Reuse of treated domestic wastewater on Mediterranean agricultural crops

Wastewater is considered as a new and unconventional source of water for agricultural production in many arid and semi-arid countries worldwide. As a result, careful monitoring of soil and plants for a range of parameters including salts, nutrients, micro-elements, heavy metals, toxic pollutants and pathogens is required.
During this study, the application of three different qualities of treated domestic wastewater on four agricultural crops was examined in Crete, Greece: a typical Mediterranean semi-arid area. Primary treated (low quality), secondary treated (medium quality) and tertiary treated (high quality) wastewater were applied to a) olive trees, b) grapevines, c) radishes and d) carnations. Tap water and fertilized tap water (controls) were also applied in all the above agricultural crops for comparison with treated wastewaters.
In general, increased concentrations of sodium, phosphorus, potassium and nitrogen in soils could be observed after wastewater irrigation. High salinity and boron concentrations in treated wastewater had no adverse effect on the examined cultivations. Low quality treated wastewater should not be used for irrigation mainly due to high levels of pathogens. In addition, they were found to a) to inhibit grapevine growth b) to degrade grape quality characteristics, and c) to accumulate polycyclic aromatic hydrocarbons (PAHs) in soil and radish roots.
On the other hand, high quality treated wastewater had no negative effect on soil, plant growth, health safety and fruit quality of all the examined agricultural crops. Furthermore, the application of tertiary treated wastewater a) improved leaf chlorophyll concentration and yield of grapevines, b) improved yield and fruit quality characteristics of radishes and c) improved plant growth of carnations. Finally, olive trees were found to be less sensitive to irrigation water quality suggesting that even medium-quality wastewater could be safely applied.