POPULATION EQUIVALENT (P.E.): DEFINITION

By population equivalent (P.E.), or specific organic load, we define the quantity of organic biodegradable substances derived from

a residential consumer or assimilable to this, conveyed into the sewer in one day (24 hours), which corresponds to a Biochemical

Oxygen Demand within 5 days (BOD

5

), equal to 60 grams of O2 per day (Legislative Decree 152/06 Art.74-Definitions).

Domestic wastewater is composed of:

HYDRAULIC LOAD: quantity of water in drainage wastewater;

ORGANIC LOAD: quantity of organic substances contained in the sludge (mainly protein, carbohydrates and fat).

The ORGANIC LOAD is measured indirectly in BOD

5

(Biochemical Oxygen Demand):

The BOD

5

is a measurement of the quantity of oxygen (O2) necessary so that bacteria can make the organic substances harmless

within 5 days.

The unit of measurement of the BOD

5

is, therefore, gBOD

5

/day (grams of BOD

5

per day = grams of O2 per day).

Example:

1 P.E. BOD

5

= 1 x 60 g/(resident x day) di O2 = 60 g/day of O2

5 A.E. BOD

5

= 5x60 g/(resident x day) di O2 = 300 g/day of O2

SUGGESTIONS TO CALCULATE THE POPULATION EQUIVALENT

The table below shows the coefficients to be used, according to the type of utility, to determine the number of P.E. (Population

Equivalent) and therefore to select the most suitable product.

Type of Utility

no. of ...

Multiplication

Coefficient

P.E.

Residential

(1)

residents

1.00

m

2

residence

0.03

m

3

residence

0.01

Hotels, Holiday Farms, Rest Homes, Campsites

(2)

Cinemas, Theatres, Museums

(2)

Hospitals, Clinics

(2)

Gyms

Companies that do not produce waste water in production

Service stations, Auto grills

(1) to determine the number of P.E. choose the greater among the three results

(2) to determine the number of P.E. add the two results

Beds

0.50

Staff

0.33

Places

0.03

Workers

0.33

Beds

0.50

Staff

0.33

Members

0.10

Employees

0.50

Cars

0.16

Restaurants, Canteens, Inns

(2)

Place

0.33

Settings

0.33

Bars, Associations, Clubs

(2)

Customers

0.14

Staff

0.33

Schools

Pupils

0.10

Offices, Shops, Shopping Centres

Employees

0.33

Barracks, Prisons

Beds

1.50

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