Waste-to-Energy: A Japanese model of efficiency

  • The wastewater treatment plant is powered by thermal fuel from the incinerators
  • Treated wastewater is pumped back into the ocean
  • The facility manages to break even by selling the gas it produces to households and industrial buyers

K. Male' 2019 Oct 10 | Thu 13:16 report 4,089

The Wastewater treatment facility in Kobe, Japan - Raajjemv

Ever heard of sewage water being recycled to be used as fertilizer? Or to be used as fuel for the city bus? Well, even though some might irk at the idea and others might think of it as dubious or rather unreal, this is exactly what the Japanese city of Kobe is doing. They are recycling sewage water to be used for a variety of purposes, at every level imaginable. From being used as fertilizer at vineyards to powering the daily commute, they are doing it all.

The bio fuel refill station for the city bus : The bus runs entirely on bio fuel

During a recent visit to Japan, I was privileged enough to see how this is being done first hand and I was flummoxed, to say the least, at a perfect model of recycling being practiced. It all starts the minute you flush down your waste down the sewage pipe. In Kobe, there are two kinds of sewer pipes running underground. They are storm water sewer pipelines to collect the rain water and sanitary sewer pipelines to collect wastewater. Whilst the rainwater goes directly to the sea or river, the wastewater is collected and sent to wastewater treatment plants to be cleaned and returned to the sea.

Here is where the magic of purifying the water starts. First the waste water is filtered through what is called a screens & grit chamber before being pumped into the wastewater recycling plant. The screens process is done in order to prevent larger items and non-dissolvable items from getting in the Waste water treatment facilities machinery. The grit chambers are where the small particles like sand and other smaller particles are filtered out and the water is pumped into a primary settling tank.

The water inside the primary settling tank is set at a steady flow. This is done to ensure that the heavy solids sink to the bottom and these solids are then pumped into the digesters. The light solids are also flowed into the bio reactor after being treated for some extent. Inside the bioreactor, the wastewater is mixed in with microorganisms and become “activated sludge”. Air is injected into the activated sludge to enable the tiny bacteria in the solution to become active and ingest smaller organic matter in the water. These bacteria tend to flock and become easier to sink.

From the bio reactor the water flow reaches the final settling tank. Organic materials consumed by the microorganisms are heavy enough the settle down and sink to the bottom and the water is purified completely. This purified water is flowed into a chlorination tank and disinfected to kill off any remaining bacteria still in the water, and then pumped back in to the sea, to where it all began.

Now what’s remaining is the activated sludge, which is what is used to make the bio fuel and fertilizer. The sewage sludge left in both settling tanks is digested in the egg-shape digester and de-watered afterwards. The digesters are where the actual magic happens. These digesters heat the sludge at a set degree to produce the bio fuel and produce methane to be used as gas for cooking. The remaining sludge is sent off to the incinerators to be burned. Even this sludge is not wasted. The thermal energy produced by burning this sludge is what powers the waste incinerators. A truly remarkable system of efficient recycling.

The egg shaped digesters : These heat the activated sludge to produce methane

Now there are certain drawbacks to the system. One being the massive investment by the city authorities to build the wastewater treatment facility. The officials at the Kobe wastewater treatment plant say that while the investment has not been recovered, the facility still manages to cover all running and maintenance expenses by selling the gas it produces. Another disadvantage is dumping the remaining ash after incineration. Currently it is being dumped into Osaka Bay, and the Kobe city officials assure that it is free of all micro plastics and other harmful material for the environment. But some environmentalists argue that this is harmful to the environment, even though there is a lack of scientific backing to this argument.

True to Japanese values, the Kobe recycling project is one modeled on efficiency and immaculate perfection. Even with the drawbacks, this system of recycling is achieving its ultimate aim of recycling and reusing wastewater with minimal impact on the environment, whilst producing methane for consumption by households and industrial buyers. The Kobe city official’s assurance that they are continuously assessing the project to further enhance the scope and ability is another point in favor of this system.

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