Tab3-6 Terminology used to quantify observed variations in flowrate and constituent concentrations Average dry-weather flow(ADWF) e of the daily flows sustained during dry-weather periods with e average of the daily flows sustained during wet-weather periods when ation is a factor annua The average flowrate occurring over a 24-h period based on annual flowrate data Highest record flowrate occurring for a period consistent with the recording quipment. In many situations the recorded peak flow may be considerably below the actual peak flow because of metering and recording equipment Peak hour The average of the peak flows sustained for a period of l hour in the record Maximum day, Max imum mont Minimum ho Minimum day Variations in Wastewater Flowrates Wastewater flowrates vary during the time of day day of the week, season of the vear, or depending upon the nature of the dischargers to the collection system. Short-term. seasonal. and industrial variations in wastewater flowrates are briefly discussed here Short-Term Variations. The variations in wastewater flows observed at treatment plants tend to follow a diurnal pattern, as shown on Fig. 3-3 Fig. 3-3 Typical hourly variations in domestic wastewater Midnight flowrates Minimum flows occur during the early morning hours when water consumption is lowest and when the base flow consists of infiltration and small quantities of sanitary wastewater. The first peak flow generall ccurs in the late morning when wastewater from the peak morning water use reaches the treatment plant between 7 and 9 PM. The time of occurre and the amplitude of the peak flowrates collection system. As the community size increases, the variations between the high and low flows decrease due to(D the increased storage in the collection system of large communities that tends to equalize flowrates and(2) changes in the economic and social makeup of the community. When Seasonal Variations. Seasonal variations in domestic wastewater flows are commonly observed at resort areas. in small communities with college campuses, and in communities that have seasonal commercial and industrial activities. The magnitude of the variations to be expected depends on both the size of the community and the seasonal activity Industrial Variations. Industrial wastewater discharges are difficult to predict. Many manufacturing facilities generate relatively constant flowrates during production, but the flowrates change markedly during cleanup and shutdown. While internal process changes may lead to reduced discharge rates, plant expansion and increased production may lead to increased wastewater generation. Where joint municipal and industrial treatment facilities are to be constructed, special attention should be given to industrial flowrate projections, whether they are prepared by the industry or jointly with the city's staff or engineering consultant. Industrial discharges are most troublesome in smaller wastewater-treatment plants where there is limited capacity to absorb shock loa Wastewater Flowrate Factors Quantifying the variations in flowrates is important in the design and operation of wastewater-treatment lants. One of the measures used in determining the"peak"or maximum flows is the peaking factor Peaking factors can be developed based on maximum hour. maximum day. maximum month or other time periods. Tile peaking factor is particularly useful in estimating the maximum hydraulic conditions that might occur and have to be accommodated Peaking factors can also be applied to mass loadings. Peaking factors are applied most frequently to determine the peak hourly flowrate. Because it is difficult to compare numerical peak flow values from different wastewater-treatment plants, peak hourly flowrate values are normalized by dividing by the long-term average flowrate. the resultant ratio. known as a3-6 Tab 3-6 Terminology used to quantify observed variations in flowrate and constituent concentrations Item Description Average dry-weather flow(ADWF) The average of the daily flows sustained during dry-weather periods with limited infiltration Average wet-weather flow(AWWF) The average of the daily flows sustained during wet-weather periods when infiltration is a factor Average annual daily flow(AADF) The average flowrate occurring over a 24-h period based on annual flowrate data Instantaneous peak Highest record flowrate occurring for a period consistent with the recording equipment. In many situations the recorded peak flow may be considerably below the actual peak flow because of metering and recording equipment limitations Peak hour The average of the peak flows sustained for a period of 1 hour in the record examined Maximum day, Maximum month, Minimum hour, Minimum day, Minimum month… … Variations in Wastewater Flowrates Wastewater flowrates vary during the time of day, day of the week, season of the year, or depending upon the nature of the dischargers to the collection system. Short-term, seasonal, and industrial variations in wastewater flowrates are briefly discussed here. Short-Term Variations. The variations in wastewater flows observed at treatment plants tend to follow a diurnal pattern, as shown on Fig. 3-3. Fig. 3-3 Typical hourly variations in domestic wastewater flowrates Minimum flows occur during the early morning hours when water consumption is lowest and when the base flow consists of infiltration and small quantities of sanitary wastewater. The first peak flow generally occurs in the late morning when wastewater from the peak morning water use reaches the treatment plant. A second peak flow generally occurs in the early evening between 7 and 9 P.M. The time of occurrence and the amplitude of the peak flowrates vary with the size of the community and the length of the collection system. As the community size increases, the variations between the high and low flows decrease due to (1) the increased storage in the collection system of large communities that tends to equalize flowrates and (2) changes in the economic and social makeup of the community. When extraneous flows are minimal, wastewater discharge curves resemble water consumption curves, but with a lag of several hours. Seasonal Variations. Seasonal variations in domestic wastewater flows are commonly observed at resort areas, in small communities with college campuses, and in communities that have seasonal commercial and industrial activities. The magnitude of the variations to be expected depends on both the size of the community and the seasonal activity. Industrial Variations. Industrial wastewater discharges are difficult to predict. Many manufacturing facilities generate relatively constant flowrates during production, but the flowrates change markedly during cleanup and shutdown. While internal process changes may lead to reduced discharge rates, plant expansion and increased production may lead to increased wastewater generation. Where joint municipal and industrial treatment facilities are to be constructed, special attention should be given to industrial flowrate projections, whether they are prepared by the industry or jointly with the city's staff or engineering consultant. Industrial discharges are most troublesome in smaller wastewater-treatment plants where there is limited capacity to absorb shock loadings. Wastewater Flowrate Factors Quantifying the variations in flowrates is important in the design and operation of wastewater-treatment plants. One of the measures used in determining the "peak" or maximum flows is the peaking factor. Peaking factors can be developed based on maximum hour, maximum day, maximum month, or other time periods. Tile peaking factor is particularly useful in estimating the maximum hydraulic conditions that might occur and have to be accommodated. Peaking factors can also be applied to mass loadings. Peaking factors are applied most frequently to determine the peak hourly flowrate. Because it is difficult to compare numerical peak flow values from different wastewater-treatment plants, peak hourly flowrate values are normalized by dividing by the long-term average flowrate. The resultant ratio, known as a