Caractérisation et traitement par coagulation-décantation d'un effluent de laiterie

Abstract

The qualitative and quantitative characterization of an effluent produced by a dairy plant located in the Doukkala region (Morocco) for one year showed that this plant consumed on average 632 m3/day of drinkable water, of which 85% was rejected as wastewater. This dairy effluent is overloaded with organic matter: [average chemical oxygen demand (COD): 6140 mg·L -1 ± 10%], total Kjeldahl nitrogen (average TKN-N: 148 mg·L-1 ± 10%), total phosphorus (average TP-P: 29 mg·L-1 ± 10%), fecal coliforms (average FC: 2.33 × 104 CFU·ml1- ± 10%) and fecal streptococci (average FS: 4.00 × 104 CFU·mL1- ± 10%). These parameters go beyond the limit values fixed by the Moroccan project of norms relative to rejected liquids, which shows the necessity of treating this polluted liquid before releasing it into the natural environment. The treatment of this effluent, which consists of coagulation-decantation by iron chloride [FeCl3,6H2O], aluminium sulfate [Al2(SO4)3,18 H2O] and calcium hydroxide [Ca(OH)2], is insufficient for the removal of organic matter and nitrogen (the percentage of elimination does not surpass 40%). However, this treatment considerably reduced the suspended matter (94%) and total phosphorus (89%) with calcium hydroxide. Consequently, it respected the Moroccan standards for these two latter parameters. In order to suggest a more efficient treatment, this chemico-physical treatment may serve as a stage of pretreatment and it would then be necessary to proceed to a complementary biological process.