Masahiro Otaki - Academia.edu (original) (raw)

Papers by Masahiro Otaki

Current water use in our daily life is by no means sustainable, and the environmental and social ... more Current water use in our daily life is by no means sustainable, and the environmental and social problems come to the surface. To improve the current situation and to develop sustainably both for human beings and the global environment, we have to think out a new paradigm. As the centerpiece of the new paradigm, we advocate the concept of water literacy. Water literacy was defined as the ability to feel familiar with water, get actively involved in water and face the issue of water as one's own issue. Water literacy was divided into three categories: practical, living, and social water literacy. Water literacy enables us to re-evaluate local water systems and water usage. Furthermore, water literacy educates those citizens who are able to associate daily life with social issue, and contributes to the recovery of a variety of relations between water and humans.

Environmental Science, 2013

The American Journal of Gastroenterology, 2013

Environmental Engineering Research, 1998

Water, 2021

Urban sanitation is a major challenge during the rapid urbanization being experienced by developi... more Urban sanitation is a major challenge during the rapid urbanization being experienced by developing countries, as a low sewerage infrastructure capacity and irregular onsite wastewater treatment raise the risk of surface water contamination. The application of specific sewage markers to characterize contaminant sources is therefore essential for managing urban sanitation issues. In this study, we investigated the concentrations of eight sewage markers (acetaminophen, caffeine, carbamazepine, cotinine, sulfamethoxazole, sulfapyridine, atenolol, and acesulfame) in various water sources within urban area of the Galle City, Sri Lanka. The total concentration of the eight markers was in the order of hospital discharge > sewage treatment plant (STP) influent > surface drainage system. Among the eight selected markers, acetaminophen was dominant in hospital discharge (70.2–123.6 µg/L) while caffeine was the largest contributor to STP influent (16.2–68.7 µg/L) and surface drainage (0....

Journal of Japan Society on Water Environment, 2016

Rapid algal growth in the water purification process often causes problems such as turbidity leak... more Rapid algal growth in the water purification process often causes problems such as turbidity leak. We investigated whether the application of ultraviolet (UV) radiation (254 nm) was effective in controlling algal growth. The objective of this study is to investigate the effect of UV irradiation on some isolated algae at a conventional UV dose (50-200 mJ cm-2) or a high UV dose (500-1000 mJ cm-2). Three algae that obstruct water purification, that is, diatoms of Cyclotella, green algae of Dictyosphaerium, and flagellate of Cryptomonas, were selected and cultivated. As a result, it was observed that the cell concentration was reduced or maintained during one week after conventional UV dose irradiation in all algae. Dictyosphaerium exhibited higher resistance or faster growth compared with Cyclotella and Cryptomonas. Moreover, it was observed that algal cells exposed to a high UV dose were simultaneously broken, and the cell number was reduced in the cases of Cryptomonas and Dictyosphaerium. On the other hand, for Cyclotella, the cell content was changed but the shape of the cell was not. In conclusion, a conventional UV dose inhibited algal growth and a high UV dose injured cellular contents directly and induced cytolysis in some algal species.

Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research), 2019

Water, 2019

This study investigated how chlorine inactivates and damages Escherichia coli cells. E. coli that... more This study investigated how chlorine inactivates and damages Escherichia coli cells. E. coli that had transformed to express enhanced green fluorescent protein (EGFP) at the cytoplasm was treated with chlorine. Damage to the cell membrane and cell wall was analyzed by measuring the fluorescence intensity of the leaked EGFP, then accounting for the fluorescence deterioration. At pH 7, E. coli was lethally damaged after treatment with chlorine, but significant leakage of EGFP was not observed. In contrast, significant leakage of EGFP was observed at pH 9, even though E. coli was not as inactivated as it was at pH 7. Flow cytometry was used to confirm the fluorescence intensity of the remaining EGFP inside the cells. No significant fluorescence loss was observed in the cells at pH 7. However, at pH 9, the fluorescence intensity in the cells decreased, indicating leakage of EGFP. These results suggest that hypochlorous acid inactivates E. coli without damaging its cell membrane and cell...

JOURNAL OF JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES, 2016

Industrial water demand is increasing rapidly because of the growth of economically developing co... more Industrial water demand is increasing rapidly because of the growth of economically developing countries. Predictions of water demand are therefore necessary for effective management. One model proposed by Takahashi et al. (2000) predicts industrial water demand based on GDP data and a coefficient related to water use efficiency (η). This study specifically examines a method of determining η to improve predictive accuracy. A cluster analysis using the gross value added of industry super-sectors was completed to divide 61 countries into four clusters ("oil producer," "developed or middle developed," "middle developed or developing," and "developing" countries). For each cluster, multi-regression analyses were conducted to elucidate the relation between η and some typical η determinants (e.g., GDP change ratio, inventory of water resources). Relations between past changes in η (Dη) and GDPPPP-per-capita or the initial η were also studied. Results of multi-regression analyses show that determinants of η were significantly different among groups. Typical determinants explained η for countries in two groups: "oil producer" and "developed or middle developed" countries. Furthermore, countries with a GDPppp-per-capita higher than 14,000 $ present almost stable Dη /year (=0.00345), whereas countries presenting a lower GDPPPP-per-capita have no tendency of Dη /year. Results show the possibility of predicting industrial water consumption more accurately by the prediction of η using the results described above.

Proceedings of the Water Environment Federation, 2005

Wastewater disinfection is practiced with the goal of reducing risks of human exposure to pathoge... more Wastewater disinfection is practiced with the goal of reducing risks of human exposure to pathogenic microorganisms. Ideally, this goal is to be met without introducing other risks, such as those that could be associated with disinfection by-products. The purpose of this research was to assess the effects of wastewater disinfection on human health. This assessment was conducted by examining two fundamental questions regarding the application of disinfection:

Water Environment Research, 2007

Wastewater disinfection is practiced with the goal of reducing risks of human exposure to pathoge... more Wastewater disinfection is practiced with the goal of reducing risks of human exposure to pathogenic microorganisms. In most circumstances, the efficacy of a wastewater disinfection process is regulated and monitored based on measurements of the responses of indicator bacteria. However, inactivation of indicator bacteria does not guarantee an acceptable degree of inactivation among other waterborne microorganisms (e.g., microbial pathogens). Undisinfected effluent samples from several municipal wastewater treatment facilities were collected for analysis. Facilities were selected to provide a broad spectrum of effluent quality, particularly as related to nitrogenous compounds. Samples were subjected to bench‐scale chlorination and dechlorination and UV irradiation under conditions that allowed compliance with relevant discharge regulations and such that disinfectant exposures could be accurately quantified. Disinfected samples were subjected to a battery of assays to assess the im...

Journal of Bioscience and Bioengineering, 2005

Annals of Microbiology, 2011

The infectivity rates of Salmonella typhi's phage was used as a bio-indicator to detect the prese... more The infectivity rates of Salmonella typhi's phage was used as a bio-indicator to detect the presence of viable but non cultivable bacteria after irradiation by an increasing number of pulsed UV light. Indeed, the combination of a conventional method used to measure colony-forming ability of UV-irradiated bacteria, and the study of relationship between host bacteria and a suitable phage can reveal the existence of active bacteria which lose the cultivability in usual culture media, but keep viability and phage susceptibility.

Annals of Microbiology, 2012

To improve the ultraviolet (UV) water disinfection process and to better understand the impact of... more To improve the ultraviolet (UV) water disinfection process and to better understand the impact of the harmful effects of germicidal radiation on the DNA molecule, we have developed a reliable biological monitoring system based on PCR 16S ribosomal DNA (rDNA) and terminal restriction fragment length polymorphism analysis. The PCR analysis was performed using the bacteria-specific 27F and 905R primers to replicate a fragment of the rDNA gene. This new and versatile method can be used to evaluate the effects of direct UV radiation on DNA (UV dose/response) and to estimate the potential of bacteria to mitigate UV lethal effects via photoreactivation and dark repair.

Annals of Microbiology, 2010

In order to qualify the germicidal efficacy of ultraviolet (UV) disinfection system, we generally... more In order to qualify the germicidal efficacy of ultraviolet (UV) disinfection system, we generally determine the reduction of viable bacteria after UV-C irradiation. However, the simple count of viable and cultivable bacteria in usual media cannot reflect whether or not the UV dose applied to disinfect water is sufficient to inactivate bacteria. Indeed, there is a bacterial mix in the UV-treated water: dead bacteria, viable and cultivable bacteria and viable but noncultivable bacteria (VBNC). The third type of bacteria can constitute a potential risk for public health. In fact, VBNC bacteria can be active and cause diseases. Consequently, the combination of a conventional method used to measure colony-forming ability after UV disinfection and the determination of adsorption constants of a lytic Qβ phage in relation to irradiated host cells by an increased UV dose (Escherichia coli ATCC 13965) allows the detection of active bacteria, which lose their cultivability in usual growth media, but keep the phage susceptibility.

Journal of Environmental Management

In the present study, the bactericidal and virucidal mechanisms in the alkaline disinfection of c... more In the present study, the bactericidal and virucidal mechanisms in the alkaline disinfection of compost with calcium lime and ash were investigated. Two indicator microorganisms, Escherichia coli and MS2 coliphage, were used as surrogates for enteric pathogens. The alkaline-treated compost with calcium oxide (CaO) or ash resulted primarily in damage to the outer membrane and enzyme activities of E. coli. The alkaline treatment of compost also led to the infectivity loss of the coliphage because of the partial capsid damage and RNA exteriorization due to a raised pH, which is proportional to the amount of alkaline agents added. These results indicate that the alkaline treatment of compost using calcium oxide and ash is effective and can contribute to the safe usage of compost from a mixing type dry toilet.

Water

In the area where household water use exceeds the capacity of the public water supply, rainwater ... more In the area where household water use exceeds the capacity of the public water supply, rainwater is considered as one of the alternative water resources. Many researchers studied rainwater potential to cover the specific value of water demand in households having the average catchment area, so that the estimated potential expresses that of the average population. In this research, the possibility of rainwater use for toilets was investigated more realistically using the probability distributions of water demand and catchment area, and precipitation in case of Hanoi, Vietnam. Monte Carlo simulations were conducted throughout this simulation and the distribution of the possibility of rainwater use was estimated. The effect of household size and seasonal variations on the potential of rainwater utilization was also assessed. These results showed that our new approach exhibited that approximately 60% of the households failed to achieve the potential that was estimated using the conventi...

Current water use in our daily life is by no means sustainable, and the environmental and social ... more Current water use in our daily life is by no means sustainable, and the environmental and social problems come to the surface. To improve the current situation and to develop sustainably both for human beings and the global environment, we have to think out a new paradigm. As the centerpiece of the new paradigm, we advocate the concept of water literacy. Water literacy was defined as the ability to feel familiar with water, get actively involved in water and face the issue of water as one's own issue. Water literacy was divided into three categories: practical, living, and social water literacy. Water literacy enables us to re-evaluate local water systems and water usage. Furthermore, water literacy educates those citizens who are able to associate daily life with social issue, and contributes to the recovery of a variety of relations between water and humans.

Environmental Science, 2013

The American Journal of Gastroenterology, 2013

Environmental Engineering Research, 1998

Water, 2021

Urban sanitation is a major challenge during the rapid urbanization being experienced by developi... more Urban sanitation is a major challenge during the rapid urbanization being experienced by developing countries, as a low sewerage infrastructure capacity and irregular onsite wastewater treatment raise the risk of surface water contamination. The application of specific sewage markers to characterize contaminant sources is therefore essential for managing urban sanitation issues. In this study, we investigated the concentrations of eight sewage markers (acetaminophen, caffeine, carbamazepine, cotinine, sulfamethoxazole, sulfapyridine, atenolol, and acesulfame) in various water sources within urban area of the Galle City, Sri Lanka. The total concentration of the eight markers was in the order of hospital discharge > sewage treatment plant (STP) influent > surface drainage system. Among the eight selected markers, acetaminophen was dominant in hospital discharge (70.2–123.6 µg/L) while caffeine was the largest contributor to STP influent (16.2–68.7 µg/L) and surface drainage (0....

Journal of Japan Society on Water Environment, 2016

Rapid algal growth in the water purification process often causes problems such as turbidity leak... more Rapid algal growth in the water purification process often causes problems such as turbidity leak. We investigated whether the application of ultraviolet (UV) radiation (254 nm) was effective in controlling algal growth. The objective of this study is to investigate the effect of UV irradiation on some isolated algae at a conventional UV dose (50-200 mJ cm-2) or a high UV dose (500-1000 mJ cm-2). Three algae that obstruct water purification, that is, diatoms of Cyclotella, green algae of Dictyosphaerium, and flagellate of Cryptomonas, were selected and cultivated. As a result, it was observed that the cell concentration was reduced or maintained during one week after conventional UV dose irradiation in all algae. Dictyosphaerium exhibited higher resistance or faster growth compared with Cyclotella and Cryptomonas. Moreover, it was observed that algal cells exposed to a high UV dose were simultaneously broken, and the cell number was reduced in the cases of Cryptomonas and Dictyosphaerium. On the other hand, for Cyclotella, the cell content was changed but the shape of the cell was not. In conclusion, a conventional UV dose inhibited algal growth and a high UV dose injured cellular contents directly and induced cytolysis in some algal species.

Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research), 2019

Water, 2019

This study investigated how chlorine inactivates and damages Escherichia coli cells. E. coli that... more This study investigated how chlorine inactivates and damages Escherichia coli cells. E. coli that had transformed to express enhanced green fluorescent protein (EGFP) at the cytoplasm was treated with chlorine. Damage to the cell membrane and cell wall was analyzed by measuring the fluorescence intensity of the leaked EGFP, then accounting for the fluorescence deterioration. At pH 7, E. coli was lethally damaged after treatment with chlorine, but significant leakage of EGFP was not observed. In contrast, significant leakage of EGFP was observed at pH 9, even though E. coli was not as inactivated as it was at pH 7. Flow cytometry was used to confirm the fluorescence intensity of the remaining EGFP inside the cells. No significant fluorescence loss was observed in the cells at pH 7. However, at pH 9, the fluorescence intensity in the cells decreased, indicating leakage of EGFP. These results suggest that hypochlorous acid inactivates E. coli without damaging its cell membrane and cell...

JOURNAL OF JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES, 2016

Industrial water demand is increasing rapidly because of the growth of economically developing co... more Industrial water demand is increasing rapidly because of the growth of economically developing countries. Predictions of water demand are therefore necessary for effective management. One model proposed by Takahashi et al. (2000) predicts industrial water demand based on GDP data and a coefficient related to water use efficiency (η). This study specifically examines a method of determining η to improve predictive accuracy. A cluster analysis using the gross value added of industry super-sectors was completed to divide 61 countries into four clusters ("oil producer," "developed or middle developed," "middle developed or developing," and "developing" countries). For each cluster, multi-regression analyses were conducted to elucidate the relation between η and some typical η determinants (e.g., GDP change ratio, inventory of water resources). Relations between past changes in η (Dη) and GDPPPP-per-capita or the initial η were also studied. Results of multi-regression analyses show that determinants of η were significantly different among groups. Typical determinants explained η for countries in two groups: "oil producer" and "developed or middle developed" countries. Furthermore, countries with a GDPppp-per-capita higher than 14,000 $ present almost stable Dη /year (=0.00345), whereas countries presenting a lower GDPPPP-per-capita have no tendency of Dη /year. Results show the possibility of predicting industrial water consumption more accurately by the prediction of η using the results described above.

Proceedings of the Water Environment Federation, 2005

Wastewater disinfection is practiced with the goal of reducing risks of human exposure to pathoge... more Wastewater disinfection is practiced with the goal of reducing risks of human exposure to pathogenic microorganisms. Ideally, this goal is to be met without introducing other risks, such as those that could be associated with disinfection by-products. The purpose of this research was to assess the effects of wastewater disinfection on human health. This assessment was conducted by examining two fundamental questions regarding the application of disinfection:

Water Environment Research, 2007

Wastewater disinfection is practiced with the goal of reducing risks of human exposure to pathoge... more Wastewater disinfection is practiced with the goal of reducing risks of human exposure to pathogenic microorganisms. In most circumstances, the efficacy of a wastewater disinfection process is regulated and monitored based on measurements of the responses of indicator bacteria. However, inactivation of indicator bacteria does not guarantee an acceptable degree of inactivation among other waterborne microorganisms (e.g., microbial pathogens). Undisinfected effluent samples from several municipal wastewater treatment facilities were collected for analysis. Facilities were selected to provide a broad spectrum of effluent quality, particularly as related to nitrogenous compounds. Samples were subjected to bench‐scale chlorination and dechlorination and UV irradiation under conditions that allowed compliance with relevant discharge regulations and such that disinfectant exposures could be accurately quantified. Disinfected samples were subjected to a battery of assays to assess the im...

Journal of Bioscience and Bioengineering, 2005

Annals of Microbiology, 2011

The infectivity rates of Salmonella typhi's phage was used as a bio-indicator to detect the prese... more The infectivity rates of Salmonella typhi's phage was used as a bio-indicator to detect the presence of viable but non cultivable bacteria after irradiation by an increasing number of pulsed UV light. Indeed, the combination of a conventional method used to measure colony-forming ability of UV-irradiated bacteria, and the study of relationship between host bacteria and a suitable phage can reveal the existence of active bacteria which lose the cultivability in usual culture media, but keep viability and phage susceptibility.

Annals of Microbiology, 2012

To improve the ultraviolet (UV) water disinfection process and to better understand the impact of... more To improve the ultraviolet (UV) water disinfection process and to better understand the impact of the harmful effects of germicidal radiation on the DNA molecule, we have developed a reliable biological monitoring system based on PCR 16S ribosomal DNA (rDNA) and terminal restriction fragment length polymorphism analysis. The PCR analysis was performed using the bacteria-specific 27F and 905R primers to replicate a fragment of the rDNA gene. This new and versatile method can be used to evaluate the effects of direct UV radiation on DNA (UV dose/response) and to estimate the potential of bacteria to mitigate UV lethal effects via photoreactivation and dark repair.

Annals of Microbiology, 2010

In order to qualify the germicidal efficacy of ultraviolet (UV) disinfection system, we generally... more In order to qualify the germicidal efficacy of ultraviolet (UV) disinfection system, we generally determine the reduction of viable bacteria after UV-C irradiation. However, the simple count of viable and cultivable bacteria in usual media cannot reflect whether or not the UV dose applied to disinfect water is sufficient to inactivate bacteria. Indeed, there is a bacterial mix in the UV-treated water: dead bacteria, viable and cultivable bacteria and viable but noncultivable bacteria (VBNC). The third type of bacteria can constitute a potential risk for public health. In fact, VBNC bacteria can be active and cause diseases. Consequently, the combination of a conventional method used to measure colony-forming ability after UV disinfection and the determination of adsorption constants of a lytic Qβ phage in relation to irradiated host cells by an increased UV dose (Escherichia coli ATCC 13965) allows the detection of active bacteria, which lose their cultivability in usual growth media, but keep the phage susceptibility.

Journal of Environmental Management

In the present study, the bactericidal and virucidal mechanisms in the alkaline disinfection of c... more In the present study, the bactericidal and virucidal mechanisms in the alkaline disinfection of compost with calcium lime and ash were investigated. Two indicator microorganisms, Escherichia coli and MS2 coliphage, were used as surrogates for enteric pathogens. The alkaline-treated compost with calcium oxide (CaO) or ash resulted primarily in damage to the outer membrane and enzyme activities of E. coli. The alkaline treatment of compost also led to the infectivity loss of the coliphage because of the partial capsid damage and RNA exteriorization due to a raised pH, which is proportional to the amount of alkaline agents added. These results indicate that the alkaline treatment of compost using calcium oxide and ash is effective and can contribute to the safe usage of compost from a mixing type dry toilet.

Water

In the area where household water use exceeds the capacity of the public water supply, rainwater ... more In the area where household water use exceeds the capacity of the public water supply, rainwater is considered as one of the alternative water resources. Many researchers studied rainwater potential to cover the specific value of water demand in households having the average catchment area, so that the estimated potential expresses that of the average population. In this research, the possibility of rainwater use for toilets was investigated more realistically using the probability distributions of water demand and catchment area, and precipitation in case of Hanoi, Vietnam. Monte Carlo simulations were conducted throughout this simulation and the distribution of the possibility of rainwater use was estimated. The effect of household size and seasonal variations on the potential of rainwater utilization was also assessed. These results showed that our new approach exhibited that approximately 60% of the households failed to achieve the potential that was estimated using the conventi...