Recently, fossil fuel depletion and global warming have become serious problems in the world. In order to solve these problems, renewable energy has attracted much attention. Here, a microalga, Euglena gracilis (E.gracilis), was focused on as a renewable biomass energy source. In our idea, E. gracilis biomass produced using nutrients in wastewater is mixed with sewage sludge, and anaerobically digested for methane recovery. It is considered that microorganisms and suspended solids in wastewater may have a negative impact against the growth of E. gracilis. Accordingly, their effect on the growth of E. gracilis was discussed in this research. Three types of culture media, supernatant fluid of wastewater, suspended solids-free wastewater, and suspended solids and microorganisms-free wastewater, were used for the cultivation test. The culturing conditions were a temperature of 25°C and photosynthetically active radiation of 98.2 μmol/(m2•s). As a result, E. gracilis was able to increase in wastewater, though both microorganisms and suspended solids gave a negative influence. Since the negative effect of suspended solids was stronger than that of microorganisms, an introduction of a pre-removal process of suspended solids would be favored for the microalgal biomass production in wastewater.
Treated water disposed from an alternative wastewater treatment system, named johkasou, contains several contaminants that may affect the quality of the local water environment. Thus, the evaluation of water quality, along with sediment content, may provide quantitative information about the effects of johkasou effluent in the open channels. Here, the physicochemical and microbial parameters were comprehensively examined in both the water and sediments of a johkasou drainage channel and open channels. Throughout the 3-year study period, the concentrations of physicochemical parameters were lower in the open channels compared to the johkasou drainage channel because of the high mixing ratio of the flow rate between the two channels. However, microbial parameters were consistently high in both the water and sediments of open channels. Microbial concentrations were not significantly different between upstream and downstream channels in any season, except for Escherichia coli (E. coli) in winter (the concentrations of which increased in the downstream channel that received johkasou effluent). Heterotrophic plate count bacteria and E. coli were positively correlated between water and sediments, indicating that microbial indicators may interact with the water and sediments in open channels.
Microbial fuel cells (MFCs) are devices that are expected to be applied to the recovery of electric energy from wastewater. We have recently demonstrated that cassette-electrode MFCs (CE-MFCs) are useful for the treatment of wastewater. A concern about CE-MFCs is however relatively low columbic efficiency that may be caused by oxygen contamination from water surfaces. In the present study, floating boards were installed at the surface of water for minimizing oxygen diffusion from the air, and their effects on organics removal, electricity generation and microbial communities were analyzed. It was found that the installation of floating boards allowed an average of 10% increases in Columbic efficiency, while organic removal efficiency remained over 80%. The improved electricity generation was associated with changes in microbial communities as analyzed by denaturing gradient gel electrophoresis of 16S rRNA-gene amplicons. These results suggest the utility of floating boards for improving electricity generation in CE-MFCs used for wastewater treatment.
An urban tidal river network is one of the most difficult targets to simulate the flow and water quality in various kinds of water areas because the model must simulate both the vertical feature of the intrusion of sea water and the horizontal feature of water quality that is affected by human activities. In this paper, we determine the applicability of a three-dimensional flow and water quality model when reproducing the process of water with high concentrations of nitrogen, phosphorus and other constituents flowing through an urban tidal river network. We applied a three-dimensional model to Neya River, its tributaries and its downstream rivers in Osaka. The model can simulate well the vertical stratification of temperature and salinity near three river mouths, the mixing process of two different sources of water originating from Yodo River, and Neya River and its tributaries, the longitudinal profiles of chemical oxygen demand (COD), dissolved oxygen (DO), total nitrogen and phosphorus. Calculated water levels in the upstream area of Neya River system, however, are not coincident with the observations. A 3D water quality model, which is a potent tool in ocean and lakes, proved to be a versatile enough tool to simulate complicated and tidal urban river networks.
Radiocesium has been deposited after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident and affix to the soils inland. The soils flowed into Lake Teganuma through Ohori River. Field observation was carried out to quantify radiocesium, associated with sediments, transported around Lake Teganuma and Ohori River from October 2011 to March 2014. We quantified the sediment transported to Ohori River and found that the total radiocesium stock in Ohori River was 2,190 MBq which was mostly attached to the fine-grained sediment of silt in 2012. The radiocesium, transported as a suspended sediment in the Ohori River watershed, was approximately 10 percent of the total fallout of 2 TBq. The total flux of radiocesium in Ohori River were 3,800 MBq in 2012 and reduced to 6.65 MBq in 2013. These results denote that most of the radiocesium-polluted sediments were transported downstream in 2011 and sharply decreased after 2012. When a similar study was conducted in Abukuma River, only 1% of the total fallout was calculated indicating transport was 10 times that of the Abukuma River. This is attributed to be urbanization of Teganuma basin in comparison to the Abukuma basin, thus more cesium were transported in a shorter time period.
Sponge carrier media can be effectively used to upgrade existing activated sludge plants to augment nitrification. With an internal anoxic zone and ambient oxic conditions, it can perform simultaneous nitrification and denitrification (SND). In order to accurately predict SND, it is essential to construct a proper mass transfer model. A simple model for the simulation of bio-clogging in sponge carrier media using multiple biofilm reactor compartments was constructed. The relation between pore diffusivity and porosity was developed which was based on a critical porosity for the transition from advection to diffusion in the pores of the sponges. By inclusion of heterotrophic organisms in the model, the pore diffusivity was calibrated with experiments of denitrifying sponges. In order to simulate SND, the model was extended using slow-growing ammonia-oxidizing organisms (AOO) and nitrite-oxidizing organisms (NOO). At the effluent, a clarifier was modelled with a defined sludge wastage rate. At low sludge recycle fractions, the heterotrophs were dominant inside the sponge and outcompeted AOO and NOO. Higher sludge recycle fractions resulted in the presence of AOO and NOO inside the sponge which made it possible for SND via nitrate or short cut SND via nitrite.
To find taxonomically novel methanogenic archaea, a clone analysis targeting mcrA gene (a functional molecular marker of methanogenic archaea) was conducted for four anaerobic granular sludges. Several mcrA gene phylotypes were clearly different from those of other groups of known methanogens. These were found to belong to an unidentified group called as MCR-2b group. Comparative phylogenetic analysis of deduced amino acid of McrA and 16S rRNA gene sequences revealed that the MCR2-b McrA group is possibly derived from a novel methanogen group; the 16S rRNA gene sequences have been classified into an uncultured archaeal group WCHA1-57. The result suggests that WCHA1-57 archaeal group may represent a putative new order of the methanogenic archaeal group that contributes to methane production in anaerobic digesters.
The genotoxicity of Japanese tap water was investigated using the umu test in order to clarify the relative and absolute genotoxic levels. Samples were collected at 25 sites in Japan and the umu test was carried out with concentrated solutions. The values of genotoxic activity (GA) varied significantly from less than 72 to 670 ng 4NQO/L depending on the site location and/or sampling period. Typical GA value among the tested tap water samples was around 200 ng 4NQO/L. According to a roughly estimated safety level, it was shown that the genotoxicity level of the tested tap water was not negligible. A comparison of the results of the present study with those of a previous investigation using Ames mutagenicity test indicates that the genotoxic level of Japanese tap water did not decrease significantly between the two investigations. In addition, it was shown that there was a weak positive correlation between the genotoxicity of the tap water and the value of the total organic carbon content.