and condition Surcharging or backwater conditions sediment load resuspended from Type of flow regulation or diversion collection system acton Calculation of Mass loadings Effect of Mass Loading Variability on Treatment Plant Performance antal immensity duo mouring the course of a day, the mass loading that is received by the treatment plant can vary widely. An xample of a diurnal mass loading curve is illustrated on Fig. 3-6. The variation in loading rates and the ompounding effects during the high-flow and concentration periods is illustrated clearly on Fig. 3-6. The variations are more pronounced in small collection systems provide a significant dampening effect. The impact of thes load variations is seen most dramatically in the effects hourly BOD loading may vary as much as 3 to minimum hourly BOD load in a 24-h period. Over longer periods of time, the mass loadings can also vary widely (see Fig. 3-7). These types of variations have to be accounted for in the design of the biological treatment system Fig. 3-5 Typical variations offlowrate, BOD, TSS, and fecal coliform in a combined collection system during a storm event 0246610121411225 Day of the month Fig 3-6 Illustration of diurnal Fig 3-7 Example variations of TSS and BoD Wastewater flow, BOD and concentrations and mass loadings Mass loading variability over a monthly period concentrations and mass loadings 3-6 Selection of Design Flowrates and Maa Loadings The rated capacity of wastewater-treatment plants is normally based on the average annual daily fl at the design vear plus an allowance for future growth. As a practical matter, hoy wastewater-treatment plants have to be designed to meet a number of conditions that are influenced by fiowrates, wastewater characteristics, and constituent concentrations, and a combination of both(mass loading). Conditions that must be considered include peak and minimum hydraulic flowrates and the maximum, minimum and sustained process constituent mass loading rates. Additionally, periods of initial operation and low flows and loads must be taken into consideration in design. The importance of wastewater flowrates and mass loadings in process design and operation is considered in this section Typical flowrate and mass loading factors that are important in the design and operation of wastewater-treatment facilities are described in Table 3-11. The overall objective of wastewater treatment is to provide a wastewater-treatment system that is capable of coping with a wide range of probable 3-103-10 and condition Surcharging or backwater conditions Type of flow regulation or diversion Capacity reduction from sediment buildup Sediment load resuspended from collection system Calculation of Mass Loadings Effect of Mass Loading Variability on Treatment Plant Performance During the course of a day, the mass loading that is received by the treatment plant can vary widely. An example of a diurnal mass loading curve is illustrated on Fig. 3-6. The variation in loading rates and the compounding effects during the high-flow and concentration periods is illustrated clearly on Fig. 3-6. The variations are more pronounced in small collection systems where the collection system storage capacity does not provide a significant dampening effect. The impact of these load variations is seen most dramatically in the effects on biological treatment operating conditions. The maximum hourly BOD loading may vary as much as 3 to 4 times the minimum hourly BOD load in a 24-h period. Over longer periods of time, the mass loadings can also vary widely (see Fig. 3-7). These types of variations have to be accounted for in the design of the biological treatment system. Fig. 3-5 Typical variations of flowrate, BOD, TSS, and fecal coliform in a combined collection system during a storm event Fig. 3-6 Illustration of diurnal Fig. 3-7 Example variations of TSS and BOD Wastewater flow,BOD and concentrations and mass loadings Mass loading variability over a monthly period concentrations and mass loadings 3-6 Selection of Design Flowrates and Maa Loadings The rated capacity of wastewater-treatment plants is normally based on the average annual daily flowrate at the design year plus an allowance for future growth. As a practical matter, however, wastewater-treatment plants have to be designed to meet a number of conditions that are influenced by fiowrates, wastewater characteristics, and constituent concentrations, and a combination of both (mass loading). Conditions that must be considered include peak and minimum hydraulic flowrates and the maximum, minimum and sustained process constituent mass loading rates. Additionally, periods of initial operation and low flows and loads must be taken into consideration in design. The importance of wastewater flowrates and mass loadings in process design and operation is considered in this section. Typical flowrate and mass loading factors that are important in the design and operation of wastewater-treatment facilities are described in Table 3-11. The overall objective of wastewater treatment is to provide a wastewater-treatment system that is capable of coping with a wide range of probable