AIR MIXING IN ANAEROBIC AND ANOXIC TANKS AT TAMATSU TREATMENT PLANT IN KOBE CITY

Kobe City, which has a population of 1.49 million people, initiated its sewerage construction project in 1951 and its sewered population percentage was nearly 98% by the end of fiscal year 2000. As concern about the preservation of the global environment continues to grow, in implementing the municipal sewerage system, Kobe City is called upon to take more energetic measures to preserve and create water resources. To accomplish the goals of recycling society, Kobe City has been steadily upgrading its wastewater treatment facilities into advanced treatment ones with comparing and searching out the effective economical advanced treatment systems. At the Tamatsu Treatment Plant, an advanced treatment facility with a maximum daily treatment capacity of 41,000 m3 went into service in October 1999. The plant has adopted the anaerobic-anoxic-aerobic process for the biological simultaneous nitrogen and phosphorous removal. And it uses the large bubbles intermittent air mixing, which can inhibit oxygen dissolution into the mixed liquor, can reduce the installation costs and maintenance costs of submerged mixers, and the anaerobic-anoxic-aerobic process with less required mixing power, thereby the cost reduction and energy saving. This is a report of the effectiveness of the large bubbles intermittent air mixing in the anaerobic tank and the anoxic tank, and of the operating conditions of the advanced treatment facility at the Tamatsu Treatment Plant.