1) In Japan, rivers are very clean due to effective wastewater treatment plants that employ technologies like ozonation to prevent ecosystem degradation while recovering beautiful environments. 2) Sewage treatment plants in Japan and other developed countries use various technologies for wastewater treatment, solid waste treatment, and energy recovery from waste. 3) Urban planning and governance are important for determining the most suitable wastewater treatment technologies for a given context and ensuring public acceptance of treated wastewater.

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.)