Yoshiyuki Nagatsu

Characteristics of electricity generation and biodegradation in tidal river sludge-used microbial fuel cells.

The electricity generation behavior of microbial fuel cell (MFC) using the sludge collected from the riverbank of a tidal river, and the biodegradation of the sludge by the electricity generation are evaluated. Although the maximum current density (150-300 mA/m(2)) was higher than that of MFC using freshwater sediment (30 mA/m(2)), the output current was greatly restricted by the mass transfer limitation. However, our results also indicate that placing the anode in different locations in the sludge could reduce the mass transfer limitation. After approximately 3 months, the removal efficiency of organic carbon was approximately 10%, demonstrated that MFC could also enhance the biodegradation of the sludge by nearly 10-fold comparing with the natural biodegradation. We also found that the biodegradation could be identified by the behavior of oxygen consumption of the sludge. Importantly, the oxygen consumption of the sludge became higher along with the electricity generation.

Measurement of Sediment Retention in a Sandy Tidal Flat Based on Pressure Drop Model

Sediment can either play an important role in subsurface environments as a food source for bacteria or deteriorate the subsurface environments by its retention. Thus, understanding sediment retention is useful for designing the management of subsurface environments. The pressure drop model derived from the Kozeny–Carman model is experimentally verified by the seepage flow in sand beds. It was found that the water head in the sand bed under steady-state flow and variations of the water head corresponding to changes in the boundary water head could be reproduced by the pressure drop model. As the porosity of the sand bed is taken into account in the pressure drop model, the sediment retention can be predicted from variations of the porosity. Experimental results showed that the water head in the sand bed varied due to sediment retention. This ensured that variances in the porosity of the sand bed could be predicted, leading to the investigation onto sediment retention. A method based on the pressure drop model is proposed to measure temporal variations of the water head in a sandy tidal flat and river water head. From field experiments, the temporal variations of the water head in the tidal flat could be predicted when the porosity of the tidal flat was used. Conversely, it is expected that sediment retention in the tidal flat can be predicted based on the variations of the porosity, if the water head in the tidal flat is observed temporally.

MEASUREMENT OF MUD FLOC–SETTLING VELOCITY USING A LASER DIFFRACTION PARTICLE SIZE DISTRIBUTION ANALYZER

In-situ and laboratory measurements of particle setting velocity through different techniques, such as settling tubes and video systems, suffer from human and random sampling errors and lack of accuracy. The development of a method to improve the accuracy of the settling velocity measurements has been a challenge for researchers. We propose a method using a laser diffraction particle size distribution analyzer (Shimadzu, SALD-2000J) to estimate the particle settling velocity with increased accuracy. SALD-2000J measures continuously the average intensity of light scattered and the particle size distribution of mud flocs, which were used to estimate the particle settling velocities. The SALD-2000J method produced high accurate results saving both labor and time. The predicted settling velocity presented the same order of magnitude of those reported in previous studies. The settling velocity was used in the simulation of particle size distribution variation, producing a relative error of particle size distributions (obtained from SALD-2000J and the simulation) interior to 5%. The results suggested that the proposed method can be applied to the prediction of settling velocities of mud flocs and inorganic particles both in fresh and saline water environments.