SEWERAGE BUSINESS MANAGEMENT CENTRE


		Secondary treatment removes mainly organic matter and suspended solid in wastewater. However, in some area, especially in closed water body such as inner bays, semi-enclosed seas, lakes and reservoirs, secondary treatment level has been insufficient to protect the receiving waters. In these areas, the load of inflowing pollutants is large and pollutants tend to accumulate. There has been progress of eutrophication caused by inflowing nutrients such as nitrogen and phosphorus, which accelerated the deterioration of water quality.

		Thus, advanced wastewater treatment or additional treatment step to remove further organic matter and suspended solids and/or to provide for removal of nutrients such as nitrogen and phosphorus has been needed for prevention of eutrophication, achievement of water quality standard, water quality preservation in water supply source, reuse of treated wastewater, etc.

		The total number of Wastewater Treatment Plants in Japan was 1,845 in 2003, and among them, advanced wastewater treatment processes were adopted in 255 WTPs. Also, the sewered population in Japan was about 85 million, and among them the sewered population with advanced treatment was about 15 million. Then, Sewered Population Rate to total population was 67%, and of which 12% was Sewered Population Rate with advanced wastewater treatment. This rate with advanced wastewater treatment was relatively low compared with other Western nations.



		As for advanced wastewater treatment process, the most widely adopted process for removal of phosphorus is Coagulant Adding Process in 383 facilities and for nitrogen removal is A2O Process; Anaerobic-anoxic-oxic Process, in 50 facilities. By A₂O Process, phosphorus is also removed.


		-----------------------------------------------------------------
		Advanced wastewater treatment means any processes designed to obtain higher effluent water quality than normally achieved by secondary treatment process, and the main purposes for advanced wastewater treatment are as follows.

1.	Water Quality Preservation in Closed Water Body
	Preventation of Eutrophication

	In closed water body like inner bays, lakes and reservoirs, the concentration of nutrient such as phosphorus and nitrogen increases by inflowing domestic wastewater and so on. Increased nutrient concentration stimulates blooms of algae, and eutrophication in these　 waters is progressed. Once eutrophication occurs,it induces depletion of oxygen concentration and death of fish and shellfish, generation of red tides and water-bloom, abnormal odor, deterioration of water quality, etc. Then, to prevent eutrophication, advanced wastewater treatment is required.	Generation of Red Tide

2.	Achievement of Water Quality Standard

	Under the Basic Environmental Law, EQS; Environmental Quality Standards for water pollutants are set as the target levels that are desirable for water quality to be achieved and maintained in public waters. There are two types of standards, EQS for protecting human health and for living environmental protection. Please refer to; Ministry of the Environment Web Page The former health items are stipulated uniformly for all public water areas. EQS values for the living environment have been established for BOD, COD, DO, and other variables, and to prevent eutrophication, EQS for nitrogen and phosphorus were established for lakes and reservoirs, and sea ares. The achievement rate of EQS is about 80% in rivers and sea area, but only 50% in lakes and reservoirs. Thus promotion of advanced wastewater treatment is needed.


3.	Water Quality Preservation in Water Supply Source

	Approximately 70% of water supply sources are surface runoff such as rivers, and public waters are greatly affected by water pollution. Especially, in recent years, the eutrophication of reservoirs has caused abnormal odors and tastes of tap water. To preserve water quality in water supply source, advanced wastewater treatment is also required.

4.	Reuse of Treated Wastewater

	Treated wastewater has been used for flush toilets, water for landscape use and recreational use, discharge for flow maintenance, etc. As for the reuse of treated wastewater, target substances for treatment and its treatment level are different depending on the purpose of reuse, so appropriate advanced wastewater treatment process should be selected based on its purpose.



	----------------------------------------------------


	By promotion of sewage works, water quality in public water bodies has been gradually improved, but in closed water bodies, the water quality has not so improved. Therefore, the advanced wastewater treatment should be promoted to remove further organic matter and suspended solid, phosphorus and/or nitrogen which are the cause of water quality deterioration.

	To cope with the situation, the sewerage law was amended on June 2005, and it was formulated that target reduction amount and reduction method for nitrogen and phosphorus in each WTP should be determined in comprehensive basin-wide planning of sewerage systems for closed water bodies like lakes and bays

	Also, partial amendment was made on the Enforcement Order of the Sewerage Law on September 2003, and it was decided that "planning final effluent water quality" in terms of BOD, Nitrogen and Phosphorus should be established by the general manager of sewerage systems considering the condition of public water bodies in which treated effluent water is discharged. According to the classification of planning effluent water quality, the appropriate wastewater treatment process should be adopted.


	*Classification of Planning Effluent Water Quality and Typical Wastewater Treatment Method*

	In amendment of sewerage law, the local government may offer a surplus nitrogen and phosphorus reduction over and above their current target removal amount to prefectural governments with the agreement of related local government. In this case, it is possible that the local government makes the related local government bear the part of O&M cost in WTP to reduce surplus nitrogen and phosphorus.

	In Japan, for further water quality preservation in public water bodies, advanced wastewater treatment is required. To accomplish that, the sewerage law and its enforcement order were amended, and several counter measures have been conducted to achieve water quality standards,prevent eutrophication in closed water bodies and so on.