Method and apparatus for measuring gas flow

There are described a method and an apparatus for measuring gas flow rate and/or volume (such as gas accumulation and consumption) based on the “rate of rise” method, particularly useful in the field of small gas flow rates, that uses a duct immersed in a liquid so as to generate a hydrostatic pressure that allows increase in pressure in a sealed chamber, so as to avoid the use of solenoid valves, producing a particular advantage when a multiple measurement system is required, when a plurality of gas flows are to be measured. The method can be applied advantageously to measure flow rates of gas produced by chemical and/or biological reactions, in particular the Biochemical Methane Potential (BMP) or the Biochemical Hydrogen Potential (BHP). A variant of the method also allows measurement of the Biochemical Oxygen Demand (BOD).