Wastewater is becoming an increasingly important source of water for reuse especially for irrigation purpose. The demands of growing communities for both food and water require the agricultural sector not only to increase food production but also to reduce its use of natural water resources. At the same time the amount of sewage is increasing. The reuse of wastewater primarly for irrigation can be a solution.

This lesson deals with the wastewater treatment technologies which are able to comply with the standards for water reuse. Usually the hygienic standard cannot be met by conventional treatment (even if it is highly efficient in removal of organics and nutrients) like activated sludge and secondary clarifier. Organic compounds and nutrients can be, contrary to conventional treatment goals, useful for irrigation because they have an additional fertilising effect on the fields.

The authors recommend therefore membrane filtration, reverse osmosis and UV radiation to disinfect the treated wastewater and to achieve the highest standard which can be used for almost all purposes. In case of reuse in restricted agriculture, other options are suitable like slow sand filtration or ponds with long residence time.