Treated wastewater is a valuable water resource in urban are, and its amount
will increase with the progress of sewered population rate.
Treated wastewater was not so much reused directly in the past.
However, the same water quality as drinking water is not always needed for
reuse of treated wastewater such as flushing toilet.
Then, treated wastewater will be more reused in future. Especially, in urban
area where population is so concentrated and it is very difficult to secure
water resources, reuse of treated wastewater is one of the effective
countermeasures for water shortage.
The total amount of treated wastewater from 1,718 Wastewater Treatment
Plants in Japan in 2001 was about 13 billion m3 per year. In more than
half of total WTPs, treated wastewater is reused in each WTPs as
antifoaming water in aeration tanks, washing water, etc.
In 2001, in 218 WTPs the treated in wastewater is transported to the outside
of WTPs and reused as industrial water, water for landscape use and so on,
and its amount was approximately 190 million m3 per year.
Table. Present Condition of Treated Wastewater Reuse
Reuse Application Number of
WTPs		 Amount of
Reuse(Unit:
10,000m3/year)		 Number of
Water Supply
Point
1.

 Flush Toilets
(Miscellaneous water system)		 40 577 362
2. Water Reuse for Environment
(1) Water for Landscape Use 72 2,770 64
(2)
 Water for Recreational Use 19 695 17
(3)
 Discharge for Flow Maintenance 11 7,992 11
3. Snow Melting Water 20 2,928 18
4. Others
(1) Sprinkling Water 134 62 107
(2) Agricultural Water 22 1,293 18
(3)
 Supply to Industrial Water Works 3 366 362
(4)
 Direct Supply to Business Institution and Factories 46 1,967 45
Total 367 19,000 1,004
Note:
The number of WTPs in the table is counted for each reuse application.
There are several WTPs which reuse treated wastewater for two or more application.
The net number of WTPs without diplication is 218.
The treated wastewater is reused mainly in the following way.
 
After the wastewater is biologically treated, treated water is further
purified by reclamation facilities which consists of chemical coagulation,
ozonation, sand filtration, chlorination, etc., and transported to office
buildings, houses, etc. Distributed treated wastewater is reused for
flush toilets.
In these office buildings and/or
houses, the distribution pipes for
treated wastewater is strictly
separated from drinking water
water pipes. For instance, these
pipes are easily distinguished by
indication or color, and cautionary
statement of using reclaimed water
is displayed near the facility.
Reclamation Facility in
Fukuoka City
(1) Water for landscape use: 15% of total reused wastewater
The treated wastewater is poured into the stream or pond in order that
people could enjoy the waterside landscape. In this case, the treated
wastewater is reused on the premise that people will not touch the
treated water.
Example of Landscape Use Example of Landscape Use
(Osaka City) (Osaka City)
Reclaimed water is partly used in
the Moat surrounding Osaka Castle
(2) Water for recreational use : 4% of total reused wastewater
Highly treated wastewater is poured into stream on the premise that people
could touch the water. In this case, it is very important to enhance the safety
of water from a hygienic point of view as people would touch the water.
(3) Discharge for flow maintenance : 42% of total reused wastewater
A certain amount of water flow should be maintained to keep the regular
function of river from the point of view of water quality protection,
prevention of damage from salt water, landscape, sightseeing, etc.,
even in dry season. Usually, the water in the upstream of the river is
taken for water supply and distributed to houses. After supply water is
used in each house, wastewater
is directly transported through sewer
pipes to Wastewater Treatment
Plant located ownstream of the
d river. For this reason, amount of
water flow in the river from the intake
of the water to the outlet of WTP is
remarkably reduced, and treated
wastewater is sometimes utilized as
discharge for flow maintenance.
Megurogawa River reemerged
through use of reclaimed water
(Tokyo Metropolitan Gov.)
Lying snow on the ground affects the urban activities by narrowing the
urban space, and the removal of lying snow on the roads is a major
concern for municipalities in nothern part of Japan in winter.
Treated wastewater, which is at 13 degrees C. is a effective heat source
to melt snow in snow-flowing conduits or snow-melting tank and ditches
where collected lying snow is transported.
Hassamu snow-flowing conduit Atsubetsu snow-melting tank
(Sapporo City) (Sapporo City)
(1) Sprinkling water for zones planted with trees, washing water for roads
and/or construction site : 0.3% of total reused wastewater
(2) Agricultural water : 7% of total reused wastewater
(3) Supply to industrial water works : 2% of total reused wastewater
(4) Direct supply to business institution and factories : 10% of total
reused wastewater
For these reuse of treated wastewater, Design Manual for Treated
Wastewater Utilization was formulated, and water quality for reused
wastewater was established as follows.
However, recently people are more concerned with water saftey because of
health hazard by Cryptosporidium, etc. Then, in 2003, Special Committee
for Water Quality for Reused Wastewater was established by Ministry of
Land Infrastructure and transport to investigate the technical standard for
reclaimad water, and water quality for reused wastewater is now being is
now reviewed and will be revised in FY 2004.
Table. Current Water Quality for Treated Wastewater Reuse
Japan Sewage Works Association
(prpposed in 1981)		 Working group composed of
Minisry of Construction and big cities (proposed in 1990)
Toilet
Flushing Use		 Spraying
Use		 Landscape
Use		 Landscape
Use *		 Recreational
Use **
Coliform Group 10 or below
(cfu/mL)		 Not
detective		 Not
detective		 1000 or below
(cfu/100mL)		 50 or below
(cfu/100mL)
Chlorine Residual
(mg/L)		 Trace
amount		 0.4 or over - - -
Appearance Not
unpleasant		 Not
unpleasant		 Not
unpleasant		 - -
Color
(color unit)		 - - - 40 or below 10 or below
Turbidity
(mg-kaolinequivalent/L)		 - - 10 or below 10 or below 5 or below
Odor Not
unpleasant		 Not
unpleasant		 Not
unpleasant		 Not
unpleasant		 Not
unpleasant
pH 5.8-8.6 5.8-8.7 5.8-8.8 5.8-8.9 5.8-8.10
BOD
(mg/L)		 - - 10 or below 10 or below 3 or below
Note:
* restricted human contact,
** limited human contact
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