In paddy fields, the drainage canal sediments can act as a pollutant source without proper management. The objective of this study is to evaluate the role of the sediments on the nitrogen (N) and organic carbon (C) concentrations in drainage water in paddy fields. Drainage canal sediments were sampled at three paddy-field districts around Lake Biwa and incubated for 28 days. Results of the experiments confirmed that the drainage canal sediments had enough potential as N and C sources. The sedimentary total N and C concentrations were 1.95 – 3.38 and 21.1 – 32.8 mg/kg, respectively. Nitrogen in the sediments existed mainly in the organic state. During the incubation experiment, large amounts of NH4-N were released from the sediments. Fluorescence peaks of humic-like substance had strong correlation with dissolved organic N and C in the overlying water on the incubated sediments. It can be concluded that large amounts of organic N in the sediments can be a long-term NH4-N source for the overlying drainage water through decomposition and release.
Polychlorinated terphenyls (PCTs) are a class of polyhalogenated compounds previously used for similar purposes as polychlorinated biphenyls (PCBs). In this study, we assessed environmental concentrations and congener profiles of PCTs in sediment core samples collected from Furuayase River, Japan. The concentrations of PCT in the sediment samples were between 300 and 3,100 ng/g-dry and were inversely correlated to the collection depth of the samples. The PCTs’ homologue profiles were similar but their congener profiles differed with varying sampling depth, particularly for nonachloroterphenyl. We compared PCT congener profiles of the sediment samples with those of an industrial sludge sample from a chemical factory located in Furuayase River basin, and with a technical-grade PCT standard: the chromatograms of the sediment samples were equivalent to the sum of the chromatograms of the industrial sludge and PCT standard. The concentration of PCTs originating from the industrial sludge was strongly correlated with that of 1,3,7,8+1,3,7,9-tetrachlorodibenzofuran (1,3,7,8+1,3,7,9-TeCDF) in sediment. We previously reported the reaction pathway which could generate 1,3,7,8+1,3,7,9-TeCDF. According to these results, we concluded that PCTs with a specific congener profile were also unintentionally generated with same pathway, and that these PCTs contaminated the sediment of Furuayase River.
Agricultural farms are considered to be non-point sources of phosphorus (P) loads to rivers and lakes. Sediment can act as a source or sink of P under different environmental conditions. Inorganic P is the major form, and is a very useful indicator to evaluate the potential release of P in sediment. This study aimed to evaluate the effects of pH and aerobic/anaerobic conditions on P release from sediment by the changes of P fractions before and after incubation. Sediment samples were collected from a drainage ditch of a livestock farm on reclaimed land in Kasaoka Bay, Japan. Experiments were conducted in a 200-mL glass serum bottle with 8 – 10 g fresh sediment and 100 mL of 0.02 M KCl solution, adjusted to pH 4, 7, or 10, and incubated under aerobic or anaerobic conditions. Phosphorus was released under both aerobic and anaerobic conditions until day 5. The amount of P released under anaerobic conditions increased continuously towards day 10 while that under aerobic conditions decreased after day 5 to the end of experiment (p < 0.05). Thus, sediment acted as a sink of P under aerobic conditions and as a source of P under anaerobic conditions. Sediment fractionations indicated that loosely sorbed P (loosely-P) and iron-bound P (Fe-P) fractions were the main sources of P released to the overlying water. The amount of P released from sediment at acidic pH was higher than that at neutral or alkaline pH under anaerobic conditions (p < 0.05). However, under aerobic conditions, the amount of P release was higher at alkaline pH than that at acidic or neutral pH (p < 0.05).
Anaerobic degradation of polyhydroxyalkanoate (PHA) accumulated in activated sludge was studied to estimate its stability during sludge thickening process. Activated sludge was incubated with acetate only or acetate and propionate under aerobic condition to allow microorganisms to accumulate PHA. After the aerobic incubation, PHA-accumulated activated sludge was incubated anaerobically at 20°C, 30°C and 37°C. At 20°C for the whole incubation period of one week and at 30°C for initial couple of days, degradation of PHA was slow. These results suggested that PHA can stably be retained during sludge thickening. On the other hand, at 37°C, PHA was easily converted to volatile fatty acids (VFA) and was expected to be utilized as substrate for methane gas generation, if the thickened sludge is to be treated by anaerobic digestion. Accelerations of PHA degradation were observed during incubation, and as an explanation for it, formation of adenosine triphosphate in the fermentation of PHA to VFA was proposed. Some part of the PHA remained undegraded. As one of the keys to understand different degradation patterns of PHA, their location, whether they are inside or outside cells, was suggested.
Accumulation of trace metals in coastal ecosystem has become a prodigious problem in Bangladesh. This study was conducted to determine seven trace metals concentration (Cr, Ni, Cu, Zn, As, Cd and Pb) in water and sediment samples collected from coastal sites of Bangladesh. Water of Cox’s Bazar hatchery site showed the highest levels of Zn (1,390 µg/L), Cu (510 µg/L) and Pb (109 µg/L), which attributed to huge discharge of different chemical compounds from the hatcheries and fish processing industries. Trace metals in water samples were in the range of Cr (2.6 − 15.3 µg/L), Ni (5.1 − 77.5 µg/L), Cu (10.2 − 510 µg/L), Zn (5.0 − 1,390 µg/L), As (2.1 − 13.3 µg/L), Cd (0.006 − 0.09 µg/L), Pb (0.4 − 109 µg/L), respectively. The elevated concentration of As (13.3 µg/L) was observed in water sample of Chittagong ship breaking area. Some metals (Zn, Cu, Pb and As) in water exceeded the international quality guidelines. Sediment samples of Chittagong ship breaking area showed the highest level of Cr (56 mg/kg dw), Ni (37 mg/kg dw), Cu (28 mg/kg dw) and Pb (41 mg/kg dw) which exceeded the Canadian Sediment Quality Guidelines. The elevated level of trace metals in this Bangladeshi coastal ecosystem should not be ignored and immediate control measure is recommended.
Sepiolite is considered as a selective adsorbent to remove ammonium from wastewater. However, ammonium adsorption capacity under different pretreatment conditions has not been well documented. In this study, batch experiments were performed to investigate the ammonium adsorption capacity of low-strength wastewater by modified sepiolite. Sepiolite was conditioned with an acid, HCl, HNO3 or H2SO4, then thermally treated. Results showed that the modification process enhanced ammonium adsorption and sepiolite treated with 1N HNO3 followed by calcination at 400°C exhibited superior adsorption property. Adsorption capacity increased with contact time and initial concentration but decreased with increasing temperature and sepiolite dosage. A maximum adsorption capacity of 143 mg/g was achieved at pH 8 and a dosage of 1/70 g sepiolite/mL solution. In contrast, an increase of dosage from 1/70 to 1/10 improved the ammonium adsorption efficiency from 45 to 75%. Overall, the ammonium adsorption followed the pseudo-second-order kinetics. The equilibrium data were best fitted with Redlich Peterson isotherm. Through thermodynamic analysis, the ammonium adsorption was not spontaneous with sepiolite dosage of 1/70. However, the spontaneity of adsorption was feasible with ΔG° of −2.5 kJ/mol at 25°C and a dosage of 1/10. This study provided a potential pathway for ammonium removal during wastewater treatment.
The investigations were carried out in 35 sites of 4 tidal flats located in Aki Nada of the Seto Inland Sea, Japan, from May 2012 until July 2012 to clarify the relationship between sediment characteristics and microbial community structure. This study focused on microbial community structure and particle size distribution. Microbial community structure was analyzed by a quinone profile. Cluster analysis and principal component analysis of sediments were conducted using particle size distribution, pH, ignition loss (IL), and water content. The sediments were classified into 6 groups by the physicochemical characteristics of sediments, mainly very coarse sand and silt+clay. The most dominant ubiquinone species in Clusters 1–5 and Cluster 6 were UQ-8 and UQ-10, respectively. Cluster 6 was the highest in silt+clay content. Cluster 4 and 6 with high IL included MK-7 (H6). Distribution of microbial community structure in sediments of tidal flats can be explained by the classified physicochemical characteristics of sediments. These results contribute to our understanding of the microbial ecosystem in Aki Nada.
Livestock manure is one of main pollution reservoirs of antibiotic-resistant bacteria (ARBs) due to excessive use of veterinary antibiotics. For preventing the environmental spread, an efficient process is required to reduce ARBs in livestock manure. In this work, we investigated the survival of ARB during mesophilic anaerobic digestion of dairy cattle manure. Effects of seed sludge and the antibiotic class were investigated for reduction of ARBs by batch digestion tests. The numbers of all ARBs were 6.34×104 to 2.08×106 before anaerobic digestion. The numbers of oxytetracycline, chlortetracycline, gentamicin and kanamycin -resistant bacteria decreased close to the detection limit after 20-day anaerobic digestion. However, reduction effects of cefazolin and streptomycin -resistant bacteria were small. The seed sludge had little influence on the survival of ARBs during the anaerobic digestion. The results showed that the ARB reduction effect was influenced by the types of antibiotics, and mostly not by seed sludge.
Biological 1,4-dioxane removal performance using newly isolated Pseudonocardia sp. D17, which can utilize 1,4-dioxane as the sole carbon source, was evaluated. A low level of influent 1,4-dioxane, at 5–50 mg/L, was treated to meet the Japanese effluent standard of 0.5 mg/L. The gel entrapment technique was used for immobilization of Pseudonocardia sp. D17 so that it is not washed out from the bioreactor under a short hydraulic retention time. Consequently, an average effluent 1,4-dioxane concentration of 0.49 mg/L was achieved at a loading rate of 0.096 kg dioxane/(m3 · d) with an influent 1,4-dioxane concentration of 50 mg/L. The startup of the bioreactor was observed at 25°C within 2 weeks. Moreover, the effluent 1,4-dioxane concentration of 0.38 mg/L on an average was confirmed at a loading rate of 0.060 kg dioxane/(m3 · d), even though the operating temperature was 15°C. The temperature effect on 1,4-dioxane removal activity was characterized on the batch experiment. The maximum 1,4-dioxane removal activity was observed at 33.9°C. Moreover, 1,4-dioxane removal activity was observed even at 7.4°C, although that was decreased to 27% compared with that at 25°C. The activation energy for 1,4-dioxane removal by Pseudonocardia sp. D17, representing the temperature dependency, was calculated as 51.9 kJ/mol.
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