Feb 26, 2016

Feb 26, 2016

Feb 26, 2016

# How to Estimate the Design Flow for a Sanitary Sewer

/ On: Feb 04, 2019 /

Design flow for sanitary sewer can be find as shown in steps below.

## Step 1: Future Population

Calculate the anticipated future (ultimate) population of area served by the sewer using ultimate population density.

## Step 2: Avg. Daily Sewage Flow

Multiply the ultimate population by per capita average daily sewage flow to obtain the average daily sewage flow e.g.

 Example Anticipated Population (P) = 200 Persons Water Consumption (q) = 400 Liters per capita per day Waste water flow per capita per day (qw )= 60% to 80% of water consumption (q) Future anticipated average waste water flow (Qw) = P*q*qw Liters per day 200*0.8*400 140,000 Liters per day

## Step 3: Peaking Factor

Select or calculate peaking factor (P.F) & Peak hourly waste water flow

P.F = $1+\frac{14}{4+\sqrt{P}}$or $1+\frac{22}{4+\sqrt{P}}\ngtr&space;4$

Or

P.F = $\frac{2.5}{Q^{0.145}}$ with max of 4

Where P = Population in 1000 & Q = Flow in MGD

P.F = 4 ..................For sewage flow upto 0.0283 m3/sec

P.F = 2 ..................For sewage flow upto 56,000 m3/

Now

Peak hourly domestic flow = P.F x Qw

## Step 4: Infiltration

Calculate the infiltration allowance at the rate of 10% of average daily waste water flow

or (3% to 5% of peak hourly domestic flow)

or 200 to 500 gallons/mile/inch-dia

or 700 to 1500 gallons/day/acre

or 30,000 (gallons per day) infiltration per mile of sewer

or 170,000 (liters per day) infiltration per km & house connections.

## Step 5: Industrial and Commercial Sewage

Calculate the allowance for industrial and commercial sewage at the rate of 3,734 m3/km2/day or 4,000 gal/acre/day.

Design flow for sanitary sewer = Peak hourly domestic [step 3] + Infiltration [step 4] + Commercial [step 5] waste water flows