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Summary - Lecture 4: Waste Management – Water and Solid Waste


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2018 ProSPER.Net Young Researchers' School
Lecture summary prepared by Wendy Wuyts (Nagoya University) & Yangyang Li (Nanyang Technological University)

Published in: Government & Nonprofit
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Summary - Lecture 4: Waste Management – Water and Solid Waste

  1. 1. Lecture 4: Waste Management - Treating sewage for sustainable development By Assoc. Prof. Kengo Kubota (Tohuko University) Reporters: Yangyang Li (Nanyang Technological University) and Wendy Wuyts (Nagoya University) In Japan, the rivers are very beautiful and clean, because of the good (but maybe high intensive energy/resource) waste management, which has co-benefits for the urban ecosystem and the improvement of human lifes. F.e. near Hirose river, the wastewater treatment plant located upper stream of this river employs ozonation for disinfection to prevent ecosystem degradation of the river. This was not the case in the past, where there were water-related diseases such as cholera, but now the beautiful environment is recovered. During the lecture, sewage is defined as 1) Discharging rainwater (reduce the risk of flood disaster in city) and 2) Collecting wastewater and treating in the treatment plant. the sewage treatment plant (as in Japan, and other developed countries) exists of two parts: wastewater treatment and solid waste treatment. Different technologies, their advantages and requirements, were explained during the lecture (see slides). As waste can generate energy, this lecture especially looked into energy recovery opportunities. Wastewater treatment consists of primary sedimentation, activated sludge process, final sedimentation and disinfection. In an aerobic process, highly treated water can be obtained. One disadvantage is the high energy demand (for aeration) and that it generates a huge amount of excess sludge. Also this system requires engineers, as it is a complex system for operation. On the other hand, technology based on anaerobic process can accept a high organic loading, but the treated water quality is not good (COD higher than 100 mg/L). The advantages of anaerobic treatment process is the generation of energy and the low excess sludge production. It is cost-effective and environmentally friendly. Also solid waste can be a source for biofuel (biogas, biodiesel, bioethanol). The waste biomass could be converted with the means of anaerobic microorganisms in intermediary products such as methane gas, biogas, and utilized in co-generation. As the Japanese law (e.g.FIT law) creates opportunities, there is a call for future applications where by-products of wastewater and solid waste treatment can provide energy sources. But a systematic assessment of economic and technical feasibility as the land requirement and availability has to be conducted. Urban planning plays here a role. As some systems (e.g. waste stabilization pond) require land, urban planners should discuss this with the sewage planners. Also urban governance is important to determine which technology is the best for the context specific needs and issues (see case study Yamuna River and river bathing in India). The discussion itself was more about the acceptability of the result of wastewater treatment. F.e. in Singapore, people do not want to drink treated water, although it is very safe. So here urban governance plays a role. There were also talks about the waste of the technologies, like the abandoned sponges, but also about the sludge. In India, farmers do buy the sludge, and in Japan they also do some composting. They investigated to use sludge for concrete, but Japanese construction people complained about the quality due to the high amount of fosfat. Thirdly, although discharging floodwater is also a part of sewage system, a limited amount of rainwater harvesting is done in Japan. Black water, grey water and rainwater is all put together in sewage system, which means missed opportunities. F.e. you can use rainwater harvesting for green space in urban contexts, which has implications for urban ecosystems. The design of urban housing and infrastructure should be adjusted for that. Lastly, to investigate if the system could sustain itself (and net energy consumption would be zero) it was asked how much energy could be generated (besides the fact it requires low energy input.)