





	In Japan, Sewerage Systems (Sewer collection systems and
	Wastewater Treatment Plant) were adopted in urban area or
	high population density area.
	All of generated wastewater in this area is collected and
	transported by sewer systems and treated by Wastewater
	Treatment Plant. Sewered Population Rate, percent of
	total population served by sewerage systems (Wastewater
	treatment plants connected with sewer systems) as of 2006
	was 70%.




	On the other hand, in rural area, individual household
	treatment system(Joukasou) which is deferent from Septic
	Tank is adopted, because the construction cost for sewer
	systems, or transportation cost of wastewater to WTP will
	increase when the sewerage systems are adopted in rural area
	of which population density is low. (This system’s population
	served rete is about 8% as of 2006.)

	In this case, on-site treatment system (JOUKASOU; individual
	household treatment system) is more cost effective than
	off-site treatment system including wastewater collection
	pipes and WTP.
	Generated wastewater in a household is treated on-site by
	Joukasou utilizing settlement, microorganisms activity, etc.
	and settled sludge is removed (usually once a year) and
	and transported to sludge treatment facility by truck.





	JOUKASOU System
	(individual household treatment system)



	Example of Construction of JOUKASOU SYSTEM

	(Above 4 Figures are quoted from “Joukasou
	Systems for Domestic Wastewater Treatment”
	published by Japan Education Center of
	Environmental Sanitation)

	The selection criteria for these systems is based on cost
	effectiveness or cost comparison between connection pipe
	construction cost between two houses, and joukasou.

	If Joukasou construction cost is higher than connecting pipe
	construction cost between two houses, sewerage systems will be
	adopted, and vice versa.
	Namely, in a low population density area (left part of next
	figure), connecting pipe construction cost per capita is higher
	than Joukasou construction cost per capita, and Joukasou will
	be adopted.



	Based on this criterion, Sewerage Basic Plan, which shows
	the suitable area for Joukasou and Sewerage Systems in each
	Prefecture has been formulated, and rational wastewater
	treatment for preservation of water quality in public water
	bodies have been promoted.