Wastewater reuse with groundwater safeguard.

Abstract

In Morocco, reuse of raw wastewater for irrigation is practised around the big cities without taking into account the sanitary and environmental concerns. All national institutions involved in wastewater problems are convinced of the need for wastewater treatment with extensive systems before it can be applied for agricultural reuse. Our experimental work on wastewater treatment using lagooning, macrophytic plants, reed beds, infiltration percolation or over-land flow showed that of all these extensive systems lead to an effluent classified into category B according to WHO guidelines. However, the amount of nitrogen largely exceeded the crops' requirements and could cause serious problems for groundwater. Using the DRASTIC method, a vulnerability map was established for groundwater in the plain surrounding the city of Marrakech. The estimates of nitrogen amounts from wastewater that can reach groundwater after crop uptakes showed that only the low vulnerability zone could be safely irrigated with the treated wastewater. The second zone of moderate vulnerability covering 50% of the area in the plain could receive the treated wastewater, but a careful program of irrigation is required to avoid nitrate contamination of groundwater. The third zone at a high vulnerability level should be protected, without any further irrigation using wastewater, even after extensive treatment. This new approach integrating the results of the preliminary vulnerability study of groundwater zones could constitute a helpful tool to improve management of regional projects of wastewater reclamation and reuse.