Benzene and toluene often contaminate groundwater and pose serious threat to human health due to their high toxicity. Anaerobic degradation can be a cost-effective method but the degradation mechanism remains poorly understood. We established benzene- and/or toluene-degrading bacterial cultures under methanogenic conditions from non-contaminated soil to compare their behaviour during and after enrichment. Benzene and toluene degradation rates increased during incubation, and this fact implied enrichment and/or adaptation of benzene/toluene-degrading microorganisms. The abundance of Hasda-A and/or related bacteria, defined by a primer set targeting uncultured putative benzene-degrading Desulfobacterales bacterium Hasda-A, increased only in the enrichments fed with benzene. This result indicated that Hasda-A and/or related bacteria played an important role on benzene degradation. Furthermore, to investigate the biodegradation range of benzene and toluene degraders, we added both benzene and toluene to all cultures. Toluene or benzene was also degraded by cultures that have been fed with benzene or toluene, respectively. The culture which was originally fed only with toluene had smaller benzene degradation rate than the culture fed with benzene. Similar result was obtained for toluene degradation in cultures fed with toluene or benzene. These data indicate that different microorganisms were likely involved in benzene and toluene degradation in our enrichments.
In recent years, heavy rainfall over 50 mm/h and heavy rainfall concentrated into short time span on the order of 10 min have occurred more frequently in Japan, owing to the effects of phenomena such as climate change. This report describes the result of simulation using simulated drainage zones to examine the specific countermeasures that are suitable for each district. We consider it important to increase the inundation control quantity across the entire area (1) using peak reduction storage infrastructure for areas at the branch line drainage zone level and for short-duration heavy rainfall, and (2) using a combination of inundation countermeasures including downflow infrastructure and storage infrastructure to upgrade the entire runoff area for heavy rainfall that continues for a long duration in areas at the main line drainage zone level. This paper also reports on progress in collecting case examples on facilities that utilized stormwater in each local government. These case examples are being collected as a resource for promoting the improvement of stormwater storage infrastructure and the effective utilization of water resources in the future.
Activated sludge microbial communities of 12 membrane bioreactors (MBRs) treating domestic wastewater were characterized in terms of their bacterial phylogenic composition and organic metabolism using eubacterial 16S rRNA gene-based terminal-restriction fragment length polymorphism (T-RFLP) analysis and carbon-utilization tests (Biolog assay). The phylogenic microbial structure of MBR sludges differed considerably among samples, depending neither on influent characteristics nor on operational modes and conditions. Comparison of the microbial community structures of the 12 MBRs and 11 conventional processes characterized in a previous study indicated that MBRs and the conventional processes differ considerably in terms of phylogenic structure. Also, dominant bacteria in MBRs differed considerably from each other, although those in the conventional processes were similar. In contrast, the carbon-utilization profile of activated sludge samples of 8 among 12 MBRs and all conventional processes tested in the previous study were mutually similar, indicating that activated sludge communities possess similar biodegradation potential against organic pollutants even if the phylogenetic bacterial composition differs. Results also demonstrated that some MBR sludge samples have unique carbon-utilization profiles, suggesting that MBRs enrich bacterial populations with unique metabolic activity.
Trace metal contamination is a major problem globally, especially in developing countries. In this study, the levels of trace metals (Cr, Ni, Cu, As, Cd, and Pb) in water and sediment of some peripheral rivers of Dhaka City, Bangladesh, were investigated. Huge amount of municipal wastes, industrial effluents and agricultural runoff from the periphery of Dhaka City notably are dumped to these rivers. Most of the effluents channeled into these rivers are not treated. Sediment and water samples were collected from selected stations along the various rivers in winter and summer seasons and analyzed for the trace metals of concern. Considering the sampling sites, the decreasing order of total metal concentration in water samples were Cr > Cu > As > Ni > Pb > Cd and in sediment were Cr > Pb > Ni > Cu > As > Cd. Total concentrations of Cr, As and Pb in the water samples were higher than WHO guidelines for drinking water quality for some sites. Geoaccumulation index (Igeo) revealed high values of Cd for all the stations. The extent of metal pollution in the rivers around Dhaka City implied that the condition is much frightening and probably severely affecting the aquatic ecology of the rivers.
Liquid chromatography-triple quadrupole mass spectrometer (LC/MS/MS) using electrospray ionization (ESI) is a commonly used analytical method for environmental safety even though there are limitations to its robustness. One of the limitations, the matrix effect (ME), is defined as the ionization suppression/enhancement by the co-eluting residual component, which creates large uncertainties in quantification. The objective of this study is to address ME in the analysis of pesticides and their transformation products in water matrices. For a set of 164 environmental samples, which were preconcentrated by a solid-phase extraction, ME was estimated by spiking standard solution containing 27 target chemicals. As a result, ionization suppression occurred in most of the analytes/matrix pairs. Variability in ME was also observed and the variability among analytes was derived from co-eluting matrix component rather than the physicochemical property of each analyte. To overcome ME, the preconcentrated samples were successively diluted and the effective dilution factor was determined. The variability among diluted samples was still observed and therefore ME needs to be confirmed in every sample for reliable quantification. Sample dilution worsens the limit of quantification; however, the limits in the method were maintained below 0.01 μg/L.
Bacterial diversity of the microbial consortia in a biological filtration pilot plant for the simultaneous removal of arsenic (As), iron (Fe) and manganese (Mn) from groundwater was analyzed. PCR-based denaturing gradient gel electrophoresis (DGGE) of bacterial 16S ribosomal RNA (rRNA) genes represented at least 6 dominant signals and many weak signals. Phylogenetic analysis using the nucleotide sequences of the 16S rRNA gene clone library constructed from the pilot plant sample showed the presence of the bacteria closely related to Gallionella and Leptothrix, which are supposed to be involved in the production of Fe and Mn oxides utilized for adsorbents of As in this system. On the other hand, aoxB gene was not detected, suggesting that arsenite-oxidizing bacterium would not be involved in the As removal of the pilot plant. These results indicated that the simultaneous removal of As, Fe and Mn from groundwater was conducted by the physicochemical sorption of As by the biogenic Fe and Mn oxides produced by the bacteria closely related to Gallionella and Leptothrix included in the microbial consortia of the pilot plant.
Many water quality conservation measures have been implemented in agricultural areas to reduce pollutant loading. However, controlling discharged drainage water enhances sedimentation of suspended solids in drainage canals in those areas. The sediment, which has high concentrations of nitrogen (N) and carbon (C), may release N and C and lower the effect of the conservation measures. In this study, we clarified the characteristics of N and C in the sediment in drainage canals. We have investigated paddy field districts around Lake Biwa and measured N and C contents in the sediment. We also conducted incubation experiment of the sediments sampled in two different paddy field districts. Changes in N and C fractions in the sediments and in the overlying water during the incubation period were analyzed. As a result, concentrations of total N and total organic C in the overlying water of the incubated sediment were respectively about two and three times those of drainage water measured at the study points. Total N flux was 33.0 - 41.1 mgN/m2/day and total organic C flux was 25.3 - 48.4 mgC/m2/day. It was indicated that the sediments had enough N and C for determining the water quality of drainage water.
Environmental monitoring of chemicals is important for risk evaluation. As almost all contaminants exist in water environments at very low concentration, appropriate concentration procedures are required. A nitrogen purge process has been used to concentrate extract containing various trace semi-volatile organic chemicals by combination with a solid-phase extraction. However, recovery loss is often caused depending on the purging conditions, and it decreases the reliability of the measurement. In this study, 166 chemicals of various physical properties were prepared and their recovery ratios were investigated under each condition. The recovery ratios in nitrogen purge were not necessarily determined by their physical properties, or overly influenced by the nitrogen purge volumetric flow rate. In contrast, the control of the solvent volume, which changes with the progress of the nitrogen purge concentration, was important in addition to the alternation of the final solvent from hexane to acetone, because the concentration of chemicals in the solvent was one of the key factors determining the recovery ratios in the nitrogen purge process. The variation of the recovery ratio was acceptably small under appropriately controlled conditions.
To make clear the necessity of vegetation in constructed wetland treating wastewater, the annual removal performances of BOD, TKN, TN and TP in planted and unplanted wetland for the first three years of operation were compared using a real-scale constructed wetland. It was common for both wetlands that the removal performance was improved significantly in the second year although its magnitude was different. There was no significant difference in the annual BOD removal performances for three years of operation between planted and unplanted wetland. However, the difference was confirmed for the annual TKN removal in the third year. On the other hand, it was in the second year that the significant difference was confirmed for TN removal while it was both in the second and third year for TP. The difference in removal performances between planted and unplanted wetland was also compared using cumulative probability distributions for influent and effluent water qualities during three years of operation. The results of this study proved the overall effect of vegetation on the treatment performance in constructed wetland without plant harvesting process as well as independent treatment performance of vegetation.
Nitrous oxide, which has 310 times the greenhouse effect of carbon dioxide, is known to be emitted from wastewater treatment processes. However, the state of emissions at actual plants and the mechanism of generation are not well understood, and measures to control emissions have not yet been established. Therefore, we investigated the generation of nitrous oxide at 10 plants with different treatment methods. We found high emissions from the conventional activated sludge process, but lower emissions from the membrane separation activated sludge process and nitrogen removal method with step feeding. In addition, molecular techniques such as denaturing gradient gel electrophoresis suggest that a wastewater treatment plant using an anaerobic/aerobic process produces high N2O emissions.
An easy and fast method for the determination of total iodine in environmental samples by cathodic stripping voltammetry combined with sodium-hydrochlorous-induced oxidation (NaClO oxidation) has been developed. Adequate conditions for NaClO oxidation of 40 - 50ºC over 2 h were determined, using three representative environmental samples (reference soil, seabed sediment, seaweed). By analyzing a mixture of thyroxin and a reference soil material, an overall recovery of > 97% for total iodine in the concentration range of 1 - 7 μmol/g was obtained. This method was compared with alkaline extraction and combustion methods for solid (reference soil, seabed sediments, seaweed, and filter) and aqueous environmental samples. Alkaline extraction exhibited lower recovery of iodine compared with the NaClO oxidation method, indicating insufficient extraction and/or interference on determination. Combustion method also showed lower iodine recovery for some samples, probably due to a trapping efficiency and incomplete combustion of organic matter.