Population equivalent (PE) or unit per capita loading, or equivalent person (EP), is a parameter for characterizing industrial wastewaters. It essentially compares the polluting potential of an industry (in terms of biodegradable organic matter) with a population (or certain number of people), which would produce the same polluting load.^[1]: 65 In other words, it is the number expressing the ratio of the sum of the pollution load produced during 24 hours by industrial facilities and services to the individual pollution load in household sewage produced by one person in the same time. This refers to the amount of oxygen-demanding substances in wastewater which will consume oxygen as it bio-degrades, usually as a result of bacterial activity.^[2]

A value frequently used in the international literature for PE, which was based on a German publication, is 54 gram of BOD (Biochemical oxygen demand) per person (or per capita or per inhabitant) per day.^{[1]: 65 [2]} This has been adopted by many countries for design purposes but other values are also in use. For example, a commonly used definition used in Europe is: 1 PE equates to 60 gram of BOD per person per day, and it also equals 200 liters of sewage per day.^[3][4][5] In the United States, a figure of 80 grams BOD per day is normally used.^[6]: 171

If the base value is taken as 60 grams of BOD per person per day, then the equation to calculate PE from an industrial wastewater is:

${\displaystyle PE={\dfrac {BOD\ load\ from\ industry\ \left[{\dfrac {kg}{day}}\right]}{0.060\ \left[{\dfrac {kg}{inhab\cdot day}}\right]}}}$

• Sewage treatment