Here is the definition of a Population Equivalent (PE) as it appears in the 1991 Directive:
"Article 2 - Paragraph 6: "a population equivalent (PE)" means the biodegradable organic load with a five-day biochemical oxygen demand (BD05) of 60 grams of oxygen per day; of theCouncil Directive 91/271/EEC of 21 May 1991 concerning urban waste water treatment ."