Abstract

In the developing countries in general, industrial effluents are discharged into the rainwater evacuation channels, on the street, or in nature, without treatment, causing immense environmental damages. This work aimed to propose, at a pilot scale, a test treatment, based on a Pistia stratiotes L., 1753 pond system, to purify wastewater from the Cotton Development Company of Cameroon (CDCC) oil mill, in Maroua (Cameroon). The system consisted of two pools containing, respectively, microphytes and macrophytes constituted of Pistia stratiotes (water lettuce) plants. The physico-chemical characterization of the liquid waste showed that the oil mill generated, at a rate of 324 m³/day, highly alkaline (pH = 9.77 ± 0.51), very low oxygenated (dissolved oxygen = 0.45 ± 0.09 mg/l), highly organic matter  (BOD₅ = 16000 ± 6850 mg/l), nitrates (510 ± 84.50 mg/l N) and orthophosphates (5560 ± 1550 mg/l) loaded effluents. Total dissolved solids, electrical conductivity, turbidity, ammonium and nitrites presented respective mean values ​​of 475 ± 70 ppm, 989 ± 98 µS/cm, 825 ± 94 NTU, 12 ± 2.60 mg/l and 6.50  ± 1.30 mg/l N. At the end of the test treatment, the mean reduction rates were of 26, 6, 3, 20, 94, 80, 56, 68, and 51%, respectively, for pH, electrical conductivity, total dissolved solids, turbidity, ammonium, nitrites, nitrates, orthophos-phates and BOD₅, in the microphytes lagoon. These values were of 27, 48, 100, 93, 76, 71 and 57%, respectively, for pH, turbidity, ammonium, nitrites, nitrates, orthophosphates and BOD₅, in the macrophytes lagoon. Dissolved oxygen had respective increasing rates of 60 and 156%, in microphytes and macrophytes tanks.

Key words: Oil mill, effluent, lagoon, Pistia stratiotes, treatment.