This work tests experimentally the capacities of water hyacinth (Eichhornia crassipes) and duckweed (Lemna gibba) to purify wastewater in Marrakesh.

  • 1)

    Eichhornia crassipes was grown in continuous culture with a constant flow rate of 10 l.min.−1 Organic, bacterial and parasitical loads were examined to determine the efficiency of the system. The results show that water hyacinth is well suited to the climatic conditions of Marrakesh. Domestic sewage purification by water hyacinth leads to satisfactory efficiency during the summer with an 87% reduction in chemical oxygen demand (COD) and 95% reduction in total suspended solids (TSS). Bacterial load reduction expressed by control of faecal contamination bacteria achieved 2 log units for a short theoretical retention time (7 days). Moreover, this process reduced parasitic helminth eggs to undetectable levels.

  • 2)

    Lemna gibba was grown in continuous culture with a constant flow rate of 3 1. day−1. Only organic loads were examined. Three categories of influents were tested to determine the system efficiency. The results obtained show that Lemna gibba has the capacity to purify a low organic load (COD:305–530 mg.l−1). The average influent COD was reduced by 82%. During the summer period the average influent COD and TSS has been reduced by 61% and 82% respectively.