Twenty-eight polychlorinated biphenyls (PCBs) in surface sediments collected from Dianchi Lake were analyzed. The objective was to provide a better understanding of the contamination levels, distributions, possible sources and environmental risk of PCBs. In the aquatic environment, PCBs were found ubiquitously. The concentrations of the total 28 PCBs ranged from 160 to 78,200 ng kg–1 dry weight. The contamination levels and distributions of PCBs among the samples were obviously different. The concentrations of PCBs decreased with the increase in distance from the sampling sites which were located in the northwest of Dianchi basin. Inflowing rivers carrying a large amount of untreated wastewater from industries were the major contributors to the high residual concentrations of PCBs. The main components of PCBs were tetrachlorobiphenyl (9.3 − 63.6%, mean: 30.8%), trichlorobiphenyl (8.7 − 49.3%, mean: 21.0%), hexachlorobiphenyl (2.7 − 36.4%, mean: 17.7%) and pentachlorobiphenyl (0 − 52.3%, mean: 14.9%). The distribution of PCBs was subject to the rivers flowing into the lake. Less chlorinated Aroclor mixtures containing 3 − 6 chlorinated atoms were the dominant components of PCBs. The northwest part of Dianchi Lake and its adjacent rivers had high contamination levels of PCBs, which could pose a potential risk to aquatic organisms.
In Ouagadougou, Burkina Faso, the scarcity of freshwater resources is a critical problem and the reuse of low quality water in urban agriculture is increasing. This study compares the parasitological characteristics of wastewater at the inlet and outlet of a wastewater treatment plant (WWTP) and inside an open channel which conveys the treated wastewater to a garden site situated downstream of the WWTP. Non-viable parasite cysts or eggs were found at the inlet and outlet of the WWTP; in contrast, parasite cysts and eggs were found at the open channel sampling point with a high percentage of viability. Additionally, an epidemiological study was performed that demonstrates that open defecation practiced by highly infected people inside the garden site caused recontamination of the treated wastewater. Therefore, to reuse treated wastewater and avoid new contamination, a safety plan is necessary. The safety plan should particularly focus on offering alternatives to open defecation by installing toilets at the garden site.
In drinking water, weak but toxic continuous exposure must be assumed throughout life. Human normal fibroblast cell, TIG-1–40, was applied to bioassay to evaluate the chronic toxicity of drinking water to humans in this study. TIG-1–40 was cultured with the culture media prepared with the treated water by membrane bioreactor (MBR) and model contaminated water (0.01 mg/L arsenic (As)) which is As standard for drinking water in WHO (World Health Organization). Linear approximate curve was drawn on the cell growth graph and the relative growth rate calculated from its gradient was able to evaluate cytotoxicity reproducibly. The MBR-treated water showed that the relative growth rate was 1.17 times of control (ultrapure water) and cytotoxicity was not detected. On the other hand, 0.01 mg/L As solution as WHO standard showed that the relative growth rate was 0.82 times. Therefore, it was suggested that there is no influence on human body when the relative growth rate is around 0.8 times.
The graphite powder was added to a microbial fuel cell (MFC) that uses soil to decrease the internal resistance and increase the electric power and electric charge (ampere hour: Ah). The effect of adding the graphite powder to soil MFC is evaluated by experiment and simulation using mathematical models. In this experiment, the total weight of the reddish granular soil and the graphite powder was 1000 g, and ratios of the graphite were set to five values between 0% and 20% by weight. The grain size of the soil was between 3 and 8 mm. The diameter of electrode was 9 cm. The initial chemical oxygen demand (COD) of synthetic wastewater was 1400 mg/L. As a result, the amount of Ah was maximized when 10% of the graphite was mixed. When the amount of the graphite increased, the internal resistance decreased; however, consumption of COD decreased and the microbial reaction decreased. This might be because the graphite covers the surface of the soil, and it disturbs the adsorption of the soil and decreases the biofilms. Therefore, a suitable proportion of the graphite exists, and it was approximately 10% in this experiment.
Wastewater irrigation using sewage and water from polluted sources is widespread in Kathmandu Valley, Nepal. Data on the prevalence of pathogens in irrigation sources are important for assessing the health risks for both farmers and consumers. In this study, 13 and 15 water samples were collected during the rainy (September 2014) and dry (April 2015) seasons, respectively, from irrigation sources [river water (n = 17), sewage (n = 5), pond water (n = 3), canal water (n = 1), and effluent of a wastewater treatment plant (WWTP; n = 2)] in Kathmandu Valley. Based on fluorescence microscopy, all the analyzed samples (n = 19) tested positive for Giardia, whereas 68% tested positive for Cryptosporidium. In addition, indicator bacteria (Escherichia coli and total coliforms) were detected in all samples (n = 28), with significantly higher concentrations during the dry season than during the rainy season (t-test, p < 0.05). Indicator bacteria and protozoan concentrations were abundant in sewage and river water samples and comparatively less in the remaining samples. Positive correlations between indicator bacteria and protozoa concentrations suggested that E. coli and total coliforms could be considered as rough indicators of protozoa contamination of wastewater irrigation sources.
Microwave pretreatment was applied to highly concentrated dewatered sludge produced from an oxidation ditch process (OD sludge) to improve its degradation and biogas production in mesophilic anaerobic digestion. In a batch experiment using methane fermentation, the biogas production potential of OD sludge was increased after microwave irradiation. The increase in the biogas potential depended on the irradiation period and the temperature. Continuous digestion of the pretreated OD sludge was carried out in mesophilic conditions using a laboratory-scale digester at 25 days of hydraulic retention time (HRT). Although the biogas yield in the control digester was 0.12 NL/g-total solids (TS), that fed with OD sludge pretreated with max 100 W of irradiation at 80°C for 60 min was 0.15 NL/g-TS. Subsequently, dewatered OD sludge was pretreated by a novel continuous microwave irradiation device at 400 W for 20 min and fed into a pilot-scale co-digester with six kinds of waste biomass. The biogas yield of the reactor was increased from 0.25 NL/g-TS to 0.28 NL/g-TS. Assuming that the biogas yield of each co-digesting biomass was constant, the biogas yield of the OD sludge was estimated to increase by 42%.
We have determined halogenated polycyclic aromatic hydrocarbons (XPAHs) in 40 samples of surface soil (n = 32) and river sediment (n = 8) collected around the E-waste recycling area in Bui Dau, northern Vietnam. Thirty-one target compounds including 21 chlorinated PAHs (ClPAHs) and 10 brominated PAHs (BrPAHs) were quantified by gas chromatography-high resolution mass spectrometry (HRGC-HRMS). The highest concentrations of XPAHs in surface soils (3,960 pg/g dry wt) and river sediments (3,930 pg/g dry wt) were detected from samples near an open burning site and an E-waste recycling workshop. Composition ratios of BrPAHs to total XPAHs in this study were higher than those in fly ash of waste incinerators (12% and 29%), because E-waste in this study contained a large amount of brominated flame retardants (BFRs). These results suggested that XPAHs occurred in E-waste recycling activities and they contaminated the surrounding soil and sediment. A large number of peaks of unidentified isomers of XPAHs, such as XnPhe/Ant (n = 1 − 4) were observed based on the isotope patterns of molecular ions [M, M+2, M+4] by HRGC-HRMS analyses. These unidentified isomers should be an important factor in the risk assessment for XPAHs.
The objective of present research was to clarify the effects of environment conditions of oxygen on FTOHs biodegradation property. The lab-scale batch tests of 8:2 FTOH biodegradation under aerobic/anoxic/anaerobic conditions were conducted with acclimated activated sludge collected from an industrial wastewater treatment plant. The results revealed that 8:2 FTOH biodegradation property differed in aerobic/anoxic/anaerobic conditions. The first-order rate constants of 8:2 FTOH were 6.10 × 10−2, 1.24 × 10−2 and 5.81 × 10−3 [L·g-SS–1·h–1] under aerobic/anoxic/anaerobic conditions, respectively. Within 24 hours, the transformed PFCAs (C4 − C9) moles to the applied 8:2 FTOH were 11.12%, 0.46% and 3.39% under aerobic/anoxic/anaerobic conditions, respectively. Under aerobic condition, PFCAs were remarkably generated. The increased moles of PFOA and PFHpA occupied the applied 8:2 FTOH as 7.87% and 1.29%, respectively. Moreover, the increasing tendency of PFCAs was maintained within 24 hours. The anoxic and anaerobic generation of PFCAs, besides PFOA, were not significant.
Internal loading of phosphorus (P) in drainage ditches may be sufficient to enhance eutrophication in aquatic systems under certain conditions. This study aimed to determine the effects of dissolved oxygen (DO) concentrations on P flux across the sediment-water interface. The study was conducted in a drainage ditch that receives discharge from livestock farms. The diffusion in situ was estimated according to Fick’s first law equation using P concentrations in pore water and the overlying water. The overlying water and intact sediment cores were taken at the same location and time and incubated under anaerobic or aerobic conditions to determine the effects of DO on P fluxes based on the time-course of changes of P concentrations in water columns for 21 days in the laboratory. The diffusion of P across the sediment-water interface in the field was 9.79 ± 0.60 mg/(m2 day) from sediment to the overlying water. In the laboratory, the fluxes of P were 1.76 ± 0.48 mg/(m2 day) from sediment to overlying water under anaerobic conditions and 1.57 ± 1.05 mg/(m2 day) from water into sediment under aerobic conditions. The upward diffusion of P under anaerobic conditions may be related to the reduction of iron-bound P. These results highlighted the role of oxygen in regulating P diffusion at the sediment-water interface. Accordingly, the low oxygen concentration in the drainage ditch was a reason for P release from sediment.
Use of the trickling filter is advantageous in the nitrification process as no mechanical aeration is required. Since all reactions are initiated on the wetted surface, as a consequence of linear velocity (LV), mass transfer through the surface area of the liquid film into the biofilm dictates the process performance. The relationship among LV, dissolved oxygen (DO) and reaction rate was obtained in a 24-L tower of 2.7 m height continuously fed with synthetic wastewater containing ammonia with the bulk pH maintained at 7.0 and air supplied at 20 L/min. By increasing the LV from 4 to 100 m/d the nitrogen oxidation rate (NOR) increased from 1.2 to 3.0 g-O2/L/d and the DO decreased from 8.5 to 4.5 mg-O2/L. When LV exceeded 100 m/d, the NOR was apparently at a maximum value of 3.0 g-O2/L/d and the DO recovered to 6.5 mg-O2/L. This response was used to construct a mathematical model where the kinetics of the biofilm were extracted based on measured parameters. The model can be used as a basis for scaling up the design of trickling filters for actual applications. Additionally, the energy consumption at the maximum NOR was estimated to be 53.1% to 87.3% less than that in the conventional activated sludge process.