Fertilizing value and polluting load of reclaimed water in Tunisia

A national survey of wastewater composition was conducted for 28 chemical constituents from 15 treatment plants located across Tunisia to provide a basis for establishing water quality and management for crop production and environmental protection. The contents of salt, nutrients and trace elements were investigated and showed that the composition was characterized by a moderate salinity and sodicity for most of the plants, a high variability of the organic parameters, and a low trace elements content. In the case of N and P, such variations may be a constraint in using the water for fertilizing purposes. An increase in salinity with time was noticed for several plants. While the salt contents of wastewater were not affected by the treatment process, total N and P removal efficiencies were 48% (62% for ammonium) and 63%, respectively. For trace elements, removals averaged: Zn 87%; Cu and Fe 78%; Pb 64%; Cr 50%; Mn 44%; Co and Cd 17%; and Ni 13%. The analyzed reclaimed water samples were consistent with the Tunisian standards regarding water quality required for agricultural reuse and had a high fertilizing content.