Tetsuya Kusuda

Chronic arsenic exposure and urinary 8-Hydroxy-2′-deoxyguanosine in an arsenic-affected area in Inner Mongolia, China

Objective:Recent studies have shown that generation of reactive oxidants during arsenic metabolism can play an important role in arsenic-induced injury. The purpose of this study was to examine the relationship between arsenic in drinking water and oxidative stress in humans by measuring 8-Hydroxy-2′-deoxyguanosine (8-OHdG).Methods:We performed a cross-sectional study in an arsenic-affected village in Hetao Plain, Inner Mongolia, China. A total of 134 of the 143 inhabitants (93.7%) of the village participated in the study. The levels of 8-OHdG, arsenic and its metabolites were measured in urine collected from the participants. Regression analyses were performed to investigate the relationship between arsenic species and 8-OHdG levels in urine.Results:In the polluted village, monomethylarsenic was significantly higher in subjects with arsenic dermatosis than those without dermatosis despite no difference in mean levels of arsenic in well water between both types of subject. For subjects with arsenic dermatosis, arsenic species and metabolites in urine are significantly associated with 8-OHdG, while there was no statistically significant relationship for subjects without arsenic dermatosis. For all residents of the polluted village, the levels of dimethylarsenic and 8-OHdG were significantly higher for those who had been exposed to well water for more than 12 years.Conclusions:These results provide evidence of a link between exposure to arsenic from drinking water and oxidative stress, which may play an important role in arsenic-involved injuries.

A kinetic study on methanogenesis by attached biomass in a fluidized bed

Abstract The objective of this study is to estimate growth kinetic constants and the concentration of “active” attached biomass in an anaerobic fluidized bed, which decomposes acetic, propionic and butyric acids. The fluidized bed was operated as a methanogenic reactor with synthetic zeolite as support media. The reactor was supplied with synthetic wastewater (1000 mg COD l −1 ), a mixture of the above-mentioned volatile fatty acids (VFA), in the range of hydraulic retention time (HRT) from 0.25 to 2 days. After the effluent has reached a steady state in quality, batch experiments in the bed reactor were conducted using acetic, propionic and butyric acids as substrate in order to investigate the decomposition characteristics of each substrate by the attached biomass. Detached biomass from the support media was also served to batch experiments under the completely mixed condition in order to estimate parameter values of the growth kinetics of the bacteria. The changes of fatty acid concentrations with time were expressed with the Monod growth model. The two kinetics parameters, maximum specific growth rates and saturation constants, and “active” biomass concentrations were obtained by the curve fitting method. The comparison of the measured concentration of volatile suspended solids (VSS) and protein with the estimated “active” biomass concentrations indicated that a large amount of inert organic matter exists in the attached growth reactor.

Arsenic in Drinking Water and Peripheral Nerve Conduction Velocity among Residents of a Chronically Arsenic-affected Area in Inner Mongolia

Background It remains unclear whether chronic ingestion of arsenic in drinking water affects the peripheral nervous system. We examined the effects of arsenic exposure on nerve conduction velocity using electromyography. Methods A cross-sectional study was conducted of a population living in an arsenic-affected village in Hetao Plain, Inner Mongolia, China. A total of 134 (93.7%) of 143 inhabitants took part in the study, and 36 (76.6%) of 47 inhabitants in a low-arsenic exposed village were recruited as a control group. Of the participants, 109 inhabitants in the arsenic-affected village and 32 in the low-arsenic exposed village aged ≥18 years were used for the analyses. An expert physician performed skin examinations, and median nerve conduction velocity was examined by electromyography. Arsenic levels in tube-well water and urine were measured. A mean level of arsenic in tube-well water in the arsenic-affected village was 158.3μg/L, while that in the low-arsenic exposed village was 5.3μg/L. Results No significant differences in the means of the motor nerve conduction velocity (MCV) and sensory nerve conduction velocity (SCV) were observed in relation to arsenic levels in tube wells, urine, and the duration of tube-well use. Further, no differences in mean MCV or SCV were found between the subjects with and without arsenic dermatosis, with mean SCV of 52.8 m/s (SD 6.3) in those without and 54.6 m/s (5.2) in subjects with arsenic dermatosis (p=0.206). Conclusion These findings suggest that chronic arsenic poisoning from drinking water is unlikely to affect nerve conduction velocity, at least within the range of arsenic in drinking water examined in the present study.

Effect of particulate biodegradable COD in a post-denitrification enhanced biological phosphorus removal system

This research studied the effects of the particulate biodegradable fraction (XS) of chemical oxygen demand (COD) in a post-denitrification configuration. Denitrifying polyphosphate-accumulating organisms (DN-PAOs) and nitrifiers were completely separated in a system also known as Dephanox. It was composed by an anaerobic-anoxic (A2) process coupled with a parallel Nitrification biofilm tank. The results of a long-term operation of the Dephanox continuous-flow lab-scale system as well as results of sludge characterization assays showed that raw wastewater feeding promoted complete phosphorus (P) removal by double via (i) providing complementary volatile fatty acids (VFAs) for a complete P removal by prefermentation of the XS fraction of COD under a long anaerobic SRT, and (ii) assisting the metabolic accumulation and selection of DN-PAOs. Complete P removal was accomplished only when the system was fed with raw wastewater (high XS concentration). When primary effluent was used as influent, lack of VFAs in the anaerobic stage led to an incomplete and instable P removal, suggesting that the use of primary treatment is not only unnecessary but detrimental for simultaneous nutrient removal in a post-denitrification configuration.

Porous structure and spatial characteristics of aerobic granules

Cryosectioned granules were observed in microstructure, Extracellur Polymeric Substances (EPS) and metal distribution. Aerobic granules composed of pores and channels that were not plugged by EPS, with rather open structure. Microorganisms proliferated mainly on the surface of granule and on the wall of channels, carbohydrate EPS mainly distributed on the surface of granules, and protein EPS mainly distributed in the interior part of granules. Also, aerobic granules accumulated considerable calcium and phosphorus, which increase the ash solid fraction of granules and thus improve the settleability. Additionally, iron was neither temporally accumulated nor heterogeneously spatially distributed.

Pollutant transformations in landfill layers

Abstract The behaviour of pollutants, in particular organic carbon and nitrogen, in solid waste landfill layers and factors affecting their decomposition have been studied using four large scale simulated lysimeters in four landfill thicknesses, and operated under semi-aerobic conditions. This paper presents about 800 days of data through November 1991. Data in this study indicate that the thicker solid waste layer has lower production rates of Total Organic Carbon (TOC) and Total Nitrogen (T-N) than does the thinner layer. If the layer, however, becomes too thick, no significant increase in the removal rate of T-N is observed, as nitrogen is leached out in the form of NO 3 − -N without being demitrified at the bottom of the landfill layer. It is also assumed that temperature and pH in the landfill layer play important roles not only in microbial degradation, but also in dissolution of organic carbon and nitrogen.

MEASUREMENTS OF DISSOLVED OXYGEN IN ATTACHED MICROBIAL FILMS OF ROTATING BIOLOGICAL CONTACTOR BY OXYGEN MICROELECTRODE

ABSTRACT As for rotating biological contactors, no measurement result has been reported as yet on dissolved oxygen (DO) concentration as well as substrate concentration both inside and outside the biofilm on the disk surface. The DO profile should be known for precisely determining the rates of substrate oxidation and studying the substrate removal phenomena. The authors developed a special oxygen microelectrode to measure DO. The conclusions in this study are summarized as follows: (1) Water layers attached on the biofilms in the air phase are about 50 μm in thickness; (2) DO concentrations in the liquid layers and in the biofilms become higher depending on the retention time in the air phase; (3) The biofilms swell when submerged into the liquid phase, and DO concentrations in the biofilms suddenly become lower; (4) The DO concentration gradient exists between the bulk liquid and the biofilm surface; (5) The DO concentration profiles in the film change locally and significantly, and differ from the averaged ones in the previous models.

ESTIMATION OF NITRIFICATION ACTIVITY IN A TIDAL RIVER SEDIMENT

ABSTRACT An estimation method was proposed for the simultaneous determination of nitrifying bacteria concentration in sediments, and the growth kinetics constants such as maximum specific growth rates and saturation constants, with assumed growth yield coefficient. Experiments to ascertain availability of the estimation method were conducted using enrichment culture of nitrite oxidizing bacteria. In the experiments nitrite was added two times as a substrate. After the initial supply of the substrate was almost consumed, the same substrate was replenished into the same incubator for the second run. The consumption time reduced because of the increase in biomass. Results of sequential batch experiments with different substrate consumption times were analyzed for the determination of initial bacteria concentrations according to the estimation method. The results showed that the estimated bacteria concentration was in good agreement with other biomass indices such as protein and volatile suspended solids of the bacteria inoculants. The estimated values meant “active” biomass concentrations based on substrate consumption. However the estimated values were much larger than those evaluated by the product of MPN count and cell weight. The indistinct judgement of color in the MPN method was probably responsible for the disagreement. The changes of nitrite concentration with time in the sequential batch experiments were clearly explained by the Monod model with the estimated initial bacteria concentration. Optimal values of two growth kinetic constants were also determined by the least square method based on the changes of the nitrite concentration with time. The acceptable results indicated that this estimation method for simultaneous determination of bacteria concentration and kinetic constants was reliable and available for the evaluation of nitrification activity in mixed cultures such as sediments and activated sludges. Then the estimation method was applied to the determination of nitrite and ammonium oxidizing bacteria concentrations in sediments and suspended solids. Determination of nitrifying bacteria concentration and evaluation of the nitrification activity in a tidal river were carried out.

Effect of Rotifers on the Stability of Aerobic Granules

The current study evaluated the effect of rotifers on the stability of aerobic granules. Two sequence batch reactors (SBRs) with airflow rates of 4 (R1) and 6 (R2) 1 min−1, respectively, were used to develop aerobic granules. Granules were well developed with excellent settleability in terms of SVI30 (sludge volume index,) of about 50 ml g−1 in both reactors at the beginning. With the outgrowth of rotifers, granules completely disintegrated in R1 around cycle 500 (a cycle was 3 hours). However, after the rotifers disappeared, i.e. cycle 550, granules re-appeared with a slow settling rate in R1 (SVI30: 200-300 ml g−1). The rotifers mechanically damaged the structure of granules, resulting in disintegration. However, granules developed under high shear force seem to have strong resistance to rotifers. During re-granulation, a long time lag between the improvements of morphology and settleability suggested that re-granulation resulted from entanglement more than bioattachment or bio-growth. Additionally, it was confirmed that the ratio of carbohydrate to protein extracellular polymeric substances (EPS) could well indicate the strength of granules. Protein EPS well correlated with the difference between SVI5 and SVI30 in R1, therefore, decreasing protein EPS would increase the compactness of granules.

Modeling of fluid mud flow on an inclined bed

Characteristics of fluid mud flow on an inclined bed were investigated in the quiescent state in an experimental flume. The slope of the inclined bed was adjustable from 0 to 1:473. Suspension concentration in the experiments ranged from 3.2 to 64 kg m −3 . With an increase in the initial concentration, the maximum velocity of fluid mud decreased but the highest concentration increased. Apparent viscosity in the fluid mud was three orders of magnitude larger than that of water. Based on these experimental results the constitutive equation, the rate of deposition and the dispersion coefficient in fluid mud were obtained. Using these equations discretized by the SIMPLE method, simulation of fluid mud flow on the bed was performed. The simulation results in the quiescent state agreed well with the experimental results, and accurately reproduced fluid mud flow on the inclined bed.