorption properties of CIP, TC, OTC, and ROX. Moreover, the physicochemical properties of the sediments were measured and the correlation between these properties and antibiotic adsorption were discussed to establish a model for predicting adsorption parameter Kd. The antibiotic adsorption performance of sediments was high in heavily polluted and grassy areas but poor in estuarine areas of the lake, suggesting that adsorption effectiveness was affected by the physicochemical properties of sediments. Based on the established model, the specific surface area, organic carbon, and cation exchange capacity played the most significant roles. The study further determined that the predicted and actual values showed a good linear fitting relationship. Therefore, the model effectively predicted the antibiotic adsorption performance of different sediments and provided recommendations for the environmental trend and risk assessment of antibiotics.

Immobilization of Cr(VI) from solution by a graphene oxide-nZVI/biochar composite.

A graphene oxide (GO)-nanoscale zerovalent iron (nZVI)-biochar composite (GO-nZVI/BC) was synthesized prior to characterization by X-ray diffraction (XRD), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy analyses. Batch experiments were performed at different initial Cr(VI) concentrations, contact times, and solution pH values. The effects of coexisting anions and chelating agents were also examined. The results indicated that the removal of Cr(VI) was highly pH-dependent and reached a maximum capacity at pH of 2. The equilibrium data were fitted well with the Langmuir isotherm model, and the kinetic data fitted better with the pseudo-second-order kinetic model. The increasing concentrations of EDTA in aqueous solutions were favorable to the removal of Cr(VI), while NO 3 - significantly inhibited adsorption. Furthermore, the GO-nZVI/BC maintained ~84.5% of its original capacity after aging in the air for 25 weeks. Based on the removal efficiency, GO-nZVI/BC can be considered to be an effective material for water treatment applications. PRACTITIONER POINTS: Biochar-supported graphene oxide-coated nanoscale zerovalent iron (GO-nZVI/BC) was synthesized and used to treat Cr(VI) from solution. Cr(VI) removal was pH-dependent and obeyed the Langmuir isotherm model and pseudo-second-order model. GO-nZVI/BC maintained ~84.5% of its original capacity after aging for 25 w in the air.

Effect of particle size on adsorption of norfloxacin and tetracycline onto suspended particulate matter in lake.

Aquatic systems are important sinks of antibiotics; however, their final destination has not been completely elucidated. Therefore, we investigated the adsorption behaviors of suspended particulate matter (SPM) in lakes to support the analysis of the migration and transformation of antibiotics in lacustrine environments. SPM was collected from Meiliang Bay (ML) and Gonghu Bay (GH) in Lake Taihu, China, which was sieved into four particle sizes of >300, 150-300, 63-150, and <63 µm for subsequent antibiotic adsorption experiments. All particles exhibited rapid and substantial adsorption of tetracycline and norfloxacin. Most size fractions fit a Langmuir model, indicative of monomolecular adsorption, except the <63-µm fraction, which fit a Freundlich model. Particle size had a substantial influence on antibiotic adsorption; the 63-150-µm fraction had the greatest adsorption capacity, while the >300-µm fraction had the lowest capacity. The influence of particle size on adsorption was mainly related to SPM physicochemical properties, such as cation exchange capacity, surface area, and organic matter content, rather than types of functional groups. Considering the mass ratios, the <63-µm fraction had the greatest contribution to adsorption. Antibiotics adsorbed onto the SPM from ML and GH exhibited different behaviors. The ML SPM settled more readily into sediment, and larger, denser particles were more resistant to resuspension. Conversely, the GH SPM was more likely to be found in the water column, and larger, less-dense particles remained in the water column. These results help improve our understanding of the interactions between SPM and antibiotics in aquatic systems.

Effects of wind-wave disturbances on adsorption and desorption of tetracycline and sulfadimidine in water-sediment systems.

Wind-wave disturbances frequently disperse sediment particles into overlying water, which facilitates the adsorption and desorption of contaminants in aquatic ecosystems. Tetracycline (TC) and sulfadimidine (SM2) are common antibiotics that are frequently found in aquatic environments. This study utilized microcosms, comprising sediment and water from Lake Taihu, China, to examine the adsorption and desorption of TC and SM2 under different wind-wave disturbances in a shallow lake environment. The adsorption experiments were conducted with three different concentrations (1, 5, 10 mg/L) of TC and SM2 in the overlying water, and two different (background and strong) wind-wave conditions for 72 h. Subsequently, four microcosms were employed in a 12-h desorption study. Analysis of adsorption progress showed that TC concentration in the overlying water decreased quickly, while SM2 remained almost constant. In the desorption experiments, SM2 released to the overlying water was an order of magnitude greater than TC. These results indicate that sediment particles strongly adsorb TC but weakly adsorb SM2. Compared to background conditions, the strong wind-wave conditions resulted in higher concentrations of TC and SM2 in sediment and facilitated their migration to deeper sediment during adsorption, correspondingly promoting greater release of TC and SM2 from sediment particles into the overlying water during desorption.

Migration of two antibiotics during resuspension under simulated wind-wave disturbances in a water-sediment system.

In this study, the migration of antibiotics (norfloxacin, NOR; and sulfamethoxazole, SMX) under simulated resuspension conditions across the sediment-water interface were quantified for two locations in China: point A, located in Meiliang Bay of Lake Taihu, and point B, located in Dapukou of Lake Taihu. The concentrations of suspended solids (SS) in the overlying water amounted to 100, 500, and 1000 mg/L during background, moderate, and strong simulated wind-wave disturbances, respectively. At each SS level, the initial concentrations of the two antibiotics were set to 1, 5, and 10 mg/L. The results showed that both resuspended SS and the initial concentration of antibiotics could influence the migration of NOR in the water-sediment system. Specifically, both higher SS and initial antibiotic concentrations were associated with higher rates of migration and accumulation of NOR from water to sediment. In contrast, the migration of SMX in the water-sediment system was not impacted by SS or initial antibiotic concentration. The adsorption capacities of sediments for NOR and SMX were significantly different at both locations, possibly reflecting differences in cation exchange capacity (CEC) and organic material (OM) contents. In general, higher CEC and OM values were found in sediments with a higher adsorption capacity for the antibiotics. When CEC and OM values of sediments were higher, the adsorption capacity reached up to 51.73 mg/kg. Large differences in the migration from water to sediment were observed for the two antibiotics, with NOR migration rates higher than those of SMX. The accumulation of NOR in surface sediment during resuspension was about 14 times higher than that of SMX. The main reason for this is that the chemical adsorption of NOR is seldom reversible. Overall, this study demonstrates that resuspension of NOR and SMX attached to sediments under simulated wind-wave disturbances can promote the migration of the antibiotics from water to sediment; these results could be useful for assessing the migration and fate of commonly used antibiotics in water-sediment systems.

Removal of chromium (VI) from water using nanoscale zerovalent iron particles supported on herb-residue biochar.

A composite material consisting of nanoscale zerovalent iron particles supported on herb-residue biochar (nZVI/BC) was synthesized and used for treatment of Cr(VI)-contaminated water. The effects of initial pH, chromium concentration, contact time, and competition with coexisting anions and natural organic matter (NOM) were also investigated. nZVI/BC was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy analysis (SEM), and the Brunauer-Emmett-Teller surface area was measured. TEM and X-ray photoelectron spectroscopy (XPS) analysis before and after reaction with Cr(VI) showed that reduction and coprecipitation occurred during hexavalent chromium adsorption. The removal of Cr(VI) was highly pH-dependent and the adsorption kinetics data agreed well with the pseudo-second-order model. The presence of SO42- and humic acid promoted Cr(VI) removal at both low and high concentrations, while the HCO3- inhibited the reaction. These results prove that nZVI/BC can be an effective reagent for removal of Cr(VI) from solutions.

Low-cost magnetic herbal biochar: characterization and application for antibiotic removal.

Magnetic biochar (M-BC) was derived from herbal medicine waste, Astragalus membranaceus residue, and was used as an adsorbent for ciprofloxacin removal from aqueous solutions. The M-BC was characterized by Brunauer-Emmett-Teller surface area analyses, Fourier transform infrared spectrometry, X-ray diffraction analysis, hysteresis loops, scanning electron microscopy energy-dispersive spectrometry, and X-ray photoelectron spectroscopy. The BET surface area increased from 4.40 to 203.70 m2/g after pyrolysis/magnetic modification. Batch experiments were performed at different dosages, initial concentrations, contact times, and solution pHs. Adsorption performances were evaluated using Langmuir and Freundlich isotherm models, and the results indicated that the Langmuir model appropriately described the adsorption process. The kinetic data were better fitted by a pseudo-second-order kinetic model. The maximum ciprofloxacin removal was observed at pH 6 (adsorption capacity of 68.9 ± 3.23 mg/g). Studies demonstrated that magnetically modified biochar might be an attractive, cost-effective, and easily separated adsorbent for contaminated water. Graphical abstract.

[Environmental Effect of Substrate Amelioration on Lake: Effects on Phragmites communis Growth and Photosynthetic Fluorescence Characteristics].

Growth of rooted aquatic macrophytes was affected by the nature and composition of lake bottom sediments. Obviously, it has been recognized as an important ecological restoration measure by improving lake substrate and then reestablishing and restoring aquatic macrophytes in order to get rid of the environmental problem of lake. This study simulated five covering thickness to give an insight into the influence of substrate amelioration on Phragmites communis growth and photosynthetic fluorescence characteristics. The results showed that the total biomass, plant height, leaf length and leaf width of Phragmites communis under capping 5 cm were much more significant than those of capping 18 cm (P < 0.01), at the 120 d, the underground: shoot biomass ratio and fine root: underground biomass ratio were also much higher than those of other treatments (P < 0.05), which indicated that capping 18 cm treatment would significantly inhibit the growth of Phragmites communis , but the growth of control group Phragmites communis was slightly constrained by eutrophicated sediment. In addition, as the capping thickness growing, the underground: shoot biomass ratio of the plant would be reduced dramatically, in order to acquire much more nutrients from sediment for plant growing, the underground biomass of Phragmites communis would be preferentially developed, especially, the biomass of fine root. However, Photosystem II (PS II) photochemical efficiency (Fv/Fm), quantum yield (Yield), photochemical quenching (qP), non-photochemical quenching (qN) of Phragmites communis under different treatments had no significant differences (P > 0.05), furthermore, with much greater capping thickness, the photosynthesis structure of PS II would be much easier destroyed, and PS II would be protected by increasing heat dissipating and reducing leaf photosynthetic area and leaf light-captured pigment contents. In terms of the influence of sediment amelioration by soil exchange on the growth and photosynthetic fluorescence characteristics of Phragmites communis, plant growth could be effectively promoted under capping 2 cm and capping 5 cm by increasing the Eh value and nutrient content, whereas plant under capping 18 cm would be much easier adaptive to low-light stress in winter season, of which capping 2 cm treatment was conducive to enhance the initial slope of RLCs (α), maximum electron transport rate (ETRmax) and minimum saturating irradiance (Ek). With regard to the harness of environmental problem of lake, the eutrophication status of lake will be mitigated by using multi-ecological measures to control the internal nutrients content once the external loading was first effectively controlled.

Beyond hypoxia: occurrence and characteristics of black blooms due to the decomposition of the submerged plant Potamogeton crispus in a shallow lake.

Organic matter-induced black blooms (hypoxia and an offensive odor) are a serious ecosystem disasters that have occurred in some large eutrophic shallow lakes in China. In this study, we investigated two separate black blooms that were induced by Potamogeton crispus in Lake Taihu, China. The main physical and chemical characteristics, including color- and odor-related substances, of the black blooms were analyzed. The black blooms were characterized by low dissolved oxygen concentration (close to 0 mg/L), low oxidation-reduction potential, and relatively low pH of overlying water. Notably higher Fe2+ and sigmaS(2-) were found in the black-bloom waters than in waters not affected by black blooms. The black color of the water may be attributable to the high concentration of these elements, as black FeS was considered to be the main substance causing the black color of blooms in freshwater lakes. Volatile organic sulfur compounds, including dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide, were very abundant in the black-bloom waters. The massive anoxic degradation of dead Potamogeton crispus plants released dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide, which were the main odor-causing compounds in the black blooms. The black blooms also induced an increase in ammonium nitrogen and soluble reactive phosphorus levels in the overlying waters. This extreme phenomenon not only heavily influenced the original lake ecosystem but also greatly changed the cycling of Fe, S, and nutrients in the water column.

Influence of chironomid larvae on oxygen and nitrogen fluxes across the sediment-water interface (Lake Taihu, China).

The microscale distribution of oxygen, the nitrogen flux and the denitrification rates in sediment inhabited by chironomid larvae (Tanypus chinensis) were measured in eutrophic Lake Taihu, China. The presence of the chironomids in the sediment increased the oxygen diffusional flux from 10.4 +/- 1.4 to 12.7 +/- 2.5 mmol O2/(m2 x day). The burrows of the larvae represented "hot spots" and strongly influenced the nitrogen cycles and diagenetic activity in the sediment. The results indicate that the bioturbation effects of Tanypus chinensis chironomid larvae increased the capacity of the sediment as a sink for nitrate and a source for ammonium. Nitrate influx and ammonium outflux were increased 8.8 and 1.7 times, respectively. Under bioturbation, the amount of nitrate consumed was greater than the amount of ammonium released. The total denitrification rate was also enhanced from 0.76 +/- 0.34 to 5.50 +/- 1.30 mmol N/(m2 x day). The net effect was that the bioturbated sediments acted as a net sink for inorganic nitrogen under direct and indirect bioturbation effects compared to the control.

Effects of sludge dredging on the prevention and control of algae-caused black bloom in Taihu Lake, China.

Algae-caused black bloom (also known as black water agglomerate) has recently become a critical problem in some Chinese lakes. It has been suggested that the occurrence of algae-caused black bloom was caused by the cooperation of nutrient-rich sediment with dead algae, and sludge dredging was adopted to control black bloom in some lakes of China. In this article, based on the simulation of black bloom using a Y-shape apparatus for modeling natural conditions, both un-dredged and dredged sites in three areas of Taihu-Lake, China were studied to estimate the effects of dredging on the prevention and control of black bloom. During the experiment, drained algae were added to all six sites as an additional organic load; subsequently, the dissolved oxygen decreased rapidly, dropping to 0 mg/L at the sediment-water interface. Black bloom did not occur in the dredged sites of Moon Bay and Nan Quan, whereas all three un-dredged sites at Fudu Port, Moon Bay and Nan Quan experienced black bloom. Black bloom also occurred at the dredged site of Fudu Port one day later than at the other sites, and the odor and color were lighter than at the other locations. The color and odor of the black water mainly result from the presence of sulfides such as metal sulfides and hydrogen sulfide, among other chemicals, under reductive conditions. The color and odor of the water, together with the high concentrations of nutrients, were mainly caused by the decomposition of the algae and the presence of nutrient-rich sediment. Overall, the removal of the nutrient-rich sediment by dredging can prevent the occurrence and control the degree of algae-caused black bloom in Taihu Lake.

Effects of physical and chemical characteristics of surface sediments in the formation of shallow lake algae-induced black bloom.

Surface sediments are closely related to lake black blooms. The dissolved oxygen (DO) distribution and its penetration depth in surface sediments as well as the migration and transformation of redox sensitive elements such as Fe and S at the sediment-water interface are important factors that could influence the formation of the black bloom. In this study, dredged and undredged sediment cores with different surface properties were used to simulate black blooms in the laboratory. The Micro Profiling System was employed to explore features of the DO and sigmaH2S distribution at the sediment-water interface. Physical and chemical characteristics in sediments and pore waters were also analyzed. The results showed that sediment dredging effectively suppressed the black blooms. In the undredged treatment, DO penetration depth was only 50 microm. Fe(2+) concentrations, sigmaH2S concentrations, and sigmaH2S production rates were remarkably higher in surface sediments and pore waters compared to control and dredged treatments. Furthermore, depletion of DO and accumulation of Fe(2+) and sigmaH2S in surface sediments and pore waters provided favorable redox environments and necessary material sources for the blooms. The study results proved that physical and chemical characteristics in surface sediments are important factors in the formation of the black bloom, and could provide scientific guidance for emergency treatment and long-term pre-control of black blooms.

[Black water bloom induced by different types of organic matters and forming mechanisms of major odorous compounds].

Self-made glass reactors were employed to study the occurrence of black water bloom induced by different types of organic matters, to clarify the precursor of volatile organic sulfur compounds (VOSCs), and then to preliminarily study its degradation mechanisms under laboratory-controlled conditions. Our research indicated that provided organic matrix were as high as 1.0 g x L(-1), all organic matters could blacken the lake water regardless of sulfur appearance or not. However, compared with sulfur-free compounds that took more than 13 d to blacken the water, sulfur containing materials could accelerate the occurrence of black color to 7-13 d and increase the water chromaticity to above 410 which causing offensive odor consisted chiefly of DMDS, DMTS and DMTeS. Based on the function of methionine on the production of VOSCs, methionine was identified to be the precursors of VOSCs. Methionine was readily broke down by sulfate-reducing bacteria (SRB) (also other bacteria) (at 95% with the duration of 35 d) to produce hydrogen sulfide, methanethiol, and dominantly dimethylpolysulfides such as DMDS, DMTS and DMTeS. And the occurrence of black color had been advanced from 13 d to 8 d. Methanogenic bacteria slightly inhibited the degradation of methionine and reduced the evolution of sulfide. Therefore, the addition of methanogenic bacteria inhibitor set the formation of black color ahead by 1 d. Methionine was also degraded by nonbiodegradation, but it was a secondary pathway and cannot completely degrade methionine to blacken the water.