Interesting question, Andre. ...

Interesting question, Andre.

Before addressing the question, it's important to see that many different countries/regions/industries use different bases for "standard" or "normal" conditions.  Typically the pressure is 1 atm (101.325 kPa), but the reference temperature often changes.  Perhaps the most common terms are:

Normal: Nm3 (0 degC; 101.325 kPa).

Standard: Sm3  (20C; 101.325 kPa).

As far as the numbers go, if you are digesting a typical mix of PS and WAS - see diagram below - the rule of thumb would say to expect about 1 m3 of digester gas per kgVSS destroyed.  That would be at field conditions, and that would mostly be digesters at about 36 C.  Perhaps the range from M&E comes from digesters over a range of temperatures, and also WAS from longer SRT systems will produce less gas.

Another rule of thumb may be to look at the decrease in COD across the digester, and expect about 0.37 m3 of methane per kgCOD removed.

If I take a BioWin Cabinet file - EBPR + Anaerobic Digester - here are the numbers:

Delta VSS = 1295 kgVSS/d

Delta COD = 2056 kgCOD/d

Gas produced from digester at 36C = 1,238 m3/d with 0.644 methane fraction.  So methane production at 36C = 0.644 x 1,238 = 797 m3/d.

Gas/VSS reduced = 0.96 m3/kgVSS

Methane/COD reduced = 0.39 m3/d

These are for 36C.  Converting to the "Normal" of o C would reduce these by a factor of 273 / (273+36) = 0.884.

Good luck and good wishes,

Peter Dold.