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The clarifier has a weir system for removal and return of floatables NOTES to aeration. The weir system is sized upon hydraulic return/surface area (square feet). One hundred percent of all weir wastewater is returned to aeration and thus is contained within the internal deten- tion time of the treatment process. Provisions are made to ensure that any residual floatable scum is not transferred into any downstream process by SNT pump elevation control. FLOW EQUALIZATION Widely fluctuating influent flow rates are typical at nearly all waste- water treatment plants. This fluctuation can result in a loss of treat- ment efficiency. With higher degrees of treatment constantly being required,some method of flow equalization is a design necessity. The objective of flow equalization is to level off the daily flow vari- ations in order to achieve a constant, batched flow rate at the down- stream treatment process steps. This is accomplished by storing in- fluent which is in excess of the daily flow-rate average, and then discharging it to the system when the influent flow rate is less than that average. By achieving this objective, overall treatment plant efficiency is dramatically improved. Several methods are available for determining equalization volume; all require generating a daily flow pattern record. If possible, this should be based upon actual plant data. If actual flow data are not available, which is frequently the case, existing communities, devel- opments,institutions, etc.,with similar flow characteristics should be studied. Design example: A. Equalization tank for 0.05-MGD plant (50,000 GPD) B. Average hourly flow(AHF) 0.05 x 1,000,000 24 = 2,083 GPH C. AHF percentage for consecutive periods of the typical 24-hour day are as follows: TIME PERIOD % of AHF 1. 0001-0300 10% 2. 0300-0600 20% 3. 0600-0900 70% 4. 0900-1200 250% 5. 1200-1500 150% 6. 1500-1800 100% 7. 1800-2100 150% 8. 2100-0000 50% 17