Abstract: We describe a method of selectively testing a liquid sample for the presence of a specific living biological entity, the method comprising: preparing a plurality of culture vessels each for selective detection of the presence of a different living biological entity, wherein preparing a said culture vessel comprises: providing a culture vessel comprising a sealable chamber for receiving and culturing a liquid sample such that presence of said biological entity is detectable by detecting a change in pressure in a head space of said chamber; providing a selective growth medium in said culture vessel, wherein said selective growth medium is in a dry form and selectively facilitates growth of a specific living biological entity, and providing the culture vessel with an identifier to identity said specific biological entity; providing a test system comprising a device to receive said culture vessel and to detect said change in pressure in said head space of said chamber, the device further comprising a temperature

Abstract: We describe a floating respirometer, in particular for monitoring an activated sludge vessel of a sewage treatment plant. The device comprises: a buoyancy device to allow the respirometer to float in an aqueous liquid; a respirometer chamber, supported by the buoyancy device and arranged such that, when the respirometer is floating in said aqueous liquid, said chamber is partially filled with said aqueous liquid and defines an enclosed head space above said aqueous liquid; and a gas sensor in gaseous communication with said head space.

Abstract: We describe a method of closed-loop control of a waste water treatment plant, the method comprising: obtaining a fluid sample from a fluid of said plant; providing said fluid sample to a sealed chamber such that said fluid sample incompletely fills said sealed chamber leaving a headspace; incubating said fluid sample in said sealed chamber; determining a change in pressure in said headspace during said incubating; and controlling a degree of aeration of said waste water treatment plant responsive to said change in pressure. We also describe a method of measuring one or both of the food content and the biomass content of a fluid of a waste water treatment plant, the method comprising determining a value for one or both of food content and biomass content from a change in pres sure.