Background: The mostly used type of waste water treatment plant in Senegal is the extensive ones. However, up today, they cannot satisfy the sanitation needs of the current population. Senegalese government, through its new developing program called “Plan Senegal Emergent”, is making tremendous effort in achieving up to 80% of sanitation access rate by 2030. Most waste water treatment plants in Senegal are activated sludge and lagoons, and treated waters are rejected in natural areas such as sea and soil, or used in agricultural activities. Most of these plants are similarly designed, since the effluents present almost the same physicochemical and biological characteristics in all Senegalese cities and regions. This Study aimed to assess the purification performance of waste water treatment plant of Thiès city, and particularly its lagoons by: • Analyzing characteristics of the waste water getting into the plant from 2013 to 2017, such as TSS, BOD5, COD. • Assessing plant performance, especially the lagoons, and investigate how to optimize. Results from this analysis show that the plant treatment, with regards to Senegalese waste water standards, is having good purifying performance. However, even with the current hydraulic load that is only half of the nominal flow, the plant already achieved its maximum in term of pollutant charge.
