The economical uplift in Egypt has caused urbanization to boom at analarming rate. To cope with this situation, the management of urban;service facilities, such as water supply and sewerage received a highpriority-from the regional governments and public. Many sewage treat-ment were constructed in the last decade. However, the design of theseplants was based on loading rates and design criteria which we’reimported from the American and European experience; and hence notsuitable for the Egyptian environment. As a result, complaints: ofdifficulties in operational control and shortcomings in the expectedefficiency are very common. Some of these plants should be modified orexpanded at an additional cost in order to achieve their target efficiency.’This research is an attempt to establish a design basis for newsewage treatment plants in the Egyptian environment.In order to achieve this objective, physical lab. models were’constructed for the main treatment processes. Raw sewage was takenfrom existing treatment plants in Damietta governorate on a daily basis.The influent and effiuent data of the model were analyzed and’ thedifferent key parameters and loading rates were determined.The study has shown that preaeration is generally recommendedbefore primary clarification, as it .promotes flocculation of fine solids andincreases solids removal up to about 70% in addition to the other benefitssuch as odor and septicity control. Primary clarifiers should be designed