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The Earth is called “The Planet of Water”. However, approximately 97.5% of the water on the Earth is seawater, and only 0.01% is fresh water that humankind can use to live. Around the world, about 1.1 billion people are in dire need of safe water to drink. The number lacking sewerage and other sanitary facilities is said to be as high as 2.6 billion *1. That is why we need to provide water recirculation systems that can contribute to the effective use of scarce water resources and to the conservation of the global environment.
Our cities have water treatment facilities such as water purification and sewage treatment plants. Thanks to these facilities, we can have water in our everyday lives, just by turning on a faucet. Water purification plants take water from rivers, clean it, and send it to homes.
Sewerage water from homes and waste water from offices and factories are carried to sewage treatment plants and cleaned before it is discharged to rivers or the sea. Most of the sewage treatment plants in Japan harness the effect of microorganisms to treat sewage and return it to clean water levels.
So, sewage treatment plants are vitally important facilities for water recirculation, and they contribute to the ecology of precious water resources that can be used over and over again.
However, as the population of the earth increases and the ways of life change, water contaminated with countless substances is sent to sewage treatment plants, causing severe problems. One of these is red tides. Red tides are a phenomenon which occurs when abnormal proliferation of plankton causes the sea to look red. They kill organisms in the sea through oxygen depletion. Red tides are caused by eutrophication, which is in turn due to nitrogen and phosphorus in sewage from homes, industrial waste water from factories, and other sources.
It requires advanced treatment to remove the nitrogen and phosphorus, which needs large amounts of treatment space and time. Hitachi,Ltd. has responded to this situation by working with the Japan Sewage Works Agency on ways to make the facilities and processes for advanced treatment more efficient. The result of development was “Integrated Immobilization Nitrogen Removal Process”.
The method of using empowered microorganisms locked into cubes to purify water is attracting attention internationally.
Conventional technology pumped air into sewage flowing out of the primary sedimentation tank to activate the microorganisms and make them proliferate, but the slow pace of proliferation necessitated adequate amounts of time and space.
Therefore, we decided to seal microorganisms called nitrifying bacteria, which remove nitrogen, into 3mm cubes of polymer to make Nitrifying Pellets. These are added to the bioreactor in order to shorten the time required for nitrogen treatment.
“Integrated Immobilization Nitrogen Removal Process” is the treatment technology that uses these Nitrifying Pellets to remove contaminants such as nitrogen and phosphorus in a shorter time and a smaller space.
In sewage treatment plants, debris mixed with the water is removed first, then floating contamination is allowed to settle out. Next, in the reactor tank, the power of microorganisms sealed into Nitrifying Pellets removes nitrogen and phosphorus, then the separated, treated water is disinfected and discharged to a river.
It is difficult to maintain high concentrations of nitrifying bacteria suspended in water, so they are immobilized in a polymer material such as polyethylene glycol and formed into cubes of approximately 3mm, creating an easy environment for multiplication. These are Nitrifying Pellets.
“Integrated Immobilization Nitrogen Removal Process” is a unique and environmentally conscious treatment method, using Nitrifying Pellets of nitrifying bacteria encased in polymer to treat sewage. It is superior to previous methods in the areas of space saving and high throughput.
Nitrifying Pellets maintain the concentration of nitrifying bacteria in the aerobic tank at a high level, so the nitrification reaction, which is the nitrogen removal process, proceeds efficiently. Processing time has been reduced by about half compared to previous methods, at 6-8 hours.
Time is not the only thing “Integrated Immobilization Nitrogen Removal Process” saves on. There is no need to provide great expanses of space for the nitrification reaction, or to build new tanks, so this system can be added smoothly to existing treatment facilities.
The treatment time for conventional methods is 12-16 hours, so it was inevitably necessary to expand the aerobic tanks.
“Integrated Immobilization Nitrogen Removal Process” is able to maintain a high concentration of nitrifying bacteria, so existing tanks can be used without modification.
Aerobic tank (interior)
The effect of Nitrifying Pellets added to the aerobic tank enables rapid nitrification treatment of ammoniac nitrogen, which is the main constituent of nitrogen in sewage.
We have also developed an energy-saving type of “Integrated Immobilization Nitrogen Removal Process” with improved energy efficiency and maintainability.
Treatment method: Recycled nitrification/denitrification
The Sanpou Sewage Treatment Plant in Sakai City, Osaka Prefecture, is located at the mouth of the Yamatogawa River in the northwestern part of the City. The plant has been in operation since 1963 and provides sewage treatment and rainwater drainage for about 160,000 people living in the northwestern area of the City. The plant has a site area of around 130,000 m² and a capacity of 120,000 m³/d.
To efficiently perform advanced sewage treatment in a limited space according to the comprehensive plan of a sewage system at Osaka Bay, the plant has adopted the "Integrated Immobilization Nitrogen Removal Process" in the form of a three-step-feed system with pellet addition.