WaterSubject

The aim of this paper is to study the performance of a combined waste stabilisation pond after three years of functioning and the reuse of treated wastewater for irrigating potatoes and lettuce culture. The combined ponds showed good functioning conditions and excellent performances either for organic load (90%), faecal coliform (6 log units) or helminth eggs (100%) and produced a high and perennial effluent quality. The effluent could be used for non-restrictive irrigation, with a clear improvement of culture production and hygienic quality for both fruits and soil.Agricultural reuse of wastewater offers an additional resource of irrigation water and high soil fertilising potential. Many studies have been undertaken on agricultural reuse of wastewater treated by classical stabilisation ponds systems. Stabilisation ponds are known as extensive treatment systems, well adapted to low socio-economic conditions in developing countries. Moreover, it has been demonstrated by several authors that these systems can lead to very satisfactory effluent quality if they are well designed.

In Morocco, several studies have been undertaken on stabilisation ponds, such as Microphytic ponds and high rate algal ponds. However, few studies have been achieved to date on combined pond systems that integrate aerated ponds and storage reservoirs to the classical filial status of stabilisation ponds. An aerated pond can greatly reduce the land area demand whilst increasing the equivalent inhabitant treatment volume. On the other hand, the integration of storage reservoirs might lead to improvement in the effluent quality as a maturation treatment and insure the sustainability of wastewater for irrigation during the driest period of the year.

Recently, combined stabilisation ponds have been built in Benslimane (Morocco) to treat the main wastewater discharged from the city. Following pre-treatment, wastewater from primary anaerobic, aerated and facultative ponds, is retained in storage reservoirs. Recently a preliminary study has been done on such a system and shown substantial performance efficiencies during the first months of functioning.

The aim of this paper is (i) to note the efficiency of this combined waste stabilisation pond to eliminate organic load, faecal coliforms and helminth eggs after three functioning years and (ii) to investigate the reuse of treated wastewater for irrigating potatoes and lettuce culture in comparison to both raw wastewater and a control (drinking water). Particular attention has been placed on irrigation water quality, especially in regard to agronomic and health parameters and on the impact of irrigation on both hygienic and chemical quality of crops and soil.

The combined stabilisation pond system of Benslimane city shows high efficiencies throughout the year for both organic load elimination and for sanitary risk parameters. Moreover, the efficiencies are similar to those described by for their studies of the same treatment plant following one operating year. The percent removals found in the present study are very important and are similar to those described by in analogue treatment systems under temperate climate but exceed those obtained in classical stabilisation ponds in Ouarzazate or in Marrakechor in Jordan.

Furthermore, the studied stabilisation pond system presents a high capacity to absorb high variability of pollutant charges as demonstrated by. This points are considerable stability in the treated effluent quality.

On the other hand, the combined stabilisation pond investigated seems to be independent of climatic conditions, even given water temperature varying between 15 °C as a minimum in the cold period and 25 °C as a maximum recorded in the hot period. This kind of treatment plant therefore leads to a high and perennial effluent quality during all the year. Investigations need to be made to confirm this conclusion for operations over an extended time period exceeding 3–5 years and especially after accumulation of sludge in the anaerobic pond.

Treated wastewater by such a combined stabilisation pond system provides for non-restrictive irrigation without any risk. A clear improvement of culture production has been noted when irrigated by treated wastewater which provides full fertiliser crop requirements in comparison to the control. Furthermore, hygienic quality of both crop and soils are very high and are equally safe as land parcels irrigated by water of drinkable quality.

This study can therefore help to make a better choice of wastewater treatment plant systems for other Moroccan and Mediterranean cities, especially those with more than 10 000 inhabitants, where classical stabilisation ponds have not been adopted due to the large area demand. Combined stabilisation pond systems such as the one investigated here, can be considered as a good alternative, and better than more expensive and less healthy intensive systems.