On the Total Load Calculation in Combined Urban Sewer Conduits

Background: Particle size of sediment is necessary to design and operation of sewer systems. In this regard, calculation of the equivalent particle diameter (EPD) is of important to determine the particle Reynolds number (Ret ) as well as total load calculation. Methods: In this research work, 5 different particle diameters (i.e. d35, d50, d65, dm and deff) have been used in three famous total load calculation methods for calculating the best EPD. For this goal, a field experimental data has been collected at the entrance grit chamber of wastewater treatment plant (WWTP) of Khomein city, Iran. The total load of the sediments has been measured and the results compared with the total loads calculated by the three famous total load computation methods (i.e. Graf & Acaroglu method, Laursen method and Yang & Lim method) by using the particle diameters. Results: The results show that the methods estimate the total load of sediments with the relative errors of 4.25, 10.80 and 1.26 by using dm, d35 and d65 as the EPDs, respectively. Also, a simplified and improved correction factor has been developed and the results show that by applying the correction factor the relative errors of the methods decrease and they are equal to 10.34, 3.45 and 496.5, respectively. The improvement of the mentioned total load methods is equal to are 82.70%, 93.10% and 34.80%, respectively. Conclusion: The proposed correction factor can be applied for the standard deviation between 2.5-4.7 and the median particle diameter between 0.84-2.90 mm.