From all the references gathered, the operational pH for digesters treating sludge from EBPR or CPR processes is similar (6.5 to 8), which bears the favorable range for methanogens growth (6.5-7.2 according to ( )). VFA levels cannot be too high in digester since they can inhibit the digestion; from 800mg/L according to or from 2000-4000mg/L according to . Concentration higher than the typical value of 100mg/L can be found for digesters working at short residence time or processing food wastes. The molar ratio VFA/Alkalinity should be <0.25 to maintain a good stability of the digestion (41, 45, 52, 53), and is commonly around 0.1 in practice . No clear difference between alkalinity in EBPR or CPR digestates was observed, even though it could decrease in presence of metal salts due to precipitation with OH -for example . During digestion, HCO3 -is produced to balance the formation of NH4 + , so an equimolar ratio can be assumed for these two ions as suggested by . This hypothesis is in line with the few cases where both ammonia and bicarbonates concentration were measured . Therefore, the bicarbonates ranges were calculated from NH4 + concentration, for which many sources exist.