Innovative Technology and System for Sustainable Water Use

　Wastewater treatment techniques are very important for a sustainable water supply. The main treatment process is the activated sludge system, a highly developed process for wastewater treatment; however, the system can still be improved from a microbiological control standpoint because activated sludge is a type of microbial flora.
　Biofouling and biofilm formation are other major problems for water supplies, drainage systems, and wastewater treatment systems. Recently a relation has been proved between the formation of a biofilm and the microbial communication system.
　It has been found that microbes can communicate with each other with certain types of signal compounds. Microbes regulate their activities with these communication systems. We have found such microbial communications in many environmental samples, such as the intestinal flora of fish, the symbiotic flora of plants, and the microbial flora in activated sludge as well as in biofilm. We have also developed microbial communication system control techniques, and methods to evaluate and diagnose microbes.
　This project aims to develop innovative techniques for wastewater treatment with nanotechnology and biotechnology. For this purpose, new techniques to regulate microbial communication systems will be developed using nanomaterials. These technologies should not only improve wastewater treatment systems that use activated sludge, but also prohibit biofouling and biofilm formation.

Go to page top

　Climate change poses a serious challenge in securing good source water for a water supply. One solution to this challenge is to reuse effluent from wastewater treatment plants, which has been performed in extremely dry regions around the world. However, this approach is usually expensive and energy consuming, and is not necessarily managed with an appropriate risk management method. Reusing wastewater tends to employ extreme methods, such as reverse osmosis, because of overreaction to the risks associated with pathogens and micropollutants.
　Given these problems, this study aims to design a water recycling system in urban areas that utilizes the treatment capability of subsurface environments. In this system, after minimum wastewater treatment, the effluent is injected into the subsurface environment of urban areas to decompose micuropollutants and inactivate pathogens. The entire system is controlled and managed with sophisticated risk assessment and management systems that combine quantitative microbial risk assessment (QMRA) and an ultra-trace micropollutant monitoring system. Then, whenever necessary (e.g., in times of water shortage), the treated groundwater is used as source water. This project consists of two parts: (1) pilot-scale experiments of the risk assessment system and the treatability of the soil aquifer treatment and (2) the construction of system implementation scenarios through numerical simulation based on experimental results and interviews with groundwater hydrology and legal experts. The specific goals are summarized below.
(1) To determine acceptable effluent water quality for soil aquifer treatment in terms of human health risk and subsurface environment conservation.
(2) To better understand the transformation and removal processes of dissolved organic matter, pathogens, and micropollutants.
(3) To assess the effects of climate change on soil aquifer treatment.
(4) To evaluate the sustainability of this water recycling system.
　This study aims to effectively utilize the urban subsurface environment in Japan and other Asian countries. By showing that the method is possible and outlining the requirements for its establishment, it is expected that the effective and rational use of urban aquifers in Japan and other Asian regions can be promoted.

Go to page top

　Global warming is one of a number of serious environmental problems we are facing. What will happen if subsurface environmental temperatures rise or fall?
　It is essential to conserve groundwater to maintain sustainable water resources for human and ecosystem consumption. Groundwater is not only used as a water resource, but also as a heat resource. Recently, geo-heat pump (GHP) systems, which use groundwater heat for air conditioning, have become popular energy systems with the potential added environmental benefits of reducing CO2 emissions and preventing the “heat-island” phenomenon.
　In GHP systems waste heat is disposed directly to the Earth’s subsurface, while in conventional heat pump systems relying on an air source the waste heat is disposed into the Earth’s atmosphere. During summer, when GHP systems are used for indoor cooling, a temperature rise in the subsurface would be expected. Conversely, a subsurface temperature decrease would be expected during winter when the purpose of the GHP system is indoor heating. Thus, if GHP systems become widely used, there is a possibility of subsurface temperature change, which we denote as “subsurface thermal pollution,” with derived negative effects on subsurface environments.
　The subsurface temperature change might affect microbial activities and the solubility of toxic substances such as heavy metals. This subsequently may cause significant groundwater and soil pollution and seriously disturb microbial ecosystems, leading to decreased biodiversity. However, the influence of thermal pollution on subsurface environments has not been clarified.
　This research project will investigate the influence of thermal pollution on mass and heat transport and microbial activities in subsurface environments. Geo-mechanical properties will also be investigated, and an assessment tool will be established to evaluate the effects of thermal disturbance. Finally, this assessment tool will be applied to sustainable groundwater management systems that will have built-in optimal protection measures for the groundwater environment.

Go to page top

　This project aims to develop a technological system for site-specific irrigation management that meets plant growth demands through a technique that precisely controls water resources in the rooting zone, and efficiently uses agricultural water.
　The goal of project is to design a plant factory system with a high-efficient water use function available for arid areas. The system involves three technologies: (1) an irrigation technology that maximizes the water supply efficiency based on monitoring the water requirements of the plant, (2) an energy-saving water supply system in the plant cultivating facility, and (3) a water management system that reuses and recycles water from different resources, such as rainwater, groundwater, and used water.
　Arid lands or areas suffering from drought require water-saving agriculture techniques that use technology to collect, store, and reuse the water resources. The proposed system will be applicable to such arid areas, and will also be useful in urban horticulture where a similar micro-climate of water shortage exists.

Go to page top

　Increases in precipitation variability with global warming and rapid population growth have led to water shortages on a global scale. The amount of running surface water varies widely during times of heavy rain or drought, but groundwater is attractive as a relatively stable water resource because of the large capacity of its reservoirs and its longer residence time. Japan belongs to a temperate humid climate zone that experiences much precipitation and it has a steep topography with mountains close to the coast.　Thus, the residence time of falling rain as it flows out to sea is very short and the regional hydrological cycle is extremely active. Surface water can be collected easily and is often used as a water supply, but recently groundwater is taking the place of surface water due to the stability of its supply. While in our hydro-climatic condition, the sustainable use of groundwater is possible as long as appropriate management ensures that the groundwater pumping rate does not exceed the recharge rate of a basin.
　For the sustainable use of groundwater resources, this project aims to develop new technologies to enhance the quality and quantity of groundwater resources. New technologies will be developed to precisely understand the groundwater flow system, such as the frequency changeable electric resistivity exploration method to evaluate an aquifer structure and a new groundwater age-tracer method to estimate the younger age. Not only in Japan but also worldwide, there are many problems about groundwater quality, including nitrate-nitrogen contamination caused by surplus fertilizer and manure, and the outflow of toxic substances from domestic and industrial waste disposal. It is necessary to understand the production mechanism in order to prevent groundwater contamination, and also to understand the degradation process of nitrate-nitrogen contamination in order to improve water quality. Therefore this project will develop new technologies to reduce nitrate-nitrogen and natural toxic substance loads before groundwater recharge, remove onsite contaminants from aquifers, and improve groundwater quality after pumping with the aid of simple and effective equipment. This project will also develop a new biological monitoring technique for local groundwater users to quickly notice signs of contamination, for example, a freshwater fish turns red when specific ion water quality worsens.
　With the procedures outlined above, this project aims to establish a groundwater management system for sustainable utilization that focuses on water quantity and quality. First, the evaluation of the local groundwater flow system by using new technologies and the three-dimensional groundwater flow simulation including nitrate-nitrogen contamination will be applied to the Kumamoto area where is the most advanced groundwater utilization area in Japan. This model will be used to estimate the maximum amount of local groundwater pumping required for sustainable utilization, simulate the reduction of nitrate contamination, and propose a reasonable groundwater management system based on the regional hydrological system. Then newly developed research techniques and methodologies will be applied to remote coral islands that are facing the problems of nitrate contamination and rising sea levels caused by global warming. Finally, this project will propose a policy of sustainable groundwater utilization based on the regional hydrological cycle.

Go to page top

　Nations and districts have various needs for their water supply including the demand for good-tasting water, the use of groundwater, and the prevention of water leakage when disaster occurs. For sustainable water use, water supply technology and system should be proposed deliberately for the best match with the needs of nations and districts so as to minimize water wastage. Regional water circulation quality monitoring networks help ensure customers can use the water safely and carefree with minimum water consumption. The core piece of equipment in the monitoring network is a compact water quality monitor suitable to be set up onsite and monitored online. Furthermore, implementation and operational instructions should be available in combination with various monitors which meet the needs of various measurement items in order to suit the individual needs of each area.
　Micro-total analysis systems (μ-TASs) have gained attention in recent years as attractive technologies which realize compact water quality monitors since, despite their compact size, their analytical performance in terms of accuracy and the diversity of measurement items is equivalent to stand-alone systems. On the other hand, they require complicated design and fabrication processes to assemble many miniaturized fluidic elements (micro-fluidic devices) such as micro-mixers, micro-reactors, and micro-pumps. A model-based design technique, which has been used mainly in motion systems, enables complicated system models to be created and simulated efficiently. Hence, as shown in Figure 1, we are using the model-based design technique to develop water quality monitoring network integration and installation technologies that allow us to check the performance efficiently without building prototype from its element design level (micro-fluidic devices, μ-TAS) to the network architecture level.
　For Step 1, we construct a model-based simulation platform for micro-fluidic devices and a unique data-gathering system of the fluid characteristics (micro-fluidic HILS; hardware in the loop simulator). In Step 2, the fluid behavior of the micro-fluidic devices (such as micro-concentrators, micro-reduction devices, etc.) which are used for water analysis is measured using the micro-fluidic HILS. For Step 3, we develop an overall model of the monitor which consists of a μ-TAS, a control unit, and a signal processing unit. We use the model to check how the conditions onsite (where the monitors will be installed) will influence the fluid behavior and the analytical performance. As the fourth and final step we develop a monitoring network model with multiple monitors and investigate the most effective way to install and implement the system.

Go to page top