Improvements relating to anaerobic digesters

Abstract

An anaerobic digester apparatus has a reactor (2) having a tank and an agitator, a feedstock inlet, a liquid outlet (11) at an intermediate vertical level of the tank, a valved gas conduit (13) at an upper vertical level of the tank, and a pressure sensor (20) arranged to sense upper tank gas pressure. The controller: a. deactivates the agitator to start an initial settlement period (101,102), b. upon expiry (102) of the initial settlement period, closes the gas conduit (13, 103) to allow gas pressure build up in the top of the tank during a final settlement period (104, 105), c. during said final settlement period monitors (104) sensed gas pressure and automatically measures liquid level as said level drops, d. opens the gas conduit (13, 22, 106) and actuates the agitator when it is determined that the liquid level has dropped to a threshold, and e. returns to step (a) after a pre-set agitation time has elapsed (108).

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