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CE 548

Analysis and Selection of Wastewater Flowrates and Constituent Loading

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OverviewOverviewDetermining ww Flowrates and mass loadings is a

fundamental step in the conceptual process design of wastewater treatment facilities.

Flowrates sizing of different treatment system components

Loading to determine capacity and operational characteristics of treatment facilities and ancillary equipment.

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Components of Wastewater FlowsComponents of Wastewater FlowsComponents:

• Domestic discharge from residential, commercial, and institutional facilities.

• Industrial

• Infiltration/inflow (I/I)

Types of sewer systems

• Sanitary Sewer carries domestic, industrial, and infiltration/inflow

• Storm Sewer carries storm water

• Combined Sewer both

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Wastewater sources and flow ratesWastewater sources and flow ratesData that can be used to estimate average wastewater flowrates from various

domestic, industrial, and I/I are presented here. 

Domestic Wastewater Sources and Flow rates:• Residential Areas : Table 3-1

• Commercial Districts: Generally expressed in gal/acre.d (m3/ha.d) range form 800 – 1500 gal/acre.d (Table 3-2)

• Institutional facilities Table 3-3

• Recreational (highly seasonal) facilities Table 3-4

Industrial Wastewater Sources and Flow rates:Range:

• 1000 –1500 gal/acre.d light industrial development

• 1500–3000 gal/acre.d medium industrial development

• 85-95% of water use industries without internal water reuse

• For large industries separate estimates must be made.

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Wastewater sources and flow ratesWastewater sources and flow rates Infiltration/Inflow (I/I)

• Infiltration defective pipes ----etc.

• Steady inflow from cellar and foundation drains, etc.

• Direct inflow from direct storm water runoff connections to sanitary sewer possible source are roof leaders, yard drains, manhole covers.

• Total inflow direct + upstream flow (overflows/pumping stations bypasses)

• Delayed inflow storm water that requires several days to drain through manholes, etc…..

Infiltration flowrate:• The amount of water that can enter a sewer from groundwater

(or infiltration) ranges from 100 - 10,000 gal/d. in-mi .

• Or 20 – 3000 gal/acre.d. (Example 3-2)

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Statistical Analysis of flowrates, Statistical Analysis of flowrates, constituent concentrations, and mass constituent concentrations, and mass loadingsloadings Statistical analysis involves the determination of statistical

parameters used to quantify a series of measurements. Important in developing wastewater management systems Common statistical parameters:

• In normal distribution, data is described using: mean, median, mode, standard deviation, and coefficient of variation. Table 3-10

• In skewed distribution, data is described using log of the value of the normal distribution (geometric). Table 3-10

Graphical analysis of data:Graphical analysis of data:

• Used to determine the nature of distribution: plotting data on both arithmetic and log-probability papers. Examples 3-4 and 3-5

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Analysis of flowrate dataAnalysis of flowrate dataBecause the hydraulic design of both collection and treatment

facilities is affected by variation in wastewater flowrates, it is important that the flowrate characteristics be carefully analyzed.

Definition of terms: (Definition of terms: (Table 3-11))

Variations in wastewater flowrates.Variations in wastewater flowrates.

• Short term variations: (Figure 3-4).

• Seasonal variations.

• Industrial variations.

Wastewater flowrate factors:Wastewater flowrate factors:

• Maximum flows are determined by peaking factor (PF).

• flowrate term-long average

daily)hourly, (e.g., flowrate peakPF

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Analysis of constituent mass loadingAnalysis of constituent mass loading• BOD and TSS mass loadings can vary up to two or three times

the average conditions.

• Design of wastewater treatment processes should consider peak conditions.

Quantities of waste discharged: (Table 3-12)Quantities of waste discharged: (Table 3-12)

• Typical BOD5 (not including kitchen waste) is .18 Ib/cap.d.

• Example:

Given: a town of 125,000 population. Estimate the BOD5 loading of the raw wastewater

BOD5 = .18 x 125,000 cap= 22,500 lb/daycap.d

Ib

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Analysis of constituent mass loadingAnalysis of constituent mass loading Composition of Wastewater in Collection SystemsComposition of Wastewater in Collection Systems.

• T3-15, p. 186. The values are based on 120 ,which is the suggested EPA flow.

• Example: The average flow is 120 and the average BOD5

is 190 mg/l. What is the BOD5 loading in

• = Conc. (mg/l) x 8.34 x Q(MGD)

• = 190 x 8.34 x 120 x

• = .19 which aggress with value stated in T3-12, p.182.

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Analysis of constituent mass loadingAnalysis of constituent mass loading

Short term variation in constituent valuesShort term variation in constituent values.• Figure 3-6: Typical hourly variations in flow and strength of

wastewater.

Variations in industrial wastewater.Variations in industrial wastewater.• Composition is highly variable depending on industry type.

• Concentrations (BOD, TSS) vary significantly throughout the day.

• Pre-treatment may be required before discharge to municipal sewer.

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Design flowrates and mass loadingsDesign flowrates and mass loadings Average daily flow Average daily flow

• It is the average flow occurring over a 24-hour period under dry weather conditions.

• used in evaluating plant capacity, estimating pumping and chemical cost, sludge production, organic loading rates

Maximum daily flow Maximum daily flow • It is the maximum flow on a typical dry weather diurnal flow curve.

• used for the design of facilities involving retention time, such as:

– Equalization basins and Chlorine Contact Tanks

Minimum daily flow Minimum daily flow • It is the minimum flow on a typical dry weather diurnal

flow curve.

• used in sizing of conduits for minimum deposition

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Design flowrates and mass loadingsDesign flowrates and mass loadings Peak hourly flow Peak hourly flow

• The peak hourly flow occurs during or after precipitation and includes a substantial amount of I/I.

• used for the design of

– Collection and interceptor sewers– Pumping stations– Flow meters, grit chambers, conduits, channels in plant 

• Peak Flowrate Factors may be projected using Figure 3-13, p.202.

Minimum hourly flowMinimum hourly flow• It is the lowest flow on a typical dry weather diurnal flow

curve.

• used in sizing wastewater flowmeters, wastewater pumping

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Design flowrates and mass loadingsDesign flowrates and mass loadings Mass loading: Mass loading:

• Table 3-20

• Important in the design of treatment facilities such as:

– Sizing aeration tanks. – Biosolids processing facilities (Biosolids produced are

directly related to BOD mass loading) – Oxygen requirements are affected by mass loading 

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