Tsuyoshi Imai

A model for membrane bioreactor process based on the concept of formation and degradation of soluble microbial products.

A mathematical model of soluble microbial products (SMPs) formation-degradation was established based on the activated sludge model no. 1 and was applied to the membrane bioreactor process with high concentration of activated sludge under intermittent aerobic operational condition. The simulation results were in good agreement with the experimental data which indicated that the coefficients used in the model could successfully describe the treatment performance. The most advantage of this modified model over the conventional one was that the significant importance of SMP existence was demonstrated and the model provided an reasonable comprehension for SMP concept. The present study demonstrated that SMPs contributed most to the organic matter in the effluent, and the results coincided well with the observations of many other researchers.

Urbanization and subsurface environmental issues: An attempt at DPSIR model application in Asian cities

This paper synthesizes existing information and knowledge on subsurface environments to understand the major cause and effect relationships of subsurface environmental issues by using the DPSIR (Driving force-Pressure-Status-Impact-Response) approach as the framework of analysis. Description is given to the major subsurface environmental issues common among the selected Asian cities (Bangkok, Jakarta, Manila, Osaka, Seoul, Taipei and Tokyo), such as excessive groundwater abstraction, land subsidence and groundwater contamination. The DPSIR framework is used to analyze the issues and problems of subsurface in key stages and suggestions are made for additional indicators to improve our description of the stages of urban development for the future.

Start-up performances of dry anaerobic mesophilic and thermophilic digestions of organic solid wastes

Two dry anaerobic digestions of organic solid wastes were conducted for 6 weeks in a lab-scale batch experiment for investigating the start-up performances under mesophilic and thermophilic conditions. The enzymatic activities, i.e., beta-glucosidase, N-alpha-benzoyl-L-argininamide (BAA)-hydrolysing protease, urease and phosphatase activities were analysed. The BAA-hydrolysing protease activity during the first 2-3 weeks was low with low pH, but was enhanced later with the pH increase. beta-Glucosidase activity showed the lowest values in weeks 1-2, and recovered with the increase of BAA-hydrolysing protease activity. Acetic acid dominated most of the total VFAs in thermophilic digestion, while propionate and butyrate dominated in mesophilic digestion. Thermophilic digestion was confirmed more feasible for achieving better performance against misbalance, especially during the start-up period in a dry anaerobic digestion process.

Cyanide removal from cassava mill wastewater using Azotobactor vinelandii TISTR 1094 with mixed microorganisms in activated sludge treatment system

Cassava mill wastewater has a high organic and cyanide content and is an important economic product of traditional and rural low technology agro-industry in many parts of the world. However, the wastewater is toxic and can pose serious threat to the environment and aquatic life in the receiving waters. The ability of Azotobactor vinelandii TISTR 1094, a N2-fixing bacterium, to grow and remove cyanide in cassava wastewater was evaluated. Results revealed that the cells in the exponential phase reduce the level of cyanide more rapidly than when the cells are at their stationary growth phase. The rate of cyanide removal by A. vinelandii depends on the initial cyanide concentration. As the initial cyanide concentration increased, removal rate increased and cyanide removal of up to 65.3% was achieved. In the subsequent pilot scale trial involving an activated sludge system, the introduction of A. vinelandii into the system resulted in cyanide removals of up to 90%. This represented an improvement of 20% when compared to the activated sludge system which did not incorporate the strain.

Effect of Enforced Aeration on In-Vessel Food Waste Composting

A laboratory composting was conducted to determine the effect of the continuously enforced aeration on the composting performance. The mixture of dog food, excess sludge, and woodchip was used as raw composting materials. The temperature changes in the decomposition process, and pH, weight loss, ash, and extract composition from the final product after 17 days composting were investigated. The results demonstrated that flow rate of enforced aeration indeed influenced the composting performance. Composting under 0.05-0.1 l min−1 condition seemed better than that under 0.2-0.4 l min−1 condition. Higher flow rate of air not only cooled the composting mixture significantly, further adversely affected temperature rise, but also evaporated moisture mostly. Thermophilic composting can occur under 0.05-–0.1 l min−1 air flow rate condition, while composting in cases of 0.2-0.4 l min−1 air flow rate mainly resulted in a mesophilic process. Microbial activity was considered to be significantly inhibited at 0.4 l min−1 air flow rate condition based on the analyses of total organic carbon and volatile fatty acids from water extraction of composting products.

A model of fish distribution in rivers according to their preference for environmental factors

Abstract We present a model of fish distribution according to the fish preference for environmental factors such as water temperature, cover, current velocity, turbidity, food amount, etc. This model can be used to estimate the influence of nearshore construction activity on fish. Our model has the good feature that the parameter values for the environmental preference and the weight values of the environmental factors can be determined separately. New environmental factors can be introduced without calibrating the preference parameters again. In our first experiment, two separate tanks with different environmental conditions are connected by a narrow junction. Fish can swim to the tank they prefer and their distribution is recorded by a video camera every minute for 50 min. The parameters are calibrated according to these observations. The second experiment uses a single tank where several environmental conditions are tested simultaneously. The observed fish distribution in the second experiment and the distribution calculated with the model show a good agreement. Finally, this model is included in the Shallow Sea Ecological Model (SSEM), and fish behavior in a virtual river is simulated to replicate fish distribution during a flood.

Potential bioremediation of mercury-contaminated substrate using filamentous fungi isolated from forest soil

The use of filamentous fungi in bioremediation of heavy metal contamination has been developed recently. This research aims to observe the capability of filamentous fungi isolated from forest soil for bioremediation of mercury contamination in a substrate. Six fungal strains were selected based on their capability to grow in 25 mg/L Hg(2+)-contaminated potato dextrose agar plates. Fungal strain KRP1 showed the highest ratio of growth diameter, 0.831, thus was chosen for further observation. Identification based on colony and cell morphology carried out by 18S rRNA analysis gave a 98% match to Aspergillus flavus strain KRP1. The fungal characteristics in mercury(II) contamination such as range of optimum pH, optimum temperature and tolerance level were 5.5-7 and 25-35°C and 100 mg/L respectively. The concentration of mercury in the media affected fungal growth during lag phases. The capability of the fungal strain to remove the mercury(II) contaminant was evaluated in 100 mL sterile 10 mg/L Hg(2+)-contaminated potato dextrose broth media in 250 mL Erlenmeyer flasks inoculated with 10(8) spore/mL fungal spore suspension and incubation at 30°C for 7 days. The mercury(II) utilization was observed for flasks shaken in a 130 r/min orbital shaker (shaken) and non-shaken flasks (static) treatments. Flasks containing contaminated media with no fungal spores were also provided as control. All treatments were done in triplicate. The strain was able to remove 97.50% and 98.73% mercury from shaken and static systems respectively. A. flavus strain KRP1 seems to have potential use in bioremediation of aqueous substrates containing mercury(II) through a biosorption mechanism.

Simulation of fish behavior and mortality in hypoxic water in an enclosed bay

A model of fish preference for environmental conditions (dissolved oxygen (DO) and water temperature) and mortality was developed and coded within a combined hydrothermal and eutrophication model. The model was applied to an enclosed bay located in the western part of Japan, where eutrophication and associated onset of hypoxia at the bottom waters would occur in every summer. A field survey of fish behavior under hypoxic and non-hypoxic waters was conducted by releasing marbled sale in the bay and tracked its movement. At the same time, vertical profiles of DO, salinity and water temperature were measured at every 0.5m vertical interval at several locations along the tracking path of fish. Moreover, a series of preference tests for DO, salinity and temperature in the laboratory were conducted in order to decide preference parameters of fish. The model could simulate reasonably the observed behavior and movement of the fish under both hypoxic and non-hypoxic waters in the bay; thereby, validated its applicability. Using the model, an assessment of the impact of the ongoing land reclamation project of about 400 ha in the bay on the fisheries resources was also conducted. The results showed that a substantial mortality of the fisheries resources would take place when hypoxic condition occurs in every summer and the construction of the artificial land will lower the mortality rate of fish during the summer period in the bay. Strong offshore winds cause the upwelling of bottom hypoxic waters in summer and the initial mortality of the fisheries resources increase under northerly offshore wind of 5 m/s or more.

A Physiological Marker for Assessing Anxiety Level in Humans: Frontal Midline Theta Activity

Abstract: The distinct theta rhythm in the frontal midline area during performance of mental tasks has been designated as Fmθ. Sixteen male university students who failed to show any appearance of Fmθ in 3 consecutive days were given diazepam 5 mg, amobarbital 80 mg, methylphenidate 15 mg and placebo, in a double‐blind, crossover design. Scores were made on the state anxiety scale of STAI; EEGs were recorded before and during performance of an arithmetic addition. The test was repeated twice: before and one hr after drug administration. Fmθ appeared following the drug administration even in those who had never shown the appearance of Fmθ, and the appearance time of Fmθ increased in the following order: diazepam > amobarbital > placebo > methylphenidate. The scores of STAI decreased in the same order. The speed of performed tasks was increased by methylphenidate and placebo, but decreased by amobarbital and diazepam. These results suggest that relief from anxiety might be reflected in the appearance of Fmθ and that Fmθ might be a useful tool to measure the anxiety level in humans.

Delignification of disposable wooden chopsticks waste for fermentative hydrogen production by an enriched culture from a hot spring

Hydrogen (H2) production from lignocellulosic materials may be enhanced by removing lignin and increasing the porosity of the material prior to enzymatic hydrolysis. Alkaline pretreatment conditions, used to delignify disposable wooden chopsticks (DWC) waste, were investigated. The effects of NaOH concentration, temperature and retention time were examined and it was found that retention time had no effect on lignin removal or carbohydrate released in enzymatic hydrolysate. The highest percentage of lignin removal (41%) was obtained with 2% NaOH at 100°C, correlated with the highest carbohydrate released (67 mg/g pretreated DWC) in the hydrolysate. An enriched culture from a hot spring was used as inoculum for fermentative H2 production, and its optimum initial pH and temperature were determined to be 7.0 and 50°C, respectively. Furthermore, enzymatic hydrolysate from pretreated DWC was successfully demonstrated as a substrate for fermentative H2 production by the enriched culture. The maximum H2 yield and production rate were achieved at 195 mL H2/g total sugars consumed and 116 mL H2/(L·day), respectively.