Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17538号 / 工博第3697号 / 新制||工||1563(附属図書館) / 30304 / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 田中 宏明, 教授 清水 芳久, 教授 伊藤 禎彦 / 学位規則第4条第1項該当

Unrestricted use of reclaimed secondary effluents for irrigation is a major goal in countries suffering from water shortage. Reverse osmosis desalination is used to provide high quality waters with reduced salinity. In order to allow water production with high economic efficiency, fouling in the membrane installation needs to be minimized. Biofouling, caused by microorganisms synthesizing high-molecular biofilms, is of major concern. Biofouling reduces the water production rate and thus increases the costs of the process. Deeper knowledge on its formation and its impact on membrane performance is needed. This is relevant especially for large-scale treatment plants, where process conditions change over length and time and influencing factors on fouling formation occur in combination. Thus, in the present thesis a membrane test cell was developed which enables the investigation of biofouling under validated, representative conditions of full-scale modules. Biofouling was studied in order to determine its impact on membrane performance. Also, appropriate, cost-effective pre-treatment prior to the reverse osmosis process minimizes fouling. Therefore, biofiltration and its suitability as stand-alone pre-treatment was studied when reusing secondary effluents with reverse osmosis. The developed membrane test cell of 1 m length can be assembled with further test cells to simulate a spiral wound module alone, as well as several modules in series in a pressure pipe. The test set-up enables the systematic study of fouling formation integrative over the full length of industrial spiral wound modules. All performance parameters (feed channel pressure drop, permeability/flux, and salt passage) can be monitored over the full length and locally connected to accumulated foulants (non-destructive fouling diagnosis). Validation studies demonstrated that the hydraulic conditions (relationship between pressure drop and flow velocity, as well as the flow profile) are exactly as in real spiral wound modules. Each test cell is a representative, validated system of full-scale dimensions and hydraulics. It was further found that for fouling formation investigations, feed spacers with the same thickness as the feed channel height need to be used. In this way, accurate experimental measurements, especially of feed channel pressure drop, are ensured. With the developed test cells, the impact of biofouling on membrane performance was determined under conditions similar to practice. Biofouling resulted in a decline of all membrane performance parameters. Feed channel pressure drop was affected earliest and most severely, indicating its suitability as a sensitive biofouling monitoring parameter. Salt rejection was moderately impacted by biofouling and influenced by several process parameters, reducing its applicability as monitoring parameter. It was further found, that most biofilm accumulated in the lead parts of the membrane test cells with a declining gradient towards the tail sections. The gradient of biofouling over the length of the membrane installation was directly referred to the declining availability of easily assimilable substrate. It emphasizes the importance to reduce the concentration of biodegradable nutrients in the feed to the membrane installation as suitable strategy to restrict biofouling. The high amount of biofilm deposits in the lead parts caused feed channel pressure drop increase over the lead test cell and affected negatively the performance of the downstream test cells: The tail test cells showed a moderate decline for the permeability (flux) and salt rejection. Biofiltration improved the quality of secondary effluents as tertiary treatment. It successfully reduced the load of substances (microbes, dissolved organic matter, biopolymers, particles) reportedly contributing to fouling of subsequent membrane processes. Especially biopolymers of secondary effluents, which are major membrane foulants, were identified to be completely biodegradable. The biopolymers were estimated to be of colloidal size. Yet, the removal of these organics was suggested to be completely caused by biodegradation; neither filtration nor adsorption mechanisms played a role to retain biopolymers and dissolved organic carbon within the biofilter. However, a combined study of biofiltration and reverse osmosis revealed, that the improving effect of biofiltration as pre-treatment on membrane performance was lower than expected. Although, both biofouling and organic fouling were reduced on the reverse osmosis membrane, only marginal improvement on performance parameters was found. The adsorption of small non-biodegradable substances on the membrane as an organic fouling layer in the early stages of the process, as well as the difference in fouling layer composition were probably reasons for the findings. Thus, the successful application of biofiltration as pre-treatment is highly depending on the feed water source and the foulant layer formation. For the present case biofiltration as stand-alone pre-treatment is not recommended; a combination of biofiltration with subsequent e.g. flocculation and UF could be more beneficial.

Clean and safe water is important for the well being of all organisms on earth. Therefore, it is important to reduce harmful emissions from industrial processes that use water in different ways. In vehicle washing processes, water is used in high-pressure processes, as a medium for detergents, and for rinsing of vehicles. The wastewater produced by these functions passes through a water reclamation system. A water reclamation system has two main functions, to produce reusable water to be used in future washing cycles, and to separate contaminants and purify the wastewater so it can be released back into the commercial grid. The reclamation system achieves this by using a combination of different water handling processes, these include: sludge tanks, an oil-water separator, a water reclamation unit, buffer tanks, and a water purification unit. The two components that stand for the more advanced cleaning processes are the water reclamation unit and the water purification unit. In this thesis, in collaboration with the company Westmatic, the water reclamation unit consists of cyclone separators that use centrifugal forces to separate heavy particles and ozone treatment to break up organic substances and combat bad odors. The Purification unit of choice is an electrocoagulation unit that, by a direct current, creates flocculants of impurities that rises to the surface and can be mechanically removed in a water volume inside the unit. This purification process is completely chemical-free thus making the process more environmentally friendly than other purification processes used in other circumstances. This master thesis aimed to develop a dynamic design tool for a modular solution of the different parts in the water reclamation system. This design tool uses specific user input to produce construction information for each instance. As an additional sub-aim, this design tool was linked with a computer-aided design program to produce parametric 3D models with underlying blueprints. This to produce a light solution, that has a short manufacturing time and that are highly customer adjusted. The first course of action was to mathematically define the complete water reclamation system and its components. These sections were described in a flowchart that shows how the different parts interact and operate. From the wash station, wastewater runs trough a course- and fine-sludge tank. From the fine sludge tank, the wastewater is directed in two different directions. Firstly, the water is pumped to the water reclamation unit and to one or multiple buffer tanks to finally be used in the wash station as reclaimed water. Secondly, the water travels to an oil separator, pump chamber, and water purification unit. In the purification unit, 99% of the inlet mass is directed out of the system as purified water. The remaining 1% is directed to a depot that acts like the end stage of the whole system. After all equations were defined and the design was related to the user-defined input flow the design tool was structured. The program of choice to house the design tool is Microsoft Excel. In this Excel document, a user interface with navigation was constructed and the intended user is directed through a series of input pages where input data is defined. This data is used in a normally hidden page where constructional dimensions are calculated. The constructional dimensions are displayed to the user on the second last page. At this stage the Excel document can be connected to a CAD program and 3D models with blueprints can be opened that depend on the output from the Excel file. Additionally, a pipe calculator is provided on the last page of the Excel document where pipe dimensions for different cases can be found. With this solution, glass fiber tanks are molded according to the resulting blueprints that are customer specific. In this way the solution is more adaptive and easier to handle. Additionally, the provided design tool enables an easier and more well-defined methodology when deriving the different needed volume and accompanied constructional dimensions for an arbitrary water reclamation system.

Wetland wastewater treatment offers low-cost, energy efficient alternatives to conventional wastewater technologies. In this study, an artificial wetland was constructed at the City of Denton, Texas Pecan Creek Water Reclamation Plant to facilitate diazinon removal from treated effluent.

Southeast Asian countries and Vietnam in particular are facing water security challenges; water reclamation is increasingly being considered as a favorable solution. Despite the availability of suitable technologies, several constraints often prevent stakeholders and especially decision makers exploiting their potential. In this paper we present the results of applying a decision support tool (DST) to evaluate water reclamation, support pre-feasibility studies and build capacity for water reclamation in Vietnam. The DST and its data are open access, providing information related to local and international water and wastewater quality standards. In this research we identified high potential Vietnamese case studies and conducted a systematic PISTLE analysis considering six dimensions (Political, Institutional, Social, Technical, Legal and Economic) at a multiple local stakeholder workshop. Key barriers and drivers for water reclamation implementation were identified. Measures proposed during the workshop could serve as a starting point for the development of water reclamation projects in Vietnam. / Các nước Đông Nam Á và đặc biệt là Việt Nam nói riêng hiện đang phải đối mặt với những thách thức về đảm bảo an ninh nguồn nước; cải tạo nguồn nước hiện đang được xem là một giải pháp thuận lợi. Mặc dù các công nghệ phù hợp đã có sẵn, nhưng một số hạn chế đã ngăn cản các bên liên quan và đặc biệt là những nhà làm chính sách có thể khai thác các tiềm năng của những công nghệ này. Trong bài báo này, chúng tôi trình bày các kết quả của việc áp dụng một công cụ hỗ trợ quyết định (DST) để đánh giá việc cải tạo nguồn nước, hỗ trợ các nghiên cứu tiền khả thi và xây dựng các khả năng cải tạo nguồn nước ở Việt Nam. DST và dữ liệu của nó là nguồn truy cập mở, cung cấp thông tin liên quan đến những tiêu chuẩn về chất lượng nước và nước thải của địa phương và quốc tế. Trong nghiên cứu này, chúng tôi đã xác định các tình huống điển hình có tiềm năng cao của Việt Nam và tiến hành phân tích PISTLE có hệ thống xem xét sáu khía cạnh (Chính trị, Thể chế, Xã hội, Kỹ thuật, Pháp lý và Kinh tế) tại một hội thảo của các bên liên quan tại địa phương. Những rào cản chính và yếu tố vận hành của việc thực hiện cải tạo nguồn nước cũng đã được xác định. Các giải pháp được đề xuất trong hội thảo này có thể đóng vai trò là điểm khởi đầu để phát triển các dự án cải tạo nguồn nước ở Việt Nam.