This study detailed the effect hydraulic retention time on characteristics of the El-Oued aerated lagoons wastewater treatment plants (WWTPs), located in Southern East Algeria. The plant performance was evaluated through descriptive and statistical analysis of quantity and quality data of both raw wastewaters and treated effluent over a period of three years (2013 -2015). Therefore, the downstream values of BOD5, COD and TSS, are enough to achieve a final effluent that would meet the Algerian standards limit. The retention time is a function of the percent removal of organic load. The retention time may vary from 12 to 20 days as the optimum operating conditions the removal efficiencies 86.5% of BOD5, 78% of COD and TSS 85%. Goodness of the model fit to the data was also evaluated through the relationship between the residuals and the model predicted values of BOD5r, CODr and TSSr. The advantage of this model is that it would allow a better process control.

The objective of this study is to show the potential of Typha latifolia in the Purification performance of wastewater in the region of El Oued (southeast of Algeria). The pilot scale consists of two beds of plastics, filled with gravel and sand. One was planted saplings Typha latifolia at 36 stems/m 2 , the second was not planted serves as a control (witness). The results show good yields for suspended solids and organic pollution, removal rates are 96,76% for (SS) 89,92% for the Chemical Oxygen Demand (COD) and 87, 98% for biochemical oxygen demand in 5 days (BOD 5 ). There is a clear increase in the concentration of dissolved oxygen (DO). The system effectively removes nitrite (88.84%), nitrate (91.20%), and orthophosphate (93.12%).