Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>
6.1 Wastewater reuse from off-site treatment plants
6.1.1 Wastewater reuse for agriculture
Treated wastewater from off-site treatment plants can be reused for
irrigation of parks and gardens, agriculture and horticulture, tree plantation
and aquaculture, if these exist or can be established not far from the
wastewater treatment plants. For these purposes the wastewater should
generally be treated to secondary wastewater standard (< 20 mg/L BOD and
< 30 mg/L SS). Total coliforms should be < 1000 organisms per 100 mL for
irrigation by spraying. When sub-surface irrigation is used this requirement
may not be necessary. A period of non-entry to irrigated sites may need to be
observed, particularly for wastewater-irrigated parks and gardens. Irrigation
of vegetables for direct human consumption requires a much stricter guideline.
Because requirement of wastewater for plant growth is governed by climatic
conditions, soil and plant type, there may be a need for storage of the
wastewater. An alternative to storage, if land area is not available for this
purpose, is to dispose of wastewater that is excess to requirement. A
combination of wastewater for irrigation and aquaculture (see below) is also
an option that can be considered.
Land application for treatment of wastewater described in Section 2 (4.2.4)
(Slow rate land application and grass filtration) when combined with growing
of grasses for grazing by sheep or cattle plus the “cut and carry' system
can properly be considered as treatment and reuse of wastewater.
6.1.2 Wastewater reuse for aquaculture
Wastewater reuse for aquaculture has been practised in many countries for a
considerable period of time. It has the potential of wider application in the
tropics. A special section in this Source Book is devoted to this important
topic. This is placed at the end of Section 2 (6). A case study is also
presented in the Regional Overview for Central & South America.
6.1.3 Wastewater reuse for industry
Treated wastewater can also be used for industrial purposes, if suitable
industries are not far from the treatment plant. Industry’s requirement for
water quality ranges widely, from very pure water for boilers of electricity
generation to lower water quality for cooling towers. Treated wastewater can
fulfil the lower range of this requirement, e.g. water for cooling towers.
Secondary-treated wastewater after chlorination may be adequate for this
With off-site treatment plants reuse of wastewater may be limited by the
need to pipe treated wastewater to where it is needed. To implement wastewater
reuse in houses for toilet flushing, watering of gardens and other purposes
which do not need drinking quality water, a third pipe-reticulation system is
required, that is in addition to the reticulation to provide drinking water
and the sewer to collect the wastewater. Care is also needed to prevent
cross-connection between drinking water and treated wastewater.
'Sewer mining' is the term given to the withdrawal of wastewater from a
sewer for reuse near to the point of withdrawal. This provides an opportunity
for reuse without having to pipe treated wastewater from the centralised
treatment plant. Wastewater needs to be treated to the standard required for
the reuse, and may duplicate the function of the centralised treatment plant.